Halsey, N., Marlowe, D. E., Mitchell, R. A.,

Moi'dfin, L., Non-metallic anten.ia -support

materials paltruded rods for c-ntenna guys,

catenaries and coinmunica t ion3 structures,

A ">i-TR-7b-42, i> 6 pages (Air Force Materials

ratory, Wright-Patterson Air Force Base,

OH, M^y 1970)
AFML-TR-76-42

NON-METALLIC ANTENNA-SUPPORT MATERIALS

PULTRUDED RODS FOR ANTENNA GUYS,

CATENARIES AND COMMUNICATIONS STRUCTURES

INSTITUTE FOR BASIC STANDARDS

NATIONAL BUREAU OF STANDARDS

WASHINGTON, D. C. 20231*

MAY 1976

TECHNICAL REPORT AFML-TR-76-42

FINAL REPORT FOR PERIOD OCTOBER 1971 - OCTOBER 1974

Approved for public release; distribution unlimited

AIR FORCE MATERIALS LABORATORY

AIR FORCE WRIGHT AERONAUTICAL LABORATORIES

AIR FORCE SYSTEMS COMMAND

WRIGHT-PATTERSON AIR FORCE BASE. OHIO 45433

NOTICE

When Government drawings, specifications, or other data are used for

any purpose other than in connection with a definitely related Government

procurement operation, the United States Government thereby incurs no responsibility nor any obligation whatsoever; and the fact that the Government

may have formulated, furnished, or in any way supplied the said drawings,

specifications, or other data, is not to be regarded by implication or otherwise as in any manner licensing the holder or any other person or corporation, or conveying any rights or permission to manufacture, use, or sell any

patented invention that may in any way be related thereto.

This final report was submitted by the National Bureau of Standards,

Washington, D.C. 20234, under contract F33615-72-M-5000 , Job Order 73810663,

with the Air Force Materials Laboratory, Wright-Patterson Air Force Base,

Ohio. Mr. John R. Rhodehamel, AFML/MXE, was the Laboratory Project Monitor.

This report has been reviewed and cleared for open publication and/or

public release by the appropriate Office of Information (01) in accordance

with AFR 190-17 and DODD 5230.9. There is no objection to unlimited

distribution of this report to the public at large, or by DDC to the

National Technical Information Service (NTIS)

.

This technical report has been reviewed and is approved for publication.

R. RHODEHAMEL

'Project Monitor

KT>T\ lufnOD T CCV // ^ 7 EDWARD MORRISEY^

Supervisor

FOR THE COMMANDER

ALBERT OLEVITCH

Chief, Materials Engineering Branch

Materials Support Division

Copies of this report should not be returned unless otherwise required by

security considerations, contractual obligations, or notice on a special

document

.

FOREWORD

This final report was submitted by the National Bureau of Standards

Washington, D.C. 20234, under contract F33615-72-M-5000, Job Order

73810663, with the Air Force Materials Laboratory, Wright-Patterson Air

Force Base, Ohio. Mr. John R. Rhodehamel, AFML/MXE, was the Laboratory

Project Monitor.

The effort was over the period of October 1971 through October 1974

The authors, Messrs. N. Halsey, D. E. Marlowe, R. A. Mitchell and

L. Mordfin were responsible for the program direction.

This report was submitted by the authors in May 1976.

6 2 1 08 2
TABLE OF CONTENTS

SECTION PAGE

I INTRODUCTION 1

II EVALUATION OF EXISTING

FRP ROD PRODUCTS 4

1. THE PULTRUSION PROCESS 4

2. DEFICIENCIES IN EXISTING

PULTRUDED PRODUCTS 6

III TEST METHODS FOR

EXPERIMENTAL MATERIALS 10

1. TENSILE TESTS 10

2. STRESS-RUPTURE TESTS ' 11

3. RESIN CONTENT 12

4. DIMENSIONAL UNIFORMITY 12

5. FIBER WETTING 12

6. DEGREE OF CURE 13

7. TRANSVERSE TENSILE STRENGTH 14

IV DEVELOPMENT OF IMPROVED END FITTINGS 15

1. ANALYTICAL STUDY 16

2. SELECTION OF POTTING COMPOUND 20

3. DEVELOPMENT OF MOD 4 END FITTING 22

4. DEVELOPMENT OF THE H3M END FITTING 28

V PARAMETER STUDY OF THE MANUFACTURING PROCESS,

PART I 36

1. PROCESS PARAMETERS 36

a. ROVING PREHEAT 36

b. ROVING TWIST 36

c. ROVING END COUNT 39

d. ROVING TENSION 39

e. ROVING COLLIMATION 39

f. IMMERSION LENGTH 41

g. ULTRASONIC AGITATION 41

• h. WETTING AGENT 43

i. RESIN SYSTEM FORMULATION 43

j . CURING CONDITIONS 43

k. POST CURING 45

2. DESIGN OF EXPERIMENT 45

3. MANUFACTURE OF EXPERIMENTAL MATERIALS 48

a. NUMBER OF ROVINGS 48

b. ULTRASONIC LOADING 51

c. RESIN TEMPERATURE 51

6 2 10 8 2
TABLE OF CONTENTS

(CONTINUED)

SECTION PAGE

V PARAMETER STUDY OF THE MANUFACTURING PROCESS,

PART I (Continued) 36

4. TEST AND RESULTS 52

a. TENSILE BREAKING LOAD 52

b. STRESS-RUPTURE TESTS 52

c. MECHANISM OF STRESS-RUPTURE UNDER

HOT, HUMID CONDITIONS 58

5. ANALYSIS AND DISCUSSION OF RESULTS 61

VI PARAMETER STUDY OF THE MANUFACTURING PROCESS,

PART II 65

1. EXPERIMENTAL MATERIALS 65

2. TEST RESULTS AND ANALYSIS 66

VII VARIATION OF THE CONSTITUENT MATERIALS 72

1. SELECTION OF THE CONSTITUENT MATERIALS 72

2. MANUFACTURE OF EXPERIMENTAL MATERIALS 74

a. VARIABLE PROCESS PARAMETERS 77

b. CONSTANT PROCESS PARAMETERS 77

c. OPERATING CONDITIONS 78

3. TEST RESULTS AND ANALYSIS 81

a. TENSILE PROPERTIES 83

b. STRESS-RUPTURE PROPERTIES 84

VIII DISCUSSION AND RECOMMENDATIONS 86

IX SUMMARY AND CONCLUSIONS 89

APPENDIX 94

ADDENDUM: A SPECIFICATION FOR ARAMID FRP ROD 112

TECHNICAL DRAFT SPECIFICATION FOR WEATHER-RESISTANT

NONMETALLIC STRUCTURAL ROD 114

REFERENCES 122

6 2 1082
LIST OF ILLUSTRATIONS

FIGURE PAGE

1

' Schematic Representation of the Pultrusion Process 5

2 Photomicrographs of Cross Section of 1/2-in (13-mm)

Diameter Pultruded Rod: X340 Magnification (above)

and X70 Magnification (below) 7 2 (con't) X9 Magnification 8

3 Representative Finite-Element Mesh for One General

Class of End Fittings 17

4 Parameters for One General Class of End Fittings 18

5 NBS MOD 4 Experimental End Fitting for 1/2-in (13-mm)

Digmeter Rod. All Dimensions in Inches ( 1 in = 25. A mm) 24

6 Commerically Available Type R/P End Fitting for 1/2-in

(13-mm) Diameter Rope 29

7 Cruciform (left) and Conical (right) Wedges for 1/2-in

(13-mm) Diameter Rod. All Dimensions in Inches

( 1 in = 25.4 mm) 30

8 NBS Aluminum - Block Experimental End Fitting for 1/2-in

(13-mm) Diameter Rod 32

9 NBS H3M Experimental End Fitting for 1/2-in (13-mm)

Diameter Rod. All Dimensions in Inches ( 1 in - 25.4 mm) 35

10 Schematic Representation of Tensioning Apparatus for

Pultrusion 40

11 Schematic Representation of Collimating Apparatus for

Pultrusion 42

12 Stress-Rupture Properties of Rod from Run 1 at 200°F

(93°C) Under Saturated Humidity. (1 Ibf = 4.45N.) 56

13 Stress-Rupture Properties of Rod From Run 2 at 160

and 200°F (71 and 93°C) Under Saturated Humidity.

(1 Ibf = 4.45N.) 57

14 Wet Breakdown Voltage Versus Transverse Tensile Strength

(1 lbf/in2 = 6.89 kPa.) 64

VI

6 2 1 08 2
LIST OF TABLES

TABLE PAGE

1 Mechanical Properties of CW-Series Potting Compounds 21

2 Pullout Tests of CW-Series Potting Compounds 23

3 Tensile Tests with MOD 4 End Fittings on 1/2-in (13-mm)

FRP Rod. Potting Compound: C2W3 26

4 Tensile Tests of 1/2-in (13-mm) Material N with

Compression-Type Potted End Fittings 33

5 Characteristics of Glass Fiber Roving 37

6 Characteristics of Isophthalic Polyester Resin 38

7 Resin System Formulation, Runs 1-11 44

8 Selected Settings of the Variable Process Parameters

for Manufacturing Runs 1 through 11 47

9 Evaluation of the Variable Process Parameters 49

10 Operating Conditions for Manufacture of Runs 1 through 11 50

11 Average Dimensions and Physical Properties, Runs 1-11 53

12 Average Tensile Breaking Loads, Runs 1-11 54

13 Estimated Stress-Rupture Loads, Runs 1-11 59

14 Effects of the Variable Process Parameters on Rod

Properties, Runs 1-11 62

15 Typical Properties of Silane Coupling Agent 67

16 Resin System Formulation, Runs 12 and 13 68

17 Operating Conditions for Manufacture of Runs 12 and 13 69

18 Dimensions and Properties Summary, Runs 12 and 13 70

19 Characteristics of Bisphenol Fumarate Polyester Resin 75

20 Characteristics of Aramid Fiber Roving 76

. 21 Resin System Formulation and Viscosity, Runs 14 and 15 79

22 Operating Conditions for Manufacture of Runs 14 and 15 80

vii

6 2 10 8 2
LIST OF TABLES

(CONTINUED)

TABLE PAGE

23 Dimensions and Properties Summary, Runs 12, 14 and 15 82

A.l Results of Conventional Tensile Tests, Runs 1-11 98,99

A. 2 Results of High-Speed Tensile Tests, Runs 1-11 100

A. 3 Results of Stress-Rupture Tests at 200°F (93°C)

and Saturated Humidity, Runs 1-11 101, 102

A. 4 Results of Stress-Rupture Tests at 160°F (71°C)

and Saturated Humidity, Runs 1-11 103, 104

A. 5 Results of Conventional Tensile Tests, Runs 12 and 13 105

A. 6 Results of High-Speed Tensile Tests, Runs 12 and 13 106

A. 7 Results of Stress-Rupture Tests Under Saturated Humidity 107

A. 8 Results of Conventional Tensile Tests on Preliminary

Sample of Aramid/Isophthalic Rod 108

A. 9 Results of Conventional Tensile Tests, Runs 14 and 15 109

A. 10 Results of High-Speed Tensile Tests, Runs 14 and 15 110

A. 11 Results of Stress-Rupture Tests Under

Saturated Humidity, Runs 14 and 15 111

viii

6 2 1 0 8 2
SECTION I

INTRODUCTION

Fiber-reinforced-plastic (FRP) rod and rope materials constitute

one of the more interesting and valuable — although lesser known —

products of composite materials technology. These products are most commonly fabricated from unidirectional glass fiber roving and a thermosetting

plastic matrix by a process called pultrusion. They are strong, lightweight,

nonconducting, corrosion resisting and comparatively inexpensive. This

combination of properties has led to the use of these products in a variety

of applications where steel wire rope had previously been employed almost

exclusively. In terms of total volume, the largest application has been

in communications towers and arrays, wherein the use of non-metallic

rod and rope as guys and catenaries has reduced corona and maintenance

problems and permitted elimination of the large, expensive, ceramic insulators

which are required when steel wire rope is used.

As frequently happens when promising new products are developed,

the rod and rope were introduced into service before they were adequately

characterized and without the benefit of carefully compiled design data.

The result has been the occurrence of failures in several field installations.

Fortunately, however, most applications have performed satisfactorily.

Some of the reported failures have involved arc tracking and flashover

damage, and burning, in intense electromagnetic fields. Most of the other

reported failures were apparently mechanical although environmental effects

were probably involved. Rope-type guys and catenaries have failed, at

6 2 10^
locations apart from their fittings by a progressive strand-by-strand

breakage. The cause of these failures is unknown but opinions that have

been advanced include undetected damage incurred during installation,

wind-induced rubbing of adjacent strands, and strength degradation due

to ultraviolet exposure. In the case of rod materials, failures have

usually entailed splitting or delamination that progressed along the

rod at a slight inclination to the longitudinal axis.

Lengthwise splitting of rods has been observed to emanate from localized surface defects. Such defects may be severe notches or gouges

from damage introduced during handling, or they may be thin, deep transverse cracks. Some of these transverse cracks are particularly interesting

because, prior to splitting, they appear only as barely visible hairlines

on the surface of the rod. The surfaces of the cracks are very smooth.

Unpublished research at NBS has verified that these cracks can result

from a two-state dynamic loading sequence. It is also believed that length

wise splitting can result from the fact that the rods are sometimes bowed,

rather than straight, when installed. In this circumstance the applied

tensile forces create lengthwise shearing stresses which may exceed the

low shear strength of the product.

Although the causes of mechanical failure in these materials are

apparently many and varied, at least one generalization can be made.

Most mechanical failures on non-metallic antenna support materials have

occurred after a period of service, ranging from months to years, during

which the materials have been under tension in a moist environment. With

this as a point of departure, the National Bureau of Standards embarked

2

6 ;g 1 e 8 4
upon a three-year program to develop a new non-metallic f iber-reinforcedplastic rod material which would exhibit superior mechanical properties

and greater resistance to moisture. The program called for the development

to be accomplished through (1) the selection of potential improvements

in the manufacturing process and in the constituent materials; (2) the

procurement of experimental materials manufactured in accordance with

these potential improvements; and (3) the subsequent evaluation of these

materials. The evaluations were based primarily upon two types of mechanical

tests: tensile tests at normal and high rates of loading, and stressrupture tests at 160 and 200°F (71 and 93°C) under saturated humidity

conditions. The results of the stress-rupture tests, when performed

on a variety of materials, were considered to be indicative of the relative

weatherabilities of the materials.

This program was carried out in the Engineering Mechanics Section

of NBS under the sponsorship and with the financial assistance of the

Air Force Materials Laboratory. Laboratory efforts were in response to

an Air Force Technical Need (TN-ESD 26-70-01) . This Category I program

required that a data base be established for (future) antenna structures

design. The authors gratefully acknowledge the valuable contributions

of Mrs. Ruth M. Woolley, Mr. Oscar 0. Owens and Mr. Raymond G. Russell

of the Engineering Mechanics Section, NBS, and of Dr. Fred A. Yeoman,

Mr. John S. Uudock and Mrs. Donna K. Nowakowski of the Westinghouse Electric

Corporation.

Since the English system of units is used almost exclusively by

the American manufacturers and users of non-metallic antenna-support

3 6 55 1 0 8 2
materials at this time, these units have been employed in this report.

In each instance, however, the English units are followed by their metric

(SI) equivalents in parentheses. Factors for converting between the two

systems of units may be found in the Standard Metric Practice Guide (ASTM

Designation E 380-72) which is available from the American Society for

Testing and Materials, 1916 Race Street, Philadelphia, Pa. 19103.

SECTION IT

EVALUATION OF EXISTING FRP ROD PRODUCTS

1. THE PULTRUSION PROCESS •

A survey of commercial FRP rod and rope manufacturers was carried

out to identify the critical features of the pultrusion process as it

is used for the manufacture of FRP materials. Although the process was

comparatively obscure at the start of this program, recent publications

(1, 2, 3) suggest that it is rapidly becoming more widely known and used.

The basic features of this process are reviewed here. Figure 1^ is a schematic

of the process which illustrates several features that are common to

most manufacturers. It should be noted, however, that no two manufacturers

were surveyed whose processes were identical.

On the left of the figure, glass rovings are drawn from a creel

in which are mounted dozens of bales or spools of roving. The rovings

are guided down into the resin tank where the individual fibers are wetted

with the matrix resin. Following this, the impregnated mass is drawn

through one or more guides and bushings which give the material its desired

cylindrical shape. Finally, the rod is cured in a heated die system.

4 62 1 OS 2

On the right of the figure is the pulling mechanism which gives the pultrusion

process its name and which supplies the considerable force that is required.

The final product is either cut to desired lengths or coiled and allowed

to cool.

2. DEFICIENCIES IN EXISTING PULTRUDED PRODUCTS

Connaercially available glass FRP rods from five different pultrusion

manufacturers were examined to identify those product characteristics

which could be responsible for the premature mechanical failures that

have been experienced in antenna-support applications. Six such deficiencies

were found to be present, in varying degrees, in all of the products.

These deficiencies, which appeared to be correctible by appropriate modifications

of the manufacturing process, are described here together with the inspection

procedures which were used to identify them.

Microscopic examinations of cross sections of an FRP rod provide

a simple means for assessing the uniformity of the distribution of fibers

in the rod. Photomicrographs, such as those shown in Figure 2 , clearly

reveal that the fibers are not uniformly distributed throughout the cross

section. Instead, they appear to be bunched together in clusters with

resin-rich areas between them. It is speculated that each cluster corresponds

to the ends of a single roving.

When a glass FRP rod is properly tested in tension, such that failure

initiates in the free length of the rod, the fracture generally causes

the fibers to broom out in a rather explosive fashion. Examination of

the fibers in such cases reveals that many do not appear to be wetted

by the resin.

6

6 2 108^
Figure 2 - Photoin.icrographs of Cross Section of 1/2-in (13-niin) Diameter

Pultruded rod. X340 Magnification (above) and X70 Magnification

(below)

7 (continued)

S 2 1 0 8 2
Figure 2 (continued) - X9 Magnification

6 2 10 8 2
Photomicrographs made under high magnification frequently show apparent

voids adjacent to individual fibers. This tends to confirm the above

observation regarding incomplete wetting. However, apparent microscopic

voids are also occasionally observed in the matrix at locations apart

from fibers. It is speculated that these voids may be created by volatilization of one or more components of the resin system under the heat

of the curing operation.

Careful examination of the surface of an uncoated FRP rod occasionally

permits the paths of individual fibers to be traced for some distance

before the fibers descend into the interior of the rod. Such examinations

reveal that the fibers are not straight but follow a rather wavy path.

Obviously, this condition is not conducive to achieving a uniform distribution of load among the fibers in a tensile application.

Further examination of surface characteristics, particularly on

fractured rods, reveals that even when the fibers are straight they are

frequently not parallel to the axis of the rod. Deviations of 10° to

20° are not uncommon. In this situation the potential tensile strengths

of the rods cannot be fully realized.

hardness measurements on FRP rods have been made, both before and

after post-curing operations. In all cases the post cure produced an

increase in hardness. This is taken to mean that the rods, in the asreceived condition, were not fully cured since a fully cured rod should

exhibit no significant increase in hardness during post curing.

6 2 1082
SECTION III

TEST METHODS FOR EXPERIMENTAL MATERIALS

The program for the development of improved FRP rod materials called

for the manufacture of a series of experimental rods, to be discussed

later. The most critical mechanical properties of the experimental rod

materials, namely, strength and weatherability , were evaluated by means

of room- temperature tensile tests, at both normal and high loading rates,

and by stress-rupture tests, at 160 and 200°F (71 and 93°C) , under

saturated humidity conditions. In addition, a variety of supplementary

test methods and measurement techniques was used to study other physical

characteristics of the experimental rod materials such as dimensional

uniformity, resin content, degree of fiber wetting, degree of cure and

transverse tensile strength.

1. TENSILE TESTS

The tensile tests at normal loading rates were performed in a 100,000-

Ibf (A50-kN) capacity, horizontal, hydraulic, universal testing machine

[4]. A crosshead speed of 0.75 in/min (0.32 mm/s) was used.

The tensile tests at high loading rates were carried out in a 50000-

Ibf (220-kN) capacity, closed loop, electrohydraulic testing machine

[A]. A calibrated load cell in series with the test specimen was used

to measure load, and the load-time trace for each test was recorded with

a calibrated storage oscilloscope. The crosshead speed in these tests

was measured using an LVDT extensometer and was found to be approximately

300 in/min (130 mm/s).

The most difficult problem to be overcome, in measuring the tensile

10

6 2 1 0^
strengths of unidirectionally reinforced rods, is avoiding premature failures

of the rods that initiate in the end fittings. It has been established

[5] that commercially available end fittings for FRP rod and rope are

not generally satisfactory for this purpose. Consequently, a concerted

effort was made to develop new end fittings which could be used to measure the full tensile strengths of the rod materials studied in this

program. This development effort is described in Section 4 of this report.

2. STRESS-RUPTURE. TESTS

The stress-rupture tests were performed in six creep-testing machines

that were designed and assembled for this task. Each of these machines

has a rated capacity of 30000 Ibf (130 kN) , which is applied by dead

weights acting through a 100:1 compound lever system. Specimens up to

9 ft (3 m) long, including the end fittings, can be accommodated. The

overall height and length of each machine are approximately 7 ft (2 m)

and 12 ft (4 m) , respectively.

Each creep-testing machine was equipped with an environmental test

chamber for providing the required temperature and humidity conditions.

The chambers are cylindrical in shape, consisting primarily of a 10-in

(0.25-m) diameter asbestos-cement pipe, 4 ft (1.2 m) long, with transparent

plastic windows at the ends. Each chamber contains a brass tube which

extends nearly the full length of the chamber. The purpose of the tube

was to provide a more uniform temperature distribution on the specimen,

which passed concentrically through the tube. The ends of the specimen,

including the end fittings and the pull rods, remained outside of the

chamber.

11

6 2 10 8 2
Heat was supplied to each chamber by twelve quartz-tube infrared

lamps which surround the brass tube. Each lamp has a capacity of 500W

at 120V. The temperature distribution in the chamber was adjusted by

regulating the power to the lamps. The test temperature was maintained

with a temperature controller.

Each chamber was furnished with an air-powered mist generator to

provide the required saturated humidity conditions. The rate of water

consumption was adjusted by regulating the air-flow rate to maintain

a light film of condensation on the windows of the chamber.

3. RESIN CONTENT

The determination of the resin content of glass FRP rods was made

by means of a burn-out test similar in principle to the ASTM ignition

loss test [6]. This test involves the use of a continuous-reading scale

which is enclosed in a muffle furnace. The furnace temperature is set

at a value at which the organic resin matrix material is completely decomposed to volatiles. The difference between the original weight of

a sample and the minimum weight achieved during heating is considered

to be the resin content. ' , , '

.

A. DIMENSIONAL UNIFORMITY

Measurements of the average diameter, the length, and the weight

(mass) of several sections of each FRP rod material were made. The densities

[71 and the weights (masses) per unit length were calculated. These determinations provide an indication of the uniformity of the product.

5. FIBER WETTING

An indirect indication of the degree of fiber wetting was obtained

12

6 2 1082
by measuring the corona inception voltage on rod samples which had been

saturated with water. This approach was based on the premise that absorbed

water will migrate to fiber-resin interfaces which are not thoroughly

adhered. The following test procedure [8] was adopted for the experimental

FRP rod materials:

(1) Cut a 1/2-in (13-mm) long specimen from 1/2-

in (13-mm) diameter rod, with the ends smooth

and parallel.

(2) Boil the specimen in distilled water for 2 h.

(3) Measure the electrical breakdown voltage across

the parallel faces within 15 min after removal

from the water, as follows:

(a) Mount the specimen between 1-in (25-mm)

diameter electrodes in an oil bath.

(b) Raise the voltage across the specimen

from 0 to 15 kV at a rate of 0.5 kV/s.

(c) Hold the voltage at 15 kV for 1 min. If

failure occurs within this interval, record

the failure voltage as 15 kV.

(d) Increase the voltage further at a rate

of 0.5 kV/s to breakdown voltage. (The

maximum voltage from the available equipment

was 50 kV.)

6. DEGREE OF CURE

Rockwell hardness measurements were made on FRP materials as an

indication of the degree of cure of the resin. For this purpose Procedure

A of ASTM Designation D785-65 [9] was used. Samples were removed from

several locations along the length of a rod. A minimum sample length

of 2 in (50 mm) was established to enable multiple measurements to be

made on the same sample. Not less than five measurements were made on

13

6 2 1 f}S 2
the cylindrical surface of each sample. Three of these were made on a

single generator line. The other two measurements were made on a second

generator line, 90° from the first line, at points intermediate to the

first three test sites.

7. TRANSVERSE TENSILE STRENGTH

A measure of the transverse tensile strength of FRP rod was obtained

by means of a diametral compression test. In this well-known test method

for brittle materials [10] a cylindrical disk-shaped specimen is compressed

diametrically between two flat platens. Under the proper conditions [11]

the test culminates in a tensile fracture along the loaded diameter,

and the transverse tensile strength (S^ of the rod is calculated from

the relation

= 2P

TlDt

where P is the compressive load at fracture, D is the diameter of the

disk and t is its thickness. These transverse tensile strength measurements

are believed to represent some combination of the tensile strengths of

the resin matrix material and the fiber/matrix bond.

Disk specimens, approximately 1/4 in (6 mm) thick, were sliced

from 1/2-in (13-mm) diameter FRP rods using a water-cooled, diamond

cutoff saw. Care was taken during this cutting process to prevent fraying

of the edges. The coolant was carefully blotted from the disks which

were then allowed to dry, under ambient laboratory conditions, for at

least 24 h prior to testing. The diameter and thickness of each specimen

14

6 2 1 0 8 ?
was measured, and the specimen was mounted, on edge, in a compression

subpress [12] and loaded to fracture in a universal testing machine.

SECTION IV

DEVELOPMENT OF IMPROVED END FITTINGS

In this task, laboratory prototypes of two new end fittings were

developed which are superior to a variety of commercial end fittings

in terms of their capability to approach the full strength of FRP rod

in a tensile test. While the development of these fittings was completed

in the present program, much of the basic work which went into the development was initiated or pursued in prior studies performed in this laboratory

[5, 13]. These prior studies were carried out under the sponsorship

and with the financial assistance of the Army Electronics Command, the

Coast Guard, the Naval Facilities Engineering Command, Rome Air Development Center (USAF) , the United States Information Agency and the National

Bureau of Standards.

The basic approach to the development of improved end fittings

consisted of an analytical parameter study of the problem and an experimental evaluation of trial prototype designs, which were pursued concurrently. The analytical study involved the axisymmetric , finite-element

stress analysis of a broad class of end connections consisting of a

metal sleeve joined to the FRP rod with a polymeric potting material.

The experimental study involved the fabrication and tensile testing

of prototype end fittings employing several different gripping concepts.

An important aspect of this parallel analytical and experimental approach

15

6 2 1082
was the free transfer of newly developed information from one study

to the other. Some aspects of the analytical study are reported in greater

detail elsewhere [14].

1. ANALYTICAL STUDY

A new computer program was developed for the axisymmetric finiteelement stress analysis of end connections. The basic finite-element

formulation used [15] had been developed for the case of isotropic elastic

materials. That earlier formulation was modified in the end-fitting

analysis in accordance with the assumption that the FRP rod is homogeneous

and transversely isotropic as defined by five independent elastic constants. The metal sleeve and the potting compound were assumed to be

isotropic elastic.

Figure 3^ shows a representative finite-element analysis mesh for

one general class of end connections. In this case, the metkl sleeve

is conically tapered, and the outer end of the FRP rod is slit into

quarters and spread with a conical metal wedge. Where the rod is spread

by the wedge, the elastic constants for the region occupied by the

spread rod were recomputed according to the volume fractions of rod

material and potting compound.

The linear elastic finite-element computer model was used in a

parameter study of the general class of end fittings represented schematically

in Figure ^. The numerals in the figure denote the eight variable

parameters studied. Parameters A and 5 are the elastic moduli of the

two potting compounds indicated.

16

6 2 108^
17 6 2 108^

It was assumed that the critical component of stress, with respect

to tensile strength, is the peak bond-shear stress at the interface

between the rod and the potting compound. This assumption was based

on the fact that rod pullout was the most common failure mode observed

in tensile tests of this class of fitting.

The analyses were carried out for a 1/2-in (13-mm) diameter FRP

rod. The assiomed properties of the metal sleeve and the conical wedge

(not shown) were those of 7075-T6 aluminum alloy.

The general indications for the eight parameters studied are:

1. End-fitting length. —Within the range of 6 to 16

in (0.15 to 0.41 m) , greater length results in significantly smaller peak bond-shear stress, but the

rate of change of peak stress decreases as length

increases

.

2. Potting thickness at inner end of fitting. —Within

the range of 0.24 to 0.48 in (6 to 12 mm), greater

thickness results in significantly smaller peak

bond-shear stress, but the rate of change of stress

decreases as thickness increases.

3. Sleeve thickness at inner end of fitting. —Within

the range of 0.02 to 0.25 in (0.5 to 6.4 mm), greater

thickness results in slightly greater peak bondshear stress.

4. Elastic modulus of inner potting compound. —Within

the range of 40000 to 316000 Ibf/in (0.28 to 2.18

GPa) greater stiffness of potting compound results

in significantly greater peak bond-shear stresses.

This is true whether a single potting compound or

a combination of two different compounds is used.

5 & 6. Elastic modulus and length of outer potting compound. —A combination of two potting compounds having

different elastic moduli produces two bond-shear

stress peaks (one at the inner end of each potting

compound). If Parameters 4, 5 and 6 are proportioned

so as to make the two stress peaks approximately

equal, the peak stress is significantly less than

for the case of a single potting material.

6 2 10 8^
7 & 8. Potting thickness and sleeve thickness at the

outer end of the fitting. —Parameters 7 and 8 have

a relatively small direct influence on the peak

bond-shear stress.

The two most significant findings of this parameter study are:

1. The potting compound should have a relatively low modulus of

elasticity, i.e., it should be flexible.

2. The potting compound layer should be relatively thick. A ratio

of rod diameter to layer thickness of not less than 4 may be used.

Both of these findings appear to be entirely logical but they were not

intuitively obvious prior to the parameter study. In particular, it

is known that adhesives with high bond strengths generally have relatively

high moduli of elasticity, and that adhesives generally exhibit higher

bond strengths when applied in thin layers, however, the parameter study

showed that a flexible, thick potting compound allows the tensile load

to be transferred from the fitting to the rod gradually, over a long

length, without developing a high peak bond-shear stress at the inner

end of the fitting. Thus, a flexible, thick potting compound performs

better in this application than a stiff, thin potting compound which

may have a greater bond strength.

2. SELECTION OF POTTING COMPOUND

On the basis of previous work in this laboratory, the selection

of an appropriate potting compound was focused on a single series of

f omulations . These consist of a 100-percent-reactive epoxy resin adhesive

and an activator. The system requires a 2-h cure at 165°F (74°C).

The two components may be combined in different resin/activator ratios

to provide different mechanical properties. The designations and some

of the properties for several mixture ratios are given in Table 1.

20

,6 511 Q ^
TABLE 1

MECHANICAL PROPERTIES OF CW-SERIES POTTING COMPOUNDS

Resin/activator ratio

2:3 1:1 3:2 2:1

(a)

Designation

Bond strength

Ibf/in^

(MPa)

Compressive strength

lbf/in2

(MPa)

(a)

Elongation (a)

Elastic modulus

lbf/in2

(GPa)

, percent

(b)

C2W3

2450

(16.9)

32200

(222)

8.0

51000

(0.35)

ClWl

3280

(22.6)

20700

(143)

7.0

275000

(1.90)

C3W2 C2W1

316000

(2.18)

(a)

According to the manufacturer.

(b)

From compressive tests on 0.5- in (13-mm) diameter specimens performed

in this laboratory.

21

6 2 1 0 8 2
A simple, shear-type end fitting was fabricated to evaluate the

relative pullout shear strengths of the several CW potting compounds.

This fitting consists of a cylindrical metal sleeve which is attached

to an FRP rod with a thick layer of potting compound.

A series of twelve tensile tests was performed using 1/2-in (13-

mm) diameter, high-strength FRP rod. All twelve specimens failed by

rod pullout and the results are given in Table _2. Although there is

great scatter in these data, the relatively high strengths of the specimens

with the most flexible potting compound are significant. These results

support the analytical parameter study which showed that a more flexible

potting compound produces significantly lower peak bond-shear stresses.

Finite-element analyses of the fitting indicate that the peak bond-shear

stress with the most flexible C2W3 potting compound is only 47 percent

of the corresponding stress with the stiff C3W2 compound.

3. DEVELOPMENT OF THE MOD 4 END FITTING

The Mod 4 end fitting. Figure _5, is a shear-type potted end fitting

which relies upon its long length to achieve high shear strength at

the interface between the rod and the potting compound. To mount the

fitting on an .FRP rod, the end of the rod, after abrasive cleaning,

is set into the hole at the base of the cavity. The rod is carefully

22

6 5^ 1 0 8 ^
TABLE 2

PULLOUT TESTS OF CW-SERIES POTTING COMPOUNDS

Test

No.

Potting

compound

71169

71170

71171

Average

71166

71167

71168

Average

71172

71173

71174

Average

C2W3

C2W3

C2W3

ClWl

ClWl

ClWl

C3W2

C3W2

C3W2

71175

71176

71177

Average

C2W1

C2W1

C2W1

Maximum load

Ibf (kN)

19850

15500

18650

18000

88.3

68.9

83.0

80.1

12200

8500

19250

13300

54.3

37.8

85.6

59.2

8000

14350

9400

10600

35.6

63.8

41.8

47.1

12350

17500

18100

16000

54.9

77.8

80.5

71.2

23

62 1

2
u

<u 4J

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rH II

J-l C3 O •H

rH C

•H w

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alined parallel and concentric with the fitting and the remaining cavity

is filled with the potting compound. The fitting was designed primarily

for 1/2- in (13 mm) diameter rod, which leaves a 3/8-in (10-mm) thickness

of potting compound around the rod.

A tensile specimen was fabricated by mounting two Mod 4 end fittings

on a length of 1/2-in (13-mm) diameter FRP rod using the C2Vi3 potting

compound. The specimen was instrumented with twenty-six resistance strain

gages for experimental stress analyses under tensile loading. The results

of these measurements [5, 14] suggest that under high loads the bondshear stress on the surface of the rod is roughly uniform over most

of the potted length. This uniformity is believed to be a major factor

contributing to the relatively high strength of the Mod 4 end fitting

which was subsequently observed with tensile specimens that had been

potted with the flexible C2W3 compound.

The performance of the Mod 4 end fitting was evaluated by means

of tensile tests on two commercially available FRP rod materials of

1/2-in (13-mm) diameter. Both are fabricated from unidirectional, continuous, E-glass roving and a polyester resin matrix. The manufacturing

process for one of these materials. Material E, results in the formation

of an integral gel coating of the matrix material on the outer surface

of the rod. The second material, Material N, is coated with a filled

epoxy for resistance to weathering.

The results of twenty tensile tests using Mod 4 fittings on Materials

E and N rods are given in Table _3. The low-modulus C2W3 potting compound

was used on all specimens. Two of the seventeen Material E specimens

25

6 2 1082
TABLE 3

TENSILE TESTS WITH MOD 4 END FITTINGS ON 1/2-IN (13-mm)

FRP ROD. POTTING COMPOUND: C2W3

Test

No. Material Maximum load Failure

X1 Vif D L

/ J. J- O VEd 'll '\^D \a.) 7 1 1 8"^

/ -L X C-> -> T?£i J ^ o ^ \J \0 ) 71 1 84 9 57 sn V -L -L J / 81 242 111 81243 E 28600 ^ w VJ W W < (a)

81244 E

^ 32600 (145) (a)

81245 E 29600 (132) (a)

81246 E 29000 V J- ^ / (a)

81247 E 31 800 CI 41") (a)

81248 E 327 50 ('146')

V XH U y (a)

81249 E 30950 (138) (a)

81250 E 31100 (138) (a)

81251 E 31500 (140) (a)

91261 E 23250 (103) (c)

101315 30100 (134) . . : - (a)

101333 E 31850 (142) (a)

101404 E 31500 (140) : . (b)

Average

:

30100 (134)

81240 N 23700 (105) (a)

81241 N 17850 ( 79) . ,

. (a)

91263 N 18900 ( 84) (a)

20150 ( 90)

(a)

Pullout. , , : , -

i

(b) _

Failure in the free length.

(c)

Pullout; potting compound did not appear to have been adequately

cured

.

26 6^1 082
failed in the free length at loads of 32850 and 31500 Ibf (146 and 140

kN) . The other fifteen Material E specimens failed by pullout with the

failure located principally at the interface between the rod and the

potting compound. The average maximum load for all of the Material E

specimens was 30100 Ibf (134 kN) , which is more than 90 percent of the

loads attained by the specimens which failed in their free lengths.

This indicates that the full tensile strength of Material E is approached

with the Mod 4 fittings.

The average maximum load for three specimens of Material N with

Mod 4 end fittings was only 20150 Ibf (90 kN) . Failure here was also by

pullout but in this case the failure was within the rods with several

of the outer layers of glass fibers being sheared off.

A comparison of these results with those obtained with commercial

end fittings [5] reveals that the Mod 4 end fitting is clearly superior

to the commercial types for Material E. For Material N the performance

of the Mod 4 fitting is equal to that of the commercial types although

it does not, apparently, allow the full tensile strength of Material

N to be approached.

Several modifications were explored in an attempt to improve the

performance of the Mod 4 end fitting on Material N. These modifications

involved (1) Increasing the size of the fitting, (2) using potting compounds with formulations different from those of the CW series, and

(3) driving wedges into the ends of the rods prior to potting. The results

of these studies [16] showed no improvement over those obtained with

the standard Mod 4 end fitting.

6 2 10 8 2
Some numerical experiments were conducted on the computer in an

effort to obtain a greater understanding of the process of load transfer from the end fitting, through the potting compound, to the rod.

This effort indicated the feasibility of incorporating the nonlinear

properties of polymeric potting compounds into the finite-element analysis.

This type of nonlinear analysis has been used in this laboratory to

study composite-reinforced cutouts in metal sheet [17]. Kowever, it

was determined that this approach could not be effectively pursued within

the resources available on the present program.

4. DEVELOPMENT OF THE H3M END FITTING

Since the Mod 4 end fitting was found to be incapable of developing

the full tensile strength of Material N, it was decided to investigate

the performance of compression- type , rather than shear-type, end fittings

for this material. Accordingly, a series of tension tests was performed

using two different compression- type potted end fittings. One of these

is a commercially available fitting and the other was developed in this

laboratory in an earlier program.

The Type R/P end fitting, Figure 6, is a commercially available,

basket type, potted, compression fitting which is intended primarily

for synthetic ropes. The conical basket, or potting head, is fitted

with a yoke and bail for attachment to thimble-eye type hardware. To

mount the Type R/P fitting on an FRP rod, a fluted, cruciform wedge

( Fig. 7 ) was first driven axially into the end of the rod. (These metal wedges

are available from the manufacturer of Material N) . The inner surface of the potting head is treated with an epoxy-release agent, then

the rod is alined parallel and concentric with the fitting, which is

28

6 2 10 8^
Figure 6 - Commercially Available Type R/P End Fitting for 1/2-in (13-mm)

Diameter Rope

29 c % 1 '} 8
Figure 7 - Cruciform (left) and Conical (right) Wedges for 1/2-ln (13-inm)

Diameter Rod. All Dimensions in Inches (1 in = 25.4 mm)
then potted and cured. The release agent permits the potted material

to slide relative to the potting head, and under tensile loads the potted end seats tightly into the conical potting head. This seating process

develops significant radial compressive stresses in the potted end which

enhance the strength of the bond between the rod and the potting compound.

The release agent also facilitates removal of the potted material for

reuse of the fitting.

The NBS aluminum-block end fittings, Figure 8, were developed in

an earlier investigation [13]. The wedging and potting procedures for

these fittings are the same as those described above the Type R/P

end fittings.

These two types of fittings were used in a series of eight tensile

tests on Material N in an earlier study [13]. For those tests conical

wedges ( Fig . 7 ) and ClWl potting compound (Table 1^) were used. Except

for one test in which the rod pulled out of the fitting prematurely,

all of the specimens failed at loads between 20500 and 22300 Ibf (91

and 99 kN) by pinching off at the fitting due to the radial compressive

stresses.

Four additional tensile tests of Material N were performed in the

present investigation using these two types of end fittings. In these

tests the cruciform wedges were used. The C2W3 potting compound was

used for two of the specimens on the basis of the analytical parameter

study. PCS potting compound* was selected for the other two specimens

because of its high compressive strength. The results of the tests are

given in Table 4. These results show that the aluminum-block end fitting

31

6 2 1082
ure 8 - NBS Aluminum-Block Experimental End Fitting for 1/2-in (13-

Diameter Rod

32

6 2 7 0 8
TABLE 4

TENSILE TESTS OF 1/2-IN (13-inm) MATERIAL N WITH COMPRESSIONTYPE POTTED END FITTINGS.

Test

No.

End

fitting

Potting

compound Maximum load Failure

101408

101410

101409

101411

R/P

R/P

Al-block

Al-block

PCS

C2W3

PCS

C2W3

Ibf

21950

21000

24350

26050

(kN)

( 98)

( 93)

(108)

(116)

(a)

(a)

(b)

(b)

(a)

Initiated in the end fitting,

(b)

In the free length.

33

6 2 1082
is capable of developing the full tensile strength of Material N rod

and verified the superiority of the C2W3 potting compound. The maximum

load in Test No. 101411 is the highest ever achieved in this laboratory

on 1/2-in (13-mm) Material N at room temperature.

The aluminum-block end fitting was subsequently redesigned [16]

in a cylindrical, one-piece configuration, and assigned the laboratory

designation H3M. See Figure 9_. These changes were made in order to reduce the cost of the fitting and to facilitate its use in the testing

machine which was employed for the tensile tests in this investigation.

The changes have no major effect on the performance of the fitting.

Two more tensile tests were performed to examine the relative performances of the conical wedge and the fluted, cruciform wedge when

used with the H3M end fitting. For these tests Material E rod and C2W3

potting compound were employed. The specimen with the cruciform wedges

failed in its free length at 33450 Ibf (14 kN) . This is the highest

breaking load ever achieved in this laboratory on 1/2-in (13 mm) Material

rod. The specimen with the conical wedges pulled out of the end fitting

at 32900 Ibf (146 kN) . On the basis of these results it was decided

to continue using the cruciform wedges, which are available commercially

at less cost than the conical wedges, which had been manufactured in-hous^

*PC8 is a two-component, 100-percent solids, liquid epoxy pouring

compound having a prescribed mixing ratio.

6 2 1 0 8 2
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SECTION V

PARAMETER STUDY OF THE MANUFACTURING PROCESS, PART I

During this part of the effort toward optimizing the manufacturing

process for pultruded FRP rod, eleven different samples of 1/2-in (13-

mm) diameter rod were manufactured using E-glass roving ( Table _5) and

an isophthalic polyester resin matrix ( Table 6^) . These samples were designed

to examine the effects of nine different process parameters using two

values, or settings, of each parameter. On the basis of the pultruder's

experience, plus the results obtained from a preliminary sample which

had been manufactured and tested previously [16], constant values were

assigned to three additional process parameters for the purposes of this

study.

1. PROCESS PARAMETERS

a. Roving Preheat . Earlier studies had shown that the wetting of

the fibers by the resin might be improved by preheating the rovings to

drive off surface moisture. This was done, in this program, by passing

the rovings through an oven prior to their entry into the dip trough.

The oven is 54 in (1.4 m) long and is capable of continuous operation

between 250 and 300°F (120 and 150°C)

.

b. Roving Twist . Glass roving is commercially available either twisted

or untwisted. The use of untwisted roving could conceivably facilitate

wetting and might also be conducive the achieving straight, parallel fibers

in the finished product. On the other hand, since twisted rovings have

36 6 2 108^
TABLE 5

CHARACTERISTICS OF GLASS FIBER ROVING

Type:

Fiber diameter:

Fibers per strand:

Roving yield:

Specific gravity^^)

Type of binder:

Percent of binder:

Tensile strength^^)

End count (b)

E-£,lass (electrical grade) , continuous

K (0.00052 in, 13 um, nominal)

400, nominal

Nominal yield

30

60

yd/lb

123 + 6

61.5 + 3.1

(m/kg)

(301 + 15)

(151 + 8)

2.45

Silane (proprietary formulation)

0.55 + 0.15, by weight (mass) of glass

>200,6oO Ibf/in^ (>1400 MPa)

(a)

According to the manufacturer, except as noted.

(b)

Number of strands per roving.

(c)

Calculated.

(d)

Per ASTM Designation D-2343 [18].

37

6 2 1 0 8 ^
TABLE 6

CHARACTERISTICS OF ISOPHTHALIC POLYESTER RESIN

(a)

Monomer:

Viscosity

:

Specific gravity:

Reactivity:

Cure data^^^

Gel time:

Time to peak:

Peak temperature;

Styrene, approximately 30 percent.

23-27 poise at 77°F (2.3-2.7 Pa's

at 25°C)

1.12 - 1.13 at 77°F (25°C)

Medium

3-4 minutes.

4.5 - 5.5 minutes

.

390 - 410°F (200 - 210°C)

(a)

According to the manufacturer, for matched-metal-die molding

applications.

(b)

Per SPI procedure [19].

38

6 2 1 0 8 2
less fuzz and catenary, these might, in fact, result in better collimated

fibers. Both twisted and untwisted rovings were used.

c. Roving End Count . Glass roving is also available in a wide range

of end counts (number of strands per roving). The pultrusion of a larger

number of rovings with a smaller end count could, perhaps, provide a more

uniform distribution of fibers throughout the cross section. At the same

time, the difficulties in achieving good collimation probably increase

with the number of rovings used. End counts of 30 to 60 were examined.

d. Roving Tension . It had been observed that the fibers in pultruded

rod are frequently not straight. In the present work, therefore, several

samples were manufactured with the fibers pretensioned to straighten them.

This was accomplished by passing the rovings over an S-bend, as shown

in Figure 10. Initially, the vertical separation of the two rods which

form the S-bend was 6 in (150 mm) and the horizontal separation was 4

in (100 mm). Later, to increase the tension, the vertical separation was

reduced to 3 in (80 mm) and the horizontal separation increased to 5 in

(130 mm). In addition, each roving was passed through an eyebolt, as shown

in the figure. The individual eyebolts were rotated, as necessary, to

approximately equalize the tension in the various rovings.

e. Roving Collimation . In addition to being straight it is also important that the rovings be alined parallel to the axis of the rod. This

was promoted by constraining the rovings to follow essentially parallel

paths through the dip trough. The rovings were passed through a series

39

6 21 1 0 8 2

of three polyethylene guide plates which were mounted in the dip trough.

Figure 11 . Each plate contained holes — one hole for each roving — arranged

in a pattern of concentric circles. All of the holes were below the resin

level in the trough, and the middle guide plate was set somewhat higher

than the other two to introduce some tension into the rovings. After passing

through the third guide plate the rovings followed an essentially horizontal

path to the die, leaving the dip trough through a 5/8-in (16-mm) orifice

beneath the surface of the resin.

This apparatus is believed to reduce the inadvertent intertwining

of rovings, and to promote resin penetration by separating the mass of

rovings in the trough.

f. Immersion Length . The wetting of the fibers with the resin could

conceivably be improved by increasing the duration of the immersion in

the dip trough. This can be accomplished either by reducing the pulling

speed of the rovings or by increasing the immersion length in the dip

trough. In this program pulling speed was maintained constant, as discussed below, and the effects of immersion time were examined by using

either a "standard" dip trough, which provides an immersion length of

approximately 23 in (0.6 m) , or a long trough, for an immersion length

of approximately 54 in (1.4 m)

.

g. Ultrasonic Agitation . Another approach to improving fiber wetout involves the use of ultrasonic excitation to agitate the fibers and

drive entrapped air from the rovings. In this program a 250-W ultrasonic

exciter, which vibrates at 20000 Hz, was used in the manufacturing process

41

6 2 10 8 2

for several samples. It was found that the ultrasonic vibrations were

damped out, and the instrument rendered inoperative, when the end of the

ultrasonic horn was immersed in the dip trough to a depth exceeding about

1/16 in (2 mm). Therefore, the end of the horn was placed in contact with

the rovings near the point of their emergence from the resin.

h. Wetting Agent . Improved wetting of the fibers was also sought

through the use of a wetting additive in the resin system. Polycaprolactone

[20] was selected for this purpose on the basis of its demonstrated ability

to facilitate the dispersion of glass particles in resins [21]. It is

commercially available in flake form and, according to the manufacturer,

is readily compatible with styrene-unsaturated polyesters. In low concentrations

it also imparts improved surface properties to glass-reinforced plastics

i. Resin System Formulation . On the basis of prior experience it

was known that the resin system should have a dynamic viscosity in the

range of 11.5 to 13.0 poise (1.15 to 1.30 Pa's) for satisfactory pultrusion.

This was accomplished by adding monostyrene to the isophthalic polyester

resin. The proportion of monostyrene had to be increased when the polycaprolactone wetting agent was used since the latter tends to raise the viscosity

of the system. The resin system formulation, both with and without the

wetting agent, is given in Table _7.

j. Curing Conditions . VJith a given resin system and a given length

of heated die, attainment of a satisfactory cure primarily depends upon

two parameters: the pulling speed and the die temperature.

[22].

43

6 2 10 8 2
TABLE 7

RESIN SYSTEM FORMULATION, RUNS 1-11

Without With

wetting wetting

agent agent

' • v'' wt (mass) pet wt (mass) pet

Monostyrene 4.91 7.09

Peroxide catalyst ' 0.73 0.70

Die lubricant . 0.92 ' r 0.86

Ultraviolet inhibitor 0.13 0.12

Wetting agent - 4.96

Isophthalic polyester resin Bal. Bal.

.1

44

e s 1 0 8
From the results on a preliminary sample [16] a pulling speed of 12 in/min

(5 mm/sec) and a thermostat setting of 350°F (177°C) on the curing die

were selected. These two processing parameters were maintained for all

of the pultrusion runs.

k. Post Curing . At normal pultruding speeds each increment of rod

is exposed to the curing die for a very short time and it is not possible

to effect a complete cure in this interval. Although cure undoubtedly

proceeds to completion under ambient conditions over a period of months,

the addition of a post cure to the manufacturing process would provide

the benefits of a complete cure from the outset. These benefits may include enhanced weather resistance as well as increased strength. This

parameter was examined by adding a post cure of 16h at 275°? (135°C)

to the manufacturing process for one sample.

2. DESIGN OF EXPERIMENT

Nine of the variable process parameters were examined in two values,

or settings, of each. For example, the effects of roving end count were

investigated by manufacturing some rod samples with 30-end roving and

others with 6-end roving. For most of the parameters, however, the two

values, or settings, consisted of a "yes" or "on" condition and a "no"

or "off" condition. Thus, the effects of ultrasonic agitation were investigated by manufacturing some rod samples with agitation (the "yes"

setting) and others without agitation (the "no" setting). The nine parameters and their settings were:

45

6 2 10 8 2
Roving preheat (yes, no)

Roving twist (yes, no)

Roving end count (60, 30)

Roving tension (yes, no)

Roving collimation (yes, no)

Immersion length (long, standard)

Ultrasonic agitation (yes, no)

Wetting agent (yes, no)

Post curing (yes, no).

Three other process parameters (resin viscosity, pulling speed, die temperature) were kept constant.

Eleven samples of rod were manufactured. Table 8^ gives the selected

settings of the nine variable process parameters for each of Runs 1 through

11. This scheme permits the effects of each of three parameters (preheat,

collimation, post curing) to be examined by comparing the properties of

two samples, which had been manufactured such that all of the process

parameters were the same for both except the parameter being studied.

Thus, for example, the process parameters for Runs 1 and 2 were nominally

identical except that the roving was preheated in Run 2 while in Run 1

it was not . . , '

, , :

The remaining six variable parameters (twist, end count, tension,

immersion length, ultrasonics, wetting agent) were investigated more extensively using eight rod samples. The parameter settings for these eight

manufacturing runs were designed by Dr. G. M. Jouris of the Mathematics

Department at the Westinghouse Research Laboratories such that each of

r the six variable parameters occurs four, times at its high or "yes" setting

and four times at its low or "no" setting. The other three variable parameters

(preheat, collimation, post curing) were kept constant throughout these

eight manufacturing runs. This method permits samples from all eight runs

6 2 10 8 2
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47

6 2 1 ^82
to be used in making a decision about each of the six variable parameters

being studied. A large difference between the average value of a given

rod property at the high setting, and the average value of that property

at the low setting, indicates that the property is sensitive to the variable parameter. Conversely, a negligible difference suggests that the

property is essentially independent of the variable parameter.

Examination of Table 8^ shows which samples must be compared in order

to evaluate the effects of each variable process parameter. This information

is summarized in Table 9_. This table shows, for example, that in order

to evaluate the effect of twist in the roving, the average properties

of the rods from Runs 2, 3, 4 and 5 (which contain twisted roving) should

be compared with the average properties of the rods from Runs 6, 7, 8

and 9 (which contain untwisted roving) .

3. MANUFACTURE OF EXPERIMENTAL MATERIALS

Eleven samples of 1/2-in (13-mm) diameter glass-reinforced-polyester

rod were manufactured in accordance with the process parameter settings

given in Table 8^. Some of the operating conditions for these manufacturing

runs are given in Table 10 and discussed below.

a. Number of Rovings . The number of rovings used in the manufacture

of each sample was not arbitrary but was determined by the amount of glass

needed to produce good quality rod under the preselected processing conditions. The use of tension, for example, made it necessary to increase

the number of rovings to properly fill out the die. The glass contents

in the finished samples were measured by the manufacturer and are reported

^8

6 2 1 0 8 2
TABLE 9

EVALUATION OF THE VARIABLE PROCESS PARAMETERS

To eva.lua.te Compare the average roa properties from

the effect these runs

(high or "yes" se

1 with

CLing^ 1 V^XOw UL IIO Jdc tting)

T* o n o a i"

I: L died L 2 1X

Collimation 10 2

Post Cure 11 2

Twist 2, 3, 4, 5 6, 7, 8, 9

End Count 2, 3, 6, 7 4, 5, 8, 9

Tension 4, 5, 6, 7 2, 3, 8, 9

Innnersion Length 3, 5, 6, 8 2, 4, 7, 9

Ultrasonics 3, 5, 7, 9 2, 4, 6, 8

Wetting Agent 3, 4, 7, 8 2, 5, 6, 9

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in Table 10 . Note that for a given glass content twice as many 30-end

rovings are required as 6-end rovings.

b. Ultrasonic Loading . The ultrasonic generator was operated at the

minimum power level required to maintain loading of the ultrasonic horn

without stalling. When tension was used on the glass roving, increased

power was required to keep the horn operating.

c. Resin Temperature . Use of ultrasonic agitation caused the temperature of the resin in the dip trough to rise, resulting in partial

polymerization of the resin. This problem was serious when the standard

immersion length was used rather than the long immersion length since,

in the latter case, the energy could be dissipated to a greater volume

of resin. In Run 9, for example, which employed the standard immersion

length, the increased resin temperature made it necessary to remove 2-

to 3-oz (60- to 90-g) chunks of gelled resin, from the vicinity of the

horn, at 15- to 20-min intervals. Small resin additions were, therefore,

frequently required in order to maintain the proper resin level, and this

helped to control the temperature rise.

The higher power levels required for ultrasonic agitation, when roving

tension was used, increased the heating problem. In Run 7, when ultrasonic

agitation was used in conduction with roving tension and a standard immersion

length, the problem became most severe and the dip trough had to be cooled

externally. This was only partially successful, and it was necessary to

discontinue this run after only about 60 ft (20 m) of rod had been pultruded.

51

6 2 1 0 8 2
A certain amount of resin heating was found to be desirable when the

wetting agent was used since it tended to separate from the resin solution

at temperatures below about 77°F (25°C) . Consequently, infrared lamps

mounted beneath the dip trough were employed when ultrasonic agitation

was not being used.

4. TESTS AND RESULTS

The more important properties of the rods, from Runs 1 through 11,

were evaluated by means of the test methods and measurement techniques

described earlier. The average results of some of these tests and measurements are given in Table 11 .

a. Tensile Breaking Load . The tensile tests of rod specimens from

Runs 1 through 11 were performed at room temperature. Forty-one tests

were carried out at a crosshead speed of 0.75 in/min (0.32 mm/s) and nineteen

at 300 in/min (130 mm/s). The results of these tests are given in the Appendix

they are summarized in Table 12 . Failure in all but two of the high-speed

tensile tests initiated in an end fitting. Such results indicate that

the breaking load of the rod was greater than that corresponding to the

maximum load. , ° : , r ,, , ,;. i

b. Stress-Rupture Tests . Eighty-three stress-rupture tests were carried

out on rod specimens from Runs 1 through 11 under saturated humidity conditions. Thirty-eight of these tests were performed at 160°F (71°C)

and forty-five at 200°F (93°C) . The original intent of the tests was

to study the stress-rupture strength of each sample of material, at each

temperature, over the time range from 1 to 1000 h. It was soon realized.

52

6 2 10 8?
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53

6 2 108^
TABLE 12

AVERAGE TENSILE BREAKING LOADS, RUNS 1-11

Average breaking load

Run

No. Conventional High-speed

Ibf (kN) Ibf (kN)

1 29000 (129) 36000 ( 160)

2 29100 (129) >34700 (>154)

3 27100 (121) . >37000 (>165)

4 22500 (100) >29000 (>129)

5 23000 (102) >32500 (>145)

6 24700 (110) 38100 ( 169)

7 26200 (117) (a) (a)

8 25900 (115) >34000 (>151)

9 28000 (125) >36000 (>160)

10 30400 (135) >34000 0151)

11 29600 (132) >32500 (>145)

(a)

Not tested.

^'^ 6 2 10 8 2
however, due to scatter in the test results and to the occasional occurrence

of failures which initiated in the end fittings, that far more tests would

be required to characterize the stress-rupture strengths than had been

planned. Some trade-offs were effected by conducting fewer tests on samples

which exhibited low stress-rupture strengths so that additional tests

could be conducted on the other samples. In particular, no tests were

carried out at loads less than 10000 Ibf (44 kN) because 1/2-in (13-mm)

rods with stress-rupture capacities below thib are clearly not competitive

with commercially available products.

The results of the stress-rupture tests are given in the Appendix.

These results show several interesting features. If the data are plotted

on semi-log coordinates (see, for example. Fig . 12 ) the slope of the curve

of load vs log time-to-rupture becomes increasingly negative with increasing

time. This is contrary to the behavior of most stress-rupture data. Also,

there was no clear distinction between the stress-rupture properties at

160°F (710C) and those at 200°? (930C). Certain samples of material

appeared to be stronger at the higher temperature, particularly at longer

rupture times (see, for example, Fig . 13)

.

An explanation of this seemingly anomalous behavior is given in Section

V.4.C in terms of identifiable, opposing damage mechanisms. The existence

of the negative temperature effect ruled out the straightforward use of

reaction-rate analysis techniques to characterize the stress-rupture properties of the various samples. In fact, the existence of the unusual

temperature and time effects made it difficult to even rank the eleven

samples in terms of their stress-rupture strengths. It was recognized.

55

6 2 10 8^
TIME TO RUPTURE, h

Figure 12 - Stress-Rupture Properties of Rod from Run 1 at 200°F (93°C)

under Saturated Humidity. (1 Ibf = 4.45 N.)

56
57 4 I . H
however, that a ranking would be very helpful in assessing the effects

of the various processing parameters. Accordingly, the 100-h stress-rupture

load was arbitrarily selected as the characteristic which would be used

for comparing the anticipated weatherabilities of the samples. Values

of the 100-h stress-rupture loads were derived by interpolating — and,

in some cases, extrapolating — the test data. In so doing, considerable

judgement had to be exercised regarding the shapes of the rupture curves

between data points. The derived values are given in Table 13 and must

be regarded as estimates at best; the table is provided solely to enable

the most general comparisons to be made between the stress-rupture strengths

of different samples.

c. Mechanism of Stress-Rupture under Hot, Humid Conditions . An explanation of the unusual stress-rupture behavior which was observed in

the pultruded rod samples may be obtained by considering the effects of

the moisture-laden environment. Before the moisture can affect the properties of the rod, it must pass through two stages. First, the water

vapor in the saturated-humidity environment must be adsorbed onto the

surface of the rod specimen. The moisture must then diffuse from the adsorbed film into the interior of the rod. Since diffusion is a time-dependent

process it might be expected that for short periods of test time (i.e.,

high test loads) the stress-rupture properties would be essentially unaffected by the humid atmosphere. As time increases, more and more moisture

is diffused further into the interior of the rod. Then the detrimental

effects of water on the elevated-temperature strength of glass-fiber composites [23, 24] produce the increasingly negative slope of the rupture

58

6 2 1 08 ^
TABLE 13

ESTIMATED STRESS-RUPTURE LOADS, RUNS 1-11

Tensile load to produce rupture in lOQh at

Run

No. 160°F (71°C) 200°F (93°C) average

Ibf (kN) Ibf (kN) Ibf (kN)

1 10500 (47) 13000 (58) 11750 (52)

2 11700 (52) 10000 (44) 10850 (48)

3 9900 (44) 9500 (42) 9700 (43)

4 9000 (40) 9300 (41) 9150 (41)

5 12300 (55) 11500 (51) 11900 (53)

6 11900 (53) 11500 (51) 11700 (52)

7 11500 (51) 9800 (44) 10650 (47)

8 4000 (18) 3000 (13) 3500 (16)

9 10700 (48) 9000 (40) 9850 (44)

10 11600 (52) 11600 (52) 11600 (52)

11 12000 (53) 13000 (58) 12500 (56)

59

6 2 1 0 8 2
curves with increasing time. At some time, the specimen becomes saturated;

beyond that point the slope of the rupture curve may remain constant.

It is not clear that this point was reached with any of the samples tested

in this program. This may require test times in excess of several thousand

hours and correspondingly reduced test loads.

The finite time required for significant amounts of water to permeate

the interior of a 1/2-in (13-mm) rod serves, in effect, like an incubation

period. The existence of this incubation period explains why short-time

stress-rupture tests (e.g., 100 h or less) have failed to show any significant

effect of humidity on the stress-rupture strength of glass-reinforced

rod and rope products [5].

The amount of water that is diffused into the interior of the rod

is limited by (among other things) the amount that is adsorbed on the

surface. The extent of adsorption of water vapor is markedly reduced by

increasing the temperature [25, 26]. This explains why, after the incubation

period, the stress-rupture strengths of the rod products decreased more

rapidly at 160°F (71°C) than at 200°F (93°C). On the basis of this

argument alone it might be surmised that the stress-rupture properties

under high humidity would be very poor at room temperature, but this is

not the case, both because the diffusion of water is relatively slow at

room temperature and because room-temperature water is not nearly so damaging

to glass-reinforced-plastic composites as hot water [2A]. This was confirmed

by one stress-rupture tests on a pultruded rod specimen which was maintained

at room temperature and saturated humidity [27].

60

6 2 1082
5. ANALYSIS ANC DISCUSSION OF RESULTS

The effects of the nine variable process parameters, on the properties

of the rods, were calculated by applying the evaluation procedures ( Table

9^) to the average low-speed tensile breaking load values ( Table 12 ) and

to the average estimated stress-rupture load values ( Table 13 ) . The results

of these evaluations are given in Table 14 . This table shows, for example,

that collimation of the rovings during the pultrusion process raised the

tensile breaking load of the rod by an average of 1300 Ibf (6 kN) and

the 100-h stress-rupture load by an average of 800 Ibf (4 kN)

.

It may be seen that four of the process parameters appeared to be

beneficial to both the tensile strength and the stress-rupture strength,

namely, collimation and ultrasonic agitation of the rovings, increased

end count, and post cure of the rod. It appears likely therefore, that

the collimation process was successful in achieving a better alinement

of the fibers, and that ultrasonic agitation did improve the wetting of

the fibers. As expected, post curing was beneficial to both strength and

weatherability . The potential benefits of pultruding a large number of

small end-count rovings (i.e., more uniform distribution of fibers) were

apparently negated by the operational difficulties of avoiding entanglements

and obtaining good alinement with a large number of rovings.

Two of the process parameters appeared to be detrimental to both

the tensile strength and the stress-rupture strength, namely, increased

immersion length and the wetting agent additive. The detrimental effect

of increased immersion length is puzzling; an explanation is not immediately

61

6 2 1 0 8 ?.
TABLE 14

EFFECTS OF THE VARIABLE PROCESS PARAMETERS ON ROD PROPERTIES, RUNS 1 - II

Incremental effect on

tensile breaking 100-h stress-rupture

Parameter load load

Ibf (kN) Ibf (kN)

Preheat + 100 (+ 0.4) - 900 (- 4.)

Collimation +1300 (+ 6. ) + 800 (+ 4.)

Post cure + 500 (+ 2. ) +1600 (+ 7.)

Twist - 800 (- 4. ) +1500 (+ 7.)

End count +1900 (+ 8. ) +2100 (+ 9.)

Tension -34'^0 (-15-. ) +2400 (+11.)

Immersion length -1300 (- 6. ) - 900 (- 4.)

Ultrasonics + 500 (+ 2. ) +1700 (+ 8.)

Wetting agent - BOO (- 4. ) -2800 (-12.)

62

6 2 108^
apparent. The wetting agent undoubtedly facilitated wetting but, presumably,

diminished the quality of the fiber/matrix interfacial bond.

Twisted rovings and added tension were both found to be beneficial

to the rupture strength but detrimental to the tensile strength. The lesser

degree of catenary and fuzz in twisted rovings presumably resulted in

a better collimation of the rovings but, at the same time, in the twisted

condition the tensile strength of the glass fibers was impaired. Added

tension also contributed to better collimation but may have left a residual

tensile stress in the fibers of the rod product.

The effect of preheating the rovings was found to be relatively insignificant, possibly because the ambient relative humidity during the

manufacture of these samples was relatively low (less than 40 percent)

.

No meaningful correlation was found between the tensile breaking

load values and the 100-h stress-rupture load values. Similarly, there

is no apparent correlation between either of these two quantities and

any of the properties given in Table 11 . On the other hand, as shown in

Figure 14 , there does appear to be some correlation between transverse

tensile strength and wet breakdouTi voltage, both of which are influenced

by the quality of the fiber/matrix bond.

Comparison of the tensile breaking loads obtained at the two crosshead speeds ( Table 12 ) shows that the maximum loads are significantly

greater at high loading rates than at normal testing speeds. This suggests

that breaking strength data for glass-reinforced-olastic rod products

are not entirely meaningful unless accompanied by information regarding

the speed of loading.

63
50

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ORUNS l-ll

+ RUNS 12.13

RUNS 14,15

J I3X 10

TRANSVERSE TENSILE STRENGTH, Ibt/in*

Figure lA - Wet Breakdown Voltage Versus Transverse Tensile Strength

(1 Ibf/in^ = 6.89 kPa)

64
SECTION VI

PARAMETER STUDY OF THE MANUFACTURING PROCESS, PART II

1. EXPERIMENTAL MATERIALS

Two additional 1/2- in (13-iran) diameter rod samples (Runs 12 and 13)

were pultruded from E-glass roving and the isophthalic polyester resin

system. The processing conditions for Run 12 were selected with the intention

of optimizing the long-term weatherability of the rod. Using the stressrupture strength under conditions of elevated temperature and saturated

humidity as the laboratory index of long-term weahterability , Table 14

indicates, in principle, what the processing conditions should be. In

practice, this optimvun combination of the variable processing parameters

could not be employed with the available manufacturing facilities. Specifically,

the special equipment required to introduce collimation is not readily

compatible with the special equipment required to introduce additional

tension into the rovings. Also, the coliimating equipment constrains

the rovings to a path which is too far below the resin surface in the

dip trough to permit the ultrasonic horn to be used. Furthermore, as described

earlier, attempts to use ultrasonic agitation in combination with added

tension in the rovings introduces overheating problems, particularly when

the standard-length dip trough is used. Accordingly, the following values

of the nine variable processing parameters were selected for Run 12. These

represent a compromise between the ideal combination, as indicated by

the results given in Table 14 , and the limitations of the available manufacturing

facilities.

Roving preheat : no Immersion length:

Ultrasonic agitation:

Collimation

:

Post cure:

std

Roving twist: yes no Roving end count : 60

Roving tension: yes

Wetting agent: no

noyes

65
The three constant processing parameters (resin viscosity, pulling speed

and die temperature) were unchanged from those used in Runs 1 through

11, and the resin system formulation was the same as that used for those

earlier samples which did not employ the wetting agent.

The singular lack of success which was achieved with the wetting

agent in Runs 1 through 11 led to a decision to use Run 13 to evaluate

the benefits of adding a coupling agent, rather than a wetting agent,

to the resin system. The coupling agent selected for this purpose is a

commercially available, cationic methacrylate functional silane having

typical properties as shown in Table 15 . The settings of the other process

parameters for Run 13 were the same as those listed above for Run 12.

The resin system formulations for the two runs are given in Table 16 and

the operating conditions are given in Table 17 .

2. TEST RESULTS AND ANALYSIS

The samples from Runs 12 and 13 were subjected to the same types

of tests as had been used for Runs 1 through 11. The results of these

tests are summarized in Table 18 . Detailed data from the tensile and stressrupture tests are given in the Appendix and the relationship between transverse tensile strength and wet breakdown voltage is shown in Figure lA .

Unfortunately, the rods were somewhat bowed as received from the

manufacturer, presumably because they had been inadequately supported

during the post-curing operation. This caused longitudinal splitting,

or delamination, to develop in the tensile tests prior to total failure.

It is felt that this splitting promoted the initiation of premature failures

in the end fittings. Nevertheless, the highest load attained with the

6 2 1 08 ^
TABLE 15

TYPICAL PROPERTIES OF SILANE COUPLING AGENT

Percent Solids: 50.

Solvents

:

Mostly diacetone alcohol.

Color

:

Amber brown.

Refractive index at 77°F (25°C): 1.457.

Specific gravity at 77°F (25°C): 1.06.

Viscosity at 77°F (25°C)

:

0.7A poise (0.074 Pa-s)

.

Flash point, open cup: 130°F (54°C).

Suitable diluents: Alcohols, water.

(a) . According to the manufacturer.

67

6 2 1082
TABLE 16

RESIN SYSTEM FORMULATION, RUNS 12 AND 13

Monostyrene

Peroxide catalyst

Die lubricant

Ultraviolet inhibiter

Coupling agent

Isophthalic polyester resin

Run 12

wt (mass) pet

4.91

0.73

0.92

'

0.13

Bal.

Run 13

wt (mass) pet

4.89

0.74

0.93

0.13

0.30

Bal.

68 ^

6 2 1 0 8 2
TABLE 17

OPERATING CONDITIONS FOR MANUFACTURE OF RUNS 12 AND 13

Ambient

Run No. of Glass relative S-bend Resin

No. rovings content humidity spacing temperature

wt (mass) pet percent in (mm)

12 24 75.4 37-39 5,3 (130,80)" (b)

13 24 75.6 39-40 5,3 (130,80) (b)

(a)

See Table 10.

(b)

Ambient

69

6 2 10 8 2
TABLE 18

DIMENSIONS AND PROPERTIES SUMMARY, RUNS 12 AND 13

Run 12 Run 13

Diameter, in 0.497 0.497

(mm) (12.6) (12.6)

Density, Ib/in^ 0.0721 0.0721

(Mg/m3) (2.00) (2.00)

Weight (mass), lb/ft 0.168 0.168

(kg/m) (0-250) (0.250)

Rockwell hardness (Scale E) 67 60

Transverse tensile strength, Ibf/in^ 1^00 1400

(MPa) (11) (10)

Wet breakdown voltage, kV 22 15

Tensile breaking load,

conventional, Ibf 26750 25250

(kN) ( 119) - ( 112)

high-speed, Ibf 34500 ^3000

(kN) ( 153) ( 1^7)

100-h stress-rupture load, estimated,

at 160°F (71°C), Ibf 12300 11300

(kN) (55) (50)

at 200OF (930C), Ibf 12250 11000

(kN) (54) (49)

average, Ibf 12300 11150

(kN) (55) • (50)

70

6 2 10 8 2
Run 12 specimens at normal speeds is close to the calculated breaking

load for this run, which is 26100 Ibf (116 kN).* Comparison of the breaking

loads for Run 13 with those for Run 12 (Table 18) shows that the coupling

agent additive in Run 13 was ineffective, at best, insofar as the tensile

breaking load is concerned.

In the high-speed tensile tests the failures also appeared to have

initiated in the end fittings. However, just as with Runs 1 through 11,

the breaking loads in the high-speed tests are significantly greater than

those achieved in the conventional tensile tests.

Some delamination due to bowing was also experienced in the stressrupture tests but the conclusion is nevertheless clear ( Table 18 ) that

the coupling agent additive in Run 13 was detrimental to the stress-rupture

strength.

The average 100-h stress-rupture load for Run 12, 12300 Ibf (55 kN)

,

is considerably less than the calculated value (from Tables 13 and 14 ).

It is, however, approximately equal to the 100-h stress-rupture load for

Run 11 (12500 Ibf, 56 kN) which was the highest of all. It is evident,

therefore, that the various process parameters are not independent in

terms of their effects on stress-rupture strength, which is the way they

were treated in the design of the experiment. In other words, if the advantages

of using twisted roving, a high end count and added tension result from

*This calculation is straightforward. Starting, for example, with

the conventional breaking load for Run 1 ( Table 12 )

, the breaking load

for Run 12 is found by algebraically adding to this value the breaking

load increments for tension and post cure ( Table 14 )

.

71

6 2 10 8 2
their tendencies toward less entanglement and better fiber collimation,

it follows that the benefits of using the three together would not necessarily

be linearly additive. Perhaps 12500 Ibf (56 kN) is about the limit of

the improvement in stress-rupture capacity that can be attained with this

resin/fiber combination through modification of the process parameters.

If this is so, further improvements, if any, would have to come from changes

in the consitituent materials of the rod.

Although this program was concerned primarily with mechanical properties,

it is interesting to note the wide differences that were observed in the

average wet breakdown voltages of the different samples ( Fig . 14 ) . These

ranges from 45 kV for rod from Run 8 to 15 kV for rod from Run 13. Largely

as a matter of curiosity, the average breakdown voltages of samples from

these two runs were measured again, this time using dry specimens. Interestingly, the average dry breakdown voltages were found to be nearly

equal; 64 kV for Run 8 and 62 kV for Run 13. It thus appeared that the

process parameters have no significant effect on dry breakdown voltage.

This conclusion was supported by subsequent tests on specimens from Run

1 which exhibited an average dry breakdown voltage of 67 kV.

SECTION VII

VARIATION OF THE CONSTITUENT MATERIALS

1. SELECTION OF THE CONSTITUENT MATERIALS -

•

This part of the program was designed to evaluate the additional

improvements in the weatherability of the pultruded rod product introduced

by changing the fiber and matrix constituents. To this end, selection

of a non-metallic fiber material and a matrix resin, which exhibit greater

72

6 2 10 8 2
moisture resistance than E-glass and isophthalic polyester, was desired.

Largely on the basis of the manufacturer's claims, aramid was selected

as the fiber material. According to these claims aramid fiber experiences

no reduction in tensile strength as a result of 24-h immersion in water,

and less than a four-percent decrease in the interlaminar shear strength

of unidirectional aramid-fiber composites following a 90-day exposure

to high humidity at 120°F (49°C) . It has also been reported [28, 29]

that the stress-rupture strength of aramid/epoxy strands is superior to

that of glass/epoxy strands.

A small, preliminary sample of 1/4-in (6-iran) diameter rod was pultruded

from a quantity of reject-grade aramid fiber and the isophthalic polyester

resin. Tensile tests on specimens of this rod (see Appendix) revealed

satisfactory short-time strength but the appearance of the fractured

specimens suggested that the fibers had been only partially wetted by

the resin. This observation was confirmed by tests conducted by the aramid

fiber manufacturer. These tests showed that aramid/isophthalic composites

exhibit poor interlaminar shear strengths. These tests also suggested

two other resin systems which provide substantially higher shear strengths

in combination with aramid fiber. One of these, a propoxylated bisphenol-A

fumarate polyester, has been used as the matrix material for a glass

mat composite that exhibited relatively little degradation of tensile

strength after two years in a hot, humid climate [30]. This fact, together

with other data that attribute higher weather resistance to polyester

composites than to epoxy composites [31], led to the selection of the

bisphenol fumarate polyester as the resin system to be used in this part

of the program.

73 6 2 1 0 8 2
It should be mentioned that what, to the eye, appears to be poor

wetting of the aramid fibers is not apparent in photomicrographs of aramidfiber composites [28, 32]. These photomicrographs do not show voids around

the fibers, even under magnifications of 2000. It might be speculated

that the fibers are, in fact, wetted by the resin but that the quality

of the bond is destroyed during the cooling process following curing as

a result of the aramid fiber's negative coefficient of thermal expansion

[33].

The characteristics of the bisphenol fumarate polyester resin and

the aramid fiber that were used in this program are given in Tables 19

and 20 , respectively.

2. MANUFACTURE OF EXPERIMENTAL MATERIALS

Two 1/2-in (13-mm) diameter samples. Runs 14 and 15, were manufactured.

Run 14 was pultruded with the bisphenol fumarate polyester resin and the

same E-glass fiber that had been used for the previous samples. Run 15

was pultruded with the bisphenol fumarate polyester resin and aramid fiber.

In order to derive the most useful information from the results,

the processing conditions for the two samples should be similar to each

other and to those used for Run 12. (Run 12, it will be recalled, was

designed to "optimize" the weatherability of the E-glass/isophthalic combination.) However, practical considerations necessitated some differences

in the settings of both the variable process parameters and the "constant"

process parameters.

74

6 2 1 0 8 2
TABLE 19

CHARACTERISTICS OF BISPHENOL FUMARATE POLYESTER RESIN ^^-^

Ilonomer

:

Styrene, 33 percent.

Viscosity

:

110 - 150 poise (11 - 15 Pa.s)

at 77°F (25°C)

Specific gravity: 1.08.

Storage life: 6 months at 75°F (24°C)

(a)

According to the manufacturer.

75

6 2 108^
TABLE 20

CHARACTERISTICS OF ARAMID FIBER ROVING

Type:

Specific gravity:

Fibers per strand:

End Count

Roving denier(c):

Fiber diameter (d):

Twist:

Finish

:

Tensile strength^^^

Tensile modulus (e):

Commercial grade, continuous

1.45.

1000.

10.

14200.

0.00046 in (12 urn).

None.

None.

525,000 lbf/in2 (3620 MPa)

.

19 X 10 Ibf/in^ (130 GPa)

.

(a)

According to the manufacturer, except as noted.

(b)

Number of strands per roving.

(c)

Mass in grams of 9000 meters, by definition,

(d)

Calculated.

(e)

Per ASTM Designation D-2343 [18].

76

6 2 1 0 8 2
a. Variable Process Parameters . Data acquired in the course of anothe

Air Force program [34] showed that pre-drying of aramid fiber is absolutely

essential to achieve good wetting by the resin. Accordingly, the rovings

for Runs 14 and 15 were preheated. This had not been done for Run 12.

The form of aramid roving that was recommended by its manufacturer for

this application (10-end, untwisted) did not match the "optimum" form

of E-glass roving (60-end, twisted). In view of these considerations the

following settings of the variable process parameters were selected for

Runs 14 and 15:

Run 14 Run 15

Roving preheat yes yes

Roving twist yes no Roving end count 60 10

Roving tension yes yes

Wetting agent no no Immersion length std std

Ultrasonic agitation no no Collimation no no Post cure yes yes

It has been reported [35] that abrasion produces a decrease in the

compressive yield strength of aramid yarn. Therefore, to minimize the

possible effects of abrasion damage on the pultruded rovings, the rods

which form the tension S-bend (Fig . 10 ) were mounted in ball bearings

for Run 15. During the pultrusion process these rods were observed to

rotate freely. Thus, while abrasion damage was probably avoided, the degree

of tension introduced into the rovings was probably reduced.

b. Constant Processing Parameters . In the manufacture of Runs 1

through 13, the settings of three processing parameters were maintained

77

6 Si 1 08 ^
constant, i.e., resin viscosity, pulling speed and die temperature. The

different cure characteristics of the bisphenol fumarate polyester resin,

as compared with the isophthalic polyester resin, necessitated some changes

in these processing parameters for the manufacture of Runs 14 and 15.

The bisphenol fumarate polyester was found to have a higher polymerization exotherm. Thus, at a pulling speed of 12 in/min (5 mm/s) (which

had been used for Runs 1-13) boiling styrene vapors ruptured or otherwise

damaged the rod as it emerged from the die. Attempts to correct this

by changing the catalyst concentration had the effect of increasing the

gel time to unacceptable levels without significantly lowering the exotherm.

The pulling speed was, therefore, lowered to 6 in/min (3 mm/s) for Runs

14 and 15.

The bisphenol fumarate polyester resin was thinned with monostyrene

to provide the required viscosities. In the case of Run 14, the resin

system viscosity was in the same range as had been used for the pultrusion

of Runs 1 through 13. The difficulties in wetting aramid fiber, however,

necessitated a further reduction in viscosity for Run 15 in order to

obtain good surface quality on the pultruded rod. The resin system formulations for Runs 14 and 15, and the resultant viscosities, are given

in Table 21. . , ^ -if

c. Operating Conditions . The operating conditions for the manufacture

of Runs 14 and 15 are given in Table 22 . Although the individual fiber

diameters of E-glass and aramid are nearly equal, each E-glass roving

contained 24000 fibers while each aramid roving contained only 10000

fibers, and this is reflected in the difference in the number of rovings

78

6 2 1 0 B 2
TABLE 21

RESIN SYSTEM FORMULATION AND VISCOSITY, RUNS 14 AND 15

Monostyrene

Peroxide catalyst

Die lubricant

Ultraviolet inhibitor

Bisphenol fumarate polyester

Run 14

wt (mass) pet

19.20

0.49

0.93

0.13

Bal.

Run 15

wt (mass) pet

22.15

0.49

0.93

0.14

Bal.

Viscosity at 77°F, poise

(Pa-s)

12.1

(1.21)

7.9

(0.79)

79

6 2 10 8 2
TABLE 22

OPERATING CONDITIONS FOR MANUFACTURE OF RUNS 14 AND 15

Run No. 14 15

Fiber type E-glass aramid

No. of rovings 25 58

Fiber content, wt (mass) pet

vol pet

78.8

61.5(a)

60.6(a)

53.0(a)

Ambient relative humidity, pet 23-27 35-37

S-bend spacing (^), in (mm) 5,3 (130,80) 5,3 (130,80)

Resin temperature (c) (c)

(a)

Calculated.

(b)

See Table 10.

(c)

Ambient, -approximately 73°F (23°C)

80

6 2 10 8^
required for each run. Nevertheless, the fiber content of the aramid

rod had to be made less than that of the glass rod because of the difficulties in wetting the aramid fiber. The ignition loss test for measuring

fiber content could not be applied to the aramid rod so the fiber fractions

shown in the table for this product were calculated. Since the density

of aramid is only about 60 percent of the density of E-glass, volume

fractions of fiber content provide a more meaningful comparison between

the two samples than weight fractions, and these data are included in

the table.

3. TEST RESULTS AND ANALYSIS

Specimens from Runs 14 and 15 were subjected to the same types of

tests as had been used on the previous samples. The results are summarized

in Table 23 . Data for Run 12 are included to facilitate comparisons.

Detailed data from the tensile and stress-rupture tests are given in

the Appendix.

As expected, the density of the aramid-reinforced rod is less than

two- thirds of that of the glass-reinforced rods. The hardness of the

glass/isophthalic rod is 67 on the Rockwell E scale. (All of the postcured glass/isophthalic samples had hardnesses of 60 or more.) Changing

to the bisphenol fumarate resin reduced the hardness to 45, and adding

aramid fiber in place of glass produced a further reduction to 34. A

similar trend is noted for the transverse tensile strength and the wet

breakdown voltage. As shown in Figure 14 , however, the relationship between

transverse tensile strength and wet breakdown voltage is maintained.

The average dry breakdown voltage was measured on specimens from Run

81

6 ;2 1 0 8 2
TABLE 23

DIMENSIONS AND PROPERTIES SUMMARY, RUNS 12, 14 AND 15

Run 12 Run 14 Run 15

Fiber E-glass E-f^lass aramid

Resin^^^ IPR BFPR BFPR

Diameter, in 0.497 0.496 0.489

(mm) (12.6) (12.6) (12.4)

Density, Ib/in'^ 0.0721 0.0718 0.0464

(Mg/m3) (2 . 00) (1 99) (1 28")

Weight (mass), lb/ft 0.168 0.167 0.105

(kg/m) (0.250) (0.249) (0.156)

Rockwell hardness (Scale E) 67 45 34

Transverse Tensile strength. Ibf/in2 1600 'L 1100 700(b)

(MPa) (11) (8) (5)(b)

Wet breakdown voltage, kV 22 17 8

Tensile breaking load.

conventional, Ibf 26750 28750 • 27650

(kN) ( 119) , (128) ( 123)

high-speed, Ibf 34500 35000 30000

(kN) ( 153) (156) (133)

100-h stress-rupture load, e stimated,

at 160°F (71°C), Ibf 12300 12400 15200

(kN) (55) (55) (68)

at 200°F (93°C), Ibf

• 12200 12800 17000

(kN) (54) (57) (76)

average , Ibf 12300 • 12600 16100

(kN) (55) (56) (72)

IPR (isophthalic polyester resin) ; BFPR (bisphenol fumarate

polyester resin)

Value is questionable; diametral compression specimens deformed

substantially before failure.

82

'> 62 1 OB 2
15 and found to be only 37 kV, whereas glass/lsophthalic rods exhibit

dry breakdown voltages of 60 kV or more. The low transverse tensile strength

and the low breakdown voltages for the aramid-reinforced rod are attributed

to the relatively poor wetting of the fiber by the matrix resin.

a. Tensile Properties . Examination of the tensile breaking loads

in Table 23 shows that these values are not greatly affected by changing

from glass fiber to aramid fiber or by changing from isophthalic to bisphenol

fumarate polyester. Perhaps the only significant effect to be noted is

that the aramid-reinforced rod did not exhibit the marked increase in

strength at high loading rates that was observed with the glass-reinforced

rods. It should also be pointed out that in the conventional tensile

tests of the aramid-reinforced specimens all failures occurred inside

an end fitting. In this case this behavior is believed to be due, only

in part, to the comparatively low shear strength of the rod product.

A major cause for the inability to attain the full strength of the aramidreinforced rod is believed to lie in the inadequacy of the H3M end fittings.

These fittings, it will be recalled, were developed specifically for

glass-reinforced products. The design of an efficient end fitting for

aramid-reinforced rod would have to be tailored to the elastic and deformational characteristics of that material.

The mode of failure of the aramid-reinforced rod specimens in tension

also merits comment. Whereas glass-reinforced rods shatter upon tensile

failure, with all of the fibers brooming out explosively, the aramidreinforced rod specimens remained relatively intact apart from the fracture

location. However, the recoil from the tensile fracture generally caused

83

6 2 1 i)S 2
the specimens to buckle compressively at another location along the length

of the rod and numerous compressive shear cracks developed on the surface.

See Figure 15 . This unusual behavior is believed to result from the relatively

poor compressive strength properties that have been reported for aramid

fiber [36, 37]. . .

The fact that Table 23 shows only minor differences in tensile breaking

load is only incidental to this program. The new fiber and resin constituents

that were used in Runs 14 and 15 were primarily selected to give improved

weatherability , i.e., increased stress-rupture life under moist conditions.

b. Stress-Rupture Properties . Several of the test specimens from

Run 14 developed longitudinal cracks during stress-rupture testing. These

seemed to be due to swelling of the specimens, as a result of the absorption

of moisture from the saturated-humidity environment, despite other data

which suggest that bisphenol polyesters should be less susceptible to

this type of damage than isophthalic polyesters [38]. The presence of

the longitudinal cracks did not appear to affect the load-carrying capability

of the specimens and, in fact, the 100-h stress-rupture capacities for

Run 14 were slightly greater than those for Run 12 (Table 23 )

.

The stress-rupture data for the specimens from Runs 14 and 15 exhibited

the same unusual characteristics as those for the glass/isophthalic specimens,

namely, (1) the slopes of the rupture curves became increasingly negative

with increasing time, and (2) the stress-rupture strength tended to be

greater at 200°F than at 160°F, particularly at long rupture times.

From this it might be inferred that these phenomena are not limited to

84

specific types of resin matrices and fiber reinforcements. Rather, it

would appear that the critical region is the fiber/matrix interface,

which tends to support the stress-rupture analysis given in Section 5.4.3.

Table 23 shows that the use of aramid-fiber reinforcement produced

a striking improvement in stress-rupture properties as compared with

glass-fiber reinforcement. This suggests that the weatherability of the

aramid-reinforced rod under moist conditions may be expected to be substantially

superior to that of glass fiber-reinforced rod.

SECTION VIII

DISCUSSION AND RECOMMENDATIONS

The principal objective of this program was the development of a

pultruded, non-metallic rod material with enhanced strength, over currently

available rods, under long-time exposure to moist environments. In pursuing

this objective the greatest emphasis was placed on the improvements

that could be achieved through modification of the manufacturing process

parameters. Nevertheless, the degree of improvement that was attained

in this way was relatively small. The test results suggest that while

individual process parameters may have significant effects on the weatherability

of the product, the effects of optimizing several such parameters are

not lineraly cumulative, and the total Improvement that was obtained

in this way is less than impressive. In fact, the properties of the glass

FRP rod which was manufactured with the "optimum" combination of the

process parameters (Run 12) are not especially noteworthy in comparison

with the properties of some commercially available products [5].

This finding may indicate that the manufacturers of high-performance

pultrusions have already optimized their processes; not necessarily by

86

6 2i 1 0 8 ^
means of formal research programs but, rather, through regular observation

of product characteristics as they are influenced by day-to-day variations

in the manufacturing process. It is also possible that the present study

did not explore the individual process parameters in sufficient depth.

Only two settings of each process parameter were examined whereas a thorough

understanding of the effects of each parameter would require a more intensive

investigation. For example, it was found that 60-end glass rovings provide

an improvement in this application over 30-end rovings. Would 120-end

rovings furnish an additional improvement? The data are inadequate to

provide a definitive answer to this question.

Although the parameter study of the manufacturing process did not

lead to major improvements in the rod product, it did lead to the development of several new test methods and testing techniques which have potential

value for future R&D programs. These accomplishments, and others, are

summarized in the next section of this report.

In contrast to the magnitude of the study devoted to the manufacturing process, a relatively small effort was directed toward an investigation

of the benefits that could be derived from changes in the material constituents of the rod. Yet, the payoff was substantial. It was found that

the stress-rupture strength of rod fabricated from aramid fiber and bisphenol

fumarate polyester resin is about thirty percent higher than that of

"optimized" E-glass/isophthalic polyester rod, under high heat and humidity.

Since the aramid FRP rod was manufactured without full knowledge of the

effects of the process parameters on the properties of this material,

87

6 2 1 0 8 2
it would seem that further improvements could be realized by optimizing

some of these parameters, such as end count, coupling agent, etc.

On the basis of these results it would seem that a significantly

improved non-metallic antenna-support material was developed, however,

several words of caution are in order.

It remains to be seen whether the results of stress-rupture tests

under high heat and humidity can, in fact, serve as measures of weatherability. This premise is being tested now by the installation of several

aramid FRP guys, similar to the rod manufactured in Run 15, on antenna

towers in Colorado and Hawaii (NBS radio stations WWV and WWVH, respectively).

Another cause for concern is the low compressive strength of aramid

FRP rod. Although antenna-support materials are primarily tension members,

compressive bending stresses introduced during handling, shipping, storage

and installation could, perhaps, cause damage. For example, it is calculated

that 1/2-in (13-mm) diameter aramid FRP rod may not be coiled to diameters

of less than 11 ft (3.4 m) lest compressive failure result. This is far

in excess- of the diameters to which glass FRP rod may safely be coiled.

It would appear that storage tests, similar to those that ha~ve been carried

out on glass FRP rod products [5], should be performed to establish the

safe limits of coil diameter and storage temperature for aramid FRP rod.

Similarly, the flexural strength under low temperatures and the resistance

to transverse vibration should be checked for aramid FRP rod, as has

been done for glass FRP rod [5]. : . ^ b .

Finally, the electrical characteristics of aramid FRP rod merit

further study, particularly for applications where the rods may be exposed

88

6 2 1 08 2
to high voltages and strong electromagnetic fields. The dielectric strength

of aramid FRP rod was examined only cursorily in the present program

and the results were less than encouraging.

SECTION IX

SUMMARY AND CONCLUSIONS

Fifteen experimental samples of pultruded FRP rod were manufactured

and tested in this program to develop a non-metallic antenna-support

material with improved weatherability . Thirteen of these samples were

lased to explore the effects of modifications of the pultrusion process

(Sections V and VI) . These samples were designed on the basis of a survey

of the pultrusion processes used by manufacturers of glass FRP rod (Section II. 1)

and an examination of the deficiencies in existing glass FRP rod

products (Section II. 2). The other two samples were used to explore the

effects of changes in the material constituents of the rod (Section VII)

.

The results of elevated- temperature stress-rupture tests, under saturated

humidity conditions, were used as the laboratory measure of weatherability.

It was found that modifications of the pultrusion process can, indeed,

improved the weatherability of glass FRP rod. Each of the following modifications were found to raise the 1-0-hour stress-rupture strength by more

than ten percent under high heat and humidity:

adding tension in the rovings,

using a roving end count of 60 rather than 30,

using twisted rather than untwisted rovings,

ultrasonically agitating the rovings in the dip trough, and

post curing the rod.

Collimating the rovings during passage through the dip trough resulted

in a lesser improvement. Of these modifications, only the addition of

89

6 2 1 0 8 2
i

tension in the rovings produced a simultaneous reduction of more than

ten percent in the short-time tensile strength of the product.

The following modifications were found to reduce the 100-hour stressrupture strength of glass FRP rod:

increasing the immersion length of the rovings in the dip trough,

adding a polycaprolactone wetting agent to the resin, and

adding a silane coupling agent to the resin.

Unfortunately, major improvements in weatherability (i.e., 30 percent

or more) could not be achieved by using all of the beneficial modifications

simultaneously, partly because limitations of the manufacturing facilities

did not permit all of the beneficial modifications to be used simultaneously,

and partly because the improvements attributable to each modification

were not linearly cumulative when used in combination. As a result, the

weatherability of glass FRP rod was not significantly improved here over

the weatherability of certain high-performance glass FRP rod products

that are commercially available at this time.

In that part of this program in which different material constituents

were examined, changing from an isophthalic polyester resin system to

a bisphenol fumarate polyester resin system produced only minor improvements

in the 100-hour stress-rupture strength of glass FRP rod under high heat

and humidity. However, replacing the E-glass fiber with aramid fiber

yielded a striking, 30-percent improvement in the 100-hour stress-rupture

strength under high heat and humidity. The short-time tensile strength

was not significantly different from that of glass FRP rod despite the

fact that the fiber volume-fraction of the aramid FRP rod was less than

that of high-performance glass FRP rod (53 percent vs 61 percent). The

90

62 1 f)S 2
properties of the aramld FRP rod were even more impressive on a strength/

weight basis since the density of this product was less than two-thirds

of that of glass FRP rod. It is logical to expect that a parameter study

of the pultrusion process for aramid FRP rod — similar to that which

was conducted here for glass FRP rod — could lead to further improvements

in the aramid FRP rod.

Despite these promising results, aramid FRP rod cannot be recommended

for antenna-support applications without additional study. There is an

indicated need for further testing and evaluation of certain peripheral

properties that were only examined cursorily in this program (Section VIII)

During the course of this investigation a number of other accomplishments and conclusions were recorded which have potential value in future

R&D studies and applications. These include:

1. Two new potted end fittings for glass FRP rod were developed

which are superior, in several respects, to a variety of commercial

end fittings with which they were compared. These new fittings, which are

generally capable of achieving the full tensile strengths of available

glass FRP materials, include a shear-type fitting (Mod A) and a compression

type fitting (H3M) (Section IV) . The method by which these fittings were

developed is believed to be applicable to the development of a highperformance end fitting for aramid FRP materials, as well.

91

6 55 1 0 8 2
2. A high-speed tensile test method for FRP rod products was

developed (Section III.l). Through the use of this method it was shown

that the tensile strength of glass FRP rod is substantially greater

at high loading rates than at conventional loading rates ( Table

12). This rate effect was not apparent for the aramid FRP rod.

. 3. Two test methods were developed which furnish indirect

evidence of the quality of the fiber/matrix interface in FRP rod.

One of these, a diametral compression test (Section III. 7), provides

a measure of the transverse tensile strength of the rod, which is

believed to be influenced by the tensile strength of the interfacial

bond. The second test method measures the electrical breakdown voltage

of wet FRP rod samples, which is believed to be influenced by the

contiguity of the fiber/matrix interface (Section III. 5). A correlation

between the results of these two tests methods was established (Fig. lA).

4. A series of six 30000-lbf (130-kN) capacity creep-testing

machines was designed and fabricated. These machines, which incorporate

a 100:1 compound-lever system, will accommodate test specimens up

to nine feet (3m) long and are equipped with environmental chambers

for use to 200°F (93°C) under saturated humidity conditions (Section III. 2).

5. The stress-rupture behavior of FRP rod, under high humidity,

was found to exhibit unusual temperature and time characteristics.

92

6 2 1 0 8 2
This behavior was explained in terms of the opposing effects of

temperature on two time-dependent processes which govern the transport

of moisture from the environment to the fiber/matrix interface (Section V.4.C)

93

6 2 1082
APPENDIX

1. TENSILE TEST RESULTS, RUNS 1-11

The results of the tensile tests at a crosshead speed of 0.75 in/min

(0.32 mm/s) are given in Table A.l . Except as otherwise noted, each

specimen was fitted with H3M end fittings using cruciform wedges and

C2W3 potting compound, and had a free length between 52 and 62 in (1.3

and 1.6 m) . Also given in Table A.l is the average breaking load for

each run. In general, this was calculated by averaging the maximum loads

that were attained with specimens that failed in their free lengths.

However, this procedure could not be applied to the results from Runs

3 and 7 because, in these cases, failures in the free lengths were not

obtained. Run 3 was one of the runs which utilized the wetting agent,

which turned out to be a very effective low-profile additive, and this,

together with a long immersion time and ultrasonic agitation, produced

a rod with an extremely slick outer surface which could not be adequately

gripped. Four tensile tests resulted in four pullouts. The average breaking

o load of Run 3 is, therefore, only estimated on the basis of the highest

maximum load attained.

Two tensile tests on rod specimens from Run 7 resulted in failures

which apparently initiated in an end fitting. The shortage of material

from Run 7 precluded additional testing and the average tensile strength

of this run is also estimated on the basis of the limited data obtained.

In calculating the average tensile strength for Run 10, the results

of two tests, which had culminated in pullouts, were included in the

94

6 2 1 0 8 2
average since the maximum loads in these two tests exceeded that obtained

with one specimen which had failed in its free length.

In the first three high-speed tensile tests that were performed

the failures appeared to initiate in an end fitting. Because of the

viscoelastic nature of the C2W3 potting compound (which is normally

used with H3M end fittings) it was surmised that the high loading rates

were causing the potting compound to behave like a stiff material.

Consequently, a new potting compound, C1W2, was formulated, which is

more flexible than C2W3. Nevertheless, failure in most of the high-speed

tensile tests appeared to initiate in an end fitting. The results of

these tests are given in Table A.

2

. The free lengths of all specimens

were 27 or 28 in (0.69 or 0.71 m) and, except as noted, all failures

appeared to have initiated in an end fitting.

2. STRESS-RUPTURE TEST RESULTS, RUNS 1-11

The results of eighty-three rupture tests on rod specimens from

Runs 1 through 11, at 160 and 200°F (71 and 93°C) , are given in Tables

A.

3

and A.

4

, respectively. Each specimen was fitted with Type R/P commercial

end fittings using cruciform wedges and C2W3 potting compound. Except

as otherwise noted, each specimen failed in its free length within the

temperature-humidity chamber.

3. TENSILE TEST RESULTS, RUNS 12 AND 13

The results of the tensile tests at a crosshead speed of 0.75 in/mln

(0.32 mm/s) are given in Table A.

5

. Each specimen was fitted with H3M

end fittings using cruciform wedges and C2W3 potting compound and, except

95

6 2 10 8 2
as otherwise noted, had a free length between 52 and 62 in (1.3 and 1.6 m)

.

The results of the tensile tests at a crosshead speed of 300 in/min

(130 mm/s) are given in Table A.

6

. Here, too, each specimen was fitted

with H3K end fittings using cruciform wedges but in this case the more

flexible ClVv2 potting compound was used. Nevertheless, all failures appeared to have initiated in an end fitting. The free lengths of all specimens

were 27 or 28 in (0.69 or 0.71 m)

.

4. STRESS-RUPTURE TEST RESULTS, RUNS 12 AND 13

The results of thirteen stress-rupture tests on rod specimens from

Runs 12 and 13 at 160 and 200°F (71 and 93°C) are given in Table A.

7

.

Each specimen was fitted with Type R/P commercial end fittings using

cruciform wedges and C2W3 potting compound. Except as otherwise noted,

each specimen failed in its free length within the temperature-humidity

chamber.

5. TENSILE TESTS ON PRELIMINARY SAMPLE OF 1/4-IN (6-mm) ARAMID/ISOPhTHALIC ROD

Six tensile tests were performed at room temperature using a crosshead

speed of 0.75 in/min (0.32 mm/s). All of the specimen failures occurred

in or adjacent to an end fitting. These were attributed to the low shear

strength of the rod which prevented the effective transfer of load from

the fittings to the interior of the rod specimens. The low shear strength

was evident from the appearance of the failed specimens, which showed

that the aramid fibers had been only sparsely wetted by the resin. The

test results are given in Table A.

8

.

96

6 1 0 8 2
6. TENSILE TEST RESULTS, RUNS lA AND 15

Fifteen tests were performed at room temperature. The results of

twelve tests at a crosshead speed of 0.75 in/min (0.32 mm/s) are given

in Table A.

9

; all of these specimens had free lengths of 47 or 48 in

(1.2 m) . The results of three tests at 300 in/min (130 mm/s) are given

in Table A. 10 ; these specimens had free lengths of 27 or 28 in (0.7 m)

.

7. STRESS-RUPTURE TEST RESULTS, RUNS 14 AND 15

Twenty-one stress-rupture tests were performed under saturated humidi

conditions, eight at 200°F (93°C) and thirteen at 160°F (71°C) . The

results are given in Table A. 11 .

6 2 10 8 2
TABLE A.l

RESULTS OF CONVENTIONAL TENSILE TESTS, RUNS 1-11

Rod diameter: 1/2 in (13 mm), nominal.

Free length: 52 to 62 in (1.3 to 1.6 m) , except as noted.

Crosshead speed: 0.75 in/min (0.32 mm/s).

End Fittings: H3M with cruciform wedges and C2W3 potting

compound, except as noted.

Run Specimen

No. No. Maximum load Notes

Ibf (kN)

1 RlPc8B 29450 (138) a

1 RlPc3B 29000 (129) a

1 RlPc6B 28600 (127) a

1 Kir CoA Z J JUU (.113; a , b

1 Average 29000 (129)

2 R2Pc5B 28700 (128) a

2 R2Pc7B 20550 ( 91) c

2 R2PclA 26550 (118) d

2 R2PclB 29450 (131) a

2

• R2Pc4B 7150 ( 32) c,e

2 Average 29100 (129)

3 R3PclA 24650 (110) c

3 R3Pc2A 11850 ( 53) c

3 R3Pc2A 25250 (112) c,f

3 R3Pc4A 27050 (120) c

3 Average 27100 (121) g

4 R4Pc3B 22950 (102) a

4 R4Pc4A 21000 ( 93) a

4 R4Pc8A 20000 ( 89) d

4 R4Pc8B 10300 ( 46) c 4 R4Pc8C 23550 (105) a

4 Average 22500 (100)

5 R5APc4A 23150 (103) a

5 R5APclB 22800 (101) a

5 R5APclA 18500 ( 82) d

5 Average 23000 (102)

6 R6Pc2B 20700 ( 92) a

6 R6Pc2A 25450 (113) a

6 R6Pc2C 28000 (125) a

6 Average 24700 (110)

(continued)

98

6 2 1 0 8 2
TABLE A.l - (Continued)

Run Specimen

No . No

.

Maximum load Notes

. Ibf (kN)

7 R7PclA 25750 (115) d

7 R7PclB 26150 (116) d

7 Average 26200 (117) g

8 RSPclA 25400 (113) a

8 R8Pc2A 26750 (119) a

8 R8Pc3A 25700 (114) a

8 Average 25900 (115)

9 R9PclA 27800 (124) a

9 R9Pc2A 28150 (125) a

9 R9Pc3A 26650 (119) d

9 Average 28000 (125)

10 RlOPclA 30700 (137) h

10 R10Pc2A 23750 (106) c 10 R10Pc3A 31400 (140) a

10 RlOPcAA 28400 (126) a,i

10 RlOPcSA 31250 (139) h,i

10 Rl0Pc7A 26100 (116) a,j

10 Average 30400 (135)

11 RllPc5 28000 (125) c 11 RllPclA 28150 (125) a

11 RllPc7B 30950 (138) a

11 Average 29600 (132)

Notes

:

a. Failed in the free length.

b. Exposed to stress-rupture conditions prior to tensile test. (See

Table A.

3

.) Result not included in the average.

c. Pulled out of end fitting. Result not included in the average.

d. Failure appeared to have initiated in an end fitting. Result not

included in the average.

e. End fittings potted with C1W2 compound. Free length, 47 in (1.2 m)

.

f. Same specimen as above, retested with Mod 4 end fittings.

g. Estimated.

h. Pulled out of end fitting. Result included in the average.

i. Free length, 48 to 51 in (1.2 to 1.3 m)

.

j . Exposed to room-temperature stress-rupture conditions prior to tensile test [27]. Result not included in the average.

6 2 10 8 2
TABLE A.

2

RESULTS OF HIGH-SPEED TENSILE TESTS, RUNS 1-11

Rod diameter: 1/2 in (13 mm), nominal.

Free length: 27 to 28 in (0.7 m)

.

Crosshead speed: 300 in/min (130 mm/s)

.

End fittings: H3M with cruciform wedges and potting

compounds as noted.

All failures appeared to have initiated in an end

fitting except as noted.

Run Specimen

1 Potting

No. No. Compound Maximum load Notes

1 Kf

1 RlPcSC C2W3 a

1 36000 (160) U

2 R2Pc7C C2W3 34700 (154)

2 R2Pc5D C1W2 33200 (148)

3 R3PclC C1W2 33500 (U9)

3 R3Pc5A Clw2 \±OjJ

4 R4Pc6A C1W2 uuu RApr 6B C1W2 28500 (127)

J 32500 (146)

6 R6Pc6A C1W2 38100 (169) b

6 R6Pc6C C1W2 17000 ( 76) c

6 R6Pc9A C1W2 35000 (156)

8 RSPcllA C1W2 34000 (151)

9 R9Pc5A C1W2 36000 (160)

10 RlOPcAC C2W3 a 10 R10Pc3C C1W2 a 10 R10Pc6A C1W2 15000 ( 67) c 10 R10Pc6B C1W2 34000 (151)

11 RllPc2A C1W2 32500 (145)

Notes

:

a . Maximum load not measured

b. Failure appeared to have initiated in the free ;Length.

c. Specimen pulled out of an end fitting.

100

6 2 10 8 2
TABLE A.

3

RESULTS OF STRESS-RUPTURE TESTS AT 200°F (93°C) AND

SATURATED HUMIDITY, RUNS 1-11

Rod diameter: 1/2 in (13 mm), nominal.

End fittings: Type R/P with cruciform wedges and

C2W3 potting compound.

All failures occurred in the free length within temperaturehumidity chamber, except as noted.

R.un ^o.

Specimen

No. Test load

Time to

rupture Not(

Ibf (kN) h

1 RlPc6C 14000 (62) 0.5

1 RlPc4A 14000 (62) 3.9

1 RlPclOA 13000 (58) 114. 3

1 RlPc3A 12000 (53) 550.

1 RlPcSA 10000 (44) a

2 R2Pc5C 14000 (62) 22.2

2 R2PclOA 13000 (58) 47.6

2 R2Pc4A 12000 (53) 37.3

2 R2PclOB 11000 (49) 76. 9

2 R2Pc6B 10000 (44) 92.8

3 R3PclB 11000 (49) 2.6

3 R3Pc4B 10000 (44) b

3 R3Pc2B 10000 (44) 29.6

4 R4Pc7A 11000 (49) 0.3

4 R4Pc7B 10000 (44) 8.3

5 R5APc8 12000 (53) 27.9

5 R5APc6A 11000 (49) 21.0 b

5 R5APc6A 11000 (49) 424. c

5 R5APc6B 11000 (49) 172.6

5 R5APc3A 10000 (44) 180.4

6 R6Pc8B 13000 (58) 4.8

6 R6Pc9 12000 (53) 57.4 d

6 R6Pc5A 11000 (49) 114.4 e,f

6 R6PclA 10000 (44) 169.6

7 R7Pcl 12000 (53) 0.8

7 R7Pc3A 11000 (49) 73.0 e

7 R7Pc2A 10000 (44) 66.0

Continued

101 ^ ^ 1 08 2
TABLE A. 3 - (Continued)

Run Specimen Time to

No. No. Test load rupture Notes

Ibf (kN) h

8 R8Pc3B 11000 (49) 0.08

8 R8PclB 10000 (44) 0.2

9 R9PclB 13000 (58) 0.05

9 R9Pc2B 12000 (53) 2.2

9 R9Pc9B 11000 (49) 26.5

9 R9Pc3B 10000 (44) 13.3

9 R9PclOA 10000 (44) 20.0

10 R10Pc3B 13000 (58) 2.0

10 R10Pc2B 12000 (53) 28.4

10 RlOPcAB 11000 (49) 450. g

11 RllPcl3A 14000 (62) 0.3

11 . RllPc4A 13000 (58) 168.

11 RllPcllA 12000 (53) 25.6 d

11 RllPcl9A 11000 (49) 0.00 b

11 RllPc20A 11000 (49) 214.5

11 RllPc9A 11000 (49) 293.3 d

11 RllPcl5 10000 (44) 67.7

11 RllPc3 10000 (44) 123.4

Notes

a. Test discontinued after lOOOh without failure.

b. Specimen pulled out of end fitting.

c. Same as specimen above. Ends repotted. Sustained 402. 8h additional

before failure.

d. failure initiated at or in end fitting.

e. Test interrupted by 3-day power outage during which load was maintained but temperature and humidity decreased to ambient.

This interval not inc] uded in time to rupture.

f. +7.5h; timer failed to function properly.

g. jf25h; timer failed to function properly,

g. +12. 2h; timer failed to function properly.

102

S 2 I o 8 2
TABLE A.

4

RESULTS OF STRESS-RUPTURE TESTS AT 160°F C71°C) and

SATURATED HUMIDITY, RUNS 1-11

Rod diameter: 1/2 in (13 mm), nominal.

End fittings: Type R/P with cruciform wedges and C2W3

potting compound.

All failures occurred in the free length within the temperature-humidity chamber, except as noted.

Run Specimen Time to

No. No. Test load rupture Notes

Ibf (kN) h

1 RlPclA 1300Q (58) 0.6

1 RlPc2B 1200C (53) 5.1

1 RlPc2A 11000 (49) 148.1

1 RlPclB 10000 (44) 83.4

1 RlPc4B 10000 (44) 229.2

1 RlPc7A 10000 (44) 270.7

2 R2Pc8 13000 (58) 0.2

2 R2Pc2 13000 (58) 0. 8

2 R2Pc6A 12000 (53) 49.4

2 R2Pc3A 11000 (49) 362.

2 R2Pc3B 10000 (44) 480.

3 R3Pc9A 10000 (44) 0.7

3 R3Pc3A 10000 (44) 4.6

4 R4Pc9 10000 (44) 2.3

5 R5APc5 13000 (58) 3.3

5 RSAPcBB 12000 (53) 167.

5 R5APc2A 11000 (49) 780.

5 R5APc3B 10000 (44) 444.

6 R6Pc8A 13000 (58) 6.2

6 R6Pc6B 12000 (53) 80.8

6 R6Pc5B 11000 (49) 540.

6 R6PclB 10000 (44) 599.

7 R7Pc4 12000 (53) 2.0

7 R7Pc3B 11000 (49) 114.4

7 R7Pc2B 10000 (44) 418.

8 R8Pc2B 10000 (44) 0.5

Continued

103

6 2 10 8 2
TABLE A. 4 - (Continued)

Run Specimen Time to

No

.

No. Test load rupture Notes

Ibf (kN) h

Qy KyrCOD liUUU U . U / 9 R9Pc8A 11000 (49) 0.5

9 R9Pcl0B 10000 (44) , 847.

10 R10Pc8 12000 (53) 2.0

10 R10Pc6A 12000 (53) 46.7

10 RlOPcSA 11000 (49) 241.5

10 RlOPcSB 10000 (44) . 411.

11 RllPcSA 13000 (58) 22.9

11 RllPcl? 12000 (53) 94.7

11 RllPcl8 11000 (49) 145.5

11 RllPcl2 10000 (44) 509.

11 RllPc6 10000 (44) 600.

Notes

a. +9.5h; timer failed to function properly.

b. +7.5h; timer failed to function properly.

c. Test interrupted by 3-day power outage during which load was

.. maintained but temperature and humidity decreased to ambient.

This interval not included in time to rupture.

d. Failure initiated at surface blemish on specimen.

e. Failure initiated at or in end fitting.

f. Specimen pulled out of end fitting.

104

6 2 1 0 8 2
TABLE A.

5

RESULTS OF CONVENTIONAL TENSILE TESTS, RUNS 12 AND 13

Rod diameter: 1/2 in (13 mm), nominal.

Free length: 52 to 62 in (1.3 to 1.6 m) , except as noted.

Crosshead speed: 0.75 in/min (0.32 mm/s).

End fittings : H3M with cruciform wedges and C2W3 potting

compound.

Run

No.

Specimen

No. Maximum load Notes

12

12

12

12

12

Rl2Pcl6

Rl2Pcl7

R12Pcl8

R12Pc2A

Rl2Pc2B

Ibf

23750

25750

24250

26750

24700

(kN)

(106)

(115)

(108)

(119)

(110)

13 R13Pcl6 23950 (107)

13 R13Pcl7 25000 (111)

13 R13Pcl8 24400 (109)

13 R13Pc2B 25250 (112)

13 R13Pc2C 23750 (106)

Notes

:

a. Failed in end fitting following delamination,

b. Failed in free length following delamination.

c. Free length, 23 to 26 in (0.6 to 0.7 m)

.

a,c

a,c

a , c

a,c

105

6 2 1 0 8 2
TABLE A.

6

RESULTS OF HIGH-SPEED TENSILE TESTS, RUNS 12 AND 13

Rod diameter: 1/2 in (13 mm), nominal.

Free length: 27 to 28 in (0.7 m)

.

Crosshead speed: 300 in/min (130 mm/s).

End fittings: II3M with cruciform wedges and C1W2

potting compound.

All failures appeared to have initiated in an end

fitting.

Run Specimen

No. No. Maximum load

Ibf (kN)

12 Rl2Pc9A 32600 (145)

12 R12Pcl5A 34500 (153)

13 Rl3Pc6A 33000 (147)

106

6 2 10 8 2
TABLE A.

7

RESULTS OF STRESS-RUPTURE TESTS UNDER SATURATED HUMIDITY,

RUNS 12 AND 13

Rod diameter: 1/2 in (13 mm), nominal.

End fittings: Type R/P with cruciform wedges and C2W3

potting compound.

All failures occurred in the free length within the temperature-humidity chamber, except as noted.

Run Specimen

No. No. Temperature Test load

Time to

rupture Notes

12

12

12

12

12

12

12

13

13

13

Rl2Pcll

Rl2Pc4

R12Pcl3

Rl2Pcl4

R12Pcl2

R12Pcl

Rl2Pc5

Rl3Pc9

Rl3Pc5

Rl3Pcl

°F

200

200

200

160

160

160

160

200

200

200

(°C)

(93)

(93)

(93)

(71)

(71)

(71)

(71)

(93)

(93)

(93)

Ibf

13000

12000

11000

13000

12000

11000

11000

12000

11000

10000

13 R13Pc3A 160 (71) 12000

13 Rl3Pcl5 160 (71) 11000

13 R13Pcl2 160 (71) 10000

Notes

:

a. Delaminated prior to failure.

b. Failure initiated at end fitting.

(kN)

(58)

(53)

(49)

(58)

(53)

(49)

(49)

(53)

(49)

(44)

(53)

(49)

(44)

h

2.4

190.1

568.

4.3

165.7

233.4

320.

24.9

96.0

400.

0.8

220.8

804.

107

6 2 1082
TABLE A.

8

RESULTS OF CONVENTIONAL TENSILE TESTS ON PRELIMINARY

SAMPLE OF ARAMID/ISOPHTHALIC ROD

Rod diameter: 1/4 in (6 nan), nominal.

Crosshead speed: 0.75 in/min (0.32 mm/s)

.

End fittings: As listed, with cruciform wedges for

the H3M and Type R/P fittings, and C2W3

potting compound except as noted.

Specimen

No

.

End

fitting Maximum load jNOte:

Ibf (kN)

22A R/P 6600 (29) a

R/P 6500 (29) a

22C Mod 4 6850 (30) b

22D Mod 4 7050 (31) b , c

22E H3M 6750 (30) d

22F H3M 3500 (16) b ,e

Notes:

a. Specimen failed adjacent to fitting.

b. Specimen pulled out of fitting.

c. Mod 4 end

length.

fitting was modified to provide additional potted

d. ClWl potting compound was used. Specimen failed inside fitting.

e. PCS potting compound was used.

108

6 2 1 08 2
TABLE A.

9

RESULTS OF CONVENTIONAL TENSILE TESTS, RUNS 14 AND 15

Rod diameter: 1/2 in (13 mm), nominal.

Free length: 47 to 48 in (1.2 m)

.

Crosshead speed: 0.75 in/min (0.32 mm/s).

End fittings: H3M with cruciform wedges and C2W3 potting

compound, except as noted.

Run

No.

Specimen

No. Maximum load Notes

14

14

14

14

R14Pc3

Rl4PclO

R14Pc20

R14APcl

Ibf

25850

28750

28050

24450

(kN)

(115)

(128)

(125)

(109) b ,c

15

15

15

15

15

15

15

15

Notes

:

Rl5Pc2

R15Pcl8

R15Pc20

Rl5Pc3

R15Pc24

R15Pc21

R15Pcl

R15Pc7

27650

25650

26950

11750

17450

22250

10600

23450

(123)

(114)

(120)

( 52)

( 77)

( 99)

( 47)

(104)

a

a,d

e,f

e,g

e,h

a,i

a.

b.

c.

d.

00 e. o f

.

grH h.

i

Specimen failed inside end fitting.

Specimen failed in free length.

Specimen pultruded at 12 in/min (5 mm/s) rather than 6 in/min

(3 mm/s); poor surface quality

Aramid fibers broomed out in fitting before potting.

Specimen pulled out of end fitting.

Reduced length of potting cavity in fitting.

Enlarged diameter of potting cavity in fitting.

Used Type P end fittings [5].

Specimen subjected to stress-rupture test ( Table A. 11 ) before

tensile test; Type R/P end fittings.

109
TABLE A. 10

RESULTS OF HIGH-SPEED TENSILE TESTS, RUNS 14 & 15

Rod diameter: 1/2 in (13 mm), nominal.

Free length: 27 to 28 in (0.7 m)

.

Crosshead speed: 300 in/min (130 mm/s).

End fittings: H3M with cruciform wedges land C1W2

potting compound.

Run Specimen

No. No

.

Maximum load Notes

Ibf (kN)

lA RlAPcl 35000 (156) a

15 Rl5Pc3 28000 (125) b

15 R15Pc22 30000 (133) a

Notes:

a. Specimen failed in free length.

b. Specimen failed inside end fitting.

110 6 2 1 0 8 2
TABLE A. 11

RESULTS OF STRESS-RUPTURE TESTS UNDER SATURATED

HUMIDITY, RUNS 14 & 15

Rod diameter: 1/2 in (13 mm), nominal.

End fittings: Type R/P (except as noted) with

cruciform wedges and C2W3 potting

compound.

Run Specimen Time to

No. No. Temperature Test load rupture Note!

F ( c) Ibf (kN) h

14 Rl4Pcl7 200 (93) 13000 (58) 22.3 a

14 Rl4Pc5 200 (93) 12000 (53) 147.5 a 14 Rl4Pcl3 200 (93) 11000 (49) 218.6 a,b

14 R14Pcl4 200 (93) 10000 (44) 591.0 a

14 R14Pcl2 160 (71) 14000 (62) 1.6 a 14 R14Pc2 160 (71) 13000 (58) 4.6 a

14 Rl4Pcl9 160 (71) 13000 (58) 417.3 a , c 14 Rl4Pcl5 160 (71) 12000 (53) 393.3 a 14 R14Pc6 160 (71) 11000 (49) 462.5 a

14 R14Pcl7 160 (71) 10000 (44) 324.9 a

14 R14Pcl8 160 (71) 10000 (44) 668.0 a

15 R15Pcl3 200 (93) 16000 (71) 18.6 a

15 Rl5Pc6 200 (93) 14000 (62) 328.8 b

15 R15Pcll 200 (93) 14000 (62) 260.6 a

15 R15Pcl2 200 (93) 12000 (53) 548.0 a

15 R15Pcl5 160 (71) 16000 (71) 351.4 b,d

15 Rl5Pcl4 160 (71) 16000 (71) 0.2 d,e

15 Rl5Pcl7 160 (71) 16000 (71) 118.6 a,e

15 R15Pc8 160 (71) 14000 (62) 470.9 a 15 Rl5Pc4 160 (71) 14000 (62) 738.3 a

15 R15Pc7 160 (71) 12000 (53) f

Notes

:

a. Specimen failed in free length within temperature-humidity

chamber.

b. +7.5 h; timer malfunctioned.

c. +10.0 h; timer malfunctioned.

d. Specimen failed inside end fitting.

e. Used H3M end fittings.

f. Test di scontinued after 2004 h without failure.

Ill

6 2 1 0 8 2
ADDENDUM

A SPECIFICATION FOR ARAMID FRP ROD

Leonard Mordfin

In the main text of this report it was shown that, in spite of its

promise of superior weatherability , aramid FRP rod cannot be recommended

for service in antenna-support applications without further study. Nevertheless, based upon the data and information acquired in the program, this

addendum contains a basic specification and briefly discusses certain

aspects of its preparation.

The data and information acquired in the program were to limited

for the preparation of a thorough, all-inclusive specification. This is

due, in large measure, to the fact that fatigue tests and real-time outdoor weathering tests, which were originally intended to be performed

in the present program, were later cancelled due to budgetary limitations.

Three approaches were explored in an attempt to overcome this paucity

of well-characterized data. First, some data from other sources were

used (e.g., [5,35]). Second, some requirements gleaned from specifications

for glass FRP rod were included in the present document where they were

considered to be applicable. These other specifications, which were found

to be extremely helpful, include the following:

Military Specification MIL-P-79C, Plastic Rods and Tubes, Thermosetting, Laminated (15 June 1961, amended 10 Sept. 1964).

112 6 2 108^
Specification No. IBS/ET-426, Antenna Guy Lines and Insulators

- Fiberglass Rods, U.S. Information Agency (Washington, revised

Dec. 4, 1974).

BPA Specification ETF 50-03.2, Technical Specification for

Fiber Glass Strain Insulators, Bonneville Power Administration

(Portland, Ore., July 10, 1972).

NAVFAC Specification No. 21-71-0900, Procurement of Fiberg.lass

Rod Insulators for the U.S. Naval Radio Station, Totsuka, Japan,

Naval Facilities Engineering Command (Washington, Aug. 10, 1972).

Despite this additional information some serious gaps still remain.

For example, virtually nothing appears to be known about the flexural

strength of aramid FRP rod; and testing for the reported tendency of organic

fibers like PRD, Nylon etc to creep under tensile stresses was not specifically

conducted. Therefore these conditions appear as applied field blank spaces

in the present specification. Also, the present specification does not

address quality assurance requirements such as dimensional tolerances

and unacceptable surface defects. In this area, fortunately, help is

on the way. Guidelines for these characteristics of pultruded rod are

presently being developed under the jurisdication of ASTM Section D20.18.02.

The third approach taken, in the effort to make the specification

sufficiently rigorous, was to include both material and fabrication requirements and performance requirements. There is a philosophy, to which

this author subscribes, that the inclusion of both of these types of

requirements in the same specification tends to produce a redundant and

unecessarily restrictive document. It will be noted, however, that an

attempt was made, in the specification which follows, to avoid these

pitfalls through the use of suitable "escape" clauses. Nevertheless,

it must not be inferred that this specification is endorsed by the National

Bureau of Standards.

* * * 113

6 2 10 8 2
Draft Technical Specification

for

WEATHER-RESISTANT NONMETALLIC STRUCTURAL ROD

1. SCOPE. This specification governs the technical requirements for

weather-resistant, nonmetallic rods intended for use in research

and evaluative programs with ultimate applications in antenna-support

systems.

2. APPLICABLE DOCUMENTS. The most recent editions of the following

documents of the American Society for Testing and Materials form

a part of this specification to the extent specified herein.

D 149 Tests for Dielectric Breakdown Voltage and Dielectric Strength

of Electrical Insulating Materials at Commercial Power Frequencies

D 257 Tests for D-C Resistance or Conductance of Insulating Materials

D 785 Test for Rockwell Hardness of Plastics and Electrical Insulating

Materials

D 2343 Test for Tensile Properties of Glass Fiber Strands, Yams,

and Rovings Used in Reinforced Plastics

D 2344 Test for Apparent Horizontal Shear Strength of Reinforced

Plastics by Short Beam Method

3. GENERAL REQUIREMENTS. The rods shall be composed of unidirectional

aramid fiber rovings impregnated with a high quality, weather-resistant

resin binder, and shall be fabricated by the pultrusion process.

All of the rovings shall be continuous throughout each length of rod.

The rods shall have smooth exterior surfaces which resist contamination.

No coating is required on the exterior surfaces. However, if a coating

other than an integral gel coating is applied to the exterior surfaces

114

6 2 1 0 8 2
then it shall be demonstrable that the rods satisfy all of the requirements of this specification in both the coated and the uncoated

conditions except as specifically noted herein.

The rods shall have a circular cross section. The lengths and the

diameters of the rods shall be as specified in the applicable procurement document. Rods of lengths less than 10 ft (3.0 m) shall

be furnished in the straight condition. Rods of greater length

may be furnished in a coiled condition.

4. MATERIALS REQUIREMENTS.

4.1 Reinforcing material . The reinforcing material for the rods shall

be continuous aramid fiber roving of commercial grade or better,

certified by its manufacturer to be suitable for aircraft and commercial

tape and filament-winding applications. The fibers shall have a

nominal diameter of 0.00046 in (0.012 mm). The roving shall have

an end count (number of strands per roving) of not less than 10,

with not less than 1000 fibers per strand. The mechanical properties

of the roving shall be certified by its manufacturer to meet or

exteed the following average requirements, determined in accordance

with the test procedures specified in ASTM D 2343 for glass fiber

roving

:

Tensile strength, 500 000 Ibf/in^ (3400 MPa)

.

Tensile modulus of elasticity, 19 x 10^ Ibf/in^ (130 GPa)

.

115

6 2 1 0 8 2
Except as noted in Paragraph 4.4, the roving shall not contain any

surface finish or sizing, nor any grease, oil, dirt or other foreign

matter. It shall not contain knots or excessive loose fibers or

fuzz which reduce the smoothness of the roving.

Resin binder material . Except as noted in Paragraph 4.4, the resin

binder material for the rods shall consist primarily of propoxylated

bisphenol-A polyester resin.

Coating material . A coating may be added to the exterior surfaces

of the rods to enhance weatherability . If used, it shall be primarily

organic although it may contain inorganic ingredients. The coating

shall be applied uniformly over the surfaces of the rods to a thickness

not exceeding 0.10 in (2.5 mm). The coating shall be flexible, welladhered, and resistant to peeling and flaking.

Exceptions . A surface finish, sizing or coupling agent may be used

on the aramid fiber roving in order to facilitate its impregnation

with the resin binder, provided that the provisions of Paragraph

4.4.1 are met.

A high quality, weather-resistant, thermosetting polyester resin

other than that specified in Paragraph 4.2 may be used in order

to facilitate the impregnation of the rovings, or to enhance the

weatherability of the rods, or both, provided that the provisions

of Paragraph 4.4.1 are met.

116

6 2 10 8^
4.4.1 If a surface finish, sizing or coupling agent is used on the rovings

or if a resin binder other than that specified in Paragraph 4.2

is used, or both, then it shall be demonstrable that the horizontal

shear strength of the rod, in the axial direction, is not less

than 6200 Ibf/in^ (43 MPa) . This demonstration shall be made in

accordance with ASTM D 2344 using flat test specimens machined

from the pultruded rod.

5. FABRICATION REQUIREMENTS. Fabrication of the rods shall be carried

out by skilled craftsmen using the best modern practices of the

pultrusion industry.

5.1 The rovings shall be dried, for not less than 8h at not less than

250°F (120°C) , immediately prior to pultrusion. They shall be

maintained in the dry condition by passing them through a suitable

heating chamber until immersion in the resin trough is effected.

5.2 The quantity of roving to be used shall be sufficient to provide

a fiber content, in the rod product, of not less than 56 percent

by weight (mass) . This fiber content shall be verifiable by means

of the following formula:

Fiber content = Weight (mass) of a unit length of roving x Number

Weight (mass) of a unit length of rod rovings

used.

5.3 The resin binder formulation shall consist of the resin specified

in Paragraph 4, thinned with the minimum concentration of monostyrene

117

6 2 108^
necessary to provide a sufficiently low viscosity for satisfactory

impregnation and pultrusion. The formulation shall also contain the

required catalyst concentration and an ultraviolet inhibitor to enhance

the weatherability of the rod product. The formulation may also

contain a die lubricant to facilitate pultrusion. The formulation

shall not contain a wetting agent or a coupling agent nor any grease,

oil, dirt or other foreign matter.

The pulling speed and the curing temperature profile shall be selected

to produce a well-cured product with good surface quality.

The immersion time, defined as the immersed length of roving in

the resin trough divided by the pulling speed, shall not exceed

4 min.

All rods of length not exceeding 10 ft (3.0 m) shall be post cured

for not less than 15h at 275°F (135°C) . The rods shall be fully

supported during post curing to avoid warping.

Coiling of the rod product, when necessary, shall not be attempted

until it has cooled to lOO^F (38oC) or less, and shall be carried

out with extreme care to assure that no portion of the rod is bent,

even momentarily, to a radius of curvature which is less than half

the coil diameter. The coil diameter shall be not less than 300

times the rod diameter unless the provisions of Paragraph 6.5 are

met.

118

6 2 1 0 8 2
6. PERFORMANCE REQUIREMENTS

6.1 Tensile strength . The rods shall be capable of sustaining a tensile

stress of not less than 125,000 Ibf/in^ (860 MPa) for not less

than one minute without visible or audible damage or other evidence

of incipient failure. This shall be demonstrable by tensile tests

on full cross-section rods, of lengths not less than 100 times the

rod diameter, to which high-performance end fittings have been attached. A mechanical failure of the rod specimen which initiates

in an end fitting prior to the completion of the one-minute interval

shall render the test invalid but shall not in itself disqualify

the product.

6.2 Stress-rupture strength . The rods shall be capable of sustaining

a tensile stress of not less than 70,000 lbf/in2 (480 MPa) for

not less than 240 h while exposed, in an environmental test chamber,

to a temperature of 160 + 5°F (73 + 3°C) and saturated-humidity conditions. This shall be demonstrable by tensile stress-rupture tests

on full cross-section rods to which suitable end fittings have been

attached. The length of rod exposed to the specified environment

shall be not less than 50 times the rod diameter but the end fittings need not be so exposed. At the completion of the test the

rod shall exhibit no evidence of structural damage or deterioration

or other evidence of incipient failure. A mechanical failure of

the rod specimen which initiates in an end fitting prior to the

completion of the 240-h interval shall render the test invalid

but shall not in itself disqualify the product.

119
6.3 Flexural Strength . When specified, the flexural strength of the

rods shall be not less than (*)

at room temperature, and not less than 90 percent of this value at a

temperature of -70°F (-57°C) . This shall be demonstrable by threepoint bending tests on full cross-section rods, at room temperature

and at -70°F (-57°C) , using a span-to-diameter ratio of 36 to 40.

6.4 Fatigue Strength . When specified, the rods shall be capable of

sustaining aeolian vibration indefinitely. This shall be demonstrable

by means of tests in which full cross-section rods, of lengths not

exceeding 600 times the rod diameter, are subjected to transverse

vibration at a resonant frequency between 45 and 90 Hz while under

an axial tensile stress of not less than 70 000 Ibf/in^ (480 MPa)

.

The double amplitude of vibration shall be not less than three times

the rod diameter. Rod specimens so tested shall be capable of enduring

Q

not less than 10° cycles of vibration without evidence of damage.

6.5 Storage Capability . Rods may be coiled to diameters less than those

specified in Paragraph 5.7 provided that the storage capability

of the coiled rods is not thereby degraded. This shall be demonstrable by means of tests in which coils of full cross-section rod,

consisting of not less than three full loops per coil, are exposed

to a temperature of not less than 200°F (93°C) for not less than

72 h. Rod material so tested shall exhibit no evidence of buckling

or other structural damage and, upon uncoiling, shall not retain

excessive permanent set.

(*) See text under the ADDENDUM

120

6 2 10 8 2
Hardness . The exterior surfaces of post-cured rods shall exhibit

an average hardness number of not less than 30 on the Rockwell E

scale. In the case of coated rods this requirement shall apply only

to the rods in the uncoated condition. This performance requirement

shall be demonstrable by means of measurements performed in accordance

with Procedure A of ASTM D 785.

Electrical resistance . The insulation resistance of the rods shall

be not less than lO-'-^ ohms per inch (40,000 T/l/m) of length. This

shall be demonstrable by means of measurements performed in accordance

with ASTM D 257 using a direct voltage of not less than 500 V.

Dielectric strength . Rod samples shall exhibit average dielectric

strengths, in the axial direction, of not less than 70 V/mil (2.8

MV/m) in the dry condition and 15 V/mil (0.6 MV/m) immediately after

immersion for 2 h in boiling distilled water. This shall be demonstrable

on full cross-section samples having lengths equal to the rod diameter'

by means of tests performed in oil in accordance with the shorttime test procedure of ASTM D 149 using a rate-of-rise of 500 V/s

at a frequency of 60 Hz.

QUALITY ASSURANCE REQUIREMENTS

(The level of experience acquired to date, on material of the kind

specified herein, is inadequate for the establishment of firm

requirements at this time for dimensional tolerances, acceptable

surface defects, etc.)

121 6 2 1 0 8 2
1. Morrison, R. S. , Pultrusion, Ilodern Plastics Encyclopedia 1973-197A ,

ed. S. Gross, pp 428-431 (McGraw-Hill, N.Y., 1973).

2. Mohr, J. G. , Oleesky, S. S. , Shook, G. D. and Meyer, L. S., Pultrusion

and Rod Stock, Chap. V-2 in SPI Handbook of Technology and Engineering

of Reinforced Plastics/Composites , 2nd Ed. , pp 269-276 (Van Nostrand

Reinhold, N.Y. , 1973)

.

3. Anon. , Pultrusion Process Puts Glass Fibers in One Direction for

High Strength, Product Engineering 44, No. 11, pp 38-40 (Nov. 1973).

4. Chwirut, D. J. (coordinator), Research and Testing Facilities of

the Engineering Mechanics Section, National Bureau of Standards,

Washington, D. C., NBS Spec Publ 370 (1973).

5. Halsey, N. , Mitchell, R. A., and Mordfin, L. , Evaluation of GRP Rod

and Rope Materials and Associated End Fittings, NBS Report IR 73-

129 (Dec. 1972).

6. Anon. , Standard Method of Test for Ignition Loss of Cured Reinforced

Resins, ASTM Designation D 2584-68, 1975 Annual Book of ASTM Standards ,

Part 36 (Am Soc Test Mat, Philadelphia, 1975).

7. Anon., Specific Gravity from Weight and Volume Measurements, Method

5012, Plastics; Methods of Testing , Fed. Test Method Std. No. 406

(General Services Administration, Washington, Oct. 5, 1971).

8. Hudock, J. A., private communication.

122

^21 082
9. Anon. , Standard Method of Test for Rockwell Hardness of Plastics

and Electrical Insulating Materials, ASTM Designation D 785-65, 1975

Annual Book of ASTM Standards , Part 35, loc. cit .

10. Anon., Standard Method of Test for Splitting Tensile Strength of

Cylindrical Concrete Specimens, ASTM Designation C 496-71, 1975 Annual

Book of ASTM Standards , Part 14, loc. cit .

11. Mordfin, L. , and Kerper, M. J., Strength Testing of Ceramics - A

Survey, Mechanical and Thermal Properties of Ceramics , ed. J. B

Wachtman, Jr., NBS Spec Publ 303, pp 243-262 (1969).

12. Aitchison, C. S., and Miller, J. A., A Subpress for Compressive Tests,

NACA TN 912 (1943).

13. Halsey, N. , Properties of Glass Fiber-Reinforced Polymers for Application to Guy-Insulator Systems of Communication Towers, Phase

2, Test Methods and Evaluations of Glass Fiber-Reinforced Polymer

Rods for Use in Guy-Insulator Systems of Loran C. Towers, NBS Report

10261 (June 1970).

14. Mitchell, R. A., Woolley, R. M. , and Kalsey, N. , liigh-Strength End

Fittings for FRP Rod and Rope, J. Engineering Mechanics Div. ASCE

100, No. EM4, pp 687-706 (Aug. 1974).

15. Mitchell, R. A., Woolley, R. M. and Fisher, C. R. , Formulation

and Experimental Verification of an Axisymmetric Finite-Element Structural Analysis, J. Res. NBS 75C36.4-322, pp 155-163 (1971).

16. Marlowe, D. E. , Halsey, N. , Mitchell, R. A. and Mordfin L. , NonMetallic Antenna-Support Materials, First Annual Interim Report,

NBS Report IR 73-233 (April 1973).

123 6 2 1 08 ^
17. Mitchell, R. A., Woolley, R. M. , and Chwirut , D. J., Analysis of

Composite-Reinforced Cutouts and Cracks, AIAA J 13, No. 6, pp 744-

749 (June 1975).

18. Anon. , Standard Method of Test for Tensile Properties of Glass Fiber

Strands, Yarns, and Rovings Used in Reinforced Plastics, ASTM Designation D 2343-67, 1975 Annual Book of ASTM Standards , Part 36, loc.

cit .

19. Anon. , Suggested SPI Procedure - Procedure for Running Exotherm Curves

Using the Block Test Method, Proc. SPI Reinforced Plastics/Composites

Division , Washington, Feb. 1969, 24th Annual Conference (Society

of the Plastics Industry, N.Y., 1969).

20. Titus, J. B., New Plastics: Properties, Processing and Potential

Uses, Plastic Special Report 9 (Plastics Technical Evaluation Center,

Picatinny Arsenal, Dover, N. J., May 1971).

21. Lundberg, R. D. , Koleske, J. V., and Walter, E. R. , Dispersing

Aids for Particulate Solids, Canadian Patent No. 866261 (Mar 16,

1971).

22. Atkins, K. E. , Karpold, M. A., Comstock, L. R. , and Smith, P. L.,

Vinyl Polymers and -Caprolactone Polymers as Low Profile Additives,

Proc. SPI Reinforced Plastics/Composites Institute , Washington, Feb

1973, 28th Annual Conference, Paper No. 1-3, loc. cit .

23. Browning, C. E. , and Hartness, J. T. , Effects of Moisture on the

Properties of High-Perf ormance Structural Resins and Composites,

in Composite Materials: Testing and Design (Third Conference) , C.

A. Berg, F. J. McGarry and S. Y. Elliott, coordinators, ASTM STP

546, pp 284-302 (1974).

124

6 2,

1
24. Ishai, 0. , and Mazor, A. , The Effect of Environmental-Loading History

on Longitudinal Strength of Glass-Fiber Reinforced Plastics, Rheologica

Acta 13, No. 3, pp 381-394 (1974).

25. Brunauer, S., The Adsorption of Gases and Vapors, Volume 1, Physical

Adsorption , p 14 (Princeton University Press, 1945). *

26. Glasstone, S., and Lewis, D. , Elements of Physical Chemistry , 2nd

ed., p 559 (D. Van Nostrand Co., Princeton, N.J.,' 1960).

27. Halsey, N. , J'arlowe, D. E. , and Mordfin, L. , Non-Metallic AntennaSupport Materials, Second Annual Interim Report, NBS Report IR 74-

557 (June 1974).

28. Chiao, T. T. , and Moore, R. L., Organic-Fiber/Epoxide Composites,

Composites 4, No. 1, pp 31-33 (England, 1973).

29. Chiao, T. T., Wells, J. E. , Moore, R. L. , and Hamstad, M. A., StressRupture Behavior of Strands of an Organic Fiber/Epoxy Matrix, in

Composite Materials: Testing and Design (Third Conference ) , pp 209-

224, loc. cit .

30. Readdy, A. F. , and Holman, B. T., Resistance of Plastics to Outdoor

Weathering, Addendum No. 6 to Technical Report 2102 (Picatinny Arsenal,

Dover, N. J. , June 1967)

.

31. Alumbaugh, R. L. , and Roe, T. , Jr., Reinforced Plastics Laminates

Panels — Physical Tests of Panels Removed after the Fourth Exposure

Period, Technical Note N-1084 (Naval Civil Engineering Laboratory,

Port Hueneme, Calif., Mar 1970).

32. Yeoman, F. A., et al, private communication.

33. Hoggatt, J. T. , Development of Cryogenic PRD-49-1 Filament-Wound

Tanks, NASA CR-120835 (Boeing Co., Seattle, Dec 1971).

125
34. Rhodehamel, J. R. , private communication.

35. Sturgeon, D. L. , Wolffe, R. A., Miner, L. II., and Wagle, D. G. , PRD49 Fiber & Composite Performance, E. I. du Pont de Nemours & Co.,

Inc., Textile Fibers Dept. (Wilmington), revised June 5, 1972.

36. Kulkarni, S. V., Rice, J. S., and Rosen, B. W. , An Investigation

of the Compressive Strength of PRD-49-III/Epoxy Composites, NASA

CR-112334 (Materials Sciences Corp., Blue Bell, Pa., undated).

37. Dickard, H. E. , Williams, R. T. , Banuk, R. E. , et al. Design and

Fabrication of an RPV Wing Panel with PRD-49/Epoxy Skins, AFFDL-TR73-31 (Mar 1973).

38. Pritchard, G. , and Taneja, N. , Nature and Extent of Water Damage

in Glass Laminates, Proc. SPI Reinforced Plastics/Composites Institute ,

Washington, Feb 1974, 29th Annual Conference, Paper No. 2-C, loc .

cit.

126

6 1 08 ^
UNCLASSIFIED

SECURITY CLASSIFICATION OF THIS PAGE (When Data Enlernd) REPORT DOCUMENTATION PAGE READ INSTRUCTIONS

BEFORE COMPLETING FORM

1. REPORT NUMBER

AFML-TR-76-42

2. GOVT ACCESSION NO. 3. RECIPIENT'S CATALOG NUMBER

4. TITLE (and Subtitle) NON-METALLIC ANTENNA- SUPPORT MATERIALS

PULTRUDED RODS FOR ANTENNA GUYS, CATENARIES AND

COMMUNICATIONS STRUCTURES

5. Type of report & period covered

Final Technical Report

6. performing org. report number

NBSIR 75-684

7. AuTHORCs; N. Halsey R. A. Mitchell

D. E. ilarlowe L. Mordfin

8. CONTRACT OR GRANT NUMBERCs;

D.O. F33615-72-M-5000

9- PERFORMING ORGANIZATION NAME AND ADDRESS

National Bureau of Standards

Washington, D.C. 20234

10. program ELEMENT, PROJECT. TASK

AREA & WORK UNIT NUMBERS

-

11. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATE

May 1976

13. NUMBER OF PAGES

14. MONITORING AGENCY NAME ft A D D R ESSf// di7/eren ( from Controlling Officej IS. SECURITY CLASS, (ol this report)

Unclassified

15a. DECLASSIFICATION DOWNGRADING

SCH EDULE

16. DISTRIBUTION STATEMENT (ot this Report)

Approved for public release; distribution unlimited.

17. DISTRIBUTION STATEMENT (ol the abstract entered in Block 20, il dillerenl Irom Report)

18. SUPPLEMENTARY NOTES

19 KEY WORDS f Continue on reverse side it necessary and identity by block number)

Aramid Environmental resistance of FRF rods

Glass Guys, antenna Test methods

Composite Materials Pultrusion Weatherability of

Fiber-reinforced-plastic (FRP) Reinforced plastics FRP rods

End-fittings for FRP rod Stress rupture of FRP rod

20 ABSTRACT f Continue on reverse side li nece s sary end identify by block nurrtber) Both E-glass and Kevlar 49 (aramid) fibers were used to reinforce an isophthalic polyester resin. These materials were used, in turn, to form

pultruded antenna rod hardware for structural tests. The aramid material

exhibited substantially improved strength-retention properties over the

glass-reinforced material under prolonged exposure to heat and humiditv. The

aramid material offers the promise of superior weatherability in antennasupport applications although further testing is warranted. The stressrupture properties of pultruded rod, under high humidity, possess unusual

DD 1 jan'tB 1473 EDITION OF 1 NOV 65 IS OBSOLETE UNCLASSIFIED

SECURITY CLASSIFICATION OF THIS PAGE 'When Data Entered)
UNCLASSIFIED

SECURITY CLASSIFICATION OF THIS PAGEfHTien Data Entered)

^

20. Abstract (Continued)

temperature and time dependencies. These are explained in terms of the

mechanisms whereby moisture is transported from the environment to the

fiber /matrix interface. The stress-rupture properties, as well as the

tensile properties, i.,ay be improved by appropriately modifying the

pultrusion process.

Two new end fittings, generally capable of attaining the full tensile

strength of glass fiber-reinforced pultruded rod, were developed.

Several new test methods were developed, including an environmental

stress-rupture test, two methods for investigating the quality of the

fiber/matrix interface, and a method for examining the rate sensitivity

of the tensile strength. A significant rate sensitivity was observed

for glass fiber-reinforced rod but not for aramid fiber-reinforced rod.

6 2 1 0 ® ^ UNCLASSIFIED

SECURITY CLASSIFICATION OF THIS P ^OE(When Dnla Entered)