..& 

NASA Contractor Report 17821 4 

DESIGN STUDY OF ADVANCED MODEL 

SUPPORT SYSTEMS FOR THE NATIONAL 

TRANSON 1 C FACILITY 

IhASB-CB- 1782 14) CZSIGY S'IUCY CF ADVANCED M87-202S7 

CCDEL SUEEOBT SYSIEPIS ECB TEE bAlIXCNAL 

IHAPSCRIIIC PACILlSY ("IF) (General 

Cynauiics/Convair) 68 F CSCL 148 Unclas 

G3/09 45408 

GENERAL DYNAMICS CONVAIR DIVISION 

P. 0. Box 85357 

San Diego, California 92138 

Purchase Order L- 99725B 

January 1987 

National Aeronautics and 

Space Administration 

Langley Research Canter 

Hampton. Virginia 23665 
FOREWORD 

This report describes the work performed on NASA Contract P.O.L.-99725B by the 

Convair and Space Systems Divisions of General Dynamics Corporation at San 

Diego. 

This work was administered by the Langley Research Center of MASA, Hampton, 

Virginia. Dr. C.P. Young, Jr. is the NASA Technical Monitor. 

The program was conducted in the Research and Engineering Departments of the 

General Dynamics Aerospace Divisions, and was managed by S.A. Griffin. 

A.A. McClain of the Aerotest Group and R. Boswell of the Materials and Process 

Laboratory were the principal investigators. 

The following personnel contributed to the study: 

Aerotest Design A.A. McClain, E.A. Collinge 

Materials and Processes Coordinator R. Boxwell 

Materials Consultant Dr. M.J. Yokota 

Composites B.D. Gilchrist 

Steels Dr. J.R. Kerr 

Stress Analysis Craig Rix 

Thermal Analysis Dr. E.A. Ibrahim 

Literary Search M. Daley 

i 
TABLE OF CONTEHTS 

Sect ion 

1 

2 

3 

4 

5 

INTRODUCTION 

1.1 DESIGN APPROACH 

1.2 TOUGHNESS VERSUS STRENGTH LIMITATIONS 

1.3 STIFFNESS LIMITATIONS OF COWBNTIONAL MATERIALS 

PROGRAII ORGANIZATION 

ESTAELISHING CRITERIA FOR A HIGH PERFORHlWCE STING 

3.1 BASELINE COWIGURATION STUDIES 

3.1.1 Stiffness Analysis 

3.1.2 Strength Analysis 

3.2 CROSS SECTION STRAIN DISTRIBUTION 

COWENTIONAL METALLURGICAL APPROACH 

4.1 

4.2 

4.3 

4.4 

4.4.1 

4.4.2 

4.4.2.1 

4.. 4.2.2 

4.4.2.3 

4.4.2.4 

4.4.2.5 

4.5 

THE USE OF 

5.1 

5.2 

5.3 

5.3.1 

5.3.2 

5.3.3 

5.4 

5.5 

GENERAL INFORMTIOM 

AN ADVANCED STING USING MP35N 

MANUFACTURING ASPECTS OF AN MP35N STING 

DESIGN CONCEPTS 

Concepts for Fabricating a Round Sting 

Fabricating a Rectangular Sting of W35N 

Diffusion Brazing 

Diffusion Welding 

Adhesive Bonding 

Laser Welding 

Electron-Beam Welding 

STRUCTURAL ANALYSIS 

ADVANCED COMPOSITES FOR A HIGH PERFORHAMCE "TING 

GENERAL INFORMTION 

ORGANIC WTRIX COMPOSITES 

STRUCTURAL ANALYSIS 

Fiber Properties 

Unidirectional Laminate Properties 

Cross Plied Laminate Properties 

RELATIONSHIP BETWEEN TENSION/SHEAR STRENGTH FOR A 

HIGH MODULUS ADVANCED COMPOSITE SYSTEM 

COMPOSITE STING DESIGN 

PaRe 

1-1 

1-1 

1-2 

1-3 

2-1 

3-1 

3-1 

3-2 

3-2 

3-4 

4-1 

4-1 

4-3 

4-6 

4-8 

4-8 

4-12 

4-13 

4-13 

4-13 

4-13 

4-13 

4-14 

5-1 

5-1 

5-1 

5-2 

5-2 

5-2 

5-5 

5-5 . 5-5 

iii 
PaRe 

TABLE OF COblTEMTS, Contd 

Sect ion 

6 HYBRID HETAL/COIIPOSIITE COWBINATIONS 

6.1 

6.2 

6.3 

6.4 

6.5 

6.6 

6.7 

6.8 

6.8.1 

6.8.1.1 

6.8.1.2 

6.8.2 

6.9 

GWERAL IMF'ORMATION 

HYBRID MATERIAL SYSTEMS USING KE"ETAL 

CLADDING 

KEMMAKETAL STIMG 

IlJTBRnITTWT STIFFENERS 

HETAL/COHPOSITE HYBRIDS 

SUMMARY OF THERMAL AMALYSIS 

Discussion 

Transient Analysis 

Heater Siting Steady-State Hodel 

Metal/Conrposite Hybrids 

FLOATIBJG STIFFENERS 

18 li-200/UHISKER REIWORCEUIEMT 

7 CAMDIDATES FOR PROOF-OF-COMCEPT TESTS 

8 coNcLusIobls 

9 REFERENCES 

6-1 

6-1 

6-3 

6-4 

6-6 

6-7 

6-8 

6-8 

6-12 

6-13 

6-13 

6-15 

6-17 

6-18 

7-1 

8-1 

9-1 

c 

. 
LIST OF FIGURES 

Finure Pane 8 

1-1 

2-1 

3-1 

3-2 

3 -3 

3-4 

3-5 

3-6 

4-1 

4-2 

4-3 

4-4 

4-5 

4-6 

5-1 

5-2 

5-3 

5-4 

6-1 

6-2 

6 -3 

6 -4 

6 -5 

6 -6 

6-7 

6-8 

Ratio Analysis Diagram for Quenched and Tempered Steels 

Study Plan for NTF Advanced Model Support Systems 

Generic Model Sting (Baseline) 

Baseline and Improved Sting Configuration Stiffness 

Parameters, AE 

Baseline and Improved Sting Configuration Stiffness 

Parameters, E1 

Baseline Sting Cross Section Geometry 

Baseline and Improved Strength Design Envelope 

Axial Strain Distribution at the Aft End of the Improved Sting 

Configuration 

Comparison of High Performance Metallic Materials 

Sting Fabrication Concept 1 

Sting Fabrication Concept 2 

Typical Section of Sting Showing Laser Weld 

Rectangular Beam Using 1/4-inch Hp35M Strip 

Alternate Design Using Strip 

Comparison of Composite Fiber Properties 

Comparison of Composite Unidirectional Laminate Properties 

Comparison of Composite Cross Plied Laminate Properties 

Comparison of Composite Cross Plied Laminate Properties 

"Ideal" Composite Sting Support 

Cross Section Geometry for kSetal/Metal Hybrid Sting 

Comparison of Hybrid Metal/kSetal Stings with Baseline Model 

Properties 

Sting (18 Mi-200) with Intermittent Stiffeners (Kennametal) 

Cross Section Geometry for the Pletal/Composite Hybrid Sting 

Comparison of Hybrid Metal/Composite Stings with Baseline 

Model Properties 

Cryogenic Wind Tunnel Advanced Sting Cross Section 

Cryogenic Wind Tunnel Advanced Sting Thermal Conduction 

Model Segment 

1-3 

2-1 

3-2 

3-3 

3-4 

3-4 

3-5 

3-7 

4-2 

4-9 

4-11 

4-12 

4-15 

4-16 

5-3 

5-4 

5-6 

5-7 

6-2 

6-3 

6-5 

6-8 

6-8 

6-11 

6-12 

6-14 

V 
LIST OF FIGURES, Contd 

FiRUre Page 

6-9 

6-10 

6-11 

6-12 

6-13 

6-14 

6-15 

6-16 

Table 

3-1 

3-2 

4-1 

4-2 

4-3 

4-4 

4-5 

4 -6 

4-7 

4-8 

5-1 

5-2 

6-1 

Cryogenic Wind Tunnel Advanced Sting Temperature Distribution 

Versus Mode Number and Time 

Cryogenic Wind Tunnel Advanced Sting Temperatures Versus Time 

Cryogenic Wind Tunnel Advanced Sting Analytical Solution 

Geometry 

Cross Section Geometry for UetaUMetal Hybrid Sting 

Comparison of Hybrid Metal/Composite Stings with Baseline 

Uodel Properties 

Conventional Steel (18 Hi-200) with Kennametal Inner Rod 

Proof of Concept, Floating Stiffener 

Experiment-Floating Stiffener-Deflection Versus Load 

LIST OF TABLES 

Baseline Sting Configuration Stiffness Parameters 

Critical Loading Conditions for the Improved Sting 

Configuration 

Potential Candidate High-Performance Sting Uaterials 

Mechanical Properties of Various Uetals 

Variation of Cvn for UP351 with Temperature 

Low Temperature Mechanical Properties of UP351 Uultiphase 

Tensile Specimens (0.250 in (0.635 cm) in diameter) Work 

Strengthened 49% and Aged at 1200F for 4 Hours 

Variation of Size and Strength for UP351 Round Bar Stock 

Manufacturer's Recommended Conditions for Machining UP351 

Alloy Work Strengthened to 260 ksi (1793 UPa) Ultimate 

Tensile Stress 

Manufacturer's Recommended Conditions for Surface Grinding 

Comparison of Fabricated and Solid Sections 

Candidate Sting Materials 

Typical Composite Properties 

Uaterial Properties for Hybrid Sting Configurations 

6-15 

6-16 

6-17 

6-18 

6-19 

6-20 

6-21 

6-22 

Paffa 

3-3 

3-6 

4-1 

4-4 

4-4 

4-5 

4-6 

4-7 

4-8 

4-14 

5-2 

5-8 

6-4 

vi 
SECTION 1 

IIRCRODUCTION 

. 

. 

The inability of conventional wind tunnels to approach or match full scale 

Reynolds numbers led to the development of the National Transonic Facility 

(NTF) now in operation at NASA*s Langley Research Center. 

continuous flow, fan driven, high pressure facility, capable of operating at 

cryogenic temperatures. 

A recent design study1*, investigated the feasibility of developing wind 

tunnel models of advanced fighter (highly maneuverable) models, for use in 

that facility. 

pointed out that test conditions (angle of attack/Reynolds number) for certain 

configurations is likely to be sting limited. 

The NTF is a 

The study indicated that such models could be developed, but 

It has been recognized for some time that the sting (or support system) is a 

very critical part of the model system. 

the model designer is frequently faced with the tradeoff of minimizing the 

sting size, thereby compromising facility and model safety, against a larger 

sting and the subsequent problems of sting interference effects, and possible 

distortion of configuration geometry. 

Even in conventional wind tunnels, 

In the blTF this problem is accentuated by the severe environment of high 

pressure/low temperature, designed into the facility to provide the desired 

high Reynolds number. 

limiting the test envelope are therefore contrary to the purposes and goals of 

the IUTF and are unacceptable, hence the need for this study of advanced model 

support systems. 

Compromises in the configuration geometry and/or 

Present day wind tunnel support system technology dictates the use of a high 

grade steel sting. The low operating temperature (-300F) of the NTF, however, 

creates a severe environment for both the model and sting, and prohibits the 

use of most steels used in conventional wind tunnels. Toughness and ductility 

must be maintained at the low temperatures and this has led to the use of a 

maraging steel (18 Ni-200). Design studied have shown that the fighter 

type model when using a 18 Ni-200 sting is likely to have a limited test 

envelope due to sting divergence. 

than strength. 

In other words, stiffness is more critical 

1.1 DESIGN APPROACH 

The goal of this study has been to investigate advanced sting materials, or 

combinations of materials that would give an improvement of 25% over 18 Ni-200 

in both ultimate tensile strength, and Young's modulus of elasticity, E. 

Weight is a key factor; the steel sting is approximately 500 pounds, creating 

obvious handling problems. From this point of view a composite sting would be 

an attractive solution. From a strength/stiffness point of view, however, the 

value of the composite sting is questionable. Limited information is 

available at cryogenic temperatures; in addition, the majority of advanced 

structural work using composites has been for applications requiring a high 

*Indicates reference. 

1-1 
strengthlweight ratio, resulting in thin wall designs. 

needs maximum strength/stiffness and within rea80n weight is a secondary issue. 

The support system 

Three basic approaches were taken to find a suitable material for the Advanced 

Sting for MTF: 

a. Conventional material sting 

b. Advanced composites 

c. Hybrid configurations 

Each approach had as its goal the following improvements in property levels: 

a. Yield strength: 220-250 ksi at room temperature 

b. Young's modulus: 32-35 Msi at room temperature 

c. Charpy V-Notch (Cvn): 25 ft-lb at -320F 

Before we discuss the results of each approach in detail, it would be 

instructive to first examine some of the known limitations of currently used 

materials. 

1.2 TOUGHBIESS VERSUS STRENGTH LIMITATIONS 

The current baseline material used in sting applications (18 Mi-200) has a 

yield strength of 200 ksi, a Young's modulus of 26.5 Hsi, and a Cvn toughness 

of 25 ft-lb at -320F. 

stiffness by 25% while maintaining the 25 ft-lb Cvn toughness at -320F. 

may not be difficult to achieve individual (strength or stiffness) 

requirements; it's difficult, however, to achieve both objectives 

simultaneously, while maintaining an acceptable toughness. Figure 1-1 shows 

the generally accepted relationship between strength and fracture toughness 

for commercially available structural alloys. 

be achieved but only through loss of toughness. 

Our initial goal was to exceed 18 Ni-200 strength and 

It 

Mote that higher strengths can 

For a number of years-, materials developers have sought to find alloying 

combinations and microstructures that divert from the general inverse trend as 

shown in Figure 1-1. Today, precipitation hardening systems of iron, nickel, 

and cobalt represent the state of the art of high strength/toughness alloys. 

They form a family of alloys that combines excellent strength, adequate 

toughness, and relatively high stiffness. 

Strength is generally achieved through a combination of solution hardening and 

precipitation hardening. In some systems, work hardening (i.e., increasing 

dislocation density through mechanical working) is also used to increase 

strength, often in conjunction with precipitation hardening. 

In Design Approach 1, we examined in greater detail the kinds of refinements 

that might be made in the iron, cobalt, and nickel systems to achieve our 

required 25% improvement in strength and stiffness. These refinements 

included microstructural changes through powder metallurgy and thermal 

mechanical treatments. 

1-2 
50 25 10 5 

I I / 12.0 

"0 400 800 1200 1600 2000 2400 2800 

Yield stress, MPa 27 1.479-1 

Figure 1-1. Ratio Analysis Diagram for Quenched and Tempered Steels 

1.3 STIFFNESS LIMITATIONS OF COWENTIONAL MATERIALS 

In conventional metallic systems, the stiffness is dominated by the basic 

interatomic bonding of the primary alloy constituent. 

rule that aluminum alloys have a modulus of 10 Msi, steels have a modulus of 

30 Msi, while titanium alloys have modulus in the range of 20 Msi. If one 

looks for ultra high stiffness systems they generally belong to the VIA, VIIA, 

and particularly VIII-A elements of the periodic table of the elements. Some 

high modulus systems include: 

We can say as a general 

~~~ 

Element 

Young * s Periodic 

Modu 1 us Table Group 

(Wsi ) 

Osmium 80 VIIIA 

Indium 79 VIIIA 

Ruthenium 68 VIIIA 

Rhenium 68 VIIIA 

Tungsten 59 VIA 

Rhodium 55 VIIIA 

1-3 
A number of filament and whiskerlfoms have been used to create a variety of 

resin matrix, metal matrix, and ceramic matrix composites. The principal 

reinforcements used, however, have been the graphites (35-120 Msi), boron (58 

Msi), and silicon carbide (62 Wsi) fibers. These reinforcements have been 

combined with relatively low density matrices (epoxy, polymides, aluminum, 

magnesium, titanium, carbon) for application primarily in the aerospace 

industry. 

IIp35M. 

Also, falling under Category 1 are the cobalt superalloys including 

W35M is a vacuum induction, vacuum arc remelted alloy based on the quaternary 

of cobalt, nickel, chromium, and molybdenum, which has shown an unusually 

favorable combination of high strength, stiffness, and corrosion resistance. 

To obtain high strength, the alloys are cold worked by rolling, swaging, 

drawing or extruding; additional strength is obtained by aging. W35M will 

give us the desired 25% improvement in properties with slight reductions in 

the required characteristics of ductility, toughness, and corrosion 

resistance. 

at the high strength in maximum sizes of 1.5-inch diameter of 1.5-inch thick 

plate. 

The primary drawback appears to be that the material is available 

This study reviews the use of W35M as a primary sting material. 

Our Design Approach 2 for finding a suitable replacement tor 18 Mi-200 was to 

investigate the possible use of composite materials in sting applications. 

Our goal was to determine if materials already developed for the aerospace 

industry might be modified or altered slightly to serve as sting materials. 

In Design Approach 3, various materials were considered for the hybrid sting, 

including 18 Mi-200, W351, and Kennametal K9, in conjunction with advanced 

composites. A common problem for all these designs is the thermal stresses 

due to the use of dissimilar materials. 

such as Kennametal K9 (E = 90 x 106) tends to have lower ultimate tensile 

stress values. 

proportion of the load, and does not achieve an acceptable safety factor. 

In addition, a highly stiff material 

When used in the hybrid design it picks up too high a 

Full scale Reynolds number in the NTF is an established goal, and everything 

must be done to achieve that objective. 

require a unique design approach. A development program, including 

proof-of-concept tests, will be needed to establish confidence in the design. 

A fail-safe feature should be a mandatory characteristic of the design, as the 

safety of the facility must not be compromised. 

The high performance sting will 

At the conclusion of this study two configurations will be selected for a 

development program that will include manufacture, and proof-of-concept 

testing. 

1-4 
SICTIOH 2 

PROGRAH ORGANIZATIOY 

General Dynamics, through its Convair and Space Systems Divisions, established 

a team within its Research and Development Departments to conduct the 

engineering study of Advanced Hodel Support Systems for the NTF. The 

Haterials and Processes Directorate of the Space Systems Division contributed 

in the area of advanced composites and special materials and processes 

suitable for us in a cryogenic environment. The design, thermal analysis, and 

wind tunnel co-ordination, was performed at the Convair Division. The team 

organized to conduct the study was led by Hr. S.A. Griffin, who reports to 

Hr. T. Sannnon, Director of Test and Evaluation. The entire organization is 

under the senior management of Dr. R.F. Beuligmann, Vice President of Research 

and Engineering. 

The program operations chart (Figure 2-11 illustrates the flow of information 

from the various technical groups through design to the final report. 

IDENTIFY I PROBLEM 

FOR A HIGH I PERFORMANCE I STING 

REVIEWTEST STR U CTU RES 

ANALYZE DESIGN 

- ESTABLISHBASELINE ENVIRONMENT 

CONCERNS 

- I 

THERMAL ANALYSIS I4 

DESIGN HEAT TRANSFER 

THERMAL STRESS 

HEATER REQMTS DESIGN PHILOSOPHY 

CONCEPTUAL DESIGN 

I d I TRADESTUDIES 

DESIGN REVIEWS 

COORDINATE PROGRAM Y PREPARE ROUGH DRAFT 

MATERIALS & PROCESSES 

LITERARY SEARCH 

VENDORDATA 

VENDOR RESEARCH 

LIAISON CI 

FIELDTRIPS 

FINAL 

REPORT 

TECHNICAL 

PUB LlCATlONS 

ROUGHDRAFT 

ARTWORK 

271.479-2 

Figure 2-1. Study Plan for IJTF Advanced Model Support Systems 
SECTIOM 3 

ESTABLISHING CRITERIA FOR A HIGH PKRF0R)IMICE STING 

Any sting designed for use in the NASA Langley Research facilities must meet 

the requirements established in the Wind Tunnel Model Systems Criteria2 

handbook. 

and torsion, and the following divergence criteria: a safety factor of 2 

against divergence demonstrated by in-depth analysis, and where possible, 

system stiffness verification. 

These requirements include an adequate margin of safety in bending, 

In this study, a goal was established, and a high performance sting was 

defined as one that could provide an improvement of 25% over the maraging 

steel (18 Mi-200) sting in ultimate tensile strength and Young's modulus of 

elasticity, E. These improvements must be achieved without adversely 

affecting fracture toughness at cryogenic temperatures. A Cvn of 25 ft-lb is 

desired. 

Other desirable features: 

0 A fail safe feature for a hybrid design 

0 Reduced weight 

0 Instrumentation to monitor stress/strain 

0 Resistance to fatigue (fracture toughness) 

Resistance to corrosion 

The structural analysis conducted for this program consisted of two phases. 

The first phase consisted of a study of the existing sting configuration to 

establish baseline performance goals. In the second phase, preliminary 

analysis was performed for several proposed alternative configurations. These 

configurations included high performance metals, advanced composite materials, 

and hybrid metal-composite combinations. For both of these efforts, the 

primary values considered were how the strength and stiffness of the various 

proposals compared to one another. 

directly in these comparisons but was instead treated as a initial screening 

mechanism. That is, materials that exhibited poor fracture toughness at 

cryogenic temperatures were eliminated From consideration before these studies 

were done to save time and narrow the range of potential candidates. 

Fracture toughness was not considered 

3.1 BASELINE CONFIGURATIOIJ STUDIES 

The baseline sting configuration consists of tapered cylindrical tube made 

from monolithic 18 Ni-200 steel as shown in Figure 3-1. 

conducted of this configuration to establish design goals for strength and 

stiffness that could be compared to proposed alternatives. 

An analysis was 

3-1 
TI 1 I I 1 

4 IN. 1 IN. I 

t I 

I 

I 

7- 

2 IN. 

96 IN. 

STA 0.e 

271.479-3 

( BASE'LI NE) 

Figure 3-1. Generic Model Sting (Baseline) 

3.1.1 STIFFNESS ANALYSIS. Plots of the stiffness versus length were 

generated for the existing sting and for the goal of a 25% improvement in 

these properties. 

calculated from the following equations: 

The desired values were the AB and E1 terms and were 

AE = s (Rg - Rf) (9) 

E1 = */4 (Ri - Rf) (E) 

where 

Ro = 2.00 - ~/96.00 

Ri = 0.50 

E = 26,500,000 psi (MIL-HDBK-SD, Table 2.5.1.0(b)) 

Substituting in the geometric values from Figure 3-1 gives the values for the 

baseline configuration summarized in Table 3-1. 

25% improvement were obtained by multiplying the AB and E1 values by 1.25. 

The results are shown graphically in Figures 3-2 and 3-3. 

Figure 3-4 shows the baseline sting cross section geometry. 

3.1.2 STRENGTH ANALYSIS. 

maximum axial loads and bending moments capable of being carried by this 

configuration. 

considered to be the design requirements for any replacement model. 

necessary since no formal design requirements were available and by 

establishing these values as minimum requirements, it ensured that any new 

sting would be at least as capable as the existing arrangement. 

The values for the desired 

The baseline sting was analyzed to determine the 

The loading conditions established in this analysis were then 

This was 

3-2 
Table 3-1. Baseline Sting Configuration Stiffness Parameters 

X R R AE E1 

(in.) (in.) (in. 1 (lb) (lb-in2) 

0 i 

0.00 2.00 0.50 308,661,000 327,952,000 

24.00 1.75 0.50 231,496,000 191,707,000 

48.00 1.50 0.50 164,619,000 102,887,000 

72.00 1.25 0.50 108,031,000 48,952,000 

96.00 1 .oo 0.50 61,732,000 19,291,000 

3.00E+08 

2.50E+08 

AE 

(W 

AE vs. Sting Station 

Goal 

0.00 12.00 24.00 36.00 48.00 60.00 72.00 84.00 96.00 

Sting Station 

(in) 271.479-4 

Figure 3-2. Baseline and Improved Sting Configuration Stiffness Parameters, AB 

The basic approach taken was to analyze the sections of the sting at the 

forward and aft ends to determine the maximum allowable axial loads and 

bending moments. 

baseline configuration using 18 Ni-200 and the desired 25% improvement. 

this, critical design conditions could be selected for use in the evaluating 

proposed configurations. A plot of the resulting design envelopes is shown in 

Figure 3-5 and a summary of the critical design conditions is given in the 

Table 3-2. Note that in selecting the critical design conditions at the aft 

end, the maximum axial load at the forward end was used as limiting value. 

This is because there is no means of introducing additional axial loads into 

the sting between the forward and aftends. 

These were then used to create design envelopes for the 

From 

3-3 
3.00E+08 

(Ibsin2) 2.50E+08 

2.00E+08 

El 

I 

El VS. Sting Station 

9 Goal 

0 Mar200 

1.50E+08 

1.00E+08 

5.00E+07 

0.00E+00 

0.00 12.00 24.00 36.00 48.00 60.00 72.00 84.00 96.00 

Stina Station 

(in) 271 A79-6 

Figure 3-3. Baseline and Improved Sting Configuration Stiffness Parameters, E1 

271 A796 

Figure 3-4. Baseline Sting Cross Section Geometry 

3.2 CROSS SECTION STRAIM DISTRIBUTIOM 

The axial strains at the cross section at the aft end of the sting were 

calculated for the critical design conditions. 

analyzing potential sting configurations using hybrid material systems where 

the stress distribution at a given cross section would no longer be linear. 

The strain at a given location for a general section subjected to axial loads 

and bending moments is given by: 

These values were required for 

E = P/AE + Mc/EI 

The values for the improved sting configuration were used and were taken from 

Figures 3-2, 3-3, and 3-5. The results are shown in Figure 3-6. 

3-4 
n 

4.0 

3.0 

2.0 

1 .o 

0.0 

0.0 1 .o 1.5 0.5 

Bending Moment 

(1,000,000 in-lbs ) 

2.0 

271.479-7 

Figure 3-5. Baseline and Improved Strength Design Envelope 

3-5 
Table 3-2. Critical Loading Conditions for the Improved Sting Configuration 

Section Properties 

A = w (Ro2 - Ri2) = w (1.002 - 0.502) 

I = (#I41 (Ro4 - Ri4) = (#I41 (1.004 - 0.504) 

Internal Stresses 

Ftu = PIA + mO/I 

P = A (Ftu - MRoI) 

ll = (IIRo) (Ftu - PIA) 

Material Properties 

18 Mi-200 

E = 26,200,000 psi 

Ftu = 200,000 psi 

Maximum Allowable Loads - Forward End 

Section Properties 

Ro = 1.00 in. 

Ri = 0.50 in. 

18 Ni-200 

Pmax = 507,240 lb 

llmax = 147,260 in-lb 

Maximum Allowable Loads - Aft End 

Section Properties 

Ro = 2.00 in. 

Ri = 0.50 in. 

18 Mi-200 

Pmax = 2,536,200 lb 

= 1,251,730 in-lb 

Goal 

E = 32,750,000 psi 

Ftu = 250,000 psi 

A = 2.5362 in2 

I = 0.7363 in4 

Goal 

Pmax = 634,050 lb 

Hmax = 184,075 in-lb 

A = 11.7810 in2 

I = 12.5173 in4 

Goal 

Pm, = 2,945,250 lb 

P4,, = 1,564,662 in-lb 

Condition Axial Load (PI Bending Moment (MI 

(lb) (in-lb) 

I 0 1,564,662 

I1 -184 , 075 1 , 460 , 872 

3 -6 
2.0 

1 -0 

0.0 

-1 .o 

-2.0 

0.0 0.005 0.01 0 -0.01 0 -0.005 

Axial Strain 

( inlin ) 

condl - 

CondII - 

27 1.4794 

Figure 3-6. Axial Strain Distribution at the Aft End 

of the Improved Sting Configuration 

3-7 
SBCTIOM 4 

CONVENTIONAL METALLURGICAL APPROACH 

4.1 GENERAL INFORIUTIOM 

For sting applications where high strength and stiffness is a general 

requirement and where cryogenic fracture toughness is a serious concern, 

maraging-type steels have been shown to be very effective. Few materials can 

presently match its combination of 200 ksi level yield strength, 26 Msi 

Young's modulus, and excellent cryogenic fracture toughness. Commercially 

available alloys that have properties similar to maraging steels are listed in 

Table 4-1. 

cryogenic toughness, but none exceed maraging steel's properties in all 

categories. 

developed Air Force alloy) and Inconel 718 or W35N. With specialized thermal 

mechanical treatments, possibly 25% improvement in strength and stiffness 

might be achievable. 

however, may still present a challenge. Of the alloys listed in Table 4-1, 

HP35N is perhaps the candidate most closely fitting our requirements. 

As can be seen, a few alloys have higher strength or stiffness or 

An exception might be alloys such as AF 1410 (a relatively newly 

Satisfaction of cryogenic fracture toughness levels, 

Table 4-1. Potential Candidate High-Performance Sting Materials 

Alloy 

Yield Young * s 

Strength Modulus Charpy V-Notch 

(At RT ksi) (At RT Msi) (At -320F, ft-lb) 

Maraging 200 

Maraging 250 

Maraging 300 

PH 13-13 MO ~1150~ 

PH 13-8 MO H950 

Custom 455 

AF 1410 

Inconel 718 

HP351 

Cold worked & aged 

Cold worked & aged 

200 

250 

290 

85 

210 

195 

230 

285 

26.2 

27.0 

27.5 

25.0 

28.6 

29.0 

29.4 

29.0 

34.8 

28 

10 

10 

30 

4 

5 

15 

16 

The high performance metallic material systems considered in this study were 

compared against the baseline configuration by plotting the strength versus 

stiffness of these materials on a common chart as shown in Figure 4-1. This 

provided a simple and easily understandable means of comparing different 

materials. 

4-1 
600 

500 

400 

300 

200 

100 

0 

Tensile Strength vs Tensile Modulus 

60 80 100 120 0 20 40- 

Tensile Modulus (300K) 

(1OA 6 psi) 

271.4799 

Figure 4-1. Comparison of High Performance Metallic Materials 

4-2 
In viewing the data shown in Figure 4-1, it is important to realize that this 

chart does not consider the availability of the material in the form required 

for the sting application. In particular, the data for W35N is for sections 

less than 1.25 inches in thickness and does not apply to currently available 

materials in the size required for this application. 

4.2 ADVANCED STING USING W35M 

W35w alloy is a vacuum induction, vacuum arc remelted alloy, comprising 10% 

molybdenum, 20% chromium, and the balance a combination of nickel and cobalt, 

normally 35% nickel and 35% cobalt. This alloy has shown unusually favorable 

combinations of high strength, stiffness, and corrosion resistance. These 

properties are obtained by cold working the material, either by drawing, 

extruding, or rolling. 

temperature range of 800 to 1200F. 

should be understood that the high strength properties of the material will be 

lost in the vicinity of weld. 

Additional strengthening is obtained by aging in the 

The material can be welded, although it 

Typical properties for W35N are shown in Table 4-2 and compared with other 

metals. 

An outstanding feature of the Hultiphase alloy system is the exceptional 

corrosion and stress corrosion resistance at very high strength levels. 

system has matched the strength developed by the high strength steels while 

maintaining the excellent corrosion resistance demonstrated by the lower 

strength stainless steels. 

This 

An indication of the variation in Cvn with temperature is shown in Table 4-3. 

This is the result of work done at NASA Marshall Space Flight Center, using a 

cold-worked W35N bar for a test specimen. 

An example of the change in modulus with decreasing temperature is shown in 

Table 4-4, using different test specimens. 

The Cvn for the very high strength use shown above does not meet the requirement of 25 ft-lb for impact strength3. 

Fult = 227 ksi, however, should give us a better Cvn value. In other words, 

strength could be tailored during the cold working process to give us a more 

acceptable Cvn value. 

Cobalt superalloys (hcp structure) are described4 as high cost, limited 

availability, poor fabricability, lacking design data, etc. PIP358 is a cobalt 

superalloy, and while the above statements are generally correct, recent 

experiences have shown that the alloy is being used in more and more 

applications. Wile we might not recommend it for the whole model system, its 

use in a high performance sting, with the advantage of a 30% increase in 

stiffness over 18 Ni-200, would appear to justify further research. 

The lower value of Fy = 217 ksi/ 

4 -3 
Table 4-2. Mechanical Properties of Various Metals 

Material Tenperature Yield U1 timate E V a Cvn KIC 

t 

stress stress 

(deg IO (ksi) (ksi (Mi 1 in/in/deg F ft-lb ksi-in1'2 

18 Ni-200 300 

78 

18 Ni-250 300 

78 

A286 300 

78 

AIS1 304 300 

78 

w35N 300 

78 

" 300 

78 

m!iN 300 

78 

205 

270 

250 

320 

100 

120 

35 

60 

215 

--- 

240 

-- 

285 

327 

210 

280 

260 

330 

160 

215 

90 

230 

230 

-- 

260 

--- 

295 

337 

27 0.311 

0.306 

28.1 0.308 

29.4 0.304 

28.4 0.300 

29.4 - 

27.4 - 

29.6 - 

35 

25 

20 

10 

55 

50 

1 55 

116 

50 

-- 

23 

- 

17 

16 

1 70 

80 

100 

40 

120 

110 

118 

I 

- 

- 

- 

- 

- 

Table 4-3. Variation of Cvn for W351 with Temperature 

Average Inpact Wr 

Test Tenp Energy (Om) Impact Energy Range of 

F (c) ft-lb (joules) ft-lb (joules) Tests 

75 (+23.9) 18.90 (25.62) 15.50-23.00 (21.01-31.18) 3 

-100 (-73.0) 17.10 (23.18) 14.75-19.25 (20.00-26.10) 3 

-200 (-129.0) 15.25 (20.68) 15.00-15.50 (20.34-21.01) 3 

-320 (-196.0) 16.10 (21.83) 14.00-18.25 (18.98-24.74) 2 

-423 (-252.8) 13.50 (18.30) 13.50-13.50 (18.30-18.30) 2 

4-4 
U 

20:: 

c 

a 

W 

IW 

z 

L 

W 

Iz: 

1s 

0 

z 

W 

0 

0 

0 

LL 

0 

W 

v1 

a 

a 

2 

2 

0 

W 

z 

m 

0 

0 

0 

-1 

0 

-1 

a 

w 

5 

4-5 
4.3 )IMNFACTURIMG ASPECTS OF MI m351 STING 

The major factor limiting the availability of HP35bl to small sizes is the 

equipment needed to cold work the material. Our research indicates that the 

higher values of strength are achieved with extensive cold working; i.e., 

strength is directly proportional to cold working. Size is also directly 

proportional; larger sizes are available but strength is reduced because the 

present equipment cannot cold work the longer sizes to the point of achieving 

maximum strength. Young's modulus, E, however, is not affected by the amount 

of cold work, which means that we can trade off size and strength while 

maintaining stiffness. For example, see Table 4-5. 

Table 4-5. Variation of Size and Strength for "351 Round Bar Stock 

Diameter (in. Ultimate Tensile (ksi) E Modulus (Msi) 

2.00 

2.14 

2.25 

2.50 

220 

200 

200 

195 

34.8 

34.8 

34.8 

34.8 

3.00 185 34.8 

Material cold worked and aged 

Machinability tests conducted by an independent laboratory have compared W351 

alloy to Waspaloy, a widely used standard for nickel-cobalt-chromium base 

alloy machinability. Comparing XP35N alloy work strengthened and aged to the 

260 ksi (1793 ma) ul.timate tensile and 240 ksi (1655 ma) 0.2% yield strength 

level, and Waspaloy in the mill-annealed condition with approximately 145 ksi 

(1000 ma) ultimate tensile and 90 ksi (621 ma) 0.2% yield strength, Waspaloy 

has approximately the same machinability in either the solution-treated or 

solution-treated-plus-aged condition. 

MP35bl alloy exhibited better machining performance than Waspaloy in all 

categories of tests except tapping where Waspaloy tapped about 15 ft/min (4.57 

m/min) faster for the same tool life of 200 holes. 

The Air Force machinability data center files do not provide comparable 

machining information for other cold-worked austenitic alloys. 

because of the unique strengthening mechanism for XP351 alloy, it may not be 

possible to make an extrapolated comparison in machinability performance to 

precipitation-strengthened alloys, transformation-strengthened alloys, or 

cold-worked alloys. 

Further, 

Specific setup practices for wP351s alloy are given in Tables 4-6 and 4-7. 

4-6 
I I 

, 

4-7 
Table 4-7. Manufacturer's Recommended Conditions for Surface Grinding 

Down Cross Trbls 

hJp8SS. inJp888. ftJmin. 

Who01 Grrde Wheal Type (mmlprss.) (mmlpms.) (mlmin) 

F0.d FOd sp..d 

32A46J8VBE 10' x 1' x 3' .w2 .050 40 

x 76.2 mm) 

Aluminum Oxide 

Wheel 

(254 mm x 25.4 mm (.051) (1.27) (12.2) 

Whool 

ftJmin. 

(mlmin) 

sp..d G 

Ratio Grinding 

Fluid 

6000 

( 1 829) 

70 Sulfurized Oil 

271.479-12 

Further information on machinability was obtained from the General Dynamics 

Materials and Processes Laboratory. They compared W35N with A286 and some of 

the Inconel materials saying that it can be machined with'high speed cutting 

tools; it isn't, however, a simple material to machine. A sample was obtained 

of the 0.625 inch diameter bar used, and the ultimate tensile stress was 

determined to be 285 ksi, and yield stress very similar. 

4.4 DESIGN CONCEPTS 

Recognizing the limitation in available size for W35N bar and plate, our 

study turned to possible ways of building up a sting, using available 

materials. 

and one for a rectangular sting. 

Two fabrication schemes were considered, one for a round sting, 

4.4.1 CONCEPTS FOR FABRICATING A ROWD STING. One method is to spiral wind 

very thin (0.020 to 0.060 inch) W35N strip around a tube of the same 

material. 

base for the spiral winding. 

winding. Strip layers would overwrap at various angles (to be determined) to 

ensure structural strength. 

desired strength level and machined to size and shape. 

developed to do this and they are described below. 

The tube would provide the 1-inch instrumentation hole and act as a 

The strip material would be cold rolled prior to 

The entire structure would then be aged to the 

Three plans were 

Plan 1 

1. Roll, cold work, and spiral wind W35N strip on W35N tubing core (see 

Figure 4-2). 

2. TIG, EB, or laser weld each of the spiral wrapped butt joints. 

Develop depth of penetration. 

3. Cold work weld area by shot peen or roll planish. 

4. Lathe turn taper on sting. 

4-8 
I 

/ 

rl 

c) 

Q 

Q) 

0 

V 

c 

0 

.-I 

Y 

x 

(v 

I 

U 

4-9 
I 5. Reweld top layer. 

6. 

Motes: Development data is need for cold working, TIG, BB, and laser 

Age sting per Latrobe Steel specifications. 

welding of W35M material. 

Plan 2 

1. Roll, cold work, and spiral wind W35M strip material and braze alloy 

on W35N tubing core (see Figure 4-3). 

2. Tack weld as required. 

3. Vacuum or retort furnace braze. Hatch braze alloy to the W35M aging 

temperature (about 1000F). 

4. Lathe turn taper on sting. 

Notes: Development data is need for cold working, brazing alloy 

selection, tack welding, and furnace brazing W35M material. 

Plan 3 

1. Roll, cold work, and spiral wind W35M strip on W35M tubing core. 

2. Tack weld as required. 

3. Diffusion weld entire sting together at a temperature to match the 

aging temperature. 

4. Lathe turn taper on sting. 

Notes: Development data is needed for cold working, tack welding, and 

diffusion bonding of m35M material. 

The spiral wind process is a process that has been used successfully at GDC; 

it is described in a report5. 

inches wide by 0.60 inch thick) was wrapped around a tube, with an adhesive 

bond used for attachment. Cross plies were used for strength. 

tube wasl.0inches in diameter. 

la inch diameter mandrel using cold rolled W35M strips, a more difficult 

task. 

indicated in the plans above, electron-beam welding, brazing, and diffusion 

welding are alternate proposals. For either case the manufacturing process 

must be such that the cold worked properties of the strip are not lost. 

manufacturing process must therefore not exceed the aging temperature of W351 

(800 to 1200F). 

In that particular case, stainless steel (3 

The finished 

For the NTF application we must wrap over a 

The cryogenic environment prohibits the use of an adhesive bond and as 

The 

4-10 

L 
I I 

> 

s 

a 

s 

A 

w 

N 

m 

b0 

c .d 

U 

m 

cc) 

I 

4-11 
4.4.2 FABRICATIMG A RECTANGULAR STING OF Mp35M. In this concept, the largest 

available plate size are used to fabricate a rectangular sting. 

l-lle-inch thick by 3-inch deep plates are keyed together on the vertical 

centerline. 

method of attachment of the two plates will take the torsional and side 

loads. 

beam can be tapered using available plate sizes. 

the beams were considered. 

TWO 

The keys will take the major load in the vertical plane, and the 

The machining task is reasonably straightforward, and the depth of the 

Various methods of attaching 

0 Diffusion brazing 

0 Diffusion welding 

0 Adhesive bonding 

0 Laser welding 

0 Electron-beam welding 

As indicated earlier, UP35bl loses it physical properties if the attachment 

temperature exceeds 1000F, and this is a critical part of the design 

analysis. The design concept for the rectangular sting is shown in Figure 4-4. 

271.479-16 

Figure 4-4. Typical Section of Sting Showing Laser Weld 

As can be seen, the W35N plates are milled to a finished size including the 

keys and a centerhole for routing instrumentation cables, etc. 

of W351 limit the thickness (the reason for the joint) and the length. For 

example, the maximum size of existing plate is on the order of 1 112 inch 

thick by 24 by 24 inches, possibly going to 2 inches thick with reduced 

strength, but maintaining stiffness, E. Research indicates, however, that 

longer length 

Available size 

4-12 
(4 or 5 feet) could be obtained in the future, but is a function of equipment, 

demand, etc. It is not unreasonable, therefore, to think in terms of sting 2 

to 3 inches wide by 3 to 6 inches deep by 5 feet long, fabricated from two 

plates. 

test. 

The design concept must therefore be developed in proof-of-concept 

Attachment method analysis follows. 

4.4.2.1 Diffusion Brazing. This process involves the use of a metal foil 

between the mating surfaces and application of heat and pressure to diffuse 

the filler metal with the base metal for an effective joint. Care must be 

taken with surface finish and cleanliness of the mating parts. To maintain 

the properties of )Ip35IV, the temperature during the diffusion braze process 

must not exceed the aging temperature (1000F). This limits the braze alloys 

that can be used as fillers. 

4.4.2.2 Diffusion Welding. This is a solid-state welding process that 

produces coalescence of the faying (or mating) surfaces by the application of 

high pressure and temperature. The process normally does not include a filler 

material. Here, because of the temperature limitation, a soft filler would be 

used as an aid to diffusion, probably copper or silver. 

4.4.2.3 Adhesive Bonding. This process was not pursued further because it 

was not felt to be fail-safe, particularly at cryogenic temperatures. 

4.4.2.4 Laser Welding. As stated previously, the desired properties of Hp351 

are produced by cold working, and it is known that the temperatures associated 

with welding will return the alloy to the annealed state. Welding therefore 

is not normally recommended by the manufacturer. W351 is, however, a 

weldable material, and in the application shown in Figure 4-4 we felt it to be 

worth further consideration. 

Prior research1 revealed that laser welding was well controlled, very clean, 

had very narrow heat affected zones, and little material distortion. At that 

time the depth of penetration for laser welding was on the order of 0.050 to 

0.10 inch maximum. Today the process is more versatile, and weld penetration 

of up to 0.75 inch has been accomplished. 

concept; the upper and lower butt joint would be laser welded to a depth not 

exceeding 0.75 inches. The heat affected zone is not expected to exceed 0.040 

to 0.050 inch, which means that a very small area of the structure will be 

reduced to an annealed condition. 

Figure 4-4 shows the design 

The primary load will be in the vertical plane, and will be taken by the two 

plates keyed together. The side and torsional loads will be taken in through , 

the welded joint, (annealed-ultimate tensile strength 130 ksi). This design 

concept would be particularly useful in applications where the vertical load 

(NF) is large in relation to the side force (SF). The mating surface for this 

process should fit well, but the finish and cleanliness are not as critical as 

in the diffusion brazing process. 

4.4.2.5 Electron-Beam Welding. This process is much more common and is also 

a good candidate. The heat affected zone, however, is much larger, resulting 

in loss of strength, and potential distortion. 

4-13 
4.5 STRUCTURAL MALYSIS 

L 

The sting cross-section shown in Figure 4-4 is a typical design concept. 

vertical load is normally larger and is taken equally by the two plates. 

keyways help to locate the plates, and take out any asymmetric loading. 

centerhole used for routing wiring, tubes, etc., would be rectangular, with 

the short axis in the vertical plane for increased moment of inertia. 

laser welded butt joint would vary in depth up to a maximum of 0.75 inch. 

?he 

The 

The 

The 

Table 4-8 is a comparison of the fabricated section as shown with a solid 

section of the same material. 

Table 4-8. Comparison of Fabricated and Solid Sections 

Load Fabricated Solid 

Vertical Strength reduced by depth of Maximum strength of full section 

weld times 0.050 inch 

(annealed). 

Side Taken by shear at welded 

surf ace 

Maximum strength of full section 

Torsion Similar to side load As above 

An alternate design for the rectangular sting was considered. 

purpose was to use available material for a longer sting. 

thicker plates are limited in length to 2 feet, whereas sheet stock to 

thicknesses of 1/4 inch are available in lengths of 6 feet. The alternate 

design is a laminated beam comprising strips of 1/4-inch sheet built up to the 

desired width, with the strips cut to the depth required. 

The main 

At present the 

The key to fabrication of this type of beam is the joining process. Various 

methods were described earlier in the section and of those, diffusion welding 

is felt to be one of the best candidates. As described earlier, a 0.003-inch 

thick film of copper or silver would be placed between the sheets of )Ip35N, 

and pressure applied at a temperature not exceeding 1000F. This process does 

not include macroscopic deformation, or melting of the filler. 

As described in several welding journal articles6, the process is diffusion 

welding if the interlayers do not melt. 

successfully accomplished using 18 Mi-200, development would be required using 

HP35N. 

diffusion welding process. 

While this process has been 

The use of comparatively thin sheets of HP35N would facilitate the 

Figure 4-5 shows the concept. 

4-14 
CAP, 4 1/4lN. 

SIDE 

Figure 4-5. Rectangular Beam Using 1/4-inch LIP351 Strip 

271 A7946 

To create a hole in the center for routing model instrumentation, it may be 

necessary to subassemble the sides, and top and bottom caps. Alternatively, 

instrumentation could be routed along the sides as shown in Figure 4-6, with 

an outer cover for protection. As a conservative measure (fail-safe) a pin 

could be used across the center, laser welded in place for positive clamping 

of the W35Y strips. 

The design using multiple shemts of W351 is potentially stronger than the two 

plate approach shown in Figure 4-4 because the thin sheets can be cold worked 

to the full allouables; in addition, the diffusion welding at 10001 will not 

reduce the properties. 

4-15 
4 1/4 IN. 

.COVER 

M35N PIN, LASER 

WELD IN PLACE 

27 1.479-1 7 

Figure 4-6. Alternate Design Using W35N Strip 

4-16 
SECTION 5 

THE USE OF ADVMCED COHPOSITES FOR A HIGH PERFORMAMCE STING 

5.1 GENERAL, INFORMTION 

In viewing the use of composites for use in a high performance sting, it is 

found that the majority of development work has been done in the area of high 

strength-to-weight ratios, in other words, relatively thin walled structures. 

The sting is essentially a solid bar, with a small centerhole, and the 

generally accepted properties for composites probably do not apply. 

purposes of their study, however, our goal was to review composite materials 

developed for the aerospace industry, and to determine if they could be 

modified or altered for use in a sting application. 

For 

5.2 ORGANIC MATRIX COMPOSITES 

In the search for high modulus organic composites, the properties of 

pitch-based graphite fibers were considered because of their moduli of 70 to 

125 Hsi. The fibers, as they are currently available, will produce epoxy 

matrix laminates with moduli of about 70 Hsi. However, the tensile strengths 

of these composites are only 180 ksi. Some of the intermediate modulus 

PAN-based polyacylonitrile fibers will produce laminates with moduli of about 

25 Hsi and tensile ultimates of 400 ksi. In compression, however, the 

PAN-based laminates show ultimates of only 140,000 psi maximum and the 

pitch-based laminates 40,000 psi and are erratic in performance. 

The properties of graphite fiber composites show promise if they can be used 

in such a manner that they are loaded only in tension. 

In this study of advanced stings, the primary load is nearly always in the 

upward direction. The sting is a cantilevered beam; therefore, the upper side 

is in compression, and the lower in tension. The feasibility of using an 

all-composite sting was reviewed on that basis. Unfortunately, there doesn't 

seem to be any obvious way to blend the material so that we use the high 

tensile modulus of pitch fibers along with the high tensile strength of PAM 

fibers. 

in strain rates between the two types of fibers. Table 5-1 lists candidate 

materials. 

Combining them did not seem to be feasible because of the differences 

Since the ultra high modulus graphite structures are unpredictable when loaded 

in compression, and the high-modulus, high strength graphites are not as 

attractive when loaded in other than tension, any improvement in properties 

over the metallic materials must be gained by loading them only in tension. 

These limitations make the design of an all-organic matrix structure very 

difficult and lead to the alternative of incorporating them into a hybrid 

design with metallic elements. 

5-1 
Table 5-1. Candidate Sting Materials 

Risks 

T-clO/Epoxy 25 470 -0.5 Very high strength and Attachent to other 

nrodulus. Failure is materials sanewhat 

usually slaw, progres- difficult. Cryogenic T-SO/Epoxy 35 205 4-54 

P-75 Epoxy 49 140 -0.97 sion not castastrophic. properties not characVery low CTE. Not sire terized. (CTE < 0) 

1 imi ted. P-lW/EpoXy 72 180 -1.15 

5.3 STRUCTURAL MlALYSIS 

The advanced composite material systems considered for this study consisted 

primarily of ultra-high modulus graphite fibers in a resin matrix. 

of the available fiber and matrix materials currently available indicated that 

this combination would be the only one that could achieve substantial 

improvements in the sting stiffness properties. Alternative fiber systems 

such as Kevlar, aluminum oxide, and silicon carbide do not offer the same 

range of moduli available in the graphite fibers. 

materials such as thermoplastics and metals are limited in the fiber volume 

content that can be achieved. Typically, material systems using these 

improved matrices are limited to 50% fiber volume compared to the 65% 

available with epoxy matrices. 

this application, any improvement achieved by these higher modulus matrices is 

more than offset by the reduced fiber volume. 

A survey 

Alternative matrix 

For the high modulus requirements needed for 

In comparing the properties of candidate composite material systems, an 

approach similar to that used for the high performance metallic materials was 

adopted. 

materials were created for several levels of each material. These consisted 

of fiber properties, unidirectional laminate properties, and cross plied 

laminate properties. The fiber properties represent the theoretical limits 

achievable with these materials. 

the reduced properties required to create a practical design. 

Comparison charts of the strength and stiffness of available 

The cross plied laminate properties reflect 

5.3.1 FIBBR PROPERTIES. A comparison of the strength and stiffness 

properties of fibers currently available or under development is shown in 

Figure 5-1. 

individual fibers and was obtained from vendor data sheets. 

This data represents the results of tensile testing done on 

5.3.2 ~IDIRBCTIOMAL MIMATB PROPERTIIS. A comparison of the strength and 

stiffness properties of unidirectional laminates is shown in Figure 5-2. This 

data was obtained from vendor data sheets and from limited test programs 

conducted by General Dynamics Space Systems Division. 

tend to represent upper bounds for the properties available for production 

parts. 

As such, these results 

5-2 
600 

500 

400 

- 2 

I 

I- 

(3 

LI 

w 

300 k 

w 

-I 

L 

w + 

3j 

200 

100 

0 

Tensile Strength vs Tensile Modulus 

I 

P120 

60 80 100 120 

Tensile Modulus (300K) 

(10 A 6 psi) 

271.479-18 

Figure 5-1. Comparison of Composite Fiber Properties 

5-3 
600 

500 

400 

300 

200 

100 

0 

Strength vs Modulus 

60 80 . 100 1 20 0 20 40 

Modulus (300K) 

(10A6 psi) 

271.479-19 

Figure 5-2. Comparison of Composite Unidirectional Laminate Properties 

5-4 
There are two factors to note when comparing this chart to the one for fiber 

properties. 

both improved strength and stiffness properties compared to the existing 

sting. 

substantially less than their tensile strengths. 

for the ultra-high modulus materials that have only a limited tensile strength 

to begin with. 

one-third to one-half of the tensile strength. 

testing done for an unrelated program and represents a definite limitation on 

the application of these materials. 

The first is that there is no longer any one system that achieves 

The second is that the compressive strengths of these materials are 

This is especially notable 

For these materials, the compressive strength is only 

This data was confirmed by 

5.3.3 CROSS PLIED LAMINATE PROPERTIES. The strength and stiffness properties 

of cross plied laminates using several material systems were calculated using 

the General Dynamics standard laminated plate analysis program SQS. 

results for the longitudinal properties of a high strength system, T40/Epoxy, 

and high modulus system, PlOO/Epoxy, are shown in Figures 5-3 and 5-4. Figure 

5-3 shows the tensile strength versus tensile modulus for a range of laminates 

for each material. Figure 5-4 shows the tensile strains to failure versus 

tensile modulus for these materials. The data in Figure 5-4 is useful in 

comparing hybrid configurations made from several material systems where the 

strain across the cross section remains linear while the stress distribution 

becomes a function of the moduli of the materials. It is important to note 

that the strength values apply to tensile stresses only. The compressive 

strength values would be less than half of these values for PlOO/Epoxy system. 

The 

5.4 RELATIONSHIP BETWEEN TENSION/SHBAR STRENGTH FOR A HIGH MODULUS ADVANCED 

COMPOSITE SYSTEM 

To meet the stringent requirements of space hardware, ordnance, electronics 

and other high modulus applications, manufacturers have developed a new family 

of prepregs. These Advanced Composite System7 high modulus prepregs combine 

state-of-the-art carbon fibers with a new proprietary, toughened epoxy, 350F 

cure resin. These systems offer, for the first time, an integrated material 

system designed specifically for the demanding environment of space, and 

feature microcrack resistance, thermal stability, and mechanical properties 

needed for advanced composite applications for many aerospace research and 

development applications. 

considerably less than the tensile strength. 

As can be seen in Table 5-2, the shear strength is 

5.5 COMPOSITE STING DESIGY 

Further research into design/fabrication concepts for advanced composite 

stings was discontinued based upon the structural/material analysis, 

particularly the lack of compressive strength. A considerable amount of 

development work is continuing in the advanced composite field, and this may 

help us in the future. For the present, however, other opportunities for a 

high performance sting look more promising. 

5 -5 
Tensile Strength vs Tensile Modulus 

600 

500 

400 

A 

200 

100 

0 

0 20 40 60 80 100 120 

Modulus WOK) 

(10A6 psi) 

271.479-20 

Figure 5-3. Comparison of Composite Cross Plied Laminate Properties 

5-6 
i 

20 

Tensile Strain vs Tensile Modulus 

0.024 

0.020 

0.01 6 

0.01 2 

0.008 

0.004 

0 

60 80 40 

Modulus (300K) 

(10A6 psi) 

1 ao 120 

271.479-21 

Figure 5-4. Comparison of Composite Cross Plied Laminate Properties 

5-7 
I Table 5-2. Typical Composite Properties 

Property 

Pitch Fiber composi test 

P-55 P-75 P-100 

Longitudinal Tension 

(ASTM D-3039) 

Strength (ksi) 

Strain (XI 

Modulus (Msi)*t 

Poisson’s Ratio 

Longitudinal Compression 

(ASTM D-3410) 

Strength (ksi) 

Modulus (Msi) 

Coefficient of Thermal Expansion* 

(10’6/dejc C) 

Longitudinal 

Transverse 

135 140 180 

35 49 72 

0.38 0.28 0.24 

0.34 0.30 0.31 

74 64 

29 46 

42 

76 

-0.76 -0.97 -1.15 

30 30 31 

hRL-1962 prepreg resin. Longitudinal properties normalized to 62 volume 

percent fiber. 

**Measured between 0.1 and 0.2% strain. 

*Measure over the range 30 to 100 C. 

~~ ~ 

I 

5-8 
SECTION 6 

HYBRID HETAL/COKPOSITB COHBINATIONS 

6.1 GENERAL INFOaTIOI 

In a previous wind tunnel model study1 by General Dynamics the limitation of 

the sting was recognized and a section describing an "ideal" sting was 

included: excerpts from that section follow as they form the basis for the 

research into the feasibility of a hybrid sting. 

"The primary objective of this section of the study is to identify advanced 

materials, or combinations of materials, that will provide increased strength 

and stiffness properties at cryogenic temperatures. 

factor; the steel sting is approximately 500 pounds, creating obvious handling 

problems. 

attractive. 

Weight is also a key 

From this point of view, composites would appear to be very 

"During the materials research, it was quickly discovered. that very little 

information is available on material properties at the cryogenic temperatures 

of the NTF. Furthermore, much of the available information is for small 

billets, and for composite materials for thins sections. For example, 

considerable research has been done in the aerospace industry on the use of 

composite materials for space applications at low temperature. High strength 

boron/aluminum tubes and various graphite epoxies have been developed; in 

space applications, however, the thrust has been to develop high 

strengthlweight ratios, and therefore the materials are relatively 

thinwalled. In sting applications, the material thickness is much greater, 

resulting in questionable material properties, and much higher manufacturing 

costs. 

"One material possessing interesting properties in Kennametal K9, a tungsten 

alloy with a stiffness three times that of steel. Again, very little 

information is available for this material at cryogenic temperatures. 

Kennametal, Inc., conducted a study of the feasibility of using Kennametal K9 

as a sting material. The study revealed that the strength and stiffness of K9 

was considerably less than the published values when applied to the physical 

size of material required to manufacture the sting. The properties had been 

developed from relatively small test samples, and the manufacturer, while 

initially optimistic, later determined that the desired characteristics of K9 

would be degraded to an unacceptable level for an item with the physical size 

of an NTF sting. Our research also showed that there would be manufacturing . problems associated with producing a K9 sting suitable for the NTF. 

Degradation of material properties due to size was, however, the key factor in 

determining the unsuitability of Kennametal K9. 

"As an alternative to a sting manufactured completely of Kennametal K9, our 

study turned to the use of Kennametal K9 with its desirable stiffness 

properties combined with other high strength materials. 

an A286 inner core was investigated, but again the K9 shell was found to be so 

A K9 outer shell and 

6-1 
large that properties were questionable and manufacture a problem. 

K9 as an inner core rather than an outer shell was also considered. 

Using the 

"General Dynamics then investigated the use of a high grade steel such as 18 

11-200, or Kennametal K9, with advanced composites such as boron/aluminum, or 

graphite epoxies. Finally a combination of Kennametal K9, boron/aluminum, and 

18 Ni-200 steel was considered. A common problem (for all these sting designs 

using dissimilar materials) is that of coefficient of expansion, and the 

resulting thermal stresses. 

and coefficients and shows a schematic of an "ideal" sting, combining the best 

available materials. In design, however, it was found that the stiff 

Kennametal K9 (modulus of elasticity = 90 x lo6) became too highly stressed, 

due to picking up too high a proportion of the total load applied to the 

sting. The very stiff materials tend to have lower ultimate stress values and 

cannot achieve an acceptable safety factor. For this reason, the stiffness of 

K9 is unacceptably high when used in a composite sting with other materials of 

less stiffness. 

required. '* 

Figure 6-1 provides a comparison of properties 

As shown in Figure 6-1, a material with E = 45 x lo6 is 

271.479-22 *BASED UPON MATERIAL THICKNESS OF 0.080 INCH MAXIMUM. 

Figure 6-1. "Ideal" Composite Sting Support 

6-2 
As pointed out in an earlier section, the search for suitable sting materials 

is complicated by the need for both high strength and high stiffness plus 

reasonable cryogenic toughness in one single material. Recognizing that this 

is a difficult design problem, a reevaluation of the hybrid concept was 

initiated. 

in critical areas, with a high strength/toughness core. 

of this approach is that a large variety of materials might be used for 

stiffeners because of the safety margin provided by the strong and tough core 

material. If the high stiffness material should fail, it would not 

necessarily be catastrophic to overall sting structure. In other words, a 

fail-safe sting feature is possible. 

The objective was to use the combination of high modulus materials 

The great advantage 

6.2 HYBRID MATERIAL SYSTMS USING KBBINAMETAL 

Hybrid sting configurations incorporating a rectangular cross section have the 

potential of placing more of the high modulus material where it will be most 

effective at a location remote from the neutral axis. 

incorporating metallmetal and metal/composite hybrids were investigated to 

determine the effects on the sting performance. 

Potential concepts 

A rectangular cross section sting configuration incorporating reinforcing 

strips of ultra high modulus Kennametal was examined to determine its bending 

strength and stiffness properties. 

6-2. The analysis approach was similar to that used with the circular 

metal/composite configuration with appropriate modifications used for 

generating section properties in the transition from a circular to a square 

section. These formulas were incorporated into a spreadsheet format to allow 

trade studies to be performed quickly and reliably. The variables considered 

were the depth the outside edge of the sting to the start of the Kennametal 

strip and the thickness of the Kennametal strip. The material properties from 

Table 6-1 were used and the results are summarized in Figure 6-3. 

The geometry considered is shown in Figure 

t 

H 

BASEMETAL 

0 HIGH MODULUS METAL 

kW+ 271.479-23 

Figure 6-2. Cross Section Geometry for Metal/Metal Hybrid Sting 

6 -3 
Table 6-1. Haterial Properties for Hybrid Sting Configurations 

Haterial Longitudinal Hodulus Longitudinal Strain Allowable 

(psi 1 (in/ in) 

18 81-200 

W35N 

Kennametal 

T40/Epoxy* 

T5O/Epoxy* 

P100/ Epoxy* 

26,200,000 

34,500,000 

80,000,000 

20,000,000 

30,000,000 

40,000,000 

0.007634 

0.007634 

0.001875 

0.017010 

0.006440 

0.003510 

*Values for (+15) Laminate 

The results in Figure 6-3 again show the tradeoff between strength and 

stiffness properties. While some very attractive improvements in stiffness 

are available, they are all accompanied by reduced strength values. 

6.3 18 Ni-200/WHISKER REINFORCEKENT 

The use of single crystal reinforcing whiskers in a matrix of 18 Ni-200 steel 

could provide a substantial increase in material properties. 

Sic whiskers were added during powder metallurgical fabrication of three 

aluminum alloys. Depending on fiber contents, tensile strength increased up 

to 60% and the elastic modulus increased to 100%. 

and aluminum oxide have been used successfully in both aluminum and nickel 

base alloys in other studiesg*lO. 

incorporate the composite whiskers during powder metallurgical fabrication of 

18 Ni-200. Although sample fabrication and actual testing would be required 

to determine the feasibility of this approach, the use of powder metallurgy 

techniques in other margin alloys has been successful, and documented by 

German and Smugerstyll. 

In a study8, 

Fibers of Sic, graphite, 

The proposed approach would attempt to 

The major difficulties to be overcome with this approach involve 

whisker-to-matrix adhesion and a loss of toughness in the material. To 

properly utilize the properties of the whiskers, the matrix and whiskers must 

not separate under loads. Also, while tensile properties and elastic modulus 

increase with increasing whisker content, there is also a corresponding 

decrease in toughness and ductility. Careful experimentation will be required 

to determine the optimal compromise in properties. 

' 

6 -4 
Relative Strength vs Relative Stiffness 

2.40 

2.00 

1.60 n 

.e 

5 

gs 

-=p 

88 

sa, 

- 

- 0.80 

0.40 

0.00 

I I I I I I_ 

Strip Depth = 0.00 in. 3- - 

Strip Depth = 0.25 in. 

Strip Depth = 0.50 in. 

4 

- 

I 

1.20 1.60 2.00 2.40 0.00 0.40 0.80 

Relative Stiffness 

( Model Stiffness I Goal Stiffness ) 27 1.479-24 

Figure 6-3. Comparison of Hybrid Metal/Metal Stings ~ 

with Baseline Model Properties 

6-5 
Current examples of material systems that have taken this approach to 

increasing stiffness are the graphite/epoxies, boron/aluminums, and 

carbon/carbon composites. Theoretically, the stiffness of these composftes 

should follow a law of mixtures relationship as follows: 

I 

I Using this relationship for example you would need only 15 volume percent Of 

tungsten filaments to increase the stiffness of 18 11-200 from 27 Hsi to 32 

Hsi, a 20% increase in elastic modulus. 

I 6.4 CLADDING 

Cladding is the deposition of a layer of one metallic alloy on a substrate of 

a second alloy. 

surface of the substrate and the cladding material, which is introduced as a 

powder, wire, or thin sheet. Thus, when solidification occurs, a layer of 

cladding material is deposited with a small region of dilution giving a 

metallurgical bond. A clad component offers the designer flexibility since it 

permits combining the properties of two alloys. For this study we reviewed 

the feasibility of adding a cap of high stiffness material to a conventional 

sting of high strength but relatively low stiffness. Laser cladding produces 

homogenous microstructures on metal surfaces. By adding metal powders to the 

beam work surface, a smooth clad layer can be provided in many shapes and 

thicknesses. 

post-cladding machining can be accomplished. 

The laser beam is used to melt both a thin layer on the 

The variety of cladding materials available is extensive and 

Present day examples of cladding are Inconel 625 over mild steel, and stellite 

over steel. Inconel 625 was clad on steel substrates by introducing a powder 

into the focused laser beam with motion controlled by robotic workstation. 

The Inconel overlay showed very little dilution into the base steel. 

Successful bend tests and dye penetrant tests were achieved. Deposition rates 

are about twice the rates achieved by conventional processing. Less heat is 

introduced so that less distortion is measured after processing. 

For the sting application we reviewed cladding a tungsten alloy to 18 Ni-200, 

using the laser beam process. 

inch, and it is preferable to do this to a rectangular rather than a round 

bar. For comparison, therefore, assume: 

Stellite has been clad to a thickness of 0.25 I 

a. A bar 3 inches deep by 2 inches wide of 18 Ni-200. 

b. A bar 2.5 inches deep by 2 inches wide of 18 Ni-200 with .25-inch tungsten 

caps added top and bottom. 

To compare the relative strengthlstiffness of section a. and section b., 

assume values of: 

18 Ni-200- 

Ptu - 200 ksi and E = 26 x lo6 psi 

, Tungsten Ftu - 100 ksi and E = 59 x 106 psi 

6 -6 
The concept is equivalent to the metal/metal hybrids shown in Figures 6-2 and 

6-3. In Figure 6-3 the strip depth would be 0.00 inch. As stated, as you 

move from left to right the Kennametal thickness is increasing, with the 

result that increasing stiffness is accompanied by decreased strength. 

It should be recognized that cladding a metallic alloy on a second alloy will 

require some development work, and that all alloys are not suitable for 

cladding. 

6.5 KENblAHETAL STING 

Kennametal is a sintered tungsten-carbide material. 

elasticity, moderate strength, but a low Cvn impact resistance. 

It has a high modulus of 

In relation to this study, Kennametal's high modulus (94 Hsi) is its primary 

asset, while its low Cvn impact strength (Cvn toughness) is perhaps its 

primary liability. 

Previous study work discounted Kennametal as possible sting material largely 

on its low Cvn value. Since the completion of that studyl, a further review 

of the material, its properties, and vendor advances in its production, was 

made. Recent research indicated that certain grades of the material have 

been used in cryogenic applications as ultra high-stiffness tooling bars. 

Kennametal Grade K9 is a possible candidate sting material; its major proper 

ties are: 1) strength; tensile 146 ksi, compression 590 ksi, 2) coefficient 

of thermal exoansion. 2.0 x in/in/deg F, 3) modulus, 83.5 x lo6 psi. 

In reviewing the above data, it can be seen that the Cvn impact continues to 

be the restricting property of the material. However, Kennametal Incorporated 

indicates that their manufacturing processes are being further developed 

continually and therefore some improvement in this area may be feasible. 

In addition to the limited Cvn impact strength, there are two areas in the 

manufacturing process.es that do not presently meet requirements. Currently, 

lengths of 2 to 3 feet are the maximum length available of the desired 

diameter of 1-1/2 to 2 inches. However, at larger diameters (3 to 4 inches), 

it may be feasible to sinter 4-fOOt length. 

Conceptually, it appears that using Kennametal as a stiffener joined to a 

conventional material is perhaps a more viable alternative to the single 

homogeneous Kennametal concept presented above. This concept has the problem 

of matching stiffnesses to effect an optimum system stiffness that meets the 

design requirements. There is also the problem of joining the Kennametal to 

the parent material. There are three techniques that may be considered: oven 

brazing, adhesive bonding, and mechanical fastening. These will be further 

discussed in Section 6.9. 

6-7 
6.6 IblTERHITTENT STIFFENERS 

The coefficient of thermal expansion (CTE) problem associated with the use of 

dissimilar materials is recognized. The use of intermittent stiffeners of 

high modulus was considered as a possible answer to the problem. As shown in 

Figure 6-4, intermittent parallel stiffeners are used to ensure added 

stiffness, with the breaks staggered so that one stiffener is always working. 

The CTB problem is minimized by using shorter stiffeners. 

tuIIu 

27 1.479-26 

Figure 6-4. Sting (18 Mi-200) with Intermittent Stiffeners (Kennametal) 

In this concept the primary sting is 18 Ni-200, and the stiffeners 

Kennametal. 

age the 18 Ni-200 at 1000F. 

The assembly would be brazed and the final operation would be to 

This concept is feasible and the smaller sections of Kennametal are readily 

available. 

maximum effect. The concept was not pursued further because other concepts 

promise a more significant increase in stiffness. 

The stiffeners would be used on the compressive side only for the 

6.7 HBTAL/COHPOSITE HYBRIDS 

A configuration consisting of a metal core wrapped with layers of high 

strength and high modulus fibers was evaluated to compare its strength and 

stiffness capabilities with those representing the desired improved sting 

configuration. The geometry of this concept is shown in Figure 6-5. 

W 

Ro 

Ri 

Rb 

Ra 

CORE 

HIGH MODULUS COMPOSITE 

HIGH STRENGTH COMPOSITE 

271.479-26 

Figure 6-5. Cross Section Geometry for the Hetal/Composite Hybrid Sting 

6 -8 
This concept offered the following advantages: 

a. The metal core could be used to carry the shear and transverse load acting 

on the sting, allowing the composite materials to be highly oriented in 

the axial direction. 

b. The high strength composite could be used as the outer layer, where it 

would be capable of carrying the higher strains resulting at that location. 

c. The high modulus composite could be placed at an intermediate location, 

where it would be more isolated from high strain levels. 

d. The composite materials are relatively insensitive to fatigue damage, and 

when damage does occur it results in a gradual degradation in strength and 

stiffness properties rather than the sudden, catastrophic failure that is 

associated with thick, high strength metallic materials. 

e. The failure modes of the composite and metallic materials are uncoupled. 

A crack staring in the composite material is unlikely to propagate across 

the boundary into the metal core. 

The disadvantages associated with this concept are: 

a. 

b. 

C. 

d. 

The mismatch in the CTE for the different materials. 

considered for this application would have CTEs of approximately -1.00 x 

in/in/deg F while the metal would have a CTE of approximately 

5.00 x in/in/deg F. 

The composites 

Under the thermal cycling experienced by the sting, the long term 

reliability of the bond between the metal and composite is suspect and 

would have to be established through more detailed analysis than was 

possible during this initial investigation and would have to be 

demonstrated through testing. 

The compressive strength of the high modulus composite material is 

questionable. 

Stiffness can be achieved, but with significant loss of strength. 

These disadvantages are discussed in detail in the following analysis. 

The analysis approach taken to establish the performance of metal/composite 

hybrid configurations was to calculate the strength and stiffness properties 

of a cross section at the aft end of the sting and compare those results with 

the values for the baseline and improved sting configurations calculated 

earlier. 

The critical values were assumed to be the bending stiffness at this section 

represented by the E1 term and the bending strength as determined by the 

maximum bending moment capable of being carried by the section. The bending 

6 -9 
stiffness properties for an axismetric cross section are determined as 

follows: 

E1total = 2 "individual segments 

where 

EIindividual segment = (E) (*I41 (Ri4 - Ri4) 

E = Modulus of material 

R& = Outer radius for a given segment 

Ri = Inner radius for a given segment 

The strength calculations involved determining the maximum bending moment 

capable of being carried by the improved sting configuration and applying this 

load to the hybrid configuration. The ratio of the maximum strain in each 

layer created by this load compared to the maximum allowable strain for each 

layer was then calculated, and the layer with the minimum value for this ratio 

determined the strength of the sting. 

f 01 lows : 

The calculations required are as 

Maximum Bending Moment 

hax improved sting = Ftu 

Ftu = 250,000 psi 

I = (~14) (2.004 - 0.504) = 12.51728 in4 

c = 2.00 in 

&ax improved sting = 1,564,662 in-lb 

Internal Strains in Hybrid Cross Section 

tmax = Mc/EI 

c = Distance from outer fiber of each layer to neutral axis 

M, E1 from above 

These formulas were incorporated into a computerized spreadsheet format that 

allowed for a rapid evaluation of numerous potential variations in material 

properties and layer thicknesses. 

study are summarized in Table 6-1. The effects of the thickness of the 

composite layers was determined by establishing a total thickness of either 

0.50 inch or 1.00 inch for all of the composite material and varying the ratio 

of the thickness of the high strength composite to the high modulus composite 

within that total thickness. The results of these calculations were plotted 

on a chart showinb the relative strength and stiffness of each concept as 

shown in Figure 6-6. 

sting configuration while a value of 1.00 represents the desired 25% 

improvement in strength and stiffness properties. 

The material properties considered for this 

On this chart a value of 0.80 represents the current 

6-10 
1.20 

1 .oo 

0.80 n 

a 

11 0.60 

- 'i 

- 8 

B - 0.40 

0.20 

0.00 

Relative Strength vs Relative Stiffness 

I 

I 

0.60 0.8Q 1 .oo 1.20 ' 

0.00 0.20 0.40 

Relative Stiffness 

( Model Stiffness I Goal Stiffness ) 271.479-27 

Figure 6-6. Comparison of Hybrid Metal/Composite Stings 

with Baseline Model Properties 

6-11 
The most notable result shown in Figure 6-6 is the tradeoff in stiffness and 

strength properties. TO achieve the stiffness values desired, significant 

losses in strength are incurred. One factor that is not accounted for in the 

data shown is the difference between the tensile and compressive strengths of 

the composite materials. 

reliable data on the compressive strengths of the high modulus composites was 

not available. 

generating the results. If the actual compressive strengths were considered, 

the relative strength values for these configurations would be less than half 

of those shown on this chart. When the data became available indicating that 

the compressive performance of these materials was poor, the concept was 

discarded from further consideration. The results are included for the sake 

of completeness and to show general trends in the behavior of this type of 

configuration if more acceptable materials become available. 

When these calculations were initially performed, 

As a result, only the tensile strengths were considered in 

Recognizing the problem of the difference in CTE between the two materials, 

and the reliability of the bond at cryogenic temperatures, it was decided to 

investigate the feasibility of heating the bond line. The objective was to 

maintain the bond line at -100 to OF, as this condition would allow the use of 

a number of high quality adhesives. Controlling the temperature at the bond 

line causes a gradient across the composite material (possibly 0 to -300F), 

and possible thermal stress problems. This should not be a significant 

problem because of the low CTE (-1.00 x in/in/deg F). 

6.8 SUHHARY OF THERMAL ANALYSIS 

A thermal analysis of a cryogenic wind tunnel cylindrical sting has been 

completed. The proposed sting consists of a hollow metal core cylinder 

wrapped with graphite epoxy as shown in Figure 6-7. During a wind tunnel test 

the sting is subjected to operational temperature as low as -300F with 

resulting high heat transfer coefficients, thereby inducing thermal stresses. 

Figure 6-1. Cryogenic Wind Tunnel Advanced Sting Cross Section 

6-12 
The objectives of this analysis were to: 

a. Determine the worst case temperature gradients. 

use to perform radial and axial thermal-stress analyses. 

These gradients will be 

b. Determine the heater sizing requirements to keep the metal core at 0 or 

-100F. 

Analysis results show that: 

a. The temperature of the epoxy will drop quickly as assumed at the beginning 

with a maximum temperature between the metal and the epoxy of 130F. 

metal temperature then decreases until the whole sting reaches the 

equilibrium temperature of -300F after about 15 minutes. 

The 

b. To maintain the core temperature at -100F a heater power of 6632 Btu/hour 

(1944 watts) is required (no safety factor). (26 watts/sq in)* 

c. To maintain the core at OF the heater power must increase by 70% to 11,290 

Btu/hour (3310 watts) (no safety factor). (44 wattslsq in)* 

d. The thermal conductivity of the epoxy is available only at two or three 

temperatures in the range of interest. Since the heater power is 

proportional to the thermal conductivity, it is recommended that a factor 

of safety of 2 be employed to size the heater; doubling the above numbers. 

e. It is important to assure good contact between the heater and the sting to 

avoid burning the heater. 

6.8.1 DISCUSSION. Two analytical models were employed. A transient model 

provided the temperature distribution and gradients versus time. A 

steady-state model was used to size the heater required to keep the metallic 

core temperature at a fixed value of -100F or OF. In both models it was 

conservatively assumed that the surface temperature of the epoxy would equal 

the nitrogen gas temperature of -300F. 

6.8.1.1 Transient Analysis. The sting thermal model shown in Figure 6-8 

consists of 10 metal nodes and 10 epoxy nodes. 

surface node 3001, which is kept at a fixed temperature of -300F. The 

computer program QMAG** was used to perform this analysis. 

Node 20 is connected to 

*Includes a safety factor of 2. 

**The input data file for the sting QMAG Model is the DECK called STIMG of the 

program library ZRECI in SD9BAI catalog. 

6-13 
MODEL 

NODE NUMBERS 

300 1 

Y/ 

V 271.479-29 

Figure 6-8. Cryogenic Wind Tunnel Advanced Sting 

Thermal Conduction Model Segment 

6-14 
Analysis results plotted in Figure 6-9 show node temperature versus distance 

from the center of the sting as (shown as node number) and time. Figure 6-10 

shows the average temperature of the epoxy alone, the metal average 

temperature, and the combined average temperature. Notice that the average 

temperature of each material is weighted by its heat capacity, i.e., 

where mi, Cpi, and Ti are the mass, specific heat, and temperature of 

node i of specific material. Figure 6-10 also shows the difference between 

the graphite and metal average temperatures. 

reaches a maximum value of 130F after 30 seconds. 

This temperature difference 

550.0 

500.0 

450.0 a 

wi 

a 

3 400.0 

Id 

z 

350.0 

I300.0 

250.0 

ZOO.[ 

150.0 

TIME = 10SECONDS 7 

I I I I 

NODE NUMBER 

I 

1.0 . 4.0 8.0 , 12.0 16.0 2 .O 

0.5 1 .o 1.5 

RADIAL DISTANCE FROM CENTER (INCHES) 271.479-30 

Figure 6-9. Cryogenic Wind Tunnel Advanced Sting Temperature 

Distribution Versus Node Number and Time 

6.8.1.2 Heater Sizing Steady-State Model. The heat input required to 

maintain the metal core at a fixed temperature was determined using a computer 

steady-state model and an analytical solution. Both approaches were used with 

good agreement between the two results. 

To maintain the surface between the metal core and the graphite epoxy at a 

fixed temperature Th, the heater must provide the conduction heat flow 

between Th and the colder surface temperature Tc. 

6-15 
wi 

a 

a 

3 

I- 2 

w 

p. 

w 

IB 

400.0 

300.0 

6oo.o 

200.0 

I 

- STING AVERAGE TEMPERATURE 

- 

- 

EPOXY AVERAGE TEMPERATURE 

I TMETAL - TEPOXY I 

100.0 200.0 300.0 400.0 500.0 

TIME, SEC 

271 A79 8-31 

Figure 6-10. Cryogenic Wind Tunnel Advanced Sting Temperatures Versus Time 

From Figure 6-11: 

Q = -2srllk(T) dT/dr (1) 

where Q is the heat conduction, r is the radius, ll is the sting length, and 

k is the thermal conductivity of the epoxy. 

From Eq 1 

r2 TC 

Q I dr/r = -2d k(T) dT 

=1 Th 

(2) 

Integrating Eq 2 

Th 

Q = 2sll I k(T) dT/ln (r2/rl) (3) 

TC 

The thermal conductivity integral for the epoxy between -300 and -100F is 214 

Btu/hr-ft, giving a heater requirement of 

Q = 2s x 2 x 214/ln (1.5) = 6632 Btu/hr 

6-16 
/ 

/ 

/ 

/ 

METAL 

‘1 ‘2 271.479-32 

Figure 6-11. Cryogenic Wind Tunnel Advanced Sting Analytical Solution Geometry 

A steady-state thermal analysis was also accomplished employing the QKAG 

program and gave a heater requirement of 6585 Btulhr, which is less that 1% 

apart from the analytical result. 

heater power of 11,290 Btu/hr. 

To keep the metal core at OF requires a 

Note that the heater load is proportional to the thermal conductivity integral 

of the graphite epoxy. Since the thermal conductivity is available only at 

two or three points in the range of interest, the integral was not expected to 

be of high accuracy. A factor of safety of 2 is suggested in the design of 

the heater. It is also very important to assure good thermal contact between 

the heater and the sfing to avoid burning the heater. Also note that these 

results are one-dimensional in nature and do not accommodate heat losses to 

the model being tested or to the sting support structure. If such losses 

exist, the result would be increased heater power requirement. 

Assuming that the heater covers 50% of the surface to be heated and taking the 

case of controlling the surface at -100F, the heater would be sized on the 

basis of 52 watts/sq in, and would be 0.30 inch thick. It would be wound in a 

spiral around the inside of the graphite epoxy. 

6.8.2 HETAL/COHPOSITE HYBRIDS. The final configuration considered consisted 

of a rectangular cross section reinforced with high strength and high modulus 

composite materials on one side only as shown in Figure 6-12. By selectively 

reinforcing one side, the sting could be oriented so that the composite 

materials would experience primarily tensile loads and only light compressive 

loads. This would solve the problem with the low compressive strengths 

present in the high modulus composites. 

6-17 
BASE METAL 

HIGH MODULUS COMPOSITE 

0 HIGH STRENGTH COMPOSITE 

271.479-33 

Figure 6-12. Cross Section Geometry for Metal/Hetal Hybrid Sting 

Analysis approach similar to that discussed previously was used and the 

results are shown in Figure 6-13. The variables considered were the total 

thickness of the composite caps and the ratio of the thickness of the high 

modulus composite to that of the high strength composite.. 

The results are similar to that of the other hybrid configurations in that 

increased stiffness is accompanied by reduced strength. 

with this configuration is the possibility of secondary failure modes due to 

the mismatch between the CTE of the composite and the CTE of the metal. By 

selectively reinforcing one side, temperature changes incurred during the 

curing of the composites would create internal stresses in the sting that 

would tend to create warpage in the finished product. This would become even 

more severe in the transition to the cryogenic temperatures encountered in the 

NTF. The effects of these temperature changes would have to be more fully 

analyzed than was possible during this limited study, and the long term 

reliability of the bond would need to be established through testing. 

An additional problem 

A thermal analysis was not done for this configuration, but one could assume 

similar heater requirements as for the circular sting. This would have to be 

confirmed with a more detailed analysis. 

6.9 FLOATING STIFFENERS 

As briefly discussed in Section 6.5, the use of Kennametal stiffeners joined 

to a conventional (18 Ni-200 or wP35N) sting, perhaps presents a viable 

approach to reducing sting support deflection. 

Also as stated, the joining method is quite critical to the success of the 

system. Kennametal, being a sintered tungsten-carbide material, is somewhat 

limited in processes suitable for successfully joining it to other materials. 

Oven brazing is one process that has been used successfully. 

application the brazing temperature (approximately 1200F) is too high in 

relation to the normal aging temperature 900F of the 18 Ni-200 steel. 

Secondly, adhesive bonding may be considered and bonding fillers such as 

American Cyanimide's FH-1000 or equivalent film have been used at temperatures 

as low as -300F. Adhesive bonding, however, may be strength limited in the 

However, in this 

6-18 
Relative Strength vs Relative Stiffness 

1.20 

1 .oo 

0.80 

0.60 

0.40 

0.20 

0.00 

0.40 0.60 0.80 1 .oo 1 .z 0.00 0.20 

Relative Stiffness 

(Model Stiffness I Goal Stiffness ) 

I 

271.479-34 

Figure 6-13. Comparison of Hybrid Hetal/Composite Stings 

with Baseline Hodel Properties 

6-19 
shear directions of the bond system. 

differential CTEs of the materials. 

The limitation is due primarily to the 

1-25 FEET-1 

Mechanical fastening also offers an approach to joining the materials 

considered. In this application, a close sliding fit of the mating diameters 

is required at the forward end of the sting. At the aft end, a tapered joint 

secured by bolts may provide the "fixity" between the mating parts. 

sting is deflected and/or subjected to temperature, the parts will have 

"relative freedom" to move in the axial direction. 

As the 

Two design concepts using sliding stiffeners have been considered. 

employs a concentric inner rod made of Kennametal. 

Mi-200 or equivalent steel as shown in Figure 6-14. 

The first 

The outer member is of 18 

FLOATING STIFFENER CONCEPT 

2 112 - 3 DIA. ,FREE SLIDING ,LOCKED TAPER JOINT 

Engineering analyses will be required to optimized the stiffness-to-strength 

ratio of the system, while minimizing temperature effects due to CTE 

differentials. 

The concept employs conventional manufacturing and materials processes that 

should facilitate the production of hardware. 

The second concept considered locates the stiffer Kennametal sliding member 

eccentrically to the centerline of the system. The Kennametal is located on 

the compressive side due to its high compressive strength. 

designed into the system will minimize the CTE problem. 

The sliding motion 

6-20 
To investigate the concept, a test specimen was fabricated using existing 

materials. A beam of rectangular cross section was grooved on its compressive 

side along the upper centerline, as shown in Figure 6-15. Two rods (one steel 

and one Kennametal) were fitted to the groove to provide "fixity" at one end, 

while sliding along its length. 

ARE INCHES 271 A79-36 

Figure 6-15. Proof of Concept, Floating Stiffener 

Deflection tests were conducted in the following sequence: 

1. Beam without a stiffener 

2. Beam with a steel stiffener 

3. Beam with a Kennametal stiffener 

The results are show in Figure 6-16. The Kennametal stiffener shows a 

definite improvement in the reduction of deflection for a given load, thereby 

indicating an improvement in the stiffness-to-strength ratio. Further 

development in this area is required to fully substantiate the viability of 

this concept. 

6-21 
U tOAD (pounds) 

271.479-37 

6-16. Experiment - Floating Stiffener - Deflection Versus Load 
SECTION 7 

CANDIDATES FOR PROOF-OF-CONCEPT TESTS 

In this study the use of advanced materials for high performance stings was 

investigated. In doing so three separate areas were reviewed: 

Conventional Metals 

Advanced Composites 

0 Hybrid Configurations 

The objective of increasing the values of the ultimate tensile strength, and 

the modulus, E, of 18 Eli-200 by 25%, while maintaining toughness values, is 

not an easy task. An innovative approach is required. 

For conventional metals, the research was directed toward the multiphase 

superalloys. Advanced composites, while promising as fibers, have limitations 

in laminate form particularly when a combination of high strength and high 

stiffness is required. Hybrids look promising, but the use of dissimilar 

materials, and the subsequent thermal stress problems due to differences in 

the coefficient of expansion, raises question with respect to the integrity of 

the design. 

This study has identified a number of concepts that appear promising, yet are 

questionable because **it hasn't been done before.** To achieve our objective, 

it becomes necessary to select the candidates with the best chance of success, 

and to further develop those concepts by building hardware, and to subject 

each design to proof-of-concept tests under environmental condition. 

The recommended configurations are: 

1. HP35N - laserweld/diffusion weld 

2. 

3. 18 Ni-200 with a Kennametal floating stiffener 

18 Mi-200 with a high modulus composite strip on the tension side 

In configurations 1 and 2, the proposed test article is a constant 

cross-section 3 inches by 2 inches wide and 2 feet long. Configuration 3 is 

2-1/2 inches in diameter by 2 feet long with a Kennametal insert. 

7-1 
SECTION 8 

COMCLUSIONS 

0 There is no simple solution. 

will require further development of the manufacturing process. 

Each of the concepts described in this report 

0 Proof-of-concept tests are necessary, and must be done under cryogenic 

conditions. 

0 Advanced composites, particularly the ultra-high modulus graphite laminates 

are unpredictable when loaded in compression. 

Hybrid concepts appear to be promising if the differences in CTE can be 

overcome. Some past tests have shown that CTE problems, while expected, 

did not occur. Proof-of-concept tests will verify this. 

0 Vendor/expert response to questions, usually are: "It's impossible," or 

"It's no problem." The real answer is in between. 

0 Some superalloys are candidates but are very limited in available sizes; 

building them into the desired shapedsizes will require fabrication 

process development. 

if there is sufficient demand. 

In the long term, the mill will produce larger sizes, 

0 In hybrid concepts, the adhesives available are suspect at cryogenic 

temperatures. It is possible to heat the bond line; however, this could 

introduce temperature to the balance and create an undesirable gradient. 

The superalloys are cold worked to obtain a high ultimate tensile stress, 

and modulus, E. If they subsequently are subjected to temperatures in 

excess of 1000F, they lose those properties. 

The cost of superalloys such as W35N is high - $50 to $100/lb. 

The high performance sting would be approximately 5 to 6 feet long, and 

adapted into an existing sting. The taper joint between the 

balance/conventional sting and the high performance sting must also be 

evaluated. 

A fail-safe feature in the sting is desirable. 

8-1 
SECTION 9 

REFERENCES 

1. S. A. Griffin, D. S. Madsen, and A. A. McClain, Design Study of Test 

Models of Maneuvering Aircraft Configurations for the National 

Transonic Facility, NASA C ontract Report 3uil/ , August 1984. 

2. Wind Tunnel Model Systems Cri teri a, LHB 1710.15, NASA Langl ey Research 

Center, August 1986. 

3. Technical Report - MP35N, Latrobe Steel Co., Latrobe, PA 15650, Report 

No. 56081, September 1983. 

4. R. L. Tobler, Materials for Cryogenic Wind Tunnel Testing, NBSIR 

79-1624, May 1-980. 

5. K. B. Meyer, Fabrication of a High Strength Tube by Spiral Winding, GDC-MRR-80-004, December 1980. 

6. A3.0-80, American Welding Society, August 1979. 

7. Advanced Composite Systems, Union Carbide Corporation Data Sheet - ACS, 

Chicago, IL 60606, 1986. 

8. D. L. McDaniels, Analysis of Stress-Strain, Fracture, and Ductility 

Behavior of Aluminum Matrix Composites Containing Discontinuous Si1 icon 

Carbi de Reinforcement, NASA L ewi s Research Center, C1 eve1 and, OH, NASA 

TM83610, March 1984. 

9. P. J. Mazzei, G. Vandrmen. and M. J. Hakins. Powder Fabrication of 

Fi ber-Rei nforced Superall oy Turbi ne 61 ades , ~ Wmise Canada Limited, 

Turbine and Generator Division, Hamil ton, Ontario, Canada, 

November, 1976. 

10. D. Webster, "Properties and Microstructure of Metal Matrix Composites ," 

Advances in Composite Materials, Proceedings of the Third International 

'Conterence of Composite Mater31 s , Paris, France, Vol . 2, Pergamon 

Press, Oxford, 1980, pp. 1165-1176, August, 1980. 

11. J. E. Smugersty and R. M. Gesman, "Hot Isostatic Pressing of Maraging 

Steels ,'I National Powder Metal1 urgy Conference 7th-8th, pp. 69-82, 

1978-1979 Proceedings. 

9- 1 
Standard Bibliographic Page 

NASA CR- 1782 14 

I. Title and Subtitle 

Design Study of Advanced Model Support Systems for the 

National Transonic Facil ity 

L. Report No. 12. Government Accession No. 13. Recipient's Catalog No. 

5. Report Date 

J~~~~~~ 1987 

6. Performing Organization Code 

T. Author(s) 

3. Performing Organization Name and Address 

General Dynamics Convai r Di vi sion 

P. 0. Box 85337 

San Diego, CA 92138 

12. Sponsoring Agency Name and Address 

Was hi ng ton, D. C . 20546 

National Aeronautics and Space Admi ni strati on 

8. Performing Organization Report NO. 

10. Work Unit No. 

11. Contract or Grant No. 

, P.0- L-99725B 

13. Type of Report and Period Covered 

Contractor Report 

14. Sponsoring Agency Code - 1 505-61-01-07 

19. Security Classif. of this report) 

Uncl assi f i e 6 

~~ ~ 

15. Supplementary Notes 

Langley Technical Monitor: Dr. C. P. Young, Jr. 

Use of trademarks or names of manufacturers in this report does not constitute 

an official endorsement of such products or manufacturers, either expressed or 

implied, by the National Aeronautics and Space Administration. 

16. AbstraFt 

It has long been recognized that the sting (or support system) is a very critical part of the model system. The designer is frequently faced with 

the tradeoff of minimizing sting size, thereby compromising facility and 

model safety, against a larger sting and the subsequent problems of sting 

interference effects. In the NASA Langley Research Center National 

Transonic Facility (NTF), this problem is accentuated by the severe 

environment of high pressure/low temperature, designed into the f a c i l i t y t o 

provide the desired high Reynolds number. Compromises in the configuration 

geometry and/or limiting the test envelope are therefore contrary to the 

purposes and goals of the NTF and are unacceptable, hence the need for this 

study of advanced model support systems. 

of an investigation aimed at improvements of 25 percent in both strength and 

Young's modulus of .elasticity as compared to high strength cryogenically 

acceptable steels currently being used. 

of materials were studied along with different design approaches. Design 

concepts were developed which included conventional material stings, 

advanced composites, and hybrid configurations. 

indicate that significant improvements in both strength and stiffness are 

possible and various promising design concepts are presented. 

configurations are recommended based on best chance of success and proposed 

proof-of-concept tests under environmental conditions. 

This paper documents the results 

Various materials or combinations 

Results of the study 

Candidate 

20. Security Classif.(of this page) 21. No. of Pages 22. Price 

Unclassified 68 A04 

17. Key Words (Suggested by Authors(s)) 

Wind Tunnel Model Support 

Cryogenic Tunnel s 

Cryogenic Materials 

18. Distribution Statement 

Unclassified - Unlimited 

Subject Category 09 

For sale by the National Technical Information Service, Springfield, Virginia 22161 

. 

* 

.