NISTIR 7627

Development of Soft Armor

Conditioning Protocols for NIJ

Standard–0101.06: Analytical

Results

Amanda L. Forster, Kirk D. Rice, Michael A. Riley,

Guillaume H. R. Messin, Sylvain Petit, Cyril Clerici, Marie-Cecile

Vigoroux, Pierre Pintus, Gale Holmes, and Joannie Chin

NISTIR 7627

Development of Soft Armor

Conditioning Protocols for NIJ

Standard–0101.06: Analytical

Results

Amanda L. Forster, Guillaume H. R. Messin, Pierre Pintus,

Michael A. Riley, and Kirk D. Rice

Office of Law Enforcement Standards

Electronics and Electrical Engineering Laboratory

Gale A. Holmes

Polymers Division

Materials Science and Engineering Laboratory

Joannie Chin, Sylvain Petit, Cyril Clerici, Marie-Cecile Vigoroux

Materials and Construction Research Division

Building and Fire Research Laboratory

September 24, 2009

U.S. Department of Commerce

Gary Locke, Secretary

National Institute of Standards and Technology

Patrick D. Gallagher, Director

Abstract

This publication details the four major phases of analytical development

work, coupled with several additional side studies, undertaken by the Office

of Law Enforcement Standards in writing the Flexible Armor Conditioning

Protocol in NIJ Standard–0101.06. This protocol partially fulfills a requirement to develop a revised performance standard for body armor to address a

number of concerns, one of which was the ability of the armor to withstand

environmental and wear conditions that an armor might see over its lifetime. This document details how the protocol was shortened from 9 weeks

in the first phase of development to 10 days, as it appears in the current

version of the standard. All major classes of ballistic materials were tested

in the protocol development. The conditions selected are found to be quite

detrimental to armors of a design that previously had problems in the field,

but are not detrimental to armors of known good design. It is important

to note that the protocol does not represent an exact period of time in the

field, but efforts to correlate the protocol to a period of time in the field are

the subject of future research.

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Standard–0101.06: Analytical Results

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vi
Acknowledgments

Financial support for this research effort was provided by the National Institute of Justice under Interagency Agreement Number 2003-IJ-R-029. Their

support is gratefully acknowledged.

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Standard–0101.06: Analytical Results

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Disclaimer

Certain commercial equipment, instruments, or materials are identified in

this paper in order to specify the experimental procedure adequately. Such

identification is not intended to imply recommendation or endorsement by

the National Institute of Standards and Technology, nor is it intended to

imply that the materials or equipment identified are necessarily the best

available for this purpose.

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Standard–0101.06: Analytical Results

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Contents

1 Introduction 1

1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.2 Theoretical Approach . . . . . . . . . . . . . . . . . . . . . . 3

1.2.1 Definition of Wear Environment . . . . . . . . . . . . 3

1.2.2 Selection of Temperature . . . . . . . . . . . . . . . . 5

1.2.3 Selection of Relative Humidity . . . . . . . . . . . . . 6

1.2.4 Simulation of Mechanical Wear . . . . . . . . . . . . . 8

2 Experimental 11

2.1 Extracted Yarn Tensile Testing . . . . . . . . . . . . . . . . . 11

2.2 Fourier Transform Infrared Analysis . . . . . . . . . . . . . . 12

2.3 Moisture Sorption Analysis . . . . . . . . . . . . . . . . . . . 12

2.4 Dynamic Mechanical Thermal Analysis . . . . . . . . . . . . . 12

3 Conditioning Protocol Development 15

3.1 Phase I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.1.1 Sample Description . . . . . . . . . . . . . . . . . . . . 15

3.1.2 Experimental Conditions . . . . . . . . . . . . . . . . 16

3.1.3 Analytical Results . . . . . . . . . . . . . . . . . . . . 17

3.2 Phase I Summary . . . . . . . . . . . . . . . . . . . . . . . . . 23

3.3 Phase II . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

3.3.1 Sample Description . . . . . . . . . . . . . . . . . . . . 24

3.3.2 Experimental Conditions . . . . . . . . . . . . . . . . 24

3.3.3 Analytical Results . . . . . . . . . . . . . . . . . . . . 25

3.3.4 Ballistic Results from Phase I and Phase II Testing . . 26

3.4 Phase II Summary . . . . . . . . . . . . . . . . . . . . . . . . 26

3.5 Phase III . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

3.5.1 Experimental Conditions . . . . . . . . . . . . . . . . 30

3.5.2 Sample Description . . . . . . . . . . . . . . . . . . . . 30

3.5.3 Analytical Results . . . . . . . . . . . . . . . . . . . . 31

3.5.4 Ballistic Results from Phase III Testing . . . . . . . . 36

3.6 Phase III Summary . . . . . . . . . . . . . . . . . . . . . . . . 36

3.7 Phase IV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

3.7.1 Sample Description . . . . . . . . . . . . . . . . . . . . 36

3.7.2 Analytical Results . . . . . . . . . . . . . . . . . . . . 37

3.8 Important Observations From Other Studies . . . . . . . . . . 38

3.9 Phase IV Summary . . . . . . . . . . . . . . . . . . . . . . . . 39

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Standard–0101.06: Analytical Results

4 Conclusions and Future Work 41

5 References 43

xii
List of Tables

1.1 “Rule of Thumb” for Kinetics of Chemical Reactions. . . . . 4

3.1 Rank Ordering of PPTA Infrared Bands; 1=greatest change;

4=least change. . . . . . . . . . . . . . . . . . . . . . . . . . . 23

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xiv
List of Figures

1.1 Dynamic Temperature Ramp Results for Common Ballistic

Fibers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.2 Representative Vehicle Temperature and Relative Humidity

Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.3 Moisture Sorption Data for PPTA (cyclic conditions). . . . . 7

1.4 Moisture Sorption Data for PBO (cyclic conditions). . . . . . 8

1.5 Moisture Sorption Data for PBO (constant conditions). . . . 9

1.6 Moisture Sorption Data for PPTA (constant conditions). . . . 10

3.1 Phase I Protocol Cycle. . . . . . . . . . . . . . . . . . . . . . 16

3.2 Phase I Breaking Strength Retention for PBO. . . . . . . . . 18

3.3 Phase I Breaking Strength Retention for PPTA. . . . . . . . 19

3.4 Phase I FTIR Difference Spectra for PBO. . . . . . . . . . . . 20

3.5 Phase I FTIR Difference Spectra for PPTA (full scale). . . . 21

3.6 Phase I FTIR Difference Spectra for PPTA (expanded scale). 22

3.7 Phase II Protocol Cycle. . . . . . . . . . . . . . . . . . . . . . 25

3.8 Phase II Breaking Strength Retention for PPTA and PBO

(all conditions). . . . . . . . . . . . . . . . . . . . . . . . . . . 27

3.9 Phase II Breaking Strength Retention for PPTA and PBO (T

& RH only). . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

3.10 Phase II Breaking Strength Retention for PPTA and PBO

(tumbling only). . . . . . . . . . . . . . . . . . . . . . . . . . 29

3.11 Phase III Breaking Strength Retention for PPTA and PBO

(all conditions). . . . . . . . . . . . . . . . . . . . . . . . . . . 32

3.12 Phase III Breaking Strength Retention for PPTA and PBO

(T & RH only). . . . . . . . . . . . . . . . . . . . . . . . . . . 33

3.13 Phase III Breaking Strength Retention for PPTA and PBO

(tumbling only). . . . . . . . . . . . . . . . . . . . . . . . . . 34

3.14 Phase III Reduction in Key Infrared Bands. . . . . . . . . . . 35

3.15 Phase IV Breaking Strength Retention for PPTA and PBO

(all conditions). . . . . . . . . . . . . . . . . . . . . . . . . . . 37

3.16 Analysis of Potential for Condensation at 70 ◦C and 90 %

Relative Humidity. . . . . . . . . . . . . . . . . . . . . . . . . 39

3.17 Analysis of Potential for Condensation at 65 ◦C and 80 %

Relative Humidity. . . . . . . . . . . . . . . . . . . . . . . . . 40

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1 Introduction

In response to the 2003 US Attorney General’s initiative to examine failures

of soft body armor containing the material poly(p-phenylene-2,6-benzobisoxazole), or PBO, the National Institute of Justice (NIJ) determined that

a significant revision of the performance standard for ballistic body armor

was required. One area that had not previously been examined was the

long term, or field performance of body armor. Historically, the National

Institute of Standards and Technology’s (NIST) Office of Law Enforcement

Standards (OLES) has been NIJ’s technical partner in the development of

performance standards for body armor. OLES and NIST had also worked

closely with NIJ to examine the issues with PBO in the field and published several papers [1, 2, 3] and reports documenting the degradation of

PBO fiber with exposure to elevated conditions of moisture and temperature. Once the issues with PBO fibers became clear, NIJ issued “NIJ Body

Armor Standard Advisory Notice # 01-2005” to inform the community of

body armor end users about the degradation issues with PBO. Concurrently,

NIJ issued the “NIJ 2005 Interim Requirements for Bullet-Resistant Body

Armor,” requiring manufacturers to state that their armor did not contain

any material listed on an NIJ Standard Advisory Notice (e.g., PBO), and

requiring that the armor “will maintain ballistic performance (consistent

with its originally declared threat level) over its declared warranty period.”

Subsequently, NIJ turned to OLES to develop a revised performance standard for body armor to address a number of concerns, one of which was the

ability of the armor to withstand environmental and wear conditions that an

armor might see over its lifetime. This document describes the development

of a soft armor conditioning protocol to address this requirement.

Previous work published at NIST documented a detailed examination of

the failure of an officer’s PBO armor in the field [4]. Two key observations

from this study were that yarns extracted from the officer’s armor showed

a 32 % reduction in tensile strength when compared with yarns extracted

from new armor, and that infrared spectroscopy analysis of yarns from the

officer’s vest showed evidence of degradation in the molecular structure of

PBO. Further studies at NIST examined degradation of PBO armors under controlled laboratory conditions. A crucial finding from these studies

was that PBO fibers degrade when exposed to elevated moisture and temperature, but are stable when exposed to elevated temperature in a dry

1
Development of Soft Armor Conditioning Protocols for NIJ

Standard–0101.06: Analytical Results

environment [5]. Studies [6, 7] also showed that PBO yarns were vulnerable to degradation by mechanical wear, showing classical fatigue behavior.

Findings from all of this fundamental research formed the basis of the theory

behind the soft armor conditioning protocol.

The primary goals of the soft armor conditioning protocol for use in NIJ

Standard–0101.06 are to develop a test protocol that would have caught the

problems with PBO-based soft body armor before they appeared in the field

and to ensure that the protocol will neither under- nor over- expose armor

with respect to the environment that armor is expected to encounter during

its lifetime. It quickly became clear that relating this protocol to an exact

period of time in the field would be impossible. Body armor is made up

of many different materials, all of which show different rates of degradation with exposure to a given set of conditions. To date, very little work

has been published on artificial or accelerated aging of fibers used in body

armor. Work is currently underway at NIST to develop the relationship

between exposure at conditions of low temperature to conditions at high

temperature. Currently, including the aspect of mechanical wear in this relationship still remains a challenge. Because of this ongoing work and the

challenges involved in developing correlations between field and laboratory

aging, this protocol will not predict the service life of body armor. Currently, the soft armor conditioning protocol in NIJ Standard–0101.06 can

be considered a “challenge test” for armor that provides an indication as to

whether or not the armor will withstand use in the field. This represents a

major change from previous versions of the ballistic body armor standard,

which gave no consideration to long term performance.

1.1 Background

Historically, there have been several efforts to assign an expected service life

to body armor. Two studies are typically cited, one undertaken by DuPont

in the mid-1980s [8] and one undertaken by NIST (then the National Bureau

of Standards, NBS) published in 1986 [9]. The DuPont study indicated

that a reduction in ballistic performance as measured by ballistic limit, or

V50 testing, was seen after 3 to 5 years of use, but that a reduction in

performance was better correlated to heavy use than to the age of the poly(pphenylene terephthalamide), or PPTA, armor. As a result of this study,

DuPont recommended that armor be replaced after 5 years, which caused

some controversy in the law enforcement community [8, 10, 11, 12, 13, 14].

The NBS study examined 24 sets of 10 year old armor of the same 100

% woven PPTA design, manufactured at the same time and distributed to

various law enforcement agencies. The sample set of armors was distributed

across various climates and saw various levels of wear, encompassing a range

from never issued to heavily worn. The author concluded that armor stored

under warehouse conditions maintained its full ballistic performance for at

least 10 years, and perhaps indefinitely. The author also concluded that

light to moderate wear may improve ballistic performance, and that heavy

wear might slightly reduce ballistic performance. It is important to note that

2
1. Introduction

the limited sample size of this study makes it difficult to draw meaningful

conclusions about the long term performance of armor in the field [9].

In more recent years, several body armor manufacturers have undertaken

programs to examine the performance of fielded PBO armor by retrieving

vests from the field, assigning a wear rating to the vests, and then conducting

ballistic limit testing on the vests. Two reports, one from Armor Holdings

Product Division [15] and one from DHB Armor Group [16] were both published in 2004. Both reports concluded that there was some loss in ballistic

performance with both age and wear of the armor, although the methods

used to report the data make it difficult to draw meaningful conclusions

about the results. Both armor manufacturers indicated that they felt that

used armor still had an adequate margin of safety. A study was also undertaken between 2001 and 2005 by the Technical Support Working Group

(TSWG) to examine the effect of environmental conditions on armor performance by exposing shoot packs of various ballistic materials to elevated

conditions of moisture and temperature. TSWG operates as a program element under the Department of Defense Combating Terrorism Technical

Support Office (CTTSO) and they serve as “the national inter-agency research and development program for combating terrorism requirements at

home and abroad.” Unfortunately, due to problems with controlling the

exposure conditions used in this study, the results were inconclusive. After

reviewing the limited body of work that had been conducted on armor service life prediction, it was determined that there was little available to draw

on for the development of the soft armor conditioning protocol.

1.2 Theoretical Approach

1.2.1 Definition of Wear Environment

In an effort to better tailor a revision of NIJ Standard–0101.04 to the needs

of the end user community, NIJ issued a Request for Information (RFI)

to the armor community, including manufacturers and end users, in the

fall of 2005. The RFI stated that “. . . NIJ is interested, though not exclusively, in operational requirements and testing methodologies that address:

Validation of used armor performance; Non-destructive testing/monitoring

methods for used armor to ensure ongoing performance; Improved requirements and testing protocols for new armor (e.g., blunt trauma, multi-shot

impacts, contact shots); Numbers and sizes of samples to be tested; Longterm performance of armor; Artificial armor aging protocols to replicate

field use; Quality control and conformity assessments. . . ” In reviewing the

responses to this request, several respondents were contacted. One of these,

Mine Safety Appliance (MSA), had a long history in the production and service life prediction of other types of safety equipment. In January 2006, a

meeting between MSA and NIST was held to discuss armor aging, in which

several approaches were discussed. In this discussion, it was suggested that

armor should be robust enough to withstand conditions typically seen during wear and those seen during transit. Based on the previously published

guidelines for armor replacement, a typical service life was defined as 5 years,

3
Development of Soft Armor Conditioning Protocols for NIJ

Standard–0101.06: Analytical Results

Temperature Exposure

◦C ◦F h weeks

35 95 10,000 59.5

45 113 5000 29.8

55 131 2500 14.8

65 149 1250 7.44

75 167 625 3.72

Table 1.1: “Rule of Thumb” for Kinetics of Chemical Reactions.

and a typical wear environment was defined as near body temperature and

humidities near complete saturation (due to perspiration of the wearer). If

one defines a typical work schedule as 8 h per day, 5 d per week, 50 weeks

per year, this works out to 2000 h of wear per year. If one then expects the

typical lifetime of a vest to be 5 years, then that corresponds to 10,000 h of

service at the wear conditions. These simple assumptions provided a starting point for the development of the protocol. To maintain the independence

of NIST and NIJ, no further input was sought from MSA after these initial

meetings in the protocol development [17].

A “rule of thumb” in chemical kinetics [18] often applied to accelerated

aging of materials is for every 10 ◦C increase in temperature, one can expect

a doubling in the rate of reaction. Application of this guideline to the defined

wear temperature of 35 ◦C, results in 10,000 h of aging in approximately

8 weeks at 65 ◦C, as shown in Table 1.1. It is important to note that

this “rule of thumb” applies to certain reactions that occur in solution and

does not directly translate to reactions of degradation in the solid state.

Additionally, body armor is made up of many different types of materials,

all of which can be assumed to degrade at different rates. So, while the

temperature 65 ◦C was chosen to accelerate degradation in the armor based

on assumptions of a 5 year service life, it definitely cannot be said to predict

armor service life because we do not know the exact relationship between

temperature and degradation rate for ballistic materials.

When attempting to apply the “Rule of Thumb” to accelerated aging

kinetics of materials, it is important to keep in mind that elevated temperatures may induce new mechanisms of degradation, rather than accelerating

mechanisms of lower-temperature degradation. For example, if temperature

is increased to the point that a material would melt or burn, different chemical reactions will occur, and the results of the accelerated study will not be

meaningful. To avoid this potential problem, dynamic mechanical thermal

analysis (DMTA) was performed on representative fiber samples from the

major material classes of body armor prior to temperature selection. A dynamic temperature ramp at a constant frequency of 1 Hz was performed on

fiber samples of PPTA, PBO, and ultrahigh molecular weight polyethylene

(UHMWPE). These results are presented in Figure 1.1. This analysis revealed that temperatures exceeding 80 ◦C might be too high due to changes

4
1. Introduction

Temperature (°C)

40 60 80 100

E' (Pa)

1e+8

1e+9

1e+10

1e+11

1e+12

PBO

PPTA 

UHMWPE 

Figure 1.1: Dynamic Temperature Ramp Results for Common Ballistic

Fibers.

in the molecular structure of the UHMWPE fibers above this temperature,

however the PPTA and PBO fibers remain essentially unchanged in the temperature range studied. In the UHMWPE system, 80 ◦C is in the range of

the α

′

-relaxation temperature, which is the temperature at which molecular

motion within the polymer begins to increase, resulting in a decrease in the

modulus of the polymer [19]. DSM Dyneema, a manufacturer of UHMWPE

fiber for ballistic applications, published results of an artificial aging study in

2007 indicating that an Arrhenius relationship existed for UHMWPE fibers

between 35 ◦C (the same as our reference base temperature) and 65 ◦C [20].

Therefore, it was determined that limiting our experiments to temperatures

below 70 ◦C would allow us to avoid introducing new mechanisms of degradation in the fibers during our studies.

1.2.2 Selection of Temperature

Questions also arose regarding the exposure of armor to a temperature of

65 ◦C—(e.g., is this condition unreasonable in the environment in which

body armor will be used?). Anecdotal evidence that officers commonly

store armor in the trunks of their cars was frequently brought up during

discussions of the armor wear environment. Additionally, armor is typically delivered across the country in trucks. However, the temperature and

relative humidity inside a vehicle can vary widely depending on season, geographical region of the country, and location inside the vehicle. In order

5
Development of Soft Armor Conditioning Protocols for NIJ

Standard–0101.06: Analytical Results

max temperature 67 °C

Time (d)

0 5 10 15 20

Temperature (°C)

10

20

30

40

50

60

70

80

Relative Humidity (%)

0

20

40

60

80

100

Temperature

Relative Humidity

Figure 1.2: Representative Vehicle Temperature and Relative Humidity

Data.

to answer this question, cooperation was sought from NIJ’s Body Armor

Technology Working Group (TWG), which is made up of law enforcement

and corrections officers who have interest or expertise in ballistics and body

armor. Small, inexpensive universal serial bus (USB)-readable temperature

and relative humidity data loggers were purchased and distributed to volunteers from the TWG from across the United States. These were placed

inside actual police vehicles throughout different seasons and the data were

examined periodically. The same data recorders were also placed inside

OLES staff members’ personal vehicles during the summer of 2006 in Maryland. A high temperature of 67 ◦C was obtained in July 2006 from the

study of OLES staff member vehicles. Readings around 63 ◦C were also

obtained in California and Illinois during the summer of 2007. An example

of representative vehicle data is shown in Figure 1.2.

1.2.3 Selection of Relative Humidity

Another parameter that must be selected is the relative humidity used in

the exposure conditions. One of the participants in the TWG vehicle conditions study, independent of the NIST study, obtained permission to have

officers wear an environmental sensor on the outside of their armor. Relative

6
1. Introduction

Time (min)

0 2000 4000 6000 8000

Moisture Content (mass %)

0

2

4

6

8

Temperature (°C)Relative Humidity (%)

20

40

60

80

100

Moisture

Content (%) 

Temperature (°C) 

Relative 

Humidity (RH)(%) 

90% RH

65 °C

90% RH

35 °C

21% RH

35 °C

Figure 1.3: Moisture Sorption Data for PPTA (cyclic conditions).

humidities and temperatures outside of the armor are probably close to, but

possibly slightly lower than, those seen within the armor. The maximum

temperature seen during this study was 41 ◦C and the maximum relative

humidity seen was 76 %. Initially, the protocol was envisoned as a cyclical

temperature and relative humidity exposure, with a low temperature condition of 35 ◦C, 90 % relative humidity. In an effort to maintain consistent

conditions at an elevated temperature of 65 ◦C, high temperature relative

humidities were envisoned as 21 %, which corresponds to the same quantity

of water per gram of dry air (0.032 gram water per gram dry air). However, prior to beginning testing, a moisture sorption study was undertaken

to examine the moisture uptake by the fiber at the two conditions of temperature and relative humidity. In changing conditions from 35 ◦C, 90 %

relative humidity to 65 ◦C, 21 % relative humidity, a large desorption was

observed in both PPTA (Fig. 1.3) and PBO (Fig. 1.4) fibers. This indicated

that the moisture content in the air around the fiber was actually the wrong

variable to control—it was more important to attempt to maintain a constant moisture content in the fiber, where the degradation reactions would

occur. After examining several conditions, it was determined that 75 % relative humidity at both 35 ◦C and 65 ◦C would result in an approximately

equal moisture content, as observed for PBO (Fig. 1.5) and PPTA (Fig. 1.6)

fibers, so this relative humidity was selected for the initial trials.

7
Development of Soft Armor Conditioning Protocols for NIJ

Standard–0101.06: Analytical Results

Time (min)

0 3000 6000 9000 12000 15000 18000

Moisture Content (mass %)

0

2

4

6

8

Temperature (°C)Relative Humidity (%)

20

40

60

80

100

Moisture 

Content (%) 

Temperature (°C) 

Relative 

Humidity (RH)(%) 

90% RH

65 °C

90% RH

35 °C

21% RH

35 °C

Figure 1.4: Moisture Sorption Data for PBO (cyclic conditions).

1.2.4 Simulation of Mechanical Wear

Determination of the temperature and relative humidity conditions for the

soft armor conditioning protocol was relatively straightforward. Defining

the wear environment to simulate involved an analysis of possible conditions. However, environmental exposure only provides part of the solution.

In the course of normal wear, armor is exposed to flexing, bending, and

abrasion. All of these conditions could potentially cause degradation in the

ballistic performance of armor. The combination of mechanical conditions

with environmental exposure is the overall goal of the soft armor conditioning protocol. However, the definition of the mechanical wear environment

is extremely challenging—tests which provide only abrasion ignore the potential fatigue aspects of folding and bending of the armor. A conservative

analysis that a body armor user might bend over (e.g., when entering or

exiting a vehicle) 4 times per hour, 40 h per week, 50 weeks per year could

result in 8000 folding cycles per year, or 40,000 folding cycles over 5 years.

Realistically, almost any movement a wearer makes results in some type of

bend or fold in the armor, which could add up to many thousands of cycles per year [6]. Significant work has been devoted to this area by Holmes

and co-workers at NIST [7]. Tests which create a single fold or bend in

the armor create challenges in assessing the ballistic performance of armor,

because very little area is available over which to conduct ballistic testing.

This would require additional samples and drive up the cost of testing, and

8
1. Introduction

Time (min)

0 500 1000 1500 2000 2500 3000

Moisture Content (mass %)

0

2

4

6

8

Temperature (°C)Relative Humidity (%)

20

40

60

80

100

Moisture Content (%) 

Temperature (°C) 

Relative 

Humidity (RH)(%) 

75% RH

65 °C

35 °C 35 °C

65 °C

Figure 1.5: Moisture Sorption Data for PBO (constant conditions).

ignores the problem of abrasion, which is more difficult to quantify. The

best solution to this challenge is to find a method of creating mechanical

wear that roughly simulates the same types of wear seen in the field and

provides a relatively uniform level of mechanical wear to the entire armor.

Tumbling was selected as the solution that best combined simulating the desired damage with cost efficiency, both in terms of capital cost of equipment

and quantities of samples. The goal of combining the tumbling with the

environmental exposure was initially challenging, so initial trials were done

by removing armor panels from an environmental chamber, and tumbling

periodically during the exposure period.

9
Development of Soft Armor Conditioning Protocols for NIJ

Standard–0101.06: Analytical Results

Time (min)

0 1000 2000 3000 4000 5000

Moisture Content (mass %)

0

2

4

6

8

Temperature (°C)Relative Humidity (%)

20

40

60

80

100

Moisture content (%) 

Temperature (°C) 

Relative 

Humidity (RH)(%) 

75% RH

65 °C

35 °C 35 °C

65 °C

Figure 1.6: Moisture Sorption Data for PPTA (constant conditions).

10
2 Experimental

A combination of analytical and ballistic characterization techniques were

used throughout the development of the soft armor conditioning protocol in

an effort to learn as much as possible from each trial. The two analytical

techniques that were most commonly used were tensile testing and Fourier

transform infrared analysis (FTIR) of yarns extracted from test armor panels. Other analytical techniques that were used include dynamic mechanical

thermal analysis (DMTA) and moisture sorption analysis (MSA). Ballistic

testing was limited to two techniques—perforation/backface signature (PBFS) testing and ballistic limit (V50) analysis.

2.1 Extracted Yarn Tensile Testing

To obtain yarn mechanical properties, tensile testing of yarns was carried

out in accordance with ASTM D2256-02,“Standard Test Method for Tensile

Properties of Yarn by the Single-Strand Method,” using an Instron Model

4482 test frame equipped with a 91 kg (200 lb) load cell, and pneumatic

yarn and cord grips (Instron model 2714-006). The jaw separation was

7.9 cm (3.1 in) and the cross-head speed was 2.3 cm/min (0.9 in/min).

In this study, yarns were nominally 38.1 cm (15 in) long, and given 60

twists1 on a custom-designed yarn twisting device. This level of twist was

maintained on the yarns as they were inserted into the pneumatic yarn and

chord grips. Strain measurements were made with an Instron non-contacting

Type 3 video extensometer in conjunction with black foam markers placed

approximately 2.5 cm apart in the gage section of the yarn. Ten to twelve

replicates from each vest were tested to failure. The standard uncertainty of

these measurements is typically 3 %, however the error bars generated for

plots presented herein are based on the relative standard deviation of the

yarn breaking strength, which is in some cases higher than 3 %.

1This twist level is within the range recommended by ASTM D2256-02, and was experimentally verified prior to beginning experiments.

11
Development of Soft Armor Conditioning Protocols for NIJ

Standard–0101.06: Analytical Results

2.2 Fourier Transform Infrared Analysis

Infrared analysis was carried out using a Nicolet Nexus Fourier Transform

Infrared (FTIR) Spectrometer equipped with a mercury-cadmium-telluride

(MCT) detector and a SensIR Durascope attenuated total reflectance (ATR)

accessory or a Bruker Vertex 80 FTIR, also equipped with a Smiths Detection Durascope ATR accessory. Air dried by passage through a standard

FTIR purge gas generator was used as the purge gas. Consistent pressure

on the yarns was applied using the force monitor on the Durascope. FTIR

spectra were recorded at a resolution of 4 cm−1 between 4000 cm−1 and

700 cm−1 and averaged over 128 scans. Three different locations on each

yarn were analyzed. Spectral analysis, including spectral subtraction, was

carried out using a custom software program developed in the Building and

Fire Research Laboratory’s Polymeric Materials Group at NIST. All spectra

were baseline corrected and normalized using the aromatic C-H deformation

peak at 848 cm−1for PBO and 820 cm−1for Kevlar. Standard uncertainties

associated with this measurement are typically 4 cm−1in wavenumber and

1 % in peak intensity.

2.3 Moisture Sorption Analysis

Moisture absorbed by the yarn specimens during the temperature/humidity

exposure period was measured using a Hiden IGAsorp Moisture Sorption

Analyzer. The IGAsorp software monitors the temporal changes in the

mass of a specimen subjected to prescribed temperature and relative humidity conditions, and calculates equilibrium parameters via curve fitting.

Specimens for sorption analysis were prepared by disassembling between

5 mg and 7 mg of yarn into individual filaments to prevent capillarity effects from dominating the sorption process. Prior to beginning a sorption

experiment, specimens were dried in the moisture sorption analyzer at ≈ 0

% relative humidity and the prescribed temperature at which the sorption

experiment would be carried out. Moisture uptake was measured at 50 ◦C

and 60 % relative humidity as well as at 60 ◦C and 37 % relative humidity.

The water sorption isotherm was generated using the isothermal mapper

mode at 40 ◦C within a range of 0 % relative humidity to 95 % relative humidity. Results are the average of two specimens. The standard uncertainty

of these measurements is typically 0.02 % mass fraction.

2.4 Dynamic Mechanical Thermal Analysis

Dynamic Mechanical Thermal Analysis (DMTA) was performed using a TA

Instruments RSA III DMTA. Dynamic temperature ramp measurements

were generated by loading a single fiber into film/fiber tension clamps, and

applying a preload of approximately 1 g force to the sample. The measurement was performed in a strain controlled mode with a strain of 0.1 % at a

frequency of 1 Hz. The temperature was increased from 30 ◦C to 110 ◦C at

a ramp rate of 3 ◦C/min. For the RSA III, the manufacturer-stated relative

12
2. Experimental

standard uncertainty [21] in the force measurement is typically ± 0.0002 g,

and the standard uncertainty in the temperature scale is typically ± 0.5

◦C.

13
Development of Soft Armor Conditioning Protocols for NIJ

Standard–0101.06: Analytical Results

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14
3 Conditioning Protocol

Development

Multiple phases of development were conducted, all utilizing slightly different methods and equipment configurations. Each phase of development will

be presented separately in this document to better describe the development

of the soft armor conditioning protocol.

3.1 Phase I

Initial experiments were performed using separate tumbling and environmental exposure steps. This allowed for “proof of concept” of tumbling as

a mechanism to provide mechanical wear, and also allowed for exploration

of potential environmental conditions.

3.1.1 Sample Description

Two types of test armors were used in the first phase of protocol development. One sample armor was constructed of 20 layers of plain woven 500

denier PBO, with 26 yarns per inch in the horizontal direction and 26 yarns

per inch in the vertical direction. The layers of fabric were stitched together

in two packs of 10 layers each with a 2.54 cm (1 in) diagonal quilt stitch

to form the ballistic package. This ballistic package was then encased in

a stitched moisture-permeable fabric cover and inserted into a lightweight

poly-cotton carrier to form an armor panel. The other sample armor was

constructed of 25 layers of plain woven 500 denier PPTA, with 24 yarns in

the horizontal direction and 24 yarns in the vertical direction. The layers

of fabric were stitched together in one package with a 3.18 cm (1.25 in) diagonal quilt stitch to form the ballistic package. This ballistic package was

then encased in a standard water-repellent treated nylon fabric cover and

inserted into a medium-weight poly-cotton carrier to form an armor panel1.

All armors were manufactured specifically for this study. The PBO armor

samples were designed to be NIJ Standard–0101.04 Level IIA compliant.

1The definitions of panel and armor panel used in this document are intended to be

consistent with the definitions of these terms as described in Section 3 of NIJ Standard–

0101.06 [22].

15
Development of Soft Armor Conditioning Protocols for NIJ

Standard–0101.06: Analytical Results

Hour

0 5 10 15 20 25

Temperature (°C)

0

20

40

60

80

100

Relative Humidity (%)

0

20

40

60

80

100

Temperature

Relative Humidity

Figure 3.1: Phase I Protocol Cycle.

The PPTA armor samples were designed to be NIJ Standard–0101.04 Level

II compliant [23]. Both armor samples were constructed to be the size required for NIJ Standard–0101.04 2005 Interim Requirements [24] compliance

testing.

Both sample sets consisted of 13 armor panels. Of these 13 panels, 7

panels were exposed to all conditions and were designated for ballistic testing, 1 sample was exposed to all conditions and was used only for analytical

testing, 2 panels were controls for heat and moisture and received no tumbling (one of these samples was designated for ballistic testing and one for

analytical testing), 2 panels were tumbling controls and received no heat

and moisture exposure (1 of these samples was designated for ballistic testing and 1 for analytical testing), and finally 1 control sample received no

heat, moisture, or tumbling exposure (was stored at room temperature and

humidity of nominally 21 ◦C and 50 % relative humidity) and was used for

analytical testing.

3.1.2 Experimental Conditions

As previously discussed, the temperature and relative humidity protocol

originally consisted of a cyclical temperature profile between 35 ◦C and

65 ◦C, with a constant relative humidity of 75 %, as depicted in Figure 3.1.

16
3. Conditioning Protocol Development

Environmental exposures of the PPTA and PBO samples were conducted

in two separate chambers. Vests were hung vertically in the humidity chamber for the environmental portion of the exposures and removed at designated times for tumbling in a standard home clothes dryer (with the heating

element disabled). The chamber was returned to room temperature and humidity before removing the armor for tumbling to avoid the formation of a

condensing atmosphere in the chamber. Samples were extracted from armor

designated for analytical testing after it was removed from the chamber for

tumbling. Extractions were performed after the tumbling was completed.

An estimate of the total number of revolutions of the armor for the first

phase is 194,400 total revolutions, based on 3 h of tumbling, 3 d per week,

for 9 weeks. The rotation speed of the standard home clothes dryer was

measured at nominally 4.19 rad/s (40 revolutions per minute) using a laser

tachometer.

3.1.3 Analytical Results

Relative tensile strengths of yarns extracted from the PBO armor panels

are depicted in Figure 3.2. This figure shows the reduction of ultimate

tensile strength, plotted as percent strength retention, of the PBO armor as

a function of exposure time. After 9 weeks, armor exposed to heat, moisture,

and tumbling had a tensile strength retention of approximately 62 %. This is

comparable to the value that was observed in the back panel of a PBO armor

that was defeated in the field, and the value that was ultimately reached after

6 months of aging in a previous study [4]. An interesting observation is that

the armor panel that was exposed to only heat and moisture had essentially

the same tensile strength retention. The armor panel that was only exposed

to tumbling had only a reduction in tensile strength of approximately 8 %.

This indicates that the tumbling did not produce enough mechanical damage

or did not happen frequently enough in the protocol to accelerate the effects

of the heat and moisture exposure.

Relative tensile strengths of yarns extracted from the PPTA armor panels are depicted in Figure 3.3. This figure shows the reduction of ultimate

tensile strength, plotted as percent strength retention, of the PPTA armor

as a function of exposure time. After 9 weeks, the armor exhibits essentially

no change in tensile strength and was apparently unaffected by the exposure

protocol.

In previous studies [4, 5], it has been shown that oxazole ring opening

is a major indicator of hydrolysis in PBO. Oxazole ring opening in previous

studies is identified by the loss of peaks attributed to the vibrations associated with the benzoxazole ring at 1496 cm−1

, 1362 cm−1, 1056 cm−1, and

914 cm−1, and by the formation of a peak at 1650 cm−1 attributed to an

amide carbonyl or carboxylic acid, which are potential products of oxazole

ring opening. Infrared difference spectra of PBO taken over the course of

the exposure study are shown in Figure 3.4. The difference spectra show

the chemical changes occurring in PBO as a function of exposure time.

The difference spectra show marked reductions in the peaks at 1492 cm−1,

1361 cm−1, 1056 cm−1, and 914 cm−1, all of which are attributed to oxazole

17
Development of Soft Armor Conditioning Protocols for NIJ

Standard–0101.06: Analytical Results

Conditioning Time (d)

0 10 20 30 40 50 60 70

Breaking Strength Retention (%)

40

60

80

100

PBO (all conditions)

Benchmark reduction

PBO (tumbling only)

PBO (T&RH only)

Figure 3.2: Phase I Breaking Strength Retention for PBO. The error bars

represent the relative standard deviation of the mean yarn breaking strength.

Points are offset horizontally for clarity.

18
3. Conditioning Protocol Development

Conditioning Time (d)

-10 0 10 20 30 40 50 60

Tensile Strength Retention (%)

40

60

80

100

120

PPTA

PPTA (tumble only) 

PPTA (T&RH) 

Benchmark reduction

Figure 3.3: Phase I Breaking Strength Retention for PPTA. The error bars

represent the relative standard deviation of the mean yarn breaking strength.

Points are offset horizontally for clarity.

19
Development of Soft Armor Conditioning Protocols for NIJ

Standard–0101.06: Analytical Results

Wavenumber (cm-1)

1800 1600 1400 1200 1000 800

Absorbance

-0.10

-0.05

0.00

0.05

0.10

week 1

week 4

week 8

1056 cm-1 and 914 cm-1

benzoxazole ring

opening

1361 cm-1

benzoxazole

ring opening

1492 cm-1

benzoxazole

ring opening

*

* *

starred peaks (*) are attributed to

loss of skeletal vibration from conjugated benzoxazole ring system

carbonyl expected

at 1647 cm-1 but

very weak for

carbonyl

Figure 3.4: Phase I FTIR Difference Spectra for PBO.

ring opening. As previously mentioned, standard uncertainties associated

with this measurement are typically 4 cm−1

in wavenumber and 1 % in peak

intensity, so the slight shift in wavenumbers for the difference spectra may

be due to variations in the individual spectra used to create the difference

spectrum. However, we do not see a large peak at 1650 cm−1to indicate the

formation of an amide carbonyl or carboxylic acid as expected. A possible

explanation is that this product is leaving the system, possibly due to the

abrasion created during tumbling, or that this product was extracted by

moisture.

The infrared subtraction spectra of PPTA yarns extracted from body

armor panels following environmental exposure are shown in Figure 3.5 and

Figure 3.6. The body armor panels were divided into four groups–one group

was subjected to tumbling alone, one to temperature/moisture exposure

alone, one to temperature/moisture combined with tumbling (designated as

“all”), and one group was sealed in plastic bags at room temperature of

nominally 22 ◦C to serve as controls.

Infrared analysis and spectral subtraction revealed that all of the conditions, even the control conditions, resulted in some degree of PPTA hydrolysis. The difference spectra in Figure 3.5 and Figure 3.6 shows negative

peaks with positions corresponding to the original amide I peak at 1640

cm−1 and amide II peak at 1513 cm−1. A new (positive) broad peak is

20
3. Conditioning Protocol Development

Wavenumber (cm-1)

4000 3500 3000 2500 2000 1500 1000

Absorbance

-0.30

-0.20

-0.10

0.00

0.10

0.20

PPTA control

PPTA (T&RH only)

PPTA (all conditions )

PPTA (tumble only)

3400 cm-1

3320 cm-1

Figure 3.5: Phase I FTIR Difference Spectra for PPTA (full scale).

21
Development of Soft Armor Conditioning Protocols for NIJ

Standard–0101.06: Analytical Results

Wavenumber (cm-1)

2000 1800 1600 1400 1200 1000 800

Absorbance

-0.30

-0.20

-0.10

0.00

0.10

0.20

PPTA control

PPTA (T&RH only)

PPTA (all conditions)

PPTA (tumble only)

1560 cm-1

1420 cm-1

1627 cm-1

Amide I

1513 cm-1

Amide II

Figure 3.6: Phase I FTIR Difference Spectra for PPTA (expanded scale).

22
3. Conditioning Protocol Development

Infrared Band T&RH Tumble

(cm−1) All Only Only Control

3320 3 1 2 4

1627 2 1 4 3

1513 3 1 2 4

1560 2 (tie) 2 (tie) 1 3

1420 2 3 (tie) 1 3 (tie)

Table 3.1: Rank Ordering of PPTA Infrared Bands; 1=greatest change;

4=least change.

observed at 3400 cm−1, which is attributed to a combination of amine N-H

stretching and carboxylic acid OH stretching. New peaks are also observed

at 1570 cm−1 and 1420 cm−1that are attributed to carboxylate ion stretching. This evidence points to the hydrolysis of the main chain amide group

to amine and carboxylic acid.

It is puzzling why even the control panels that were not subjected to any

environmental stresses also underwent hydrolysis, albeit to a lesser extent.

It is likely that as long as moisture is present, hydrolytic reactions in the

PPTAs can occur.

In an attempt to determine which environmental conditioning treatment

caused the most hydrolytic damage, intensities of the difference bands were

examined and rank-ordered. A tabulation of the major difference bands

(except for the bands at 3400 cm−1 which were too close to distinguish) and

their intensity rankings is given in Table 3.1 below.

No clear or consistent pattern can be found in the above table; the

intensity rank order differs for each infrared band. Since the tensile strengths

of the yarns extracted from the environmentally conditioned panels did not

exhibit any changes over the course of the conditioning treatments, it is

possible that these chemical changes are beneath the threshold necessary to

influence mechanical properties and may fall within the standard deviations

of the infrared measurements.

3.2 Phase I Summary

This phase of development showed that it was possible to develop a protocol

of elevated temperature and relative humidity that would cause damage to

PBO armor after 9 weeks of exposure, but would not cause similar damage

in PPTA armor in this time period. However, the 8 week exposure time was

deemed too long for practical implementation in the new NIJ Standard–

0101.06. After this first phase, it was determined that the duration of the

protocol must be reduced. Reduction of the time required to complete the

protocol was the primary goal for Phase II.

23
Development of Soft Armor Conditioning Protocols for NIJ

Standard–0101.06: Analytical Results

3.3 Phase II

As was the case in Phase I, in order to meet the timetable for development of

the conditioning protocol, initial exposures were performed using separate

tumbling and environmental exposure for Phase II. This allowed for “proof

of concept” of tumbling as a mechanism to provide mechanical wear, and

also allowed for further exploration of potential environmental conditions.

3.3.1 Sample Description

Three sets of armors were used in the second phase of protocol development.

Two woven armors were the same as those discussed in the Phase I testing.

The additional armor was a nonwoven armor, constructed of 30 sheets of

unidirectional (UD) laminated UHMWPE fibers. In a UD layer, all fibers

are laid parallel, in the same plane. In this study, the sheets of UHMWPE

armors were made of 4 layers of fibers, with the orientation of fibers in each

layer at 90 ◦to the direction of the fibers in the adjacent layers (0 ◦, 90 ◦, 0 ◦,

90 ◦). The sheets of UHMWPE were stitched together in three places at the

top of the vest and one place at the bottom of the vest. Phase II also used

two chambers and two sample sets. Chamber 1 contained 15 panels of PBO

armor and 6 panels of UHMWPE armor. The PBO panels were tested as

follows—in chamber 1, one of the PBO samples was a control and was not

exposed to any heat, humidity, or tumbling exposure. Three panels were

exposed to only tumbling (two of these were for ballistic testing and one

was for analytical testing), two panels were exposed to only temperature

and relative humidity (one of these was used for ballistic testing and one

for analytical testing), 8 panels were exposed to all conditions and were

designated for ballistic testing, and 1 sample was exposed to all conditions

and was only tested analytically. All six of the UHMWPE panels were

tested ballistically. The results of the ballistic testing will be the subject of

a separate publication.

Chamber 2 consisted of 15 panels of PPTA armor and 5 panels of

UHMWPE armor. The PPTA panels were used as follows—in chamber

2, one of the PPTA samples was a control and was not exposed to any

heat, humidity, or tumbling exposure. Three panels were exposed to only

tumbling (two of these were for ballistic testing and one was for analytical

testing), two panels were exposed to only temperature and relative humidity (one of these was for ballistic testing and one was for analytical testing),

8 panels were exposed to all conditions and were designated for ballistic

testing, and 1 sample was exposed to all conditions and was used only for

analytical testing. All five of the UHMWPE panels were for ballistic testing.

3.3.2 Experimental Conditions

In an effort to shorten the time required to achieve the target degradation

from Phase I, the temperature and relative humidity protocol was adjusted

to allow for two cycles within a 24 h time period with a temperature profile

between 35 ◦C and 65 ◦C, with a constant relative humidity of 75 % except

24
3. Conditioning Protocol Development

Hour

0 5 10 15 20 25

Temperature (°C)

0

20

40

60

80

100

Relative Humidity (%)

0

20

40

60

80

100

Temperature

Relative Humidity

Figure 3.7: Phase II Protocol Cycle.

on the cooling parts of the cycle to avoid condensation, where the relative

humidity was dropped to 65 % as depicted in Figure 3.7.

Environmental exposures of the PPTA and PBO samples were conducted

in two separate chambers. Vests were hung vertically in the humidity chamber for the environmental portion of the exposures and removed periodically

for tumbling in a standard home clothes dryer (with the heating element

disabled). The chamber was returned to room temperature and humidity

before removing armor for tumbling to avoid the formation of a condensing

atmosphere in the chamber. Samples were extracted from armor designated

for analytical testing when it was removed from the chamber for tumbling.

An estimate of the total number of revolutions of the armor for the first

phase is 115,200 total revolutions, based on 2 h of tumbling, 2 d per week,

for 6 weeks. The rotation speed of the standard home clothes dryer was measured at nominally 4.19 rad/s (40 rpm) using a laser tachometer. The load

in each individual tumbler was increased in an effort to increase mechanical

damage caused by tumbling.

3.3.3 Analytical Results

Tensile breaking strength testing of yarns extracted from the armor panels

are depicted in Figures 3.8 through 3.10. Figure 3.8 shows the reduction

25
Development of Soft Armor Conditioning Protocols for NIJ

Standard–0101.06: Analytical Results

of breaking tensile strength, plotted as a percent strength retention, of the

PBO armor and PPTA armor as a function of exposure time. After 6 weeks,

the PBO sample which was exposed to the conditions of heat, moisture, and

tumbling had a tensile strength retention of approximately 58 %. This is

slightly lower than the target value established by previous studies. By

comparison, the PPTA armor showed no reduction in tensile strength in

this time. Figure 3.9 shows the results of testing on yarns that had been

extracted from vests that were only exposed to temperature and relative

humidity. The PBO yarns had an approximate tensile strength retention

of 80 %, as compared to no strength reduction in the PPTA armor panels. Figure 3.10 shows tensile strength reduction data for armors that were

tumbled at room temperature and humidity. Once again, the PBO armor

had an approximate tensile strength reduction of 80 %, but the PPTA armor was essentially unaffected. It is important to note that for the PBO

armors, the panels exposed to only temperature and relative humidity and

the panels that were exposed to only tumbling had approximately equal

strength retentions. This indicates that the contribution of each mechanism

(environmental vs. mechanical) to overall degradation in this study was approximately equal, and that the combination of the two mechanisms had a

synergistic effect. Infrared results indicated similar trends to those observed

in the previous study and are not included here for brevity.

3.3.4 Ballistic Results from Phase I and Phase II Testing

Ballistic testing, including V50 and perfortion/backface signature testing

(P-BFS) was performed on armor samples used throughout this study. The

results of this testing will be the subject of a separate publication.

3.4 Phase II Summary

In this phase of development, the time per cycle was compressed so that

two temperature and humidity cycles were completed per 24 h period, and

the armor was tumbled more frequently. However, the protocol was only

shortened from 9 weeks to 6 weeks with these changes. The 6 week exposure

time was still deemed too long for practical implementation in the new NIJ

Standard–0101.06. Therefore, major changes were planned for Phase III in

order to further reduce the duration of the test.

3.5 Phase III

Phase III is a very significant phase in the development of Soft Armor Conditioning Protocols because it represents the first phase in which mechanical

conditioning was combined with environmental conditioning in one test. Details and specifications of the device which was fabricated in our laboratory

at NIST to perform this testing are available via the NIST File Transfer

Protocol (FTP) site [25] and will be the subject of a future NIST publication.

26
3. Conditioning Protocol Development

Conditioning Time (d)

0 10 20 30 40 50

Breaking Strength Retention (%)

40

50

60

70

80

90

100

110

120

PBO (all conditions)

PPTA (all conditions) 

Benchmark reduction

Figure 3.8: Phase II Breaking Strength Retention for PPTA and PBO (all

conditions). The error bars represent the relative standard deviation of the

mean yarn breaking strength. PPTA points are offset horizontally for clarity.

27
Development of Soft Armor Conditioning Protocols for NIJ

Standard–0101.06: Analytical Results

Conditioning Time (d)

0 10 20 30 40 50

Breaking Strength Retention (%)

50

60

70

80

90

100

110

120

Benchmark reduction

PBO (T&RH only)

PPTA (T&RH only) 

Figure 3.9: Phase II Breaking Strength Retention for PPTA and PBO (T

& RH only). The error bars represent the relative standard deviation of

the mean yarn breaking strength. PPTA points are offset horizontally for

clarity.

28
3. Conditioning Protocol Development

Conditioning time (d)

0 10 20 30 40 50

Breaking Strength Retention (%)

50

60

70

80

90

100

110

120

Benchmark reduction

PBO (tumble only)

PPTA (tumble only)

Figure 3.10: Phase II Breaking Strength Retention for PPTA and PBO

(tumbling only). The error bars represent the relative standard deviation of

the mean yarn breaking strength. PPTA points are offset horizontally for

clarity.

29
Development of Soft Armor Conditioning Protocols for NIJ

Standard–0101.06: Analytical Results

3.5.1 Experimental Conditions

In an effort to accelerate the degradation achieved in Phases I and II, the

temperature and relative humidity protocol were adjusted to a constant

condition of 70 ◦C and 90 % relative humidity. The rationale behind this

change was to shorten the test protocol by spending all of the conditioning

time at the high heat, high relative humidity condition instead of cycling

between two conditions. At this point in the development, it was determined

that 8 armors would be tumbled at a time, so efforts were made to try to keep

tumbler loads as close to 8 armors, or 16 armor panels, as possible. Tumbling

was performed at 0.523 rad/s (5 rpm) continuously throughout the exposure.

A specific time interval for exposure was not set at the beginning of the

study, the intention was to track the chemical and physical degradation of

the armor to determine when the target reduction in tensile strength had

been obtained.

3.5.2 Sample Description

Three types of armors were used in the third phase of protocol development. The two woven sample armors were the same as those discussed in

the Phase I and Phase II testing. A new set of armor was obtained for

Phase III, also constructed of 30 sheets of UD laminated UHMWPE fibers,

as described previously. There was no stitching of the sheets of UHMWPE.

After ballistic testing was completed, it was discovered that these samples

had been fabricated incorrectly. Instead of cutting each sheet of the material

separately in order to achieve the correct 0◦, 90◦, 0◦, 90◦ orientation, the

material was rolled out in a back and forth direction and all layers were cut

out at once. Additionally, the layers were not aligned properly and portions

of layers were missing from all of the armor panels that were manufactured

in this way. This construction problem was determined to affect the ballistic

properties of the material that were measured after conditioning, as will be

discussed in a future publication. One environmental chamber in which a

tumbler had been installed was used in Phase III with two sets of samples.

The first sample set consisted of 6 PBO armor panels, 7 UHMWPE armor

panels, and 6 PPTA armor panels. One of each type of armor panel was

exposed to only temperature and relative humidity and used for analytical

testing. One of the PBO armor panels and one of the PPTA armor panels

that were exposed to all conditions were used for analytical testing. The remaining armor panels (4 PBO, 4 PPTA, and 6 UHMWPE) were designated

for ballistic testing. The chamber was programmed at constant conditions

of 70 ◦C and 90 % relative humidity, with a constant tumbling speed of 0.52

rad/s (5 rpm). A separate second set of testing was performed to obtain

armors that had only been exposed to mechanical conditioning. In this test,

5 PBO panels, 6 UHMWPE panels, and 5 PPTA panels were tumbled at

room temperature and humidity at 0.52 rad/s (5 rpm).

30
3. Conditioning Protocol Development

3.5.3 Analytical Results

Tensile breaking strength testing of yarns extracted from the PBO and

PPTA armor panels are depicted in Figure 3.11 through Figure 3.13. Figure 3.11 shows the reduction of ultimate tensile strength, plotted as a percent

strength retention, of the PBO and PPTA armors exposed to all conditions

as a function of exposure time. After 10 d, the PBO sample that was exposed

to the conditions of heat, moisture, and tumbling had a tensile strength retention of approximately 62 %, though we continued the test until day 13.

In this phase, for the first time, there was an indication of strength loss in

the PPTA armor. Samples that were exposed to all conditions had a tensile

strength retention of approximately 88 % after 13 days of exposure. Figure 3.12 compares the PBO and PPTA armor panels that were exposed to

only temperature and relative humidity. The PBO armor panels had a tensile strength retention of approximately 77 % and the PPTA armor panels

had a tensile strength retention of 90 %. Figure 3.13 shows panels that were

exposed to only tumbling. The PBO armor panels had a tensile strength

retention of approximately 78 % and the PPTA armor panels showed no reduction in tensile strength. There are a few conclusions that can be drawn

from these results. The first is that for PBO, the test combining environmental exposure and tumbling still had approximately equal contributions

of each mechanisms (environmental vs. mechanical) to overall degradation

of the material. In the case of the PPTA armor, it is puzzling that there

was a slight reduction in tensile strength in the samples that were only exposed to temperature and relative humidity. A possible explanation is that

the armor could have been more sensitive to the slightly higher temperature

and relative humidity in this study, which could have also been responsible

for the slight reduction in strength observed in the armor exposed to all

conditions.

Results from infrared analysis of yarns extracted from the PBO armor

panels are depicted in Figure 3.14. Similar to the infrared analysis presented

in Phases I and II of the study, these results show an overall reduction in

the peak absorbance at 1606 cm−1, 1302 cm−1, 1257 cm−1, 1136 cm−1, 1036

cm−1, and 909 cm−1, which are typically associated with the benzoxazole

and an increase in the peak absorbance at 1635 cm−1, which is associated

with carbonyl formation after opening of the benzoxazole ring. These two

trends, taken together, indicate that hydrolysis was achieved in the PBO

samples. One may note in Figure 3.14 that there is not a trend indicating

a steady decline in absorbance for the benzoxazole ring. There is a sharp

decline between day 0 and day 3, then at day 8, there was an apparent

increase in the absorbance of the benzoxazole peak. This may be attributed

to differences in the samples removed from the armor for testing on the

different days, or may be due to the continual mechanical damage occurring

in the system due to tumbling. This tumbling may abrade the degraded layer

of material and expose fresh material underneath, which would lead to an

apparent increase in the absorbance of the benzoxazole peak as referenced

to the data obtained on day 3. Analysis of the PPTA samples indicated

similar trends to those seen in previous phases of the study.

31
Development of Soft Armor Conditioning Protocols for NIJ

Standard–0101.06: Analytical Results

Conditioning time (d)

0 2 4 6 8 10 12

Breaking Strength Retention (%)

40

60

80

100

PBO (all conditions)

PPTA (all conditions)

Benchmark reduction

Figure 3.11: Phase III Breaking Strength Retention for PPTA and PBO

(all conditions). The error bars represent the relative standard deviation of

the mean yarn breaking strength. PPTA points are offset horizontally for

clarity.

32
3. Conditioning Protocol Development

Conditioning time (d)

0 2 4 6 8 10 12 14

Breaking Strength Retention (%)

40

60

80

100

120

Benchmark reduction

PPTA (T&RH only)

PBO (T&RH only)

Figure 3.12: Phase III Breaking Strength Retention for PPTA and PBO (T

& RH only). The error bars represent the relative standard deviation of

the mean yarn breaking strength. PPTA points are offset horizontally for

clarity.

33
Development of Soft Armor Conditioning Protocols for NIJ

Standard–0101.06: Analytical Results

Conditioning time (d)

0 2 4 6 8 10 12 14

Breaking Strength Retention (%)

40

60

80

100

120

Benchmark reduction

PPTA (tumbling only) 

PBO (tumbling only)

Figure 3.13: Phase III Breaking Strength Retention for PPTA and PBO

(tumbling only). The error bars represent the relative standard deviation of

the mean yarn breaking strength. PPTA points are offset horizontally for

clarity.

34
3. Conditioning Protocol Development

Conditioning Time (d)

0 2 4 6 8 10 12 14

Peak Absorbance

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

1635 cm-1 

1606 cm-1 

1302 cm-1

1257 cm-1

1136 cm-1

1036 cm-1

909 cm-1

Figure 3.14: Phase III Reduction in Key Infrared Bands.

35
Development of Soft Armor Conditioning Protocols for NIJ

Standard–0101.06: Analytical Results

3.5.4 Ballistic Results from Phase III Testing

Ballistic testing, including V50 and perforation/backface signature testing

(P-BFS) was performed on armor samples used throughout this study. As

previously indicated, the results of this testing will be the subject of a separate publication.

3.6 Phase III Summary

Major changes to the protocol occurred in Phase III. The concept of cyclical

conditions of temperature and relative humidity exposure were abandoned

in favor of a constant high heat, high relative humidity condition. The

tumbling and environmental exposure were combined into one test with

the development of a custom-built tumbler inside of the humidity chamber.

While the test presented in Phase III ran for 13 days, the target degradation

was achieved before the end of the test. Therefore, it was determined that

the changes made in Phase III allowed the exposure time to be reduced to

a much more practical 10 days. The 10 d test was deemed acceptable for

practical implementation into NIJ Standard–0101.06.

3.7 Phase IV

The Phase IV study was designed to verify the conditions selected in Phase

III, and verify that 10 d was the appropriate period of time for the test.

Conditions of exposure remained the same in this phase as in Phase III.

3.7.1 Sample Description

Three sets of armor samples were used in the fourth phase of protocol development. Two of the armors were the same woven armors as those discussed

in the Phase I, Phase II, and Phase III testing. A new set of armor was

obtained for Phase IV. This armor model consisted of 18 layers of four plies

each of UD PPTA fiber, crossplied at 0◦, 90◦, 0◦, 90◦sandwiched between

thermoplastic film inside of a nylon armor panel cover. The panel cover

seams were heat-sealed and the interior surface of the panel covers were

coated for water repellency. There was no stitching of the sheets of UD

PPTA. Phase IV used one environmental chamber in which a tumbler had

been installed, and one sample set. This sample set consisted of 5 PBO

armor panels, 6 UD PPTA armor panels, and 5 woven PPTA armor panels.

One of the PBO armor panels and one of the PPTA armor panels which were

exposed to all conditions were used for analytical testing. The remaining

armor panels (4 PBO, 4 woven PPTA, and 6 UD PPTA) were used for ballistic testing. The chamber was maintained at constant conditions of 70 ◦C

and 90 % relative humidity, with a constant tumbling speed of 0.52 rad/s

(5 rpm).

36
3. Conditioning Protocol Development

Conditioning Time (d)

0 2 4 6 8 10 12

Strength Retention (%)

40

60

80

100

PPTA 

PBO

Benchmark reduction

Figure 3.15: Phase IV Breaking Strength Retention for PPTA and PBO

(all conditions). The error bars represent the relative standard deviation of

the mean yarn breaking strength. PPTA points are offset horizontally for

clarity.

3.7.2 Analytical Results

Tensile breaking strengths of yarns extracted from PPTA and PBO armor

panels are depicted in Figure 3.15. As discussed in previous trials, this figure shows the reduction of ultimate tensile strength, plotted as a percent

strength retention of both types of armor as a function of exposure time.

After 10 d, the PBO sample that was exposed to all of the conditions of

heat, moisture, and tumbling had a tensile strength retention of approximately 68 %. The PPTA sample exposed to all of these conditions had a

tensile strength retention of approximately 85 %. This strength loss in the

PPTA armor was greater than that observed in previous studies. This could

potentially be due to variations between the samples tested, or the fact that

the operator who performed these tests was not as experienced in performing yarn sample extraction and testing as the previous operators. Infrared

analysis of fibers extracted from both the PBO and PPTA armors was performed, but analysis of this data did not provide any additional information

beyond what has already been discussed herein.

37
Development of Soft Armor Conditioning Protocols for NIJ

Standard–0101.06: Analytical Results

3.8 Important Observations From Other Studies

Some of the studies performed in development of the Flexible Armor Conditioning Protocol did not result in a full analysis appropriate for treatment

within this document. Some of these observations may be important and

they will be summarized below. A set of armor was received that had been

enclosed in a heat-sealed panel-covering material, but supplied without armor carriers. Some prior work had been performed to evaluate the effect of

tumbling with or without a carrier, but only with armors that were encased

in sewn panel-covering materials. In these trials, there was no discernible

difference between the armors tumbled with and without the carriers. Based

on the results of these previous studies, the heat-sealed armors were placed

in the tumbler without carriers. However, within a few days, the edges of

the heat-sealed panel-covering material started to peel away from the main

body of the panel cover. This caused the remaining panel cover to separate

and exposed the ballistic package to the tumbler. This experience was one

of the factors that led to the decision that all armors would be tested in a

specified, generic carrier in NIJ Standard–0101.06.

After the completion of Phase IV testing, a concern was raised that,

even within the specified tolerances of relative humidity and temperature, a

condensing atmosphere could be achieved within the tumbler. In response

to this concern, the saturated vapor curve for water vapor was examined

in relation to the specified conditions. Figure 3.16 shows this analysis for

conditions of 70 ◦C and 90 % relative humidity, with tolerances of ± 2

◦C

and ± 5 % relative humidity. It was discovered from this analysis that if

the temperature dropped from the upper limit of 72 ◦C to the lower limit

of 68 ◦C, while maintaining the relative humidity at 95 %, condensation

would indeed occur in the chamber by the time the temperature dropped

near 70 ◦C, the specified temperature (as indicated by the tolerance bar

crossing the saturated vapor curve to transition from vapor to liquid water). Reexamination of possible conditions lead to the decision to reduce

both the temperature and humidity specified in the protocol. The temperature was reduced to 65 ◦C and the relative humidity was reduced to 80 %.

These conditions were selected based on the vehicle data study which had

indicated that temperatures of 65 ◦C were not unreasonable with respect to

the potential operating environment of the armor, and the previous work

performed at 65 ◦C. The relative humidity was reduced to 80 % in an effort

to avoid the issues with condensation. Figure 3.17 shows the tolerance associated with a drop from the upper limit of 67 ◦C to the lower limit of 63 ◦C,

while maintaing the relative humidity at 85 %. In this case, the tolerance

does not touch the saturated vapor curve until the temperature drops very

near 63 ◦C, so condensation is much less likely with these revised conditions. These changes were included in the soft armor conditioning protocol

released in NIJ Standard–0101.06 in July 2008.

38
3. Conditioning Protocol Development

Temperature (°C)

60 62 64 66 68 70 72 74

Moisture (kg/m

3

)

0.10

0.12

0.14

0.16

0.18

0.20

0.22

saturated vapor 

curve

85 % RH

95 % RH

95 % RH 90 % RH

85 % RH

tolerance

water vapor

liquid water

Figure 3.16: Analysis of Potential for Condensation at 70 ◦C and 90 %

Relative Humidity.

3.9 Phase IV Summary

Minor adjustments to the protocol occurred in Phase IV. The environmental conditions were adjusted to prevent problems with condensation during

minor, allowable excursions in conditions of temperature and relative humidity. The protocol used during this phase was adopted as Section 5, the

Flexible Armor Conditioning Protocol in NIJ Standard–0101.06.

39
Development of Soft Armor Conditioning Protocols for NIJ

Standard–0101.06: Analytical Results

Temperature (°C)

60 62 64 66 68 70 72 74

Moisture (kg/m

3

)

0.10

0.12

0.14

0.16

0.18

0.20

0.22

saturated 

vapor curve

85 % RH

75 % RH 80 % RH

75 % RH

85 % RH

tolerance

liquid water

water vapor

Figure 3.17: Analysis of Potential for Condensation at 65 ◦C and 80 %

Relative Humidity.

40
4 Conclusions and Future Work

After four major phases of development work, the Flexible Armor Conditioning Protocol in NIJ Standard–0101.06 (as it appears at the time of this

publication) was finalized. The duration of the protocol was shortened from

9 weeks in the first efforts to 10 d. All major classes of materials were tested,

and the conditions selected are found to be quite detrimental to PBO armors of designs that previously had exhibited problems in the field. The

conditions have not been found to be excessively detrimental to other commonly used types of armor. However, the protocol does not represent an

exact period of time in the field.

Current and future work will attempt to validate this protocol to reflect

a period of field service for armor. Two major efforts will work to create

this validation. The first of these is an extensive study to examine the

aging properties of most of the ballistic fibers used in body armor, which

will attempt to determine the correlation between natural aging and accelerated (elevated temperature and relative humidity) aging. Methods will

be explored to better correlate artificial mechanical damage to actual wear.

Additionally, a large study to examine the physical and ballistic properties

of fielded armor is currently being planned and initial work on this project

is underway. As opportunities arise, more studies to examine fielded armor

in support of the validation of this protocol will be performed.

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5 References

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[2] NIJ. Supplement I: Status report to the Attorney General of body

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[3] NIJ. Third status report to the Attorney General on body armor safety

initative testing and activities. NIJ Special Report, 2005.

[4] J. Chin, E. Byrd, A.L. Forster, X. Gu, T. Nguyen, S. Scierka, L. Sung,

P. Stutzman, J. Sieber, and K. Rice. Chemical and Physical Characterization of Poly (p-phenylene-2,6-benzobisoxazole) Fibers Used in Body

Armor. NISTIR 7237, 2006.

[5] J. Chin, E. Byrd, C. Clerici, M. Oudina, L. Sung, A.L. Forster, and

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[9] D.E. Frank. Ballistic Tests of Used Soft Body Armor. NBSIR 86-3444,

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[10] National Institute of Justice. Response to DuPont’s Rational Replacement Policy, 1985.

[11] DuPont Kevlar Survivor’s Club. Personal body armor facts book. Technical report, 1989.

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Development of Soft Armor Conditioning Protocols for NIJ

Standard–0101.06: Analytical Results

[12] Police body armor standards and testing Volume I: Report. Congress

of the United States Office of Technology Assessment, 1992.

[13] Police body armor standards and testing Volume II: Appendixes.

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[14] E. Hoffman. Soft Body Armor. Police Product News, 1986.

[15] Armor Holdings. Interim Report on Body Armor Testing: Investigations and Actions. Technical report, 2004.

[16] DHB Armor Group. DHB Armor Group Armor Safety Report. Technical report, 2004.

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[20] S. Chabba, M. van Es, E.J. van Klinken, M.J. Jongedijk, D. Vanek,

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2893, 2007.

[21] Rheometrics Series User Manual. RSA III Manufacturer’s Specifications. TA Instruments, New Castle, DE, pn902-30027 edition, 2003.

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44