Development of a Robust Static Punch Experiment 

for Screening Unprocessed Ultra-High Molecular 

Weight Polyethylene (UHMWPE) Unidirectional 

Cross-Ply Material

by David Gray, Robert Kaste, and Paul Moy

ARL-TR-7090 September 2014

Approved for public release; distribution is unlimited.
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Army Research Laboratory

Aberdeen Proving Ground, MD 21005-5066

ARL-TR-7090 September 2014

Development of a Robust Static Punch Experiment 

for Screening Unprocessed Ultra-High Molecular 

Weight Polyethylene (UHMWPE) Unidirectional 

Cross-Ply Material

David Gray, Robert Kaste, and Paul Moy

Weapons and Materials Research Directorate, ARL

Approved for public release; distribution is unlimited.
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January 2013–May 2014

4. TITLE AND SUBTITLE

Development of a Robust Static Punch Experiment for Screening Unprocessed 

Ultra-High Molecular Weight Polyethylene (UHMWPE) Unidirectional Cross-Ply 

Material

5a. CONTRACT NUMBER

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6. AUTHOR(S)

David Gray, Robert Kaste, and Paul Moy

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7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

US Army Research Laboratory

ATTN: RDRL-WMM-B

Aberdeen Proving Ground, MD 21005-5066

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 REPORT NUMBER

ARL-TR-7090

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Approved for public release; distribution is unlimited.

13. SUPPLEMENTARY NOTES

14. ABSTRACT

At the request of the US Army Research Laboratory’s Specifications and Standards Office, a novel experimental methodology for punch 

testing of Ultra-High Molecular Weight Polyethylene (UHMWPE) composites was developed. This test procedure will act as a qualityassurance test method and subsequently be an addendum to the new military specification MIL-DTL-32398. There are currently no 

intermediate mechanical testing methods to evaluate the production quality of new, unprocessed sheet material from UHWMPE 

manufacturers. Such methods are essential for assessing and predicting the acceptability of sheet goods prior to the curing/molding process 

relative to the product’s ballistic performance. The primary challenge all laboratories face when testing unprocessed UHMWPE is gripping 

the slippery material to achieve repeatable data. We have designed and developed a relatively simple, cost-effective punch test procedure that 

addresses the issues associated with gripping UHMWPE composites during tests. A test protocol is presented that is simple, and the overall 

execution of the technique does not impose significant expense for test fixtures. This report details design iterations for the test fixture, 

specimen geometry, and gripping methods. Punch test results from the final fixture concept and experimental procedures have demonstrated 

repeatability for both load-displacement response and failure behavior in an unprocessed UHMWPE cross-ply composite sheet configuration.

15. SUBJECT TERMS

punch experiment, UHMWPE, punch resistance testing, static punch strength testing

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OF ABSTRACT

UU

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OF PAGES

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David Gray

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(410) 306-0852

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Prescribed by ANSI Std. Z39.18
iii

Contents

List of Figures iv

List of Tables iv

1. Introduction 5

1.1 Initial Test Fixture Design...............................................................................................7

1.2 Novel Test Coupon Concept and Preliminary Results....................................................8

1.3 Test Fixture and Coupon Redesign ...............................................................................10

1.4 Punch Tool Geometry ...................................................................................................12

2. Initial Test Trial Results 14

3. Fixture and Process Improvements 17

4. Summary 19

5. References and Notes 20

Appendix. Punch Test Procedure 21

Punch Test Procedure 22

Distribution List 23
iv

List of Figures

Fig. 1 Adapted reference schematic of ASTM D6241’s punch-test fixture and setup..................6

Fig. 2 Details of bottom plate of new UHMWPE test fixture .......................................................7

Fig. 3 Sectioned view of test fixture with UHMWPE coupon. View on right is a blow-up of 

the sheet material and a knurled rod. .........................................................................................8

Fig. 4 Initial designs of 3 different coupon dimensions and shapes..............................................9

Fig. 5 Post-test photographs of coupon Design 1 and Design 2 ....................................................9

Fig. 6 Initial test results of UHMWPE cross-ply from different coupon designs........................10

Fig. 7 16 inch × 16 inch cruciform coupon in photograph and computer-aided design (CAD)..11

Fig. 8 Photograph: relocated knurled rods at outer plate edge with new cruciform geometry 

and wrapping of coupon. CAD cross-section: top plate raised to show coupon tabs..............11

Fig. 9 60-grit surface coating of top and bottom plates...............................................................12

Fig. 10 Hemispherical 1-inch-radius end punch’s detail and top and bottom views...................13

Fig. 11 Flat-ended punch’s detail and top and bottom views......................................................13

Fig. 12 8-inch-radius punch’s detail and top and bottom views..................................................14

Fig. 13 Load-displacement curve vs. punch geometry ................................................................15

Fig. 14 Damage-pattern impressions made on the UHMWPE coupons: a) 1-inch-radius 

hemispherical, b) 8-inch-radius, and c) 1-inch-radius flat.......................................................16

Fig. 15 SolidWorks3 CAD view and photograph of diamond-serrated plate surface and CAD 

details.......................................................................................................................................18

Fig. 16 Punch-test results for UHMWPE material with the 60-grit sand paper vs. diamondserrated surface finish ..............................................................................................................19

List of Tables

Table Average, Standard Deviation, and percentage of punch-tool maximum load...................17
5

1. Introduction

A novel punch test method was developed to support the ongoing efforts within the US Army 

Research Laboratory’s Specifications and Standards Office to establish a new military 

specification, MIL-DTL-32398 “Laminate: Cross-Plied Ultra-High Molecular Weight 

Polyethylene (UHMWPE) Unidirectionally Reinforced Plastic Armor”.1 Currently there are no 

mechanical testing methods available to assess the quality of unprocessed, unidirectional crossply UHMWPE sheet material from the manufacturers’ production lines. A quality-assurance

(QA) test methodology is needed to provide insight into the effects of material variability on 

ballistic performance. The test protocol developed in this effort resembles ASTM D6241.

2 In 

addition, as a standard to determine the punch strength, this test protocol offers a relatively

straightforward setup and cost-effective QA without the need for expensive test components. The 

ASTM D6241 standard utilizes a simple, supported test fixture that holds the coupon between 2

concentric plates with an internal diameter hole of approximately 5.9 inches and a flat-ended

plunger about 2 inches in diameter. 

Figure 1 is an adapted reference schematic of the ASTM D6241 test fixture and setup.
6

Fig. 1 Adapted reference schematic of ASTM D6241’s punch-test fixture and setup
7

1.1 Initial Test Fixture Design

Based on the fundamental concept of the ASTM punch technique, which uses a round fixturing 

theory and produces insufficient grip for UHMWPE sheet coupons, a new test fixture with a 

square boundary condition was designed and fabricated that would help prevent the material

from slipping during the applied punch loads. The square boundary conditions provide better 

support and facilitate loading of the UHMWPE cross-ply composite. The fixture comprises 2 

steel plates with external dimensions approximately 9 inch × 9 inch with a 4 inch × 4 inch

opening at the center. The bottom half of the plate is supported and bolted at each corner to four 

1.5-inch diameter steel posts. This allowed the plates to be suspended and thus provides enough 

clearance for the punch to travel below the test fixture, if needed. A 0.375-inch diameter hemispherical groove was machined on the contacting surface for base plate. The grooves were about 

0.5 inch from edge of the inner opening. 

Figure 2 shows the engineering drawing of the bottom plate of the test fixture. 

Fig. 2 Details of bottom plate of new UHMWPE test fixture
8

The unprocessed unidirectional cross-ply coupon is sandwiched between 2 plates similar to the 

ASTM D6241 procedure and then followed by a knurled rod that was placed in a slotted groove 

at all 4 sides. The length of the knurled rods was 6 inches. Since the UHMWPE sheet material is 

relatively pliable, the coupon was able to be wrapped under and over the knurled rod and then 

held down with the upper portion of the fixture. Figure 3 provides a cross-sectioned view of the 

coupon clamped between the top and bottom plates. This provides a high pinch force to mitigate 

slippage. However, experimental results from this initial concept proved only partially successful

with some slippage occurring. Another contributing factor for the slippage is the coupon 

geometry utilized. ASTM D6241 references a requirement of 10 mm (0.4 inch) of excess 

material to be extended past grip section. Use of that reference produced 3 unsuccessful designs 

for this application. The following sections of this report describe improvements that were made 

to further address gripping issues, including the novel coupon design developed. 

Fig. 3 Sectioned view of test fixture with UHMWPE coupon. View on right is a blow-up of the sheet

material and a knurled rod.

1.2 Novel Test Coupon Concept and Preliminary Results

Figure 4 shows the 3 different specimen configurations that were conceptualized to be adapted

into the new clamping fixture. These 3 configurations were all tested with the tabs wrapped 

around the knurled rods as described above. The variation was in the tab size and direction of the 

cut in the coupon to create the tab. The results from all 3 coupon designs were inconsistent as 

slippage of the coupons in the fixture remained to be a source of undesirable variability in the 

loading. Figure 5 shows a post-test photograph of coupon Design 1 and Design 2. These images 

reveal that some degree of slippage of the cross-ply material occurred. The black and red 

reference lines were traced with a Sharpie marker along the inside edge before and after testing, 

respectively. If no slippage had occurred, these lines would be similar to each other. The damage 

to the coupons was limited as ram displacement was stopped once a substantial drop in the load 

response was observed. 
9

Fig. 4 Initial designs of 3 different coupon dimensions and shapes

Fig. 5 Post-test photographs of coupon Design 1 and Design 2
10

Figure 6 provides a summary of the results from the initial test methodology and coupon designs. 

The punch force versus displacement shows a significant amount of variation. Results were 

inconsistent and slippage was evident from observation for each test coupon. Any indication of 

slippage invalidates the test data.

Fig. 6 Initial test results of UHMWPE cross-ply from different coupon designs

1.3 Test Fixture and Coupon Redesign

The coupon geometry was changed to a larger cruciform design as seen in Fig. 7 (the dimensions 

shown are in inches). The longer ends allowed the coupon to be wrapped around the knurled 

rods, which have been relocated to the outer plate edge changing the clamping means of the 

fixture. The cruciform ends are then inserted back in between the 2 plates gripping the

UHMWPE sheet in place as seen in Fig. 8.
11

Fig. 7 16 inch × 16 inch cruciform coupon in photograph and computer-aided design (CAD)

Fig. 8 Photograph: relocated knurled rods at outer plate edge with new cruciform geometry and wrapping of 

coupon. CAD cross-section: top plate raised to show coupon tabs.

An adhesively bonded 60-grit sandpaper (as referenced in ASTM D6241-04) was applied to the 

top and bottom plates’ contact surfaces to further assist in stopping slippage, as in Fig. 9. The 

ends of the cruciform are pulled through the inner opening to draw the material taut to remove 

any wrinkles or slack in the coupon. A series of incremental bolt-torque tests were performed to 

determine the necessary torque on the 3/8-inch grade-8 bolts clamping the coupon between the 

top and bottom plates of the fixture. A torque of 40 ft-lb was determined to be sufficient to 

eliminate slippage while under load without exceeding the bolt strength.
12

Fig. 9 60-grit surface coating of top and bottom plates

1.4 Punch Tool Geometry

In addition to enhancing the gripping techniques for UHMWPE materials, the effects of punchtool geometry were investigated to assess the unconventional use of a rectangular fixture to 

perform the compressive testing. It was desirable to have a large punch-contact surface to 

provide more uniform loading on the coupon. It was also desirable to have some radius on the 

punch to promote uniform contact with the specimen as the loading progressed. A large radius 

was used to minimize the tendency to separate or perforate the plies within the coupon and to 

provide a smooth transition at the interface where the coupon left the punch.

Three punch geometries were examined. One was a hemispherical shape with a 1-inch-radius 

end. The second has a flat bottom with a small radius (0.098 inch) at the cylinder wall as per the 

ASTM 6241. Lastly, the third punch had an end radius of 8 inches with a transitional radius of 

0.1875 inch. Figures 10–12 show the sectional drawing views (with dimensions in inches) and 

the top and bottom test views of each punch head that has traveled to a displacement of 

0.8 inches. The regions of contact between the punch and the test coupon can be seen in the 

drawings. The flat punch yields the highest contact area, followed by the 8-inch-radius end, and 

finally the hemispherical shape with significantly less area of contact. All 3 punch heads were 

2 inches in diameter and fabricated out of hardened steel. Three different punch designs were 

evaluated by systematically conducting a series of load experiments for each punch on the new 

cruciform-shaped coupon.
13

Fig. 10 Hemispherical 1-inch-radius end punch’s detail and top and bottom views

Fig. 11 Flat-ended punch’s detail and top and bottom views
14

Fig. 12 8-inch-radius punch’s detail and top and bottom views

Distinct demarcation of the coupon from edges formed by the end and side walls of the punch 

raised concerns that the flat-bottom punch may not test uniformly or could create undesirable 

loading at its edge. The hemispherical 1-inch punch produced noticeable separations of the fibers 

within the layers and had more variability in failure loads. This is largely due to the interaction of 

the relatively small radius with the 0/90 layup of the plies, also seen in Fig. 11.

2. Initial Test Trial Results

Experiments with the new gripping technique and different punch shapes were conducted on 

unprocessed UHMWPE cross-ply materials in the cruciform-shape geometry as previously

discussed. The load frame’s cross-head speed was set to 2 inch/minute as referenced in ASTM D 

6241. Results of the load-displacement plots for each punch shape are shown in Fig. 13. The flatended punch obviously produced the highest load to failure as well as showing an effectively 

stiffer response. The results from the 8-inch-radius end punch reveal a drop of 20% in the peak 

load and that the 1-inch-radius punch produced the lowest load to failure. The flatter tool has less 

sliding and engages more fibers. Typical damage-pattern impressions on the coupons, due to 

interaction with the punch, are shown in Fig.14a–c for the hemispherical, 8-inch-radius, and flatended punches, respectively.

 

 
15

Fig. 13 Load-displacement curve vs. punch geometry

0

500

1000

1500

2000

2500

3000

3500

4000

0 0.2 0.4 0.6 0.8 1 1.2

Compressive Load (lb)

Cross Head Displacement (in)

Punch Loading and Tool End Shape

1" RAD #10 

1" RAD #11 

1" RAD #12 

8" RAD #13

8" RAD #14 

8" RAD #15 

FLAT #18 

FLAT #19 

FLAT #20
16

Fig. 14 Damage-pattern impressions made on the UHMWPE coupons:

a) 1-inch-radius hemispherical, b) 8-inch-radius, and c) 1-

inch-radius flat.

(a)

 (b)

 

 (c)
17

Table 1 shows the average maximum failure load and apparent stiffness or slope of the loaddisplacement curve for each of the punch geometries along with the associated variations. The 

term “apparent stiffness” in this report is defined as the change in load relative to the change in 

cross-head displacement. While the sampling sizes were limited to 3 tests for each condition, the 

least amount of variation in maximum load to failure occurred with the use of the 8-inch-radius 

punch. The 1-inch-radius hemispherical punch’s head had a significantly lower load to failure 

with more variation in this load due to the fibers sliding off the rounded punch.

The results also indicate that for a given punch shape, the variations of the apparent stiffness are 

less than the variations of the loads to failure. The apparent stiffness was also found to be 

greatest for the flat punch and lowest for the 1-inch-radius punch. The flatter tool has less sliding 

and has more fibers engaged. The relative differences in apparent stiffness for the 3 punch 

geometries are similar to that of the differences in load to failure.

There are substantial differences in the way the hemispherical shaped punch and the flat-end 

punch interact with the UHMWPE coupon. This is probably due to the effective contact area 

between the steel punch and the UHMWPE material. The concern that the flat-end punch would 

have more detrimental edge effects than the 8-inch-radius punch did not bear out in the results. 

Based on these results, the flat-end punch would be used for all tests going forward due to its 

higher peak loads before lamina failure. Step-by-step test procedures are detailed in the 

Appendix.

Table Average, Standard Deviation, and percentage of punch-tool maximum load

Shape

Avg Max 

Load

(lb)

SD Max 

Load

(lb)

SD % of 

Load

Avg

Avg Slope 

(lb/in)

SD Slope 

(lb/in)

SD % of 

Slope Avg

Hemi 1687 235 13.9% 3863 290 7.5%

8-in RAD 2867 40 1.4% 7019 309 4.4%

Flat 3478 78 2.2% 8277 307 3.7%

3. Fixture and Process Improvements

Another enhancement to achieve consistent grip clamping for a range of UHMWPE materials 

types was also investigated. Both upper and lower plate surfaces with the 60-grit adhesivebacked sandpaper were replaced with steel plates having a 1/16-inch diamond-serrated finish 

machined directly into the contact surfaces. Figure 15 shows the CAD and photograph of the 

finished plates with the diamond-serrated pattern. It was found that the diamond-serrated surface 

finish substantially increased the clamping efficiency (i.e., decreased the material slippage). This 

produced more consistent failure loads. (The grooves in the base plate are artifacts of past 
18

revisions and are no longer needed for future fixture construction.) The serrations used were 

about .025-inch deep with a pitch of .05 inch as shown in the detail view in Fig. 15. Figure 16

shows a comparison of 3 separate tests with the diamond-serrated plates and a typical sandpaper 

test on UHMWPE material. Use of the diamond-serrated pattern produced an increase in load of 

about 20% over the original sandpaper design. It was also found that the repetitive torquing and 

untorquing of the bolts developed galling and friction between the bolt and washer. This friction 

reduces the torque employed to apply clamping force to the fixture. This problem was reduced 

though the use of 2 grade-8 hardened washers under each bolt head and exchanging them for 

new ones every 15–20 coupons. Using this procedure the fixture has maintained the desired 

clamping grip load. 

Fig. 15 SolidWorks3 CAD view and photograph of diamond-serrated plate surface and CAD details
19

Fig. 16 Punch-test results for UHMWPE material with the 60-grit sand paper vs. diamond-serrated 

surface finish

4. Summary

A novel punch-test method was developed for evaluating unprocessed UHMWPE cross-ply sheet 

material. Development of this test procedure involved design of a gripping strategy to eliminate 

slippage of the material and the establishment of preferred punch-shape geometry. There are 

substantial differences between the interaction of the hemispherical punch and the UHMWPE 

sheet and the interaction of the flat-ended and 8-inch-radius ended punches. The flat-ended 

punch provided the highest load to failure and effective stiffness. The coupon geometry was 

redesigned to a larger cruciform pattern with longer ends that allows it to be wrapped around 

knurled rods located on outer-plate edge. The use of a machined diamond-serrated surface for 

gripping was found to be more desirable experimentally than adhesively attached sandpaper’s

grit in light of consistency of results and ease of performing the testing. The preferred texture or 

coarseness of the diamond serrations could be dependent upon the material and thickness of the 

coupons being tested. It was also noted that most UHMWPE sheet material was sensitive to 

relaxation/creep after the coupon was torqued into fixture and let stand for periods greater than 

10 minutes. The data on material responses to testing will be published in future reports. 
20

5. References and Notes

1. MIL-DTL-32398. Laminate: cross-plied ultra-high molecular weight polyethylene 

(UHMWPE) unidirectionally reinforced plastic armor. Aberdeen Proving Ground (MD): 

Specifications and Standards Office, US Army Weapons and Materials Research Directorate; 

2013 Jun 9.

2. ASTM D 6241 Standard test method for the static puncture strength of geotextiles and 

geotextile-related products using a 50-mm probe. West Conshohocken (PA): 

ASTM International; 2009. 

3. Dassault Systemes SolidWorks Corp., 300 Baker Avenue Concord, MA 01742.
21

Appendix. Punch Test Procedure
22

Punch Test Procedure

1. Mount the bottom test-frame fixture to the load test frame. Ensure the bottom test fixture is 

properly bolted and tightly secured to the load test frame and that the center axis of the 

fixture is aligned with the load axis of the test frame.

2. Affix the punch head to the load cell. Be sure the load cell meets the load capacity for the 

test. 

3. Inspect the fixture for damage and residual material in between the serrations. Clean the 

surfaces, if necessary.

4. Place the coupon on top of the bottom fixture. Position and center it relative to the test 

fixture.

5. Position the top plate over the test specimen and rest it on a wedge to leave an 

approximately 3/8-inch gap between the bottom and top plates. 

6. Place the knurled rod on top of the test specimen where it extends from the test fixture, and 

bend the material over the rod. Insert the rest of the material back between the 2 plates. 

Repeat for the other 3 sides. There should be enough material so that it may protrude into 

the fixture.

7. Remove the wedge and lower the top plate of the test fixture and snug the bolts. 

8. Torque each bolt (3/8 inch, grade 8) to 40 ft-lbs. tighten the bolts in crisscross pattern. 

Torquing the bolts should pull the material taut. Note: 2 thick, hardened washers should be 

placed on each bolt so that the washers are between the top plate and bolt head to reduce 

friction.

9. Lower the punch head until it comes in contact with the top of the test specimen.

10. Begin testing with the crosshead speed at 2 inches/minute. Record the load, displacement, 

and time.

11. Stop the test when the load drops off significantly.

12. Take the test specimen out of the fixture after removing all of the bolts securing the top 

plate. 

13. Inspect the fixture for damage and residual material in between the serrations. Clean the 

surfaces, if necessary.

14. Repeat Steps 3 through 13 for the next test coupon.
23

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