Fabrication of Novel Bumper and Skirt 

Components for a Ground Vehicle 

by William A. Spurgeon 

and David J. Thomas 

Approved for public release; distribution is unlimited. 
J 

The findings in this report are not to be construed as an official 

Department of the Army position unless so designated by other 

authorized documents. 

Citation of manufacturer’s or trade names does not constitute an 

official endorsement or approval of the use thereof. 

Destroy this report when it is no longer needed. Do not return 

it to the originator. 
Army Research Laboratory 

Aberdeen Proving Ground, MD 21005-5069 

ARL-TR-2327 SeDtember 2000 

Fabrication of Novel Bumper and Skirt 

Components for a Ground Vehicle 

William A. Spurgeon 

Weapons and Materials Research Directorate, ARL 

David J. Thomas 

U.S. Army Tank-Automotive Research, Development, 

and Engineering Center, Warren, MI 
Abstract 

This report discusses the materials selection for and fabrication of novel “bumper” and skirt 

panels for an experimental ground vehicle improvement project. These components were 

fabricated from E-glass reinforced polyurethane resin so that they would have a unique 

combination of rigidity and flexibility required for successful field use. Alternative components 

for future consideration are discussed, and some initial work on adhesive bonding of polyurethane 

matrix composites is presented. 
Acknowledgments 

The author would like to thank David Hansen of the U.S. Army Tank-Automotive Research, 

Development, and Engineering Center (TARDEC) for suggesting and financially supporting this 

effort. Craig Hughes of the Keewenaw Research Center, Houghton, MI, provided the drawings 

in Figures 1 and 2. Michael Leadore of the U.S. Army Research Laboratory (ARL) provided 

Figure 10. Eric Fine, Michael Poot, and Scott Vandry of the University of Delaware, and 

Christopher Klug of the University of Maryland each helped with the parts fabrication, as did 

Melissa Klusewicz and, especially, John Brown of ARL. Alan Teets of ARL assisted with the 

mechanical testing. Critical readings by Peter G. Dehmer, Dana M. Granville, and Robert Lieb 

significantly improved this report. Everyone’s help .was critical in successfully completing this 

project and is gratefully acknowledged. 

. . . 

111 
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iv 
Table of Contents 

1. 

2. 

2.1 

2.2 

3. 

4. 

4.1 

4.2 

4.3 

4.4 

5. 

5.1 

5.2 

6. 

7. 

. . . 

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..*.......... . . . . . . . . . . . . . . ill 

List of Figures vii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

List of Tables ix 

. . . . . . . . . . . . . . ..*............. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 

Materials Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 

Matrix Polymer ................................................................................................ 1 

Glass Reinforcement ........................................................................................ 4 

Composite Material Mechanical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 

Composite Fabrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 

General Considerations .................................................................................... 7 

Flat Panel Fabrication ....................................................................................... 8 

Skirt Panel Fabrication ..................................................................................... 10 

Bumper Panel Fabrication ................................................................................ 15 

Possible Design Alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 

Skirt Panels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Bumper Panels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..I...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

21 

21 

Conclusions.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 

References 27 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Appendix: Adhesive Bonding Adiprene Matrix Composites: Preliminary 

Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 

Distribution List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 

Report Documentation Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 

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vi 
List of Figures 

Figure 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

8. 

9. 

10. 

11. 

12. 

13. 

14. 

A Drawing of the Proposed Skirt Panel Required for the Project .*.......................... 

A Drawing of the Proposed Bumper Panels Required for the Project . . . . . . . . . . . . . . . . . . . . . . 

The 24-oz,5 x 4 Woven Roving Fabric and the 15-oz,2 x 2 Twill 

Weave Fabric . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

A Typical Flexure Displacement vs. Applied Load Curve for an 

Adiprene Composite Sample . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

The “V” Mold Used to Fabricate the Skirt Panels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

A Skirt Panel Prior to Final Trimming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

A Skirt Panel After Trimming to Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

The Left-Handed Box Mold Used to Fabricate Bumper Panel 

Components in the Attempt at a Full-Up Bumper Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

The Cross and Crown Cutting Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

The lo-Ply Part Fabricated on the Male Mold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Two Initial Subassemblies for a Bumper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

The Open Box Subassembly, Oversized Top, and Four Special L Brackets 

Ready for Final Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Bonding the Top to the Rest of the Bumper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Completed Left and Right Bumpers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

PaJg 

2 

3 

6 

9 

11 

13 

14 

16 

17 

19 

20 

22 

23 

24 

Vii 
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. . . 

Vlll 
List of Tables 

Table 

1. 

.g 2. 

3. 

J 

4. 

A-l. 

A-2. 

Solvent and Water Stability Data for Adiprene L-100 With Catur 21 . . . . . . . . . . . . . . . . . . . . . 

Tensile Strengths (ksi) for E-Glass-Adiprene Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Flexure Strength and Modulus Data for E-Glass-Adiprene Composites................. 

The Sequence of Release and Bleeder/Breather Fabrics Used in the 

Composite Fabrication Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Adhesive Bond Strengths for Glass-Reinforced Adiprene Matrix Composite 

to Itself . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Adhesive Bond Strengths for Glass-Reinforced Adiprene Matrix Composite 

to Other Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..*............................................. 

‘J 

i 

ix 
INTENTIONALLY us-r BLANK. 

X 
1. Introduction 

d 

4 

J 

d 

In support of an experimental Army ground vehicle improvement program, the U.S. Army 

Research Laboratory (ARL) composite development team was asked to fabricate four new 

composite vehicle components (shown as conceptual drawings in Figures 1 and 2). The two 

“bumper” panels were selected to fill out the front corners of the vehicle. The other two 

components are L-shaped skirt panels that get bolted to the bumper panels. These components 

were fabricated from glass-reinforced polyurethane resin. Skirt panels made from this composite 

material are stiff enough not to wobble or sway while the vehicle is being driven, but retain the 

ability to flex when necessary. The composite is also appropriate for the bumper panels, which 

need to be able to compress or flex on impact and return to their original shape without breaking. 

The mounting arrangements for the bumpers to the vehicle and the skirt panels to the bumpers 

must also be able to sustain the impact. The designs considered in this report are a first attempt 

at the necessary components. 

This report discusses the materials selection for the project, mechanical properties of the 

composite materials, and component fabrication. The results of the field evaluation of the 

components were satisfactory and will be reported separately. Section 5 discusses alternative 

components for future consideration that could work as well or better and would be easier to 

fabricate. Some work on the adhesive bonding of the polyurethane matrix composites was also 

needed to complete the project and is discussed in the appendix. 

2. 

2.1 

Materials Selection 

Matrix Polymer. The matrix polymer resin selected for this project was Adiprene L100 cured with Catur 21. Both the resin and curing agent were obtained from the Uniroyal 

Chemical Company.* Dr. Roger Crane of the Naval Surface Warfare Center (NSWC), 

* Uniroyal Chemical Company, Inc., World Headquarters, Middlebury, CT 06749. 

1 
omTW 

Figure 1. A Drawing of the Proposed Skirt Panel Required for the Project. 

2 
Figure 2. A Drawing of the Proposed Bumper Panels Required for the Project (Mirror 

Image Versions of Both the Skirt and Bumper Panels Were Also Needed). 
Carderock Division, Bethesda, MD, provided the original recommendation to use this resin 

based on his extensive experience with such resins. 

In previous ARL work [l], this polyether-based polyurethane resin exhibited a hardness of 

Shore-A 85, which is somewhat harder than an automobile tire (Shore-A 75) and softer than a 

typewriter roller (Shore-A 90). Nearly all of the toluene-diisocyanate it contains is chemically 

bound (as opposed to free), which makes it relatively safe to handle. Its most desirable feature is 

that it has a long working life at temperatures below 150 OF, and it cures quickly at temperatures 

above 212 “F. Its glass transition temperature is below the -60 “F limit of the differential 

scanning calorimeter used for this test. The resin had been used in other ARL projects that 

required a semi-flexible composite. Its selection followed an extensive search for appropriate 

thermoset polyurethane resins through vendor contacts and in-house tests. Its cost depends on 

the quantity purchased, but it is under $5/lb when purchased in 5-gal containers (convenient for 

laboratory work) that weigh approximately 45 lb. 

Solvent and water stability tests were run as part of a previous project; the results are 

summarized in Table 1. The hydrolytic stability of the resin was not as good as might be desired, 

but was deemed suitable to use for this project. A strong point in its favor is that the Navy uses 

the resin on underwater control surfaces [2]. In Navy tests, it exhibited no degradation in 

strength after a 2-year soak in 75 “F water, although it does degrade at higher temperatures as 

indicated in Table 1. 

2.2. Glass Reinforcement. Standard E-glass was selected for a reinforcement fiber since 

the application did not require the higher-strength, more expensive S-2 glass. The tensile 

strength of the E-glass is not dramatically lower than that of S-2 glass (500-550 vs. 

665-700 ksi). It is much less expensive than S-2 glass ($1.29 vs. _ $7/lb).* Another advantage 

is that its composites can generally be machined with standard metal cutting tools, whereas S-2 

glass composites usually require diamond-tipped tools. 

* Owens-Coming Brochure. “Advanced Materials.” Pub. No. 1 -PL- 16052-D, Owens-Coming World Headquarters, 

One Owens-Coming Parkway, Toledo, OH 43659, September 1996. 

4 
Table 1. Solvent and Water Stability Data for Adiprene L-100 With Catur 21 

Strength 

for 200% 

Volume Tensile Elongation Elongations 

Test Performed Material Swell Retained Retained Retained 

(%I (%I (%> (%ro> 

Immersion in Adiprene L- 100 

Fuel-B 70/30 With Catur 21 18.12 51.77 78.43 76.68 

150-Octane/Toluene 

for 7 Days at RTa 

Immersion in Adiprene L- 100 

IP-8 ST Reference Fuel With Catur 21 13.19 55.49 79.99 76.68 

for 7 Days at RT 

Immersion in Adiprene L- 100 

Hydraulic Fluid With Catur 21 3.11 75.72 93.66 87.33 

for 7 Days at RT 

Immersion in Adiprene L- 100 

Water With Catur 21 27.52 33.26 39.87 105.43 

for 14 Days at 160 OF 

>--- &-- ^__^ &.__A 

Two glass fabric styles were used which are shown in Figure 3. The first was a relatively 

stiff 5 x 4, 24-0~ woven roving that contributed about 30 mil per ply to the composites made in 

this project. This fabric was made from Owens-Corning’s E-glass roving and was woven by 

Owens-Corning Fabrics.* It had an Owens-Corning Type 111 epoxy-polyester-vinylester 

compatible sizing. The other fabric was a very flexible 15-oz, 2 x 2 twill weave that contributed 

about 15 rnil per ply to composites. It was obtained from Fabric Development, Inc.,t and is 

made from PPG E-glass. $ This fabric has PPG-type 2002 sizing that is epoxy, polyester, and 

cyanate-ester compatible. 

* Owens-Corning Fabrics, 1851 Seguin Road, New Braunfils, TX 78130. 

+ Fabric Development Inc., 1217 Mill Street, Quakertown, PA 18951. 

$ Pittsburgh Paint and Glass, 1 PPG Place, Pittsburgh, PA 15272. 

5 
5X4 WOVEN ROVING I 

\ 

2x2 TWILL WEAVE 

Figure 3. The 24oz, 5 x 4 Woven Roving Fabric (Left) and the 15oz, 2 x 2 Twill Weave Fabric (Right). 

L 
3. Composite Material Mechanical Properties 

The mechanical properties of the E-glass-Adiprene composites have not been previously 

measured. The tensile strengths were measured per the American Society for Testing and 

Materials (ASTM) standard-D638 [3] for both types of fabric. Dumbbell-shaped samples were 

stamped out using a rubber cutting die. Two sets of samples were prepared: one with the sample 

axis along both the warp direction (the long direction of the roll), and the other with the sample 

axis in the orthogonal fill direction. The test results are presented in Table 2. It was expected 

that the test results for the two fabric styles would be quite different. 

Table 2. Tensile Strengths (ksi) for E-Glass-Adiprene Composites 

The apparent flexure strength and modulus of the composites were also measured per ASTM 

D790-96A [4]. These results are presented in Table 3. The samples for this test were stamped 

out of a flat sheet of material using a die 1 in wide x 6 in long. The apparent flexure strength 

was considered the maximum load the samples will support in the flexure test. The samples do 

not actually break; rather, they continue to bend as the test instrument tries to increase the load. 

A typical flexure displacement vs. applied load curve is shown in Figure 4. The samples return 

to their original shape when the load is removed. 

4. Composite Fabrication 

4.1. General Considerations. All Adiprene composite fabrication was done by hand using 

wet layup techniques. This was done to make a composite that was somewhat resin rich for 

flexibility and, also, for convenience because of the small number of parts needed. A new 

7 
Table 3. Flexure Strength and Modulus Data for E-Glass-Adiprene Composites 

Fabric Style 1 Flexure Strength Flexure Modulus 

Twill Warn 

(ksi) 

5.82 *to.65 

(msi) 

1.07 * 0.18 

Twill Fill 5.89 + 0.33 1.01 It 0.13 

Roving Warp 7.05 i 0.28 1.48 * 0.07 

Roving Fill 7.23 * 0.63 1.29 f 0.09 

vacuum-assisted resin transfer molding (VARTM) technique known as “Vmin” has been 

developed at ARL for fabricating composites with low-fiber volume percentages [5]. If more 

parts were needed, this would have been the fabrication method of choice. For large volume 

production, a regular resin transfer molding process might be the preferred fabrication method. 

In processing the composite parts, it was necessary to draw excess resin through the top and 

bottom surfaces of the part rather than just from the sides. To effect this, the stack of release 

films and breather fabrics shown in Table 4 was employed. It was absolutely necessary to use 

this arrangement to obtain a part free of objectionably large voids. 

The Adiprene resin was preheated to 150 OF prior to being weighed out. One hundred and 

five percent by weight of the stoichiometric quantity of room temperature Catur 21 was then 

weighed out and thoroughly mixed with the Adiprene. One percent (by weight) of graphite 

powder (Fischer Grade 38*) was added to improve the ultraviolet (UV) stability of the polymer 

by making it black. In actual use, the parts would be painted or otherwise covered and thus 

protected from UV radiation. 

4.2 Flat Panel Fabrication. Flat panel layups using the woven roving fabric were done on 

a heat table warmed to 140 “F, to ensure that the viscosity of the mixed resin would remain low. 

The resin will not cure below 212 “F, although it will hydrolyze and harden slowly in moist air. 

After vacuum bagging, the parts were heated to 165 “F and held for 1 hr, heated quickly to 

* Fischer Scientific, 711 Forbes Avenue, Pittsburgh, PA 15219-4785. 

8 
14 

12 

30 

8 

6 

4 

2 

0 

- 

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 

Displacement in 

Figure 4. A Typical Flexure Displacement vs. Applied Load Curve for an Adiprene Composite Sample. 
Table 4. The Sequence of Release and Bleeder/Breather Fabrics Used in the Composite 

Fa .brication Process 

Capran Vacuum Bag” 

10-0~ Spun Polyester Breather Fabric’ 

l/4-in Aluminum Caul Plate or Capran Sheeta 

II Nonporous Teflon-Coated Glass Release FilmC 

A8888 Green Porous Release Fabricd 

4-0~ Spun Polyester Breather Fabrice 

II A8888 Green Porous Release Fabricd (2 Plies) 

II Porous Teflon-Coated Glass Release Filme 

Fabric Stack 

Porous Teflon-Coated Glass Release Filmf 

4-0~ Spun Polyester Breather Fabrice 

II Porous Teflon-Coated Glass Release Filme 

Note: All materials were obtained from Northern Fiberglass Sales, Inc., 

P.O. Box 2010, Hampton, NH 03843-5098. 

a Capran 5 12,0.002 in thick. 

b Part No. RC-A3000-10, 10-0~ nonwoven polyester bleeder/breather. 

’ Richmond 200TFNP release fabric. 

d Richmond A8888 open-weave polyamide release fabric. 

’ Part No. RC-A3000-4,4-oz nonwoven polyester bleeder/breather. 

f Richmond 200 TFP release fabric. 

II Mold Release Caul Plate or Hot Table 

185 “F for 30 min, then heated rapidly to 250 “F and held for 90 min. This curing cycle was also 

used for the molded parts. The cure cycle allowed time for the viscous resin to flow and better 

wet-out the part, and for volatile materials to be removed from the part. Two 34-in x 50-in 

panels of flat stock and several smaller panels were made without incident in this manner. 

4.3 Skirt Panel Fabrication. A V-shaped 0.5-n-r thick aluminum mold, 48 in on each side 

and 48 in wide, was used to fabricate the L-shaped skirt panels. The prepared mold, with the 

bottom three layers of the stack of release and breather fabrics in place, is shown in Figure 5. A 

0.38-in radius was built into the mold at the joint. The side brackets hold the large sides of the 

mold at a 90” angle. They were generally removed during the layup process, then replaced after 

10 
11 
bagging. The mold was preheated to 150 OF in a large oven prior to the layup process. Most of 

the skirt was fabricated using only eight plies of the woven roving fabric, which resulted in a 

thickness of about 0.23 in. Four additional plies of the woven roving were added to the portion 

of the skirt that would be attached to the bumper, resulting in a total thickness in this area of 

about 0.35 in, which was required to stiffen and strengthen this part of the skirt. 

Y 

The woven roving fabric did not conform well to the 0.38~in radius of the mold. As a 

consequence, the radius on the outside of the skirt panel was closer to 0.75 in. This would not 

present a problem in using the skirt; however, the inside of the skirt panel had a much smaller 

radius. This, too, would not present a problem as long as the bumper panel was made to fit to the 

smaller radius. The main problem was that excess resin from the layup process tended to sink to 

the bottom of the mold where it partially filled the inner radius of the part. An extra 6-in-wide 

strip of 4-0~ breather fabric placed in this area did not soak up all of the excess. The excess resin 

that remained after curing was either cut away with sharp knives or sanded away with a disk 

sander. The excess could have been left in place, except for the portion that joins the bumper. 

l 

Three parts were made using this mold. In the first, the mold was set with one edge flat 

against the worktable. This arrangement allowed several plies to slip down during the vacuum 

bagging operation, These slipped plies caused a wrinkle in the fabrics in the joint, and 

consequently, a rejected part. For subsequent parts, the mold was placed in a cradle, with the 

radiused joint at the bottom and both sides sloping upward. A second part came out very well. 

On the third attempt, one of the side braces was left off and the mold slipped away from a 90” 

angle by about 7”. This part was still acceptable since it could be pushed into shape very easily. 

All three parts were made with the fill direction of the fabric vertical in the finished part. The 

fabric was only 50 in wide, and fabricating the part in this manner allowed the most economical 

use of the fabric. 

. 

The molded skirt panel was trimmed to the desired size and shape using an ordinary 

saber saw with a steel blade. A skirt panel prior to trimming is shown in Figure 6, and a finished 

panel is shown in Figure 7. Each finished panel weighed 14.8 lb. 

12 
13 
Figure 7. A Skirt Panel After Trimming to Size. 

f 
4.4. Bumper Panel Fabrication. The bumper panels in Figure 1 were surprisingly hard to 

fabricate as drawn, and only one serious attempt was made to do so. It was necessary to make 

the part on a male mold-the 90” angles made using a female mold too difficult for a wet layup 

or a VARTM process. Laying of the dry fabrics for the VARTM process would require bonding 

the individual fabric plies to each other with an adhesive that is soluble in the resin. It was 

expected that extensive experimentation would be required to identify an appropriate adhesive; 

this could take longer than the time available for the project. An alternative to this approach 

would be a stitched preform, but this would require extensive lead time. 

Left- and right-handed male molds, 0.38 in smaller on all sides than the desired part size, 

were fabricated from l-in Grade-A plywood. The molds were first dried in an oven at 250 “F for 

4 hr. They were then coated with multiple coats of Shell Epon-826 epoxy resin,* and cured with 

Shell Epicure 3140 (formerly V40)+ at 160 OF. The epoxy resin was sanded smooth between 

coats and given a final cure at 250 OF for 2 hr. A trial vacuum bag was built over each mold to 

ensure that it was leak tight prior to further preparation. 

Once the molds were vacuum tight, five coats of Frekote-700-W mold release* were 

applied. One ply of 5-mil nonporous Teflon-coated glass release fabric was then placed over the 

mold and secured in place with high-temperature tape. The bottom three layers of 

release/breather fabrics listed in Table 4 were then attached to the mold, which was then ready 

for use. A mold prepared to this stage is shown in Figure 8. 

The 15oz, 2 x 2 twill weave fabric was selected for fabrication of the part. This fabric is 

very flexible and can drape over the sides of the mold with ease. The fabric plies were cut in 

“cross” and “crown” patterns, shown in Figure 9. These were alternately applied to the mold. 

* Inland Leidy, 2225 Evergreen Street, Baltimore, MD 21216. 

’ Miller-Stephenson Chemical Company, Inc., George Washington Highway, Danbury, CT 06810. 

’ The Dexter Corporation, Frekote Products, 1 Seabrook Drive, Seabrook, NH 03874. 

15 
Figure 8. The Left-Handed Box Mold Used to Fabricate Bumper Panel Components in the 

Attempt at a Full-Up Bumper Panel. 

16 
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. . 

: 

i 

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‘/ -. I 

:.r.-.. ,_ : . . _ _. .:. 

1 ’ 

17 
The crown pattern was selected with the expectation that it would not need to be stitched 

together in a wet layup process. If stitching had been needed (none was), it was also expected 

that the stitching could be done most easily in this configuration. The side cut in the crown plies 

was rotated to different sides on successive crown plies. 

A lo-ply part (0.150 in thick) fabricated in this manner is shown in Figure 10. The biggest 

problem with the part was that none of the edges turned out even minimally well. A crossshaped piece of 0.25-in silicone rubber was placed between the release/breather fabrics and the 

vacuum bag to help form the edges of the part; however, this did not help sufficiently. The edges 

would not have been a problem with a female mold. A female mold, through, presented other 

difficulties, as previously described. 

The other problem encountered was that the part had to be cut to remove it from the mold, 

despite all precautions taken to apply sufficient release materials. The part quality would have 

undoubtedly improved on subsequent fabrication attempts. However, there was no expectation 

that a satisfactory part could have been made on a male mold. Since this was the case, another 

approach to making a bumper panel was adopted. 

In the new approach, two flat 8-ply panels of the 24-0~ woven roving, each 34 in x 50 in, 

were first fabricated. For each bumper, five pieces of material corresponding to the four sides 

and an oversized top were cut from the flat stock. Two aluminum 90” V molds were used to 

fabricate eight L brackets approximately 10 in per side. The two wooden molds were used to 

fabricate special L brackets with the proper acute and obtuse angles, four for each bumper. Each 

of the 16 brackets was made with 10 plies of the 15-0~ twill weave fabric. 

The 90” L brackets and the flat stock for the two longer sides of the bumper were then 

bonded together in a simple fixture with Adiprene L-100 resin. Adhesive bond strength data for 

this resin is presented in the appendix. After trimming, these subassemblies were similar to 

those shown in Figure 11. The other two pieces of side flat stock were then bonded on, resulting 

in a 4-sided open box subassembly. This subassembly, four special L brackets, and the top are 

. 

18 
Y 

19 
* 

T--L’. 

Figure 11. Two Initial Subassemblies for a Bumper. 
shown ready for final assembly in Figure 12. Figure 13 shows the top being bonded to the open 

box. The edges of the top were then trimmed to size. Finally, about 1 in of unreinforced 

Adiprene resin was poured inside the bumper and cured. This was added to strengthen the 

bumper to what was thought to be an acceptable level. The finished bumpers are shown in 

Figure 14. Each weighed about 18.7 lb. 

5. Possible Design Alternatives 

5.1. Skirt Panels. The L-shaped skirt panels in this project require a mold for fabrication. 

Although the mold can be a relatively simple one-sided affair (such as the mold used in this 

project) for wet layup or VARTM, it complicates the fabrication of the panels. Aligning the 

panels for trimming to size is also somewhat complicated. Using two flat panels instead of the 

one L-shaped panel is a much simpler possibility to be considered for future efforts. The two 

panels would be able to move independently and could be made stiffer at the top if necessary. 

The two flat panels could also be joined using a molded rubber part which would allow them to 

move with a modest degree of independence. This would not be a difficult modification to 

implement. 

5.2. Bumper Panels. The bumper panels fabricated for this project are complicated parts. 

Several simpler alternatives are possible and should be explored. The first of these is a thick (1.5 

to 2 in), 5-sided box, similar to that shown in Figure 1, molded from hard polyurethane resin. 

The Adiprene L-100 is probably stiff and hard enough for this. If not, it can be stiffened by 

adding short (0.25 in) milled glass fibers to the resin. To attach the skirts, prefabricated glassreinforced polyurethane matrix composite panels would be bonded to the hard rubber bumper on 

the four sides that are attached to the skirt panels or to the vehicle. These four panels would be 

molded in (if possible) and would not overlap, Holes for passing bolts or nuts and washers 

would also be molded into the polyurethane resin. This appears to be the simplest, least 

expensive option for the bumper. 

21 
. 

R 

22 
23 
L 

24 
A variation on this theme would shape the composite panels so that they also bond to the top. 

This would increase the bond area between the panels and the molded resin, thereby 

strengthening the part. 

A third option would be to fabricate a composite part using only the cross pattern in 

Figure 10. This would then be placed in a female mold, and the thick polyurethane resin box 

would be poured in to finish the part. This seems more complex than necessary, however. 

6. Conclusions 

The materials selection for and fabrication of successful bumper and skirt panels for a niche 

application on an experimental ground vehicle have been described in detail. Possibilities for 

other uses of the bumper panels on Army ground vehicles should be explored. 

25 
L 

INTENTIONALLY LEFT BLANK. 

26 
7. References 

1. Spurgeon, W. A., R. B. Dooley, E. Rigas, D. Spagnuolo, A. Teets, and J. Bennett. 

“Development of a New Low Signature Track Skirt.” ARL-TR-2141, U.S. Army Research 

Laboratory, Aberdeen Proving Ground, MD, 1999. 

2. Crane, Roger. Personal communication with William Spurgeon. Naval Surface Warfare 

Center, Bethesda, MD, 1.997. 

3. American Society for Testing and Materials. Standard Test Method for Tensile Properties of 

Plastics. ASTM D638-97, West Conshohocken, PA, 1997. 

4. American Society for Testing and Materials. Standard Test Methods for Flexural Properties 

of Unreinforced and Reinforced Plastics and Insulating Materials. ASTM D790-96A, West 

Conshohocken, PA, 1996. 

5. Spurgeon, W. A. “Method of Fabricating Polymer Matrix Composites With a Low Volume 

Fraction of Fiber Reinforcement.” ARL Invention Disclosure, March 1999. 

27 
INTENTIONALLYLEFTBLANK. 

28 
Appendix: 

Adhesive Bonding Adiprene Matrix 

Composites - Preliminary Results 

29 
INTENTIONALLYLEFTBLANK. 

30 
The ability to adhesive-bond the Adiprene L-100 matrix composite to itself was clearly 

needed for this project. A number of commercially available adhesives were tested, as was the 

Adiprene resin itself. The flexible adhesives included: Scotch-Grip 1300 Rubber & Gasket 

Adhesive,* Scotch-Grip 1357 High Performance Contact Adhesive,* and PR 1440-2-B 

polysuhide adhesive?. Chemlock 220’ and Chemlock 233$ adhesives, as well as Shell Epon-828 

epoxy§ were tried as nonflexible adhesives. Shell Epon-828 epoxy was cured with 40 weightpercent Shell Epicure 3140 (formerly V40),** and was thickened with 25 weight-percent of 

milled E-glass fibers. Coupons of the Adiprene matrix composite 3 in long x 1 in wide were 

bonded together over a l-in-long strip, and pulled apart, per American Society for Testing and 

Materials (ASTM) standard D3164-92A.’ The test results are shown in Table A-l. 

Table A-l. Adhesive Bond Strengths for Glass-Reinforced Adiprene Matrix Composite 

to Itself 

Adhesive Strength 

(lb) 

Chemlock 233 No Bond 

Chemlock 220 257 rt 90 

Scotch-Grip 1300 125 + 15 

Scotch-Grip 1357 73 * 10 

Adiprene L- 100 701 + 14 

PR 1440 polysulfide 205 + 14 

Epon 828-epoxy 428 + 44 

The Adiprene composites had been fabricated using a 3-mil porous Teflon-coated glass 

release fabric on either side. The release fabric left a surface rough enough for good adhesive 

bonding without further preparation. The samples were stamped out using a rubber cutting die. 

1 

i 

c * 3-M Industrial Tape and Specialties Division, St. Paul, MN 55144-1000. 

’ PRC-DeSoto International, 14126 NE 190th Street, Woodinville, WA 98072. 

’ Lord Corporation, Chemical Products Division, Erie, PA 16514-0038. 

9 Inland Leidy, 2225 Evergreen Street, Baltimore, MD 21216. 

l * Miller-Stephenson Chemical Company, Inc., George Washington Highway, Danbury, CT 06810. 

’ American Society for Testing and Materials. Standard Test Methodfor Strength Properties of Adhesively Bonded 

Plastic Lap-Shear Sandwich Joints in Shear by Tension Loading. ASTM-D3164-92, West Conshohocken, PA, 

1992. 

31 
All samples except the polysulfide and epoxy were cured by applying heat-l hr at 250 “F 

for the samples bonded with Adiprene, and 4 hr at 160 “F for the others. The Chemlock 

adhesives normally do not require heat to cure; however unacceptably poor bond strengths were 

obtained if the coupons were not cured with heat. The polysulfide was cured at room 

temperature for 120 hr (48 hr should be sufficient). The epoxy was allowed to cure for seven 

days, at room temperature. 

Every sample bonded with the Adiprene failed at the glass-resin matrix interface (the 

maximum bond strength that can be expected for this composite). In contrast, the Chemlock 220 

and polysulfide adhesives pulled away from the Adiprene resin in the composite. All of the 

epoxy-bonded samples+xcept one-also failed in this manner. 

The exception (not included in the data in Table A-l) pulled the Adiprene off the glass in the 

composite at about 630 lb of force. This indicated that the bonding with the epoxy could be 

improved, probably with better surface preparation. The Scotch-Grip adhesives both failed 

internally. 

The ability to bond the Adiprene-based composite to steel and aluminum, to other composites 

such as glass-reinforced polyester, and to cured Adiprene resin was also desired for anticipated 

future applications. Only the polysulfide and epoxy adhesives were tried since room temperature 

bonding was desired. As before, the Adiprene composites were given no special preparation. 

The aluminum and steel samples were cleaned in acetone and alcohol, roughened extensively 

with 80-grit sandpaper, and recleaned. The cured polyurethane resin was roughened with a disc 

sander prior to use. The bond strength results are shown in Table A-2. 

The steel, aluminum, and cured resin samples bonded to the composite with the polysulfide 

failed within the adhesive. The polyester-matrix composite bonded to the Adiprene-matrix 

composite failed at the polyester surface for both adhesives. The aluminum samples bonded to 

the Adiprene-matrix composite with the epoxy failed at the epoxy-aluminum interface. The 

epoxy bonded very well to the stainless steel-the best samples slipped in their grips at about 

32 
Table A-2. Adhesive Bond Strengths for Glass-Reinforced Adiprene Matrix Composite to 

Other Materials 

Material 

Strength (lb) 

1 Polvsulfide 1 

f 22 > 630 

+ 36 f 11 

> 180 

1 178 f 17 1 207 + 41 

630 lb of force. However, epoxy also bonded surprisingly well to the cured Adiprene-the 

Adiprene portion of the sample broke away from the rest of the sample at the edge of the bond to 

the epoxy at about 180 lb of force. 

Finally, bonding the cured Adiprene resin to the polyester-glass composite was examined. A 

bond strength of 89 * 5 lb was found for the polysulfide adhesive. As expected, every 

polysulfide-bonded sample failed at the adhesive-polyester interface. The cured Adiprene resin 

bonded to the polyester matrix with the epoxy also broke away from the rest of the sample at 

about 180 lb of force. 

These results are intended only as an initial survey of adhesives for bonding the Adiprene 

resin and its composites to various materials. They indicate that good adhesive bonding to the 

polyurethane resin is possible and not difficult to obtain. Additional work, however, is needed in 

this area. 

c 

33 
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40 
REPORT DOCUMENTATION PAGE Fom Ap/woved 

OMBNo. 07044188 

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1. AGENCY USE ONLY peeve blenk) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED 

September 2000 Final, Apr 99-Sep 99 

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS 

Fabrication of Novel Bumper and Skirt Components for a Ground Vehicle 

622618AH80 

6. AUTHOR(S) 

William A. Spurgeon and David J. Thomas* 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS 6. PERFORMING ORGANWTION 

REPORT NUMBER 

U.S. Army Research Laboratory 

Al-l-N: AMSRL-WM-MB ARL-TR-2327 

Aberdeen Proving Ground, MD 2 1005-5069 

9. SPONSORING/MONITORING AGENCY NAMES(S) AND ADDRESS ,lO.SPONSORINGIMONITDRlNG 

AGENCY REPORT NUMBER 

11. SUPPLEMENTARY NOTES 

” U.S. Army Tank-Automotive Research, Development, and Engineering Center, Warren, MI 48397-5000 

128. DlSTR~BUTiON/AVAlLABiLiTY STATEMENT 12b. DISTRIBUTION CODE 

Approved for public release; distribution is unlimited. 

13. ABSTRACT (Maximum 200 words) 

This report discusses the materials selection for and fabrication of novel “bumper” and skirt panels for an 

experimental ground vehicle improvement project. These components were fabricated from E-glass reinforced 

polyurethane resin so that they would have a unique combination of rigidity and flexibility required for successful field 

use. Alternative components for future consideration are discussed, and some initial work on adhesive bonding of 

polyurethane matrix composites is presented. 

14. SUBJECT TERMS 15. NUMBER OF PAGES 

42 

track skirt, bumpers, polyurethane resin composites 16. PRICE CODE 

17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACT 

OF REPORT OF THIS PAGE OF ABSTRACT 

UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED UL 

NSN 7540-01-280-5500 

41 

Standard Form 298 (Rev. 2-89) 

Prescribed by ANSI Std. 23918 296-102 
INTENTIONALLY LEFT BLANK. 

42