HYPERVELOCITY IMPACT RESPONSE OF SPACED COMPOSITE MATERIAL STRUCTURES

Int. J. Impact Engng Vol. 10, pp. 50~523, 199(I 1173,1-743X/90 $3.00 + 0.00 Pergamon Press pie Printed in Great Britain HYPERVELOCITY IMPACT RESPON...
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Int. J. Impact Engng Vol. 10, pp. 50~523, 199(I

1173,1-743X/90 $3.00 + 0.00 Pergamon Press pie

Printed in Great Britain

HYPERVELOCITY IMPACT RESPONSE OF SPACED COMPOSITE MATERIAL STRUCTURES

William P. Schonberg Department of Mechanical Engineering University of Alabama in Huntsville Huntsville, Alabama 35899

ABSTRACT

The design of a spacecraft for a long-duration mission must take into account the possibility of high-speed impacts by meteoroids and orbiting space debris and the effects of such impacts on the spacecraft structure. With the advent of many new high-strength composite materials and their proliferation in aircraft applications, it has become necessary to evaluate their potential for use in long-duration space and aerospace structural systems. One aspect of this evaluation is the analysis of their response to hypervelocity projectile impact loadings. The analyses performed in this study indicate that the extent of damage to a dual-wall composite structure can be written as a function of the geometric and material properties of the projectile/structure system. A comparative analysis of impact damage in composite specimens and in geometrically similar aluminum specimens is also performed to determine the advantages and disadvantages of employing certain composite materials in the design of structural wall systems for long-duration spacecraft.

INTRODUCTION All large spacecraft with a mission duration of more than a few days are susceptible to impacts by meteoroids and pieces of orbiting space debris. These impacts occur at extremely high speeds and can damage the flight-critical systems of a spacecraft, which can in turn lead to catastrophic failure of the spacecraft. Therefore, the design of a spacecraft for a long-duration mission must take into account the possibility of such impacts and their effects on the spacecraft structure and on all of its exposed subsystem components, such as instrumentation units and solar arrays. Structural walls for crew compartments and spacecraft modules have traditionally consisted of a bumper plate that is placed at a small distance away from the main pressure wall of the compartment or module. This concept was first proposed by Whipple (1947) and has been studied extensively in the last two decades as a means of reducing the penetration threat of hypervelocity projectiles (see, e.g., D'Anna, 1965; Maiden and McMillan, 1964; Maiden, et.al., 1963; Nysmith, 1969; Schonberg, 1989a,b; Schonberg and Taylor, 1989; Wallace, et.al., 1962). However, in the majority of these investigations, the bumper and structural wall were typically made from high-strength metallic materials, such as aluminum or steel. With the advent of many new high-strength composite materials and their proliferation in aircraft applications, it has become necessary to evaluate their potential for use in long-duration space and aerospace structural systems. One aspect of composite materials evaluation for use in space and aerospace structural systems is the analysis of their response to hypervelocity impact loadings. Unfortunately, information on hypervelocity impact of composite materials is scarce because work in this area has just begun (Cour-Palais, 1987). A recent phenomenological investigation of the damage sustained by thick single-panel graphite/epoxy specimens under hypervelocity projectile impact showed that panel damage was a combination of multiple delamination and breakage of the fiber and matrix materials (Yew and Kendrick, 1987). However, the use of composite materials in multi-wall structural systems has yet to be addressed. This paper presents the results of an investigation into the response of dual-wall structural systems with composite bumper plates under normal hypervelocity projectile impact loadings. Test results for dual-wall specimens employing two different composites materials are reviewed qualitatively and quantitatively. Impact damage is characterized according to the extent of penetration, crater, and spall damage in the structural system. The analysis indicates that the extent of damage can be written as a function of the geometric and material properties of the projectile/dual-wall structural system. These functions can be used to 509

510

William P. Schonberg

perform parameter sensitivity studies and to evaluate hypothetical design configurations. The damage in the composite material specimens is also compared to the damage in geometrically similar aluminum specimens caused by hypervelocity projectiles with similar impact energies. This comparative analysis, together with the overall composite system impact response analysis, is used to determine the advantages and disadvantages of employing composite materials in structural wall systems for long-duration spacecraft.

HYPERVELOCITY

IMPACT TESTING OF COMPOSITE MATERIALS

The hypervelocity impact testing of the dual-wall structural systems was performed at the Space Debris Simulation Facility of the Materials and Processes Laboratory at the NASA/Marshall Space Flight Center. The facility consists of a light gas gun capable of launching 2.5 mm to 12.7 mm projectiles at velocities of 2 to 8 km/sec (Taylor, 1987). Projectile velocity measurements were accomplished via pulsed X-ray, laser diode detectors, and a Hall photographic station. In each test, a projectile of diameter d and velocity V impacted a bumper plate of thickness t along a trajectory perpendicular to the plane of the bumper plate (see Fig. i). The s . . projectlle shattered upon impact and formed a hole of diameter D in the bumper plate. Secondary projectile and bumper plate debris fragments created during the impact were sprayed upon a pressure wall plate of thickness t located a distance S behind the bumper plate. These w secondary debris impacts created an area of damage A d on the pressure wall plate; the angle 7 is the cone angle of the secondary debris fragment cloud and represents the spread of the debris fragments. Occasionally, the impacts of the secondary debris fragments resulted in the creation of spall fragments ejected from the rear side of the pressure wall plate. In these instances, the total spalled area on the rear surface is denoted by A . s The conditions of the impact tests were chosen to simulate space debris impact of lightweight space structures as closely as possible, and still remain within the realm of experimental feasibility. Kessler (1989) states that the average mass density for pieces of orbital debris less than I0 mm in diameter is approximately 2.8 gm/cm 3, which is approximately the same as that of aluminum. Although it is anticipated that the shape of the impacting projectile will affect the formation and spread of secondary debris particles, spherical projectiles were used in the test program to maintain repeatability and consistency. Thus, the testing was conducted with solid spherical ii00 aluminum projectiles with diameters ranging from 4.75 mm to 8.89 mm. The velocities of the impacting projectiles ranged from 3.43 to 7.40 km/sec. A total of 21 aluminum and 12 composite structural systems were used to study and evaluate the penetration resistance of dual-wall systems with composite bumpers. In the aluminum systems, the bumper and the pressure wall plates were made of 6061-T6 and 2219-T87 aluminum, respectively. In the composite systems, the bumper plates were made of a fiber reinforced composite material while the pressure wall plates were made of 2219-T87 aluminum. The composite materials used as bumper plates were Kevlar 49 and IM6/3501-6 graphite/epoxy. The thicknesses of the aluminum bumper plates were chosen so that they would have approximately the same areal density as the composite material plates, that is, ts,aluminum = (Pcomposite/Paluminum)ts,composite

(i)

The mechanical properties and the laminae lay-up of the composite material bumper plates are given in Tables i and 2, respectively. Additional test parameters are given in Tables 3 and 4. The results of the hypervelocity impact test firings are given in Tables 5 and 6; column entries of ' .... ' indicate that penetration and/or spall of the pressure wall plate did not occur. Photographs of impacted dual-wall Kevlar, graphite/epoxy, and aluminum test specimens are shown in Figs. 2-7. Penetration and spall functions for the Kevlar and aluminum systems are presented in Figs. 8 and 9. Detailed post-mortem analyses of the damaged test specimens revealed many interesting features and characteristics of composite materials hypervelocity impact response.

HYPERVELOCITY

IMPACT RESPONSE OF KEVLAR SYSTEMS

Bumper Plate Damage Analysis The impact damage in the Kevlar bumper plates typically consisted of a circular hole and large areas of delamination on the front and rear surfaces of the plates (Figs. 2a,b and 4a,b). Although the edge of the hole was usually frayed, its roundness was evident nonetheless. The delamination area of the front surface extended far beyond the the vicinity of the hole and was approximately twice as large as the delamination area of the rear surface. On both surfaces, the delamination was generally restricted to the outer layers, with the peeling in the direction of the surface laminate fibers. These observations are similar to those made in the preceding study of the hypervelocity impact response of thick gra-

Hypervelocity

phite/epoxy panels

impact response of spaced composite material

(Yew and Kendrick,

structures

511

1987).

Pressure Wall Plate Damage Analysis In Tables 7 and 8, penetration characteristics are summarized for test shots grouped according to both geometric and impact energy similarity. Table 7 shows results for impact energies below 2,000 joules (the 'low impact energy regime') while Table 8 shows results for energies greater than I0,000 joules (the 'high impact energy regime'). A penetration function for the Kevlar systems in the low and high energy regimes and the corresponding aluminum systems is shown in Fig. 8. Using these Tables and the detailed penetration data in Tables 5 and 6, a comparison of penetration response characteristics was performed. In the low impact energy regime, the pressure wall plate damage areas of the Kevlar systems were highly concentrated and consisted of either a single hole (a penetrating impact) or a single crater (a non-penetrating impact) (Figs. 2c,d). The damage areas in similar aluminum systems were more wide-spread and contained numerous small holes and/or craters (Fig. 3c). Among the high energy impacts, for a 101.6 mm stand-off distance, penetration of the pressure wall plates occurred in the Kevlar as well as in the aluminum systems. The damage areas on the pressure wall plates of both structural systems were observed to be similar in size. However, when the wall spacing was increased to 152.4 mm, the Kevlar systems were penetrated while the corresponding aluminum systems were not (Figs. 4c, 5b). Furthermore, at this stand-off distance, pressure wall plate damage areas in the aluminum systems were significantly larger than those in the Kevlar systems. The relative magnitudes of the damage areas are also evident in Tables 5 and 6 where the secondary debris cloud cone angles in the aluminum system impacts are seen to be much larger than those in the corresponding Kevlar system impacts. These differences in response characteristics between the aluminum and Kevlar systems indicate that aluminum bumpers are generally more effective in spreading out the secondary debris that is created by the initial projectile impact on the bumper plate, especially for impact energies above I0,000 joules. The concentration of the debris clouds and the resultant small damage areas on the pressure wall plates in the Kevlar systems can be explained in part by a mismatch in shock impedance between the Kevlar bumper plates and the aluminum projectiles (Coronado, et.al., 1987). The shock waves in the projectile and the bumper plate created by the initial impact interacted in a manner that prevented the complete break-up of the projectile. As a result, the dispersion of the secondary projectile and bumper plate fragments also decreased. An increased probability of pressure wall plate penetration also resulted from the increased concentration of the secondary debris fragment clouds. It is interesting to note that the reverse sides of the pressure wall plates of the Kevlar systems did not exhibit any spall at either stand-off distance, while those of the aluminum systems exhibited significant spalling at both stand-off distances (see, e.g., Fig. 5c). A spall function for the aluminum systems considered in this investigation is presented in Fig. 9. This increased tendency for spall in the aluminum specimens is a direct consequence of the wider areal distribution of the impulse delivered by the secondary debris fragment cloud. The impulse delivered to the pressure wall plate in the Kevlar systems is more concentrated and therefore serves to penetrate the plate rather than cause spall. Regression Analysis of Damage Data A standard multiple linear regression analysis of the hole dimension data was performed to obtain an equation for hole diameter as a function the impact parameters and the material and geometric parameters of the bumper plate with the following result: D/d - 1.923(V/C)0"968(ts/d) 0"218 + 1.04

(2)

where C = ~(El/P) ; E 1 is the uni-directional ply tensile modulus in the fiber direction, and p is the mass density of the bumper plate material. The average error of this equation was calculated to be 0.001% with a standard deviation of 4.824% and a correlation coefficient R 2 = 0.873. These values imply that eqn (2) is a fairly good fit to the experimental hole diameter data. It is interesting to note that the velocity dependence in eqn (2) is approximately that in the equation of hole diameter in aluminum plates subjected to normal hypervelocity projectile impact (Maiden, et.al., 1963). Using the data in Tables 5 and 6, the following equations were obtained for cone angle, pressure wall damage area, pressure wall hole diameter, and pressure wall rear side spall area as functions of the geometric, material, and impact parameters of the Kevlar 49 and aluminum dual-wall systems. Cone Angle,

Kevlar System

cos7 ~ 0.332(V/c)-l'053(ts/d)-0'599

(3)

512

William P. Schonberg

Cone Angle~ Aluminum System cos~ = 0.489(V/c)-l'068(ts/d)-0'188

(4)

Pressure Wall Damage Area~ Kevlar System Ad/A p = 817.79(V/c)l'253(ts/d)O'679(S/d) -0'158

(5)

Pressure Wall Damage Area, Aluminum System Ad/A p = 25.110(V/C) 2"

423 t d) 0 764(S/d)i'125 ( s/ "

Pressure Wall Hole Diameter, dh/d

=

5.836(V/C)2"I71(t

Pressure Wall Hole Diameter,

(6)

Kevlar System s/

"d)O'iB9(s/d) 0"155

(7)

Aluminum System

dh/d = O.093(V/c)-B'895(ts/d)-2"380(tw/d)-B'833(S/d) -0"894

(8)

Pressure Wall Rear Spall Area~ Aluminum Systems As/A p = 225.40(V/C)-12.044(ts/d)-0.463. (tw/d) 2 "688(S/d)0" 803

(9)

where A = ~d2/4, and dh is the equivalent hole diameter of the total penetrated area if penetration of the pressure wall plate occurs. The average errors, standard deviations, and correlation coefficients for eqns (3-8) are given in Table 9. Based on the data in Table 9, it is evident that eqns (3-8) fit the experimental data fairly well. It is noted that eqns (2-9) are valid only for normal impacts of aluminum projectiles on Kevlar 49 and aluminum dual-wall specimens of similar lay-up and construction. Furthermore, eqns (2-8) are valid for impact velocities between 3.4 and 7.4 km/sec, while eqn (9) is only valid for velocities between 6.6 and 7.2 km/sec. It is also noted that curves such as those in Figs. 8 and 9 must first be consulted to determine whether or not pressure wall penetration or spall will occur as a result of a particular hypervelocity impact. If penetration or spall will indeed occur, then eqns (7,8) may be used to estimate the equivalent diameter of the resulting hole in the pressure wall plate and eqn (9) may be used to calculate the anticipated area of rear side spall. Additionally, since eqns (2-9) are based on a relatively small number of tests, additional testing is recommended for further verification of these equations.

HYPERVELOCITY IMPACT OF GRAPHITE/EPOXY SYSTEMS To determine if there would be a difference in resistance to pressure wall plate penetration between dual-wall specimens with bumper plates made of Kevlar 49, aluminum 6061-T6, and graphite/epoxy, two high energy impact tests were conducted with IM6/3501-6 graphite/epoxy as the bumper plate material. A summary of the resulting penetration and spall characteristics for the graphite/epoxy and corresponding aluminum tests is presented in Table i0. An examination of the damaged graphite/epoxy bumper plates revealed that, unlike the delamination in the Kevlar bumper plates, the impact-induced delamination on the front and rear surfaces of the graphite/epoxy plates were not very extensive (Figs. 6a,b). However, the delamination was primarily restricted to the outer layers of both surfaces and were in the general direction of the outer laminate fibers. The holes in the graphite/epoxy bumper plates were also more clearly defined than those in the Kevlar plate impacts. The damage areas on the pressure wall plates of the graphite/epoxy systems were more widespread diffuse than those of the Kevlar systems (Figs. 6c,d). Although the pressure wall plates in the graphite/epoxy systems were still penetrated by the secondary debris fragments, the penetrations consisted of several small holes or craters rather than a single large hole or crater as in the Kevlar systems. Additionally, even though pressure wall plate penetration occurred in both the graphite/epoxy and the corresponding aluminum systems, the equivalent hole diameters of the penetrated pressure wall plates of the graphite/epoxy systems were significantly larger than those in the corresponding aluminum systems (Figs. 6c and 7b). Thus, the penetrations in the graphite/epoxy systems were more 'critical' than those in similar aluminum systems. Had these been on-orbit impacts, the l~rger penetrated areas in the graphite/epoxy systems would have allowed air to escape from a pressurized module at a higher rate than would the penetrations in the corresponding aluminum systems. It is also noted that the pressure wall plates in the aluminum systems also exhibited significant rear side spall whereas the pressure wall plates of the graphite/epoxy systems did not (Figs. 6d and 7c). As discussed previously, this response characteristic of aluminum dual-

Hypervelocity impact response of spaced composite material structures

513

wall systems is a serious matter and deserves further investigation.

CONCLUSIONS Based on these observations, it is concluded that thin Kevlar 49 and IM6/3501-6 graphite/epoxy panels offer no advantage over equivalent aluminum 6061-T6 panels in reducing the penetration threat of hypervelocity projectiles. However, it must be noted that significant pressure wall plate rear surface spall was observed in the aluminum systems while no spalling was observed in either the Kevlar or the graphite/epoxy systems. It is becoming increasingly apparent that, because of the high speeds with which spall fragments can travel, impactinduced spall can be as deleterious to mission success and crew safety as an actual penetration. Naturally, the major difference between a spall event and a penetration event is the lack of a pressure leak in a spall event. However, the lethality of the high-speed spall fragments must not be overlooked.

ACKNOWLEDGMENTS The author is grateful for support from the NASA/Marshall Space Flight Center under contract NASS-36955/DOI6. The author would also like to acknowledge the assistance of Mr. Kent Darzi during the data acquisition phase of this investigation.

REFERENCES Coronado, A.R., Gibbins, M.N., Wright, M.A., and Stern, P.H. (1987). Space Station Integrated Wall Design and Penetration Damage Control, D180-30550-I, Boeing Aerospace Co., Seattle, Washington. Cour-Palais, B.G. (1987). Impact Engng., 5, 221-237.

"Hypervelocity Impact in Metals, Glass, and Composites",

Int. J.

D'Anna, P.J. (1965). "A Combined System Concept for Control of the Meteoroid Hazard to Space Vehicles", J. Spacecraft, 2, 33-37. Kessler, D.J., Reynolds, R.C., and Anz-Meador, P.D. (1989). Orbital Debris Environment for Spacecraft Designed to Operate in Low Earth Orbit, NASA TM 100471, Houston, Texas. Maiden, C.J., Gehring, J.W. and McMillan, A.R. (1963). Investigation of Fundamental Mechanism of Damage to Thin Targets by Hypervelocity Projectiles, GM-DRL-TR-63-225, General Motors Defense Research Laboratory, Santa Barbara, California. Maiden, C.J. and McMillan, A.R. (1964). "An Investigation of the Protection Afforded a Spacecraft by a Thin Shield", AIAA Journal, 2, 1992-1998. Nysmith, C.R. (1969). "An Experimental Impact Investigation of Aluminum Double-Sheet Structures", Proceedings of the AIAA Hypervelocity Impact Conference, AIAA Paper No. 69-375. Schonberg, W.P. (1989a). "Characterizing the Damage Potential of Ricochet Damage Debris Due to an Oblique Hypervelocity Impact", Proceedings of the Thirtieth AIAA Structures, Structural Dynamics, and Materials Confer.ence, AIAA Paper No. 89-1410. Schonberg, W.P. (1989b). "Hypervelocity Structures", J. Aero. Engng., in press.

Impact Penetration Phenomena in

Aluminum

Space

Schonberg, W.P. and Taylor, R.A. (1989). "Penetration and Ricochet Phenomena in Oblique Hypervelocity Impact", AIAA Journal, 27, 639-646. Taylor, R.A. (1987). "A Space Debris Simulation Facility for Spacecraft Materials Evaluation", SAMPE Quarterly, 18, 28-34. Wallace, R.R., Vinson, J.R. and Kornhauser, M. (1962). on Shielded Structures", ARS Journal', 1231-1237. Whipple, E.L. (1947).

"Effects of Hypervelocity Particles

"Meteorites and Space Travel", Astron. Journal, 52, 137.

Yew, C.H. and Kendrick, R.B. (1987). "A Study of Damage in Composite Panels Produced by Hypervelocity Impact", Int. J. Impact Engng., 5, 729-738.

514

William P. Schonberg

Table I. Unidirectional Ply Properties of Kevlar 49 (67% fiber volume) and IM6/3501-6 Graphite/Epoxy (63% fiber volume) [courtesy of NASA/MSFC]

Kevlar 49

IM6/3501-6

E1

(xl09 N/m 2)

76.0

203.0

E2

(xl09 N/m 2)

5.5

Ii.0

GI2 (xlO 9 N/m s )

2.3

8.3

v12

.340

.320

v21

.025

.017

Density (kg/m 3 )

1340

1541

Table 2. Geometric Properties of Composite Material Bumper Plates

Panel ID Number

Material

Number of Plies

Thickness (mm)

Lamina Lay-up

CI

Kevlar 49

12

2.032

[0,±60,$60,0]s

C2

Kevlar 49

18

2.921

(0,±60,$60,0)3

C3

Kevlar 49

24

3.810

[(0,±60,$60,0)2]

C4

Graphite/ Epoxy

24

3.810

[(0,±60,+60,0)2 ]

Table 3. Test Parameters for Composite Systems

Test Number

Bumper ID Number

V (km/s)

d (mm)

t (m~)

t (~)

S (mm)

Kevlar 49

103 103A 103B I03C 1031 104 104A 104B 1221 1222

CI C3 C3 C3 C3 C3 C3 C3 C2 C2

4.62 3.52 3.43 3.84 4.24 6.72 6.65 7.01 7.15 7.40

4.75 4.75 4.75 4.75 4.75 7.62 7.62 7.62 7.62 7.62

2.032 3.810 3.810 3.810 3.810 3.810 3.810 3.810 2.921 2.921

3.175 3.175 3.175 3.175 3.175 3.175 3.175 3.175 3.175 3.175

101.6 101.6 101.6 101.6 101.6 101.6 101.6 101.6 152.4 152.4

3.175 3.175

101.6 101.6

IM6/3501-6 Graphite/Epoxy

177A 177B

C4 C4

6.91 7.38

6.35 6.35

3.810 3.810

Hypervelocity

impact response of spaced composite material structures

Table 4. Test Parameters for Aluminum Systems

Test Number

V (km/s)

d (mm)

t (ss)

t (m~W)

S (mm)

P05 PI6E PI6G P20B P20C P21 P21A P27 P27A P27B P33 P34 I01 101A 101B 107 107A I07B 109B EH3A EH6C

6.90 6.78 7.18 6.98 6.63 6.63 6.47 4.53 3.87 4.15 7.21 6.80 3.09 3.96 4.27 6.80 6.74 6.82 3.61 6.64 6.58

6.35 7.62 7.62 7.62 7.62 7.62 7.62 4.75 4.75 4.75 6.35 6.35 4.75 4.75 4.75 8.89 8.89 8.89 4.75 7.95 7.95

1.600 1.600 1.600 1.600 1.600 1.600 1.600 1.600 1.600 1.600 1.016 1.600 2.032 2.032 2.032 2.032 2.032 2.032 2.032 1.600 1.600

3.175 3.175 3.175 3.175 3.175 3.175 3.175 3.175 3.175 3.175 3.175 2.540 3.175 3.175 3.175 4.445 5.080 5.715 3.175 3.175 3.175

101.6 152.4 152.4 152.4 152.4 101.6 101.6 101.6 101.6 101.6 101.6 101.6 101.6 101.6 101.6 101.6 101.6 101.6 101.6 101.6 101.6

Table 5. Hypervelocity Impact Test Results for Composite Systems

Test Number

D (nun)

~ (deg)

Ad (cm 2 )

m~ ~ ( )

A (c~ ~ )

Kevlar 49

103 103A 103B I03C 1031 104 I04A 104B 1221 1222

9.271 9.677 9.423 9.271 9.093 20.193 19.685 19.050 19.558 20.193

37.9 34.1 30.7 26.7 43.6 56.5 64.0 61.0 40.8 43.1

31.68 30.39 24.52 26.71 51.87 139.68 126.64 145.68 102.58 114.32

13.538 8.103 8.103 .... .... 48.387 50.063 46.660 54.458 61.874

IM6/3501-6 Graphite/Epoxy

177A 177B

15.596 15.191

49.4 55.4

81.03 85.16

11.075 13.716

.... ....

515

516

William P. Schonberg

Table 6. Hypervelocity Impact Test Results for Aluminum Systems

Test Number

D (mm)

V (deg)

Ad (cm 2 )

P05 PI6E PI6G P20B P20C P21 P21A P27 P27A P27B P33 P34 i01 IOIA IOIB 107 107A 107B I09B EH3A EH6C

14.224 15.748 16.510 15.875 15.240 15.875 14.300 10.668 8.636 10.033 13.005 14.122 10.135 9.398 14.224 19.050 18.288 19.050 10.160 15.138 17.475

55.9 53.1 60.5 56.8 56.9 63.9 58.1 40.9 29.0 34.6 64.0 64.0 28.1 31.3 52.8 66.5 69.1 66.5 44.2 75.4 63.7

91.55 182.39 248.39 214.06 214.06 126.64 102.58 45.61 21.74 31.68 126.64 153.29 20.25 25.61 81.03 139.61 154.97 139.68 62.06 206.19 126.64

md~m ( )

A (c~ 2 )

4.699 23.368 .... .... 2.166 28.804 33.782 .... 4.445 3.048 crack 10.363 6.655 4.347 .... 15.434 9.018 crack .... 49.835 31.979

0.19 12 65 2 88 5 08 6 B7 5 29

3.34 2.68

12.13 15.48 13.68

Table 7. Penetration Comparison of Kevlar and Aluminum Systems (Impact Energy < 2,000 joules)

Test Number

Bumper Plate Material

impact Energy (J)

103A I09B I03B

Kevlar Aluminum Kevlar

924.9 991.8 895.3

P27A I03C IOIA

Aluminum Kevlar Aluminum

P27B 1031 IOIB

103 P27

Impact Momentum (kg-m/s)

Pressure Wall Plate Penetrated?

Spalled?

0.536 0.549 0.522

yes no yes

no no no

1139.8 1122.1 1041.8

0.589 0.584 0.563

yes no yes

no no no

Aluminum Kevlar Aluminum

1310.7 1368.1 1387.5

0.632 0.645 0.650

yes no no

no no no

Kevlar Aluminum

1624.3 1561.7

0.703 0.689

yes no

no no

Hypervelocity

impact response of spaced composite material

structures

Table 8. Penetration Comparison of Kevlar and Aluminum Systems Energy > I0,000 joules)

Stand Off Dist.

101.6 mm

152.4 mm

Test Number

Bumper Plate Material

Impact Energy (J)

104B EH6C/3A

Kevlar Aluminum

15,441 15,733

P21 104 104A P21A

Aluminum Kevlar Kevlar Aluminum

1221 P20B PI6G 1222

Kevlar Aluminum Aluminum Kevlar

(Impact

Pressure Wall Plate

Impact Momentum (kg-m/s)

Penetrated?

Spalled?

4.405 4.739

yes yes

no no

13,812 14,274 13,896 13,154

4.166 4.236 4.179 4.066

yes yes yes yes

yes no no no

16,064 15,309 16,199 16,699

4.493 4.386 4.512 4.581

yes no no yes

no yes yes no

Table 9. Regression Analysis of Cone Angle and Pressure Wall Plate Damage Data, Error Summary Regression Function

~

a(~)

R=

avg Kevlar Systems

cos ?

1.067

15.669

0.624

Ad/A p

1.052

14.950

0.750

dh/d

0.134

5.603

0.933

Aluminum Systems

cos V

1.028

14.881

0.742

Ad/A p

3.713

27.439

0.618

dh/d

1.852

20.065

0.934

As/A p

3.414

25.884

0.660

Table i0. Penetration

Comparison of Graphite/Epoxy

Test Number

Bumper Plate Material

Impact Energy (J)

P05 177A 177B P34 P33

Aluminum Graphite/Epoxy Graphite/Epoxy Aluminum Aluminum

8657.4 8682.5 9903.8 8408.2 9452.7

Impact Momentum (kg-m/s)

2.509 2.513 2.684 2.473 2.622

and Aluminum Systems Pressure Wall Plate

Penetrated?

Spalled?

yes yes yes yes crack

yes no no yes yes

517

Fig.

Fig.

i.

tw

ts,

2b.

Plate,

Rear

(Test No.

Impact Test Configuration

Bumper

Normal

Ad

--As

V

d

103)

and Parameters

S

Fig.

2c.

2a.

Pressure Wall Plate, Front (Test No. 103)

Fig.

Bumper

Plate,

UJ~I

(Test No.

~s~e

Front

103)

!ii!ii~iiiiiiiiill

o

L~ oo

Fig. 2d.

Pressure Wall Plate, Rear (Test No. 103)

Pressure Wall Plate, Front (Test No. P27)

~'~/~.~

Fig. 3b.

q.6z

3a.

Bumper P l a t e ,

.III'T

~esl~ce ~

Fig.

Pro~.. ! I I

Fig. 3c.

Pressure Wall Plate, Rear (Test No. P27)

F r o n t (Test No. P27)

Ln

o

o

O

O

==

~.

Fig. 4c. Pressure Wall Plate, Front (Test No. 1221)

Fig. 4a. Bumper Plate, Front (Test No. 1221)

L122-1 - ~2a- 1

Fig. 4d.

•30o~;~

~r ",°~s~ce~ \ Pressure W a l l P l a t e ,

I

Rear

~z~im ( T e s t No. 1221)

Fig. 4b. Bumper Plate, Rear (Test No. 1221)

.30Ose

P ~

zr o

o

Fig. 5c.

. oo

~

~

I

~

SS-I

Pro_'v . 3 0 0

R

205

Bumper Plate, Front (Test No. P2OB)

Pressure Wall Plate, Rear (Test No. P2OB)

Fig. 5a.

........

Fig. 5b.

Fig. 6a.

Pressure Wall Plate, Front (Test No. P2OB)

:i¸ i>i~()j

~?

Bumper Plate, Front (Test No. 177B)

-'.:J, : R

~}: J/:;'i: ~ L~,:~ ~i !

e-

r'1-

i11

o co

e~

m

o Ph

o m

m o

o

m:

Fig. 6d.

Bumper Plate, Rear (Test No. 177B)

Pressure Wall Plate, Rear (Test No. 177B)

Fig. 6b.

Fig. 6c.

Fig. 7a.

Pressure Wall Plate, Front (Test No. 177B)

~

Bumper Plate, Front (Test No. P33)

i < ~i'~,~ ~ ! ~ ~ i~ ~'~ i~l-~Li

i

b~

~n

W 5 < 4 n 3 2-

I

3

I

4

0

5

i

6

I

7

I

NOT PENETRATED

PENETRATED

~

§d~ o /

IMPACT VELOCITY (KM SEC)

I

2





I

D

0

I

ALUMINUM

00

KEVLAR

Pressure Wall Plate, F r o n t (Test No. P33)

1

8

Fig. 8. PenetrationFunction for Kevlar (t =3.81 mm) and Aluminum (ts=l.6 mm) Dual-Wall Structures (~w=3.175mm, S=I01.6 mm)

Fig. 7b.

8

I0

Fig.