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Experimental investigation of the ballistic resistance of steel-fiberglass reinforced polyester laminated plates
PII: S 1359-8368(96)00011-X
ELSEVIER
Composites: Part B 27B (1996) 447-458 Copyright © 1996 Elsevier Science Limited Printed in Great Britain. All rights reserved 1359-8368/96/$15.00
Experimental investigation of the ballistic resistance of steel-fiberglass reinforced polyester laminated plates A. A. A l m o h a n d e s AFTRC, Egypt
and M. S. A b d e I - K a d e r Department of Mechanical Engineering, M. T.C., Cairo, Egypt
and A. M. Eleiche* Department of Mechanical Engineering, United Arab Emirates University, United Arab Emirates (Received 25 September 1995; accepted 15 November 1995) The present experimental study is undertaken to investigate the effect of target configuration on ballistic performance when struck by standard bullets of different velocities. At first, single mild steel plates, 1-8 mm thick, are tested, and the effect of thickness and mechanical properties of plate material are explored. Secondly, in-contact laminae comprising an 8 mm-thick target, and spaced laminae of the same total steel thickness, with spacing distances equal to or multiples of the bullet core diameter (6 ram) are tested and the effect of number, thickness, and arrangement of laminae sought. In addition, fiberglass reinforced polyester (FRP) is used as a filler material for targets with spaced steel laminae. The influence of FRP's physical and mechanical properties on the ballistic performance of steel-FRP targets is investigated. In order to perform the ballistic tests, a special setup is constructed, which consists of a launcher, a target clamp and a velocity-measuring device. In each experiment, the change in the projectile velocity (while penetrating the target) divided by the length of penetration is established as a measure of target performance. Results show that single targets are more effective than laminated targets of the same total thickness, regardless of the configuration or striking velocity. It is noted, however, that the difference in performance diminishes as the striking velocity increases. Moreover, the effectiveness of laminated targets, in contact or spaced, increases as the number of laminae comprising each target decreases. Ballistic performance of laminated targets is further enhanced by using the thickest lamina as the back lamina. Results also emphasize the dependence of target performance on mechanical properties. Steel-FRP targets show better performance than weight-equivalent steel targets. Performance of a steel-FRP target is further improved by increasing fiber weight fraction in the FRP. Copyright © 1996 Elsevier Science Limited
(Keywords:bamstic; impact; laminated plates; damage; polyester)
1 INTRODUCTION The subject of penetration has long been studied, primarily because o f its importance in military and civilian fields. Many parameters are found to control the mutual interaction between the impacting projectile and * On leave from Department of Mechanical Design and Production, Cairo University, Egypt.
the target. These include impact conditions as well as projectile and target characteristics, and result in many failure modes, such as brittle fracture, ductile hole enlargement, petaUing, spalling and plugging 1'2. Target plates may be monolithic or multi-layered. In the latter type, individual layers may be spaced or in-contact. A filler material, metallic or non-metallic, m a y be used with spaced laminae, thus constituting sandwich substructures.
447
Ballistic resistance of steeI-FRP laminated plates." A. A. Alrnohandes et al. Table 1 Hardness and tensile properties of mild steel Plate thickness t(mm)
Hardness BHN
Yield stress Cry (MPa)
U.T.S. tru (MPa)
Failure strain ef
l, 2, 4 and 6 8
96-103 134
210-247 311
316-346 448
0.29-0.32 0.28
Table 2 Density, fiber weight fraction and tensile properties of FRP FRP
Density Fiber weight p (g/cm3) fraction (%)
Fracture stress O'f (MPa)
Fracture strain ~;f (%)
Type 1" Type 2t
1.83 1.50
258 194
4.79 4.83
0.7 0.5
* 4.00 plies per ram, 0.50 weight percent hardener * 2.67 plies per ram, 0.75 weight percent hardener
properties were measured in compliance with DIN specifications and average values are listed in Table 1. Two types of FRP-composite were used as filler material between the steel laminae, Type 1 and Type 2. The tensile properties, fiber weight fraction and density were determined for both types according to ASTM specifications and average values are listed in Table 2. Ballistic tests were mainly concerned with the determination of projectile impact and post-perforation velocities. A scheme of the test setup is shown in Figure 1, which consists mainly of: (i) 7.62 mm launcher with smooth-bore launching tube, (ii) test stand, (iii) target plate and (iv) velocity measuring instrument, consisting of an OEHLER chronograph and two Sky Screen III frames. Cartridge
2000(ram) Q
1100{rnrn)
A
j:o
E "
L ,,0,mm,J
,')/,~-~///
,'9,"/2/
2000 fmm)
II
I
IJl ~
~!
/
//4~'///
-
Figure 1 Ballistic test setup: (1) Launcher. (2) Test stand: (a) Lower stand, (b) front firing box, (c) rear firing box, (d) target clamping-vice, (e) measuring frames stand, (f) blast baffle. (3) target plate. (4) Velocity measuring screens (frames)
In this paper, the ballistic performance of mild steel single and laminated targets, with in-contact and spaced laminae, having a total steel thickness of 8mm is investigated experimentally. Effects of number, thickness, arrangement and properties of laminae are sought for different impact velocities ranging from 706 to 826 m/s. In case of spaced laminae, interspatial distances or filler thickness are chosen to be equal to, or multiples of the projectile core diameter (6 mm). In all tests, the 7.62 mm bullet, having a mass of 11.75 gm and a slenderness ratio of 4.2, is used. The ballistic test program also investigates the effect of the filler material type and configuration on target resistance to penetration. The effects of filler thickness and density are of prime concern. These tests are limited to the highest impact velocity (826 m/s) only.
2 EXPERIMENTAL WORK Mild steel sheets (1 × 2m) having 1, 2, 4, 6 and 8mm thicknesses were used to prepare square plates (215x 215 mm) with four corner holes. Hardness and tensile
448
cases were initially emptied and then refilled with prescribed charges, in order to vary the impact velocity. Complete experimental details are given elsewhere 3.
3 BALLISTIC TEST RESULTS In the present study, the specific velocity change, A Vp, defined as the change in projectile velocity divided by the length of travel through the target, was adopted to represent target resistance. Velocity change (Vi - Vr, where Vi and Vr are the impact and residual velocities, respectively) or energy loss have been alternatively used by other investigators for the same purpose, e.g. Recht and Ipson 4. To account for the effect of target thickness, the 'specific energy loss', i.e. the loss in projectile kinetic energy divided by the total plate thickness, was also adopted as a representative parameter 5. Table 3 lists all the ballistic test results obtained. 3.1 Results for laminated steel targets
The first set of ballistic test results for the steel
Ballistic resistance of steeI-FRP laminated plates." A. A. Almohandes et al.
Table 3
Ballistic test results
Expt. NO.
Target configuration and code
I. Single and laminated steel targets: CCI: (8S) 8 mm single steel target.
CC2: (2S-0A-6S) 2 mm steel + 6 mm steel; in contact.
(6S-0A-2S) 6 mm steel + 2 mm steel; in contact.
CC3: (4S-0A-.4S) 2 (4 mm steel ); in contact.
CC4: (2S-6A-6S) 2 mm steel + 6 mm steel; with 6 mm air gap.
(6S-6A-2S) 6 mm steel + 2 mm steel: with 6 mm air gap,
CC5: (4S-6A-4S) 2 (4 mm steel); with 6 mm air gap.
"H CC6: (IS-6A-IS-6A-6S) 2 (1 mm steel) + 6 mm steel; with 6 mm air gaps.
-ff[B (6S-6A-1 S-6A-I S) 6 mm steel + 2 ( 1 mm steel); with 6 mm air gaps.
-"E[Hl0
CC7: (2S-6A-2S-6A-4S) 2 (2 mm steel) + 4 mm steel; with 6 mm air gaps.
-qi[l)B (4S-6A-2S-6A-2S) 4 mm steel + 2 (2 mm steel); with 6 mm air gaps.
12
CC8: (I S-6A-I S-6A-I S-6A- I S-6A-4S) 4 (I mm steel) + 4 mm steel; with 6 mm ait g a p s
-liliiliI,iB-
Impact velocity Vi (m/s)
Residual velocity V, (m/s)
Velocity change AV (m/s)
706.0 754.5 775.4 804.5 826.2 706.0 754.5 775.4 804.5 826.2 706.0 754.5 775.4 804.5 826.2 706.0 754.5 775.4 804.5 826.2 706.0 754.5 775.4 804.5 826.2 706.0 754.5 775.4 804.5 826.2 706.0 754.5 775.4 804.5 826.2 706.0 754.5 775.4 804.5 826.2 706.0 754.5 775.4 804.5 826.2 706.0 754.5 775.4 804.5 826.2 706.0 754.5 775.4 81)4.5 826.2 706.0 754.5 775,4 81)4.5 826.2
446.4 488.7 528.1 611.3 647. I 477.4 514.0 549.5 609.1 658.3 471.2 522.4 522.4 615.7 654.1 486.4 533.0 567.1 643.1 667.2 474.3 521.8 544.6 611.9 653.7 476.9 522.6 550.2 615.4 665.4 488.0 535.4 562.2 644.3 668.9 483.9 538.4 565.5 644.3 667.4 475.7 509,9 536.4 637.6 663.9 492.9 538.9 580. I 654.7 679.5 494.6 542.1 578.6 643.6 673.6 527.4 573.3 608.7 653.5 683.8
259.6 265.8 274.3 103.2 179.1 228.6 240.5 225.9 195.4 167.0 234.8 232.1 232.1 188.8 172.1 219.6 221.5 208.3 161.4 159.0 231.7 232.7 230.8
192.6 172.5 229.1 231.9 225.2 189.1 160.8 218.0 219.1 202.2 160.2 157.3 222.1 216.1 209.9 160.2 158.8 230.3 244.6 239.0 166.9
162.3 213.1 215.6 195.3 149.8 146.7 211.4 212.4 196.8 160.9 153.2 178.6 181.2 166.7 151.0 142.4
Specific V-change AVp
(m/s.mm) 32.45 33.26 30.91 24.15 22.39 28.58 30.06 28.33 24.43 20.90 29.35 29.01 29.56 23.60 21.51 27.45 27.69 26.04 20.18 19.88 16.55 16.62 16.49 13.76 16.36 16.36 16.65
16.09 13.51
11.49 15.57 15.65 14.51
11.44 11.24 11.52 12.23
11.95 8.345 8.115 11.31
11.52 11.22 8.178 8.030 10.66 10.78 9.765 7.490 7.335 10.57 10.62 9.840 8.045 7.6611 5.5"1 5.6~3 5.220 4.719 4.450
449
Ballistic resistance of steeI-FRP laminated plates." A. A. Almohandes et al.
Table 3
Ballistic test results
(continued)
Target configuration and code
Expt.
No.
(4S-6A-IS-6A-['.S'-6A-I S-.6A-IS)
13
4 mm steel + 4 (I mm steel): with 6 mm air gaps.
14'
I!. Laminated steeI-FRP-I targets: (4S-6FIz4-4S) 2 (4 mm steel); with 6 mm FRP-1 (24 plies).
6S
15
16
Impact velocity Vi (m/s)
Residual velocity Vr (m/s)
Velocity change
706.0 754.5 775.4 804.5 826.2
518.8 553.1 613.1 660.5 675.4
187.2 191.4 t 62.3 150.8
5.850 5.981 5.072 4.500 4.713
826.2
609.2
217.0
15.50
826.2
410.0
416.1
20.81
(4S- 12F',1,-4S) 2 (4 mm steel); with 12 mm FRP-I (48 plie~;).
(4S-24F'gs "4S) 2 (4 mm steel); with 24 mmFRP-I (96 plies). Projectile seized inside
(4S-24A-4S) 2 (4ram steel); with 24 mm air gap. /.
18
/,
20
21
826.2
638.0
188.2
5.881
826.2
268.1
558.1
17.44.
(4S-9A-6S-9A-4S) 4 mm steel + 6 mm steel + 4 mm steel; with 9 mm air gaps ,~
19
144.0
z,S
826.2
17
AV
(m/s)
Specific V-change AVp (m/s.mm)
6
t.
(4S-SA-SS-SA-4S) 4 mm steel + 8 mm steel + 4 mm steel; with 8 mm air gaps 826.2
Incomplete penetration
826,2
Incomplete penetration
(2S-12F'4a-2S-12F'484S) 2 (2 mm steel) + 4 mm steel: with 2 (12 mm FRP-I, 48 plies).
(2S-12A-2S-12A.-4S) 2 (2 mm steel ) + 4 mm steel: with 12 mm air gaps. 2
22
2
4
651.3
174.9
5.466
826.2
273. I
553.1
17.28
(2S-4.5A-3S4.5A-2,S-4.5A-3S4.5A-4s) 2 (2 mm steel) + 2 (3 mm steel) + 4 nun steel: with 4.5 mm air gaps.
23
826.2
(2S-4A-4S-4A-2S-4A-2S-4A--iS) 2 (2 mm steel) + 3 (4 nun steel); with 4 111111air gaps. 826.2
450
Incomplete penetration
Ballistic resistance of steeI-FRP laminated plates: A. A. Almohandes et al.
Table 3
Expt.
Ballistic test results
(continued)
Target configuration and code
No. 24
25
26
27
(2S-12F'41-4S-12F'+,-2S) 2 mm steel + 4 mm steel + 2 mm steel; with 2 (12 mm FRP-1, 48 plies) 2 ~ 2
29
30
31
32
33
34
35
Residual velocity
V, (m/s)
826.2
Velocity change AV (m/s)
Specific V-change AVp (m/$.mm)
Incomplete pcnetratmn
(2S- 12A-4S- 12A-2S) 2 mm steel ÷ 4 mm steel + 2 mm steel: with 12 mm air gaps.
(2S-4.5A-3S-4.5A-4S-4.5A-3S-4.5A-2S) 2 (2 mm steel) + 2 (3 mm steel) + 4 mm steel: with 4.5 mm air gaps. 2 3 ~ 2 2
826.2
668.1
158.1
4.941
826.2
285.4
540.8
16.90
(2S-4A-4S-4A-4S-4A-4S-4A-2S) 2 (2 mm steel) + 3 (4 mm steel); with 4.5 mm air gaps. 2
28
Impact velocity V+ (m/s)
L
2
t.
t,
826.2
(6S-0A-8S) 6mm steel + 8 mm steel; in contact. 6 8
826.2
(8S-0A-8S) 2 (8mm steel); in contact. 8 e
826.2
Incomplete penetration
261.0
265.2
17.66
Incomplete penetration
(2S-24A-6S)" 2 m m steel + 6 mm steel: with 8 mm air gaps 826.2
635.0
191.2
5.975
826.2
451.1
375.1
I 1.72
(4S%24F'56-4S ~) 2 (4 mm steel); with 24 mm FRP-2 (56 plies).
826.2
375.2
451.0
14.09
(4S"-24F'~-4S ") 2 (4 mm steel); with 24 mm FRP-2 (64 plies).
826.2
IlL Laminated steeI-FRP-2 targets: (4SL24FZ4s-4SR) 2 (4 mm steel, machined from 8 mm plates); with 24 mm FRP-2 (48 plies).
(4S"-24A4S") 2 (4 mm steel): with 24 mm air gap. 2kA
826.2
(4,S"-9.5 A-5S"-95 A-4S ~) 2 (4 mm steel) + 5 mm steel: with 9.5 mm air gaps. 55
826.2
Projectile seized inside
631.3
194.9
6.091
Incomplete penetration
451
Ballistic resistance of steeI-FRP laminated plates." A. A. Almohandes et al.
Table 3
Expt. No. 36
37
Ballistic test results (continued)
Target configuration and code
(4S "- I 0A-4S"- I 0A-4S ") 3 (4 mm steel ); with 10 mm air gaps. kS
Impact velocity Vi (m/s)
Residual velocity Vr (m/s)
Velocity change (m/s)
Specific V-change AVp (m/s.mm)
826.2
355.1
471.1
14.72
(2S"-24FZ,4-6S") 2 m m steel + 6 m m steel: with 24 m m FRP-2 (64 plies).
826.2
38
Projectile seized inside
(2S"-24A-6S") 2 mm steel + 6 mm steel); with 24 mm air gap. 8 ~ 6 "~
39
AV
625.3
200.9
6.278
(2S"-9.5A-5S%9.5A-6S ") 2 mm steel + 5 mm steel + 6 mm steel; with 9.5 mm air gaps. Incomplete penetratmn
826.2
_g_d___NI 40
41
(2S% 10A-4S ~-I 0A-6S') 2 m m steel + 4 mm steel + 6 mm steel; with 10 mm air gaps. t.$
826.2
348.2
478.0
14.94
(2S% 12F~32-2S%12F'3r-4S ~) 2 (2 mm steel) + 4 mm steel; with 2 (12 mm FRP-2.32 plies). Incomplete penetration
826.2
42
43
44
(2S%12A-2S %12A-4S') 2 (2 mm steel ) * 4 mm steel; with 12 mm air gaps. r2A 12A
(2S%4.75A-2.5S%4.75A-2S'-4.75A-2.5S%4.75A-4S ~) 2 (2 m m steel) + 2 (2.5 m m steel) + 4 m m steel:with 4.75 m m air gaps. 7.55 255
5.650
Incomplete penetration
826.2
826.2
360.1
466. I
14.57
826.2
705.3
120.9
3.778
826.2
150.2
676.0
I0.24
(66F'~7,) 66 mm FRP-2 (176 plies).
66Fz
S 8 Steel laminae machined from originally 8 mm-thick plates
452
180.8
(32F~s,) 32 mm FRP-2 (86 plies).
~2F 2
46
645.4
(2S"-5A-2S%5A-2S'-5A-2S"-5A-4S") 4 (2 m m steel) + 4 m m steel: with 5 m m air gaps. 25 25
45
826.2
Ballistic resistance of steeI-FRP laminated plates." A. A. Almohandes et al.
35.0 Viz Vil
Vii = Vi2 = Vi3 = Vi4 = Vi5 =
Vi3
300
706.0 754.5 775.4 804.5 826.2
m/s m/s m/s m/s m/s
250 Vi4
E
3.1.1 Effect of target configuration. This effect is depicted in Figure 2, which shows that configurations consisting of in-contact steel plates have higher ballistic resistance than those having the same number of laminae, but spaced. Moreover, ballistic resistance is also highest for two-lamina targets having a thick single-lamina component. For example, the two-lamina target consisting of a 6 mm lamina in contact with a 2 mm lamina is more effective than the target with two 4mm laminae in contact, and so on. In this respect, Corran et al. 6 argued that the improved strength of multi-layer shields, consisting of a thin front plate backed by a thicker rear plate, is essentially due to the fact that plastic deformation is promoted while plugging is inhibited. They expected that further improvements may be achieved by a thin, flexible and hard front plate backed by a thicker plate having low stress and capable of absorbing energy with large plastic deformation.
~5
>~ <3
20.0
t
l
~.0
i
i
c
I
T
I
i
r~
15.0
CC2
,
6S-0A-2S CC3 45-0A-45 CC4 2S-6A-6S
> ,_
2S-OA-rS
10.0
6sr D. O~
5.0
~
'
~
N
,
,
~
.2s
CC5 4S-6A-4S CC6 1S-6A-1S-6A-6S ! 6S-6A-IS-6A-IS m CC7 25-6A-2S-6A-45 45-6A-2S-6A-2S i~ I CC8 l S-6A-1S-6A-IS-6A-IS-6A-4S~ d 45-6A-1S-6A-IS-6A-IS-6A-IS
r ~ ~,
,
I
i
I
i
I
I
i
i
1
2
3
4
5
6
7
Configuration Code, CC
Figure 2 Specific velocity change
versus
target configuration
35.0
CCltP--~- - - " ~ 30.0
CC2a_______~.'~ CC3,w--- - ---a~ . "~ ~,
25.0
E.
, Single lamina ' ~ ~ " ~ target - - 2 in-contact --4 laminae
E
20.0 eel
;>
CC44~--- ----i~- t CC5E-------~ \
5.0
10.0
o
laminae
CC8¢& . - ~ .
5.0
-~q-----q5 separate laminae
|
650
700
I
I
I
750
800
850
Impact Velocity, Vi (m/s)
Figure 3 Specific velocity change
versus
impact velocity
laminated targets constitute 12 different configurations in addition to the monolithic one (cf. Table 3, experiments 1-13). Because no discernible differences in performance were found, configurations of experiments 2 and 3 were given the same code, CC2. Similarly, experiments 5 and 6 were coded CC4, experiments 10 and 11 coded CC7, and experiments 12 and 13 coded CC8.
900
3.1.2 Effect of profectile impact velocity. Figure 3 depicts the dependence of the specific velocity change, A Vp, on the impact velocity, Vi, for different target configuration groups considered. It is clear that, within the test conditions reported, the specific velocity change first increases, at a moderate rate, in the impact velocity range from 706 to 756 m/s. Then, it rapidly decreases in the range from 755 to 805 m/s, and continues to decrease, but at a much slower rate, in the range from 805 to 826m/s. The effect of impact velocity has been studied by many other investigators, such as Zaid and Travis 7, AbdelKader 5 and Corran et al. 6 Zaid and Travis 7 found that at low impact velocities target damage is usually associated with considerable widespread deformation, or dishing, and with localized bulging at the impact zone. The dishing increases with velocity until perforation occurs at some critical velocity and then decreases for higher velocities. Abdel-Kader 5 had noticed that with the increase in projectile impact velocity, the specific energy loss of steel targets of 1-4 mm thickness first decreases to a minimum, which depends on the plate thickness, and then increases. This phenomenon was also observed and discussed by Recht a n d Ipson 4 and Osborn and Maj 8, who experimented with thin plates as well. It was noticed that at velocities near the ballistic limit, Vlim, thermal effects lower the material strength and consequently its resistance to penetration; at higher velocities, the effect of strain rate on raising the material fracture resistance is predominating. It seems, therefore, that for the 8 mm targets the present impact velocities pertain to the small
453
Ballistic resistance of steeI-FRP laminated plates." A. A. Almohandes
e t al.
Zt s
E E ""
E
> <3
Tt~ = 12 mm
Vi = 826.2 m/s
=14 turn
1Z~_~-'~T
"~1
Machined from 8 mvn-plales
15.0
# Test number (c/: Table 3).
eEts = 8 mm
6.28~
6.09
> •
°~
.
.
u
-.1~
...11
Configuration l 3
!1-~! !l.~J
.36 tn4~
42
34 t
I J I<, ,.tl
I
e
I~!
I
,
!
I,,-!
I
o:
!
.<{
I
O !
t/l!
1
tOI
}tOl I
2n--d Group - ~
I
I
~rll
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3 r-d G r o u I.
4 Effect of number of steel laminae
velocity range, where thermal effects dominate, thus reducing ballistic performance. Figure 3 also shows that ballistic performance of the target plate is reduced by lamination (both in-contact and spaced), the amount of reduction being increased with the number of laminae comprising the target. This effect is more pronounced at the lower impact velocities, and will be discussed in the following section.
3.1.3 Effect of number and thickness of laminae. Results of different target configurations were categorized according to thickness into three groups in Figure 4. The first group of targets have a total steel thickness of 8mm each, the second group 12mm and the third group 14mm. It is clear 'from this figure that target effectiveness, expressed by the specific velocity change, increases with the total target thickness. Furthermore, the energy required to cause target failure can be considered to consist of two parts, failure initiation and propagation. For relatively thin plates, fracture propagation energy may be negligible; for thicker plates, this energy dissipation mechanism considerably increases the plate's resistance to penetration 5. Previous researchers arrived at similar findings. For instance, Zaid and Travis 7 found that the major parameter affecting the amount of
454
,~|
!1
I%1
{
! I !
1st Group Figure
i[ oe
o
-JI
#
38
O, C
~a
energy absorbed during projectile penetration is the ratio of the target thickness to the projectile diameter. It is obvious from Figure 4 that target effectiveness decreases with an increase in the number of laminae. This is apparently caused by the entirely independent deformation of each lamina, since the structural deformation taking place during penetration acts as an energy absorbing mechanism 9, in case of relatively thin plates, less specific energy is required to cause target failure (as discussed above). Moreover, for the same number of laminae, targets with thicker back plates exhibit higher resistance to penetration. The same phenomenon was also observed by previous investigations. Abdel-Kader 5, for instance, attributed this response to the increase in amount of energy absorbed in bulging the thick back plate. When the back plate is relatively thin, it fails in tension due to lack of structural rigidity.
3.1.4 Effect of the target mechanicalproperties.
Figure
5 compares the effectiveness of two groups of laminated target configurations consisting of spaced steel laminae. The first group was prepared from as-received plates of thickness 2 and 4 mm. The second group, however, was prepared by machining 8-mm thick plates (having higher
Ballistic resistance of steeI-FRP laminated plates." A. A. Almohandes et al.
,~
E. ~E
7.0
may also be seen in Figure 5. Toughness of a laminated target was calculated as:
Vi = 826.2 m/s
8.0 • Machined from 8 ram-plates
o
• As-received plates
t3
U =
~
6.0
E E
"~-
--n
5.0 1.5
>
E
>= < U e~
~Vu 1.0
>
'ilj
" ~'
o Z
Configuration
Figure 5 Effect of mechanical properties of steel laminae
Vi = 826.2 m/s
E 20.0
/
r...)
..~
E
E E
E
E \
a" ~•
ti, i=1
where U is the target toughness, Ui is the toughness of the ith lamina, ti is its thickness, and n is the number of laminae constituting the target.
3.2 Results for steel-FRP laminated targets The second and third sets of ballistic tests include experiments 14-30 for laminated targets with filler Type 1, and experiments 31-46 for laminated targets with steel plates manufactured from the 8-mm thick plates and filler Type 2.
0.5
.E
30,0
Uit i i=1
~Vp
3.2.1 Effect of FRP thickness. Figure 6 shows the dependence of the specific velocity change on FRP thickness. As one would expect, it is seen that A Vp increases with filler thickness at a decreasing rate. Conversely, Gupta and Davids 1° reported that the relation between energy loss and target thickness for steel and FRP of varying density was found to be approximately linear with a slope increasing with density. 3.2.2 Effect of fiber weight fraction. Fiber weight fraction can be considered as a measure of FRP density. Figure 7 shows the relation between the specific velocity change and fiber weight fraction (expressed in terms of number of plies of FRP per mm). It is obvious that A Vp increases, at an increasing rate, with the number of plies of F R P per ram. Note that Type 2 FRP was used in these tests, together with steel plates generated from the 8-mm thick steel plates. In agreement with the present results, Gupta and Davids 1° stated that the projectile energy loss increases with FRP density. In contrast, they found that the stopping power of FRP increases linearly with density.
10.0
3.2.3 Effect of target configuration.
L 15 14
~
6
12
18
24
F R P T y p e I T h i c k n e s s , tf ( r a m )
Figure 6 Effectof FRP thickness strength and toughness) into the required dimensions. It is seen from this figure that, for the same configuration, the specific velocity change A Vp is lower for the as-received plates than for those prepared from the 8-mm thick plates. Normalizing A Vp with respect to toughness (which combines both stress and strain), both groups were found to give almost identical results, as
(a) SteeI-FRP-I As listed in Table 3 three different target configurations having a total steel thickness of 8 mm and FRP Type 1 thickness of 24 mm were tested (experiments 16, 20, 24). In each case, the projectile was unable to complete target penetration successfully, as shown in Figure 8. Three experiments were run with the FRP Type 1 filler removed (experiments 17, 21, 25), thus enabling the projectile to perforate the three configurations although at different residual velocities. It was observed that the configuration consisting of two 4-mm steel plates is more effective than the other two (each having three laminae). It was also observed that the 3-lamina target with the 4-mm back plate is more effective than the one having a 2-mm back plate, as may be seen from Figure 8. This behaviour of steel plates was also observed by Abdel-Kader 5.
455
Ballistic resistance of steeI-FRP laminated plates." A. A. Almohandes
25.0
Next, a steel plate of weight equivalent to that of the 24-mm thick FRP Type 1 was found to be 5.5 mm thick. Since such a steel plate was not available, a 6 mm steel plate was used instead. Thus three equivalent configurations were tested (experiments 18, 22, 26). It was found that these configurations were less effective than those with the FRP Type 1 filler, although the equivalent steel thickness was increased from 5.5 mm to 6 mm, as shown in Figure 8. The equivalent steel thickness was further increased to 8mm and three more configurations were tested (experiments 19, 23, 27). The projectile could hardly perforate any of these configurations, as may be seen from Figure 8. Furthermore, two laminated steel configurations with total thickness 14 and 16ram, respectively, were tested (experiments 28 and 29). Whereas the first configuration was successfully perforated, the second one was not. Based on these results, it can be concluded that the steel plate thickness equivalent to the 24 mm FRP Type l lies between 6 and 8 mm, thus possessing more weight. Thus from a practical point of view, especially when considering light-weight requirement, it is advantageous to use steel-FRP composites rather than steel alone.
7 /
V~= 826.2 m/s
E
t-
~. 20.0
i5.0
;:> ~0.0 ,
to~
to,
5.0
I
ZOO
2.33
2.66
Numberof Type2 Pliesper mm Figure 7
Effectof fiber weightfraction
(b) SteeI-FRP 2 To further confirm the above findings, another set of ballistic tests were performed using steel plates prepared from the 8mm thick material, (thus eliminating the
25.82
re.g1/mm
TI
25.0
E "~ 20.0
e t al.
l
li
17.~
I
17.28
17.66
16.91
T
e~ 15.0 e=
r,.) .~- 10.0
Vi = 826.2 m/s
0
> ~
l
5.88
5 .)7
..
5.0
4 94
-~
(~Incomplete penetration • ~ vrojectde is seized " ~ inside back lamina ~Complete penetration
I
I
e~
~
(
Configuration 16
I:'"~"l
17
I
I
18 u~
m
I
I
I'~1
I
T ~ - F RIS T Figure
456
8
u')
21
u')
22 I
"v'l
!
I
~1
I
I
OI I
Iml
SECOND GROUP
Effect o f s t e e l - F R P T y p e 1 l a m i n a t e d t a r g e t c o n f i g u r a t i o n
~
u")
i
,
GROUP
0
×I
25
^ 26
.
2
i I ~ i t n l I i.^' ! I~,'~I~I~ I
(./')
<~[IV)
t~
=--~THIRD GROUP
u3
V) I
:-
28
29
Ballistic resistance of steeI-FRP laminated plates: A. A. Almohandes et al.
25.82 (m,s-llmm)
i- i'-i
.... 25.0
E 20.0
Vi = 826.2 m/s ]~
Incomplete penetration
I
1
( ~ Complete penetration 1/-..56
~5.0
10.24
LL
6.09
6,28'
.~
e.j, e'~ C,/3
5,0
'
:!
5.66
7 Configuration
37 u'l
38
4,4
39
~ft
u3
,. ~I~CXl
I
iv'l%;I I
'~l~"~"~li~
lOt , i I
[ ',~!
INGroup
I
i
| -,.
I.t.
I..-
2n--OGroup
-~
I
L~-
qff, l tt~
3rdGroup
~
--,.1
'
z._ Group
Figure 9 Effect of steel-FRP Type 2 laminated target configuration
effect of the difference in mechanical properties), and FRP Type 2 as a filler. The results are listed in Table 3 (experiments 31-46). The same experimental procedure followed in case of steel-FRP-1 was repeated for steel-FRP-2, but for different configurations. Tests were divided into four groups. Each of the first three groups consisted of four tests. In the first test, a steel-FRP-2 configuration was used. In the second test, the FRP Type 2 was removed. The equivalent (by weight) steel plate, to the 24-mm thick FRP Type 2 was calculated and found to be 4.6ram. Because such a plate was not available, 5 and 4 mm thick steel plates replaced the FRP Type 2 in the third and fourth test of each group, respectively. The fourth group consisted of two tests only, as will be explained shortly. The results are shown in Figure 9. In experiments 33, 37 and 41, (steel-FRP-2 configurations), incomplete penetration was encountered. In experiments 34, 38 and 42 (steel laminae without filler) the projectile was able to penetrate the target with a specific velocity change that increases with increased thickness of back plate and/or decreased number of laminae. The same trend was
exhibited with the 4-mm thick equivalent steel targets, while incomplete penetration was exhibited in case of 5-mm thick equivalent steel targets. These results are qualitatively in agreement with those of steel-FRP-1. Quantitatively, however, the laminated targets encompassing FRP Type 1 are more effective than those having FRP Type 2: This is expected since the fiber weight fraction, alternatively the number of plies per mm, is greater in the former material. Gupta and Davids ~° have also found that the energy loss increases with the density of FRP. In addition to the aforementioned tests, two more target configurations were tested. In the first one (experiment 45), a FRP Type 2 target was used having a thickness of 32 mm, equal to total thickness of target configuration in this group. This target was found to be less effective than any other one used in this set of tests. The second configuration (experiment 46), FRP Type 2 had a total thickness of 66 mm, equivalent to 8 mm steel with 24mm FRP Type 2 composite target. It was also perforated, thus confirming the conclusion that the most effective configuration should combine steel and FRP laminae.
457
Ballistic resistance of steeI-FRP laminated plates: A. A. Almohandes et al. 4 CONCLUSIONS Based on the results and findings reported herein, the following conclusions can be drawn: (a) Single steel target plates are more effective than laminated targets (consisting o f in-contact or separated plies) o f the same total thickness. The difference in effectiveness diminishes with impact velocity. (b) Ballistic resistance o f steel targets increases as target material toughness increases. (c) In terms o f specific velocity change, the ballistic resistance o f steel targets first increases slightly and then decreases with impact velocity. (d) Resistance o f laminated steel targets increases as: (i) the n u m b e r o f laminae decreases, and (ii) the thickness o f back plate increases. (e) Use o f F R P as filler in spaced laminated steel targets improves the ballistic resistance. (f) Increase o f F R P thickness and density further improves ballistic performance o f s t e e l - F R P targets.
458
REFERENCES 1 2 3 4 5 6 7
8 9 10
Backman,M. and Goldsmith, W, The mechanics of penetration of projectiles into targets. Int. J. Engng. Sci. 1978, 16, 1-99 Zukas, J.A., Nicholas, T., Swift, H.F., Greszcuk, L.B. and Curran, D.R. 'Impact Dynamics', John Wiley & Sons, New York. 1982, Vol. 5, Chapter 5, pp. 157-210 Almohandes, A.A. 'Ballistic resistance of steel-fiberglass reinforced polyester laminated plates', Master of Science Thesis, Faculty of Engineering, Cairo University, Egypt, 1993 Recht, R.F. and Ipson, T.W. Ballistic penetration resistance and its measurements. Exp. Mech. 1975, 15, 249-257 Abdel-Kader, M.S. 'The penetration capability of high-speed projectiles fired against brass and steel plates', Master of Science Thesis, M.T.C., Cairo, Egypt, 1981 Corran, R.S.J., Ruiz, C. and Shadbolt, P.J. On the design of containment shields. Computer and Structures, 1983, 16, 563-572 Zaid, A.T. and Travis, F.W. A comparison of single and multiplate shields subjected to impact by a high speed projectile. In 'Mechanical properties of materials at high rates of strain', (Ed. J. Harding), Conf. Series No 21, Inst. Phy., London, 1974, 417-428 Osborn, C.J. and Maj, S. The effect of striking velocity on penetration energy for mild steel plates. In 'Proc. Int. Conf. on Fracture', Pergamon Press, New York, 1977, Vol. 3, pp. 617-20 Marom, I. and Bodner, S.R. Projectile perforation of multilayered beams, lnt. J. Mech. Sci. 1978, 21, 489-504 Gupta, B.P. and Davids, N. Experiments with fiberglass-reinforced plastics. Exp. Mech. 1966, 6, 445-450
ELSEVIER
Composites: Part B 27B (1996) 447-458 Copyright © 1996 Elsevier Science Limited Printed in Great Britain. All rights reserved 1359-8368/96/$15.00
Experimental investigation of the ballistic resistance of steel-fiberglass reinforced polyester laminated plates A. A. A l m o h a n d e s AFTRC, Egypt
and M. S. A b d e I - K a d e r Department of Mechanical Engineering, M. T.C., Cairo, Egypt
and A. M. Eleiche* Department of Mechanical Engineering, United Arab Emirates University, United Arab Emirates (Received 25 September 1995; accepted 15 November 1995) The present experimental study is undertaken to investigate the effect of target configuration on ballistic performance when struck by standard bullets of different velocities. At first, single mild steel plates, 1-8 mm thick, are tested, and the effect of thickness and mechanical properties of plate material are explored. Secondly, in-contact laminae comprising an 8 mm-thick target, and spaced laminae of the same total steel thickness, with spacing distances equal to or multiples of the bullet core diameter (6 ram) are tested and the effect of number, thickness, and arrangement of laminae sought. In addition, fiberglass reinforced polyester (FRP) is used as a filler material for targets with spaced steel laminae. The influence of FRP's physical and mechanical properties on the ballistic performance of steel-FRP targets is investigated. In order to perform the ballistic tests, a special setup is constructed, which consists of a launcher, a target clamp and a velocity-measuring device. In each experiment, the change in the projectile velocity (while penetrating the target) divided by the length of penetration is established as a measure of target performance. Results show that single targets are more effective than laminated targets of the same total thickness, regardless of the configuration or striking velocity. It is noted, however, that the difference in performance diminishes as the striking velocity increases. Moreover, the effectiveness of laminated targets, in contact or spaced, increases as the number of laminae comprising each target decreases. Ballistic performance of laminated targets is further enhanced by using the thickest lamina as the back lamina. Results also emphasize the dependence of target performance on mechanical properties. Steel-FRP targets show better performance than weight-equivalent steel targets. Performance of a steel-FRP target is further improved by increasing fiber weight fraction in the FRP. Copyright © 1996 Elsevier Science Limited
(Keywords:bamstic; impact; laminated plates; damage; polyester)
1 INTRODUCTION The subject of penetration has long been studied, primarily because o f its importance in military and civilian fields. Many parameters are found to control the mutual interaction between the impacting projectile and * On leave from Department of Mechanical Design and Production, Cairo University, Egypt.
the target. These include impact conditions as well as projectile and target characteristics, and result in many failure modes, such as brittle fracture, ductile hole enlargement, petaUing, spalling and plugging 1'2. Target plates may be monolithic or multi-layered. In the latter type, individual layers may be spaced or in-contact. A filler material, metallic or non-metallic, m a y be used with spaced laminae, thus constituting sandwich substructures.
447
Ballistic resistance of steeI-FRP laminated plates." A. A. Alrnohandes et al. Table 1 Hardness and tensile properties of mild steel Plate thickness t(mm)
Hardness BHN
Yield stress Cry (MPa)
U.T.S. tru (MPa)
Failure strain ef
l, 2, 4 and 6 8
96-103 134
210-247 311
316-346 448
0.29-0.32 0.28
Table 2 Density, fiber weight fraction and tensile properties of FRP FRP
Density Fiber weight p (g/cm3) fraction (%)
Fracture stress O'f (MPa)
Fracture strain ~;f (%)
Type 1" Type 2t
1.83 1.50
258 194
4.79 4.83
0.7 0.5
* 4.00 plies per ram, 0.50 weight percent hardener * 2.67 plies per ram, 0.75 weight percent hardener
properties were measured in compliance with DIN specifications and average values are listed in Table 1. Two types of FRP-composite were used as filler material between the steel laminae, Type 1 and Type 2. The tensile properties, fiber weight fraction and density were determined for both types according to ASTM specifications and average values are listed in Table 2. Ballistic tests were mainly concerned with the determination of projectile impact and post-perforation velocities. A scheme of the test setup is shown in Figure 1, which consists mainly of: (i) 7.62 mm launcher with smooth-bore launching tube, (ii) test stand, (iii) target plate and (iv) velocity measuring instrument, consisting of an OEHLER chronograph and two Sky Screen III frames. Cartridge
2000(ram) Q
1100{rnrn)
A
j:o
E "
L ,,0,mm,J
,')/,~-~///
,'9,"/2/
2000 fmm)
II
I
IJl ~
~!
/
//4~'///
-
Figure 1 Ballistic test setup: (1) Launcher. (2) Test stand: (a) Lower stand, (b) front firing box, (c) rear firing box, (d) target clamping-vice, (e) measuring frames stand, (f) blast baffle. (3) target plate. (4) Velocity measuring screens (frames)
In this paper, the ballistic performance of mild steel single and laminated targets, with in-contact and spaced laminae, having a total steel thickness of 8mm is investigated experimentally. Effects of number, thickness, arrangement and properties of laminae are sought for different impact velocities ranging from 706 to 826 m/s. In case of spaced laminae, interspatial distances or filler thickness are chosen to be equal to, or multiples of the projectile core diameter (6 mm). In all tests, the 7.62 mm bullet, having a mass of 11.75 gm and a slenderness ratio of 4.2, is used. The ballistic test program also investigates the effect of the filler material type and configuration on target resistance to penetration. The effects of filler thickness and density are of prime concern. These tests are limited to the highest impact velocity (826 m/s) only.
2 EXPERIMENTAL WORK Mild steel sheets (1 × 2m) having 1, 2, 4, 6 and 8mm thicknesses were used to prepare square plates (215x 215 mm) with four corner holes. Hardness and tensile
448
cases were initially emptied and then refilled with prescribed charges, in order to vary the impact velocity. Complete experimental details are given elsewhere 3.
3 BALLISTIC TEST RESULTS In the present study, the specific velocity change, A Vp, defined as the change in projectile velocity divided by the length of travel through the target, was adopted to represent target resistance. Velocity change (Vi - Vr, where Vi and Vr are the impact and residual velocities, respectively) or energy loss have been alternatively used by other investigators for the same purpose, e.g. Recht and Ipson 4. To account for the effect of target thickness, the 'specific energy loss', i.e. the loss in projectile kinetic energy divided by the total plate thickness, was also adopted as a representative parameter 5. Table 3 lists all the ballistic test results obtained. 3.1 Results for laminated steel targets
The first set of ballistic test results for the steel
Ballistic resistance of steeI-FRP laminated plates." A. A. Almohandes et al.
Table 3
Ballistic test results
Expt. NO.
Target configuration and code
I. Single and laminated steel targets: CCI: (8S) 8 mm single steel target.
CC2: (2S-0A-6S) 2 mm steel + 6 mm steel; in contact.
(6S-0A-2S) 6 mm steel + 2 mm steel; in contact.
CC3: (4S-0A-.4S) 2 (4 mm steel ); in contact.
CC4: (2S-6A-6S) 2 mm steel + 6 mm steel; with 6 mm air gap.
(6S-6A-2S) 6 mm steel + 2 mm steel: with 6 mm air gap,
CC5: (4S-6A-4S) 2 (4 mm steel); with 6 mm air gap.
"H CC6: (IS-6A-IS-6A-6S) 2 (1 mm steel) + 6 mm steel; with 6 mm air gaps.
-ff[B (6S-6A-1 S-6A-I S) 6 mm steel + 2 ( 1 mm steel); with 6 mm air gaps.
-"E[Hl0
CC7: (2S-6A-2S-6A-4S) 2 (2 mm steel) + 4 mm steel; with 6 mm air gaps.
-qi[l)B (4S-6A-2S-6A-2S) 4 mm steel + 2 (2 mm steel); with 6 mm air gaps.
12
CC8: (I S-6A-I S-6A-I S-6A- I S-6A-4S) 4 (I mm steel) + 4 mm steel; with 6 mm ait g a p s
-liliiliI,iB-
Impact velocity Vi (m/s)
Residual velocity V, (m/s)
Velocity change AV (m/s)
706.0 754.5 775.4 804.5 826.2 706.0 754.5 775.4 804.5 826.2 706.0 754.5 775.4 804.5 826.2 706.0 754.5 775.4 804.5 826.2 706.0 754.5 775.4 804.5 826.2 706.0 754.5 775.4 804.5 826.2 706.0 754.5 775.4 804.5 826.2 706.0 754.5 775.4 804.5 826.2 706.0 754.5 775.4 804.5 826.2 706.0 754.5 775.4 804.5 826.2 706.0 754.5 775.4 81)4.5 826.2 706.0 754.5 775,4 81)4.5 826.2
446.4 488.7 528.1 611.3 647. I 477.4 514.0 549.5 609.1 658.3 471.2 522.4 522.4 615.7 654.1 486.4 533.0 567.1 643.1 667.2 474.3 521.8 544.6 611.9 653.7 476.9 522.6 550.2 615.4 665.4 488.0 535.4 562.2 644.3 668.9 483.9 538.4 565.5 644.3 667.4 475.7 509,9 536.4 637.6 663.9 492.9 538.9 580. I 654.7 679.5 494.6 542.1 578.6 643.6 673.6 527.4 573.3 608.7 653.5 683.8
259.6 265.8 274.3 103.2 179.1 228.6 240.5 225.9 195.4 167.0 234.8 232.1 232.1 188.8 172.1 219.6 221.5 208.3 161.4 159.0 231.7 232.7 230.8
192.6 172.5 229.1 231.9 225.2 189.1 160.8 218.0 219.1 202.2 160.2 157.3 222.1 216.1 209.9 160.2 158.8 230.3 244.6 239.0 166.9
162.3 213.1 215.6 195.3 149.8 146.7 211.4 212.4 196.8 160.9 153.2 178.6 181.2 166.7 151.0 142.4
Specific V-change AVp
(m/s.mm) 32.45 33.26 30.91 24.15 22.39 28.58 30.06 28.33 24.43 20.90 29.35 29.01 29.56 23.60 21.51 27.45 27.69 26.04 20.18 19.88 16.55 16.62 16.49 13.76 16.36 16.36 16.65
16.09 13.51
11.49 15.57 15.65 14.51
11.44 11.24 11.52 12.23
11.95 8.345 8.115 11.31
11.52 11.22 8.178 8.030 10.66 10.78 9.765 7.490 7.335 10.57 10.62 9.840 8.045 7.6611 5.5"1 5.6~3 5.220 4.719 4.450
449
Ballistic resistance of steeI-FRP laminated plates." A. A. Almohandes et al.
Table 3
Ballistic test results
(continued)
Target configuration and code
Expt.
No.
(4S-6A-IS-6A-['.S'-6A-I S-.6A-IS)
13
4 mm steel + 4 (I mm steel): with 6 mm air gaps.
14'
I!. Laminated steeI-FRP-I targets: (4S-6FIz4-4S) 2 (4 mm steel); with 6 mm FRP-1 (24 plies).
6S
15
16
Impact velocity Vi (m/s)
Residual velocity Vr (m/s)
Velocity change
706.0 754.5 775.4 804.5 826.2
518.8 553.1 613.1 660.5 675.4
187.2 191.4 t 62.3 150.8
5.850 5.981 5.072 4.500 4.713
826.2
609.2
217.0
15.50
826.2
410.0
416.1
20.81
(4S- 12F',1,-4S) 2 (4 mm steel); with 12 mm FRP-I (48 plie~;).
(4S-24F'gs "4S) 2 (4 mm steel); with 24 mmFRP-I (96 plies). Projectile seized inside
(4S-24A-4S) 2 (4ram steel); with 24 mm air gap. /.
18
/,
20
21
826.2
638.0
188.2
5.881
826.2
268.1
558.1
17.44.
(4S-9A-6S-9A-4S) 4 mm steel + 6 mm steel + 4 mm steel; with 9 mm air gaps ,~
19
144.0
z,S
826.2
17
AV
(m/s)
Specific V-change AVp (m/s.mm)
6
t.
(4S-SA-SS-SA-4S) 4 mm steel + 8 mm steel + 4 mm steel; with 8 mm air gaps 826.2
Incomplete penetration
826,2
Incomplete penetration
(2S-12F'4a-2S-12F'484S) 2 (2 mm steel) + 4 mm steel: with 2 (12 mm FRP-I, 48 plies).
(2S-12A-2S-12A.-4S) 2 (2 mm steel ) + 4 mm steel: with 12 mm air gaps. 2
22
2
4
651.3
174.9
5.466
826.2
273. I
553.1
17.28
(2S-4.5A-3S4.5A-2,S-4.5A-3S4.5A-4s) 2 (2 mm steel) + 2 (3 mm steel) + 4 nun steel: with 4.5 mm air gaps.
23
826.2
(2S-4A-4S-4A-2S-4A-2S-4A--iS) 2 (2 mm steel) + 3 (4 nun steel); with 4 111111air gaps. 826.2
450
Incomplete penetration
Ballistic resistance of steeI-FRP laminated plates: A. A. Almohandes et al.
Table 3
Expt.
Ballistic test results
(continued)
Target configuration and code
No. 24
25
26
27
(2S-12F'41-4S-12F'+,-2S) 2 mm steel + 4 mm steel + 2 mm steel; with 2 (12 mm FRP-1, 48 plies) 2 ~ 2
29
30
31
32
33
34
35
Residual velocity
V, (m/s)
826.2
Velocity change AV (m/s)
Specific V-change AVp (m/$.mm)
Incomplete pcnetratmn
(2S- 12A-4S- 12A-2S) 2 mm steel ÷ 4 mm steel + 2 mm steel: with 12 mm air gaps.
(2S-4.5A-3S-4.5A-4S-4.5A-3S-4.5A-2S) 2 (2 mm steel) + 2 (3 mm steel) + 4 mm steel: with 4.5 mm air gaps. 2 3 ~ 2 2
826.2
668.1
158.1
4.941
826.2
285.4
540.8
16.90
(2S-4A-4S-4A-4S-4A-4S-4A-2S) 2 (2 mm steel) + 3 (4 mm steel); with 4.5 mm air gaps. 2
28
Impact velocity V+ (m/s)
L
2
t.
t,
826.2
(6S-0A-8S) 6mm steel + 8 mm steel; in contact. 6 8
826.2
(8S-0A-8S) 2 (8mm steel); in contact. 8 e
826.2
Incomplete penetration
261.0
265.2
17.66
Incomplete penetration
(2S-24A-6S)" 2 m m steel + 6 mm steel: with 8 mm air gaps 826.2
635.0
191.2
5.975
826.2
451.1
375.1
I 1.72
(4S%24F'56-4S ~) 2 (4 mm steel); with 24 mm FRP-2 (56 plies).
826.2
375.2
451.0
14.09
(4S"-24F'~-4S ") 2 (4 mm steel); with 24 mm FRP-2 (64 plies).
826.2
IlL Laminated steeI-FRP-2 targets: (4SL24FZ4s-4SR) 2 (4 mm steel, machined from 8 mm plates); with 24 mm FRP-2 (48 plies).
(4S"-24A4S") 2 (4 mm steel): with 24 mm air gap. 2kA
826.2
(4,S"-9.5 A-5S"-95 A-4S ~) 2 (4 mm steel) + 5 mm steel: with 9.5 mm air gaps. 55
826.2
Projectile seized inside
631.3
194.9
6.091
Incomplete penetration
451
Ballistic resistance of steeI-FRP laminated plates." A. A. Almohandes et al.
Table 3
Expt. No. 36
37
Ballistic test results (continued)
Target configuration and code
(4S "- I 0A-4S"- I 0A-4S ") 3 (4 mm steel ); with 10 mm air gaps. kS
Impact velocity Vi (m/s)
Residual velocity Vr (m/s)
Velocity change (m/s)
Specific V-change AVp (m/s.mm)
826.2
355.1
471.1
14.72
(2S"-24FZ,4-6S") 2 m m steel + 6 m m steel: with 24 m m FRP-2 (64 plies).
826.2
38
Projectile seized inside
(2S"-24A-6S") 2 mm steel + 6 mm steel); with 24 mm air gap. 8 ~ 6 "~
39
AV
625.3
200.9
6.278
(2S"-9.5A-5S%9.5A-6S ") 2 mm steel + 5 mm steel + 6 mm steel; with 9.5 mm air gaps. Incomplete penetratmn
826.2
_g_d___NI 40
41
(2S% 10A-4S ~-I 0A-6S') 2 m m steel + 4 mm steel + 6 mm steel; with 10 mm air gaps. t.$
826.2
348.2
478.0
14.94
(2S% 12F~32-2S%12F'3r-4S ~) 2 (2 mm steel) + 4 mm steel; with 2 (12 mm FRP-2.32 plies). Incomplete penetration
826.2
42
43
44
(2S%12A-2S %12A-4S') 2 (2 mm steel ) * 4 mm steel; with 12 mm air gaps. r2A 12A
(2S%4.75A-2.5S%4.75A-2S'-4.75A-2.5S%4.75A-4S ~) 2 (2 m m steel) + 2 (2.5 m m steel) + 4 m m steel:with 4.75 m m air gaps. 7.55 255
5.650
Incomplete penetration
826.2
826.2
360.1
466. I
14.57
826.2
705.3
120.9
3.778
826.2
150.2
676.0
I0.24
(66F'~7,) 66 mm FRP-2 (176 plies).
66Fz
S 8 Steel laminae machined from originally 8 mm-thick plates
452
180.8
(32F~s,) 32 mm FRP-2 (86 plies).
~2F 2
46
645.4
(2S"-5A-2S%5A-2S'-5A-2S"-5A-4S") 4 (2 m m steel) + 4 m m steel: with 5 m m air gaps. 25 25
45
826.2
Ballistic resistance of steeI-FRP laminated plates." A. A. Almohandes et al.
35.0 Viz Vil
Vii = Vi2 = Vi3 = Vi4 = Vi5 =
Vi3
300
706.0 754.5 775.4 804.5 826.2
m/s m/s m/s m/s m/s
250 Vi4
E
3.1.1 Effect of target configuration. This effect is depicted in Figure 2, which shows that configurations consisting of in-contact steel plates have higher ballistic resistance than those having the same number of laminae, but spaced. Moreover, ballistic resistance is also highest for two-lamina targets having a thick single-lamina component. For example, the two-lamina target consisting of a 6 mm lamina in contact with a 2 mm lamina is more effective than the target with two 4mm laminae in contact, and so on. In this respect, Corran et al. 6 argued that the improved strength of multi-layer shields, consisting of a thin front plate backed by a thicker rear plate, is essentially due to the fact that plastic deformation is promoted while plugging is inhibited. They expected that further improvements may be achieved by a thin, flexible and hard front plate backed by a thicker plate having low stress and capable of absorbing energy with large plastic deformation.
~5
>~ <3
20.0
t
l
~.0
i
i
c
I
T
I
i
r~
15.0
CC2
,
6S-0A-2S CC3 45-0A-45 CC4 2S-6A-6S
> ,_
2S-OA-rS
10.0
6sr D. O~
5.0
~
'
~
N
,
,
~
.2s
CC5 4S-6A-4S CC6 1S-6A-1S-6A-6S ! 6S-6A-IS-6A-IS m CC7 25-6A-2S-6A-45 45-6A-2S-6A-2S i~ I CC8 l S-6A-1S-6A-IS-6A-IS-6A-4S~ d 45-6A-1S-6A-IS-6A-IS-6A-IS
r ~ ~,
,
I
i
I
i
I
I
i
i
1
2
3
4
5
6
7
Configuration Code, CC
Figure 2 Specific velocity change
versus
target configuration
35.0
CCltP--~- - - " ~ 30.0
CC2a_______~.'~ CC3,w--- - ---a~ . "~ ~,
25.0
E.
, Single lamina ' ~ ~ " ~ target - - 2 in-contact --4 laminae
E
20.0 eel
;>
CC44~--- ----i~- t CC5E-------~ \
5.0
10.0
o
laminae
CC8¢& . - ~ .
5.0
-~q-----q5 separate laminae
|
650
700
I
I
I
750
800
850
Impact Velocity, Vi (m/s)
Figure 3 Specific velocity change
versus
impact velocity
laminated targets constitute 12 different configurations in addition to the monolithic one (cf. Table 3, experiments 1-13). Because no discernible differences in performance were found, configurations of experiments 2 and 3 were given the same code, CC2. Similarly, experiments 5 and 6 were coded CC4, experiments 10 and 11 coded CC7, and experiments 12 and 13 coded CC8.
900
3.1.2 Effect of profectile impact velocity. Figure 3 depicts the dependence of the specific velocity change, A Vp, on the impact velocity, Vi, for different target configuration groups considered. It is clear that, within the test conditions reported, the specific velocity change first increases, at a moderate rate, in the impact velocity range from 706 to 756 m/s. Then, it rapidly decreases in the range from 755 to 805 m/s, and continues to decrease, but at a much slower rate, in the range from 805 to 826m/s. The effect of impact velocity has been studied by many other investigators, such as Zaid and Travis 7, AbdelKader 5 and Corran et al. 6 Zaid and Travis 7 found that at low impact velocities target damage is usually associated with considerable widespread deformation, or dishing, and with localized bulging at the impact zone. The dishing increases with velocity until perforation occurs at some critical velocity and then decreases for higher velocities. Abdel-Kader 5 had noticed that with the increase in projectile impact velocity, the specific energy loss of steel targets of 1-4 mm thickness first decreases to a minimum, which depends on the plate thickness, and then increases. This phenomenon was also observed and discussed by Recht a n d Ipson 4 and Osborn and Maj 8, who experimented with thin plates as well. It was noticed that at velocities near the ballistic limit, Vlim, thermal effects lower the material strength and consequently its resistance to penetration; at higher velocities, the effect of strain rate on raising the material fracture resistance is predominating. It seems, therefore, that for the 8 mm targets the present impact velocities pertain to the small
453
Ballistic resistance of steeI-FRP laminated plates." A. A. Almohandes
e t al.
Zt s
E E ""
E
> <3
Tt~ = 12 mm
Vi = 826.2 m/s
=14 turn
1Z~_~-'~T
"~1
Machined from 8 mvn-plales
15.0
# Test number (c/: Table 3).
eEts = 8 mm
6.28~
6.09
> •
°~
.
.
u
-.1~
...11
Configuration l 3
!1-~! !l.~J
.36 tn4~
42
34 t
I J I<, ,.tl
I
e
I~!
I
,
!
I,,-!
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o:
!
.<{
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O !
t/l!
1
tOI
}tOl I
2n--d Group - ~
I
I
~rll
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3 r-d G r o u I.
4 Effect of number of steel laminae
velocity range, where thermal effects dominate, thus reducing ballistic performance. Figure 3 also shows that ballistic performance of the target plate is reduced by lamination (both in-contact and spaced), the amount of reduction being increased with the number of laminae comprising the target. This effect is more pronounced at the lower impact velocities, and will be discussed in the following section.
3.1.3 Effect of number and thickness of laminae. Results of different target configurations were categorized according to thickness into three groups in Figure 4. The first group of targets have a total steel thickness of 8mm each, the second group 12mm and the third group 14mm. It is clear 'from this figure that target effectiveness, expressed by the specific velocity change, increases with the total target thickness. Furthermore, the energy required to cause target failure can be considered to consist of two parts, failure initiation and propagation. For relatively thin plates, fracture propagation energy may be negligible; for thicker plates, this energy dissipation mechanism considerably increases the plate's resistance to penetration 5. Previous researchers arrived at similar findings. For instance, Zaid and Travis 7 found that the major parameter affecting the amount of
454
,~|
!1
I%1
{
! I !
1st Group Figure
i[ oe
o
-JI
#
38
O, C
~a
energy absorbed during projectile penetration is the ratio of the target thickness to the projectile diameter. It is obvious from Figure 4 that target effectiveness decreases with an increase in the number of laminae. This is apparently caused by the entirely independent deformation of each lamina, since the structural deformation taking place during penetration acts as an energy absorbing mechanism 9, in case of relatively thin plates, less specific energy is required to cause target failure (as discussed above). Moreover, for the same number of laminae, targets with thicker back plates exhibit higher resistance to penetration. The same phenomenon was also observed by previous investigations. Abdel-Kader 5, for instance, attributed this response to the increase in amount of energy absorbed in bulging the thick back plate. When the back plate is relatively thin, it fails in tension due to lack of structural rigidity.
3.1.4 Effect of the target mechanicalproperties.
Figure
5 compares the effectiveness of two groups of laminated target configurations consisting of spaced steel laminae. The first group was prepared from as-received plates of thickness 2 and 4 mm. The second group, however, was prepared by machining 8-mm thick plates (having higher
Ballistic resistance of steeI-FRP laminated plates." A. A. Almohandes et al.
,~
E. ~E
7.0
may also be seen in Figure 5. Toughness of a laminated target was calculated as:
Vi = 826.2 m/s
8.0 • Machined from 8 ram-plates
o
• As-received plates
t3
U =
~
6.0
E E
"~-
--n
5.0 1.5
>
E
>= < U e~
~Vu 1.0
>
'ilj
" ~'
o Z
Configuration
Figure 5 Effect of mechanical properties of steel laminae
Vi = 826.2 m/s
E 20.0
/
r...)
..~
E
E E
E
E \
a" ~•
ti, i=1
where U is the target toughness, Ui is the toughness of the ith lamina, ti is its thickness, and n is the number of laminae constituting the target.
3.2 Results for steel-FRP laminated targets The second and third sets of ballistic tests include experiments 14-30 for laminated targets with filler Type 1, and experiments 31-46 for laminated targets with steel plates manufactured from the 8-mm thick plates and filler Type 2.
0.5
.E
30,0
Uit i i=1
~Vp
3.2.1 Effect of FRP thickness. Figure 6 shows the dependence of the specific velocity change on FRP thickness. As one would expect, it is seen that A Vp increases with filler thickness at a decreasing rate. Conversely, Gupta and Davids 1° reported that the relation between energy loss and target thickness for steel and FRP of varying density was found to be approximately linear with a slope increasing with density. 3.2.2 Effect of fiber weight fraction. Fiber weight fraction can be considered as a measure of FRP density. Figure 7 shows the relation between the specific velocity change and fiber weight fraction (expressed in terms of number of plies of FRP per mm). It is obvious that A Vp increases, at an increasing rate, with the number of plies of F R P per ram. Note that Type 2 FRP was used in these tests, together with steel plates generated from the 8-mm thick steel plates. In agreement with the present results, Gupta and Davids 1° stated that the projectile energy loss increases with FRP density. In contrast, they found that the stopping power of FRP increases linearly with density.
10.0
3.2.3 Effect of target configuration.
L 15 14
~
6
12
18
24
F R P T y p e I T h i c k n e s s , tf ( r a m )
Figure 6 Effectof FRP thickness strength and toughness) into the required dimensions. It is seen from this figure that, for the same configuration, the specific velocity change A Vp is lower for the as-received plates than for those prepared from the 8-mm thick plates. Normalizing A Vp with respect to toughness (which combines both stress and strain), both groups were found to give almost identical results, as
(a) SteeI-FRP-I As listed in Table 3 three different target configurations having a total steel thickness of 8 mm and FRP Type 1 thickness of 24 mm were tested (experiments 16, 20, 24). In each case, the projectile was unable to complete target penetration successfully, as shown in Figure 8. Three experiments were run with the FRP Type 1 filler removed (experiments 17, 21, 25), thus enabling the projectile to perforate the three configurations although at different residual velocities. It was observed that the configuration consisting of two 4-mm steel plates is more effective than the other two (each having three laminae). It was also observed that the 3-lamina target with the 4-mm back plate is more effective than the one having a 2-mm back plate, as may be seen from Figure 8. This behaviour of steel plates was also observed by Abdel-Kader 5.
455
Ballistic resistance of steeI-FRP laminated plates." A. A. Almohandes
25.0
Next, a steel plate of weight equivalent to that of the 24-mm thick FRP Type 1 was found to be 5.5 mm thick. Since such a steel plate was not available, a 6 mm steel plate was used instead. Thus three equivalent configurations were tested (experiments 18, 22, 26). It was found that these configurations were less effective than those with the FRP Type 1 filler, although the equivalent steel thickness was increased from 5.5 mm to 6 mm, as shown in Figure 8. The equivalent steel thickness was further increased to 8mm and three more configurations were tested (experiments 19, 23, 27). The projectile could hardly perforate any of these configurations, as may be seen from Figure 8. Furthermore, two laminated steel configurations with total thickness 14 and 16ram, respectively, were tested (experiments 28 and 29). Whereas the first configuration was successfully perforated, the second one was not. Based on these results, it can be concluded that the steel plate thickness equivalent to the 24 mm FRP Type l lies between 6 and 8 mm, thus possessing more weight. Thus from a practical point of view, especially when considering light-weight requirement, it is advantageous to use steel-FRP composites rather than steel alone.
7 /
V~= 826.2 m/s
E
t-
~. 20.0
i5.0
;:> ~0.0 ,
to~
to,
5.0
I
ZOO
2.33
2.66
Numberof Type2 Pliesper mm Figure 7
Effectof fiber weightfraction
(b) SteeI-FRP 2 To further confirm the above findings, another set of ballistic tests were performed using steel plates prepared from the 8mm thick material, (thus eliminating the
25.82
re.g1/mm
TI
25.0
E "~ 20.0
e t al.
l
li
17.~
I
17.28
17.66
16.91
T
e~ 15.0 e=
r,.) .~- 10.0
Vi = 826.2 m/s
0
> ~
l
5.88
5 .)7
..
5.0
4 94
-~
(~Incomplete penetration • ~ vrojectde is seized " ~ inside back lamina ~Complete penetration
I
I
e~
~
(
Configuration 16
I:'"~"l
17
I
I
18 u~
m
I
I
I'~1
I
T ~ - F RIS T Figure
456
8
u')
21
u')
22 I
"v'l
!
I
~1
I
I
OI I
Iml
SECOND GROUP
Effect o f s t e e l - F R P T y p e 1 l a m i n a t e d t a r g e t c o n f i g u r a t i o n
~
u")
i
,
GROUP
0
×I
25
^ 26
.
2
i I ~ i t n l I i.^' ! I~,'~I~I~ I
(./')
<~[IV)
t~
=--~THIRD GROUP
u3
V) I
:-
28
29
Ballistic resistance of steeI-FRP laminated plates: A. A. Almohandes et al.
25.82 (m,s-llmm)
i- i'-i
.... 25.0
E 20.0
Vi = 826.2 m/s ]~
Incomplete penetration
I
1
( ~ Complete penetration 1/-..56
~5.0
10.24
LL
6.09
6,28'
.~
e.j, e'~ C,/3
5,0
'
:!
5.66
7 Configuration
37 u'l
38
4,4
39
~ft
u3
,. ~I~CXl
I
iv'l%;I I
'~l~"~"~li~
lOt , i I
[ ',~!
INGroup
I
i
| -,.
I.t.
I..-
2n--OGroup
-~
I
L~-
qff, l tt~
3rdGroup
~
--,.1
'
z._ Group
Figure 9 Effect of steel-FRP Type 2 laminated target configuration
effect of the difference in mechanical properties), and FRP Type 2 as a filler. The results are listed in Table 3 (experiments 31-46). The same experimental procedure followed in case of steel-FRP-1 was repeated for steel-FRP-2, but for different configurations. Tests were divided into four groups. Each of the first three groups consisted of four tests. In the first test, a steel-FRP-2 configuration was used. In the second test, the FRP Type 2 was removed. The equivalent (by weight) steel plate, to the 24-mm thick FRP Type 2 was calculated and found to be 4.6ram. Because such a plate was not available, 5 and 4 mm thick steel plates replaced the FRP Type 2 in the third and fourth test of each group, respectively. The fourth group consisted of two tests only, as will be explained shortly. The results are shown in Figure 9. In experiments 33, 37 and 41, (steel-FRP-2 configurations), incomplete penetration was encountered. In experiments 34, 38 and 42 (steel laminae without filler) the projectile was able to penetrate the target with a specific velocity change that increases with increased thickness of back plate and/or decreased number of laminae. The same trend was
exhibited with the 4-mm thick equivalent steel targets, while incomplete penetration was exhibited in case of 5-mm thick equivalent steel targets. These results are qualitatively in agreement with those of steel-FRP-1. Quantitatively, however, the laminated targets encompassing FRP Type 1 are more effective than those having FRP Type 2: This is expected since the fiber weight fraction, alternatively the number of plies per mm, is greater in the former material. Gupta and Davids ~° have also found that the energy loss increases with the density of FRP. In addition to the aforementioned tests, two more target configurations were tested. In the first one (experiment 45), a FRP Type 2 target was used having a thickness of 32 mm, equal to total thickness of target configuration in this group. This target was found to be less effective than any other one used in this set of tests. The second configuration (experiment 46), FRP Type 2 had a total thickness of 66 mm, equivalent to 8 mm steel with 24mm FRP Type 2 composite target. It was also perforated, thus confirming the conclusion that the most effective configuration should combine steel and FRP laminae.
457
Ballistic resistance of steeI-FRP laminated plates: A. A. Almohandes et al. 4 CONCLUSIONS Based on the results and findings reported herein, the following conclusions can be drawn: (a) Single steel target plates are more effective than laminated targets (consisting o f in-contact or separated plies) o f the same total thickness. The difference in effectiveness diminishes with impact velocity. (b) Ballistic resistance o f steel targets increases as target material toughness increases. (c) In terms o f specific velocity change, the ballistic resistance o f steel targets first increases slightly and then decreases with impact velocity. (d) Resistance o f laminated steel targets increases as: (i) the n u m b e r o f laminae decreases, and (ii) the thickness o f back plate increases. (e) Use o f F R P as filler in spaced laminated steel targets improves the ballistic resistance. (f) Increase o f F R P thickness and density further improves ballistic performance o f s t e e l - F R P targets.
458
REFERENCES 1 2 3 4 5 6 7
8 9 10
Backman,M. and Goldsmith, W, The mechanics of penetration of projectiles into targets. Int. J. Engng. Sci. 1978, 16, 1-99 Zukas, J.A., Nicholas, T., Swift, H.F., Greszcuk, L.B. and Curran, D.R. 'Impact Dynamics', John Wiley & Sons, New York. 1982, Vol. 5, Chapter 5, pp. 157-210 Almohandes, A.A. 'Ballistic resistance of steel-fiberglass reinforced polyester laminated plates', Master of Science Thesis, Faculty of Engineering, Cairo University, Egypt, 1993 Recht, R.F. and Ipson, T.W. Ballistic penetration resistance and its measurements. Exp. Mech. 1975, 15, 249-257 Abdel-Kader, M.S. 'The penetration capability of high-speed projectiles fired against brass and steel plates', Master of Science Thesis, M.T.C., Cairo, Egypt, 1981 Corran, R.S.J., Ruiz, C. and Shadbolt, P.J. On the design of containment shields. Computer and Structures, 1983, 16, 563-572 Zaid, A.T. and Travis, F.W. A comparison of single and multiplate shields subjected to impact by a high speed projectile. In 'Mechanical properties of materials at high rates of strain', (Ed. J. Harding), Conf. Series No 21, Inst. Phy., London, 1974, 417-428 Osborn, C.J. and Maj, S. The effect of striking velocity on penetration energy for mild steel plates. In 'Proc. Int. Conf. on Fracture', Pergamon Press, New York, 1977, Vol. 3, pp. 617-20 Marom, I. and Bodner, S.R. Projectile perforation of multilayered beams, lnt. J. Mech. Sci. 1978, 21, 489-504 Gupta, B.P. and Davids, N. Experiments with fiberglass-reinforced plastics. Exp. Mech. 1966, 6, 445-450