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Development of cost effective personnel armour through structural hybridization
Defence Technology xxx (xxxx) xxx
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Development of cost effective personnel armour through structural hybridization P. Rama Subba Reddy a, *, T. Sreekantha Reddy a, I. Srikanth b, Juhi Kushwaha b, V. Madhu a a b
Defence Metallurgical Research Laboratory, Hyderabad, 500 058, India Advanced Systems Laboratory, Hyderabad, 500058, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 30 July 2019 Received in revised form 29 October 2019 Accepted 9 December 2019 Available online xxx
The objective of the present study is to develop cost effective thermoplastic hybrid laminate using Dyneema® HB50 and Tensylon®HSBD 30A through structural hybridization method. Laminates having 20 mm thickness were fabricated and subjected to 7.62 39 mm mild steel core projectile with an impact velocity of 730 ± 10 ms1. Parameters such as energy absorption, back face deformation and rate of back face deformation were measured as a function of hybridization ratio. It was observed that hybrid laminate with 50:50 ratio (w/w) of Tensylon® and Dyneema® with Tensylon® as front face showed 200% more energy absorption when compared to 100% Tensylon® laminate and showed equal energy absorption as that of expensive 100% Dyneema® laminate. Moreover, hybrid laminate with TD50:50 ratio showed 40% lower in terms of final back face deformation than Dyneema® laminate. Rate of back face deformation was also found to be slow for hybrid laminate as compared to Dyneema® laminate. Dynamic mechanical analysis showed that, Tensylon® laminate has got higher stiffness and lower damping factor than Dyneema® and hybrid laminates. The interface between Tensylon® and Dyneema® layers was found to be separating during the penetration process due to the poor interfacial bonding. Failure behaviour of laminates for different hybridization ratios were studied by sectioning the impacted laminates. It was observed that, the Tensylon® laminate has undergone shear cutting of fibers as major failure mode whereas the hybrid laminate showed shear cutting followed by tensile stretching, fiber pull out and delamination. These inputs are highly useful for body armour applications to design cost effective armour with enhanced performance. © 2019 The Authors. Production and hosting by Elsevier B.V. on behalf of China Ordnance Society. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).
Keywords: Dyneema® Tensylon® Hybrid laminate Ballistic impact Energy absorption Back face signature
1. Introduction Fiber reinforced composite laminates undergo different failure modes across the penetration path during ballistic impact. This behaviour is more predominant in thicker laminates where target thickness is twice as that of projectile calibre [1,2]. Therefore it is advantage to have different materials along the thickness of armour to get higher energy absorption and to obtain more penetration resistance against the projectile impact. Further, a plateau has reached in ballistic performance of existing materials, yet the requirement of improving the performance still exists. Developing altogether new materials is a time taking process. Hence, efficient
* Corresponding author. E-mail address: [email protected] (P.R.S. Reddy). Peer review under responsibility of China Ordnance Society
use of available materials by selective stacking of them across the thickness is a good option. Armour research fraternity is exploring such options by hybridization concept to design improved and cost effective armour solutions. Various researchers have carried out experimental and numerical simulation studies on effect of hybridization on ballistic performance [3e7]. For instance, Kedar S Pandya et al. studied ballistic behaviour of carbon and E-glass fiber based hybrid laminates against steel projectiles. They observed higher V50 ballistic limit for hybrid laminates having carbon fiber as front face [8]. In another study Larsson and Svensson carried out impact tests on Dyneema®, Carbon and Zylon® fiber based hybrid laminates against fragment simulating projectiles (FSPs). They concluded that ballistic performance of carbon composites has increased due to the hybridization. They made a hybrid laminate of 25% by weight of Dyneema® SK66 at rear side and remaining with carbon at front which showed maximum ballistic limit [9]. In another study, Cenk Yanen and Murat Yavuz Solmaz reported
https://doi.org/10.1016/j.dt.2019.12.004 2214-9147/© 2019 The Authors. Production and hosting by Elsevier B.V. on behalf of China Ordnance Society. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
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ballistic performance of glass/carbon/aramid hybrid composite laminate against 9 mm calibre lead projectile. It was reported that, hybrid laminates having 45 ply orientation have shown optimum ballistic performance [10]. Similarly, Zulkifl et al. have studied the strategic positioning of carbon fabric layers in carbon/UHMWPE hybrid laminate against 9 mm caliber lead projectile. It was reported that, the hybrid laminate having carbon fiber facing the impact of bullet has exhibited significant reduction in back face signature as compared to the carbon fiber positioning at other locations [11]. Chen et al. carried out architectural hybridization studies on unidirectional (UD) and woven fabrics made of Dyneema® material against 5.5 mm diameter steel cylindrical projectile with impact velocity of 400e500 ms1. It was reported that, significant increase in ballistic performance was observed when a few percent of woven plies at front face and large amount of UD plies at rear face were used [12]. Tomasz K Cwik et al. studied design and ballistic evaluation of different hybrid composite laminates against 20 mm FSPs and reported that cost effective hybrid laminate can be made using polypropylene and Dyneema® HB26 material [13]. Sapozhnikov et al. studied the effect of weave structure and hybridization on thermoplastic hybrid composite laminates made up of ultra high molecular weight polyethylene (UHMWPE), aramid and polyethylene sheets against 1 g mass steel projectile. It was reported that, hybrid laminates having front aramid material followed by UHMWPE have shown higher ballistic properties. The dense weave structure at front face is preferable to get higher ballistic performance [14]. Lionel Vargas-Gonzalez et al. carried out systematic study on material hybridization and architectural hybridization using thermoset and thermoplastic materials and found that thermoset material hybridization did not show any improvement in ballistic performance whereas architectural hybridization of thermoplastic material has shown improvement in ballistic property [15]. Detailed experimental studies were carried out on hybrid laminates using natural fiber (kneaf) and aramid fiber under quasi-static and ballistic impact conditions by making flat panels and ballistic helmets. It was reported that, the addition of kenaf fibers has resulted in positive hybridization effect by increasing the energy absorption and improving the damage resistance. Addition of 30% vol of kenaf fibers in hybrid laminate showed optimum in energy absorption [16e19]. Such hybridization also gives advantage of lower cost. M Bunea et al. investigated the effect of matrix and hybrid fabrics on low velocity impact behaviour of hybrid laminates. It was reported that, matrix ply angle and number of hybrid fiber layers have significant effect on energy absorption of laminate [20]. Chenhui et al. studied the impact response of Kevlar based sandwich structure under low and high velocity impact tests and it was reported that, the sandwich structure has shown higher energy dissipation under high velocity impact [21]. Martínez-Hergueta et al. studied the ballistic performance of hybrid non-woven and woven polyethylene dry fabrics against 0.22 caliber steel sphere with an impact velocity of 280e380 ms1. It was reported that, the hybrid configuration having woven fabrics as rear layers have shown higher ballistic performance with reduced back face signature [22]. All these studies were carried out against FSPs, and steel balls having very low mass and low impact velocity. A few studies were reported against service ammunition. Besides the performance and cost point of view, hybrid composites are also essential from specific weight point of view to develop light weight composite armour solutions. Therefore the study on different hybrid configurations against service ammunition to achieve low cost and better ballistic performance armour solutions is a useful study for armour designers and end users. The objective of the present study is optimization of hybridization ratio between Dyneema®HB50 and Tensylon® HBS 30A
material as a function of energy absorption and change in back face signature against 7.62 39 mm service ammunition. The reason for choosing this combination of materials is the production cost of Tensylon® tape is one third of the cost of gel spun fibers [23]. In the current scenario, 7.62 39 mm ammunition is considered to be the major threat to the humans. Failure behaviour of hybrid laminates and various mechanisms responsible for energy absorption and back face deformation for different hybrid configurations are highlighted using high speed photography and images of post impacted laminates. 2. Experimental details 2.1. Materials & fabrication Dyneema® HB50 UD fabric and Tensylon® HSBD 30A tape manufactured by M/s. DSM, The Netherlands and M/s. E I Dupont, USA, respectively were used in the present study. Both the materials are representative of UHMWPE produced in different forms and manufacturing methods. Dyneema® HB50 consists of four mono layers of UHMWPE gel spun fibers oriented in 0/90/0/90 with respect to each other with Styrene-Isoprene-Styrene (SIS) thermoplastic matrix [24]. Tensylon® is a bi directional 0/90 criss-cross non fibrous tape produced through solid state extrusion (SSE) method [25]. Hybrid laminates of 20 mm thickness with varying hybridization ratio were fabricated through hot compaction method. The cure cycle that followed was 128 ± 2 C core temperature under 200 bar pressure. Three varieties of hybrid laminates were prepared by varying the weight ratio of Tensylon®:Dyneema® in the ratio of 75:25, 50:50 and 25:75. Laminates with Tensylon® material alone i.e T100 and Dyneema® alone i.e. D100 were also fabricated for comparison purpose. Hereafter these laminates shall be referred as T100, TD75:25 (Tensylon®: 75% and Dyneema®:25%), TD 50:50, TD 25:75 and D100 through the manuscript. Details of the layers, areal weight and cost comparison for different hybridization ratios are shown in Table 1. 2.2. Ballistic impact tests Ballistic impact tests were carried out at small arms range of Defence Metallurgical Research Laboratory using 7.62 39 mm caliber mild steel core projectile. Universal breech 2002 AZ with 7.62 39 mm rifle barrel was used for launching the projectile with muzzle velocity of 730 ± 10 ms1. The distance between the target and muzzle end of the barrel was maintained at 10 m and the target was positioned at normal impact angle. The above projectile is specified as threat level 2 in IS17051-2018 standard which is used for ballistic testing of personnel armour materials [26]. Projectile strike velocity and residual velocity was measured using velocity measuring instrument. Details of experimental setup and projectile are shown in Fig. 1. Energy absorbed by the laminate is determined using projectile strike and residual velocities and its mass as shown in Eq. (1). Further details of the calculation are explained elsewhere [2]. Total three specimens were tested for each of the configuration and average value with standard deviation is calculated.
Table 1 Details of layers, weight and cost for different hybrid laminates. Laminate ID
T100
TD75:25
TD50:50
TD25:75
D100
No. of layers of T:D Areal weight/(Kg$m2) Cost comparison
167 20.04 1.00
125:23 15.0:5.06 1.17
84:45 10.08:9.9 1.35
42:68 5.04:14.96 1.50
91 20.02 1.70
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Fig. 1. Ballistic experimental test setup (a) schematic layout and 7.62 39 mm bullet (b) Firing unit (c) velocity measuring equipment (d) Target and high speed camera setup.
2.3. Testing of laminates
1 Eabs ¼ m V 2i V 2r 2
(1)
Where, m - mass of the projectile (g) Vi - striking velocity (m/s) Vr - residual velocity (m/s) Eabs - Energy absorbed by the laminate (J) During the tests, high speed video camera (Phantom V1210) was positioned to capture the projectileetarget interaction process. The camera recording frame rate was kept at 100000 fps with a resolution of 256 256 pixels. Effect of hybridization on laminate back face deformation was analyzed quantitatively by using high speed videography.
Inter laminar shear strength (ILSS) and dynamic mechanical analysis (DMA) were carried out for Tensylon®, Dyneema® and optimized hybrid laminate for further understanding. ILSS of the laminates was measured using universal testing machine (Make:United 50 kN) as per ASTM D 2344 test method. Viscoelastic properties such as storage modulus and tan delta were determined using dynamic mechanical analyser (Make:Q800, TA instruments). DMA tests were carried out in dual cantilever mode with sample size of 60 mm 12.5 mm 4 mm with frequency range from zero to eighty Hz at room temperature. Fig. 2 shows the photographs of the testing equipments used for carrying out the above tests. 2.4. Analysis of post impacted laminates Impacted laminates were sectioned using abrasive water jet
Fig. 2. Photographs of equipments used for testing laminates (a) DMA and (b) ILSS test setup along with tested samples.
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cutting machine for studying the failure mode of the laminates. Garnet powder was used as abrasive during the cutting process and the water jet pressure was maintained at 35000 psi with abrasive flow rate of 0.32 kg/min. Overall deformation and failure mode of fibers along the projectile path were studied with the help of optical (Make: Leica micro systems, Model: M165C) and scanning electron microscopy (Make:ZEISS, Model:EVO18) with an applied voltage of 10 kV and a vacuum level of 7.03 106 torr. 3. Results and discussion 3.1. Energy absorption Fig. 3 shows energy absorption of different laminates subjected to projectile impact. From the results it is observed that, T100 laminate showed lowest energy absorption i.e. 687 J. This may be mainly due to the tape structure in Tensylon® laminate which imparted higher stiffness to the laminate and restricted the deformation of layers. The film based laminate is known to have higher inplane shear modulus than the fiber based laminate. The laminate with the film structure exhibits a definite yield point followed by strain hardening, whereas in the case of fiber based laminates a progressive yielding behaviour with the movement of fibers is reported [27]. Though having similar areal weight, due to the lack of deformation Tensylon® laminate has shown very low energy absorption when compared to the other laminates. It can also be noted that, delamination and deformation are the major energy absorption mechanisms in ballistic applications. Hence it is essential for a laminate to undergo deformation and delamination while interacting with the projectile for better energy absorption. In absence of such damage to the laminate, the projectile can cut the fibers easily as it is harder than the fibers leading to lower energy absorption. In order to overcome this limitation, the rear portion of the laminate was replaced with Dyneema® layers with different weight ratios. It can be seen from Fig. 3 that in the case of TD 75:25 laminate there is an improvement in energy absorption over T100 laminate, but failed to absorb the complete impact energy of the projectile. This may be due to insufficient amount of Dyneema® layers at rear side for providing enough deformation thereby resisting the projectile movement. Further increase of Dyneema® up to 50% by weight (i.e. TD 50:50) showed significant improvement in energy absorption. The energy absorption was found to be 2200 J which is the maximum impact energy. It is also observed that TD 50:50 has shown maximum energy absorption.
Beyond this, there is no change in energy absorption with the increase of Dyneema® content. Since there is a limitation in maximum impact energy with the service ammunition, the difference in energy absorption among TD 50:50, TD 25:75 and D100 could not be measured. 3.2. DMA and ILSS analysis To understand the role of viscoelastic and interfacial properties for absorption and dissipation of impact energy, DMA and ILSS test were carried out for different composite laminates. Fig. 4 shows storage modulus and tan delta data of laminates measured as a function of frequency. Storage modulus indicates stiffness or measure of material elastic property. Tan delta is the ratio of loss modulus to storage modulus and is called as damping factor of the material. It is observed from DMA analysis that, Tensylon® laminate has got 10 times higher stiffness than that of Dyneema® laminate. On the other hand, Dyneema® laminate has shown higher damping factor. Hybrid laminates have shown intermediate behaviour in stiffness and damping properties. Dyneema® and hybrid laminates did not show any significant increase in stiffness with increase of frequency whereas Tensylon® showed increase in stiffness with increase of frequency. The reason for Dyneema® laminate to show lower stiffness and higher damping factor is due to the presence of SIS elastomeric matrix which allows the fibers to move freely and undergo deformation upon loading. However, in the case of Tensylon® material, such type of elastomeric matrix is not there. In the Tensylon ultra higher molecular weight polyethylene fibrils are simply embedded in polyethylene matrix itself. Since the polyethylene matrix is brittle when compared to SIS matrix, Tensylon® laminate has shown higher stiffness and lower damping factor than Dyneema® and hybrid laminates. From Fig. 4 it is also observed that, Dyneema laminate has shown raise in tan delta at 50 Hz frequency, this may be due to the fact that, from 50 Hz frequency onwards the loss modulus became flat, whereas the storage modulus continued to raise. Thus, from 50 Hz the difference between storage modulus and loss modulus was found to increase suddenly as compared to the previous frequencies, hence a sudden jump in tan delta is observed at 50 Hz. This can be attributed to that the molecules in viscous matrix fail to be in phase with the applied frequency beyond a critical value which is 50 Hz in the present case. However, further study is required to understand this phenomenon completely. Inter laminar shear strength test shows that, Tensylon® laminate has shown inter laminar failure whereas the hybrid laminates have shown inter laminar and interface failure between the two materials (Fig. 2). The measured ILSS was found to be 5.7 MPa and 2.5 MPa for Tensylon® laminate and hybrid laminate respectively. The results suggest that, Tensylon® laminate has got better fiber and matrix interfacial bonding since the fibrils are embedded in polyethylene matrix. In the case of hybrid laminate only 50% of the Tensylon® material is used, therefore there is a reduction in ILSS compared to 100% Tensylon® laminate. ILSS property for Dyneema® laminate could not be measured due to slippage of material during the test. Both DMA and ILSS tests indicated that, Dyneema® laminate has got lower stiffness, poor interfacial bonding and higher damping characters. All these properties support Dyneema® to undergo wide deformation at rear side of the laminate compared to Tensylon® and hybrid laminates. 3.3. Back face signature during penetration
Fig. 3. Laminate energy absorption for different configurations.
Being a softer material, during ballistic impact thermoplastic laminates bend easily and undergo deformation by forming a cone shape bulge on rear side of the laminate which is also called as back
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Fig. 4. DMA analysis of different composite laminates.
face signature of the laminate. This deformation is more visible when the projectile is successfully defeated by the laminate. The cone height and size increases initially at a faster rate and comes back due to elastic recovery of material before it is stabilized. It is very important to control this back face signature in armour applications especially in human protection apart from energy absorption. Sometimes the deformation may create serious injury to the person though there is no complete penetration of bullet. Fig. 5 shows high speed video images of T100 and TD 75:25 laminates interaction with projectile at different time intervals. It can be seen from the images that, in case of T100 laminate there was no deformation at rear side of laminate and the projectile could perforate the laminate within 100 ms. In the case of TD 75:25 laminate, some amount of deformation is visible at rear side of the laminate due to this, the interaction time between the projectile and laminate has doubled i.e. 200 ms and thus resulted in increase in energy absorption. In the same way, Fig. 6 shows high speed video images of TD 50:50, TD 25:75 and D100 laminates respectively. The extent of deformation or bulge at different time intervals for the studied laminate configurations is shown in images for comparison purpose. It is clearly visible that, the presence of Dyneema® at rear side has contributed in significant deformation, due to which all the laminates have shown good energy absorption. Although there is no difference in energy absorption, variation in the extent of deformation was observed. The images were presented up to 3000 ms beyond which there was no change in deformation. TD 50:50 laminate showed maximum bulge of 34.2 mm at 500 ms and it got reduced to 12.4 mm at 3000 ms. This may be due to complete arrest of projectile movement within the laminate. In the case of D100 laminate, the bulge was found to be 38 mm at 500 ms and it got reduced to 20.6 mm at 3000 ms. This can be attributed to the lower
stiffness of D100 laminate as compared to TD 50:50 hybrid laminate. Hence more bulge for D 100 laminate was observed. Though TD 25:75 has shown bulge reduction, the magnitude of reduction was inferior as compared to TD 50:50 hybrid laminate. Fig. 7 shows the variation in bulged cone height at different time intervals during the penetration process. It was observed that, the cone height increased initially and it got decreased gradually as the projectile penetration has come down. This behaviour is similar for all the laminates. However, the maximum cone height was observed for D100 laminate followed by TD 50:50 and TD 25:75 hybrids laminate respectively. D100 laminate has shown cone height of 36.1 mm at 1000 ms whereas TD 50:50 has shown only 31.2 mm at the same time interval which is about 13% less than the former one. The final cone height was found to be 20.6 mm and 12.4 mm at 3000 ms for D100 and TD 50:50 laminates respectively. In the case of TD 25:75 laminate, initial cone height is similar to TD50:50 laminate but the final cone height is higher than TD50:50. Cone height for T100 and TD 75:25 laminates could not be determined due to complete perforation. The reduction in cone height in the case of hybrid laminates while maintaining the higher energy absorption is due to the presence of Tensylon® tape at front side which imparted higher stiffness to hybrid laminate. Rate of cone expansion indicates how fast the impact energy and momentum has got transferred to the rear side of the panel. It is desirable to have slower rate in cone expansion so that the rate of energy transfer to the object behind the armour will be less. Cone expansion rate as a function of interaction time is calculated from high speed images and shown in Fig. 8. Initially the cone expanded rapidly and reached its maximum value at about 100e150 ms, afterwards there was a deceleration in expansion and finally stabilized at 1000 ms. In the case of D100 laminate the maximum cone
Fig. 5. High speed video images for T100 and TD 75:25 laminate configurations.
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Fig. 6. High speed video images for D100 and TD 25:75 and TD 50:50 laminate configurations.
expansion pace was found to be 220 m/s whereas for hybrid laminate it was only 175 m/s which is 20% lower. This is significant to reduce the trauma effect. This shows the importance of having higher stiffness material at front face. However, it is effective only up to a certain thickness beyond that, the effect of higher stiffness (Tensylon® in this case) material on rate of cone expansion is found to be negligible which is the reason for similar expansion rate for TD 50:50 and TD 25:75 laminates. The final back face signatures (BFS) and percentage of its recovery was calculated from the images and shown in Fig. 9. It was observed that D100 laminate has shown maximum BFS of 21 mm whereas TD 50:50 hybrid laminate has showed only 12.4 mm which is 40% lower as compared to D100 laminate. The percentage recovery in BFS was found to be more for hybrid laminates than D100 laminate. This may due to improvement in overall stiffness of hybrid laminate. 3.4. Failure analysis Fig. 7. Change in cone height for different laminate configurations.
Fig. 8. Rate of increase in cone height for different configurations.
The presence of layered structure is known to provide better attenuation of shock waves than monolithic materials. From Fig. 10 it can be seen that, there is a clear cut separation of interface at Tensylon® and Dyneema® layers. This can be attributed to the fact that, though both the fibers are chemically same, there is a difference in impedance levels between Tensylon® and Dyneema® laminate due to the difference in matrix. Tensylon® material has got higher impedance over Dyneema® laminate due to its higher modulus and lack of viscous matrix. Hence, excessive delamination is observed at the interface between the two materials. In the case of Dyneema® laminate, more attenuation of shock waves can be expected due to the presence of viscous SIS matrix and layered structure. During the projectile penetration process laminates exhibit different failure mechanisms along the penetration path. Penetration in thick laminate is generally observed in two stages i.e. shear plugging or punching of fibers at entry stage of projectile followed by large deformation at rear side of the panel accompanied by delamination and fiber stretching [28]. At projectile entry point, due to high velocities there is no sufficient time for the fibers to dissipate the impact load in transverse direction, hence shear cutting of fibers is observed as major failure mode. As the penetration progresses, there is deceleration of projectile and laminate
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Fig. 9. Effect of laminate configuration on back face signatures (a) final BFS (b) % recovery.
Fig. 10. Cross section images of post impacted laminates.
also undergoes delamination, bending and tensile stretching of fibers due to the impact pulse travelling ahead of the projectile. Laminates having low ILSS and low modulus such as thermoplastics can undergo severe deformation, fiber stretching and thus gives better energy absorption. Hence the failure of laminate along the projectile path will be in the form of inverted ‘V’ shape for thermoplastic laminates. This phenomena is studied carefully for the present laminates. Fig. 10 shows cross section images of post impacted laminates and arrow mark shows projectile impact direction. It was observed that, in the case of T100, the laminate suffered complete penetration without a significant global deformation at rear side which is otherwise expected. The cross section image gives an impression of a monolithic polyethylene sheet though it is not so. The shear cutting of fibers was seen as primary failure mechanism and hardly any deformation at rear side of the panel was observed. This can be attributed to the higher bending stiffness and lack of long fiber structure in Tensylon® laminate. The Tensylon® tape is made of UHMWPE fibrils embedded in low density polyethylene matrix [29]. This type of matrix has got poor elongation under tensile load as compared to rubbery matrix. Due to the lack of continuous fibers in laminate, there was no effective transfer of impact energy in the lateral direction. Hence it is inferred that, energy dissipation mechanism is through thickness direction there by creating high strains along the projectile path resulting into shear cutting of layers. Therefore Tensylon® laminate could not undergo any
deformation at rear side of the panel. It has shown ‘U’ shape penetration path. Due to this type of failure behaviour, T100 laminate has shown significantly lower energy absorption as compared to other laminates. On the other hand, in case of D100 laminate, shear cutting of fibers at the entry of the projectile followed by delamination and deformation of layers at rear side of the laminate was observed. The projectile was completely stopped within the laminate. Since the Dyneema® laminate has got poor ILSS property and higher damping character, it could undergo delamination, tensile stretching and deformation in a wide area. Tensile stretching of fibers and global deformation of laminate absorbed more amount of projectile energy and decelerated it effectively. Intern, deceleration of projectile allowed more contact duration between the projectile and fiber resulting into participation of larger volume of laminate in absorbing the energy. The increased contact duration promoted to inverted ‘V’ shape failure pattern with higher energy absorption and extensive damage at rear side of the laminate. Hybrid laminate having TD 50:50 ratio has shown lowest damage area as compared to other laminates, such reduction in damage area helps in multihit protection. The extent of fiber bending in transverse direction from the center of the projectile path was observed to be more in D100 than in TD50:50. This may be due to the presence of soft matrix and continuous long fiber structure in Dyneema® laminate. In the case of hybrid laminate, the interface between Tensylon and Dyneema laminas was found to be separating during the penetration process due to difference in stiffness of two materials and poor interlaminar shear strength. D100 and TD 50:50 laminates have undergone different failure modes involving more energy absorption during projectile penetration. Hence they have exhibited higher energy absorption. Though TD50:50 and D100 laminates have shown similar energy absorption due to the limitation of projectile muzzle energy, the hybrid laminate has shown less extent of fiber bending in transverse direction and non-penetration thickness is found to be 2e3 mm whereas in the case of D100 laminate the nonpenetration thickness is found to be 1e1.5 mm and also the extent of fiber bending in transverse direction is found to be more (Fig. 10). The improvement in hybrid laminate interms of less extent of bending and less penetration is due to increased laminate stiffness and compressive resistance which can help in decelerating the projectile during the penetration process. Fig. 11 shows failure mode of Tensylon® material across the projectile path. It is observed that, in all the cases, at strike face and at the center of the projectile path shear cutting and melting of
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Fig. 11. Failure mode of Tensylon fibers across the projectile path.
fibers has occurred. As UHMWPE has got lower melting point, it can undergo melting easily due to the frictional heat generated during the penetration process. There is hardly any tensile stretching and delaminations. It appears that, shear cutting of fibers is not an effective energy absorption mechanism which is the reason for lower energy absorption in T100 laminate among all the studied laminates. In the case of TD50:50 and D100 laminate, the Dyneema
laminas has undergone significant bending, delamination and tensile stretching. Fig. 12 shows the failure mode of dyneema fibers across the projectile path. It is observed that at front side shear cutting of fibers is observed which is on the expected lines, whereas at center and rear side of the laminate, fiber bending, stretching and fiber sliding are observed.
Fig. 12. Failure modes dyneema fibers across the projectile path.
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4. Conclusions Hybrid composite laminates having 20 mm thickness were fabricated using Dyneema® HB50 and cost effective Tensylon® HSBD 30A through structural hybridization. Laminates were fabricated with different weight ratios of Tensylon® and Dyneema® and subjected to ballistic impact against 7.62 39 mm mild steel projectile. Results suggest that hybrid laminate with 50:50 wt ratio of Tensylon® and Dyneema® has shown significant increase in energy absorption over tensylon laminate. Back face signature, rate of back face bulge formation and extent of damage were found to be minimum for TD50:50 hybrid laminate as compared to the other laminates. This is due to the optimum combination of two different types of fiber structures which supported for better ballistic performance. This study shows that cost effective armour with superior ballistic property can be designed through structural hybridization method. Laminates have shown different failure behaviour. In the case of T100 laminate shear cutting of fibers is found to be predominant failure behaviour and has resulted in very low energy absorption. In the case of hybrid and D100 laminates, shear cutting at entry point of the projectile followed by delamination, bending and tensile stretching at projectile exit side of the laminate was observed. The failure analysis of post impacted laminates suggest that, it is desirable to have material with higher stiffness at entry side of the projectile to resist the compressive load and thus to slow down the projectile penetration. Simultaneously there is a need to have low interlaminar shear strength to promote delamination planes ahead of the projectile penetration. This helps in tensile stretching with wide deformation at the rear side of the laminate which delays the failure of fibers by distributing the impact energy over a large volume of material. Therefore, it is essential to have a balance in combination of different materials to get the optimum energy absorption with reduced back face signature at a lower cost. Acknowledgements Authors gratefully acknowledge Director, Defence Metallurgical Research Laboratory (DMRL), Hyderabad for his encouragement to publish this work. The authors also acknowledge the support rendered by the staff of Armour Design and Development Division (ADDD). References [1] Gellert EP, Cimpocru SJ, Woodward RL. A study of the effect of target thickness on the ballistic perforation of glass-fibre reinforced plastic composites. Int J Impact Eng 2000;24:445e56. [2] Reddy PRama Subba, Reddy TSreekantha, Madhu V, Gogia AK, Rao KVenkateswara. Behaviour of E-glass composite laminates under ballistic impact. Mater Des 2015;84:79e86. [3] Zhang Jin, Chaisombat Khunlavit, He Shuai, Wang Chun H. Hybrid composite laminates reinforced with glass/carbon woven fabrics for lightweight load bearing structures. Mater Des 2012;36:75e80. [4] Sevkat Ercan, Liaw Benjamin, Delale Feridun. Drop-weight impact response of hybrid composites impacted by impactor of various geometries. Mater Des 2013;52:67e77. [5] Munoz R, Martinez-Hergueta F, Galvez F, Gonzalez C, Lorca JL. Ballistic performance of hybrid 3D woven composites: experiments and simulations. Compos Struct 2015;127:141e51.
9
[6] Kumar Bandaru Aswani, Vetiyatil Lakshimi, Ahmad Suhail. The effect of hybridization on the ballistic impact behaviour of hybrid composite armours. Compos Part B 2015;76:300e19. [7] Yahaya R, Sapuan SM, Jawaid M, Leman Z, Zainudin ES. Measurement of ballistic impact properties of woven kenafearamid hybrid composites. Measurement 2016;77:335e43. [8] Pandya Kedar S, Pothnis Jayaram R, Ravikumar G, Naik NK. Ballistic impact behavior of hybrid composites. Mater Des 2013;44:128e35. [9] Larsson F, Svensson L. Carbon, polyethylene and PBO hybrid fibre composites for structural lightweight armour. Compos A: Appl Sci Manuf 2002;33: 221e31. [10] Yanen Cenk, Yavuz Solmaz Murat. Ballistic performance of 21 layered hybrid composites. In: 12th international conference on latest trends in engineering and technology (ICLTET’2017) May 22-24; 2017 [Kuala Lumpur (Malaysia)]. [11] Zulkifl Faiz, Jan Stolk, Ulrich Heisserer, Yong Alex Tuck-Mun, Li Zhiyi, Hu Xiao Matthew. Strategic positioning of carbon fiber layers in an UHMwPE ballistic hybrid composite panel. Int J Impact Eng 2019;129:119e27. [12] Chen X, Zhou Y, Wells G. Numerical and experimental investigations into ballistic performance of hybrid fabric panels. Compos Part B 2014;58:35e42. [13] Cwik Tomasz K, Iannucci Lorenzo, Curtis Paul, Pope Dan. Design and ballistic performance of hybrid. Composite laminates. Appl Compos Mater 2017;24: 717e33. [14] Sapozhnikov SB, Kudryavtsev OA, Zhikharev MV. Fragment ballistic performance of homogenous and hybrid thermoplastic composites. Int J Impact Eng 2015;81:8e16. [15] Vargas-Gonzalez Lionel, Walsh Shawn M, James Wolbert. Impact and ballistic response of hybridized thermoplastic laminates. ARL-MR-0769; February 2011. [16] Yahaya R, Sapuan SM, Jawaid M, Leman Z, Zainudin ES. Effect of layering sequence and chemical treatment on the mechanical properties of woven kenafearamid hybrid laminated composites. Mater Des 2015;85:431e7. [17] Salman Suhad D, Leman Z, Sultan MTH, Ishak MR, Cardona F. Quasi-static penetration behavior of plain woven kenaf/aramid reinforced polyvinyl butyral hybrid laminates. J IndText 2018;47(7):1427e46. https://doi.org/ 10.1177/1528083717692593. [18] Salman Suhad D, Leman Z, Sultan MTH, Ishak MR, Cardona F. Effect of kenaf fibers on trauma penetration depth and ballistic impact resistance for laminated composites. Text Res J 2017;87(17):2051e65. https://doi.org/10.1177/ 0040517516663155. [19] Salman Suhad D, Leman Z, Ishak MR, Sultan MTH, Cardona F. Ballistic impact resistance of plain woven kenaf/aramid reinforced poly vinyl butyral laminated hybrid composite. Bio Resour 2016;11(3):7282e95. [20] Bunea M, Cîrciumaru A, Buciumeanu M, Bîrsan IG, Silva FS. Low velocity impact response of fabric reinforced hybrid composites with stratified filled epoxy matrix. Compos SciTechnol 2019;169:242e8. [21] Xu Chenhui, Wang Yu, Wu Jie, Song Shichao, Cao Saisai, Xuan Shouhu, Jiang Wanquan, Gong Xinglong. Anti-impact response of Kevlar sandwich structure with silly putty core. Compos SciTechnol 2017;153:168e77. [22] Martínez-Hergueta F, Ridruejo A, Gonzalez C, LLorca J. Ballistic performance of hybrid nonwoven/woven polyethylene fabric shields. Int J Impact Eng 2017;111:55e65. [23] Gene C. Weedon, Kenneth C Harding, Lisa Owen, Non-fibrous high modulus ultra high molecular weight polyethylene tape for ballistic applications. US Patent no.US/0318016A1, 2008. [24] Singletary J, Lauke B. Polyolefin film reinforced composites for personal protection. In: Chapter-13, Advanced fibrous composite materials for ballistic applications. Woodheed publishing; 2016. [25] Alil LC, Arrigoni M, Badea S, Ginghina R, Matache L-C, Mostovykh P. Ballistic study of Tensylon® e based panels. Express Polym Lett 2018;12(6):491e504. [26] Indian Standard. Textiles-bullet resistant jackets-performance requirements. IS17051. 2018. [27] Cline Jula, Bogetti Travis, Love Bryan. Comparison of the in-plane shear behaviour of UHMWPE fiber and highly oriented film composites. In: Proceedings of 32nd technical conference. America Society of Composites; 2017. https://doi.org/10.12783/asc2017/15182. November. [28] Rama Subba Reddy P, Sreekantha Reddy T, Srikanth I, Madhu V, Gogia AK, Venkateswara Rao K. Effect of viscoelastic behaviour of glass laminates on their energy absorption subjected to high velocity impact. Mater Des 2016;98: 272e9. [29] Hine PJ, Ward IM, Jordan ND, Olley RH, Bassett DC. A comparison of the hotcompaction behaviour of oriented high-modulus polyethylene fibers and tapes. J Macro Sci Part B Phys 2001;40:959e89.
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Defence Technology journal homepage: www.elsevier.com/locate/dt
Development of cost effective personnel armour through structural hybridization P. Rama Subba Reddy a, *, T. Sreekantha Reddy a, I. Srikanth b, Juhi Kushwaha b, V. Madhu a a b
Defence Metallurgical Research Laboratory, Hyderabad, 500 058, India Advanced Systems Laboratory, Hyderabad, 500058, India
a r t i c l e i n f o
a b s t r a c t
Article history: Received 30 July 2019 Received in revised form 29 October 2019 Accepted 9 December 2019 Available online xxx
The objective of the present study is to develop cost effective thermoplastic hybrid laminate using Dyneema® HB50 and Tensylon®HSBD 30A through structural hybridization method. Laminates having 20 mm thickness were fabricated and subjected to 7.62 39 mm mild steel core projectile with an impact velocity of 730 ± 10 ms1. Parameters such as energy absorption, back face deformation and rate of back face deformation were measured as a function of hybridization ratio. It was observed that hybrid laminate with 50:50 ratio (w/w) of Tensylon® and Dyneema® with Tensylon® as front face showed 200% more energy absorption when compared to 100% Tensylon® laminate and showed equal energy absorption as that of expensive 100% Dyneema® laminate. Moreover, hybrid laminate with TD50:50 ratio showed 40% lower in terms of final back face deformation than Dyneema® laminate. Rate of back face deformation was also found to be slow for hybrid laminate as compared to Dyneema® laminate. Dynamic mechanical analysis showed that, Tensylon® laminate has got higher stiffness and lower damping factor than Dyneema® and hybrid laminates. The interface between Tensylon® and Dyneema® layers was found to be separating during the penetration process due to the poor interfacial bonding. Failure behaviour of laminates for different hybridization ratios were studied by sectioning the impacted laminates. It was observed that, the Tensylon® laminate has undergone shear cutting of fibers as major failure mode whereas the hybrid laminate showed shear cutting followed by tensile stretching, fiber pull out and delamination. These inputs are highly useful for body armour applications to design cost effective armour with enhanced performance. © 2019 The Authors. Production and hosting by Elsevier B.V. on behalf of China Ordnance Society. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).
Keywords: Dyneema® Tensylon® Hybrid laminate Ballistic impact Energy absorption Back face signature
1. Introduction Fiber reinforced composite laminates undergo different failure modes across the penetration path during ballistic impact. This behaviour is more predominant in thicker laminates where target thickness is twice as that of projectile calibre [1,2]. Therefore it is advantage to have different materials along the thickness of armour to get higher energy absorption and to obtain more penetration resistance against the projectile impact. Further, a plateau has reached in ballistic performance of existing materials, yet the requirement of improving the performance still exists. Developing altogether new materials is a time taking process. Hence, efficient
* Corresponding author. E-mail address: [email protected] (P.R.S. Reddy). Peer review under responsibility of China Ordnance Society
use of available materials by selective stacking of them across the thickness is a good option. Armour research fraternity is exploring such options by hybridization concept to design improved and cost effective armour solutions. Various researchers have carried out experimental and numerical simulation studies on effect of hybridization on ballistic performance [3e7]. For instance, Kedar S Pandya et al. studied ballistic behaviour of carbon and E-glass fiber based hybrid laminates against steel projectiles. They observed higher V50 ballistic limit for hybrid laminates having carbon fiber as front face [8]. In another study Larsson and Svensson carried out impact tests on Dyneema®, Carbon and Zylon® fiber based hybrid laminates against fragment simulating projectiles (FSPs). They concluded that ballistic performance of carbon composites has increased due to the hybridization. They made a hybrid laminate of 25% by weight of Dyneema® SK66 at rear side and remaining with carbon at front which showed maximum ballistic limit [9]. In another study, Cenk Yanen and Murat Yavuz Solmaz reported
https://doi.org/10.1016/j.dt.2019.12.004 2214-9147/© 2019 The Authors. Production and hosting by Elsevier B.V. on behalf of China Ordnance Society. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
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ballistic performance of glass/carbon/aramid hybrid composite laminate against 9 mm calibre lead projectile. It was reported that, hybrid laminates having 45 ply orientation have shown optimum ballistic performance [10]. Similarly, Zulkifl et al. have studied the strategic positioning of carbon fabric layers in carbon/UHMWPE hybrid laminate against 9 mm caliber lead projectile. It was reported that, the hybrid laminate having carbon fiber facing the impact of bullet has exhibited significant reduction in back face signature as compared to the carbon fiber positioning at other locations [11]. Chen et al. carried out architectural hybridization studies on unidirectional (UD) and woven fabrics made of Dyneema® material against 5.5 mm diameter steel cylindrical projectile with impact velocity of 400e500 ms1. It was reported that, significant increase in ballistic performance was observed when a few percent of woven plies at front face and large amount of UD plies at rear face were used [12]. Tomasz K Cwik et al. studied design and ballistic evaluation of different hybrid composite laminates against 20 mm FSPs and reported that cost effective hybrid laminate can be made using polypropylene and Dyneema® HB26 material [13]. Sapozhnikov et al. studied the effect of weave structure and hybridization on thermoplastic hybrid composite laminates made up of ultra high molecular weight polyethylene (UHMWPE), aramid and polyethylene sheets against 1 g mass steel projectile. It was reported that, hybrid laminates having front aramid material followed by UHMWPE have shown higher ballistic properties. The dense weave structure at front face is preferable to get higher ballistic performance [14]. Lionel Vargas-Gonzalez et al. carried out systematic study on material hybridization and architectural hybridization using thermoset and thermoplastic materials and found that thermoset material hybridization did not show any improvement in ballistic performance whereas architectural hybridization of thermoplastic material has shown improvement in ballistic property [15]. Detailed experimental studies were carried out on hybrid laminates using natural fiber (kneaf) and aramid fiber under quasi-static and ballistic impact conditions by making flat panels and ballistic helmets. It was reported that, the addition of kenaf fibers has resulted in positive hybridization effect by increasing the energy absorption and improving the damage resistance. Addition of 30% vol of kenaf fibers in hybrid laminate showed optimum in energy absorption [16e19]. Such hybridization also gives advantage of lower cost. M Bunea et al. investigated the effect of matrix and hybrid fabrics on low velocity impact behaviour of hybrid laminates. It was reported that, matrix ply angle and number of hybrid fiber layers have significant effect on energy absorption of laminate [20]. Chenhui et al. studied the impact response of Kevlar based sandwich structure under low and high velocity impact tests and it was reported that, the sandwich structure has shown higher energy dissipation under high velocity impact [21]. Martínez-Hergueta et al. studied the ballistic performance of hybrid non-woven and woven polyethylene dry fabrics against 0.22 caliber steel sphere with an impact velocity of 280e380 ms1. It was reported that, the hybrid configuration having woven fabrics as rear layers have shown higher ballistic performance with reduced back face signature [22]. All these studies were carried out against FSPs, and steel balls having very low mass and low impact velocity. A few studies were reported against service ammunition. Besides the performance and cost point of view, hybrid composites are also essential from specific weight point of view to develop light weight composite armour solutions. Therefore the study on different hybrid configurations against service ammunition to achieve low cost and better ballistic performance armour solutions is a useful study for armour designers and end users. The objective of the present study is optimization of hybridization ratio between Dyneema®HB50 and Tensylon® HBS 30A
material as a function of energy absorption and change in back face signature against 7.62 39 mm service ammunition. The reason for choosing this combination of materials is the production cost of Tensylon® tape is one third of the cost of gel spun fibers [23]. In the current scenario, 7.62 39 mm ammunition is considered to be the major threat to the humans. Failure behaviour of hybrid laminates and various mechanisms responsible for energy absorption and back face deformation for different hybrid configurations are highlighted using high speed photography and images of post impacted laminates. 2. Experimental details 2.1. Materials & fabrication Dyneema® HB50 UD fabric and Tensylon® HSBD 30A tape manufactured by M/s. DSM, The Netherlands and M/s. E I Dupont, USA, respectively were used in the present study. Both the materials are representative of UHMWPE produced in different forms and manufacturing methods. Dyneema® HB50 consists of four mono layers of UHMWPE gel spun fibers oriented in 0/90/0/90 with respect to each other with Styrene-Isoprene-Styrene (SIS) thermoplastic matrix [24]. Tensylon® is a bi directional 0/90 criss-cross non fibrous tape produced through solid state extrusion (SSE) method [25]. Hybrid laminates of 20 mm thickness with varying hybridization ratio were fabricated through hot compaction method. The cure cycle that followed was 128 ± 2 C core temperature under 200 bar pressure. Three varieties of hybrid laminates were prepared by varying the weight ratio of Tensylon®:Dyneema® in the ratio of 75:25, 50:50 and 25:75. Laminates with Tensylon® material alone i.e T100 and Dyneema® alone i.e. D100 were also fabricated for comparison purpose. Hereafter these laminates shall be referred as T100, TD75:25 (Tensylon®: 75% and Dyneema®:25%), TD 50:50, TD 25:75 and D100 through the manuscript. Details of the layers, areal weight and cost comparison for different hybridization ratios are shown in Table 1. 2.2. Ballistic impact tests Ballistic impact tests were carried out at small arms range of Defence Metallurgical Research Laboratory using 7.62 39 mm caliber mild steel core projectile. Universal breech 2002 AZ with 7.62 39 mm rifle barrel was used for launching the projectile with muzzle velocity of 730 ± 10 ms1. The distance between the target and muzzle end of the barrel was maintained at 10 m and the target was positioned at normal impact angle. The above projectile is specified as threat level 2 in IS17051-2018 standard which is used for ballistic testing of personnel armour materials [26]. Projectile strike velocity and residual velocity was measured using velocity measuring instrument. Details of experimental setup and projectile are shown in Fig. 1. Energy absorbed by the laminate is determined using projectile strike and residual velocities and its mass as shown in Eq. (1). Further details of the calculation are explained elsewhere [2]. Total three specimens were tested for each of the configuration and average value with standard deviation is calculated.
Table 1 Details of layers, weight and cost for different hybrid laminates. Laminate ID
T100
TD75:25
TD50:50
TD25:75
D100
No. of layers of T:D Areal weight/(Kg$m2) Cost comparison
167 20.04 1.00
125:23 15.0:5.06 1.17
84:45 10.08:9.9 1.35
42:68 5.04:14.96 1.50
91 20.02 1.70
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Fig. 1. Ballistic experimental test setup (a) schematic layout and 7.62 39 mm bullet (b) Firing unit (c) velocity measuring equipment (d) Target and high speed camera setup.
2.3. Testing of laminates
1 Eabs ¼ m V 2i V 2r 2
(1)
Where, m - mass of the projectile (g) Vi - striking velocity (m/s) Vr - residual velocity (m/s) Eabs - Energy absorbed by the laminate (J) During the tests, high speed video camera (Phantom V1210) was positioned to capture the projectileetarget interaction process. The camera recording frame rate was kept at 100000 fps with a resolution of 256 256 pixels. Effect of hybridization on laminate back face deformation was analyzed quantitatively by using high speed videography.
Inter laminar shear strength (ILSS) and dynamic mechanical analysis (DMA) were carried out for Tensylon®, Dyneema® and optimized hybrid laminate for further understanding. ILSS of the laminates was measured using universal testing machine (Make:United 50 kN) as per ASTM D 2344 test method. Viscoelastic properties such as storage modulus and tan delta were determined using dynamic mechanical analyser (Make:Q800, TA instruments). DMA tests were carried out in dual cantilever mode with sample size of 60 mm 12.5 mm 4 mm with frequency range from zero to eighty Hz at room temperature. Fig. 2 shows the photographs of the testing equipments used for carrying out the above tests. 2.4. Analysis of post impacted laminates Impacted laminates were sectioned using abrasive water jet
Fig. 2. Photographs of equipments used for testing laminates (a) DMA and (b) ILSS test setup along with tested samples.
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cutting machine for studying the failure mode of the laminates. Garnet powder was used as abrasive during the cutting process and the water jet pressure was maintained at 35000 psi with abrasive flow rate of 0.32 kg/min. Overall deformation and failure mode of fibers along the projectile path were studied with the help of optical (Make: Leica micro systems, Model: M165C) and scanning electron microscopy (Make:ZEISS, Model:EVO18) with an applied voltage of 10 kV and a vacuum level of 7.03 106 torr. 3. Results and discussion 3.1. Energy absorption Fig. 3 shows energy absorption of different laminates subjected to projectile impact. From the results it is observed that, T100 laminate showed lowest energy absorption i.e. 687 J. This may be mainly due to the tape structure in Tensylon® laminate which imparted higher stiffness to the laminate and restricted the deformation of layers. The film based laminate is known to have higher inplane shear modulus than the fiber based laminate. The laminate with the film structure exhibits a definite yield point followed by strain hardening, whereas in the case of fiber based laminates a progressive yielding behaviour with the movement of fibers is reported [27]. Though having similar areal weight, due to the lack of deformation Tensylon® laminate has shown very low energy absorption when compared to the other laminates. It can also be noted that, delamination and deformation are the major energy absorption mechanisms in ballistic applications. Hence it is essential for a laminate to undergo deformation and delamination while interacting with the projectile for better energy absorption. In absence of such damage to the laminate, the projectile can cut the fibers easily as it is harder than the fibers leading to lower energy absorption. In order to overcome this limitation, the rear portion of the laminate was replaced with Dyneema® layers with different weight ratios. It can be seen from Fig. 3 that in the case of TD 75:25 laminate there is an improvement in energy absorption over T100 laminate, but failed to absorb the complete impact energy of the projectile. This may be due to insufficient amount of Dyneema® layers at rear side for providing enough deformation thereby resisting the projectile movement. Further increase of Dyneema® up to 50% by weight (i.e. TD 50:50) showed significant improvement in energy absorption. The energy absorption was found to be 2200 J which is the maximum impact energy. It is also observed that TD 50:50 has shown maximum energy absorption.
Beyond this, there is no change in energy absorption with the increase of Dyneema® content. Since there is a limitation in maximum impact energy with the service ammunition, the difference in energy absorption among TD 50:50, TD 25:75 and D100 could not be measured. 3.2. DMA and ILSS analysis To understand the role of viscoelastic and interfacial properties for absorption and dissipation of impact energy, DMA and ILSS test were carried out for different composite laminates. Fig. 4 shows storage modulus and tan delta data of laminates measured as a function of frequency. Storage modulus indicates stiffness or measure of material elastic property. Tan delta is the ratio of loss modulus to storage modulus and is called as damping factor of the material. It is observed from DMA analysis that, Tensylon® laminate has got 10 times higher stiffness than that of Dyneema® laminate. On the other hand, Dyneema® laminate has shown higher damping factor. Hybrid laminates have shown intermediate behaviour in stiffness and damping properties. Dyneema® and hybrid laminates did not show any significant increase in stiffness with increase of frequency whereas Tensylon® showed increase in stiffness with increase of frequency. The reason for Dyneema® laminate to show lower stiffness and higher damping factor is due to the presence of SIS elastomeric matrix which allows the fibers to move freely and undergo deformation upon loading. However, in the case of Tensylon® material, such type of elastomeric matrix is not there. In the Tensylon ultra higher molecular weight polyethylene fibrils are simply embedded in polyethylene matrix itself. Since the polyethylene matrix is brittle when compared to SIS matrix, Tensylon® laminate has shown higher stiffness and lower damping factor than Dyneema® and hybrid laminates. From Fig. 4 it is also observed that, Dyneema laminate has shown raise in tan delta at 50 Hz frequency, this may be due to the fact that, from 50 Hz frequency onwards the loss modulus became flat, whereas the storage modulus continued to raise. Thus, from 50 Hz the difference between storage modulus and loss modulus was found to increase suddenly as compared to the previous frequencies, hence a sudden jump in tan delta is observed at 50 Hz. This can be attributed to that the molecules in viscous matrix fail to be in phase with the applied frequency beyond a critical value which is 50 Hz in the present case. However, further study is required to understand this phenomenon completely. Inter laminar shear strength test shows that, Tensylon® laminate has shown inter laminar failure whereas the hybrid laminates have shown inter laminar and interface failure between the two materials (Fig. 2). The measured ILSS was found to be 5.7 MPa and 2.5 MPa for Tensylon® laminate and hybrid laminate respectively. The results suggest that, Tensylon® laminate has got better fiber and matrix interfacial bonding since the fibrils are embedded in polyethylene matrix. In the case of hybrid laminate only 50% of the Tensylon® material is used, therefore there is a reduction in ILSS compared to 100% Tensylon® laminate. ILSS property for Dyneema® laminate could not be measured due to slippage of material during the test. Both DMA and ILSS tests indicated that, Dyneema® laminate has got lower stiffness, poor interfacial bonding and higher damping characters. All these properties support Dyneema® to undergo wide deformation at rear side of the laminate compared to Tensylon® and hybrid laminates. 3.3. Back face signature during penetration
Fig. 3. Laminate energy absorption for different configurations.
Being a softer material, during ballistic impact thermoplastic laminates bend easily and undergo deformation by forming a cone shape bulge on rear side of the laminate which is also called as back
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Fig. 4. DMA analysis of different composite laminates.
face signature of the laminate. This deformation is more visible when the projectile is successfully defeated by the laminate. The cone height and size increases initially at a faster rate and comes back due to elastic recovery of material before it is stabilized. It is very important to control this back face signature in armour applications especially in human protection apart from energy absorption. Sometimes the deformation may create serious injury to the person though there is no complete penetration of bullet. Fig. 5 shows high speed video images of T100 and TD 75:25 laminates interaction with projectile at different time intervals. It can be seen from the images that, in case of T100 laminate there was no deformation at rear side of laminate and the projectile could perforate the laminate within 100 ms. In the case of TD 75:25 laminate, some amount of deformation is visible at rear side of the laminate due to this, the interaction time between the projectile and laminate has doubled i.e. 200 ms and thus resulted in increase in energy absorption. In the same way, Fig. 6 shows high speed video images of TD 50:50, TD 25:75 and D100 laminates respectively. The extent of deformation or bulge at different time intervals for the studied laminate configurations is shown in images for comparison purpose. It is clearly visible that, the presence of Dyneema® at rear side has contributed in significant deformation, due to which all the laminates have shown good energy absorption. Although there is no difference in energy absorption, variation in the extent of deformation was observed. The images were presented up to 3000 ms beyond which there was no change in deformation. TD 50:50 laminate showed maximum bulge of 34.2 mm at 500 ms and it got reduced to 12.4 mm at 3000 ms. This may be due to complete arrest of projectile movement within the laminate. In the case of D100 laminate, the bulge was found to be 38 mm at 500 ms and it got reduced to 20.6 mm at 3000 ms. This can be attributed to the lower
stiffness of D100 laminate as compared to TD 50:50 hybrid laminate. Hence more bulge for D 100 laminate was observed. Though TD 25:75 has shown bulge reduction, the magnitude of reduction was inferior as compared to TD 50:50 hybrid laminate. Fig. 7 shows the variation in bulged cone height at different time intervals during the penetration process. It was observed that, the cone height increased initially and it got decreased gradually as the projectile penetration has come down. This behaviour is similar for all the laminates. However, the maximum cone height was observed for D100 laminate followed by TD 50:50 and TD 25:75 hybrids laminate respectively. D100 laminate has shown cone height of 36.1 mm at 1000 ms whereas TD 50:50 has shown only 31.2 mm at the same time interval which is about 13% less than the former one. The final cone height was found to be 20.6 mm and 12.4 mm at 3000 ms for D100 and TD 50:50 laminates respectively. In the case of TD 25:75 laminate, initial cone height is similar to TD50:50 laminate but the final cone height is higher than TD50:50. Cone height for T100 and TD 75:25 laminates could not be determined due to complete perforation. The reduction in cone height in the case of hybrid laminates while maintaining the higher energy absorption is due to the presence of Tensylon® tape at front side which imparted higher stiffness to hybrid laminate. Rate of cone expansion indicates how fast the impact energy and momentum has got transferred to the rear side of the panel. It is desirable to have slower rate in cone expansion so that the rate of energy transfer to the object behind the armour will be less. Cone expansion rate as a function of interaction time is calculated from high speed images and shown in Fig. 8. Initially the cone expanded rapidly and reached its maximum value at about 100e150 ms, afterwards there was a deceleration in expansion and finally stabilized at 1000 ms. In the case of D100 laminate the maximum cone
Fig. 5. High speed video images for T100 and TD 75:25 laminate configurations.
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Fig. 6. High speed video images for D100 and TD 25:75 and TD 50:50 laminate configurations.
expansion pace was found to be 220 m/s whereas for hybrid laminate it was only 175 m/s which is 20% lower. This is significant to reduce the trauma effect. This shows the importance of having higher stiffness material at front face. However, it is effective only up to a certain thickness beyond that, the effect of higher stiffness (Tensylon® in this case) material on rate of cone expansion is found to be negligible which is the reason for similar expansion rate for TD 50:50 and TD 25:75 laminates. The final back face signatures (BFS) and percentage of its recovery was calculated from the images and shown in Fig. 9. It was observed that D100 laminate has shown maximum BFS of 21 mm whereas TD 50:50 hybrid laminate has showed only 12.4 mm which is 40% lower as compared to D100 laminate. The percentage recovery in BFS was found to be more for hybrid laminates than D100 laminate. This may due to improvement in overall stiffness of hybrid laminate. 3.4. Failure analysis Fig. 7. Change in cone height for different laminate configurations.
Fig. 8. Rate of increase in cone height for different configurations.
The presence of layered structure is known to provide better attenuation of shock waves than monolithic materials. From Fig. 10 it can be seen that, there is a clear cut separation of interface at Tensylon® and Dyneema® layers. This can be attributed to the fact that, though both the fibers are chemically same, there is a difference in impedance levels between Tensylon® and Dyneema® laminate due to the difference in matrix. Tensylon® material has got higher impedance over Dyneema® laminate due to its higher modulus and lack of viscous matrix. Hence, excessive delamination is observed at the interface between the two materials. In the case of Dyneema® laminate, more attenuation of shock waves can be expected due to the presence of viscous SIS matrix and layered structure. During the projectile penetration process laminates exhibit different failure mechanisms along the penetration path. Penetration in thick laminate is generally observed in two stages i.e. shear plugging or punching of fibers at entry stage of projectile followed by large deformation at rear side of the panel accompanied by delamination and fiber stretching [28]. At projectile entry point, due to high velocities there is no sufficient time for the fibers to dissipate the impact load in transverse direction, hence shear cutting of fibers is observed as major failure mode. As the penetration progresses, there is deceleration of projectile and laminate
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Fig. 9. Effect of laminate configuration on back face signatures (a) final BFS (b) % recovery.
Fig. 10. Cross section images of post impacted laminates.
also undergoes delamination, bending and tensile stretching of fibers due to the impact pulse travelling ahead of the projectile. Laminates having low ILSS and low modulus such as thermoplastics can undergo severe deformation, fiber stretching and thus gives better energy absorption. Hence the failure of laminate along the projectile path will be in the form of inverted ‘V’ shape for thermoplastic laminates. This phenomena is studied carefully for the present laminates. Fig. 10 shows cross section images of post impacted laminates and arrow mark shows projectile impact direction. It was observed that, in the case of T100, the laminate suffered complete penetration without a significant global deformation at rear side which is otherwise expected. The cross section image gives an impression of a monolithic polyethylene sheet though it is not so. The shear cutting of fibers was seen as primary failure mechanism and hardly any deformation at rear side of the panel was observed. This can be attributed to the higher bending stiffness and lack of long fiber structure in Tensylon® laminate. The Tensylon® tape is made of UHMWPE fibrils embedded in low density polyethylene matrix [29]. This type of matrix has got poor elongation under tensile load as compared to rubbery matrix. Due to the lack of continuous fibers in laminate, there was no effective transfer of impact energy in the lateral direction. Hence it is inferred that, energy dissipation mechanism is through thickness direction there by creating high strains along the projectile path resulting into shear cutting of layers. Therefore Tensylon® laminate could not undergo any
deformation at rear side of the panel. It has shown ‘U’ shape penetration path. Due to this type of failure behaviour, T100 laminate has shown significantly lower energy absorption as compared to other laminates. On the other hand, in case of D100 laminate, shear cutting of fibers at the entry of the projectile followed by delamination and deformation of layers at rear side of the laminate was observed. The projectile was completely stopped within the laminate. Since the Dyneema® laminate has got poor ILSS property and higher damping character, it could undergo delamination, tensile stretching and deformation in a wide area. Tensile stretching of fibers and global deformation of laminate absorbed more amount of projectile energy and decelerated it effectively. Intern, deceleration of projectile allowed more contact duration between the projectile and fiber resulting into participation of larger volume of laminate in absorbing the energy. The increased contact duration promoted to inverted ‘V’ shape failure pattern with higher energy absorption and extensive damage at rear side of the laminate. Hybrid laminate having TD 50:50 ratio has shown lowest damage area as compared to other laminates, such reduction in damage area helps in multihit protection. The extent of fiber bending in transverse direction from the center of the projectile path was observed to be more in D100 than in TD50:50. This may be due to the presence of soft matrix and continuous long fiber structure in Dyneema® laminate. In the case of hybrid laminate, the interface between Tensylon and Dyneema laminas was found to be separating during the penetration process due to difference in stiffness of two materials and poor interlaminar shear strength. D100 and TD 50:50 laminates have undergone different failure modes involving more energy absorption during projectile penetration. Hence they have exhibited higher energy absorption. Though TD50:50 and D100 laminates have shown similar energy absorption due to the limitation of projectile muzzle energy, the hybrid laminate has shown less extent of fiber bending in transverse direction and non-penetration thickness is found to be 2e3 mm whereas in the case of D100 laminate the nonpenetration thickness is found to be 1e1.5 mm and also the extent of fiber bending in transverse direction is found to be more (Fig. 10). The improvement in hybrid laminate interms of less extent of bending and less penetration is due to increased laminate stiffness and compressive resistance which can help in decelerating the projectile during the penetration process. Fig. 11 shows failure mode of Tensylon® material across the projectile path. It is observed that, in all the cases, at strike face and at the center of the projectile path shear cutting and melting of
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Fig. 11. Failure mode of Tensylon fibers across the projectile path.
fibers has occurred. As UHMWPE has got lower melting point, it can undergo melting easily due to the frictional heat generated during the penetration process. There is hardly any tensile stretching and delaminations. It appears that, shear cutting of fibers is not an effective energy absorption mechanism which is the reason for lower energy absorption in T100 laminate among all the studied laminates. In the case of TD50:50 and D100 laminate, the Dyneema
laminas has undergone significant bending, delamination and tensile stretching. Fig. 12 shows the failure mode of dyneema fibers across the projectile path. It is observed that at front side shear cutting of fibers is observed which is on the expected lines, whereas at center and rear side of the laminate, fiber bending, stretching and fiber sliding are observed.
Fig. 12. Failure modes dyneema fibers across the projectile path.
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4. Conclusions Hybrid composite laminates having 20 mm thickness were fabricated using Dyneema® HB50 and cost effective Tensylon® HSBD 30A through structural hybridization. Laminates were fabricated with different weight ratios of Tensylon® and Dyneema® and subjected to ballistic impact against 7.62 39 mm mild steel projectile. Results suggest that hybrid laminate with 50:50 wt ratio of Tensylon® and Dyneema® has shown significant increase in energy absorption over tensylon laminate. Back face signature, rate of back face bulge formation and extent of damage were found to be minimum for TD50:50 hybrid laminate as compared to the other laminates. This is due to the optimum combination of two different types of fiber structures which supported for better ballistic performance. This study shows that cost effective armour with superior ballistic property can be designed through structural hybridization method. Laminates have shown different failure behaviour. In the case of T100 laminate shear cutting of fibers is found to be predominant failure behaviour and has resulted in very low energy absorption. In the case of hybrid and D100 laminates, shear cutting at entry point of the projectile followed by delamination, bending and tensile stretching at projectile exit side of the laminate was observed. The failure analysis of post impacted laminates suggest that, it is desirable to have material with higher stiffness at entry side of the projectile to resist the compressive load and thus to slow down the projectile penetration. Simultaneously there is a need to have low interlaminar shear strength to promote delamination planes ahead of the projectile penetration. This helps in tensile stretching with wide deformation at the rear side of the laminate which delays the failure of fibers by distributing the impact energy over a large volume of material. Therefore, it is essential to have a balance in combination of different materials to get the optimum energy absorption with reduced back face signature at a lower cost. Acknowledgements Authors gratefully acknowledge Director, Defence Metallurgical Research Laboratory (DMRL), Hyderabad for his encouragement to publish this work. The authors also acknowledge the support rendered by the staff of Armour Design and Development Division (ADDD). References [1] Gellert EP, Cimpocru SJ, Woodward RL. A study of the effect of target thickness on the ballistic perforation of glass-fibre reinforced plastic composites. Int J Impact Eng 2000;24:445e56. [2] Reddy PRama Subba, Reddy TSreekantha, Madhu V, Gogia AK, Rao KVenkateswara. Behaviour of E-glass composite laminates under ballistic impact. Mater Des 2015;84:79e86. [3] Zhang Jin, Chaisombat Khunlavit, He Shuai, Wang Chun H. Hybrid composite laminates reinforced with glass/carbon woven fabrics for lightweight load bearing structures. Mater Des 2012;36:75e80. [4] Sevkat Ercan, Liaw Benjamin, Delale Feridun. Drop-weight impact response of hybrid composites impacted by impactor of various geometries. Mater Des 2013;52:67e77. [5] Munoz R, Martinez-Hergueta F, Galvez F, Gonzalez C, Lorca JL. Ballistic performance of hybrid 3D woven composites: experiments and simulations. Compos Struct 2015;127:141e51.
9
[6] Kumar Bandaru Aswani, Vetiyatil Lakshimi, Ahmad Suhail. The effect of hybridization on the ballistic impact behaviour of hybrid composite armours. Compos Part B 2015;76:300e19. [7] Yahaya R, Sapuan SM, Jawaid M, Leman Z, Zainudin ES. Measurement of ballistic impact properties of woven kenafearamid hybrid composites. Measurement 2016;77:335e43. [8] Pandya Kedar S, Pothnis Jayaram R, Ravikumar G, Naik NK. Ballistic impact behavior of hybrid composites. Mater Des 2013;44:128e35. [9] Larsson F, Svensson L. Carbon, polyethylene and PBO hybrid fibre composites for structural lightweight armour. Compos A: Appl Sci Manuf 2002;33: 221e31. [10] Yanen Cenk, Yavuz Solmaz Murat. Ballistic performance of 21 layered hybrid composites. In: 12th international conference on latest trends in engineering and technology (ICLTET’2017) May 22-24; 2017 [Kuala Lumpur (Malaysia)]. [11] Zulkifl Faiz, Jan Stolk, Ulrich Heisserer, Yong Alex Tuck-Mun, Li Zhiyi, Hu Xiao Matthew. Strategic positioning of carbon fiber layers in an UHMwPE ballistic hybrid composite panel. Int J Impact Eng 2019;129:119e27. [12] Chen X, Zhou Y, Wells G. Numerical and experimental investigations into ballistic performance of hybrid fabric panels. Compos Part B 2014;58:35e42. [13] Cwik Tomasz K, Iannucci Lorenzo, Curtis Paul, Pope Dan. Design and ballistic performance of hybrid. Composite laminates. Appl Compos Mater 2017;24: 717e33. [14] Sapozhnikov SB, Kudryavtsev OA, Zhikharev MV. Fragment ballistic performance of homogenous and hybrid thermoplastic composites. Int J Impact Eng 2015;81:8e16. [15] Vargas-Gonzalez Lionel, Walsh Shawn M, James Wolbert. Impact and ballistic response of hybridized thermoplastic laminates. ARL-MR-0769; February 2011. [16] Yahaya R, Sapuan SM, Jawaid M, Leman Z, Zainudin ES. Effect of layering sequence and chemical treatment on the mechanical properties of woven kenafearamid hybrid laminated composites. Mater Des 2015;85:431e7. [17] Salman Suhad D, Leman Z, Sultan MTH, Ishak MR, Cardona F. Quasi-static penetration behavior of plain woven kenaf/aramid reinforced polyvinyl butyral hybrid laminates. J IndText 2018;47(7):1427e46. https://doi.org/ 10.1177/1528083717692593. [18] Salman Suhad D, Leman Z, Sultan MTH, Ishak MR, Cardona F. Effect of kenaf fibers on trauma penetration depth and ballistic impact resistance for laminated composites. Text Res J 2017;87(17):2051e65. https://doi.org/10.1177/ 0040517516663155. [19] Salman Suhad D, Leman Z, Ishak MR, Sultan MTH, Cardona F. Ballistic impact resistance of plain woven kenaf/aramid reinforced poly vinyl butyral laminated hybrid composite. Bio Resour 2016;11(3):7282e95. [20] Bunea M, Cîrciumaru A, Buciumeanu M, Bîrsan IG, Silva FS. Low velocity impact response of fabric reinforced hybrid composites with stratified filled epoxy matrix. Compos SciTechnol 2019;169:242e8. [21] Xu Chenhui, Wang Yu, Wu Jie, Song Shichao, Cao Saisai, Xuan Shouhu, Jiang Wanquan, Gong Xinglong. Anti-impact response of Kevlar sandwich structure with silly putty core. Compos SciTechnol 2017;153:168e77. [22] Martínez-Hergueta F, Ridruejo A, Gonzalez C, LLorca J. Ballistic performance of hybrid nonwoven/woven polyethylene fabric shields. Int J Impact Eng 2017;111:55e65. [23] Gene C. Weedon, Kenneth C Harding, Lisa Owen, Non-fibrous high modulus ultra high molecular weight polyethylene tape for ballistic applications. US Patent no.US/0318016A1, 2008. [24] Singletary J, Lauke B. Polyolefin film reinforced composites for personal protection. In: Chapter-13, Advanced fibrous composite materials for ballistic applications. Woodheed publishing; 2016. [25] Alil LC, Arrigoni M, Badea S, Ginghina R, Matache L-C, Mostovykh P. Ballistic study of Tensylon® e based panels. Express Polym Lett 2018;12(6):491e504. [26] Indian Standard. Textiles-bullet resistant jackets-performance requirements. IS17051. 2018. [27] Cline Jula, Bogetti Travis, Love Bryan. Comparison of the in-plane shear behaviour of UHMWPE fiber and highly oriented film composites. In: Proceedings of 32nd technical conference. America Society of Composites; 2017. https://doi.org/10.12783/asc2017/15182. November. [28] Rama Subba Reddy P, Sreekantha Reddy T, Srikanth I, Madhu V, Gogia AK, Venkateswara Rao K. Effect of viscoelastic behaviour of glass laminates on their energy absorption subjected to high velocity impact. Mater Des 2016;98: 272e9. [29] Hine PJ, Ward IM, Jordan ND, Olley RH, Bassett DC. A comparison of the hotcompaction behaviour of oriented high-modulus polyethylene fibers and tapes. J Macro Sci Part B Phys 2001;40:959e89.
Please cite this article as: Reddy PRS et al., Development of cost effective personnel armour through structural hybridization, Defence Technology, https://doi.org/10.1016/j.dt.2019.12.004