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Investigation on Energy Absorption Efficiency of Each Layer in Ballistic

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Composite Structures 164 (2017) 1–9 Contents lists available at ScienceDirect Composite Structures journal homepage: www.elsevier.com/locate/compstruct Investigation on energy absorption efficiency of each layer in ballistic armour panel for applications in hybrid design ⇑ Yanfei Yang a,b, , Xiaogang Chen b a School of Textile, Zhongyuan University of Technology, Zhengzhou, Henan, China b School of Materials, University of Manchester, Manchester, UK article info abstract Article history: This study aims to reveal different energy absorption efficiency of each layer when armour panel is under Received 30 September 2016 ballistic impact. Through Finite Element (FE) modelling and ballistic tests, it is found that when fabrics Revised 8 December 2016 are layered up in a panel, energy absorption efficiency is only 30%–60% of an individual fabric layer with Accepted 15 December 2016 free boundary condition. In addition, fabric layers in front, middle, and back exhibit different ballistic Available online 19 December 2016 characteristics. Therefore, a new hybrid design principle has been proposed. A multilayer panel can be divided into three groups. Two hybrid panels that are combined different Twaron fabrics and Dyneema Keywords: UD laminates are designed. Ballistic tests results show that for a given areal density of the panel, BFS Ballistic armour panel behind the hybrid panel decreases 31.54% than that of the woven fabric panel. When the areal density Finite Element (FE) Ballistic test of armour panel is reduced, the hybrid panel is more likely to stop the projectile. These findings provide Energy absorption efficiency a guide for hybrid design of ballistic armour panel. Hybrid design Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction absorption of each layer is increased from front to back in the panel. In our previous studies [10–12], it was found that when a Ballistic body armour made from high performance fibres, such multilayer panel is under ballistic impact, energy absorption of as aramid, and Ultra High Molecular Weight Polyethylene each layer is increased from the front layer to the peak value at (UHMWPE) fibres, is widely used in personnel ballistic protective the last perforated layer and then gradually decreased in following clothing for military and law enforcement application, due to typ- back layers of the panel. Such pattern has not been influenced by ical flexibility, and light-weight [1–3]. Traditionally, an armour the total number of layers in the panel. When increasing the threat panel is manufactured by layering numerous woven fabric layers level, only the position of the peak value of energy absorption with with weight of 3–5 kg [1]. However, according to previous studies, the last perforated layer is shifted towards back of the panel. each fabric layers at different positions of a multilayer panel plays Due to different roles of each layer in ballistic resistance, layer- different roles in ballistic resistance [4–8]. ing up same fabrics in a panel cannot be the most efficient method Joo and Kang [4] used FE model to analyse energy absorption of for ballistic performance. In recent years, many patents and com- each layer in multilayer panels. He concluded that in the non- mercial hybrid products have been proved to be very efficient in perforation case, the absorbed energy is the highest for the first providing superior ballistic performances and reductions in weight layer followed by the subsequent layers. When the perforation [13–16]. The Honeywell Company [15] designed 21-layers hybrid occurs, the sequence is reversed. Cunniff [6] reported that material armour panel with a sandwich structure by combining Spectra near the striking face has little influence on ballistic performance ShieldsÒ, Gold FlexÒ, and KevlarÒ. It possesses lighter weight, a of an armour panel when the impact velocity is much higher than greater range of threat protection, and improved comfort, flexibil- the ballistic limit. Chen [5–9] explained that the front layers of fab- ity. The desired ballistic performance can be achieved by manipu- ric in a multi-layer panel are more likely to be broken in shear, and lating the order of layering up and the number of layers. Karahan the back layers of fabric tend to fail in tension. As a result, energy [16] observed that hybrid panels combining para-aramid woven fabrics and K-FlexÒ UD laminate can achieve around 4.5% reduction in BFS and 8.5% improvement in energy absorption per unit weight compared to 100% woven fabric panels. In Chabba’s patent [13],a ⇑ Corresponding author at: School of Textile, Zhongyuan University of Technol- multi-layered panel combines sub-stacks of trauma reducing lay- ogy, 41 Zhongyuan Road, Zhengzhou 450007, China. ers and fibrous layers. The decreasing BFS of the hybrid panel can E-mail address: [email protected] (Y. Yang). http://dx.doi.org/10.1016/j.compstruct.2016.12.057 0263-8223/Ó 2016 Elsevier Ltd. All rights reserved. 2 Y. Yang, X. Chen / Composite Structures 164 (2017) 1–9 reach 9.52% compared to the DyneemaÒ UD panel. Although the (0.26 mm) and the weave density of the fabric (10.9ends/cm), the positive hybrid effect on ballistic performance of the multi-layer width of the yarn cross-section and the length of the crimp wave system has already been demonstrated, most of these studies only can be calculated as 0.0881 cm and 0.1832 cm respectively. The focused on the layering up effect of hybridisation. A general design same yarns are assembled in warp and weft directions to construct principle for hybrid armour panel has not been identified. a single layer of plain fabric with the size of 75 Â 75 mm. The FE In addition, mechanisms responding to the hybridisation effect model of an individual fabric panel under impact is shown in have never been fully understood. Cunniff [17]experimentally Fig. 1(c). studied the effect of layering sequence of a two-layer system com- In a non-perforation case, three FE models of multilayer panels bining KevlarÒ (low modulus) and SpectraÒ (high modulus) woven with 24, 36 and 48 layers which can stop the projectile were cre- fabrics. Ballistic performance of V50 shows differences between ated, namely 11F24, 11F36 and 11F48. A multilayer panel is created these two hybrid panels with reverse layering sequence. He by overlapping a certain number of fabric layers. According to NIJ explained that different modulus of materials can result in the standard-0101.06 [21], Roma Plastilina No.1 oil based modelling interference of transverse deflection under ballistic impact. This clay is used as backing material to record the configuration of leads to reduction of energy absorption in a panel when a material the indentation after impact. It is modelled as a 3D solid contin- with high modulus was placed before a material with low modu- uum block with the size of 75 Â 75 Â 50 mm. FE model of a multi- lus. Above test results have been investigated by Porwal and Phoe- layer panel under impact is shown in Fig. 1(d). nix [18] through a theoretical and numerical model. It was found For the non-perforated panels, free boundary conditions are that the interference between two layers had a significant influ- assigned for the outer edges of the panel. The other two edges ence on strain evolution in layers, in particularly near the edge of crossing at the impact area are applied symmetry conditions. The the projectile where failure initiates. Park et al. [19] concluded clay is placed inside a container. Therefore, the constraint bound- the hybridization effect is determined by the modulus of materials. ary conditions are assigned for the outer edges and the back of He found that the hybrid panel with components in the order of the clay. The symmetry conditions are applied for the other two decreasing modulus enhanced the penetration resistance. The lay- edges crossing at the impact area. For the FE model of an individual ering up sequence of components with the increasing modulus is layer of fabric under impact, the back clay is removed. A free beneficial to reduce BFS. In Rahman’s study, FE results showed that boundary condition is applied for the individual layer. the contact force of woven panel was higher than that of rigid lam- In order to reduce the number of elements and ensure the accu- inate panel. This results in more energy absorption in the woven racy of calculation, fine mesh size and coarse mesh size are used for panel [20]. Although a considerable work on ballistic responses primary yarns and secondary yarns respectively. For the clay of multilayer panel has been done, the different contribution of model, a transition mesh sizes are adopted. Eight node hexahedron each layer in ballistic resistance still need to be further investi- elements (C3D8R) were used for yarns, projectile and clay in the gated. Such understanding is important for the construction opti- model. The general contact algorithm and simple coulomb friction mising of ballistic armour panel. is used for all contact surfaces in the FE model. The friction coeffi- Our previous studies focus on identifying a general energy cient is assumed to be 0.2 according to Rao’s tests results [22]. The absorption distribution in a multilayer armour panel at different impact velocity of 483 m/s is assigned to the projectile perpendic- ballistic impact conditions [10,11]. This study aims to further ular to the armour plane. quantify energy absorption efficiency of each layer, and propose Assignment of material properties for FE model is also referred a new hybrid design principle. Finite Element (FE) simulation and to our previous study [10]. The yarn model and clay are assumed to ballistic tests are used to explore different ballistic characteristics be homogeneous and isotropic material.
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