Elsevier

Composite Structures

Volume 213, 1 April 2019, Pages 209-219
Composite Structures

Ballistic reliability study on SiC/UHMWPE composite armor against armor-piercing bullet

https://doi.org/10.1016/j.compstruct.2019.01.078Get rights and content

Abstract

The ballistic reliability of composite armors is significantly affected by the random material properties. In this paper, the mosaic SiC ceramics/ultra high molecular weight polyethylene (UHMWPE) composite targets with bonding adhesives are tested near the limit ballistic penetration conditions. The uncertain material and adhesive properties led to complete penetration and partial penetration at bullet initial velocity of 776 m/s and 791 m/s, respectively, and a contrary tendency is also observed in the tests between the bulging deformation and the minimum target thickness of back plate. A state function of penetration for reliability evaluation is formulated based on a validated numerical model. Results from sensitivity analysis indicate that twelve uncertain material parameters are strongly sensitive to the penetration state. Then, the ballistic reliability under the test velocities is obtained by both Monte Carlo method and design point method. Finally, an optimization problem with a probability constraint is established in order to achieve a minimum deformation. The results show that the bulging deformation and the value of penetration state function vary with the adhesive strengths oppositely. Therefore, the adhesive strengths are designed to control the contradiction between the deformation and the minimum target thickness. It is significant to recognize the uncertain properties of composite armors and to improve the ballistic performance against armor-piercing bullet.

Introduction

Composite armors combine the advantages of two or more material properties and have been widely used in the protection of human body and special vehicles. Generally, the composite armor is characterized by low density, high modulus, high yielding stress and high dynamic tensile stress. A typical composite armor consisting of a relatively hard face plate and a relatively tough back plate attracts increasing attentions [1], [2], [3], [4]. This typical armor may be considered as three-phase composites consisting of the hard face plate, the tough back plate and the bonding interface between the face plate and back plate. It is important to clarify the complex influence of composite armors with three-phase structure on the ballistic performance.

For the three-phase composite armor, the interaction effects between different parts are essential to the ballistic behaviors. Ceramics with high hardness and low density can blunt and smash the bullet effectively. Experimental research works [5], [6], [7] show that the ballistic behaviors of ceramics are sensitive to the surrounding constraint materials. The mechanism for the composite armors has been studied analytically. Feli et al. [8] established a theoretical model for ceramic/metal armor considering bullet erosion and flattening. Tang [9] established a theoretical model including bullet deformation and erosion, ceramic compression and shear failure mechanism. However, the cracking details during the penetration process cannot be well described by the theoretical model. Due to the brittle material property of ceramics, the impact cracks may also extend easily over the entire surface of a ceramic tile. Rabczuk et al. [10], [11], [12] proposed several effective meshfree methods for numerical modeling of impact cracks. Dual-horizen peridynamics [13], [14], a newly developed peridynamics method, has been an advantageous way for dynamic fracture modeling. One way for restricting the cracking area is to design a whole plate of ceramic into small tiles so that the damage affects only the adjacent tiles [15]. Adhesives applied between ceramics tiles provide another way for attenuating the impact stresses. Goel et al. [16] explained the adhesives attenuation effects in mosaic ceramic tiles through a micro-macro analytical model. López-Puente and Zaera [17], [18] investigated the adhesive effects on ballistic performance of mosaic alumina/aluminium armors. The results showed that thicker adhesive leads to wider deformation area on the back plate but earlier damage of the ceramic tile while thinner adhesive leads to more impact damages on the adjacent ceramics tiles. Advanced fiber reinforced composites [19], [20], [21] with high energy absorption ratio can resist the fragments and attenuate stresses. Grujicic et al. [22] established a numerical model for ceramic/polymer–matrix composite with polyurea adhesives. The influence of adhesives on composite back plate has not been clearly investigated. As various material properties of the composite armors are mutually affected with each other, the correlations cannot be neglected.

Uncertain material properties commonly exist in the composite armors. The scatter material properties of fiber reinforced composite are related to fibers, matrix and adhesives [23], [24], [25]. Experimental research [26] also shows that the mechanical properties of ceramics depend largely on the internal defects distributions. Several stochastic methods have been applied to solve the structure and material uncertainty problems [27], [28], [29], in which the Monte Carlo simulation [30] is a method to calculate the scatter of structural responses by numerous repetitions of deterministic analysis. Non-probabilistic methods [31], [32], [33] are suitable when the bounds of uncertainty are more easily obtainable compared with the precise probability distributions. Global sensitivity analysis approaches, especially the screening based methods [34] and variance based methods [35], have been developed for solving fracturing problems [36]. However, few literatures have focused on the uncertain material property of composite armors. Ignatova [37] studied the uncertain ballistic performance of porous ceramics through a mesoscopic model. Santos et al. [38] investigated the reliability of a bi-hardness composite armor against ballistic impact. The evaluation of material contributions to the ballistic performance and the reliability of penetration limit have not been studied thoroughly.

For studying the uncertainty and reliability of composite armors against the armor-piercing bullet, the mosaic ceramics/UHMWPE targets are tested under ballistic conditions. The dynamic deformation responses are captured by a high speed camera. A validated numerical model is established to calculate the dynamic responses. The penetration state function for reliability analysis is formulated with the residual bullet velocity and the minimum target thickness. Then, the reliability of ceramics/UHMWPE armor is calculated with both the design point method and the Monte Carlo method under experimental conditions. Finally, the strength of the adhesive interfaces among mosaic tiles and between the mosaic tiles and UHMWPE back plate is designed with a reliability-based optimization method to improve the ballistic performance.

Section snippets

Test settings

The SiC/UHMWPE composite armors are prepared for ballistic tests in which the mosaic SiC ceramics and the UHMWPE laminate are respectively used as the face plate and back plate. The face plate consists of nine 50 mm × 50 mm × 8 mm SiC ceramic tiles that made from the reactive sintering processes. The UHMWPE laminate is formed by the hot pressing process using the unidirectional fiber fabrics coated with polyurethane. The layer angle is [0°/90°/0°/90°] and the size is 200 mm × 200 mm × 8 mm. The

Model establishment

The whole model of SiC/UHMWPE composite armor against armor-piercing bullet is calculated by the 3D Lagrange solver in AUTODYN 18.0. The initial velocity of the bullet materials is set according to the tests. Fixed boundaries are set to the two sides of target frame to support the SiC/UHMWPE composite armor. Fig. 6 gives the numerical model with distribution of meshes. The target plate, the lead sleeve and steel core of bullet are divided into hexahedral meshes. The copper shell of bullet is

Reliability evaluation

For probability analysis, a penetration state function is formulated to describe the limit state between partial penetration and complete penetration. The limit penetration state means the target is completely penetrated and the bullet kinetic energy is 0. Both responses of minimum target thickness t and residual velocity vr have to be used in the penetration state function for either of them is not sensitive to all the penetration state. The target thickness t indicates the degree of partial

Reliability design

The bonding interfaces exhibit different levels of strength for different type of adhesives. Strong adhesives may reduce the deformation but the reliability of composite armors may decrease accordingly. It can be seen from simulation results that the target deformation decreases with the increase of adhesive strengths, as shown in Fig. 14. When the plastic deformation of the back plate is small, the energy absorption may be insufficient. The value of the penetration state function increases

Conclusions

The uncertain ballistic behavior of mosaic SiC/UHMWPE composite armors is studied through experiments and simulations. In ballistic tests, the targets went through partial penetration under a relatively higher bullet velocity and complete penetration under a relatively lower bullet velocity, which means that the uncertain penetration performances should be characterized by the uncertain material parameters. Besides, the tests results indicate a contradiction between the bulging deformation of

Acknowledgement

The supports from National Natural Science Foundation of China (51621004, 11672105) and Natural Science Foundation of Hunan Province (2016JJ1009) are gratefully acknowledged.

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