The Journal of Strain Analysis for Engineering Design

Composite materials are increasingly being used in the design of structures that will be subjected to high-velocity impact during their lifetime. In this review we will look at the recent advances in our understanding of how rigid composite materials behave under high-velocity impact. In particular, this review will focus on rigid structural composites such as carbon fibre reinforced plastic and glass fibre reinforced plastic laminates and what we have learned with regards to how they respond under ballistic-loading conditions. We will focus on a velocity regime that includes impacts from explosively-driven fragments, ice particles and bullets. The hypervelocity-impact response and how these materials behave under one-dimensional shock loading will be studied in an accompanying review (Part II).

The combination of high strength and low density has resulted in increasing use of composite materials in structures such as aerospace systems that may be subjected to high-velocity impact during their in-service lives. In this review we focus on recent work surrounding the response of composites, primarily carbon fibre reinforced plastic and glass fibre reinforced plastic-based laminates to very high (hyper)-velocity impacts. To this end, the review is divided into two halves. In the first, hypervelocity impacts (e.g. impacts with velocities greater than ca. 2 km/s) that are likely to be encountered by aerospace systems are considered; while in the second, resultant material behaviour – in the form of shock response – is discussed. This review is designed to (1) build on previous studies which have typically largely focused on high-velocity impacts from the perspective of spacecraft protection against on-orbit impact, and; (2) complement an earlier part which focused on the lower impact velocity regime associated with ballistic-loading (Part 1).

Performance of three-dimensional orthogonal woven E-glass/epoxy composites under high velocity impact is presented. The analytical method used is based on wave propagation and energy balance between the projectile and the target. Different damage and energy absorbing mechanisms for a typical three-dimensional orthogonal woven composite are compression of the target directly below the projectile, compression in the surrounding region of the impacted zone, tension in the region consisting of primary yarns, tensile deformation in the region consisting of secondary yarns, shear plugging, bulge formation on the back face of the target, matrix cracking and friction between the target and the projectile. Experimental studies are also presented on high strain rate characterization, shear plugging behavior and high velocity impact behavior. For comparison, studies are also presented on the performance of two-dimensional plain weave E-glass/epoxy composites. A good match is observed between the analytical predictions and experimentally obtained limit velocities for complete penetration. It is observed that limit velocity for complete penetration for three-dimensional woven composite is higher than that for two-dimensional plain weave composite.

The high-velocity impact response of fibre metal laminates based on a woven polypropylene fibre reinforced polypropylene, termed a self-reinforced polypropylene, and a glass reinforced polypropylene has been investigated. Two types of aluminium alloy were considered, these being the 2024-O and 2024-T3 alloys. Tests on these composite–metal hybrids were undertaken using a gas gun over a wide range of incident impact energies. In this study, attention focused specifically on the perforation threshold. Following impact, the fracture mechanisms in the two types of fibre metal laminates were elucidated by sectioning and polishing samples through the point of impact and also by measuring the residual deformation of the hybrid plates. Cross-sections of the failed samples highlighted significant plasticity within the volume of these hybrid materials, indicating that considerable energy had been absorbed in plastically deforming the aluminium and composite plies. The impact resistances of the various laminates were compared by determining their specific perforation energies. Here, it was shown that fibre metal laminates based on the glass reinforced polypropylene composite offer a slightly higher perforation resistance than the self-reinforced polypropylene fibre metal laminates. Also, the fibre metal laminates based on the stronger 2024-T3 alloy out-performed their 2024-O counterparts. Finally, the perforation resistances of the fibre metal laminates were predicted using the previously reported Reid–Wen impact perforation model. Good agreement was observed between this impact model and the measured experimental data.

This work analyses the influence that the areal density of a composite thin-plate, made of glass-fibre woven laminates and subjected to high-velocity impact, exerts on perforation-threshold energy, contact time, and energy-absorption mechanisms. The perforation-threshold energy increased with the areal density. Also, the contact time increased at impact energies above the perforation-threshold energy and decreased below this threshold. The main energy-absorption mechanisms at impact energies close to that causing perforation were found to be the deformation and failure of the fibres, regardless of the areal density. For higher impact energies, the main mechanisms were fibre failure and the energy absorbed by acceleration of the laminate.

This paper presents an experimental and numerical study to understand ballistic behavior of plain-weave hybrid and non-hybrid composites. The effect of hybridization on ballistic limit (V₅₀) was investigated. The hybrid S2 glass-IM7 graphite fibers/toughened SC-79 resin, non-hybrid S2 glass-fiber/toughened SC-79 resin, and non-hybrid IM7 graphite fibers/toughened SC-79 resin composites plates were impacted at various velocities. The three-dimensional dynamic nonlinear finite element code, LS-DYNA, modified with a proposed user-defined nonlinear-orthotropic damage model, was adopted to simulate the experimental results. The combined results obtained from experiments and finite element simulations were then used for determining V ₅₀ for each lay-up configuration. Good agreement between experimental and FE results was found from the comparison of dynamic strain and damage patterns. The hybridization found to be very effective on ballistic limit velocities of woven composites.

Carbon fiber reinforced plastic composite materials have unique mechanical properties and could substitute aluminum alloys used in harsh environments. We performed high-speed impact experiments to study carbon fiber reinforced plastic fracture behavior at cryogenic temperatures for two specimens of different laminated constitution. The effect of temperature, impact velocity, and layered composition on the fracture behavior of carbon fiber reinforced plastic was examined. Perforation hole-sizes and shapes, as well as damaged regions on the specimens varied systematically depending on layered compositions. We found that carbon fiber reinforced plastic layered composition played an important role and damage regions were controllable by manipulating carbon fiber reinforced plastic layered compositions.

Multi-hit ballistic impact and damage behavior of thick-section composites are of interest to many military and aerospace applications. The effect of support spans on single-hit penetration resistance and the effect of relative distance between multiple impacts on the penetration resistance are the subject matter of the present investigation. In order to study the effect of support spans on penetration resistance, single-hit ballistic experiments are conducted on two plain-weave (PW) S-2 glass/SC15 composite laminates of thickness, 13.5 mm (22 layers, 22L) and 20.4 mm (33 layers, 33L), respectively at two different support span diameters, i.e. 102 mm and 203 mm. On the other hand, the effect of multiple impacts on penetration resistance has been investigated by impacting both the laminates (22L and 33L) at four additional radial shot locations (90 degrees apart) with a support span diameter of 203 mm. In both the impact scenarios, 0.50cal fragment simulating projectiles (0.50cal FSP) were used while the composite laminates were clamped between a cover and a support plate. In addition, the maximum dynamic deflection of the composite laminates were recorded using a thin aluminum witness plate at the rear end of the laminate, and the through-thickness ballistic damage of the composite laminates was investigated by sectioning through the impact centers, dying with an ink-alcohol solution, and taking optical photographs of the cross-sections.

Results show that the single-hit ballistic limit velocity increases marginally with support span diameter investigated. The curvatures of the dynamic deflection profiles at the support edge suggest that the dynamic deflection was constrained by the smaller support span while the dynamic deflection was not constrained by the larger support span. There was no noticeable difference in the single-hit maximum dynamic deflection between the two laminate thicknesses as a function of impact velocity to ballistic limit velocity ratios. Single-hit through-thickness damage extended toward the edges of the larger support spans such that the subsequent multiple impacts were on partially damaged laminates; however, the pre-existing ballistic damage showed about 4.5% and 9.0% decrease in site specific multi-hit ballistic limit and energy, respectively.

The effect of support spans on single-hit ballistic limit and the effect of pre-existing ballistic damage on multi-hit ballistic limit for two S-2 glass/SC15 composite laminate thicknesses (i.e. 13.6 mm and 20.5 mm) using 0.50cal fragment simulating projectiles have been experimentally investigated in a companion paper. The main objective of this paper is to simulate and correlate the multi-hit ballistic experiments using finite element analyses. One multi-hit ballistic impact scenario on two different composite laminate thicknesses is considered in the present analyses. Finite element model of the impact scenario is developed using three-dimensional solid elements and are solved using LS-DYNA and the progressive composite damage model MAT162. The MAT162 properties and parameters of plain-weave S-2 glass/SC15 composites used in the present simulations were validated in our previous work. Multi-hit impact cases are simulated by sequentially impacting the composite laminate with five different fragment simulating projectiles at five different impact locations at an interval of 200 micro-seconds. Good correlations of ballistic limit velocities between experiments and finite element analyses are obtained. In addition, finite element analyses provided time histories of projectile and laminate dynamics, and damage evolution and interactions for the multi-hit impact cases. Detailed simulation results and comparison with the experiments are presented.

A numerical study is performed herein on the perforation of fiber reinforced plastic laminates struck normally by flat-nosed projectiles at high velocities. First, some previous constitutive models for fiber reinforced plastic composites are briefly reviewed and then a constitutive model is proposed to predict the perforation of fiber reinforced plastic laminates. The present constitutive model is developed based on the concept of continuum damage mechanics and criteria for different failure modes which take the quadratic form of various stress parameters. The effects of strain rate on the strength as well as the modulus of fiber reinforced plastic laminated materials are also considered in the model. It transpires that the present numerical simulations are in good agreement with experimental observations for the perforation of carbon fiber reinforced plastic, glass fiber reinforced plastic and kevlar fiber reinforced plastic laminates impacted by flat-ended projectiles in terms of deformation profile, ballistic limit and residual velocity. It also transpires that the present constitutive model is advantageous over the existing models.

A numerical model of ballistic impact on a two-dimensional Kevlar KM2^® plain-woven fabric has been validated by experiment. This paper shows that it is necessary to experimentally measure material constants of yarns for having good input parameters of the model. Effects of yarn Poisson’s ratio, transverse and shear modulus on impact behaviors of a simple crimped yarn and a complete fabric have been carried out. The effect of the Poisson’s ratio can be negligible in both impact cases: on a single crimped yarn and a complete fabric. The same conclusion has been proven for the effect of the transversal modulus except the cases of its so low values that can cause yarn early damage. The shear modulus of a yarn appears to be an important material parameter that mainly influences the ballistic performance of a two-dimensional plain-woven fabric. When using a very high value of a shear modulus of yarn, a crimped single yarn is broken immediately after contact with projectile in pure shearing mode.