# Modelling of High-Velocity Impact on Woven Carbon Fibre-Reinforced Plastic Laminate
## 3 Experimental Programme  
A number of sphere impact tests on woven CFRP plates was carried out at Cranfield Defence and Security Shrivenham [39]. A range of velocities from 179 m/s to 1875 m/s were tested to provide the data for numerical model validation and study the failure mechanisms, specific for composite materials in aerospace applications. Kinetic energy in all considered tests was well above the ballistic limit of the target plates and covers the range of loading conditions where the material undergoes different failure modes, including shock loading. The impact test configuration is shown in Figure 1.  
To investigate the effects of the target thickness on the material response to the high-speed sphere impact, two Hexcel composite plates were chosen for the impact trials: a 6 mm thick plate and 12 mm thick plate, which consisted of 16 and 32 plies, respectively. The thinner target plate was made of an asymmetric layup [0/90, \(\pm\)45\({}_{2}\), 0/90, \(\pm\)45\({}_{2}\),0/90\({}_{2}\), (\(\pm\)45, 0/90)\({}_{4}\)], as shown in Figure 1. The layup effects on the target response and the energy transferred were investigated by impacting the target panels in two normal impact directions. A set of impact cases denoted with A were impacted in the direction denoted in the figure; the impact test performed in the opposite direction was denoted as B. The  
Figure 1: Sphere projectile impact on woven CFRP laminate. simulation programme was focused on the former cases, as the experiments showed that energy transferred to the panel for the range of impact energies 0-500 J (impact velocity from 0 to 375 m/s) was independent of the symmetry of the target plate. The thick panels, denoted as C, were made of two 6 mm panels bonded together by Loctite 0151 (under load for 24 h) to create a symmetric 12 mm thick target plate. These tests aimed to test the thickness effects on the panel response. In all test cases, the projectile was annealed SS304 stainless steel, 12 mm in diameter (average of \(Q11.97\pm 0.1\) mm) with a mass of 7.165 g [39]. A detailed metallurgical test of the grain structure of a number of the projectiles used in this experimental work showed that the mechanical properties of the annealed spheres were proven to be isotropic. The yield stress and tensile strength of the material are 450 MPa and 675 MPa, respectively, with the other material properties used in the finite element model are given in Section 4. The experiments showed that energy transferred to the target increased with the increase in impact energy, which can be attributed to an increased number of damage and failure mechanisms triggered in the composites, such as fibre breakage, fibre pull-out, matrix cracking, matrix crashing, delamination, inelastic deformation of the projectile, etc. A simple calculation showed that over half of the initial kinetic energy was transferred to the particles generated during the penetration of the target, including the remaining kinetic energy of the projectile [39]. More importantly, a change in failure mechanism was observed as a function of the impact velocity, i.e., energy of impact. For a relatively low range of velocities (from 186 m/s to 194 m/s), just above the ballistic limit, material failure started at the rear face of the target and the major failure mechanism was fibre breakage due to the tensile load. The cracking then progressed towards the front face of the target, allowing for the projectile to push the material away and pass through the target. After the projectile had passed through, the previously banded fibres relaxed back to an equilibrium position. As a result, the diameter of the hole made by projectile was significantly smaller than the diameter of the projectile and no plug was formed during the perforation. This type of failure is usually referred to as the petalling type of failure and an image of the rear side of the penetrated target is shown in Figure 2a, whilst the post-impact XCT image of the cross-section through the impact axis is shown in Figure 2b.