Impact-Induced Through-Thickness Stress Wave Propagation and Damage in Woven Composites

Studies of impact on plain weave composites often consider radial stress waves and transverse deformation, but neglect through-thickness stress waves, which propagate at the earliest timescale (~ 1–10 μs) following projectile impact. The role of through-thickness stress waves on initiation and evolution of damage under high velocity projectile impact is not well understood. A through-thickness stress wave finite element modeling approach, verified with one-dimensional stress wave theory, is developed for S-glass/epoxy to study wave propagation effects on damage mechanisms. Then, a three-dimensional, mesoscale model of a plain weave composite uses a rate-dependent cohesive zone model to simulate delamination between interwoven, undulating tows in a single layer composite. Damage investigated includes damage within continuum undulating tows and matrix and tow–tow delamination for a range of impact velocities. The model suggests that, under the projectile, damage is dominated by through-thickness compression and crushing, and this damage suppresses delamination cracking. Further, at the perimeter of the projectile, damage is dominated by punch shear and the development of in-plane tension in the tows. The model also suggests that through-thickness stress wave propagation degrades stiffness and combines with punch shear and in-plane tension to cause mixed-mode loading of the tow–tow interface, which can cause delamination and transverse cracking away from the projectile perimeter. The study indicates the importance of through-thickness stress wave propagation on damage initiation in woven composites at the earliest timescales of projectile impact.