Impact response of thermoplastic composites – Experiments and modeling

This study investigates the impact response of thermoplastic composite materials. The material system under consideration is a carbon fiber reinforced low melt semi-crystalline resin TC1225 LMPAEK reinforced with T700 G (T700/LMPAEK). Several High Energy Dynamic Impact (HEDI) tests were performed wherein an aluminum projectile impacted T700/LMPAEK panels at different velocities. In the impact experiment studied herein, the projectile impacted the T700/LMPAEK panel at 73.8 m/s and rebounded. The ensuing damage to the T700/LMPAEK panel was characterized via ultrasonic C-scans, which enabled visualizing delamination extent and through-thickness matrix cracks as the boundaries between delaminations at individual interfaces. Since the projectile rebounded after impact in the current test, the fiber damage mode, while present, was not as significant as in the case of tests wherein the projectile perforated the panel. The impact event was modeled using a combined continuum damage mechanics and cohesive zone analysis approach with the commercially available hydrocode LS-DYNA®. The dynamic deformation and damage of the continuum, that is, the plies in the T700/LMPAEK laminate, were modeled using a Deformation Gradient Decomposition (DGD) material model, that is, MAT299 available within LS-DYNA. The interlaminar regions were treated as zero-thickness cohesive zones, wherein the dynamic delamination mechanics were modeled using a traction-separation formulation. Mixed-mode delamination growth was captured using the Benzegaggh-Kenane (B-K) traction-separation interpolation law. Strain-rate sensitivity of interlaminar fracture toughness was included using approximations based on published literature. The outcomes of the modeling effort demonstrate good correlations with test data regarding panel deflection, panel-projectile interactions, damage modes and damage extent.