Energy Absorbing Damage Mechanisms in Progressive Crushing of Composite Tubes

Abstract

Progressive crush is an important mechanism by which the kinetic energy associated with an impact event is dissipated. Unfortunately, the mechanisms governing the progressive-crush response of advanced composite materials are not well understood. Also, many of these materials are known to exhibit responses that are sensitive to loading rate. Therefore, understanding the influence of impact velocity and laminate design on the crush response is critically important for modelling the crashworthiness of a given composite structure. Laminate design of composite structures can be tailored by placing the fiber in the direction of the applied load. For axial progressive crush the fiber path can play a different role by promoting certain failure or energy absorbing mechanisms. To quantify this by experimentation, tubes were chosen as the primary structural component and different geometries (circular and square cross-sections) and laminate architectures were then chosen with the goal being to initiate different damage mechanisms. Three different layups were designed so that their failure modes corresponded to the three broad classifications (fragmentation, fiber splaying, and brittle fracture) that are typically observed during axial crushing. Tests were conducted using a servo-hydraulic test machine in closed-loop mode at quasi-static rates (less than 100 mm/s) and in open-loop mode for dynamic rates (up to 6000 mm/s). High speed video was used during testing, in conjunction with postmortem inspection, to identify the damage mechanisms associated with the different test configurations. Results showed that circular cross sections were more efficient than square cross sections when comparing similar test variables. Quantitative