Translaminar enveloping ply for CFRP interlaminar toughening

Developing low-cost and high-performance interlaminar toughening strategies for the advanced CFRP products has great engineering significances. Combining features on practical automated fiber placement and well-recognized 3D reinforcement technologies in the field of CFRP composites, herein, we alternately introduced a reinforcement ply in the manner of translaminar enveloping to generate interlocking and binding action into conventional lay-ups. Remarkably, more than 1700% for mode I (DCB) and 500% for mode Ⅱ (ELS) propagation fracture toughness improvements were experimentally investigated. The evolution of interlaminar toughening behaviors was specifically revealed. Multiple fracture energy absorption stages, successively including delamination tolerance, partial interface pull-out and through-thickness ruptures, reflect long-acting mode I toughening capacity. Under the multi-interface synergistic shear-delamination mechanism, the mode Ⅱ crack growth gets far more effectively suppressed. Meanwhile, the in-plane tensile and compressive strength could be maintained acceptably. We also gave insights into the technical superiorities of this original ply-level reinforcing work.