Controlled energy dissipation in fibrous composites I. Controlled delamination

Abstract

Delamination mechanisms in continuous fiber reinforced composites were investigated. The concept of controlled interlaminar bonding (CIB) is proposed as a guideline for preparing fiber‐epoxy composite laminates with enhanced fracture toughness without significant degradation in strength properties. The interlaminar bonding was manipulated by several specialized techniques including insertion of delamination promotors and surface modification of laminae. Results indicated that the plane‐strain fracture toughness of E‐glass‐epoxy laminates could be improved by inserting perforated interlaminar films of aluminum, paper, polyester and polyimide, and fabrics. Such interlayers were used to promote delamination which dissipate strain energy by blunting and diverting a propagating crack. The fracture resistance of a laminate was found to be dependent on the degree of delamination. The competition between the growth of delamination cracks and the propagation of a main crack is controlled by the relative magnitude of the interlaminar bonding strength and the lamina cohesive strength. The interlaminar bonding is controlled by the degree of interlayer perforation and the adhesion between interlayer and lamina. The loading direction was found to be very important in dictating the failure processes. Experimental results from several composite systems are presented and discussed along with post‐failure analysis data.

Experimental optimization of the impact energy absorption of epoxy–carbon laminates through controlled delamination

“…In fact, using multi-layers of perforated Mylar films, Jea and Felbeck [35] reached a remarkable 500 % increase of the transverse fracture toughness (determined on reinforced modified compact tension speciemens) of CFRPs, while the tensile transverse strength dropped about 20 % and the Young's modulus remained the same. The transverse fracture toughness was determined by Jang et al [36] on fibrous composites with several other types of delamination promoters, including aluminium foils, bleached papers, polyester textile fabrics and polyimide Mylar. They found that the energy absorption mechanisms strongly depend on the loading direction and other testing parameters such as loading speed and span-to-depth ratio in bending.…”