Mode I Interlaminar Fracture Toughness of Through-Thickness Reinforced Laminated Structures

Abstract

The main objective of the study is to understand the mechanisms of the preform reinforcement (2D, stitched and 2.5D) in laminated composite materials. The study is focusing on the mode I interlaminar fracture toughness for glass/vinylester based composites. Starting from DCB tests we quantify the critical energy release rate for the various cases of reinforcement, conclusive that 2.5D reinforcement can increase resistance x7 in comparison with the standard composite. Moreover, the existence of z-fibres made the fracture more complex and caused several characteristic phenomena, so that the required fracture energy for crack propagation was strongly increased. It is shown that a finite element model is successful in reproducing qualitatively the cracking initiation and propagation through the un-reinforced and 3D reinforced sample provided that the action of the through-thickness reinforcement is modelled by discrete nodal forces so as to replicate the physical phenomena.