In-situ strength effects in long fibre reinforced composites: a micro-mechanical analysis using the phase field approach of fracture

Abstract Transverse intralaminar cracks in layers with perpendicular orientation referred to the main loading direction have a significant affection on the apparent ultimate strength of the corresponding composite laminate. This effect stems from the fact that such transverse cracks generally promote the occurrence of other failure mechanisms leading to the specimen collapse in subsequent stages of the loading process. With the aim of conducting a careful investigation regarding the onset and progression of transverse intralaminar cracking events, in this investigation, a micro-mechanical analysis of cross-ply laminates is performed. Particularly, the cross-ply laminates belonging to the family [ 0 ° 2 / 90 ° n / 0 ° 2 ] are considered via the generation of high-fidelity micro-mechanical models, which reproduce the direct representation of internal fiber arrangements using the reference results addressed in Saito et al. 2012, Experimental evaluation of the damage growth restraining in 90° layer of thin-ply CFRP cross ply laminates, Adv. Comp Mat, 21:1,57-66. Differing from alternative approaches, current predictions are equipped with the combined used of two fracture-based modeling methods: (i) the variational phase field (PF) approach for triggering crack events into the matrix, and (ii) the bilinear cohesive zone model (CZM) for the simulation of fibre-matrix decohesion failures. Relying on this computational methodology, the focus of this work is to analyze the influence of the transverse ply thickness (n) on the onset and propagation of damage under tensile conditions, in conjunction with the transition from micro-cracking to meso-scale damage states. For this purpose, several models are generated into the FE package ABAQUS using user-defined capabilities replicating configurations of specimens included in previous experimental investigations, i.e. through the consideration of different transverse ply thickness (n=1, 2, 4). Present results show the potential of the proposed methodology to predict the transverse matrix cracking phenomena and the ability and reliability for capturing the delay of the crack with thinner plies, a phenomenon which is usually denominated as in-situ effect in the related literature.