A modified cohesive zone model for the simulation of mixed-mode fracture of co-consolidated thermoplastic laminates considering fiber bridging

Summary

Fiber bridging is a mechanism that may significantly alter the fracture behavior of composite laminates, adhesively bonded laminates, welded laminates, and co-consolidated laminates. It is therefore quite important for the finite element to take that mechanism into consideration. Such models have been developed for thermosetting laminates; however, this is not the case for thermoplastic laminates and thermoplastic joints. In the present work, a numerical model based on the cohesive zone modelling (CZM) approach has been developed to simulate mixed-mode fracture of co-consolidated thermoplastic laminates by considering fiber bridging. A modified traction separation law of tri-linear form has been developed by superimposing the bi-linear behaviors of the matrix and fibers. Initially, the data from mode I (DCB) and mode II (ENF) fracture toughness tests were used to construct the R-curves of the joints in the opening and sliding directions. The aforementioned curves were embedded into the numerical models through a user-defined material subroutine developed in the LS-Dyna FE code, in order to extract the fiber bridging law directly from the simulation results. The model was used to simulate fracture of a Single-Lap-Shear (SLS) specimen in which a considerable amount of fiber bridging was observed on the fracture area. The numerical results show that the developed model presented improved accuracy in comparison to the CZM employing the bilinear traction-separation law.

Abstract

Full Paper