Fatigue Delamination Modeling in Composite Structures Based on J-Integral and Application to Tapered Structural Element with Internal Ply Drops

This work presents the development and application of a methodology for predicting fatigue life, implemented within the modern progressive failure analysis software tool CDMat, developed at the Advanced Materials and Structures Laboratory of the University of Texas at Arlington. CDMat is designed as an extension to the general-purpose finite element analysis program ABAQUS/Explicit. The set of user-defined subroutines for describing material behavior can be expanded by adding new subroutines. A recent development in CDMat is a computational model capable of predicting delamination crack growth under quasi-static and fatigue loading, based on a fracture mechanics approach using the J-integral. The J-integral is calculated by integrating stresses and displacements along a line defined by the negative gradient of displacements in the cohesive interface. Due to the large integration path, the J-integral allows for a highly accurate estimation of the energy release rate, which makes it possible to reasonably estimate the crack growth rate using Paris's law. A comprehensive verification of the J-integral-based fatigue prediction methodology was performed using a tapered structural element with internal ply drops. Experimental determination of the static and fatigue properties of the materials, static and fatigue tests of a tapered structural element, and numerical simulation of fatigue crack growth were performed. The predicted fatigue crack growth showed good agreement with experimental results.