Constitutive Modeling for High-Fidelity Analysis of Bondline Failure in Polymeric Matrix Composites

Abstract

Adhesively bonded Polymeric Matrix Composite (PMC) structures could offer significant cost savings and increase production rates in the fabrication and assembly of future composite airframes. In particular, bonded PMCs may eliminate the use of thousands of mechanical fasteners and allow incorporation of multiple aircraft composite primary structures into a unitized structural design. However, increased susceptibility to defects and manufacturing irregularities, including voids, disbonds, and geometry variations, as well as complex interacting failure mechanisms, hinder a widespread use of bonded PMCs. High-fidelity computational materials-based analysis methods that can capture the effect of defects and improve the understanding of failure mechanisms that govern bondline failure are needed to support qualification and certification of next-generation bonded PMCs and safely reduce redundant fasteners. The objective of this work is to contribute to such development. A continuous-discontinuous framework is considered for capturing quasi-brittle failure within the epoxy adhesive and predicting growth of arbitrary solution-dependent crack paths in presence of bondline defects. In this approach, an elasto-plastic constitutive model with isotropic damage is enhanced with the introduction of extended finite element method (XFEM) enrichments that incorporate non-local features. The implementation of the approach in commercial FE software Abaqus using built-in XFEM capabilities in combination with a set of user-defined subroutines is presented and illustrated in two-dimensional FE models representative of adhesively-bonded double-cantilever beam (DCB) specimens.