Crack Path Selection in Microstructurally Tailored Inhomogeneous Polymers

Abstract

In this work the photodegradation of a polyethylene co-polymer, ECO, is exploited to generate inhomogeneous arrangements of model “granular” media that aids in the experimental study of crack path selection problems. The advantage of our approach is that the well-known sensitivity of ECO’s properties to ultraviolet (UV) light allows knowledge of both grain and grain boundary response a priori to performing the experiments. A model granular arrangement with identical grain structure and of three different levels of grain boundary strength was constructed. Each microstructure was loaded in uniaxial tension, and the resulting strain fields were recorded using digital image correlation (DIC). Depending on the applied load and the local microstructure, crack initiation and growth occurred differently: either one main crack developed and became responsible for failure, or an initial crack formed but arrested, and a host of secondary cracks appeared at different critical locations, including grain boundaries and grain interiors. Thus, the experimental configuration can be used to produce controllable amounts of intergranular vs. transgranular failure. The DIC results were correlated with global load–displacement measurements and were compared to finite element models using ABAQUS that simulated the configurations tested in each case. A von Mises and Tresca yield criterion was used to illustrate areas where failure was possible, and the results were favorably compared with the experimental failure initiation sites in each case.