Modelling and Analysis of Complex Shaped Cracks

This study provides an extensive analysis through finite element analysis (FEA) on the effects of fatigue crack growth in three different materials: Structural steel, Titanium alloy (Ti Grade 2), and printed circuit board (PCB) laminates based on epoxy/aramid. A simulation of the materials was created using ANSYS Workbench with static and cyclic loading to examine how the materials were expected to fail. The method was based on LEFM and made use of the Maximum Circumferential Stress Criterion to predict where cracks would happen and how they would progress. Normalizing SIFs while a crack was under mixed loading conditions was achieved using the EDI method [84]. We used Paris Law to model fatigue crack growth using constants (C and m) for the materials from previous studies and/or tests. For example, in the case of titanium Grade 2, we found Paris Law constants with C values from 1.8 × 10^-10 to 7.9 × 10^-12 m/cycle and m values from 2.4 to 4.3, which illustrate differing effects of their manufacture processes and microstructure. Detailed Paris Law constants are limited for the epoxy/aramid laminates, but other similar composite materials, for example, VARTM composites, have shown that under certain conditions the Paris Law could be applicable. In determining the performance of the materials, we assessed various mechanical responses (total deformation, directional stiffness) and all were also noted with respect to the likely progression of these fatigue cracks given the long-term nature of the study.