Understanding Post-Impact Compressive/ Bending Performance of Composites Using Linear Elastic Fracture Mechanics Model

Abstract

In this study, we employ the use of a linear elastic fracture mechanics (LEFM) model to understand and predict the post-impact performance of composites. Compressive-after-impact (CAI) and bending-after-impact (BAI) strength of carbon fiber reinforced polymer (CFRP) composites are important design considerations in the aerospace industry. Although CFRP composites are light-weight and highstrength, their susceptibility to impact results in barely visible impact damage (BVID), consisting of complex damage modes (matric cracking, delamination, fiber breakage, etc.) often hidden beneath the surface of the composite material. BVID subsequently leads to drastic reduction in CAI and BAI strength. We utilize a LEFM model to understand how impact damage affects post-impact performance. In particular, we study how impact damage depth (d), damage width (l) and impact-induced delamination (a) affects brittle fracture of composites during compressive and flexural loading. Strain energy release rate (SERR) is calculated to predict crack growth based on fracture mechanics. Results show that increasing damage depth (d) results in higher SERR. Moreover, decreasing undamaged depth, h, also causes higher SERR, thereby resulting in CAI brittle fracture. Interestingly, when the total depth is kept constant, an exponential increase in SERR is evident when damage depth reaches around 60% of total depth. Results in the analytical models are compared to experimental results of CAI and BAI tests of CFRP composite foam-core sandwich structures, with the aim to study the influence of low temperature Arctic conditions. The motivation of this study is fueled by the recent global trend to explore the Arctic region due to greater accessibility to the area, as new sea routes are opened as a result of Arctic ice melting. Our study demonstrates a significant influence of low temperature on impact behavior and post-impact performance.