Progressive Fatigue Failure Characterization of Bonded Repaired Sandwich Composites Using Experimental and Multiscale Modelling Approaches

Abstract Predicting fatigue failure of composite materials is crucial for ensuring the structural integrity of aerospace structures. Both experimental and multiscale modelling (MSM) approaches were developed to characterize the failure of the bonded-repaired sandwich composites. A four-point bending setup under fatigue loading conditions was employed for experimental characterization of failure behaviors, while the MSM approach bridged micro, meso and macro length scales to analyze these behaviors. The experimental and MSM results were compared at each scale to validate the proposed MSM-based fatigue failure prediction. At the microscale level, the experimental specimen exhibited cusp-like failures due to fatigue loading. The MSM analysis showed complete failure of matrix elements after 100 cycles, while the fibre elements remained intact. At the mesoscale, both the experimental and MSM results showed steaks-like failures with distinct staggered patterns, stopping at the edge of the warp tows. Additionally, extensive inter-two failures were seen across large surface areas of the weft and warp tows. At the macroscale, the failure surfaces were wide with deep cracks resulting from progressive matrix cracking as the fatigue cycles increased. Though the focus was on critical point B, similar behaviours were also observed on critical point A as well.