Investigation of Fatigue Behavior of Three Dimensional Interlock Composites by Time-Lapse Micro-Computed Tomography

The mechanism of the crack propagation in three dimensional (3D) glass-fiber warp interlock epoxy composites under fatigue loading was investigated via time-lapse micro-computed tomography (mu CT) observations. Two different composite samples were manufactured by means of a resin transfer molding (RTM) process under two different constant injection pressure conditions to generate intrayarn and interyarn voids separately. Fatigue loads were applied by blocks of 10(5) cycles and followed by mu CT measurements. Regions of interest for micro tomography scans were selected based on hot spots detected by infrared thermography. After the analysis of the obtained data, it was observed that detectable cracks were generally initiated by debonding in the zone between two adjacent warp yarns and grew along their interface. Then, these cracks propagated along one of the warp yarns aligned in the loading direction while remaining in the middle of the specimen cross-section. The coalescence of the cracks and further propagation to the weakest zones were observed around and after the middle lifetime. Finally, we demonstrated the influence of the void defects at different material scales. I was found that interyarn voids have relatively little influence on the fatigue performance whereas they can, sometimes, attract and deviate cracks in the matrix zone between adjacent yarns. It was also shown that the intrayarn voids are crucial to degenerate the fatigue performance of the yarns at the micro-scale.

Automated summary

This study investigated the mechanism of crack propagation in three-dimensional glass-fiber warp interlock epoxy composites under fatigue loading using time-lapse micro-computed tomography observations. The results showed that detectable cracks were initiated by debonding between adjacent warp yarns and grew along their interface. Further crack propagation occurred along one of the warp yarns aligned in the loading direction. The coalescence of cracks and propagation to weaker zones were observed around the middle lifetime. The influence of void defects at different material scales was also demonstrated, with interyarn voids having little impact on fatigue performance and intrayarn voids significantly degrading the fatigue performance at the micro-scale.