Effect of Microstructure on the tensile-tensile fatigue response and damage behavior of laminated braided composites

This study systematically investigates the impact of microstructural characteristics on the fatigue performance and damage evolution of braided composites. Laminated composites with identical total thickness but distinct microstructural configurations were fabricated using mandrels of varying diameters. Quasi-static and fatigue tension tests were conducted, complemented by macroscopic observations and microscopic analyses to characterize the damage progression. The results show that damage in the thick ply configuration originates at the edge of specimen and gradually propagates toward the center. This progressive damage evolution is attributed to the increased yarn undulation amplitude resulting from the thicker layers. This microstructural feature triggers multiple damage mechanisms during crack propagation, significantly enhancing damage tolerance through synergistic energy dissipation. In contrast, the thin ply configuration, characterized by a larger yarn interlacing region due to the increased yarn width, exhibits pronounced stress concentrations at yarn crossover regions. The thinner layer thickness makes this configuration more susceptible to interfacial debonding and fiber splitting. As the number of fatigue cycles increases, damage at the edges quickly spreads toward the center, leading to rapid failure. The significant differences in damage mechanisms between the two configurations confirm that subtle variations in microstructural parameters, play a crucial role in the fatigue performance and damage evolution of braided composites.