Interaction of multiple micro-defects on the strengths and failure mechanisms of UD composites by computational micromechanics

Abstract: The mechanical properties of unidirectional fiber-reinforced plastic (UD-FRP) are affected by internal micro-defects, such as random fiber arrangement, fiber misalignment, and micro#2;voids. This study aims to investigate how these multiple micro-defects interact with each other and how they affect the strength and failure mechanisms of UD-FRP through computational micromechanics. The failure behavior was simulated by the finite element analysis of a representative volume element; both matrix and interface failure were considered for the different loadings and their combinations. It was found that these micro-defects significantly weakened the compressive strength of UD-FRP along the longitudinal direction. Especially the fiber misalignment magnified the effect of fiber arrangement, while the micro-voids reduced the effect. Besides, the fiber arrangement and micro-voids significantly weakened the tensile and compressive strength of UD-FRP along the transverse direction. Moreover, transverse and longitudinal shear strengths are significantly affected by micro-voids, but only longitudinal shear is affected by fiber arrangement, and this effect is also weakened by micro-voids. Finally, the damage envelope under the combined longitudinal compression and transverse loads was obtained and compared with the Tsai-Wu failure criterion. The results showed that the Tsai-Wu criteria can provide an effective estimation for the failure locus under this biaxial loading condition.