The effects of fiber radius and fiber shape deviations and of matrix void content on the strengths and failure mechanisms of UD composites by computational micromechanics

Manufacturing plays an important role in the properties of composites, which may lead to two types of uncertainties: (1) carbon fiber manufacturing deviations, such as the bean-shaped PAN carbon fibers, the lognormal-distributed fiber radius, etc. (2) composites manufacturing deviations, such as the inter-fiber voids and matrix voids. Although several experiments have been conducted to assess their effects on the mechanical properties of composites, a satisfactory result of quantitative characterization of fiber radius and fiber shape deviations and of matrix void content have not been obtained. In this paper, a parametric study based on the computational micromechanics is conducted to reveal the effects of fiber radius and fiber shape deviations and of matrix void content on the strengths and failure mechanisms of UD composites under four loading conditions, i.e. the transverse tension, compression, shear and longitudinal shear. Firstly, the constitutive laws of constituents, i.e. carbon fiber, matrix and interface, are established to characterize their mechanical responses. Then, the UD RVEs with fiber radius and fiber shape deviations and with matrix void are modeled individually based on experimental observation and statistical distribution. After qualitative validation of failure modes and quantitative validation of stress-strain curves, the methodology is applied to predict the stress-strain curves and failure modes of UD RVE with manufacturing uncertainties and the results show that not all manufacturing uncertainties have a detrimental effect on the mechanical properties of UD composites.