Tensile-strength-controlling factors in unidirectional carbon fiber reinforced plastic composites

Abstract Factors governing the tensile strength of unidirectional carbon fiber reinforced plastic (CFRP) composites were experimentally investigated by focusing on the mechanical characteristics of the epoxy matrix. Correlation analysis was conducted to reveal the mechanical characteristics of the matrix that affect the surface stress concentration of an intact fiber caused by a fracture site in an adjacent fiber. The stress concentration factors (SCFs) were evaluated by implementing double-fiber fragmentation tests in conjunction with spring element model simulations. From investigating six types of epoxy materials, a reasonable correlation was observed between the matrix crack tip opening displacement (CTOD) and the SCF; the SCF increased approximately linearly with increasing CTOD. The results reported here suggest that CTOD is one of the important tensile-strength-controlling factors to consider for the development of stronger CFRP composites.