Initiation and propagation of fiber kinking from fiber undulation in a unidirectional carbon fiber reinforced plastic

Abstract

Micromechanical two-dimensional finite element analyses were performed on the axial compression of a unidirectional carbon fiber reinforced plastic. The initiation and propagation of fiber kinking were studied using fiber undulation models, in which the fiber angles followed a normal distribution. Matrix yielding was initiated at different locations with an increase in the compressive load. The yielded area spread in the direction that was orthogonal to the fiber, which promoted shear deformation of the entire model to form fiber kinking. The compressive strength of the undulation model decreased with an increase in the mean fiber angle. The compressive strength of the undulation model with mean fiber angle µ = 0.4° and standard deviation σ = 1.09° agreed well with the reported experimental value of compressive strength. As fiber kinking is caused by the shear deformation of the matrix, the effect of the microscopic arrangement of fibers (i.e., local fiber angle and local interfiber spacing) on the shear deformation of the matrix was quantitatively evaluated using a sensitivity analysis. In the presence of a fiber angle cluster, the sensitivity analysis predicted the starting point of fiber kinking to be matrix yielding.

Keywords

• Polymer-matrix composite (PMC)
• Carbon fiber
• Strength
• Finite element analysis (FEA)