Considering the stress concentration of fiber surfaces in the prediction of the tensile strength of unidirectional carbon fiber-reinforced plastic composites

The tensile strengths of unidirectional carbon fiber-reinforced plastic (CFRP) were predicted by using a spring element model that considers the surface stress concentration on fibers caused by a fracture site in an adjacent fiber. The surface stress concentration on the fibers was experimentally evaluated by implementing multi-fiber fragmentation tests in conjunction with a spring element model simulation. Four types of epoxy materials were utilized to explore the effects of matrix polymer properties on the surface stress concentration of the fibers. The size scaling results, coupled with the results of the spring element model simulation, designed to take into account the surface stress concentration, were reasonably consistent with the experimental data on the tensile strengths of the unidirectional CFRP composites, regardless of the differences in the matrix mechanical properties. Possible mechanisms by which additional stress concentration is generated on an intact fiber surface were analyzed numerically using the finite element method.