Estimation of Plastic Zone Size in Cracked Continuous Fiber-Reinforced Plastics

Fiber-reinforced plastics (FRP) were modeled by a two-dimensional laminated structure composed of an isotropic matrix and orthotropic fibers. The size of the plastic zone ahead of a delamination crack in the matrix under mode I and II loadings was estimated from the elastic stress distribution, and the estimated values were compared with the results computed by using an elastic-plastic finite element method. The height of the plastic zone was estimated from the contour of the Mises equivalent stress based on the elastic stress distribution without considering the stress redistribution due to yielding. The length of the plastic zone was estimated by considering the redistribution of matrix stresses due to yielding. The estimated sizes of the plastic zone height and length agree fairly well with the results computed by using the elastic-plastic finite element method. The limitation of the present estimation method was also clarified. For the case of small plastic zone under mode I and II loadings, the elastic stress distribution in the unreinforced matrix material under the same stress intensity factor can be used for the estimation of the plastic zone size. For the case of large plastic zone, the elastic stress distribution in homogeneous FRP model under the same load can be used only for the estimation of the plastic zone height under mode I loading.