Single and multiple delamination behavior in composite plates

Two topics on the single and multiple delamination behavior in composite plates are investigated: (1) Stress intensity factor (SIF) calculation for fully anisotropic rectangular plate. (2) Buckling and post-buckling analysis of delaminated composite plates. A novel method that combines the continuous dislocation technique and the conformal transformation is developed to calculate the mixed-mode SIF for a fully anisotropic rectangular plate. Numerical results for an isotropic plate with a central crack and double edge cracks under different load conditions are compared with available experimental data. The effects of anisotropy on both SIF and mode mixity are investigated by considering a cracked unidirectional graphite/epoxy plate. The methodology developed in the first topic may be extended to study the growth of delaminations in a composite plate under compression, which requires a thorough understanding of the post-buckling behavior of the delaminated composite plate. To predict its buckling load and post-buckling behavior, a delaminated composite plate is divided into subplates. Each subplate is treated as a beam-plate and the nonlinear differential beam equation is thus applicable, which is linearized in the prediction of buckling load. Imposing the appropriate kinematic continuity and equilibrium conditions at the interfaces of the subplates, a closed-form characteristics equation is achieved and the buckling load can be determined. For post-buckling analysis, a perturbation technique is employed to transform the non-linear beam equations and their constraints into two series of linear equations. An asymptotic solution of the post-buckling behavior of the plate is thus obtained and its buckling modes are discussed in detail. Calculation results are compared with available data from previous publications and the effects of delaminations on both the buckling load and the post-buckling response are investigated.