Sublaminate- or Ply-Level Analysis of Composites and Strain Energy Release Rates of End-Notch and Mixed-Mode Fracture Specimens

Abstract

A computational procedure is described for the sublaminate- or ply-level analysis of composite structures. This procedure is useful to obtain stresses in regions affected by delaminations, transverse cracks, and discontinuities related to material properties, geometry, and loads. In this analysis, attention is focused on those layers or groups of layers (sublaminates) which are immediately affected by flaws. These layers are analyzed as if they were homogeneous bodies in equilibrium in isolation from the rest of the laminate. The theoretical model used for the analysis of individual layers allows the relevant stresses and displacements near discontinuities to be represented in the form of pure decay type solutions. As a result, the exponential-precision-related problems that are inherent to sublaminate- or ply-level analysis are removed. This allows sublaminate analysis of laminates without any restriction on the maximum number of layers, delaminations, transverse cracks, and other types of discontinuities. In conjunction with the strain energy release rate (SERR) concept and composite micromechanics, this computational procedure is used to model select cases of end-notch and mixed-mode fracture specimens. The computed stresses are in good agreement with those from a three-dimensional finite-element analysis. The SERRs also compare well with limited experimental data.