Theoretical and Applied Fracture Mechanics 19 (1993) 29-48 29 Elsevier First-ply failure of laminated composite plates D. Bruno, G. Spadea and R. Zinno Department of Structural Engineering, University of Calabria, 87030-- Arcavacata di Rende, Cosenza, Italy Composite laminates offer superior load carryingcapacity. Reliable application of such structures requires a knowledge of their stress/strain and failure behavior. Past treatments involved assumptions in both the stress and failure analyses; they become increasinglymore difficult when the failure of the microstructure constituents is to be included in the continuum analysis of the laminates. Recognizingthe conventional failure criteria used for composite material analyses, this work adopts the first-ply failure criterion by application of a polynomial function and the finite element procedure. The laminates are modeled by the Reissner-Mindlin plate theory that accounts for moderate rotation. This is because shear effects are more pronounced in composite laminates whose transverse shear modulus is low relative to the Young's modulus. Failure loads are obtained for different laminate thicknesses, stacking sequences and aspect ratios and different failure criteria. The results show that predictions made from the maximum stress criterion are nearly the same as the others, except for those obtained by the Hill criterion. 1. Introduction Composites made from metallic or nonmetallic matrices reinforced by continuous or discontinuous fibers are being used more frequently as high performance and ordinary construction materials. Their tailorability for specific applications has been one of the greatest attractions of composites in that they could be designed to reduce weight and to increase performance in addition to enhancing service life and maintenance. Reliable application of any materials, however, rests on a knowledge of their load carrying capacity to which address must be made on the failure behavior. Such is the objective of this investigation where the first-ply failure (FPF) load for composite laminates will be determined. Failure prediction of composites is more difficult and complex because the material is inherently anisotropic and nonhomogeneous. Physical properties of the constituents influence the overall behavior of the composites and should be reflected in the analytical model. Initial mechanical defects or flaws, and processing variability could contribute additional uncertainties. Some of the commonly observed failure modes are breaking, microbuckling and dewetting of fibers; voids and crazes in matrix; and debonding or delamination of interface. It is difficult to consider these individual modes in the analysis. Failure criteria based on the strength and yielding of anisotropic materials have been considered [1-3]; their application relies on test data obtained from simple specimens subjected to tensile and shear loadings. Strength anisotropy is considered. In what follows, the first-ply failure assumption is invoked and assessed in terms of a polynomial function for the composite laminate, the deformation behavior of which is modelled by the Reissner-Mindlin plate theory. 2. Plate theory and constitutive relation To be summarized are the governing equations for the composite laminates and the constitutive relation of the material. 2.1. Reissner-Mindlin plate theory Consider a laminate made of n orthotropic layers whose preferred directions are referred to the x- and y-axis in an arbitrary manner. The z-axis is normal to the xy-plane that coincides with the mid-plane 0167-8442/93/$06.00 © 1993 - Elsevier Science Publishers B.V. All rights reserved