Interlaminar stresses in composite laminates: a perturbation analysis

Abstract

A general method of solution for an elastic balanced symmetric composite laminate subject to a uniaxial extension has been developed based upon a perturbation analysis of a limiting free body containing an interfacial plane. The solution satisfies more physical requirements and boundary conditions than previous investigations, predicts smooth continuous interlaminar stresses with no instabilities, determines the finite maximum intensity for the interlaminar normal stress σ_𝒛 in all laminates, provides mathematical evidences for the singular stresses τ_xz and τ_yz in angle-ply laminates, suggests the need for the experimental determination of an important problem parameter, and introduces a viable means for solving related problems of practical interest.

The results indicate that for bidirectional laminates, the sign of σ_𝒛 depends upon the stacking sequence, while for angle-ply laminates is σ_𝒛 independent of the stacking sequence and is always a finite maximum tensile value at the free edge. Moreover, the results for bidirectional laminates compare favorably with Pipes’ finite difference solution. On the other hand, the results for the angle-ply laminates reveal that the present analysis has attained an improved solution for all interlaminar stresses.

Typical results are presented for graphite-epoxy laminates.