Transverse Cracking and Stiffness Reduction in Composite Laminates

A study of transverse cracking mechanism in composite laminates is pre sented using a singular hybrid finite element model. The model provides the global struc tural response as well as the precise local crack-tip stress fields. An elasticity basis for the problem is established by employing Lekhnitskii's complex variable potentials and method of eigenfunction expansion. Stress singularities associated with the transverse crack are obtained by decomposing the deformation into the symmetric and antisymmetric modes and proper boundary conditions. A singular hybrid element is thereby formulated based on the variational principle of a modified hybrid functional to incorporate local crack sin gularities. Axial stiffness reduction due to transverse cracking is studied. Numerical ex amples are illustrated for [0n/90m]s and [θn/90 m]s composite laminates with glass/epoxy and graphite/epoxy. The results are shown to be in very good agreement with the existing experimental data. Comparison with simple shear lag analysis is also given. The effects of stress intensity factors and strain energy density on the increase of crack density are ana lyzed. The results reveal that the parameters approach definite limits when crack densities are saturated, an evidence of the existence of Characteristic Damage State (CDS).

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