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 provide s the global structural response as well as the precise local crack-ti p stress fields. An elasticity basis for the problem is established by employing Lekhnitskii's complex variable potentials and method of eig enfunction expansion. Stress singularities associated with the transve rse crack are obtained by decomposing the deformation into the symmetr ic and antisymmetric modes and proper boundary conditions. A singular hybrid element is thereby formulated based on the variational principl e of a modified hybrid functional to incorporate local crack singulari ties. Axial stiffness reduction due to transverse cracking is studied. Numerical examples are illustrated for [0n/90m]s and [theta(n)/90m]s composite laminates with glass/epoxy and graphite/epoxy. The results a re shown to be in very good agreement with the existing experimental d ata. Comparison with simple shear lag analysis is also given. The effe cts of stress intensity factors and strain energy density on the incre ase of crack density are analyzed. The results reveal that the paramet ers approach definite limits when crack densities are saturated, an ev idence of the existence of Characteristic Damage State (CDS).