Micromechanics modelling of anisotropic damage in cross-ply laminates

Abstract

A micromechanics model is developed to detail various aspects of anisotropic damage behaviour of cross-ply composite laminates. Attention is focused on multi-ply laminates so that a calculation model can be devised, which is composed of a cracked transversely isotropic ply sandwiched between two self-consistent orthotropic plates of relatively large thickness. Under inplane loadings restricted to the laminate plane, intralaminar cracks first develop from two families of plies independently, subject to mode I and mode III crack driving forces. The stabilized crack configuration is that of parallel trans-ply cracks with a mutual shielding effect. As the intralaminar cracks touch the interlaminar boundaries, the initial delamination is triggered by large interfacial shear stress and then terminated by a dramatic drop in the driving force. An interaction calculation shows that interlaminar cracking is priviliged at relatively low load level, but then overrun by interlaminar cracking at a relatively high load level. This switch in crack formation constitutes the so-called Characteristic Damage State. By introducing a higher order model allowing shear deformation in the central broken ply, a finite value of the interlaminar shear stress at bonding edges can be achieved. A pseudo-elastic damage behaviour can be predicted, along with the absence of permanent damage strain, if perfect interlaminar adhesion is maintained. The solution in an idealized non-interactive intcrlaminar slip model is henceforth constructed, which gives rise to permanent damage strain, stabilized hysteresis loop und residual interlaminar stress after unloading.