On a damage mesomodel for laminates:: micromechanics basis and improvement

The so-called "damage mesomodel for laminates" developed in the past fifteen years, particularly at Cachan, is being reconsidered in the light of the recent works, theoretical as well as experimental, done on the microscale. Previous works have already proved that this mesomodel can be interpreted as the homogenized result of micromodels involving common microdamage mechanisms: transverse microcracking, delamination at the tips of transverse microcracks and fiber-matrix debonding. Here, we are going one step further by considering microcracking in skin plies of various thicknesses. To fit experimental results better, we introduced a modification of the coupling of the three microdamage scenarios in all plies. Contrary to the classical approach, the critical values of the energy release rate are not associated with a healthy material but with a damaged material; the first damage mechanism to occur is associated with non-transverse microcracks due to nearly uniformly distributed fiber-matrix debonding in the damaged ply. These mechanisms and this coupling are homogenized on the mesoscale, which leads to an improved version of the "damage mesomodel for laminates" involving only a small number of material constants which can be interpreted on the microscale. Thickness effects are taken into account: the improved version, unlike the previous one, is valid for arbitrary values of the thickness. We discuss experimental data and identification using carbon-epoxy laminates at room temperature. (C) 2002 Elsevier Science Ltd. All rights reserved.