Jean-Mathieu Guimard

Micro-mechanical prediction of UD laminates behavior under combined compression up to failure: influence of matrix degradation

This article aims to model the behavior of carbon fiber-reinforced polymer laminates up to failure and predict the corresponding energy absorption, under mixed loadings involving compression. In Guimard JM, Allix O, Pechnik N and Thévenet P. [Statistical energy and failure analysis of CFRP compression behavior using a uniaxial microbuckling model. J Compos Mater 2007; 41: 2807–2828], a simplified 2D micro-model has been used in order to assess the influence of the fiber misalignment parameters on the micro-structural compression behavior, both in terms of critical stresses and dissipated energies. This article goes further by introducing the influence of a shear pre-stress and by considering an inelastic and damageable constitutive behavior for the matrix and not only an inelastic one as it is done in the literature. Together with fiber waviness, these three parameters are proven to be critical for the simulation of the kinking phenomenon. Particularly, the main effect of the damageable behavior of the matrix is to avoid unrealistically high hardening of the epoxy. This affects the results significantly and allows a better correlation of the model with experimental data. It is shown, by a statistical analysis, that failure stresses are sensitive to both shear pre-stresses and fiber waviness. Dissipated energies and kink-band size are found to be affected by a shear pre-stress as well but rather less sensitive to fiber waviness.

A micromechanics-based mesomodel for unidirectional laminates in compression up to failure

This study introduces an enriched description of a mesomodel for laminates in compression. The improvements are based on previous micromechanical studies regarding failure by kinking under combined compression and shear. The homogenization of the micromechanical response is based on an equivalence in recoverable, stored, and dissipated energy. This leads to a modified constitutive relation at the mesoscale which is probabilistic, i.e., parametrized by a measure of the statistical fiber misalignment, and features a nonlinear elastic potential in compression. The identification procedure is precisely detailed and applied on a T300/BSL-914C UD ply. It is shown that, thanks to simple deterministic relations, the mesoscale constitutive behavior is able to closely represent the homogenized plys response of the underlying microstructure.