Verification of damage model of ceramic matrix composites and analysis of cyclic deformation behavior

Ceramics are excellent in heat, abrasion and corrosion resistances, but their strength reliability for structural materials is not enough due to their brittle nature. On the other hand, ceramic matrix composites (CMCs) reinforced with ceramic fibers attract attention as a damage tolerating material, because toughness of CMCs is improved through various mechanisms such as fiber bridging, fiber breakage, pullout, interfacial debonding and crack deflection. Thus, clarification of the mechanical behavior of CMCs including such damages deepens its engineering significance. In this study, a new finite element (FE) model for the damage analysis of this material is proposed, in which the effect of Coulomb friction at the interface after fiber breaking or matrix cracking followed by the fiber/matrix debonding is taken into account. Although a limitation condition is incorporated into the model, the advantage of this model is that stress and strain distributions can be obtained by merely one calculation without iteration. The accuracy of this FE model was validated by comparing with the results of both the general-purpose FE analysis software and theoretical matrix crack model. In addition, we proposed a new interfacial contact state to apply this model to the hysteresis behavior of CMC under cyclic loading, and discussed its causes about changes in the hysteresis loop. Results of the present FE model showed that the fiber and matrix stress distributions behaved non-linearly in the interfacial debonding area, while these displayed a constant in the bonding area. This model also showed a good compatibility with the theoretical model and the general-purpose FE analysis. Thus, it is expected that this model can be applied for damage states such as matrix crack deflection, indeed difficult through the conventional theoretical models or general-purpose FE analysis. The present model also simulated well the shift and shape of the hysteresis loop with cyclic loading.