The damage-induced bi-modulus characteristic of C/SiC materials and experimental validation

The credibility of structural stress response predictions is critical in the design and analysis of increasingly used C/SiC structures. The complexities of the damage mechanisms pose a challenge to the accuracy of the predictions. In this paper, the bi-modulus characteristic of C/SiC, which is induced by the micro cracks opening and closing under tensile and compressive load respectively, were studied. A phenomenological macroscopic approach based on irreversible thermodynamics was applied to model the constitutive behavior of C/SiC. Four-point flexure experiments were conducted on C/SiC specimens to validate the model. A simulation model analogous to the experimental setup was built and the effects of the bi-modulus were analyzed. The strain responses in the experiments and the simulation corresponded well with each other. In both the experiments and the simulations conducted, neutral planes of the specimens were deviated from the geometric center due to the bi-modulus characteristic of the material. Compared to the simulation results using the developed constitutive law, the model employing a linear elastic law over-predicts the tensile stress by 31.6% and underestimates the compressive stress by 15.2% of the C/SiC specimen under a four-point flexural load of 1600 N.