A damage constitutive model for the nonlinear mechanical behavior of C/SiC composites during mechanical cyclical loading/unloading

In this study, the nonlinear mechanical behavior and corresponding damage mechanisms of C/SiC composites
during cyclic loading/unloading tensile tests were studied. Besides, based on the composite microstructure and
damage mechanisms, the damage evolution model and single fiber unit model are proposed to explain the
stiffness degradation, inelastic deformation accumulation, and elastic deformation. According to the stiffness
degradation law, the damage evolution model based on Weibull failure probability is established, which can fit
damage-strain curves well. Additionally, the single fiber unit model considering the microscopic mechanisms of
matrix cracking, interfacial debonding, and sliding is established. In the model, the stress distributions before and
after loading and unloading are analyzed to obtain the elastic strain and inelastic strain formulas of the com-
posite that can perfectly fit the experimental results (R2 > 99.9%). Because the model reflects the deformation
mechanisms of the composites in a much more simplified way, the deformation and damage law of the composite
can be well predicted with basic macroscopic parameters such as the composition of the composite, the elastic
modulus of the fiber, matrix, and composite, the strength of the matrix and the residual thermal stress of the
matrix.