Shear nonlinear constitutive relationship of needled C/C-SiC composite

In order to investigate the shear damage behavior of needled C/C-SiC composite, in-plane shear load-unload experiments were conducted firstly, and the shear fracture morphologies of the composites were observed by SEM. Then, a plasticity-damage combined nonlinear constitutive model was established to describe the nonlinear mechanical behavior of the composite, and the power function was used to characterize the relationship between equivalent plastic strain and equivalent stress. Finally, an exponent-form damage variable was introduced to describe the shear stiffness degradation based on the Weibull distribution law of shear strength, and the parameters in model were determined by fitting of the experimental data. The results show that the composite has obvious residual deformation after unloading, the unloading modulus degenerates with the increase of load continually, which exhibits obvious shear nonlinearity characteristic. A large number of fiber bundles and fiber single yarns in non-woven cloth were pulled out, and the failures tend to occur at needling positions. For the irregular distribution of imperfection at needling positions, shear strength possesses dispersibility at some extent, and conforms to exponent-form Weibull statistical distribution law. The shear nonlinearity of the composite was induced by inner damages such as matrix cracking and fiber/matrix interfacial debonding etc., which can be described by plasticity deformation and stiffness properties degradation from a macro perspective. The conclusions obtained verify that the constitutive model can fully describe the in-plane shear nonlinear behavior of needled C/C-SiC composite.