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为研究针刺C/C-SiC复合材料的剪切损伤行为,首先,进行了面内剪切加卸载实验,并利用SEM对复合材料的剪切破坏形貌进行了观测;然后,建立了一种塑性与损伤相结合的非线性本构模型描述复合材料的非线性力学行为,以幂函数描述等效塑性应变与等效应力的关系;最后,基于剪切强度的Weibull分布规律提出了一种指数型损伤变量表征剪切刚度的退化,并通过实验数据拟合得到模型中的参数。结果表明:复合材料在卸载后存在明显的残余应变,卸载模量随载荷的增加不断降低,表现出明显的剪切非线性特征;大量无纬布纤维束和纤维单丝拔出,且易在针刺部位发生破坏;由于针刺部位等缺陷的不规律分布,剪切强度存在一定的分散性,符合指数型Weibull统计分布规律;复合材料的剪切非线性主要由基体开裂和纤维/基体界面脱粘等内部损伤引起,从宏观上可以解释为塑性变形和刚度性能折减。所得结论表明本构模型能够很好地表征C/C-SiC复合材料的面内剪切非线性行为。
In order to study the shear damage behavior of acupuncture C / C-SiC composites, firstly, in-plane shear loading and unloading experiments were carried out and the shear failure morphology of the composites was observed by SEM. Then, The non-linear constitutive model combining plasticity and damage describes the nonlinear mechanical behavior of composites. The relationship between equivalent plastic strain and equivalent stress is described by power function. Finally, based on Weibull distribution law of shear strength, Exponential damage variables characterize the degradation of shear stiffness, and the parameters in the model are obtained by fitting the experimental data. The results show that there is a significant residual strain after unloading, and the unloading modulus decreases with the increase of load, showing obvious shear nonlinear characteristics. A large number of non-woven fabric fiber bundles and fiber monofilament are pulled out, Due to the irregular distribution of defects such as acupuncture points, the shear strength has some dispersity, which accords with the exponential Weibull statistical distribution law. The shear nonlinearity of composites mainly consists of matrix cracking and fiber / matrix interface Debonding and other internal damage caused, macroscopically can be interpreted as plastic deformation and stiffness reduction. The results show that the constitutive model can well characterize the in-plane shear nonlinear behavior of C / C-SiC composites.