纤维增强陶瓷基复合材料的D失效判据

经典唯象强度理论适用于正交各向异性线弹性体.对于非线性纤维增强复合材料,通过加卸载试验和损伤力学的分析方法,可以得到一种虚拟的线性化应力-应变关系;依据损伤等效假设,针对线性损伤和非线性损伤,对基于应力的经典二次失效准则进行变换,建立了一种基于损伤的强度理论,即"D失效判据",这一强度理论可以作为经典判据的补充和扩展.针对平纹编织C/SiC复合材料的拉/剪组合试验,进行了实例计算,结果表明:利用D失效判据预测的失效包络线比蔡-希尔准则的预测曲线低,而且,失效曲线的形式与材料的损伤演化规律相关.

D failure criterion for fiber reinforced ceramic matrix composites

Classical phenomenological strength theories are reasonable for orthotropic composites that present linear elastic mechanical behavior. For nonlinear/damageable fiber reinforced ceramic matrix composites (CMCs), there is few failure criterion developed in recent years to account for their rupture characteristics. In order to promote the engineering applications of CMCs, new failure criterion is of interest for structural strength design. In this paper, we deal with nonlinear and anisotropic problems and consider the influence of damage evolution process on failure strength. Firstly, virtual linearization of the inelastic behavior of CMCs was performed based on the phenomenon that a kind of approximately linear stress-strain relationship being observed in CMCs during the loading/unloading experiment. And then, a completely linearized stress-strain relation was formulated by a simple analytical method of damage mechanics. Subsequently, on the basis of damage equivalence assumption, the relationship between the principle damage variables and the associated stress components was deduced. Afterwards, the classical stress-based quadratic failure criteria were modified under both linear and nonlinear damage evolutionary cases by introducing damage parameters into the theoretical equations to replace those stress parameters. As a result, a new damage-based failure criterion named “D failure criterion” was established. This failure theory is capable to be the supplement and extension of the well-known phenomenological failure criteria. In addition, verification towards “D failure criterion” was conducted through a calculation example involving the tension-shear combined experiment of a plain woven C/SiC composite. The demanded damage evolution laws of the material were obtained by literature reserch. The simulated results show that: the failure envelope given by the newly proposed failure criterion is lower than Tsai-Hill criterion, and the failure curve is associated with the damage evolution laws. This also reveals the potential of “D failure criterion” for further applications in advanced ceramic composites within the framwork of continuum damage mechanics.