连续纤维增强陶瓷基复合材料基体开裂应力

Cracking stress in continuous fiber reinforced ceramic matrix composites

关键词:  陶瓷基复合材料  开裂应力  基体裂纹  残余应力  纤维桥连增韧

Key words:  ceramic matrix composites  cracking stress  matrix cracks  residual stress  fiber bridging toughening

摘要:

为深入揭示连续纤维增强陶瓷基复合材料基体裂纹演化的微观机理,系统研究了基体初始裂纹以及界面性能、残余应力、径向应力等对基体开裂应力的影响规律。首先,基于简化库仑摩擦模型,综合考虑库仑摩擦以及泊松效应、残余应力、径向应力等对摩擦力的影响,解析推导了纤维桥连应力-裂纹张开位移关系。其次,运用断裂力学方法,通过裂尖应力强度因子分析建立了开裂应力理论模型,分析了开裂应力与基体初始裂纹长度之间的定量关系。最后,讨论了基体断裂韧性、界面摩擦系数等材料性能以及环境温度、径向应力等外部条件的影响。结果表明,长初始裂纹在低应力水平下扩展,短初始裂纹在高应力水平下扩展,初始裂纹长度的分布决定了基体裂纹演化过程；此外,除了提高基体断裂韧性、界面摩擦系数和界面脱粘能以外,施加径向压应力也能显著提升基体开裂应力。因此,在连续纤维增强维陶瓷基复合材料结构设计中应充分考虑径向应力的影响,并尽可能使径向处于压应力状态,以抑制裂纹扩展,提升结构性能。

Abstract:

To elucidate the micro-mechanisms of matrix crack evolution in continuous fiber reinforced ceramic-matrix composites (FRCMCs), this study systematically investigates the influences of the initial matrix crack length, interfacial properties, thermal residual stresses, and radial stress on the matrix cracking stress. First, a simplified Coulomb-friction model that comprehensively accounts for Coulomb friction, Poisson’s effect, residual stresses and radial stress, is introduced to derive the analytical formula between the fiber bridging stress and the crack opening displacement. Then, a theoretical model for the matrix cracking stress is established by combining this bridging law with linear-elastic fracture mechanics. By this theoretical model, a quantitative relationship between the cracking stress and the initial crack length is obtained. Subsequently, the roles of constituent properties and the external factors including the ambient temperature and the radial stress are studied. The results show that long initial cracks propagate at low stress levels, whereas short initial cracks require high stress levels to grow, and the distribution of initial crack lengths thus governs the evolution of matrix cracking. Moreover, in addition to increasing matrix fracture toughness, interface friction coefficient and interface debonding energy, the application of radial compressive stress can significantly raise the matrix cracking stress. Therefore, the effect of radial stress must be fully considered in the structural design of continuous-fiber-reinforced ceramic matrix composites, and a radial compressive state should be maintained as far as possible to suppress crack propagation and enhance structural performance.