Mechanical response of ceramic matrix composites is critically dependent on properties of fibers and fiber coatings. In the present study, we examine effects of these and other constituent properties on the tensile response of unidirectionally-reinforced composites through a combination of existing models of fiber fracture, Monte Carlo simulations of concurrent matrix and fiber fragmentation, and complementary experimental measurements. The results show that, contrary to prevailing understanding, the process of fiber fragmentation cannot go to completion in a uniaxial tensile test. At low stresses (before the maximum), fiber breaks are essentially random throughout the bundle; in contrast, at the stress maximum, all additional breaks are localized to regions close to the fracture plane (within a distance dictated by the characteristic transfer length). Therefore, the resulting distributions in fiber pullout length and strength of pulled-out fibers do not match predictions from existing models. Although the composite stress-strain response associated with fragmentation can be accurately predicted by existing fragmentation models, accurate prediction of the point of instability requires consideration of the local response of fibers in the most heavily strained regions (within matrix crack planes). The response in the latter regions leads to instability at stresses and strains that are lower than those obtained from the average stress-strain response. Additionally, the composite strength and failure strain are found to be sensitive to the fiber volume fraction and the matrix strength distribution. One implication is that the full potential of the fibers may not be realizable in composites of practical interest.

陶瓷基复合材料的机械响应主要取决于纤维和纤维涂层的性能。在本研究中，我们通过结合现有的纤维断裂模型，同时发生的基体和纤维断裂的蒙特卡罗模拟以及互补的实验测量，研究了这些和其他组成特性对单向增强复合材料拉伸响应的影响。结果表明，与普遍的理解相反，纤维断裂的过程不能在单轴拉伸试验中完成。在低应力下（最大应力之前），整个纤维束的纤维断裂基本上是随机的。相反，在最大压力下 所有其他断裂都位于靠近断裂面的区域内（在特征传递长度所决定的距离内）。因此，所得的纤维拉出长度和拉出的纤维强度分布与现有模型的预测不符。尽管可以通过现有的碎裂模型准确预测与碎裂有关的复合应力应变响应，但要准确预测失稳点，需要考虑纤维在应变最大的区域（基体裂纹平面内）的局部响应。后面区域的响应导致应力和应变的不稳定性低于从平均应力应变响应获得的应力和应变。另外，发现复合强度和破坏应变对纤维体积分数和基体强度分布敏感。一种含义是，在具有实际意义的复合材料中可能无法实现纤维的全部潜力。