The degradation of SiC-based ceramic matrix composites (CMCs) in conditions typical of gas turbine engine operation proceeds via the stress-rupture of fiber bundles. The degradation is accelerated when oxygen and water invade the composite through matrix microcracks and react with fiber coatings and the fibers themselves. We review micromechanical models of the main rate-determining phenomena involved, including the the diffusion of gases and reaction products through matrix microcracks, oxidation of SiC (in both matrix and fibers) leading to the loss of stiffness and strength in exposed fibers, the formation of oxide scale on SiC fiber and along matrix crack surfaces that cause the partial closure of microcracks, and the concomitant and synergistic loss of BN fiber coatings. The micromechanical models could be formulated as time-dependent coupled differential equations in time, which must be solved dynamically, e.g., as an iterated user-defined material element, within a finite element simulation. A paradigm is thus established for incorporating the time-dependent evolution of local material properties according to the local environmental and stress conditions that exist within a material, in a simulation of the damage evolution of a composite component. We exemplify the calibration of typical micromechanical degradation models using thermodynamic data for the oxidation and/or volatilization of BN and SiC by oxygen and water, mechanical test data for the rate of stress-rupture of SiC fibers, and kinetic data for the processes involved in gas permeation through microcracks. We discuss approaches for validating computational simulations that include the micromechanical models of environmental degradation. A special challenge is achieving validated predictions of trends with temperature, which are expected to vary in a complex manner during use.. This article is protected by copyright. All rights reserved.

中文翻译：

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模拟 SiC/BN/SiC 陶瓷基复合材料的环境引起的性能退化

碳化硅基陶瓷基复合材料 (CMC) 在燃气涡轮发动机运行的典型条件下的降解通过纤维束的应力断裂进行。当氧气和水通过基体微裂纹侵入复合材料并与纤维涂层和纤维本身发生反应时，降解会加速。我们回顾了所涉及的主要速率决定现象的微观力学模型，包括气体和反应产物通过基体微裂纹的扩散、碳化硅的氧化（在基体和纤维中）导致暴露纤维的刚度和强度损失，形成SiC 纤维上和沿基体裂纹表面的氧化皮导致微裂纹的部分闭合，以及 BN 纤维涂层的伴随和协同损失。微机械模型可以制定为时间相关的耦合微分方程，必须动态求解，例如，作为迭代用户定义的材料元素，在有限元模拟中。因此，建立了一种范式，用于根据材料内存在的局部环境和应力条件，在复合材料部件损伤演变的模拟中结合局部材料特性的时间相关演变。我们使用氧和水氧化和/或挥发 BN 和 SiC 的热力学数据、碳化硅纤维应力断裂速率的机械测试数据以及所涉及过程的动力学数据，举例说明了典型微机械降解模型的校准。气体通过微裂纹渗透。我们讨论了验证计算模拟的方法，包括环境退化的微机械模型。一个特殊的挑战是实现对温度趋势的有效预测，预计在使用过程中会以复杂的方式变化。本文受版权保护。版权所有。