ABSTRACT A model for predicting residual stiffness of unidirectional SiC/SiC composite in a stress-oxygen environment over 900°C is developed based on an improved two-stage oxidation kinetics model. Two differential equations relating to the oxygen concentration are derived according to the conservation of mass. As a result, the thickness of the oxide on the fiber, the matrix, and the length of the interface consumed by oxidation can be calculated. The elastic modulus of the fiber and its stress redistribution are analyzed considering the change of the crack in different stress conditions, the oxidation defect on the fiber, the recession length of the interface, and the residual stress caused by the interface debonding. The residual stiffness of the SiC/SiC composite versus time after oxidation is drawn as curves under different stress levels which shows that the applied load does not affect the oxidation behavior of the matrix; it only changes the oxidation time of the composite. In addition, the residual stiffness of the composite decreases rapidly in the beginning for a while, then the degenerate rate stays stable until the interface is fully consumed. The predicted residual stiffness from the model is consistent with the experimental data. Graphical Abstract

中文翻译：

---

应力氧化环境下单向SiC/SiC复合材料残余刚度预测模型

摘要 基于改进的两阶段氧化动力学模型，开发了一种预测单向 SiC/SiC 复合材料在超过 900°C 的应力-氧环境中的残余刚度的模型。根据质量守恒推导出与氧浓度有关的两个微分方程。结果，可以计算出纤维上氧化物的厚度、基体以及氧化消耗的界面长度。考虑不同应力条件下裂纹的变化、纤维上的氧化缺陷、界面的后退长度以及界面脱粘引起的残余应力，分析了纤维的弹性模量及其应力重新分布。SiC/SiC复合材料的残余刚度随氧化时间的变化在不同应力水平下绘制为曲线，表明施加的载荷不影响基体的氧化行为；它只会改变复合材料的氧化时间。此外，复合材料的残余刚度在开始时迅速下降一段时间，然后退化率保持稳定，直到界面完全消耗。模型预测的残余刚度与实验数据一致。图形概要 然后退化率保持稳定，直到界面被完全消耗。模型预测的残余刚度与实验数据一致。图形概要 然后退化率保持稳定，直到界面被完全消耗。模型预测的残余刚度与实验数据一致。图形概要