BN fiber coatings in SiC-SiC composites are vulnerable to oxidation and volatilization at elevated temperature in the presence of water vapor. These processes lead to coating recession in the composite interior with recession fronts starting from matrix cracks and proceeding axially along the fibers. In some operational domains, the main effect of recession is to de-couple the fibers from the matrix, precluding load transfer that would otherwise occur through frictional sliding. Here we present a modelling framework to address effects of coating recession on composite strength. The framework is built upon the characteristic strengths and transfer lengths that govern fiber and matrix fragmentation during tensile loading. Four dominant behavioral domains are identified and analyzed. Recession causes shifts in the domain boundaries and reductions in composite strength. Variations in degraded strength with the extent of recession are interpreted in terms of stress rupture plots. In the regime where recession leads to time-dependent fracture, the composite response is defined by two strengths: (i) the pristine composite strength (governed by the in situ fiber bundle properties) and (ii) a threshold stress below which failure is not predicted to occur (governed by the strength of an equivalent fiber bundle in the absence of a matrix). The time scales are set by the square of the ratio of recession length and the matrix crack spacing, the latter governed by a combination of the matrix strength distribution, interface sliding stress, fiber content and applied stress.

SiC-SiC 复合材料中的 BN 纤维涂层在水蒸气存在的高温下容易氧化和挥发。这些过程导致复合材料内部的涂层衰退，衰退前沿从基体裂纹开始并沿纤维轴向前进。在某些操作领域中，后退的主要作用是使纤维与基体分离，从而防止通过摩擦滑动而发生的载荷转移。在这里，我们提出了一个建模框架来解决涂层衰退对复合材料强度的影响。该框架建立在控制拉伸载荷期间纤维和基体碎裂的特征强度和转移长度上。识别和分析了四个主要行为域。衰退导致域边界的变化和复合强度的降低。强度退化随衰退程度的变化可以用应力断裂图来解释。在衰退导致时间相关断裂的情况下，复合响应由两个强度定义：（i）原始复合强度（由原位纤维束特性）和 (ii) 阈值应力，低于该应力不会发生故障（由没有基体的等效纤维束的强度控制）。时间尺度由衰退长度和基体裂纹间距的比值的平方设定，后者受基体强度分布、界面滑动应力、纤维含量和施加应力的组合控制。