A multiscale model is developed to predict mixed-mode fatigue crack growth (FCG) behavior in laminated composites by considering the micromechanical effects of fiber bridging. The proposed model consists of a micromechanical part dedicated to the fiber bridging mechanism near the crack tip, a macroscopic FCG model based on the maximum principal strain criterion, and an effective crack tip processing zone (i.e., an equivalent critical distance) connecting the two parts of the model. The core novelty of the presented model is to connect two scales (micro and meso) through a measurable physical quantity – called equivalent critical distance – accounting for various micromechanical as well as macroscopic phenomena occurring at both scales. The suggested model is validated against FCG test data available in the literature for laminated glass fiber composites under mode I, mode II, and mixed mode I/II conditions. It is found that the proposed framework is superior to its conventional (pure macroscopic) version, which eliminates fiber bridging effects, in the prediction of the cyclic mixed-mode crack propagation behavior in laminated composites. The multiscale nature of the proposed FCG model offers less complexity than fully micromechanical approaches while providing higher accuracy as compared to pure macroscopic models that ignore micromechanical phenomena occurring at the fiber scale.

通过考虑纤维桥接的微观机械效应，开发了一个多尺度模型来预测层合复合材料中的混合模式疲劳裂纹扩展 (FCG) 行为。所提出的模型由专用于裂纹尖端附近纤维桥接机制的微观机械部分、基于最大主应变准则的宏观 FCG 模型以及连接这两个部分的有效裂纹尖端处理区（即等效临界距离）组成模型的。所提出模型的核心新颖之处在于连接两个尺度（微观和中观) 通过一个可测量的物理量——称为等效临界距离——解释了在两个尺度上发生的各种微观机械和宏观现象。建议的模型根据文献中可用的 FCG 测试数据对模式 I、模式 II 和混合模式 I/II 条件下的层压玻璃纤维复合材料进行了验证。结果发现，在预测层合复合材料的循环混合模式裂纹扩展行为时，所提出的框架优于其传统（纯宏观）版本，后者消除了纤维桥接效应。所提出的 FCG 模型的多尺度性质提供了比完全微机械方法更少的复杂性，同时与忽略纤维尺度上发生的微机械现象的纯宏观模型相比提供了更高的精度。