A mesh size objective multiscale modeling is developed for fatigue failure prediction of long fiber-reinforced composites based on the multiscale discrete damage theory (MDDT). MDDT tracks the failure processes along discrete failure surfaces at the microscale and concurrently bridges it to continuum-based description of damage at the macroscale. The proposed approach achieves mesh-size objectivity by introducing a length scale operator which effectively adjusts the microstructure size as a function of macroscale element size; and when a non-additive fatigue damage evolution law is used to describe progressive cracking at the microscale. Temporal multiscaling is used to track long-term fatigue damage evolution with high computational efficiency. The performance of the proposed model is demonstrated by the analysis of unnotched and open-hole laminate configurations. The results indicate mesh-size objectivity even in the presence of multiple failure mechanisms including splitting, delamination and transverse matrix cracks. The interaction between splitting and transverse cracks is investigated by a parametric study, which reveals the effects of mode I and mode II dominated degradation on the failure behavior under fatigue loading.

基于多尺度离散损伤理论（MDDT），开发了一种网格尺寸目标多尺度模型，用于长纤维增强复合材料的疲劳破坏预测。MDDT在微观尺度上沿着离散的失效面跟踪失效过程，并同时将其桥接到宏观尺度上基于连续性的损伤描述。所提出的方法通过引入长度尺度运算符来实现网格大小的客观性，该长度尺度运算符有效地调整了微观结构的大小，作为宏观元素大小的函数。当使用非累加的疲劳损伤演化定律描述微观尺度上的渐进裂纹时。时间多标度用于以高计算效率跟踪长期疲劳损伤的演变。拟议模型的性能通过无缺口和裸眼层压板配置的分析得到证明。结果表明，即使存在多种破坏机制，包括分裂，分层和横向基体裂纹，网格大小的客观性也是如此。通过参数研究研究了裂痕和横向裂纹之间的相互作用，该研究揭示了疲劳载荷下，I型和II型主导降解对失效行为的影响。