Due to the inhomogeneity and anisotropy of short fiber-reinforced polymers (SFRP), even uniaxial loading can induce multiaxial stress states inside them, which significantly increases the difficulty of grasping their fatigue behavior. To efficiently predict the fatigue life of SFRP under proportional multiaxial stress, a multiaxial high-cycle fatigue model is proposed, relying upon the multiscale modeling strategy capable of integrating the influence of fiber microstructure. Taking the fiber-matrix interface stress at the critical region as the internal driving factor of fatigue fracture is the core assumption verified by microscopic observations. Off-axial fatigue tests with different orientations and stress ratios are performed to validate the fatigue model. Results show that the prediction accuracy has reached an acceptable level, and the quadratic polynomial surface can well represent the relationship between fatigue life and multiaxial stresses. This work provides an efficient tool for multiaxial fatigue life prediction and expounds the failure behavior of SFRP from multiscale perspectives.

中文翻译：

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高周比例载荷下短纤维增强聚合物复合材料多尺度多轴疲劳模型

由于短纤维增强聚合物（SFRP）的不均匀性和各向异性，即使是单轴载荷也会在其内部引起多轴应力状态，这显着增加了掌握其疲劳行为的难度。为了有效预测比例多轴应力下 SFRP 的疲劳寿命，基于能够整合纤维微观结构影响的多尺度建模策略，提出了多轴高周疲劳模型。将临界区纤维-基体界面应力作为疲劳断裂的内驱因素，是通过微观观察验证的核心假设。进行不同方向和应力比的离轴疲劳测试以验证疲劳模型。结果表明，预测精度达到了可接受的水平，二次多项式曲面能够很好地表征疲劳寿命与多轴应力之间的关系。这项工作为多轴疲劳寿命预测提供了一种有效的工具，并从多尺度角度阐述了 SFRP 的失效行为。