Internal pores in composite materials generated during fabrication processing can induce negative influences on the physical properties. Among them, the fatigue life under repetitive loadings is one of the most detrimentally influenced properties by the undesirable pores. In this paper, we investigated the effect of pore geometries – 1) sizes and 2) aspect ratios on the fatigue life of polyamide 12 (PA12) by combining two different fatigue life prediction approaches. Considering that the typical failure mechanism of structural materials follows the initiation of the crack, propagation, and ultimate separation, the present approach counts the fatigue life until crack initiation and fatigue cycles during the crack growth until complete separation. For the prediction, a crack growth model by Castillo-Canteli-Siegele model (CCS model) with initial defects was adopted. In addition, to reflect the elastoplastic behavior better, an extended CCS model with the cyclic J-integral was used. The simulation results show that the presence of the pores in the plastic material can significantly affect the fatigue life. The characteristics of fatigue properties on the geometric conditions of pores were discussed by comparing the results. The proposed method can be seamlessly used for the evaluation of fatigue life of polymer matrix composite materials.

中文翻译：

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考虑裂纹萌生和扩展的孔隙率对聚酰胺12疲劳寿命的影响

在制造过程中产生的复合材料中的内部孔隙会对物理性能产生负面影响。其中，重复载荷下的疲劳寿命是受不良气孔影响最大的性能之一。在本文中，我们通过结合两种不同的疲劳寿命预测方法研究了孔隙几何形状 - 1) 尺寸和 2) 纵横比对聚酰胺 12 (PA12) 疲劳寿命的影响。考虑到结构材料的典型失效机制遵循裂纹萌生、扩展和最终分离，本方法计算裂纹萌生之前的疲劳寿命和裂纹扩展期间直至完全分离的疲劳循环。对于预测，采用具有初始缺陷的 Castillo-Canteli-Siegele 模型（CCS 模型）的裂纹扩展模型。此外，为了更好地反映弹塑性行为，使用了具有循环 J 积分的扩展 CCS 模型。模拟结果表明，塑料材料中气孔的存在会显着影响疲劳寿命。通过比较结果，讨论了孔隙几何条件下疲劳性能的特点。该方法可无缝用于聚合物基复合材料疲劳寿命的评价。通过比较结果，讨论了孔隙几何条件下疲劳性能的特点。该方法可无缝用于聚合物基复合材料疲劳寿命的评价。通过比较结果，讨论了孔隙几何条件下疲劳性能的特点。该方法可无缝用于聚合物基复合材料疲劳寿命的评价。