Abstract This study focuses on the notch effect on the fatigue failure of chopped carbon fiber chip-reinforced sheet molding compound (SMC) composites by using both experimental and numerical methods. The S-N diagrams of notched specimens are first obtained experimentally, which exhibit large scatter and are shown to depend on the spatial distribution of local fiber orientations. After considering the effect of this spatial distribution by adopting a new fatigue damage parameter to normalize the results, we achieve a much better correlation in the normalized S-N diagram for all the notched specimens with different hole diameters. Next, compared with the fatigue results of smooth specimens without notches, we find that SMC composites under tension-tension fatigue loading exhibit notch-insensitivity, which renders this type of composites a better candidate in joints or similar applications. Meanwhile, the fatigue failure mechanisms of notched SMC composites are explored through a microstructure characterization procedure. On this basis, a computational micromechanics model considering the notch effect and an improved multi-scale progressive damage fatigue law, calibrated by coupon-level fatigue tests of smooth SMC composites under different loading conditions, are employed to predict the fatigue behavior of notched SMC composites. We show that detailed failure processes and fatigue life of notched SMC composites can be efficiently and adequately predicted by this computational framework.

中文翻译：

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使用实验和计算分析的短切碳纤维芯片增强复合材料疲劳失效中的缺口不敏感性

摘要 本研究通过实验和数值方法研究了缺口对短切碳纤维片增强片状模塑料 (SMC) 复合材料疲劳失效的影响。缺口试样的 SN 图首先通过实验获得，其表现出大的散射，并显示出取决于局部纤维取向的空间分布。在通过采用新的疲劳损伤参数对结果进行归一化来考虑这种空间分布的影响后，我们在归一化 SN 图中对于具有不同孔径的所有缺口试样实现了更好的相关性。接下来，与没有缺口的光滑试样的疲劳结果相比，我们发现 SMC 复合材料在拉-拉疲劳载荷下表现出缺口不敏感性，这使得这种类型的复合材料成为接头或类似应用的更好选择。同时，通过微观结构表征程序探索了缺口 SMC 复合材料的疲劳失效机制。在此基础上，采用考虑缺口效应的计算微观力学模型和改进的多尺度渐进损伤疲劳规律，通过不同加载条件下光滑SMC复合材料的试样级疲劳试验校准，预测缺口SMC复合材料的疲劳行为. 我们表明，该计算框架可以有效且充分地预测缺口 SMC 复合材料的详细失效过程和疲劳寿命。通过微观结构表征程序探索了缺口 SMC 复合材料的疲劳失效机制。在此基础上，采用考虑缺口效应的计算微观力学模型和改进的多尺度渐进损伤疲劳规律，通过不同加载条件下光滑SMC复合材料的试样级疲劳试验校准，预测缺口SMC复合材料的疲劳行为. 我们表明，该计算框架可以有效且充分地预测缺口 SMC 复合材料的详细失效过程和疲劳寿命。通过微观结构表征程序探索了缺口 SMC 复合材料的疲劳失效机制。在此基础上，采用考虑缺口效应的计算微观力学模型和改进的多尺度渐进损伤疲劳规律，通过不同加载条件下光滑SMC复合材料的试样级疲劳试验校准，预测缺口SMC复合材料的疲劳行为. 我们表明，该计算框架可以有效且充分地预测缺口 SMC 复合材料的详细失效过程和疲劳寿命。用于预测缺口 SMC 复合材料的疲劳行为。我们表明，该计算框架可以有效且充分地预测缺口 SMC 复合材料的详细失效过程和疲劳寿命。用于预测缺口 SMC 复合材料的疲劳行为。我们表明，该计算框架可以有效且充分地预测缺口 SMC 复合材料的详细失效过程和疲劳寿命。