Abstract In the machining process of Carbon Fiber Reinforced Plastic (CFRP), fibers fracture in two modes, including shearing fracture and bending fracture. Studies show that both fractures originate from the combined action of normal and shear stresses, while specific stress states are different. In the present study, novel fiber fracture criteria are proposed, which are closely correlated with the specific stress state corresponding to each fracture mode. Obtained results demonstrate that in the proposed criteria, calculation accuracy of the main cutting force improves by over 30 % when the comparison is made with the conventional criteria. Moreover, the removal processes of fibers at the hole-exit during drilling CFRP are simulated to analyze the forming mechanisms of burrs and cracking. Results suggest that although all burrs and cracking are induced by the out-of-plane deformation of fibers, the main causes of such deformations at the hole-exit in different regions are not the same. In the region corresponding to the fiber cutting angle of 90°, deformation originates from the squeezing action among fibers fracturing at different times, while in the region corresponding to the fiber cutting angle of 0°, deformation is directly caused by the squeezing action of the cylindrical surface on the main cutting edge.

中文翻译：

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揭示钻孔毛刺和孔口开裂形成机制的新型纤维断裂标准 碳纤维增强塑料

摘要 在碳纤维增强塑料（CFRP）的加工过程中，纤维以两种方式断裂，包括剪切断裂和弯曲断裂。研究表明，两种裂缝均源于正应力和剪应力的共同作用，而具体应力状态不同。在本研究中，提出了新的纤维断裂准则，该准则与对应于每种断裂模式的特定应力状态密切相关。得到的结果表明，在提出的准则中，与传统准则相比，主切削力的计算精度提高了30%以上。此外，还模拟了碳纤维复合材料钻孔过程中孔出口处纤维的去除过程，分析了毛刺和裂纹的形成机制。结果表明，虽然所有毛刺和开裂都是由纤维的平面外变形引起的，但不同区域孔出口处变形的主要原因并不相同。在90°纤维切割角对应的区域，变形来源于不同时间断裂的纤维之间的挤压作用，而在0°纤维切割角对应的区域，变形是由纤维的挤压作用直接引起的。主切削刃上的圆柱面。