采用三维景深显微镜和扫描电镜，对某进口弩的部件弩钩(材料为纤维增强复合材料)断裂原因进行了分析。结果表明: 弩钩在日常的使用过程中，由于其表面硬度较低,易与金属部分碰擦而产生表面微损伤;同时由于断裂处内部的增强纤维较少且其方向与断裂面平行，导致弩钩局部强度降低;在弩弓拉开时，弩钩从表面微损伤处启裂而引发低应力断裂失效。

The fracture reasons of a crossbow hook with material of fiber reinforced composite were analyzed by three-dimensional optical microscope and scanning electron microscope. The results show that the crossbow hook would be injured easily by the metal parts of the crossbow in daily use because of its low hardness, which induced micro defect on the hook surface. At the same time, it was found the inside enforced fibers at the fracture area were rather less and the direction of most of them was parallel to the fracture surface, which caused the local strength decrease of the hook. And when the crossbow was drawn, cracking initiated from the surface micro defect position, and then fracture failure happened under low stress.