某造船厂一台龙门起重机车轮轴在服役4 a(年)之后发生断裂, 通过现场勘查并对试样进行理化检验, 分析了该车轮轴断裂的原因。结果表明：该车轮轴轴肩部位存在较深加工痕迹和缺欠, 在承受较大交变剪切应力之后, 表层加工痕迹和缺欠成为疲劳裂纹源, 撕裂表层针状铁素体向内扩展, 最终导致车轮轴发生断裂失效。

The axle of a shipbuilding gantry crane fractured after 4 years of service, and the fracture reasons were analyzed through field investigation and physical and chemical test. The results show that there were deep machining marks and defects which became fatigue crack sources when bearing large alternating shear stress at the axle shoulder position. Then the cracks tore the surface acicular ferrite and extended to the inside, and finally resulted in the fracture of the axle.