While surface crack formation and propagation in Electric Multiple Unit (EMU) brake discs has been an active research topic, relatively few studies have considered similar behavior in deep cracks which become unstable. Moreover, most analyses assume nominal design conditions which does not reflect changes which may have been occurred during service. In the present study, a steel brake disc was analyzed after a deep crack was discovered during a maintenance check. The objective was to identify the impetus for deep crack propagation and characteristic semi-elliptical shape. Finite element (FEM) and extended finite element (XFEM) models which included residual stress effects from service were used to analyze the thermo-mechanical history and resulting crack propagation. The simulated and actual fracture surfaces demonstrated satisfactory agreement and showed that the crack preferentially initiated at the bolt hole corners and that transient temperature differences between adjacent hot spots help to define the crack orientation. It was also found that unstable propagation along the axial direction was due to a steep temperature gradient. Service induced distortion was also found to indicate the presence of internal stresses which can have a strong effect on crack behavior. It is expected that the findings will contribute toward a better understanding of how braking conditions and service effects influence unstable crack behavior in EMU brake discs.

虽然电动车组 (EMU) 制动盘中的表面裂纹形成和扩展一直是一个活跃的研究课题，但相对较少的研究考虑了在变得不稳定的深裂纹中的类似行为。此外，大多数分析假设标称设计条件不反映服务期间可能发生的变化。在本研究中，在维护检查期间发现深裂纹后，对钢制制动盘进行了分析。目的是确定深裂纹扩展和特征半椭圆形的推动力。有限元 (FEM) 和扩展有限元 (XFEM) 模型包括使用中的残余应力影响，用于分析热机械历史和由此产生的裂纹扩展。模拟和实际断裂表面显示出令人满意的一致性，并表明裂纹优先在螺栓孔角处产生，并且相邻热点之间的瞬态温差有助于确定裂纹方向。还发现沿轴向的不稳定传播是由于陡峭的温度梯度。还发现服务引起的变形表明存在内应力，这会对裂纹行为产生很大的影响。预计这些发现将有助于更好地了解制动条件和服务效果如何影响动车组制动盘的不稳定裂纹行为。