发生在铁路部件和构件中的断裂通常是从先已存在的缺陷尖端处开始的,这些缺陷多数为疲劳裂纹,其它的则是淬火裂纹、应力腐蚀裂纹、分层、夹杂物和焊接缺陷。直到最近为止,技术上还不能用以定量阐明最终突然失效的条件,也不能预测裂纹扩展至其临界尺寸所需的循环周次或时间,因而难以确定象钢轨、车轴、车轮、轮箍、弹簧、转向架之类带裂纹部件 Fractures that occur in railway components and components usually begin with preexisting defect tips. Most of these defects are fatigue cracks, others are quench cracks, stress corrosion cracking, delamination, inclusions, and weld defects. Until recently it has not been technically possible to quantify the conditions for eventual sudden failure nor to predict the number of cycles or times required for the crack to propagate to its critical dimensions, making it difficult to determine the critical mass of steel such as rails, axles, wheels, wheels, springs , Bogies and the like with cracked parts