Fatigue failure analysis of HSLA steel sheets holed by conventional and flow drilling processes

ABSTRACT Flow drilling process produces bushes for removable joints that can be threaded by forming tapping process, reducing stages in production of components of automobile industry and in construction sheds. High strength and low alloy steels (HSLA) are employed on several applications in the processing industry. Benefits provided by these materials make them an efficient solution, since their high cold resistance allows reducing weight on structures, as well as maintaining the required mechanical properties. The present study evaluated the conventional and friction drilling processes in HSLA steel sheets with a thickness of 4.25 mm. Specimens were subjected to cyclic loadings, with no rework after holemaking, so the resultant characteristics of each process were maintained. Fractured surfaces were analyzed with a scanning electron microscope (SEM) to identify the fracture mechanism in different drilling processes. Fractographies obtained on both processes indicated that the failure mechanism occurred due to ductile fracture resulting from the nucleation, growth and coalescence of micro cavities.

摘要：流动钻孔工艺（Flow drilling process）可加工出可通过成型攻丝工艺制备螺纹的可拆卸接头衬套，能够缩减汽车工业构件及建筑棚架的生产工序。高强度低合金钢（High Strength and Low Alloy Steels，HSLA）在加工工业的诸多场景中得到应用，该材料凭借自身优势成为高效的解决方案：其优异的抗冷性能可降低结构件自重，同时维持所需的力学性能。本研究针对厚度为4.25mm的高强度低合金钢板材，对比评估了常规钻孔工艺与摩擦钻孔工艺的效果。试样均经受循环载荷作用，且钻孔后未进行返工处理，以保留各工艺的原始成型特性。采用扫描电子显微镜（Scanning Electron Microscope，SEM）对断口表面进行分析，以明确不同钻孔工艺下的断裂机制。两种工艺所获得的断口形貌均表明，其失效机制为微孔形核、长大与聚合所导致的韧性断裂。