一种中碳钢的疲劳短裂纹特性

用复型技术研究含碳0.4%钢的扭转疲劳的起始阶段和短裂纹特性。发现疲劳短裂纹在铁素体中发生并扩展。裂纹增长速度取决于裂纹端部塑性范围的大小和程度。因而每循环的裂纹增长正比于滑移带强度。裂纹扩展的减速和可能停止证明晶界是裂纹扩展的强障碍。升高应力值后,原有的不扩展裂纹可能产生支裂纹或连接其它裂纹继续扩展。这个过程反复到一个或多个主导性裂纹的应力达到能导至破坏的继续增长的临界值为止。

SHORT CRACK FATIGUE BEHAVIOUR in a MEDIUM CARBON STEEL

The initiation stage and short crack behaviour in torsional fatigue of a 0.4% C steel was investigated by a replication technique. The initiation and propagation of fatigue crachs ware obserred in the ferrite phase. It is proposed that the crack growth rate depends on the extent and intensity of the plasticity at the tip of the crack. Crack growth per cycle is thus proportional to the strength of the slip hand. The ferritepearlite boundaries are strong barriers to the crack, propagaton which is manifested by a deceleration of growth and possible arrest. On raising the seress level the original non-propagating crak may continue to grow by branching or connecting with other crachs. This process is repeated until the stress fields of one or more dominant cracks attain a critical value to Isustain continued growth that leads to failure.