2000 Volume 86 Issue 12 Pages 830-836
The purpose of this study is to clarify the effect of hardness distribution on the propagation behavior of torsional fatigue crack of induction hardened steels for automotive shafts. The effect of hardness distribution on the propagation rate of mode III crack and fatigue fracture toughness were investigated.
In the torsional fatigue test, mode III fatigue crack propagated in early stage after crack initiation. And, when fatigue crack length achieved a certain critical level, the fracture mode changed from mode III to mode I and static final fracture occurred with intergranular fracture at almost the same time.
The propagation rate of mode III crack decreased with increasing the hardness of crack propagation region. On the other hand, the length of mode III crack propagation at the fracture was decreased by increasing case hardness. This indicates that increasing case hardness enhance the shift from fatigus crack propagating at mode III to static final fracture, namely decreased fatigue fracture toughness.