Hiromichi Ishiduka

Possibility of Fatigue Crack Extension Under Cyclic Large Compressive Stress by Medium Frequency Induction Hardening

Induction hardened axles have been used since the start of the Shinkansen (Japanese Bullet train) service in 1964. Axles are subjected to cyclic loading, and induction hardened axles are used under cyclic compressive stress conditions because of the large compressive stress state caused by induction hardening along the axle surface. Japanese Railways regularly inspect its axles, and if any crack larger than 0.15 mm in depth is found, the axle is taken out of service. The compressive stress is around −500 MPa, and magnetic particle inspection is conducted at intervals of 2.2×108 and 4.4×108 rotation. The issue of whether or not a crack more than 0.15 mm in depth will propagate under cyclic large compressive stress conditions is of great importance from the viewpoint of railroad safety. From the above mentioned background, a literature survey and experiment of fatigue crack extension under a cyclic large compressive stress condition were conducted. The results show that the crack did extend in the range of around 3.6–5.0×108 cycles under the condition of −500∼0 MPa cycle. Elastic-perfectly plastic stress analysis was also conducted to understand the possibility of tensile residual stress origination, which is considered to be a cause of extension. The analysis of −500∼0 MPa cycle showed that a large tensile stress of about 89.5 MPa originated at the crack tip when unloading. Whereas, the analysis of −560∼−440 MPa cycle for actual maximum stress in the field showed compressive when unloading.Copyright