Fatigue Crack Propagation Behavior under Stress Changing in SCM 435 Steel

Abstract

The constant and variable stress amplitude fatigue tests were carried out on smooth and pinholed specimens of SCM 435 steel under rotating bending conditions.
In the constant stress amplitude tests, the fatigue crack propagation rate was not affected by the stress level and it was represented well by ΔK.
The crack initiated by the over-stress σ_a1 cycles was retarded by the under-stress σ_a2 cycles, when the difference between σ_a1 and σ_a2 was large. In the case of non-propagating cracks, their length was shorter than that in plain carbon steels. The condition of crack retardation under σ_a1 repetition following σ_a2 application was elucidated.
The crack propagation behavior of pin-holed specimens in two step multi-fold tests was similar to that in two step two-or three-fold tests. The discussion was made on the shift from unity in cumulative cycle ratio for smooth specimens, based on the results of crack propagation behavior of pin-holed specimens.