Low-cycle fatigue tests were carried out on spring steels at room temperature under a triangular strain wave form to obtain basic information about low-cycle fatigue behavior of springs.
The results obtained are summarized as follows:
(1) Cyclic softening behavior was observed under cyclic straining with plastic strain component.
(2) Fatigue life properties and cyclic deformation properties of spring steel are the same as those which obtained by extrapolating properties of tempered steels for machine structural use to higher level of hardness.
(3) Estimation method of low-cycle fatigue lives from tensile properties is proposed by modifying Manson's Universal Slope Method.
(4) Total damage under incremental step tests becomes 1 to 1.8 at failure. Miner's cumulative rule is applicable to fatigue life estimation under straining of randon amplitudes.
(5) Total damage is very small compared with 1 at failure, when stress controlled fatigue tests are carried out after a part of strain controlled test with plastic strain component. Cyclic softening by strain cycling promotes fatigue damage due to stress cycling.
