Cyclic Stress, Strain, and Energy Variations under Cumulative Damage Tests in Low-Cycle Fatigue

Cumulative fatigue damage tests have been carried out on two pressure vessel steels at room temperature with five increasing or decreasing levels of stresses or strains. Variations of stress, strain, and energy are discussed. In the low-cycle region, the behavior of the materials is relatively more stable under strain-controlled than under stress-controlled tests. The total plastic energy at failure is dependent upon the strain range and not upon the strain ratio. A relation is suggested for estimating the plastic energy required for fatigue failure under cumulative damage tests. On a basis of absorbed plastic energy, both materials investigated have the same fatigue resistance at about 10,000 cycles at failure.