Multiaxial ratchetting–fatigue interactions of annealed and tempered 42CrMo steels: Experimental observations

The multiaxial ratchetting and low-cycle fatigue failure behaviour, i.e., the multiaxial ratchetting–fatigue interactions of annealed and tempered 42CrMo steels were experimentally observed under the proportionally and non-proportionally multiaxial stress-controlled (and strain-controlled) cyclic loading tests. The multiaxial whole-life ratchetting behaviour and fatigue lives of the steels were obtained in the multiaxial stress cycling tests with different stress levels and loading paths. The effects of mean stress, stress amplitude and loading path on the multiaxial whole-life ratchetting and failure life of the steels were discussed. Some low-cycle fatigue tests were carried out under the strain-controlled cyclic loading. The experimental results show that the multiaxial whole-life ratchetting and fatigue failure behaviour of the annealed 42CrMo steel are different from those of the tempered steel due to their different cyclic softening/hardening features. Two kinds of failure modes (i.e., ductile ratchetting failure and brittle low-cycle fatigue failure) occur in the 42CrMo steels, depending on the stress level and resultant value of final ratchetting strain. The evolution of multiaxial ratchetting is greatly dependent on the proportional and non-proportional loading paths. The failure life in the multiaxial stress cycling is apparently shorter than that in the uniaxial case, and depends on the shapes of multiaxial loading paths. The fatigue damage caused by the cyclic loading accelerates the evolution of multiaxial ratchetting, especially at the end stage of cyclic loading; the multiaxial ratchetting produced in the stress cycling shortens the failure life of the steels apparently.