Fatigue Life Prediction Of Metal Under Multiaxial Nonproportional Loading

The majority of the loading acted on the components of engineering structure in service aremultiaxial. Although there have got some progress in domestic and international research onmultiaxial fatigue, but because of the complexity of multiaxial fatigue itself, the current theoreticaland experimental research is still immature. Therefore, a systematic study on the multiaxial fatiguelife prediction methods has important theoretical significance and engineering application value.The fatigue life of the metal will be shorter under multiaxial loading than axial loading of thesame equivalent stress(strain) amplitude. The degree of the fatigue life reduction is influenced by thematerial dctility, the stress(strain) amplitude and the stress(strain) path. The three influencing factorsare analyzed in detail, and an additional hardening degree is defined. This factor has good relationwith the reduction degree of the fatigue life under multiaxial loading and axial loading for manymaterials, many loading paths and both the low cycle fatigue life and high fatigue life phases.Combined the additional hardening degree and the Ramberg-Osgood model, a new constitutivemodel is proposed. The new model is checked against the experimental data of45steel, and the resultis satisfactory.Based on the macro-integral method, a new multiaxial high-cycle fatigue criterion is proposed.The proposed criterion corrects the mean stress effect and extends the applicable range for moremetals. The capability of fatigue life prediction for the proposed model was checked against fourmetals, and the predicted results are compared with results from five common multiaxial high-cyclefatigue models. It is demonstrated that the predicted results of the proposed criterion show goodagreement with experimental results.Finally, the multiaxial low-cycle fatigue life prediction models are summarised and analyzed.Considering the additional hardening effect of the multiaxial loading, a critical plane method isproposed. The new method is checked against the experimental data of45steel and1045steel, andthe result is satisfactory.