Research On Multiaxial Fatigue Life Prediction Based On Critical Plane Energy Method

The geometrical discontinuity in parts is often due to actual engineering requirements,resulting in stress concentration and the notch tip partially serving under multiaxial stress conditions,such as grooves,keys,holes,joints and other irregular structures.The uniaxial fatigue problem is relatively simple,so great results have been achieved in both theoretical and experimental research.Since the multiaxial fatigue problem is particularly complicated,there is still no research method or fatigue life prediction model that can be accepted by everyone,and,actual engineering components are mostly served under multiaxial stress,therefore,for multiaxial fatigue researchers,how to accurately predict multiaxial fatigue life still needs more indepth research.In this thesis,the axial notched members are taken as the research objects,fatigue damage mechanism and life prediction method of multiaxis notch members are analyzed by theoretical derivation,numerical Analysis and multiaxial notch fatigue test data verification.The main research contents are as follows:(1)A method for determining the critical surface of a notched member is proposed.Physical modeling of notched members is modeled in ANSYS,define the constraints and load modes of the physical model,the stress-strain state at the notch tip is calculated,and the plastic strain energy density is defined as the damage parameter.The plane where the maximum strain energy density is calculated by the coordinate transformation matrix is the critical plane.(2)Based on the energy method,with the energy parameter on the critical surface as the damage parameter,used the critical plane concept,a multiaxial fatigue life estimation model for brittle and plastic materials was proposed.The model can automatically change the critical plane direction according to different materials and stress states.At the same time,with the help of the Mroz-Garud hardening criterion,the effect of non-proportional additional reinforcement is explicitly considered,which overcomes the shortcoming of previous models that only use strain terms and cannot consider non-proportional additional reinforcement effect.(3)Multiaxial nonlinear fatigue life prediction model is proposed based on the damage mechanics-critical surface method.This model considers the contribution of shear strain and normal stress on the critical surface to crack initiation and propagation,and also considers the non-proportional additional strengthening effect on fatigue.The effect of life,and the model is suitable for proportional/non-proportional,symmetrical/asymmetric loads.After experimental verification,the prediction results of this model are consistent with the experimental results.