Prediction Method Based On Damage Mechanics For Multiaxial High Cycle Fatigue Life

Fatigue failure and life prediction of components have become an important subject in industrial areas, which relate to the safe operation of mechanical equipment and whether can give full play to the potential of material strength. With the demand of long lifetime for mechanical components and complexity of the component service environment, most of failure destruction of components gradually transform to the form of multiaxial high cycle fatigue damage. Therefore, it is critical for anti-fatigue design of modern component to establish a high-precision life prediction model of multiaxial high cycle fatigue.For fatigue damage of multiaxial non-proportional loading, materials generally have characteristics of additional intensive behavior. In this paper, based on method of modified micro-plastic circulation coefficient to investigate the influence of non-proportional loading on fatigue life of material and establish a high cycle fatigue damage evolution model combining with continuum damage mechanics, and then verify the validity of new model to predict fatigue form with fatigue test results.Firstly, the basic constraints are derived based on basic theory of thermodynamics and continuum damage mechanics, which are satisfied when extending uniaxial high cycle fatigue damage evolution model to the multiaxial loading conditions. The derived results indicate that elastic strain energy at any time equals to a uniaxial load in the case of multiaxial loading. At this point, the fatigue damage process are equivalent.Secondly, more material slip system is actuated in the case of multiaxial loads, the interaction between slip systems makes the material a non-proportional and additional hardening behavior. Since the constitutive relation of material under cyclic loads is closely related to dislocation glide configuration, additional hardening behavior of the material affects its cyclic stress-strain response. This paper presents micro plastic constitutive relations based on the modified micro-plasitc cyclic strength method.Thirdly, substitute the proposed micro-plastic constitutive relation into general sense Lemaitre damage evolution equation, and then establish incremental describes formultiaxial high cycle fatigue damage evolution model considering non-proportional and additional strengthening effect. In order to facilitate the calculation of damage accumulation, rewrite damage evolution model under incremental describes into N description according to the equivalent condition of fatigue damage processes.Considering that there are many material parameters in damage evolution model, the material parameter identification method of model is given according to theoretical S-N curve equation and the life prediction closed-form solutions under biaxial symmetry tension-torsion sine wave center loading path given by model in this paper.Finally, take the multiaxial high cycle fatigue test data of Al alloy LY12 CZ and30Cr Mn Si A steel commonly used in aeronautic industry as examples to verify the effectiveness of damage evolution proposed in this paper and the feasibility of material parameters identification method. First, Use the high cycle fatigue test data of two materials in uniaxial and circular loading path to verify material parameters in damage evolution model, and then embed the damage evolution model into the UMAT subroutine in ABAQUS, and realize injury tracking and life prediction for damaged specimens. The calculation results show that the predictive effect of models both in the error of less than 3times, and it is significantly better than model without enhancement, Mcdiamid model and Papadopoulos microscopic integration model.