| The development of modern society is inseparable from a large number of mechanical equipment and various bearing structures,and 80% of the failure of these structures is caused by fatigue.With the development of science and technology,mechanical equipment and structure bear more and more complex load,the working environment is more and more severe,multi-axis high cycle fatigue failure has become the main form of mechanical failure,to the operation of machinery brings significant safety risks,seriously threatening the production safety.At the same time,under the action of multi-axis non-proportional load,the fatigue damage of materials generally has additional strengthening behavior,which brings difficulties to the study of multi-axis high-cycle fatigue.Therefore,it is of great significance for social security and economic development to study the multi-axis highcycle fatigue damage of materials under non-proportional loading.First,starting from the basic theory of damage mechanics and irreversible thermodynamics,the damage evolution equation discussed by uniaxial loading situation spread to the equivalent conditions of multiaxial loading conditions,namely: when the multiaxial loading situation,if the elastic strain energy density of materials and under the condition of uniaxial loading in the whole process of loading are equal,then the two kinds of material damage evolution process of equivalent load conditions.Second,starting from the principle of metallography unconstrained additional reinforcement effect is discussed of metallography mechanism,in order to consider the effect of non proportional loading paths on fatigue life,based on double shear unified yield criterion,is established considering the additional reinforcement effect of the equivalent shear stress amplitude ratio model,boundary conditions and consider the equivalent of fatigue limit,the equivalent shear stress amplitude converted into equivalent normal stress amplitude,into the fatigue life prediction model to describe the unconstrained degrees of multiaxial loading effects on high cycle fatigue life.Third,the general damage evolution equation Lemaitre t combined with micro plastic constitutive relation,the fatigue life prediction model for uniaxial tension and compression load and extend up to axial load,using the equivalent shear stress amplitude after conversion into model,got to consider the proportion of additional reinforcement effect of multiaxial high cycle fatigue life prediction model.The parameter acquisition method in the model is also described.Finally,by citing the high cycle fatigue test data of LY12 CZ strengthened aluminum alloy and SM45 C carbon structural steel in the literature,the material parameters of the two materials in the fatigue life prediction model established in this paper were calculated respectively.In order to prove the progressiveness of the fatigue life prediction model established in this paper,the computer program is written with Visual Basic language,including the fatigue life prediction model established in this paper and three other comparative models.For fatigue life prediction is used to calculate program for each model to strengthen the LY12 CZ aluminium alloy and SM45 C carbon structural steel two kinds of material fatigue life prediction,by contrast,found that the fatigue life prediction model is established for the nonproportional loading of multiaxial high cycle fatigue life prediction compared to other models more accurate,stable,more suitable for the material of nonproportional multiaxial high cycle fatigue life prediction.The model can be applied to a wider range of materials due to the characteristics of the unified yield criterion of double shear. |
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