Study On Fatigue Life Of Metal Materials Based On Nonlinear Cumulative Damage Theory

With the progress of modern industry and technology,industrial equipment is developing towards large-scale and complex.The service environment of key components of many mechanical equipment is also getting worse,resulting in frequent fatigue failure accidents of various components.Fatigue damage is characterized by strong suddenness and concealment.Components are difficult to detect before damage,which brings great hidden dangers to the normal operation of equipment.Once damaged,it is easy to cause major safety accidents,which poses a great threat to people’s lives and property.The fatigue life of mechanical equipment components is a key factor that restricts the life and reliability of the whole machine.Therefore,accurate and reliable prediction model and life prediction method is an important guarantee for the stable operation of engineering equipment in the service period.It is of great significance to reasonably formulate equipment maintenance decision,give full play to the maximum use value of equipment,save cost and improve economic efficiency.The fatigue failure process has the characteristics of complexity and randomness.The traditional fatigue theory and life prediction method cannot explain the fatigue failure thoroughly,and there are still many deficiencies and unresolved problems.Therefore,based on nonlinear fatigue cumulative damage theory,a series of exploratory research work has been carried out in fatigue damage failure theory model construction,fatigue life prediction method and fatigue simulation.The main research contents and results are as follows:(1)From the perspective of residual fatigue life of materials,considering the influence of load interaction and introducing correction parameters,an improved nonlinear fatigue cumulative damage model with load interaction effect is proposed based on S-N curve.The classical fatigue test data of three common materials were used to verify the improved model,and the prediction results were compared with Miner criterion and Zhu Shunpeng’s model to verify the effectiveness and accuracy of the improved model.(2)Combined with the characteristics of Ye Duyi’s model and its related improved model,starting from the common points of its existence,the parameter k of load interaction influence factor is introduced,and the generalized expression based on Ye’s model is proposed.This formula can realize the conversion between several different models by changing the value of parameter k,and the Ye’s related model is expressed in a unified form.The new improved model with parameter k value of 3 was compared with four existing Ye’s related models under two-stage load and multi-stage load.It was found that the prediction accuracy of fatigue life prediction model for different materials was related to parameter k.(3)A new fatigue life prediction method is proposed based on the generalized expression.The fatigue test data of four kinds of commonly used classical metals such as 45 steel were used to verify the new method from two aspects of two-stage load and multi-stage load,and the results were compared with those of the Ye’s model and its related models.The results show that the new fatigue life prediction method further improves the fatigue life prediction accuracy on the basis of the original model.(4)In this paper,the stress fatigue life simulation commonly used in engineering is discussed and briefly analyzed.The problems and shortcomings of fatigue simulation are pointed out,and the research direction of fatigue simulation software on nonlinear fatigue cumulative damage theory is clarified.