Research On Energy Dissipation And Rapid Evaluation Method For High-Cycle Fatigue Performance Of Metallic Materials

Unexpected disasters and huge economic losses may be caused because of the burstiness of fatigue failure.With the development of modern industry,the demand for fatigue properties of mechanical structures and equipments is increasing.The essence of the fatigue is relatively complex,and the fatigue and damage mechanism of materials still need further research.Therefore,the macro-and-micro mechanism research of fatigue and the evaluation of fatigue performance on materials can provide guarantee for the reliability and safety of mechanical structures,so as to avoid the serious consequences caused by fatigue failure.The disadvantages,such as the very long period,high cost and low efficiency,of the traditional fatigue experiments seriously limit the development of the design process of new materials and structures,during the fatigue performance evaluating.A large number of studies have shown that the fatigue process of materials is essentially an irreversible energy dissipation process accompanied with temperature evolution.According to the evolution of temperature field during the process of material fatigue,not only the mechanism of fatigue damage can be explored based on the essential factor:energy dissipation,but also the fatigue performance parameters of materials can be predicted rapidly.The technical support can be provided for the above research procedure of material fatigue performance due to the nondestructive,real-time and non-contact characteristics of infrared thermal imaging technology during the temperature measurement.Based on the temperature field evolution and energy dissipation theory,the high-cycle fatigue of metals is studied.And a more accurate calculation method of energy dissipation is derived,so as to further improve the theoretical system of infrared thermographic method on rapidly evaluation of the high-cycle fatigue performance.The validity and precision of the method are verified by experiment and numerical simulation,and the fatigue of martensitic stainless steel with different aging treatment is studied to discuss the correlation between fatigue and microstructure of the material.The main works are as follows:(1)Based on the law of energy conservation and entropy increase in continuum thermodynamics and the heat transfer theories,the influence of convection and radiation heat transfer is considered in the thermodynamic coupling model of high-cycle fatigue process of metals,and an improved double exponential function method is proposed to improve the accuracy of energy dissipation measurement.The error sources of several commonly used energy dissipation estimation methods and the present method are compared and analyzed,and the correctness and accuracy of the present method are verified by experiment and simulation.It is found that the heat losses caused by thermal convection(including natural and forced convections)and radiation are relatively large and cannot be ignored directly when estimating the energy dissipation during the high-cycle fatigue of metals.Energy dissipation is the key index for the rapid evaluation of fatigue performance through infrared thermography.Therefore,the improvement of its accuracy is of great significance for the study of fatigue mechanism and for the accurate prediction of fatigue parameters.(2)Due to the fact that the temperature rise can be observed when the stress level is lower than the fatigue limit during the fatigue experiment,the irreversible energy dissipation can be divided into anelastic and inelastic dissipations through whether the fatigue damage is caused.By introducing anelastic and elasto-plastic constitutions,the relationships between energy dissipations and fatigue load are established respectively,and a new rapid evaluation method for high-cycle fatigue performance of metals,including the fatigue limit and three-parameter S-N curve,is proposed.Considering the dispersion of fatigue and combining with the probabilistic statistical theories,a rapid evaluation method for high-cycle fatigue reliability:three-parameter P-S-N curve of metallic materials is developed.The above researches can further improve the theoretical system for rapid evaluation of high-cycle fatigue performance and reliability of metals based on temperature field evolution(3)The fatigue performance parameters of FV520B,a martensite precipitation hardening stainless steels,with three different aging heat treatments are rapidly predicted by infrared thermography,and the relationships between the microstructure and energy dissipation as well as fatigue performance are analyzed by the microstructure and fatigue fracture.The rapid evaluation of fatigue properties can greatly shorten the development process of new materials,and has guiding significance for obtaining the materials heat treatment procedure with an optimal mechanical propertie.