Uniaxial-multiaxial Fatigue And Life Assessment Of Metallic Materials Based On Energy Dissipation Method

In engineering practice,fatigue failure is one of the most important forms of failure.Moreover,fatigue failures are often accompanied by obvious signs,but they can lead to catastrophic consequences and huge economic losses.In recent years,fatigue failure has also received more and more attention.Fatigue failure often occurs in a local hazardous area in a part or structure,where local stress or plastic strain is above the fatigue limit.In the process of fatigue,the plastic strain occurring in these local areas is accompanied by the generation of heat dissipation,which will lead to an increase in the surface temperature of the part or structurerelated area.The surface temperature of the object can be obtained by the instrument.The infrared thermal imaging method takes temperature as a damage parameter for damage assessment,which has been well developed in recent years.Different from the traditional damage parameters based on stress and strain,it has the advantages of non-destructive,real-time and non-contact.However,since the surface temperature distribution of the object is affected by heat conduction,heat exchange,etc.,it is inaccurate to directly use temperature as the damage parameter to characterize the fatigue damage state.In this paper,the inherent dissipative energy is used instead of temperature as the damage parameter,which can consider the effect of heat conduction and heat,thus for more accurate characterization of damage status.In this paper,the rapid evaluation method of fatigue strength and life based on infrared thermal imaging is studied.The main contents are as follows:(1)Overview of the theoretical basis of infrared thermography.In this part,firstly,the thermodynamic theorem related to fatigue is introduced,and the heat conduction equation for calculating the dissipated energy in the fatigue process is obtained.Then introduces the principle of infrared thermal imaging,and finally gives the calculation method of dissipative energy based on infrared thermal image data.(2)Rapid evaluation method of fatigue strength.Firstly,an experimental system for rapid evaluation of fatigue strength is introduced,which includes an ultrasonic fatigue test system for fatigue test and an infrared thermal imager for temperature acquisition,and then an experiment was conducted on a pure copper material.Secondly,a fast prediction method of fatigue strength is proposed.The prediction ability is verified by experiments and compared with the traditional Risitano method and Luong method.The results show that the proposed method has the advantages of simplicity,fast prediction and high precision.(3)Rapid prediction method for fatigue life.Firstly,a quantitative thermal imaging method based on dissipated energy is introduced,which can realize fast and high-precision life prediction in the field of uniaxial fatigue.This paper attempts to apply it to the multiaxial fatigue field including multiple load paths,and quickly predicts the fatigue life under each path.Verification by citing multiaxial fatigue data from a set of papers,the prediction result shows that the quantitative thermal imaging method after considering the energy tolerance associated with the path has a slightly better life prediction than the Fatemi-Socie life prediction model.