Study On Fatigue Behavior Of Nonferrous Metals Based On Infrared Thermography Method

The infrared thermography method is a new fatigue test method based on dissipation theory.Compared with traditional fatigue testing methods,this method has many advantages such as faster,non-destructive,real-time.At the same time,by studying the relationship between intrinsic dissipation and material microstructure evolution,it is helpful to re-understand the fatigue phenomenon from the perspective of thermodynamics and reveal the metal fatigue mechanism more profoundly.Whether in engineering design or in the research of new materials,the infrared thermography methods have broad application prospects.In this paper,the influence of external heat sources,thermo-elasticity,heat conduction and intrinsic dissipation on the test results was explored.It is found that intrinsic dissipation is the main factor that causes the temperature change of the sample surface.The thermo-elasticity and heat conduction have little effect on the experimental results,and the temperature noise caused by the external heat source has an impact on the results,and measures need to be taken to remove it.The key step of using infrared thermography method to obtain the fatigue limit is to determine the "inflection point" in the temperature rise,Luong method was not clearly specified how to recognize the experimental points below and above the fatigue limit in details.Based on intrinsic dissipation and the fatigue damage mechanism,this paper proposes to use the elastic limit as the border between experimental data below and above the fatigue limit.The fatigue limit of commercially pure titanium is quickly and accurately determined by the use of the above optimized Luong method.Through experiments on aluminum alloys,the applicable of this method was discussed.To made clear the relationship between intrinsic dissipation and microstructure evolution from elastic to plastic,the microstructure of specimen subjected to different stresses loading was observed by the position-tracing method,and the strain evolution was measured by Digital Image Correlation(DIC)technology.The fatigue limit was obtained by using Static Thermographic Method proposed by Risitano,the result was compared with the results of Stair-case method and the optimized Luong method.