Study On Rapid Determination For Metallic Material Fatigue Limit Based On The Temperature Distirbution Characteristics

As one kind of new structural materials with great potential, magnesiumalloys often undergo fatigue loading for applications in aerospace industry andother traffic transport structures, which are prone to fatigue failure under cyclicloading. Fatigue failure often occurs at low stress level and has no obviousplastic deformation before the final failure. It is a serious threat for people livesand property, once the fatigue accidents appeared.It is well-known that the mechanical work mainly dissipates as heat duringfatigue evolution, and the temperature rises up at the same time. As reported inmany literatures, the fatigue heating process is closely related to the fatiguedamage process. Thermographic technique can be used to fast detect the real-time temperature variation of object. Therefore, the thermographic technique hasbeen widely applied to investigate the fatigue process of materials andmechanical details.Infrared thermography coupled with a special image processing wasemployed to study the heating process of AZ31B magnesium alloy during thehigh-cycle fatigue process.Heat-conduction effect was subtracted from thermal data provided by aninfrared camera to study the heat-dissipation rate evolutions. Three stages oftemperature variation were observed before the initiation of macroscopic crack,when the stresses were above the fatigue limit and below the yield limit. Severework-hardening effect led to a drastically degradation in plastic deformability, and also caused the heat-dissipation rate dropped steeply from the maximum tothe saturation value.Based on the research of the temperature and heat-dissipation rate evolutionat the center of fatigue specimen. The correlation between temperaturedistribution and stress distribution was also investigated. At different stress level,the temperature distributions in a single sample are different. Finally, animproved graphical method was proposed to estimate with good approximationof the fatigue limit of AZ31B magnesium alloy, as well as446stainless steel,more readily. The proposed method showed basically satisfied results comparingwith the conventional method.