Applying Infrared Thermography Ot Study Stress Concentration Factor Of AZ31B Magniesium Alloy

In the21st century, as a lightweight alloy, high-strength structural materials,the magnesium alloy has been used in building structures, rail transportation,defense equipment. Because magnesium alloy components is always subjectedin alternating load, so the study of the fatigue properties of magnesium alloy isof great importance. The initiation of fatigue crack occurred in the region ofstress concentration, so the determination and monitoring of the region of stressconcentration are beneficial to its security service.In this paper, infrared thermography method was applied in stress controltensile test, and the specimens were made of AZ31B magnesium alloy whichwere double V-notch, infrared thermal data were analyzed to obtain the stressconcentration factor, and the results were compared with that obtained by straingauges and FEM, aiming that whether the infrared thermography method wassuitable for the determination of stress concentration of magnesium alloy.Infrared thermography method was also used in the determination of thetemperature evolution in fatigue process of AZ31B base metal and doubleV-notch specimen, the results were compared. The results showed that: stress concentration factor obtained by infraredthermography method was2.14, and the other results obtained by resistancestrain gauges, FEM simulation, fatigue notch coefficient methods wererespectively1.78,2.20,2.29, compared those results with the result obtainedinfrared thermography method, errors were respectively16.8%,2.8%,7.0%.The temperature decline in the region of stress concentration measured byinfrared thermography method is-0.36K; and without considering the thermalconductivity, the result of FEM is-0.37K, taking the thermal conductivity intoconsideration, the result is-0.20K, and the errors compared with infraredthermography method were respectively2.8%and44.4%, it is obvious that theprevious one has a good agreement with infrared thermography method.The results of fatigue test showed that when the fatigue loading is greaterthan the fatigue limit, the temperature evolution of magnesium alloy undergoesfive stages: plastic temperature rise stage,temperature decrease stage,temperature stabilizedstage, a rapid temperature increase stage, temperaturedecrease stage after failure. When the fatigue loading is greater than the cyclicelastic limit and smallerthan the fatigue limit, the temperature rise wasunapparent. When the loading is smaller than the cyclic elastic limit, thetemperature of the specimenwoulddecrease obviously. By contrast, the notchedspecimensof the magnesium alloy subjected fatigue fracture, when the loading isgreater than the fatigue limit, the temperature evolution undergoes three stages:a temperature rise stage, a rapidtemperature rise stage, a temperature decrease stage. When the loading is greater than the elastic limit, the temperatureevolution undergoes three stages:a slight temperature increasestage, a rapidtemperatureincrease stage, a temperature decreasestage. When the loading issmaller than the cyclic elastic limit, the temperature evolution undergoes threestages three stages: a slight temperature decreasestage, a rapidtemperatureincrease stage, a temperature decreasestage. Temperature evolutioncan be applied to monitor the safety of magnesium alloy components.