Life prediction of metals undergoing fatigue load based on temperature evolution

Fatigue failure of metals undergoing cyclic load is evaluated based on the evolution of surface temperature. Aluminum Alloy 6061 and Stainless Steel 304 are selected as testing materials and specimens are subjected to completely reversed torsion load. A thermographic technique is used to measure the temperature increase of the specimen due to hysteresis heating during the fatigue testing. Experimental results indicate that the initial rate of temperature rise as a function of time can be utilized as an index for prediction of fatigue life. An empirical correlation of the form Nf=c1Rθc2 with constants c1 and c2 is derived that relates the rate of temperature rise, Rθ, at the beginning of the test to the number of cycles to failure, Nf. It is shown that c1 is dependent upon the material properties and stress state whilst c2 is a constant. Experimental results are consolidated into a single curve which gives the time to failure as a function of initial slope of temperature rise, thereby enabling fast prediction of fatigue failure.