Abstract
Laser used thermal shock fatigue testing method was established. In this test, acoustic emission technique allows detecting the number of cycle to crack initiation. Infrared thermography image monitoring results and computer-aided engineering (CAE) simulation figure out stress and strain distribution during fatigue testing. It was found that the number of cycle to crack initiation was depending on the difference in temperature condition during the test. Damage factor was introduced as a parameter to evaluate the cumulative fatigue damage during the test. Damage factor was defined as a strain-energy of micro region in each cycle test. When cumulative damage factor exceeds critical condition, fatigue crack initiation was observed. The critical condition may be described with equivalent plastic strain. Increasing cooling rate in thermal cycle, induced stress and strain were larger. Accompanying this change is an increasing damage factor, and the fatigue life is shorter. This study suggests a possible beneficial effect of life prediction with damage factor.
