2019 Volume 2019 Issue 64 Pages 89-94
Positron annihilation spectroscopy was applied on the spring steel SUP10 specimens which had been subjected to a certain number of fatigue loading cycles by four-point rotary bending fatigue testing to investigate the applicability for evaluating fatigue damage. First, fatigue tests were conducted to obtain the S-N diagram. The fatigue limit σw of the material was 550 MPa. Then additional fatigue tests were conducted at two different stress amplitude σa levels, σa = 650 MPa and σa = 550 MPa using specimens with a shallow notch the radius of which was 1 mm. The fatigue tests were periodically terminated, the surface of the specimen was observed to investigate whether fatigue cracks initiated and to measure the crack length, and positron annihilation spectroscopy was conducted by means of the positron lifetime analysis and the line-shape analysis to calculate the positron lifetime and the S-parameter, respectively. Before fatigue crack initiation, positron lifetime and S-parameter did not exhibit large change or even decreased in some occasions. However after fatigue crack initiation, the both parameters tend to increase monotonically, which indicates that positron annihilation spectroscopy could evaluate fatigue damage in SUP10.
