Fatigue Damage Detection and Micromechanism Analysis of 30CrMnSiA Materials Using Laser
Gou Wenxuan, Lu Zhixian, Wang Anqiang
(Department of Engineering Mechanics, Northwestern Polytechnical University, Xi'an 710072£©

Abstract: ln this paper, the authors make use of a physical quantity, the intensity ratio K of laser diffraction spectrum, directly connected with surface roughness of metals, and define a fatigue damage parameter D(K). The detection of tension-tension non-s ymmetry fatigue damage of 30CrMnSiA is proceeded, the results of the test show the method is reliable. Moreover, the micromechanism of fatigue damage in different fatigue cycles is investigated by the use of the scaninge letron microscope. Analysis of the test results gives: (1) Theintensity ratio K of laser diffraction spectrum is sensitive to fatigue damage of metal materials, especial at the beginning of fatigue. The method needs non-contact, non-damage, simple equipment and convenient measurements.
(2) The curve relating N to D(K) can be divided into three regions, decelerated( AB region), linear (BC region) and accelerated (CD region). 90% of the life belong to the decelerated and linear regions. (3) The metallographic observation indicates that the variation of intensity ratio K is result from the surface roughening. The AB region is correspond to strain adjustment region which slip bands appear and reach the saturation state. In the BC region, the microcrack and microvoid are initiated, propagated and got together. The CD region is the region which cracks growth and intensity ratio reductoin are raped, and so the fatigue damage happens. (4) Compare with two kinds of specimens, the mechanic properties (including fati gue life) of the specimen which axis is parallel to the rolling direction (T) are better than that which axis is perpendicular to the rolling direction (L).
Keywords: diffraction intensity ratio, fatigue damage, damage variable.