Influence of Change of Microstructure and residual stress field in surface Shot Peen Strain Layer on Fatigue Behavior

Author:  Qiu, Q. and Wang, R.
Source:  Conf Proc: ICSP-3, (p.231-238)
Doc ID:  1987047
Year of Publication:  1987
Abstract:  
The microstructure and the residual compressive stress field in the surface shot-peening straining layer are two strengthening factors for improving the fatigue behavior of materials. It was shown that the monotonic yield strength of materials is the main factor effecting the fatigue behavior. But the further study shows that there is a difference between the monotonic yield strength and the cyclic yield strength of materials and the monotonic mechanical property of materials can not represent the slipping property of crystals under the alternating stresses. In shot peening process, the cyclic strain produces in the surface layer and therefore the cyclic hardening/softening in the surface layer would occur, resulting in the change of cyclic property of material. The relationship between the cyclic property and the fatigue behavior of materials has been investigated in this paper. Moreover, the residual stress field (RSF) induced by shot peening (SP) can relax during fatigue. The relaxation of RSF could be divided into the static load relaxation (SLR) at the initial fatigue stage and the dynamic load relaxation (DLR) at the medium and last fatigue stage. The damage of material in the surface layer caused by SLR and the harmful effect of the damage on the fatigue behavior has been investigated also. To avoid SLR, the optimum RSF is discussed.