The Effect Of Shot Peening On Strain-controlled Fatigue Behaviours

Author:  Yonghe, Y.
Source:  Conf Proc: ICSP-4, (p.411-418)
Doc ID:  1990086
Year of Publication:  1990
Abstract:  
Material's strain-stress behaviours under strain-controlled loading are examined before and after shot peened. SEM analysis for fatigue fractographies shows, although the beneficial compressive residual stress in surface layer can be induced by shot peening, the fatigue cracks in low-cycle range initiate all from the sample surfaces for both peened and unpeened. The relaxation rates of residual stress increase with strain amplitudes, but some residual stresses can be still retained when the strain amplitude is not large enough. Shot peening makes cyclical deformation resistance increase due to work-hardening. Shot peening has little effect on Bauschinger effect for static but some effect on that for cyclical. The strain-life curves of peening and unpeening cross each other at Nc. The inverse effects of shot peening on the low cycle fatigue lives are illustrated below and over Nc, below Nc, the strain amplitude is larger, shot peening makes fatigue life decrease due to increases of surface hardness and roughness; over Nc, some beneficial residual compressive stress can be retained and favourable to lengthening life, so does average compressive stress induced by Bauschinger effect. Descriptors: Strain-controlled fatigue; Residual stress; Relaxation; Bauschinger effect; Shot peening