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A B S T R A C TThe effects of shot-peening intensity on fretting fatigue crack-initiation behaviour of titanium alloy, Ti-6Al-4V, were investigated. Three intensities, 4A, 7A and 10A with 100% surface coverage, were employed. The contact geometry involved a cylinder-on-flat configuration. Residual stress and improvement in fretting fatigue life were directly related to shot-peening intensity. The magnitude of compensatory tensile stress and its location away from the contact surface increased with increasing intensity. The relaxation of residual stress occurred during fretting fatigue which increased with increasing the number of cycles. An analysis using a critical plane-based fatigue crack-initiation model showed that stress relaxation during the fretting fatigue affects life and location of crack initiation. Greater relaxation of the residual stress caused greater reduction of fatigue life and shifted the location of crack initiation from inside towards the contact surface. Modified shear stress range (MSSR) parameter was able to predict fretting fatigue crack-initiation location, which agreed with the experimental counterparts. Also, the computed parameter showed an appropriate trend with the experimental observations of the measured fretting fatigue life based on the shot-peening intensity. a = half-width of a contact zone m = coefficient N = number of cycles N f = fatigue life s 11 = normalized longitudinal normal stress s 22 = normalized transverse normal stress s 12 = normalized shear stress S 11 = longitudinal normal stresses S 22 = transverse normal stress S 12 = shear stress S 12 max = shear stresses due to the maximum applied axial force S 12 min = shear stresses due to the minimum applied axial force S b max = maximum applied force of fatigue cycle S b min = minimum applied forces of fatigue cycle Correspondence: S. Mall.

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Recently, it has been shown that shot-peened nickel-base superalloys exhibit an approximately 1% increase in apparent eddy current conductivity at high inspection frequencies, which can be exploited for nondestructive subsurface residual stress assessment. Unfortunately, microstructural inhomogeneity in certain as-forged and precipitation hardened nickel-base superalloys, like Waspaloy, can lead to significantly larger electrical conductivity variations of as much as 4-6%. This intrinsic conductivity variation adversely affects the accuracy of residual stress evaluation in shot-peened and subsequently thermalrelaxed specimens, but does not completely prevent it. Experimental results are presented to demonstrate that the conductivity variation resulting from volumetric inhomogeneities in as-forged engine alloys do not display significant frequency dependence. This characteristic independence of frequency can be exploited to distinguish these inhomogeneities from nearsurface residual stress and cold work effects caused by surface treatment, which, in contrast, are strongly frequency-dependent.