Abstract
As the fatigue strength of metallic components may be affected by residual stress variation at small length scales, an evaluation method for studying residual stress at sub-mm scale is needed. The sin2ψ method using X-ray diffraction (XRD) is a common method to measure residual stress. However, this method has a lower limit on length scale. In the present study, a method using at a 2D XRD detector with ω-oscillation is proposed, and the measured residual stress obtained by the 2D method is compared to results obtained from the sin2ψ method and the slitting method. The results show that the 2D method can evaluate residual stress in areas with a diameter of 0.2 mm or less in a stainless steel with average grain size of 7 μm. The 2D method was further applied to assess residual stress in the stainless steel after treatment by laser cavitation peening (LCP). The diameter of the laser spot used for LCP was about 0.5 mm, and the stainless steel was treated with evenly spaced laser spots at 4 pulses/mm2. The 2D method revealed fluctuations of LCP-induced residual stress at sub-mm scale that are consistent with fluctuations in the height of the peened surface.
Highlights
As residual stress is one of the most important factors related to the fatigue strength of metallic materials [1,2,3,4,5,6,7,8], it is worth measuring the residual stress in local areas subject to fatigue crack nucleation
In order to compare the residual stress measured by the slitting method, the sin2 ψ method and the 2D method, Figure 6 illustrates the residual stress σRy of specimen A
In order to compare the residual stress measured by the slitting method, the sin2ψ of 17 method and the 2D method, Figure 6 illustrates the residual stress σRy of specimen A. 7For the sin ψ method and the 2D method, the effect of the measuring area was investigated by changing diameter of the collimator dcol
Summary
As residual stress is one of the most important factors related to the fatigue strength of metallic materials [1,2,3,4,5,6,7,8], it is worth measuring the residual stress in local areas subject to fatigue crack nucleation. It is well known that conventional welding causes tensile residual stress near the welded line due to the heat-affected zone (HAZ) [9,10,11,12]. As the distribution of the residual stress of conventional welding and the FSWed part drastically changes with distance from the welding line, the residual stress of the laser-peened surface is distributed with a laser spot size of the mm-order. As the size of the measured area using X-ray diffraction is similar to that of the distribution of the residual stress of the welding part and/or the laser-peened surface in sub-millimeter order, it is necessary to improve the accuracy of residual stress measurements by using X-ray diffraction. Note that the most important factor of the stresses measurement accuracy in local area using X-ray diffraction is the number of the grains
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