PSI - Issue 48

V.M.G. Gomes et al. / Procedia Structural Integrity 48 (2023) 142–148 Gomes et al/ Structural Integrity Procedia 00 (2023) 000–000

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Fig. 5. Variation of the surface bending stress throughout testing time for point 1 and 2 using the stress relief method.

3.3. Effect on the Fatigue Limit The effect of shot peening residual stresses and assembling stress on the fatigue limit may be estimated. Taking into account the superposition principle given by equation (2) (Kaiser, 1987):   =  0 + ݊  + 0.33  ݁  (2) where the conventional fatigue limit stress,   0 , is 700 MPa for high-strength steels, 50% of   , and  ݊  , prestress given by the assembling bending level, and the stress shot peening,  ݁  , determined to an average value according to the propagation threshold length,  ℎ , which is determined by the combination of fracture mechanics with the line method of the theory of critical distances such that (Taylor, 2007):  ℎ = 0.5 ∆ ℎ   0 2 (3) Considering the threshold of stress intensity, ∆ ℎ , approximately 9 MPa m (Gubeljak, et al . 2011) results in a propagation threshold length,  ℎ , of the order of 50 μm. Considering  ℎ in the calculation of the average stress results that for point 1, a residual stress of -40 %   and for point 2 a residual stress of -46 %   . Applying equation (3), it is verified that for point 1 there is an increase of around +31.4 %, and for point 2 an increase of +56.4 % in the fatigue limit. Such increases in fatigue resistance due to stress shot peening processes have been found in the literature (Malikoutsakis, et al ., 2021).

Fig. 6. Residual stress profiles obtained using the X-ray diffraction method for point 1 and 2.