PSI - Issue 76

Christina Mamagkinidou et al. / Procedia Structural Integrity 76 (2026) 82–88

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1. Introduction The significance of residual stresses for the fatigue strength of a material lies in their ability to linearly superimpose with applied cyclic stresses. Processes like shot peening, surface rolling, or case hardening intentionally induce near surface compressive residual stresses, which significantly enhances fatigue life by retarding surface crack initiation and growth. Adversely, tensile residual stresses increase the effective maximum and minimum stresses, accelerating fatigue crack initiation and propagation. The latter are often present in the sub-surface and, therefore, affect the very high cycle fatigue (VHCF) properties. While the influence of surface and sub-surface residual stresses has been the subject of numerous fatigue studies, investigations focusing on the effect of through-thickness residual stress profiles in cyclically loaded steel sheet components are – to the authors’ knowledge – limited. The present study is a continuation of a prior work that has been reported by Khatammanesh et al . (2025) in the current proceedings. It is based on VHCF investigations conducted with a precipitation-hardened martensitic stainless steel sheet with a thickness of 1.8 mm. S-N test results obtained with this material are shown in Fig. 1(a).

Fig. 1. (a) S-N test results and (b) stress intensity factor range normalised by the size-dependent threshold, Δ K / Δ K th vs. number of cycles to failure, N f , for a precipitation-hardened martensitic stainless steel sheet. (according to Khatammanesh et al., 2025)

Based on a fracture-mechanics evaluation of these test results, Khatammanesh et al. (2025) hypothesised that compressive surface and interior tensile residual stresses significantly affect the fatigue strength of the investigated steel sheet. This can be deduced from the normalised lifetime curve shown in Fig. 1(b) as follows. In this graph, the stress intensity factor ranges, Δ K , calculated for all crack-initiating inclusions, are normalised by the size-dependent threshold, Δ K th , which has been predicted according to the well-established √ area -parameter model proposed by Murakami and Endo (1986). This model considers only the size of the crack-initiating defect and the Vickers hardness of the material, and typically exhibits an accuracy of 10 – 20 %. Without a correction for mean stresses, the original prediction equation can only be applicable to fully-reversed tension-compression loading. As shown in Fig. 1(b), the √ area -parameter model leads to highly non-conservative predictions in the VHCF regime. Failure was observed even at Δ K / Δ K th = 0.70, i.e., 30 % below the predicted threshold. Furthermore, all surface failures – represented by open symbols in Fig. 1(b) – occurred at Δ K / Δ K th -values above 1.28. Thus, both the predicted threshold values for surface and interior failure must be considered as inaccurate. For a more detailed analysis of the fatigue properties of this and similar steel sheet materials, the reader is referred to Khatammanesh et al. (2025). In the present study, residual stresses were measured with X-ray diffraction by incremental surface layer removal. The impact of mathematical correction for as-measured residual stress profiles is evaluated. Furthermore,