Fatigue damage of AISI 304 LN stainless steel: Role of mean stress

Abstract This investigation examines the influence of varied combinations of mean stress (V m ) and alternating stress (V a ) on strain accumulation during fatigue tests and the resultant in-situ microstructural and substructural variations of AISI 304 LN stainle ss steel. Stress-controlled fatigue tests have been carried out at 300 K using positive, zero, and negative mean stress conditions,supplemented by microstructural and substructural analyses using TEM and XRD. The results highlight that the characteristics ofstrain accumulation in the selected steel is governed by the magnitude of V m and V a , apart from considerable dependence on in-situ formation of deformation induced martensite and substructural changes. Keywords: Mean stress; stress amplitude; strain accumulation; deformation induced martensite; AISI 304LN stainless steel. 1. Introduction The damage of structural components under cyclic loading is a century-old well known engineering problem but significant emphasis is still being laid on this domain of research. Cyclic loading behaviour of structural materials is commonly dealt with low cycle fatigue (LCF), high cycle fatigue (HCF) and fatigue crack growth rate (FCGR). One of the current problems related to LCF is to understand the influence of symmetric (mean stress = 0) vis-a-vis asymmetric (mean stress 0) loading conditions. The primary driving force to achieve this understanding is: imposition of asymmetric stress cycle leads to enhanced strain accumulation in an engineering component [1-3]. Accumulation of this type of addition al plastic strain decreases fatigue life [4, 5] and limits the predictive capability of the Coffin-Manson relation [6]. This is one of the serious issues in critical engineering structures such as in nuclear power plants, since the accumulated plastic strain governs the life of engineering components subjected to LCF. Thus one should critically examine the influence of strain accumulation in engineering components in order to safe guard these against both symmetric and asymmetric loading conditions. Literature pertinent to this discipline provides information related to strain accumulation behaviour under uniaxial or multiaxial loading conditions for cyclic hardening and cyclic soften ing type metallic materials [7-9]; but the existing information and the generated knowledge is still insufficient to crystallize our concepts to make comparative assessment of strain accumulation

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