Abstract
This work investigates the axial-torsional fatigue and cyclic deformation behaviour of 304L stainless steel at room temperature. Four fully reversed strain-controlled loading paths (axial, torsional, proportional axial-torsional, and 90º out-of-phase axial-torsional) and a fully-reversed shear strain-controlled with static axial stress loading were investigated. For axial, torsional, torsional with static stress and few proportional experiments, an initial cyclic softening was followed by secondary hardening related to martensitic transformation. Secondary hardening was not observed for non-proportional loading nor for some proportional experiments. The influence of the non-stabilized cyclic deformation behaviour on the fatigue life estimates of two multiaxial critical plane fatigue models (Smith–Watson–Topper and Fatemi–Socie) was investigated. Life estimates based on the stress-strain hysteresis loops corresponding to the maximum softening and to the half-life were similar for the two models.
Highlights
Stainless steels are used in a wide range of industrial applications that usually involve cyclic multiaxial loading, such as nuclear reactors, pipelines, and pressure vessels
The influence secondary hardening on fatigue life estimates have been addressed by few works: Vincent and co-workers [3] observed that fatigue life estimates calculated using the hysteresis loop at the minimum stress amplitude were significantly better than those obtained from the half-life loop
To investigate the cyclic hardening and softening behaviour of the 304L stainless steel, the variation of the equivalent stress amplitude, σawith number of loading cycles is plotted in Fig. 3 for the investigated loading conditions
Summary
Stainless steels are used in a wide range of industrial applications that usually involve cyclic multiaxial loading, such as nuclear reactors, pipelines, and pressure vessels. Stainless steels may undergo martensitic transformation induced by plastic strain during cyclic loading at room temperature [1,2]. Under strain-controlled loading conditions, this phase transformation may lead to an increase in the stress amplitude throughout the loading cycles, known as secondary hardening. The influence secondary hardening on fatigue life estimates have been addressed by few works: Vincent and co-workers [3] observed that fatigue life estimates calculated using the hysteresis loop at the minimum stress amplitude (i.e. the maximum softening cycle) were significantly better than those obtained from the half-life loop. This work is an experimental investigation of secondary hardening and of the fatigue behaviour of the 304L stainless steel at room temperature under axial-torsional loading. The usual fatigue analysis based on the half-life hysteresis loop was compared with the one based on the maximum softening cycle for two multiaxial critical plane fatigue models (Smith–Watson–Topper [4,5] and Fatemi–Socie [6])
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