A series of multiaxial low-cycle fatigue experiments was performed on 45 steel under non-proportional loading. The present evaluations of multiaxial low-cycle fatigue life were systematically analysed. A combined energy density and critical plane concept is proposed that considers different failure mechanisms for a shear-type failure and a tensile-type failure, and from which different damage parameters for the critical plane-strain energy density are proposed. For tensile-type failures in material 45 steel and shear-type failures in material 42CrMo steel, the new damage parameters permit a good prediction for multiaxial low-cycle fatigue failure under non-proportional loading. The currently used critical plane models are a special and simple form of the new model.

A critical plane-strain energy density criterion for multiaxial low-cycle fatigue life under non-proportional loading

Multiaxial fatigue life prediction for various metallic materials based on the critical plane approach

Simulation of cyclic stress/strain evolutions for multiaxial fatigue life prediction

The fatigue behaviour of base metal and weld joints of 1Cr-18Ni-9Ti stainless steel has been studied under uniaxial, torsional and 90° out-of-phase loading. A significant degree of additional hardening is found for both base metal and weld metal under 90° out-of-phase loading. Both base metal and weld metal have the same cyclic stable stress-strain relationship under torsional cyclic loading and 90° out-of-phase cyclic loading. Base metal exhibits higher cyclic stress than weld metal under uniaxial loading, and Young's modulus and yield stress of weld metal are smaller than those of base metal. Weld metal exhibited lower fatigue resistance than base metal under uniaxial and torsional loading, but no significant difference was found between the two materials under 90° out-of-phase loading. A large scatter of fatigue life is observed for weld metal, perhaps because of heterogeneity of the microstructure. The Wang-Brown (WB) damage parameter and the Fatemi-Socie (FS) damage parameter, both based on the shear critical plane approach, were evaluated relative to the fatigue data obtained.

Low-cycle fatigue of 1Cr–18Ni–9Ti stainless steel and related weld metal under axial, torsional and 90° out-of-phase loading

Lifetime estimation in the low/medium-cycle regime using the Carpinteri–Spagnoli multiaxial fatigue criterion

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A series of strain-controlled, low-cycle fatigue experiments have been conducted on 42CrMo steel under various loading paths including circular, square, cruciform, and rectangular paths Present experiments have shown that there is additional hardening under non-proportional cyclic loading Non-proportional cyclic additional hardening also results in a shorter life for multiaxial low cycle fatigue A non-proportionality measure of strain path based on both a physical basis and macromechanical phenomena is proposed The loading path effect on additional hardening is also described well Low-cycle fatigue damage accumulation and the evolution process under non-proportional loading is analysed via the Continuum Damage Mechanics Model of Chaboche A non-proportinality measure is introduced in the damage evolution equation and a modified Coffin-Manson type formula is derived A novel fatigue life prediction approach based on the critical-plane concept of Brown and Miller is proposed

Q. Gao

Papers

Low‐cycle fatigue under non‐proportional loading