Mean Stress Effects in Multiaxial Fatigue

Abstract

A multiaxial fatigue strain energy density parameter has been formulated which normalizes fatigue data obtained under a variety of mean stress levels and loading combinations. This parameter represents that proportion of the overall strain energy contributed by the stresses and strains on the critical or fracture plane. It is shown that multiaxial fatigue life data may be accurately correlated by applying this parameter to the experimental results of Inconel 718 alloy subjected to a variety of mean normal and shear stress levels, as well as to SAE 1045 steel tested under tension, torsion and simultaneous tension and torsion. NOMENCLATURE k, K = material constants Nf = number of cycles to failure or to the initiation of a 1.0 mm crack n', K' = cyclic strain hardening exponent and strength coefficient respectively R,, = average radius of a thin wall tube t = wall thickness of a thin wall tube W * = multiaxial fatigue strain energy density parameter y* = multiaxial fatigue parameter Sl = amplitude of shear strain component in the critical plane AP = axial load range S, = yield stress AT= torsion moment range AW =elastic strain energy density AWP = plastic strain energy density Ay,, = shear strain range in the critical plane Ae2, = normal strain range in the critical plane Aa,, = shear stress range in the critical plane Aa,, = normal stress range in the critical plane 4 ; = strain components in fixed coordinate system co-axial with the specimen axis E:, = amplitude of normal strain component in the critical plane v , , = effective Poisson's ratio cri. = stress components associated with the critical plane 4 = stress components in fixed coordinate system co-axial with the specimen axis vc, vp = elastic and plastic Poisson's ratios respectively =maximum absolute value of shear stress in the critical plane =maximum value of normal stress in the critical plane e2 = amplitude of normal stress component in the critical plane 6, = amplitude of shear stress component in the critical plane a; = axial cyclic fatigue strength coefficient r; = torsional cyclic fatigue strength coefficient

Ermüdungsfestigkeit

“…Nach Glinka et al [316] kann DW Ã als Versagenskriterium durch folgende einfachere Beziehung ausgedrückt werden, die nur noch die Scherenergie mit einer Mittelspannungskorrektur enthält:…”

A modification of Smith–Watson–Topper damage parameter for fatigue life prediction under non‐proportional loading

“…Therefore, it is inconvenient to use Jiang's model for multiaxial fatigue life prediction. 2 Glinka et al 23 noted that Chu's model may ignore the effect of a static mean stress in the case of non-proportional loading when the normal strain range is zero. And then the SWT parameter was modified by including the shear strain energy density.…”

“…Chen et al (CXH) 18 reported that the contribution of the shear components to damage is significant on the maximum principal strain range plane under the circular path. 23 In this model, Glinka et al 23 considered that the normal mean stress will assist in the opening of a crack and shear mean stress will help to overcome sliding friction by deforming asperities on the crack surface. Garud 19 reported that the normal and shear strain energy should be with different contributions to fatigue life.…”

“…The physical basis of Chu's model attempts to average the contribution from tensile and shear stresses and strains. 2 Glinka et al 23 noted that Chu's model may ignore the effect of a static mean stress in the case of non-proportional loading when the normal strain range is zero. They consider only the shear work and add a mean stress correction similar to the Morrow mean stress model to account for crack surface sliding and opening.…”

“…They consider only the shear work and add a mean stress correction similar to the Morrow mean stress model to account for crack surface sliding and opening. 23 In this model, Glinka et al 23 considered that the normal mean stress will assist in the opening of a crack and shear mean stress will help to overcome sliding friction by deforming asperities on the crack surface. However, Sines and Ohgi 24 reported that shear mean stress has been shown to have little effect on fatigue strength.…”