Experimental Study on Uniaxial and Multiaxial Strain CyclicCharacteristics and Ratcheting of 316L Stainless Steel

An experimental study was carried out on the strain cyclic characteristics and ratcheting of 316L stainless steel subjected to uniaxial and multiaxial cyclic loading. The strain cyclic characteristics were researched under the strain-controlled uniaxial tension-compression and multiaxial circular paths of loading. The ratcheting tests were conducted for the stress-controlled uniaxial tension-compression and multiaxial circular, rhombic and linear paths of loading with different mean stresses, stress amplitudes and histories. The experiment results show that 316L stainless steel features the cyclic hardening, and its strain cyclic characteristics depend on the strain amplitude and its history apparently. The ratcheting of 316L stainless steel depends greatly on the Values of mean stress, stress amplitude and their histories. In the meantime, the shape of load path and its history also apparently influence the ratcheting.

Fatigue limit assessment of a 6061 aluminum alloy based on infrared thermography and steady ratcheting effect

To quickly predict the fatigue limit of 6061 aluminum alloy,two assessment methods based on the temperature evolution and the steady ratcheting strain difference under cyclic loading,respectively,were proposed.The temperature evolutions during static and cyclic loadings were both measured by infrared thermography.Fatigue tests show that the temperature evolution was closely related to the cyclic loading,and the cyclic loading range can be divided into three sections according to the regular of temperature evolution in different section.The mechanism of temperature evolution under different cyclic loadings was also analyzed due to the thermoelastic,viscous,and thermoplastic effects.Additionally,ratcheting strain under cyclic loading was also measured,and the results show that the evolution of the ratcheting strain under cyclic loading above the fatigue limit undergone three stages:the first increasing stage,the second steady state,and the final abrupt increase stage.The fatigue limit of the 6061 aluminum alloy was quickly estimated based on transition point of linear fitting of temperature increase and the steady value of ratcheting strain difference.Besides,it is feasible and quick of the two methods by the proof of the traditional S-N curve.

Ratcheting behavior of notched stainless steel samples subjected to asymmetric loading cycles

The ratcheting response of 316 stainless steel samples at the vicinity of notch roots under single-and multi-step loading conditions is evaluated.Multi-step tests were conducted to examine local ratcheting at different low–high–high and high–low–low loading sequences.The stress levels over loading steps and their sequences highly influenced ratcheting magnitude and rate.The change of stress level from low to high promoted ratcheting over proceeding cycles while ratcheting strains dropped in magnitude for opposing sequence where stress level dropped from high to low.Local ratcheting strain values at the vicinity of notch root were found noticeably larger than nominal ratcheting values measured at farer distances from notch edge through use of strain gauges.Ratcheting values in both mediums of local and nominal were promoted as notch diameter increased.To assess progressive ratcheting response and stress relaxation concurrently,the Ahmadzadeh-Varvani(A-V)kinematic hardening rule was coupled with Neuber’s rule enabling to calculate local stress at notch root of steel samples.Local stress/strain values were progressed at notch root over applied asymmetric stress cycles resulting in ratcheting buildup through A-V model.The relaxation of stress values at a given peak-valley strain event was governed through the Neuber’s rule.Experimental ratcheting data were found agreeable with those predicted through the coupled framework.