Search

Investigating the ratcheting behavior of magnesium alloys is significant for the structure's reliable design. The uniaxial ratcheting behavior of AZ31B magnesium alloy is studied by the asymmetric cyclic stress-controlled experiments at room temperature. A modified kinematic hardening model is established to describe the uniaxial ratcheting behavior of the studied alloy. In the modified model, the material parameter m is improved as an exponential function of the maximum equivalent stress. The modified model can be used to predict the ratcheting strain evolution of the studied alloy under the single-step and multi-step asymmetric stress-controlled cyclic loadings. Additionally, due to the significant effect of twinning on the plastic deformation of magnesium alloy, the relationship between the material parameter m and the linear density of twins is discussed. It is found that there is a linear relationship between the material parameter m and the linear density of twins induced by the cyclic loadings. [ABSTRACT FROM AUTHOR]

Abstract: Uniaxial ratcheting and low-cycle fatigue failure behaviors of the hot-rolled AZ31B magnesium alloy are studied by uniaxial asymmetrical cyclic stress-controlled experiments at room temperature. The effects of mean stress, stress amplitude and stress rate on the uniaxial ratcheting response and ratcheting life of the studied magnesium alloy are analyzed. The microscopic observations near fracture surface are carried out. In addition, a fatigue parameter is introduced to describe the ratcheting damage and fatigue damage processes, and a new model is established to describe the relationship between the linear density of twins and the fatigue parameter. Results show that (1) the mean stress and stress amplitude has a great influence on the ratcheting strain and fatigue failure life. When the mean stress or stress amplitude is increased, the ratcheting strain and its rate rapidly increase. So, the fatigue failure life is reduced. (2) The increase of mean stress and stress amplitude can accelerate the generation of twins, which decreases the fatigue resistance and increases the ratcheting strain. However, the stress rate has little effect on the twinning. So, the effects of stress rate on ratcheting and low-cycle fatigue failure behaviors are not obvious under the tested conditions. This is because the studied magnesium alloy shows highly rate-independent property at room temperature within the tested strain rate range. (3) The established model can accurately describe the relationship between the linear density of twins and the fatigue parameter. Furthermore, the threshold fatigue parameter for twinning is found. [Copyright &y& Elsevier]

Abstract: The uniaxial low-cycle fatigue behavior of hot-rolled AZ91 magnesium alloy was investigated by asymmetric cyclic stress-controlled experiments at room temperature. The effects of the sampling direction, peak stress and stress ratio on the fatigue life were discussed. The fatigue life increases with increasing the stress ratio or decreasing the peak stress. Due to the anisotropic property, the specimen in transverse direction shows superior fatigue resistance. Considering the effects of mean stress on the fatigue strength coefficient and fatigue strength exponent, a modified Basquin model was proposed and validated to evaluate the fatigue life of AZ91 magnesium alloy. [Copyright &y& Elsevier]