In this paper, deformation behaviors and microstructure evolution of a hot-rolled AZ31B magnesium alloy under cyclic loadings are investigated. The relationship between plastic deformation and microstructure evolution and the crack formation mechanisms are discussed. Under a high cyclic stress (90–140 MPa), steady ratcheting effect occurred in the material and the development of ratcheting strain went through three stages: 1) Stage I - initial rapid increase stage; 2) Stage II - steady stage; and 3) Stage III - final abrupt increase stage. Under a low cyclic stress (≤ 90 MPa), inconspicuous ratcheting effect was found in the material, indicating a light damage in the material. When the cyclic stress is below 30 MPa, no ratcheting effect is found and only elastic deformation occurs in the material. The formation of cracks in Stages I & II is mainly due to the activation of the basal slip system. The mean geometrically necessary dislocations (GND) are calculated to analyze the relationship between the basal slip and the ratcheting effect during the cyclic loading. Finally, a new approach is proposed to estimate the AZ31B magnesium alloy’s cyclic strength (at 107 cycles) according to the cyclic stress at which steady ratcheting effect starts to occur in the material.

Deformation behaviors and cyclic strength assessment of AZ31B magnesium alloy based on steady ratcheting effect

An experimental study of cyclic plastic deformation of extruded ZK60 magnesium alloy under uniaxial loading at room temperature

The effect of material orientation on cyclic deformation and fatigue behavior of rolled AZ80 magnesium (Mg) alloy was experimentally investigated under fully reversed strain-controlled loading in ambient. The testing specimens were taken from a rolled AZ80 Mg plate at four orientations with respect to rolled plane: 0°(ND, normal direction), 30°(ND30), 60°(ND60), and 90°(RD, rolled direction). Fatigue fracture morphologies of specimens along different orientation were analyzed by scanning electron microscopy (SEM). Overall cyclic hardening was observed for the material loaded in different directions. For a given strain amplitude, the ND specimens had the lowest fatigue resistance among the specimens of all material orientations. The fatigue life of an ND30 specimens is similar to that of an ND60 specimen at a given strain amplitude and both are higher than that of an RD specimen when the strain amplitude is higher than 0.4%, whereas an RD specimen exhibits a better fatigue resistance when the strain amplitude is lower than 0.4%. A mixed fracture mode with transgranular and intergranular cracking related to lamellar-like features occurred during stable crack growth, and an intergranular fracture mode related to dimple-like features exhibited in the fast fracture region. A multiaxial fatigue model based on the strain energy density can correlate all the fatigue experiments of the material at different material orientations.

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Cyclic deformation and fatigue of rolled AZ80 magnesium alloy along different material orientations

Low-cycle fatigue behaviors of hot-rolled AZ91 magnesium alloy under asymmetrical stress-controlled cyclic loadings

The uniaxial ratchetting of extruded AZ31 magnesium alloy was investigated in the cyclic tests with different mean stresses and at room temperature. The prescribed mean stresses and corresponding stress amplitudes were chosen to make the different plastic deformation mechanisms such as dislocation slipping, twinning and detwinning occur individually or simultaneously during the cyclic deformation of the AZ31 magnesium alloy with a hexagonal close packed crystal structure, and then the effect of mean stress on the uniaxial ratchetting of the magnesium alloy was discussed. It is seen that ratchetting occurs in the AZ31 magnesium alloy during the stress-controlled cyclic loading, but different evolution features are observed in the uniaxial ratchetting tests with different mean stresses. Different ratchetting behaviors are determined by the different deformation mechanisms of extruded AZ31 magnesium alloy occurring in the tensile and compressive parts of cyclic loading. A sigmoidal stress–strain hysteresis loop of the magnesium alloy presented in the cyclic tension–compression tests with some suitable mean stresses and stress amplitudes is caused by the twinning/detwinning deformation mechanism, which should be reasonably considered in constructing a cyclic constitutive model to describe the uniaxial ratchetting of magnesium alloys.

Uniaxial ratchetting of extruded AZ31 magnesium alloy: Effect of mean stress

Uniaxial cyclic loading tests were carried out to investigate the effects of percent reduction and specimen orientation on the ratcheting behavior of hot-rolled AZ31B magnesium alloy. It was found that the alloy exhibited the following characteristic behaviors with increasing numbers of loading cycles: an apparent cyclic softening was observed first, then a cyclic hardening occurred, and finally a tendency toward stabilization appeared. Anisotropic ratcheting behavior was observed in all the alloys. The percent reduction and specimen orientation did not influence the cyclic softening/hardening behavior or the final ratcheting strain variation trend of with the mean stress, the peak stress and the stress amplitude. The percent reduction only reduced the ratcheting strain.

Effects of percent reduction and specimen orientation on the ratcheting behavior of hot-rolled AZ31B magnesium alloy

Three-dimensional adaptive fixed-time cooperative guidance law with impact time and angle constraints

Before cavitation occurs, the underwater vehicle’ noise is mainly composed of structural noise, mechanical noise, instrument noise, etc. The noise mainly radiate in multipole form. And the line and non-line spectrums coexist in the noise spectrum. Besides, it changes with the flow velocity and the environmental pressure. Once the cavitation occurs, there are obvious differences in the noise spectrum. In order to study the noise characteristics of underwater high-speed vehicle, a numerical model of LES/FW-H coupling is established based on VOF multiphase flow and Schnerr and Sauer cavitation model. Then, the numerical simulation and water tunnel experiments are carried out to obtain the noise characteristics of the vehicle on different working conditions. The source of the noise is analyzed. The influence of velocity, pressure and cavitation on the noise and the directivity of the noise are revealed. The results of this paper can provide some reference for the study of the noise characteristics of underwater high-speed vehicle. It is helpful to better grasp the related technology of underwater high-speed vehicle and provide some support for reducing the noise of the high-speed vehicle or its detection.

Flow Noise Characteristics Analysis of Underwater High-Speed Vehicle Based on LES/FW-H Coupling Model

Taking maximum power transmission and power stable transmission as research objectives, optimal design for the wireless power transmission system based on magnetic resonance coupling is carried out in this paper. Firstly, based on the mutual coupling model, mathematical expressions of optimal coupling coefficients for the maximum power transmission target are deduced. Whereafter, methods of enhancing power transmission stability based on parameters optimal design are investigated. It is found that the sensitivity of the load power to the transmission parameters can be reduced and the power transmission stability can be enhanced by improving the system resonance frequency or coupling coefficient between the driving/pick-up coil and the transmission/receiving coil. Experiment results are well conformed to the theoretical analysis conclusions.

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He Zhang

Papers

Effects of percent reduction and specimen orientation on the ratcheting behavior of hot-rolled AZ31B magnesium alloy

Three-dimensional adaptive fixed-time cooperative guidance law with impact time and angle constraints

Flow Noise Characteristics Analysis of Underwater High-Speed Vehicle Based on LES/FW-H Coupling Model

Parameters Optimization for Magnetic Resonance Coupling Wireless Power Transmission

Development of compact seed source with high-precision discharge switch for magnetic flux compression generator