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| Dynamic mechanical responses and microstructural evolution of DZ2 axle steel under medium strain-rate tension loading |
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Abstract Impacts at low velocity is one of the typical operation conditions that the domestic axle for high-speed trains always suffers. Understanding the mechanical response and deformation-damage behavior of the axle under this condition is of significant importance for the designing and maintenance of the axle. This paper analyzed the tensile mechanical properties and microstructural evolution of the DZ2 axle steel within the medium strain rate range (0.1~100 s-1) at room temperature. The plastic deformation and fracture mechanisms of the DZ2 axle steel had been revealed, and the Zerilli-Armstron constitutive model which could accurately describe the dynamic response behavior of the axle steel was proposed. The experimental results showed that the dislocation motion and ductile fracture were the plastic deformation and failure mechanisms of the DZ2 axle steel under the tensile deformation process. However, the dependence of the strength on the strain rate varied with the increasing strain rate. When the strain rate was below 10 s-1, a small number of the dislocations were generated. The resistance to dislocation movement was low, and in consequence, the strength of DZ2 axle steel would not be apparently enhanced with the increase of strain rates. The DZ2 axle steel exhibited low strain rate sensitivity. When the tensile deformation was carried out at the strain rate extended 10 s-1, the mobile dislocation density in the axle steel increased substantially. Because the velocity of dislocation slipping was very fast, the short-range interaction of dislocations was enhanced significantly. In this case, the tensile deformation resistance of DZ2 axle steel became more and more stronger with the increasing strain rate, leading to a remarkable strength dependence of DZ2 axle steel on the strain rates. Its strain rate sensitivity became pronounced. Compared the experimental one, it was found that the simulation date by the proposed Zerilli-Armstron constitutive relation had high related coefficient and low average absolute relative error, indicating the applicability in predicting the dynamic mechanical properties of DZ2 axle in the intermediate tensile strain rate range. All abovementioned results could provide support for the operational safety assessment of the domestic DZ2 axle.
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Received: 28 April 2023
Published: 27 December 2023
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2023, Vol. 44 
