Hot deformation characteristics of as-cast high-Cr ultra-super-critical rotor steel with columnar grains

Isothermal hot compression tests of as-cast high-Cr ultra-super-critical（USC） rotor steel with columnar grains perpendicular to the compression direction were carried out in the temperature range from 950 to 1250°C at strain rates ranging from 0.001 to 1 s^（-1）. The softening mechanism was dynamic recovery（DRV） at 950°C and the strain rate of 1 s^（-1）, whereas it was dynamic recrystallization（DRX） under the other conditions. A modified constitutive equation based on the Arrhenius model with strain compensation reasonably predicted the flow stress under various deformation conditions, and the activation energy was calculated to be 643.92 kJ ×mol^（-1）. The critical stresses of dynamic recrystallization under different conditions were determined from the work-hardening rate（θ）–flow stress（σ） and-θ/σ–σ curves. The optimum processing parameters via analysis of the processing map and the softening mechanism were determined to be a deformation temperature range from 1100 to 1200°C and a strain-rate range from 0.001 to 0.08 s^（-1）, with a power dissipation efficiency η greater than 31%.

Model of critical strain for dynamic recrystallization in 10%TiC/Cu-Al_2O_3 composite

Using the Gleeble-1500 D simulator, the hot deformation behavior and dynamic recrystallization critical conditions of the 10%Ti C/Cu-Al2O3(volume fraction) composite were investigated by compression tests at the temperatures from 450 °C to 850 °C with the strain rates from 0.001 s-1 to 1 s-1. The results show that the softening mechanism of the dynamic recrystallization is a feature of high-temperature flow true stress-strain curves of the composite, and the peak stress increases with the decreasing deformation temperature or the increasing strain rate. The thermal deformation activation energy was calculated as 170.732 k J/mol and the constitutive equation was established. The inflection point in the lnθ-ε curve appears and the minimum value of-(lnθ)/ε-ε curve is presented when the critical state is attained for this composite. The critical strain increases with the increasing strain rate or the decreasing deformation temperature. There is linear relationship between critical strain and peak strain, i.e., εc=0.572εp. The predicting model of critical strain is described by the function of εc=1.062×10-2Z0.0826.

Buckling analysis of functionally graded nanobeams under non-uniform temperature using stress-driven nonlocal elasticity

In this work,the size-dependent buckling of functionally graded(FG)Bernoulli-Euler beams under non-uniform temperature is analyzed based on the stressdriven nonlocal elasticity and nonlocal heat conduction.By utilizing the variational principle of virtual work,the governing equations and the associated standard boundary conditions are systematically extracted,and the thermal effect,equivalent to the induced thermal load,is explicitly assessed by using the nonlocal heat conduction law.The stressdriven constitutive integral equation is equivalently transformed into a differential form with two non-standard constitutive boundary conditions.By employing the eigenvalue method,the critical buckling loads of the beams with different boundary conditions are obtained.The numerically predicted results reveal that the growth of the nonlocal parameter leads to a consistently strengthening effect on the dimensionless critical buckling loads for all boundary cases.Additionally,the effects of the influential factors pertinent to the nonlocal heat conduction on the buckling behavior are carefully examined.