Study of the critical deformation dependence for dynamic recrystallization in low-carbon steels on the chemical composition

The article considers dependence of the critical deformation for dynamic recrystallization in low-alloy steels on the chemical composition. The article shows an improved model for forecasting the critical deformation for dynamic recrystallization, which allows considering the content of chemical elements in steel. The article analyzes the influence of the chemical composition of low-alloy steels on the value of critical deformation during hot deformation. The article shows that the developed mathematical model can be used in the system of automated control of the structure and properties of steels during hot rolling to forecast conditions for the development of dynamic recrystallization and to select the optimal chemical composition of steels.

Gas molding of structure parts at non-linear ductile deformation of anisotropic materials

There are offered correlations for the computation of gas shaping technological parameters of structure elements. A state of material non-linear viscosity (creep) is accepted. The energetic equilibrium equation, equations of damage capacity and a criterion of local deformation stability are used. There is computed gas pressure, operation duration (time), material damage capacity, critical deformation at the formation of volume casing. Product samples are presented.

Estimation for normal contact stiffness of joint surfaces by considering the variation of critical deformation

Purpose This paper aims to study the relationship between normal contact stiffness and contact load. It purpose a new calculation model of the normal contact stiffness of joint surfaces by considering the elastic–plastic critical deformation change of asperities contact. Design/methodology/approach The paper described the surface topography of joint surfaces based on fractal geometry, and fractal parameters and of fractal function derived from measurement data. According to the plastic–elastic contact theory, the contact deformation characteristic of asperities was analyzed; the critical deformation estimation model was presented, which expressed critical deformation as the function of fractal parameters and contact deformation; the contact stiffness calculation model of single asperity was brought forward by considering critical deformation change. Findings The paper combined the surface topography description function, analyzed the asperity contact states by considering the critical deformation change, and calculated normal contact stiffness based on fractal theory and contact deformation analysis. The comparison between theoretical contact stiffness and experimental data indicated that the theoretical normal contact stiffness agreed with the experimental data, and the estimation model for normal contact stiffness was appropriate. Research limitations/implications Owing to the possibility of plastic deformation during the loading process, the experimental curve between the contact stiffness and the contact load is nonlinear, resulting in an error between the experimental results and the theoretical calculation results. Originality/value The paper established the relationship between critical deformation and fractal surface topography by constructing asperity distribution function. The paper proposed a new normal contact stiffness calculation model of joint surfaces by considering the variation of critical deformation in contact process.

Study on Protective Coal Pillar Size Design for Ultra High Voltage Line Tower Mining in Mountain Areas

High voltage line towers in mining areas are sensitive to surface deformation caused by mining. Protective coal pillar design for high voltage towers is one of the commonly-used technical measures. Aiming to solve the coal mining safety problem under the Ultra High Voltage transmission line in Sihe Coal Mine of Shanxi Province, the angle and size of protective coal pillars with the vertical line method were analyzed in this paper. The effect of additional displacement caused by landslide or slippage mining in mountain areas and repeated mining was considered. Based on the principle of the vertical line method, the protective coal pillar range and size were calculated. The amount of coal deposited in coal pillars for high voltage line towers was compared and analyzed between the vertical line method and the linear structure method. The results showed that the angle of critical deformation decreased by 2~10° caused by slippage due to mining in a mountainous area, and the angle in the uphill direction of building decreased more than that in the downhill direction; when multi-seams were mined repeatedly, the angle of critical deformation in the lower seam coal mining was reduced by 5~10° compared with that of the upper seam. The protective coal pillar design with the vertical line method can protect the high voltage line towers more effectively, and the amount of protective coal pillars with the vertical line method was 5.8 million tons less, which avoided the waste of coal resources.