NEW METHOD OF REDUCING HEAT DEFORMATION OF SLIDEWAY GRINDERS

A new concept used for designing large-scale and high-precision NC slideway grinders which are called self-collimation slideway grinders is introduced to eliminate thermal deformation of them. Its principle is to make use of gravitational deformation of machine beds and their foundations automatically to compensate for thermal deformation caused by environmental temperature fluctuation and friction heat between machine tables and machine beds by decreasing longitudinal section stiffness of machine beds and foundations. By FEM analysis and application of more than 10 years, it shows that they have advantages of high precision and low cost, moreover, no constant temperature rooms are required. The linearity error of parts machined with them is less than 0.003 mm/m, and machining precision can almost keep constant for a long time.

Numerical analysis of joint temperature evolution during friction stir welding based on plastic deformation heat

3D numerical model for friction stir welding （FSW） was developed by using ABAQUS software considering the plastic deformation heat. Effects of the rotation and welding speeds on the temperature field of FSW 2024-73 aluminum alloy were systematicaUy investigated. The temperature measurement was performed to validate the reliability of the model. The simulation results are in good agreement with the experiments. Results show that changing the rotation speed has no influence on the time for reaching the peak temperature at certain point in the workpiece at a constant welding speed. While increasing the welding speed has significant effect on the time for reaching the peak temperature but the value of peak temperature changes little.

Influence of deformation and heat treatment on electrical conductivity of CuMoCr alloy

The solution heat treatment,cold deformation and subsequent aging were performed on CuMoCr alloy.And the influence of deformation and aging treatment on the electrical conductivity of CuMoCr alloy was studied through metallograph,transmission electron microscopy(TEM) and electrical conductivity measurement.Results show that deformation without subsequent aging can reduce the electrical conductivity of CuMoCr alloy,but deformation followed by the optimum aging treatment can effectively improve the electrical conductivity of CuMoCr alloy.Aging at 500 ℃ for 4 h after 80% deformation,the much better electrical conductivity of CuMoCr alloy can be obtained.Reduction of Cr content in the Cu matrix could be the reason for the enhancement of electrical conductivity.

Simulating and validating the effects of slope frost heaving on canal bed saturated soil using coupled heat-moisture-deformation model

The lining canals in seasonal frozen soil areas can be severely damaged by frost heaving.The freezing and thawing contributes to the continual change of the temperature field and moisture field beneath lining canal,which will seriously affect the safe operation of the canal.In order to study the frost heaving damage mechanism of lining canal and to solve the associated engineering problems,the permafrost body was regarded as an elastomer,and a three-field,coupled,partial differential equation describing the temperature,moisture and deformation fields for a saturated two-dimensional canal bed was derived and established based on the Harlan model.The coupling equations were discretized using the finite element method in space and the finite difference method in time.The parameters were simplified appropriately based on compliance with the actual conditions and were simulated using finite element software.The results of a sample simulation showed that the simulated results and test results were basically consistent with variation laws,which proved the correctness of the numerical simulation theory and solution methods and the reliability of the calculation.The model can simulate the water,heat and deformation issues in the side slope of saturated canal bed soil in a seasonally frozen area and forecast freezing damage in the canals.

Effect of DH treatment on microstructure and mechanical properties of an LM28-0.3wt.%Nd hypereutectic aluminum silicon alloy

In this article, a novel heat treatment method, deformation heat （DH） treatment （extrusion ＋ aging）, was employed on a hypereutectic aluminum silicon alloy （LM28-0.3wt.%Nd）, and its effect on microstructure and mechanical properties of this alloy was investigated. It can be concluded that the eutectic microstructure disappears after the DH treatment, in the meantime the morphology of α（Al） solid solution was transformed from fir-troe and cellular to equiaxed, Si was refined with grain sizes of about 1-10 μn and distributed dispersedly, even some of them became globular shape, which can reduce stress accumulation effectively. Mechanical properties test indicated that the DH treatment could significantly improve the room-ternperature strength and have little effect on the high-temperature strength of LM28-0.3wt.%Nd alloy. The fracture mechanism is ductile fracture by fracture morphology analysis.

Improving Local Temperature Rise in Rotational Incremental Sheet Forming Process by Modifying Forming Parameters Using Response Surface Method

In rotational incremental sheet forming( RISF) process,the friction heating of rotational tool could lead to local temperature rise of the sheet and cause the improvement of sheet's formability.Lightweight metal,such as magnesium alloy,could be deformed by RISF without additional heating. The objective of this study is to investigate the effects of forming parameters,namely,tool rotational speed,feed-rate,step size and wall angle,on the local temperature rise. Using response surface methodology and central composite design( CCD) experimental design,the significance,sequence of parameters and regression models would be analyzed with AZ31 B as the experimental material,and 3D response surface plots would be shown. Combined with actual processing conditions,the measures to improve the local temperature rise by modifying each parameter would be discussed in the end. The results showed that hierarchy of the parameters with respect to the significance of their effects on the local temperature at the side wall was: feed-rate,step size,and rotational speed,while at the bottom it was: feed-rate,step size,wall angle, and rotational speed, and no significant interaction appeared. It was found that the most significant parameter was not rotational speed,but feed-rate,followed by step size,for both test positions. In addition, the local temperature would increase by elevating step size,wall angle,rotating rate,and bringing down of feed-rate.

Constitutive Model of Warm Deformation Behavior of Medium Carbon Steel

The compressive behaviors of medium carbon steel specimens were investigated over a wide range of tem- peratures and strain rates using a Gleeble-3500 thermo-simulation machine. The results show that the flow stress in- creased with strain at first, and then gradually decreased after reaching a peak value. The flow stress softening rate at a high strain rate was larger than that at a low strain rate. The effects of deformation heating and friction on flow stress were analyzed. A new friction correction method, wherein the effect of strain on frictional coefficient was con- sidered, was established here. The stresses revised by the new method deviated from the measured stresses with in- creasing strain. Meanwhile, the apparent frictional coefficient variation law with strain was obtained. The frictional coefficient increased as the strain increased and then slightly decreased after maintaining a constant value. The stress was corrected by considering deformation heating. The accuracy of the temperature correction method was verified using a special experiment. The results of the verification experiment show that the temperature correction method exhibited a good accuracy in calculating the variation of stress caused by deformation heating. A constitutive model considering strain was proposed here to describe the deformation behaviors. Compared with experimental data, the modified constitutive model exhibited a good accuracy as to constitutive correlation.

Quantitative analysis of microstructure evolution induced by temperature rise during(α＋β) deformation of TA15 titanium alloy

Temperature rise is a significant factor influencing microstructure during（α＋β） deformation of TA15 titanium alloy.An experiment was designed to explore microstructure evolution induced by temperature rise due to deformation heat.The experiment was carried out in（α＋β） phase field at typical temperature rise rates.The microstructures of the alloy under different temperature rise rates were observed by scanning electron microscopy（SEM）.It is found that the dissolution rate of primary equiaxed a phase increases with the increase in both temperature and temperature rise rate.In the same temperature range,the higher the temperature rise rate is,the larger the final content and grain size of primary equiaxed a phase are due to less dissolution time.To quantitatively depict the evolution behavior of primary equiaxed a phase under any temperature rise rates,the dissolution kinetics of primary equiaxed a phase were well described by a diffusion model.The model predictions,including content and grain size of primary equiaxed a phase,are in good agreement with experimental observations.The work provides an important basis for the prediction and control of microstructure during hot working of titanium alloy.

Growth Kinetics of Laves Phase and Its Effect on Creep Rupture Behavior in 9Cr Heat Resistant Steel

The effects of Laves phase formation and growth on creep rupture behaviors of P92 steel at 883 K were studied.The microstructural evolution was characterized using scanning electron microscopy and transmission electron microscopy.Kinetic modeling was carried out using the software DICTRA.The results indicated Fe_2（W,Mo）Laves phase has formed during creep with 200 MPa applied stress at 883 Kfor 243 h.The experimental results showed a good agreement with thermodynamic calculations.The plastic deformation of laths is the main reason of creep rupture under the applied stress beyond 160 MPa,whereas,creep voids initiated by coarser Laves phase play an effective role in creep rupture under the applied stress lower than 160 MPa.Laves phase particles with the mean size of 243 nm lead to the change of creep rupture feature.Microstructures at the vicinity of fracture surface,the gage portion and the threaded ends of creep rupture specimens were also observed,indicating that creep tensile stress enhances the coarsening of Laves phase.

Theoretical Explanation of Uneven Transverse Temperature Distribution in Wide Thin Strip Rolling Process

A new theoretical thermomechanical explanation of the uneven transverse temperature distribution, along the width for thin and wide hot rolled strip was proposed. In particular, starting from the irregular pressure and friction distribution which led to an uneven heat generation, a 2D mathematical model of calculating the transverse termperature distribution was presented. A physical explanation for this problem was given and the model was used as an essential basis to build a corresponding FEM simulation model, in which heat loss and generation were considered. Deformation and friction heat were described in details. For a clearer and more logical analysis, the heat generation problem was split into two parts： one for the strip centre, and one for the sides, in correspondence with the temperature peak points at 100 mm from the strip edge. Finally, the result shows that how thenew theoretical model can lead to the exact interpretation of the measured uneven temperature distribution.

Computational fluid dynamics simulation of friction stir welding:A comparative study on different frictional boundary conditions

Numerical simulation based on computational fluid dynamics （CFD） is a useful approach for quantitatively investigating the underlying thermal-mechanical conditions during FSW, such as temperature field and material deformation field. One of the critical issues in CFD simulation of FSW is the use of the frictional boundary condition, which represents the friction between the welding tool and the workpiece in the numerical models. In this study, three-dimensional numerical simulation is conducted to analyze the heat transfer and plastic deformation behaviors during the FSW of AA2024. For comparison purposes, both the boundary velocity （BV） models and the boundary shear stress （BSS） models are employed in order to assess their performances in predicting the temperature and material deformation in FSW. It is interesting to note that different boundary conditions yield similar predictions on temperature, but quite different predictions on material deformation. The numerical predictions are compared with the experimental results. The predicted deformation zone geometry by the BSS model is consistent with the experimental results while there is large difference between the predictions by the BV models and the experimental measurements. The fact that the BSS model yields more reasonable predictions on the deformation zone geometry is attributed to its capacity to automatically adjust the contact state at the tool/workpiece interface. Based on the favorable predictions on both the temperature field and the material deformation field, the BSS model is suggested to have a better performance in numerical simulation of FSW than the BV model.