Papers by Keyword: Thermal Deformation

Abstract: LNG carrier is purposed to transport a liquefied LNG cargo which is reduced to 1/600 of volume in temperature condition of -163°C. In the context of structural performance on LNG cargo hold, the mechanical and thermal behaviors of insulation material under cryogenic temperature are considered as one of the critical factors for the hold design. This paper deals with the thermal deformation and the compressive strength of the reinforced polyurethane foam (RPUF) adapted for the insulation material of membrane type LNG carrier via both material tests and numerical simulations realizing the cryogenic condition. The material tests related to the thermal deformation are carried out to investigate the characteristics for thermal transfer on the actual RPUF specimen. The heat transfer simulations based on finite element analysis (FEA) are carried out using forced convection theory. The results of heat transfer analyses are compared to the material test results. Reasonable cryogenic conditions on RPUF are reviewed from both the analyses and the test results. In the regard of static material strength for the RPUF, the compressive material tests are carried out. The cryogenic temperature effect on the compressive strength of RPUF is evaluated by comparing to the room temperature material test results. From the compressive material tests, the effect of temperature on the ultimate compressive strength is investigated with variation of elongation.

Abstract: X-ray diffraction and EBSD techniques were applied to investigate microstructure evolution and phase transition of thermal deformed TA15 titanium alloy under different heating methods(β phase zone heating and conventional heating). The results indicate that microstructures of thermal deformed TA15 titanium alloy after water quenching appear grain refinement undergoing these two kinds of heating methods. A large number of primary equiaxed α grains are retained after two phase zone deformation under conventional heating method. Meanwhile more regular arrangement and greater cluster of acicular plate martensite microstructure and clear original β grains are obtained through β phase deformation and water quenching. The diffraction peak of (200) crystal face of Al-rich α phase disappears under β phase zone heating method. The preferential orientation of TA15 titanium alloy after thermal deformation and water quenching is reduced obviously under β phase zone heating method.

Abstract: Taking a vertical machining center as an example, thermal characteristics of the spindle system were researched by finite element simulation and experimental test. Firstly, temperature field and thermal deformation of the spindle system were simulated considering boundary conditions of the finite element model, such as heat sources, convective heat transfer coefficients and thermal contact resistances between joints. Accuracy of the simulation was verified compared with test. The results shows that key areas of temperature rise locate at spindle bearing; thermal deformation of Y and Z directions are large; thermal characteristics of the spindle system has little influence on other parts. Thermal characteristics of the spindle system were optimized by changing structures and sizes of the cooling passage located at the headstock, and effectiveness of the optimization was verified by finite element simulation. The research results provide guidance for thermal characteristic simulation and optimization of a machining center.

Abstract: Journal bearings are widely used in heavy industry and in internal combustion engine applications. There is a need to increase the power density of various machine parts which leads to increased bearing loads and reduced lubrication film thicknesses. This type of development may increase deformations on the bearing surfaces which need to be considered in the bearing design process.The main purpose of this work was to develop a parameterized calculation model for hydrodynamic radial journal bearings which takes into account elastic and thermal deformations of the bearing surfaces. Hydrodynamic calculations were based on the numerical solving of the Reynolds equation by assuming rigid surfaces. Elastic and thermal deformations of the bearing and shaft surfaces were calculated by using the finite element method. It is concluded that elastic and thermal deformations are partly canceling each other out at the loaded side of the bearing and depending on the sliding speed and the external normal force either one of them could be more significant.

Abstract: In surface grinding of a large workpiece used for a sliding surface of the machine tool, high shape accuracy is required for the ground surface. Therefore, it is important to investigate the causes of the shape error observed in a large workpiece machined by surface grinding. In this study, we focused on the thermal deformation and residual stress as the causes of shape error. The in-process measurement of the workpiece temperature distribution was carried out to estimate the effect of the thermal deformation to the shape error. The estimated value of the shape error calculated from the measured temperature distribution was much less than the actual measured shape error. Therefore, the residual stress on the ground surface was measured with a portable X-ray stress measurement device. The residual stress was changed from compressed state to tensile state as the grinding pass increased. The ground shape was also deformed to concave shape as the grinding pass increased. The value of the shape error was finally reached to the constant value in several grinding conditions. From these experimental results, it is suggested that the shape error of the large workpiece is caused by the residual stress applied to the ground surface.

Abstract: Thermal deformation of large size hydrostatic bearing rotary workbench is the most direct factor that affects the machining accuracy of work-piece. The thesis puts forward the method of adding reinforcing plate structure to restrain the workbench thermal deformation, establishes three-dimensional supporting workbench model, with finite element method and sequence of fluid-solid coupling technology have carried on the thermal deformation calculation workbench, and reveals the influence law of different installation position of rib plate on the workbench thermal deformation. The results of the study shows that the method of adding reinforcing plate structure to reduce the thermal deformation of hydrostatic bearing worktable is feasible, and determine the optimal position of reinforcing plate by comparing different results.

Abstract: A rear cradle as one of the suspension system takes a role to connect a tie rod, suspension arm, transmissions and rubber bush. It consists of the side member and cross member which are joined by welding process. However, the rear cradle may be distorted due to thermal deformation during welding process, which cause dimensional tolerance problem when assembling. So, it is necessary to predict the thermal deformation and the optimal welding conditions should be suggested to reduce the dimensional tolerances. In this paper, MAG(metal active gas) welding process was applied in the simulation model using the SYSWELD^R, commercial S/W for welding simulation. And then, It should be predicted on the results about the gap and thermal deformation of main cylinder and derived the phase transformation, temperature distribution, residual stress and thermal deformation of total model shape.

Abstract: The paper presents a compensation system of thermal deformation for conventional feed axes applied in CNC machine tools allowing for an effective reduction in the impact of heat generated during its operation on the positioning accuracy of the axis. The result has been achieved by equipping feed screws with thermistor temperature sensors. Wiring sensors was led out through an axial bore in the screw and through a rotating electrical connector to an acquisition device coupled with the control system of the CNC machine. An algorithm based on neural networks was implemented in the machine control system, which allows for the online calculation and compensation of heat deformation of feed screws. The algorithm takes into account a variation of thermal deformation values as a function of the table position and the current distribution of the temperature field of the screw and machine. The paper presents a user-friendly method for implementing algorithms containing neural networks in the machine control system. The proposed compensation method has been verified by measuring the linear accuracy of the feed axis positioning. The obtained results confirm the effectiveness of the proposed method in reducing the impact of thermal deformation errors on the positioning accuracy of the axis in CNC machine tools.

Abstract: Thermal deformation of concrete at low temperature expands from-20°C to-50°C and contracts from-30°C to-10°C. Based on previous studies, the paper tries to explain the deformaion trend by analyzing freezing point of bulk solution and pore solution in saturated hardened cement paste. The result shows that it is critical to thermal deformation of cement-based materials at low temperature that pore solution in the pores smaller than 8 nm freezes.

Abstract: To solve the issue of machine barrel skewed to one side, when the XJ150×25 was running. Under the conditions that the needs of strength was met, by designed three types of cooling channels and analyzed the temperature field for the barrel by using ANSYS, as well as thermal deformation. The results show that cooling channel of center symmetric form can solve the problem that uneven temperature field causing the barrel to produce thermal deformation. It can guarantee the coaxial degree between screw and barrels and can improve the quality of products.