Papers by Keyword: Temperature Field

Abstract: Developed was a computer model of temperature field in the tool and parts in the process of their friction stir welding (FSW). Modeling of the temperature field was carried out for both successive stages of welding process, i.e. plunging of pin of tool working element into the part (1^st stage) and progressive motion of plunged pin in the part (2^nd stage). The mathematical model represents a nonlinear equation of transient heat conduction, which takes into account progressive pin movement during the 2^nd stage of welding. Two constituents describe the heat sources, appearing in welding. The first one considers power of heat sources, caused by friction of the tool with the parts on contact surfaces, the second one takes into account heat generation, promoted by mechanical deformation of the part material. Mathematical modeling and experimental examination of temperature field were carried out for tool from cubic boron nitride (cubonit) and hard alloy in copper parts during FSW. Adequacy of the developed model was determined based on correlation of numerical and experimental results.

Abstract: A finite element model was developed to determine the temperature distribution in the preheating phase of the friction surfacing (FS) process. In the present study consumable rod was used as a tool. As a model of the heat source, a model applicable to the traditional friction stir welding (FSW) was used. The developed model has been validated by a full-scale experiment. Temperature fields were obtained for different modes of the FS process, where the variable parameters were the axial force and the speed of rotation of the consumable rod. The difference between calculated and experimental data is less than 10%. Influence of the axial force magnitude on the consumable rod and the rod rotation speed on the temperature field generated by friction and plastic deformation of the consumable rod was established.

Abstract: The laser metal deposition is an advanced manufacturing technology enabling the production of large-sized parts and partially or completely elimination of machining and welding. The process is characterised by a non-uniform local heating of the buildup leading to a stress distribution, which may exceed the yield strength of the material and leads to loss of dimensional accuracy. The interlayer dwell time has a strong influence on the temperature field. The effect of the interlayer dwell time on the distortion and the stress distribution during laser metal deposition of a single-pass wall on the edge of 2 mm thick plate was studied experimentally and numerically. The deposited material was IN625 and the substrate material was AISI 316. A decrease of the residual displacement, due to a uniform shrinkage after the deposition of the last layer and a lower level of the residual compressive longitudinal plastic strain, has been observed in the studies without a dwell time. The peak increment of the free edge displacement corresponds to the first layer and hence the subsequent layers will be deposited on the already plastically deformed buildup. The tensile residual longitudinal stress near the top of the buildup and transverse stress near the edges of the buildup is higher than yield strength in the studies with dwell time.

Abstract: Additive technologies, in particular, wire-feed laser deposition, can significantly reduce the production cycle of manufacturing large-sized parts or parts of complex shape due to partial or complete elimination of technological operations such as casting, machining and welding. The aim of the work is to develop an analytical model of heating and melting of the filler wire during wire-feed laser deposition. The heat conduction problem was solved by the functional-analytical methods. The practical effectiveness of the functional-analytical methods with respect to computational time is several orders of magnitude higher than numerical ones. Obtained analytical solution made it possible to determine the temperature field for heat flux arbitrarily distributed on the filler wire surface. It is established that at a higher feed rate, the wire tip is completely melted at a greater distance from the laser axis. The shape of the melting surface also depends on the feed rate. At a slow feed rate, a more uniform heating of the wire over the cross section occurs. The melting surface has a small angle of inclination.

Abstract: The transient electromagnetic phenomena and solidification of Al-Cu alloy under a typical pulsed magnetic field (PMF) are numerically studied by a two-dimensional (2D) axisymmetric model. The results show that the magnetic flux density, eddy current density, Lorentz force and Joule heat all inherit the instantaneous and intermittent feature of the PMF, and their amplitudes and phases decrease with the increasing distance to the side surface of the ingot. The Lorentz force appears alternatively as pressure force and pull force mainly in the radial direction. Forced convection is induced in the liquid metal, and the flow field is composed of a clockwise vortex and a counter-clockwise vortex in the meridian plane of the ingot. The melt velocity is accompanied with a dramatic periodic oscillation. The temperature field in the ingot with the PMF tends uniform due to the mixing effect of the melt flow. However, the convection is damped soon after the solidification starts due to the increasing penetration resistance, and the temperature field gradually approximates that in the case without the PMF.

Abstract: The paper presents the housing wall structure for the digital X-ray flat panel which can operate in extremely low temperature conditions. A technology of three-dimensional printing is proposed for making the detector housing with heat conductors incorporated in its wall structure.

Abstract: The determination of the stress-strain state of a polymer body has many difficulties. This is due to the fact that the properties of polymers vary greatly from various perturbations, and are especially strongly dependent on temperature changes. Currently, rotating structures and their elements are increasingly made of polymer materials. Particularly it is possible to single out the problem if a change in temperature is observed along the radius, which leads to a change in the properties of the material. This circumstance can radically change the picture of the distribution of stresses and deformations in the thickness of the structure under study. Neglect of this fact can adversely affect the reliability of the structure as a whole.

Abstract: A review of a three-dimensional finite element calculation for a non-stationary heating regime of a compound structure with a complex shape. The accuracy of thermal processes modeling is determined. The temperature fields for the wind power plants blade elements have been determined at the stage of their manufacturing, which made it possible to identify the characteristic features of the technological process for these structures production.

Abstract: Cement-concrete pavement not only has a long service life even at high loads but also has competitive production costs and fewer significant maintenance costs. The concrete road surfaces, thus, are rather economical. In this article, the Vietnamese Standard TCVN 9382 - 2012 was used to determine the heavyweight concrete composition for rural road construction. Assessment of the crack appearance in the concrete block body was made by the temperature field analysis, the thermal stress and cracking index. The conducted studies' result provided with the possibility of obtaining heavyweight concrete from Vietnam local raw materials regarding to the concrete mixture workability of 11-13 cm standard cone, 31-36 MPa compressive strength of heavyweight concrete at the age of 28 - day - normal hardening and 0.30 - 0.42 MPa average water resistance of samples. Using natural pozzolan to replace 20% of mass cement in the concrete mixture leads to a decrease in the concrete strength characteristics at different ages. The concrete compressive strength of composition No2 decreased mostly by 23% at the age of 3 days and least by 14% at the age of 28 days in comparison these values of composition No1. However, all of these concrete compressive strengths at the age 28 days are higher than 30 MPa. Replacing 20% of the mass Portland cement by natural pozzolan in a concrete mix will decrease price for 1 m³ concrete of 219.96 rubles. By applying the computer program MIDAS CIVIL, the maximum temperature in the concrete block center which was determined after 12 hours from the commencement of mixing of raw materials with water, equals to T_max = 34.61 ⁰С. At the same time, the structure temperature difference between the center (node793) and surface (nodes 120 and 898) of the concrete pavement can be neglected because of its insignificance. Besides, the cracking indexes at three hazardous locations of investigated structure are higher than 1, the cement-concrete pavement will be considered as non-appearance of cracks. However, the cracking index at center (node 793) is always less than this on the surface (nodes 120 and 898), equally to higher thermal crack occurrence at center. Therefore, it is necessary to monitor the development and expansion of thermal cracks to ensure the concrete mixture proper care during the hardening process.

Abstract: The work is devoted to the study of defect formation processes in the near-surface layers of silicon under thermal shock conditions and to the effect of preliminary exposure in a constant magnetic field on this process. As a result of investigations it was established that dislocation half-loops near the local heat source are formed in the near-surface layers of Si (with a depth of up to 30 μm) after a current pulse of density j> 5.1010 A / m2 passing through the metallized film on the silicon surface. In addition, it was found that preliminary exposure of samples in a constant magnetic field leads to an increase in the dislocation density compared to samples not exposed in a magnetic field.