Papers by Keyword: Temperature Gradient

Abstract: Setting in the youshui Bridge Project and referring to the stipulation on the temperature gradient in current code, this aims to investigate the effects on the stress condition of concrete box-girder bridges caused by the overall heating, cooling or standard temperature changes. The process was carried out by virtue of the general finite element analysis software—MIDAS/CIVIL. The result showed that temperature would greatly affect the structural behavior of a bridge, in particular that the stress condition of the top plate is sensitive to temperature changes. It was therefore suggested that climate conditions should be taken into consideration when determining the temperature gradient values in the code.

Abstract: In this paper, we use numerical methods, reveal that the temperature distribution regularity of the concrete box girder, find the direct cause of the temperature gradient, and explain the reason about internal cracks of box girder.

Abstract: Flow outside the water-lifting aerator was simulated with FLUENT software, and the effects of temperature gradient on the in-situ algae inhibition zone were numerically analyzed. Flow characteristics directly influence the effect of algal inhibition using water-lifting aeration technology. Under quasi-steady state of flow outside the water-lifting aerator, the clockwise flow near the inlet and counter-clockwise flow in other domains coexisted, zone and strength of inlet circulation weakened as the water temperature gradient increased, flow velocity decreased as the distance from the water-lifting aerator increased. When the temperature gradient within the depth of 30 m increased from 0.17 °C/m to 0.73 °C/m, the radius of the core algal growth inhibition zone increased from 100 m to 150 m, and the ratio of the algal growth inhibition zone to the whole flow domain increased from 25.16% to 28.60%. The proper design intervals of water-lifting aerators in reservoirs were proposed as 100m-150m.

Abstract: Aluminum alloys are often used as the aircraft fuselage materials. Three materials of aluminum alloys 2A16, 7A09 and titanium alloy TC11 are selected in this work. The fracture behaviors of these materials are investigated under the combination of thermal and mechanical loads. The analytical model is an infinite plate with a line crack subjected to the uniform tension stress and thermal loading. The temperature boundary condition is that the temperature remains unchanged on the crack surfaces while the uniform heat flow is imposed at infinite. The analytical solutions of temperature field, stress field, stress intensity factor, strain energy density factor are solved by the complex function method. The failure stresses under the different conditions are calculated and compared for three materials by using the strain energy density theory. It is seen that the temperature effect would play an important role for the fracture behavior of aircraft fuselage materials.

Abstract: Dissimilar welds were prepared between 4 mm thick AA5083 and AA6061 sheets using Nd-YAG laser welding with different laser power, beam spot sizes and welding speeds. The results show that the temperature gradient and cooling rates play a major role in resultant microstructures of the weldments. Room temperature hardness and tensile properties of the weldments in the as-welded condition were studied and correlated with the microstructure. The microhardness examination showed that there was significant variation in hardness values at AA6061 side when compared with AA5083 side due to steeper temperature gradient. It has been observed that welds prepared with 3.5kW laser power, 3.5 m/min welding speed and 180 µm beam spot size exhibited highest tensile strength of 241 MPa.

Abstract: 260T hot-metal car is a huge shape machinery product used in iron and steel plant for the short distance transportation. The work conditions of the hot-metal car are bad, so the reliability of the product structure must be guaranteed. During the structure design, theoretical study and computer simulation analysis of the car frame are taken using the commercial finite element software. The tests for the 260T hot-metal car product are accomplished by using the modern static testing technology to verify the theoretical calculation. The paper describes the test scheme and field test process, extracts the strain and stress value of key points on the car frame and analyses the test data. At last, the test result data are compared with the finite element computation result data, verifying the theoretical calculation.

Abstract: Temperature field on the road inside the tunnel has a significant difference with normal road surface temperature field, according to the actual situation of the temperature inside the tunnel, calculate the slab length of the cement concrete pavement, obtained the conclusion that cement concrete road slab can be longer inside the tunnel, the conclusion has practical significance for the construction of cement concrete pavement inside the tunnel.

Abstract: To repair a directionally solidified aero blade, laser cladding on GH710 substrate using stainless steel powder and Ni-based alloy powder by Nd:YAG laser was carried out. The condition of achieving directional solidification in the open and normal temperature environment was researched. The effect of technical parameter and powder composition on the microstructure of the cladding layer was analysed. The microstructure of the cladding layer was investigated. The results show that the directionally solidified cladding layer was acquired by the appropriate technical parameter. It was difficult for the Ni-based powder cladding layer to get directionally solidified cladding layer in comparison with the stainless steel powder.

Abstract: The numerically simulation of temperature field was carried out by the ANSYS software in multi-layer powder-feeding laser cladding forming.3-D finite element model was found, which nonlinear characteristics of the material thermal properties and the boundary conditions of the convective transfer heat was considered; The process of powder falling into the substrate and cladding element growing was accomplished by “Element Birth and Death technology” in the process of numerical simulation. The result shown that the primarily solidified cladding layer to the following cladding layer has a preheating function in the process of multi-layer laser cladding forming, the initial temperature of following cladding layer is higher than primarily melted cladding layer; The thermal cycling curves of the molten pool nodes takes on periodic variation and basic similar in every layer cladding; The end effect problem is apt to happen in cladding layer, which the phenomenon of edge collapsing or partially burnt is formed; The temperature gradient distribution is divided into two parts, the temperature gradient level distribution along the laser scanning direction in the top and perpendicular distribution in the bottom, The temperature gradient appearances mutation and maximum value in the junction of the substrate and cladding layer, which the crack is apt to be caused in this region.

Abstract: We introduce a method to grow 4H-SiC single polytype stably by controlling the surface morphology. The polytype transition on on-axis 4H-SiC C-face was investigated from a viewpoint of surface morphology of grown layers. At the area where several hillock-like structures grew adjacently, the polytype transition from 4H-SiC to 6H-SiC or 15R-SiC often occurred. Therefore, we tried a modified seeded method to suppress the formation of hillock-like structures. As a result, the hillock-like structure on the grown layer was dramatically reduced. Moreover, the ratio of 4H-SiC polytype to the whole grown surface was increased to be almost 100%.