Thermal stresses modelling

Pure Spot FSW. Awang et al. (Ref 23) presented some results on finite element modeling of FSSW using ABAQUS/Explicit (ABAQUS, Inc.) as a finite element solver. A three-dimensional (3-D) coupled thermal-stress model was used to calculate the thermomechanical response of the FSSW process. Adaptive meshing and advection schemes, which make it possible to maintain mesh quality under large deformations, were used to simulate the material flow and temperature distribution in the FSSW process. 

A finite-element thermal-stress model of continuous casting mold is conducted to predict deformation of copper plates and its change with different cooling structure. The results show that deformation behavior of copper plates is mainly governed by cooling structure and thermal-mechanical conditions, deformation amount is related to structure geometry, and a small deformation mutation occurs in cooper-nickel boundary due to different properties. The maximum deformation of hot surface centricities of wide face locate at 100 mm below meniscus and that of narrow face locate at meniscus and terminal of water slots and sigiiiiicant curvature fluctuations on both sides of copper-nickel boundary. The maximum deformation of centricities is increased up to 0.05 mm with thickness increment 5 mm of copper plates, and maximum deformations are only depressed 0.01 mm and 0.02 mm with increments of 1 mm nickel layer thickness and 2 mm water slot depth respectively. 

ELEMENTARY FAILURE MECHANISMS IN THERMALLY STRESSED MODELS OF FIBER REINFORCED COMPOSITES... 

In the North American market, water heaters are almost always made with the cold water inlet and hot water outlet lines coming out of the top of the tank. The hot water outlet opens right into the top of the tank and so draws off the hottest water. The hot water has risen to the top of the tank because of its lower density. The cold water on the inlet side is directed to the bottom of the tank by a plastic dip-tube. In some models the dip-tube is curved or bent at the end to increase the turbulence at the bottom of the tank. This is to keep any sediment from settling on the bottom of the tank. As sediment— usually calcium carbonate or lime—precipitated out of the water by the increased temperature builds up, it will increase the thermal stress on the bottom of a gas-fired water heater and increase the likelihood of tank failure. On electric water heaters the sediment builds up on the surface of the elements, especially if the elements are high-density elements. Low-density elements spread the same amount of power over a larger surface of the element so the temperatures are not as high and lime doesn t build up as quickly. If the lower elements get completely buried in the sediment, the element will likely overheat and burn out. 

Nakajo A., Stiller C., Harkegard G. and Bolland O., 2006. Modeling of thermal stresses and probability of survival of tubular SOFC. Journal of Power Sources 158(1), 287-294. 

Thermal stress calculations in the five cell stack for the temperature distribution presented above were performed by Vallum (2005) using the solid modeling software ANSYS . The stack is modeled to be consisting of five cells with one air channel and gas channel in each cell. Two dimensional stress modeling was performed at six different cross-sections of the cell. The temperature in each layer obtained from the above model of Burt et al. (2005) is used as the nodal value at a single point in the corresponding layer of the model developed in ANSYS and steady state thermal analysis is done in ANSYS to re-construct a two-dimensional temperature distribution in each of the cross-sections. The reconstructed two dimensional temperature is then used for thermal stress analysis. The boundary conditions applied for calculations presented here are the bottom of the cell is fixed in v-dircction (stack direction), the node on the bottom left is fixed in x-direction (cross flow direction) and y-direction and the top part is left free to... 

Numerical calculations for the residual stresses in the anode-supported cells are carried out using ABAQUS. After modeling the geometry of the cell of the electro-lyte/anode bi-layer, the residual thermal stresses at room temperature are calculated. The cell model is divided into 10 by 10 meshes in the in-plane direction and 20 submeshes in the out-plane direction. In the calculation, it is assumed that both the electrolyte and anode are constrained each other below 1400°C and that the origin of the residual stresses in the cell is only due to the mismatch of TEC between the electrolyte and anode. The model geometry is 50 mm x 50 mm x 2 mm. The mechanical properties and cell size used for the stress calculation are listed in Table 10.5. 

Fig. 10.41 The calculated distribution of the principal stress in the Lao.8Sro.2Cro.95Nio.o5C>3 3 interconnector for the standard counter-flow case 1 in Table 10.2 (a) the stress is calculated considering both the temperature and distributions in the interconnector, (b) the stress is only the thermal stress. The model geometry with 16-channels is used, and half the model is drawn in the figure.

Blissett et al. (1997) used the concentric cylinder model of Powell et al. (1993) to obtain residual stresses, whereas Boccaccini (1998) utilised the results of a simple force balance in 1-D performed by Wang et al. (1996), which gives the residual thermal stresses in the matrix along the axial direction as ... 

Based on this model, the thermal stress in the matrix has been deduced by Yu et al. (2002a) to be ... 

The calculation of thermal stresses in functionally graded materials is already a relatively old topic (Yang et al., 2003). Two methods can be distinguished analytical methods and finite element methods. However, the complicating effect of the elastic modulus variation with the position severely limits the scope of problems that can be solved analytically. Therefore, the majority of the analytical work has been for FGM films or other simple structures (Becker et al., 2000). Analytical models have been developed for the calculation of thermal stresses for 1-D FGM symmetrical plates (Jung et al., 2003), non-... 

Equation (10) was shown to follow from a thermally activated model of Eyring s type, that is a stress-assisted thermally activated process for viscous flow [154]. For rough surfaces the area of true molecular contact is very small and, hence, the adhesion contribution to the total friction force is usually negligible, as manifested by a zero friction at zero load [148]. Yet in the microscopic limit of the SFM experiment employing a comparatively sharp... 

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