Papers by Keyword: Thermal Stress

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Authors: Hou Kui Fu, De Bo Lu, Zi Guo Li
Abstract: In-situ observation of stress in Al interconnects under electromigration and thermal effect by using the synchrotron radiation x-ray diffraction. The test temperature was controlled by changing the current density of W (self-heating structure). The EM-induced stress was also investigated with current densities from 3x105A/cm2 to 4x106A/cm2.The conclusion agreed well with the simulation results.
Authors: Bang Hung Tsao, Jacob Lawson, James D. Scofield, Clinton Laing, Jeffery Brown
Abstract: Three dimensional models of both single-chip and multiple-chip power sub-modules were generated using ANSYS in order to simulate the effects of various substrate materials, heat fluxes, heat transfer coefficients, and device placement configurations on temperature and thermal stress contours. Alumina, aluminum-nitride, and CVD diamond were compared as substrates. Heat fluxes of 100 to 500 watts/cm2 resulted in SiC device junction temperatures in the range of 350 to 650 K. The predicted maximum operating temperature for a chip, to which 300 watts/cm2 of heat flux was applied, would be 239°C (512 K). In the applied heat flux range, the minimum and maximum Von Mises stress of a simulated single SiC device sub-module was between 1.2 MPa to 2.4 GPa. The maximum shear stress at 300 watts/cm2 was predicted to be 243 MPa. Both the maximum and minimum chip temperature decreased with increasing heat transfer coefficient from 25 to 2500 watts/m2 K. With modest cooling, represented by a heat transfer coefficient (hconv) of 250 watts/m2 K, SiC chips operated at 300 watts/cm2 power density maintained junction temperatures Tj < 400 K. If consistent with simulation results, CVD diamond integrated substrates should be superior to those comprised of AlN or Al2O3. Asymmetric device placement in the multi-chip module proved more effective at avoiding potential hot spots than the symmetric configuration.
Authors: Feng Xu, Bo Wang, Hai Long Zhang
Abstract: According to the definition about the positive and negative gradient temperature distribution of structural cross section in the Chinese bridge design specification of General Code for Design of Highway Bridge and Culverts (JTG D60-2004), same temperature loads are applied to beam model and solid model of a typical there-span prestressed concrete continuous box-girder bridge to compare the numerical results of thermal stresses calculated from the two finite element models. The beam model is built through professional software Doctor Bridge that is prevailing in China for structural static analysis of bridge design, while the solid model is built using ANSYS. Between the two models, the numerical results of total thermal stress regarded to be added up with self-restrained stress and secondary stress are compared. The results from solid model are found to be much more conservative than from element model. The identity and diversity of the two series of results and the reasons for the generation of the diversity are expounded. It is recommended that the thermal stress calculated from solid model be better to be taken into account in a design so as to examine or amend the results that calculated through the professional software based on bar system FEM theory.
Authors: Min Wu, Joe Dong, Andy Zhao, Wai Ching Tang, Willy Sher, Guang Wei Chen, Shuo Chen, Zhi Dan Qin, Yan Zhou, Yin Wang
Abstract: Construction workers are vulnerable to heat stress, and a number of heat-related injuries and deaths have been reported. This study thus introduces a phase change material (PCM) based cooling garment designed for construction workers. The PCM cooling garment will be effective in reducing the workers body temperature and can extend their maximum tolerable time on sites.
Authors: Mikio Oda, Binti Ibrahim Anis Farhana, Y. Nakamura
Abstract: A laminated beam containing an initial delamination subjected to thermal gradient is analyzed on the basis of classical beam theory. The axial forces are induced in the parts of the constituent beams above and below the delamination. For the case where crack faces are open, a nonlinear equation for determining the in-plane forces is derived by modeling the delaminated part as two lapped beams hinged at both ends, and by imposing the compatibility condition of the deformations of the two beams. Numerical solutions are obtained for some model beams. It is shown that the relative displacement at the center of the delamination increases gradually with the increase very rapidly, i.e., local delamination buckling occurs. Energy release rate is small for temperature gradient below the critical value, but it takes a large value when the temperature gradient is increased beyond the critical value.
Authors: Zhi Li, Min You, Xiao Ling Zheng, Mei Rong Zhao, Jia Ling Yan
Abstract: The 3-D elasto-plastic finite element method (FEM) was used to analyze the thermal stress in the laminated composite (SiC/6061Al) under the condition of a temperature cycling of 200 0C-30 0C- 200 0C-30 0C. The results from the FEM analysis showed that the hysteretic peak value of the von Mises equivalent stress in the substrate 6061Al was increased significantly as the temperature loading cycles processed on but it was nearly the same after the first cycle in the interface layer SiC of the laminated composite. The elastic strain in the substrate 6061Al varied within the range of -0.15% to 0.15% and the maximum plastic deformation was equal to about 0.26 %. The results also showed that the maximum normal stress Sx was increased from 32.8 MPa to 87.9 MPa after ten cycles and the work-hardening of the substrate 6061Al occurred during the stress and strain hysteresis loop.
Authors: M.A. Ali, S.T. Hasan, D.P. Myriounis
Abstract: An empirical solution for the thermal shock stresses in cylindrical shell presented when cylinder is subjected to heating or re-heating case and down-shock cooling by forced air case. Linear equations are developed to describe the severity of thermal shock loading. When thermal gradient and time period are in consideration, it is shown the equations displays good approximation for major characteristics of the thermal shock stress profiles.
Authors: Xiao Yu Yang, Wei Zhou
Abstract: To perform the temperature compensation, a bimetallic thin film with different thermal expansion coefficients is deposited on the surface of the crystal plate. The thermal stress generated in the crystal and the thin film will cancel each other when temperature changes, thus improve the frequency stability of the crystal oscillator. In this paper, a finite element simulation was carried out for the crystal plate with bimetal, and then an experiment was performed to verify the FEM simulation results. The result shows that this approach achieves good temperature - frequency characteristics and reduces the frequency shift of crystal oscillator.
Authors: Ye Hu Lu, Xiao Hui Li, Jun Li, Dai Wei Wu
Abstract: Various intensity heat fluxes firefighters encountered will produce thermal stress on skin, resulting in thermal pain and tissue damage. In this paper, a new approach to evaluate thermal stress under flashover with short duration was carried out based on plain-stress theory. Instant heat flux under fabric was calculated so as to determine temperature and thermal stress distribution. The results obtained were as follows: temperature increased slightly at initial stage and then sharply increased linearly, moreover, temperature was much higher when sensor directly contacted with specimen, comparing with that of 6mm air gap; heat flux under fabric quickly reached its maximum, and higher heat flux was observed as no air gap generated; thermal stress rapidly increased and then gradually decreased, moreover, higher thermal stress produced without air gap. The newly proposed method could well distinct heat transfer performance of fabric under different conditions, which might provide helpful guideline to performance evaluation of thermal protective clothing.
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