Papers by Keyword: Thermo-Mechanical Stress

Abstract: In this paper the fracture problem of exhaust valve of the piston engine was investigated. Visual inspection showed that on the fractured surface of the valve the beach marks, typical for fatigue failure were observed. The crack origin was not covered by corrosion products or material defects. In order to explain the reasons of damage of the valve, the non-linear finite element method was utilized. The numerical model composed of the poppet valve, the guide and the seat face was defined. In the analysis both the mechanical load resulting from the valve spring and also the thermal load arising from a non-uniform temperature field were defined. The loads were at first defined separately in order to check which load component has a dominant influence on the stress level. In third load case (which represents the operational thermo-mechanical engine conditions) the mentioned loads were defined simultaneously. The results of performed computations showed that the operational dynamic stress (in the critical zone of the valve where the crack appeared) is more than 12 times lower than the yield stress of the material. It means that the premature fatigue fracture of the valve was probably caused by any phenomenon concerned with the increase of the operational stress in the valve. The additional observation of the second (non-damaged) valve from the same engine head showed that the carbon deposit was located on the valve face. The results of the stress analysis of the valve with additional carbon particle showed, that in the valve stem a high bending stress was observed.

Abstract: A super wedge tip element for application to a bi-material wedge is develop utilizing the thermo-mechanical stress and displacement field solutions in which the singular parts are numerical solutions. Singular stresses near apex of an arbitrary bi-material wedge under mechanical and thermal loading can be obtained from the coupling between the super wedge tip element and conventional finite elements. The validity of this novel finite element method is established through existing asymptotic solutions and conventional detailed finite element analysis.

Abstract: Thermo-mechanical stresses analysis of laminated hollow circular cylinder with finite length are carried out in this study based on the theory of laminated composites. The hollow circular cylinders with finite length are simply supported at four edges and are subjected to nonuniform thermal and mechanical loadings on the inner and outer surfaces. Analytical solutions of temperature distribution and thermo-mechanical stress fields are derived by using variable separation approach and series solving method. A four -layer laminated hollow circular cylinder with finite length is numerically analyzed by using the present method. All results are graphically presented and briefly discussed.

Abstract: The ambient and denuded trench top corner at the step of gate oxidation play an important role to generate defect. Furthermore, dislocation-free flash process is proposed, and its mechanism as well. The impact on dislocation of the other processes is also discussed. And we knew that using of dry oxidation for gate oxide has the characteristic to reduce the dislocation. Consequently, the dislocation free wafer is obtained by changing gate oxide from wet to dry in manufacturing embedded flash.

Abstract: The volume-averaged hydrostatic parts of thermo-mechanical stresses in the metal interconnect line determined by XRD method and finite element method are compared with each other. Two typical shapes of passivated Al-0.5%Cu thin film with SiN or FOx(Flowable Oxide) are selected for this study. For the numerical calculation, the stress concentration effect around the edge of Al-Cu thin film and elastic-plastic behavior of the film following its hardening rule are considered. For the stress obtained by XRD, the experimental results of Park and Jeon[Microelectron. Eng., 69 (2003) p.26] are introduced. A good agreement is found between the volume-averaged hydrostatic stresses obtained from each method.