Yuanzhong Hu¹, Yuchuan Liu, Hui Wang

CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.4, pp. 447-454, 2002, DOI:10.3970/cmes.2002.003.447

Abstract Scuffing, a major cause of failure in automobile engines, is considered as a dynamic process in this study. Local adhesions may occur randomly in lubricated contacts due to the existence of asperity contact and breakdown of lubricating films. Scuffing would take place if the local events develop rapidly into a large-scale plastic deformation and catastrophic failure. A system dynamic model established in the present paper allows one to predict dynamic behavior of a tribological system through numerical solutions of a group of differential equations. Results show that a transition to adhesion begins when the surface More >

George D. Manolis¹, Stavros Pavlou²

CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.3, pp. 399-416, 2002, DOI:10.3970/cmes.2002.003.399

Abstract A free-space Green's function for problems involving time-harmonic elastic waves in variable density materials under plane strain conditions is developed herein by means of Hormander's method in the context of matrix algebra formalism. The challenge when solving problems involving inhomogenous media is that the coefficients appearing in the governing equations of motion are position-dependent. Furthermore, an additional difficulty stems from the fact that these governing equations are vectorial, which implies that coordinate transformation techniques that have been successful with scalar waves can no longer be used. Thus, the present work aims at establishing the necessary More >

Ch. Zhang²

CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.3, pp. 381-398, 2002, DOI:10.3970/cmes.2002.003.381

Abstract A 2-D time-domain boundary integral equation method (BIEM) for transient dynamic analysis of cracked orthotropic solids is presented in this paper. A finite crack in an unbounded orthotropic solid subjected to an impact loading is considered. Hypersingular time-domain traction boundary integral equations (BIEs) are applied in the analysis. A time-stepping scheme is developed for solving the hypersingular time-domain traction BIEs. The scheme uses a convolution quadrature formula for temporal and a Galerkin method for spatial discretizations. Numerical examples are given to show that the presented time-domain BIEM is highly efficient and accurate. More >

Chengyu Wei^{1, 2}, Deepak Srivastava ², Kyeongjae Cho¹

CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.2, pp. 255-262, 2002, DOI:10.3970/cmes.2002.003.255

Abstract The temperature dependence of the plastic collapse of single-wall carbon nanotubes under axial compression has been studied with classical molecular dynamics simulations using Tersoff-Brenner potential for C-C interactions. At zero temperature, an (8,0) single-wall carbon nanotube under axial compression collapses by forming fins-like structure which remains within the elastic limit of the system, in agreement of previous molecular dynamics study. At finite temperatures, however, we find that temperature dependent fluctuations can activate the formation of sp3 bonds, in agreement with a recently proposed plastic collapse mechanism of the same nanotube with a generalized tight-binding molecular More >

R. Martinez¹, N. M. Ghoniem²

CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.2, pp. 229-244, 2002, DOI:10.3970/cmes.2002.003.229

Abstract We focus here on the direct coupling of Dislocation Dynamics (DD) computer simulations with the Finite Element Method (FEM) to simulate plastic deformation of micro-scale structures, and investigate the influence of crystal surfaces on dislocation motion. A series of three-dimensional (3-d) DD simulations of BCC single crystals with a single shear loop in the (101)-[111] slip system are first presented. The purpose of these simulations is to explore the relationship between loop force distributions and the proximity of the loop to the crystal boundary. Traction boundary conditions on a single crystal model are satisfied through… More >

W. C. Liu, S. Q. Shi, C. H. Woo, Hanchen Huang¹

CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.2, pp. 213-218, 2002, DOI:10.3970/cmes.2002.003.213

Abstract Using molecular dynamics method, we study the nucleation of dislocations and their subsequent propagation during the deposition of tungsten thin films under tension. Aiming to reveal the generic mechanisms of dislocation nucleation during the deposition of polycrystalline thin films, the case of tungsten on a substrate of the same material is considered. The substrate is under uniaxial tension along the [111] direction, with the thermodynamically favored (01^ˉˉ1) surface being horizontal. The simulation results indicate that the nucleation starts with a surface step, where a surface atom is pressed into the film along the [111^ˉˉ] More >

T. Nishioka¹, J. Furutuka¹, S. Tchouikov¹, T. Fujimoto¹

CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.1, pp. 129-146, 2002, DOI:10.3970/cmes.2002.003.129

Abstract The governing condition of dynamic crack bifurcation phenomena had not been fully elucidated until our recent experimental studies. We found from the experimental results that the energy flux per unit time into a propagating crack tip or into a fracture process zone governs the crack bifurcation. Regarding the numerical simulation of dynamic crack bifurcation, to the authors' knowledge, no accurate simulations have been carried out, due to several unresolved difficulties. In order to overcome the difficulties, for the analysis of dynamic crack bifurcation, we developed a moving finite element method based on Delaunay automatic triangulation. More >

António Tadeu, Julieta António¹

CMES-Computer Modeling in Engineering & Sciences, Vol.2, No.4, pp. 477-496, 2001, DOI:10.3970/cmes.2001.002.477

Abstract This paper presents analytical solutions, together with explicit expressions, for the steady state response of homogeneous three-dimensional layered acoustic and elastic formations subjected to a spatially sinusoidal harmonic line load. These formulas are theoretically interesting in themselves and they are also useful as benchmark solutions for numerical applications. In particular, they are very important in formulating three-dimensional elastodynamic problems in layered fluid and solid formations using integral transform methods and/or boundary elements, avoiding the discretization of the solid-fluid interfaces. The proposed Green's functions will allow the solution to be obtained for high frequencies, for which More >

KwangsooHo¹

CMES-Computer Modeling in Engineering & Sciences, Vol.2, No.3, pp. 351-364, 2001, DOI:10.3970/cmes.2001.002.351

Abstract Negative, zero or positive rate sensitivity of the flow stress can be observed in metals and alloys over a certain range of strain, strain rate and temperature. It is believed that negative rate sensitivity is an essential feature of dynamic strain aging, of which the Portevin-Le Chatelier effect is one other manifestation. The viscoplasticity theory based on overstress (VBO), one of the unified state variable theories, is generalized to model zero (rate independence) and negative as well as positive rate sensitivity in a consistent way. The present model does not have the stress rate term… More >

R. Sedaghati, A. Suleman¹, S. Dost, B. Tabarrok²

CMES-Computer Modeling in Engineering & Sciences, Vol.2, No.2, pp. 259-272, 2001, DOI:10.3970/cmes.2001.002.259

Abstract A structural analysis and optimization method is developed to find the optimal topology of adaptive determinate truss structures under various impact loading conditions. The objective function is based on the maximization of the structural strength subject to geometric constraints. The dynamic structural analysis is based on the integrated finite element force method and the optimization procedure is based on the Sequential Quadratic Programming (SQP) method. The equilibrium matrix is generated automatically through the finite element analysis and the compatibility matrix is obtained directly using the displacement-deformation relations and the Single Value Decomposition (SVD) technique. By More >