S.Y. Wang^1,2, K.M. Lim^2,3, B.C. Khoo^2,3, M.Y. Wang⁴

CMES-Computer Modeling in Engineering & Sciences, Vol.18, No.3, pp. 155-182, 2007, DOI:10.3970/cmes.2007.018.155

Abstract In this paper, a geometric deformation constrained level set method is presented as an effective approach for structural shape and topology optimization. A level set method is used to capture the motion of the free boundary of a structure. Furthermore, the geometric deformation of the free boundary is constrained to preserve the structural connectivity and/or topology during the level set evolution. An image-processing-based structural connectivity and topology preserving approach is proposed. A connected components labeling technique based on the 4-neighborhood connectivity measure and a binary image is used for the present region identification. The corresponding binary image after an exploratory… More >

Chein-Shan Liu ^1,2

CMES-Computer Modeling in Engineering & Sciences, Vol.17, No.2, pp. 73-94, 2007, DOI:10.3970/cmes.2007.017.073

Abstract The primary objectives of the present exposition focus on five different types of representations of the plastic equations obtained from an elastic-perfectly plastic model by employing different corotational stress rates. They are (a) an affine nonlinear system with a finite-dimensional Lie algebra, (b) a canonical linear system in the Minkowski space, (c) a non-canonical linear system in the Minkowski space, (d) the Lie-Poisson bracket formulation, and (e) a two-generator and two-bracket formulation. For the affine nonlinear system we prove that the Lie algebra of the vector fields is so(5,1), which has dimensions fifteen, and by the Lie theory the superposition… More >

Masanori Kikuchi ¹

CMES-Computer Modeling in Engineering & Sciences, Vol.11, No.2, pp. 49-60, 2006, DOI:10.3970/cmes.2006.011.049

Abstract Three kinds of fracture specimens are tested under different constraint conditions. By the SEM(Scanning Electron Microscope) observation, it is shown that the roughness of fracture surface is different from each other largely. This is the effect of constraint condition. The dimple fracture process is simulated by the finite element method using Gurson’s constitutive equation, and the crack tip stress fields are obtained. The distributions of stress triaxiality qualitatively agree with the experimental results. The J-R curves obtained also qualitatively agree with those of experiments, and the fracture surface roughness is well simulated. More >

Michihiko Nakagaki¹, Shuji Takashima², Ryosuke Matsumoto¹, Noriyuki Miyazaki²

CMES-Computer Modeling in Engineering & Sciences, Vol.10, No.3, pp. 199-208, 2005, DOI:10.3970/cmes.2005.010.199

Abstract The present paper focuses on the micromechanical phenomena occurring in the polycrystalline metal materials. Correlations between the material hardening and the plastic lattice dislocation were discussed with the presence of the grain boundary. The characteristic distribution of the plastic strain gradient is numerically recognized, and hence the validity of incorporating the strain gradient term in the constitutive law is demonstrated. Also, the modeling of the inclusion interface sliding and debonding was performed on the equivalent inclusion theory to develop the constitutive law for the composite. The sliding model is considered to be effective to model the superplastic behavior of highly… More >

V.K. Tewary², D.T. Read²

CMES-Computer Modeling in Engineering & Sciences, Vol.6, No.4, pp. 359-372, 2004, DOI:10.3970/cmes.2004.006.359

Abstract An integrated Green's function and molecular dynamics technique is developed for multiscale modeling of a nanostructure in a semi-infinite crystal lattice. The equilibrium configuration of the atoms inside and around the nanostructure is calculated by using molecular dynamics that accounts for nonlinear interatomic forces. The molecular dynamics is coupled with the lattice statics Green's function for a large crystallite containing a million or more atoms. This gives a fully atomistic description of a nanostructure in a large crystallite that includes the effect of nonlinear forces. The lattice statics Green's function is then related to the anisotropic continuum Green's function that… More >

Jihan Kim¹, Yong Hyup Kim¹, Sung Won Lee²

CMES-Computer Modeling in Engineering & Sciences, Vol.6, No.3, pp. 263-276, 2004, DOI:10.3970/cmes.2004.006.263

Abstract The Koiter's asymptotic method is combined with the assumed strain solid shell element formulation for postbuckling analysis of composite and sandwich structures. The assumed strain solid shell element is free of locking and the small angle assumption, and it allows multiple plies through the element thickness. While laminated composite structures are modeled with single element through the thickness, sandwich structures are modeled with three elements stacked through the thickness to model the face sheets and the core independently. The Koiter's method is used to trace initial postbuckling path. Subsequently, the Koiter's method is switched to the arc-length method to investigate… More >

Y. Başar, O. Kintzel¹

CMES-Computer Modeling in Engineering & Sciences, Vol.4, No.2, pp. 217-230, 2003, DOI:10.3970/cmes.2003.004.217

Abstract The objective of this contribution is the development of a finite element model for finite rotation and large strain analysis of thin walled shells involving geometry intersections. The shell configuration is described by a linear polynomial in the thickness coordinate. The director of the shell is multiplicatively decomposed into a stretching parameter and an inextensible unit vector whose rotation is accomplished by an updated-rotation formulation. A rotation vector with three independent components is used throughout the shell which permits advantageously to consider smooth shells and compound shells by a unified procedure. This formulation is introduced into an isoparametric four-node element.… More >

Z.Tang, S. Shen, S.N. Atluri¹

CMES-Computer Modeling in Engineering & Sciences, Vol.4, No.1, pp. 177-196, 2003, DOI:10.3970/cmes.2003.004.177

Abstract A meshless numerical implementation is reported of the 2-D Fleck-Hutchinson phenomenological strain-gradient theory, which fits within the framework of the Toupin-Mindlin theories and deals with first-order strain gradients and the associated work-conjugate higher-order stresses. From a mathematical point of view, the two-dimensional Toupin-Mindlin strain gradient theory is a generalization of the Poisson-Kirchhoff plate theories, involving, in addition to the fourth-order derivatives of the displacements, also a second-order derivative. In the conventional displacement-based approaches in FEM, the interpolation of displacement requires C$^{1}$ --continuity (in order to ensure convergence of the finite element procedure for 4$^{th}$ order theories), which inevitably involves very… More >

E. H. Glaessgen¹, W.T. Riddell², I. S. Raju¹

CMES-Computer Modeling in Engineering & Sciences, Vol.3, No.1, pp. 103-116, 2002, DOI:10.3970/cmes.2002.003.103

Abstract The effects of several critical assumptions and parameters on the computation of strain energy release rates for delamination and debond configurations modeled with plate elements have been quantified. The method of calculation is based on the virtual crack closure technique (VCCT), and models of the upper and lower surface of the delamination or debond that use two-dimensional (2D) plate elements rather than three-dimensional (3D) solid elements. The major advantages of the plate element modeling technique are a smaller model size and simpler configurational modeling. Specific issues that are discussed include: constraint of translational degrees of freedom, rotational degrees of freedom… More >

K. Nesnas¹, A. Abdul-Latif²

CMES-Computer Modeling in Engineering & Sciences, Vol.2, No.3, pp. 373-388, 2001, DOI:10.3970/cmes.2001.002.373

Abstract Large plastic collapse of an identical pair of cylinders of various geometries having the same length and volume is studied under lateral compressive load. Superplastic material is employed as a representative material to simulate the classical engineering material behavior under high strain rate. The effects of the strain rate and the geometry of cylinders on the plastic collapse are taken into account. The experimental study is conducted using a structure in which one cylinder is superplastic and the other is steel (referred to as deformable and non-deformable situation "DND''). The actual structure (DND) and that one investigated experimentally by Abdul-Latif… More >