Q. Ma¹, C. Levy², M. Perl³

CMES-Computer Modeling in Engineering & Sciences, Vol.29, No.2, pp. 95-110, 2008, DOI:10.3970/cmes.2008.029.095

Abstract Networks of radial and longitudinally-coplanar, internal, surface cracks are typical in rifled, autofrettaged, gun barrels. In two previous papers, the separate effects of large arrays of either radial or longitudinally-coplanar semi-elliptical, internal, surface cracks in a thick-walled, cylindrical, pressure vessel under both ideal and realistic autofrettage were studied. When pressure is considered solely, radial crack density and longitudinal crack spacing were found to have opposing effects on the prevailing stress intensity factor, K_IP. Furthermore, the addition of the negative stress intensity factor (SIF), K_IA, resulting from the residual stress field due to autofrettage, whether ideal or realistic, tended to decrease… More >

Jyoti Ranjan Majhi, Ranjan Ganguli¹

CMES-Computer Modeling in Engineering & Sciences, Vol.27, No.1&2, pp. 25-36, 2008, DOI:10.3970/cmes.2008.027.025

Abstract The flapping equation for a rotating rigid helicopter blade is typically derived by considering 1) small flap angle, 2) small induced angle of attack and 3) linear aerodynamics. However, the use of nonlinear aerodynamics can make the assumptions of small angles suspect. A general equation describing helicopter blade flap dynamics for large flap angle and large induced inflow angle of attack is derived in this paper with nonlinear aerodynamics . Numerical simulations are performed by solving the nonlinear flapping ordinary differential equation for steady state conditions and the validity of the small angle approximations are examined. It is shown that… More >

Hanqing Jiang¹, Junqiang Lu², Min-Feng Yu², Yonggang Huang³

CMES-Computer Modeling in Engineering & Sciences, Vol.24, No.2&3, pp. 95-102, 2008, DOI:10.3970/cmes.2008.024.095

Abstract The periodic lattice registry of multi-walled carbon nanotubes (MWCNTs) have been exploited for the possibilities of development of nanodevices. This paper studied the telescoping behaviors of double-walled carbon nanotubes (DWCNTs) by atomic-scale finite element and tight-bind Green function methods. It was found that telescoping a DWCNT (e.g., (6,3)/(12,6)) will induce a rotational motion of the inner CNT that has a chirl angle θ (0° < θ < 30°). This telescoping-induced rotational motion does not exist for armchair and zigzag DWCNTs due to the symmetry of CNTs. The rotational angle is completely determined by the chirality of the inner CNT and… More >

S. Chen^1,2, Y. Liu^1,3, B.C. Khoo⁴, X.J. Fan⁵, J.T. Fan⁶

CMES-Computer Modeling in Engineering & Sciences, Vol.19, No.3, pp. 181-196, 2007, DOI:10.3970/cmes.2007.019.181

Abstract The mesoscopic simulation for fluids flow in a square microchannel is investigated using dissipative particle dynamics. The velocity distribution for single fluid in a square channel is compared with the solutions of CFD solver, which is found to be in good agreement with each other. The no-slip boundary condition could be well held for the repulsive coefficient ranged from 9.68 to 18.0. For the same range of repulsive coefficient, various wettabilities could be obtained by changing the repulsive coefficient for binary immiscible fluids, in which the immiscible fluids are achieved by increasing the repulsive force between species. The typical motion… More >

M. Akamatsu¹, K. Nakane², N. Ohno^1,2

CMES-Computer Modeling in Engineering & Sciences, Vol.10, No.3, pp. 217-228, 2005, DOI:10.3970/cmes.2005.010.217

Abstract In this study, a fully implicit integration scheme is developed for a nonisothermal viscoplastic, nonlinear kinematic hardening model. Nonlinear dynamic recovery in addition to strain hardening is assumed for the evolution of multiple back stresses so that ratcheting and mean-stress relaxation can be properly simulated. Temperature dependence of back stress evolution is also taken into account in the constitutive model. By discretizing a set of such advanced constitutive relations using the backward Euler method, a tensor equation is derived and linearized to iteratively achieve the implicit integration of constitutive variables. The fully implicit integration scheme developed is programmed as a… More >

Qing-Sheng Yang^1,2, Wilfried Becker³

CMES-Computer Modeling in Engineering & Sciences, Vol.6, No.4, pp. 319-332, 2004, DOI:10.3970/cmes.2004.006.319

Abstract The present paper focuses on the comparative investigation of different homogenization methods for fiber composites, void solids and rigid inclusion media. The effective properties of multi-phase media are calculated by three methods, i.e. direct average method of stress and strain, direct average method of strain energy and two-scale expansion method. A comprehensive comparison, in principle and numerically, of these methods is emphasized. It is obvious that the two direct average methods are identical in principle and therefore they give the same numerical results. It is shown that the two-scale expansion method is the same as the direct average concept of… 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 the superposition of the "image''… 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 in the evolution law for… More >

Samuel Olukayode Akinwamide¹, Serge Mudinga Lemika¹, Babatunde Abiodun Obadele^1,3, Ojo Jeremiah Akinribide¹, Bolanle Tolulope Abe², Peter Apata Olubambi¹

FDMP-Fluid Dynamics & Materials Processing, Vol.15, No.1, pp. 15-26, 2019, DOI:10.32604/fdmp.2019.04761

Abstract Development of metal matrix composite is becoming widespread in most engineering applications where excellent mechanical properties are required. Mechanical and microstructural properties of aluminium reinforced with silicon carbide was investigated. Ingot of aluminium was melted in a furnace at temperature ranging between 650-700 ℃. Ferrotitanium and silicon carbide were preheated in a muffle furnace before addition to molten aluminium in a crucible furnace. Fixed proportions of magnesium, ferrotitanium and varying proportions of silicon carbide were utilized as reinforcements. Stirring was carried out manually for a minimum of 10 mins after the addition of each weight percent of silicon carbide. Resulting… More >

Mohsen Ghorbani¹, Hossein Eisazadeh²

FDMP-Fluid Dynamics & Materials Processing, Vol.6, No.2, pp. 153-164, 2010, DOI:10.3970/fdmp.2010.006.153

Abstract Polypyrrole/Poly(vinyl acetate) (PPy/PVAc) copolymer was prepared by the copolymerization of vinyl acetate and pyrrole using FeCl3and benzoylperoxide as an oxidant in the presence of various surfactants such as sodium dodecylbenzenesulfonate and poly(ethylene glycol) in the aqueous/non-aqueous media. The PPy/PVAc copolymer was characterized in terms of conductivity, morphology, chemical structure, particle size and yield. The results indicate that the morphology, particle size, yield and electrical conductivity of the products are dependent on the type of surfactant and the arrangement of monomer injection. The chemical structure of obtained product was determined by FTIR spectroscopy. By comparison FTIR spectra between pure PPy and… More >