Simulation Of Mechanical Behavior Research Articles

543 寸法依存性を有するゴム充てんポリマー材の変形挙動シミュレーション

543 寸法依存性を有するゴム充てんポリマー材の変形挙動シミュレーション

A coupled atomistic/continuum model of defects in solids

A method is introduced for reducing the degrees of freedom in simulations of mechanical behavior of materials without sacrificing important physics. The method essentially combines the quasicontinuum (QC) method with continuum defect models such as the discrete dislocation (DD) method. The QC formulation is used to couple a fully atomistic region to a defect-free elastic continuum. Defects existing in the elastic continuum region of the full problem of interest are treated by the DD-like methods with special boundary conditions. The full coupled problem is then solved by an Eshelby-like procedure involving superposition of the QC and DD problems, and is appropriate in both 2d and 3d. Special attention is given to dealing with dislocation defects. A procedure for the “passing” of dislocation defects from the atomistic to the continuum description in 2d problems is also presented. The overall 2d method with dislocation defects is validated by comparing the predictions of the coupled model to “exact” fully atomistic models for several equilibrium dislocation geometries and a nanoindentation problem in aluminum, and excellent agreement is obtained. The method proposed here should find application to a broad host of problems associated with the multiscale modeling of atomistic, nano- and micromechanical behavior of crystalline solids under mechanical loads.

Characterization of thin film elastic properties using X-ray diffraction and mechanical methods: application to polycrystalline stainless steel

The Young's modulus and Poisson's ratio of reduced thickness layers are generally unknown whereas simulation of mechanical behavior of thin film/substrate systems or stress determination by X-ray diffraction cannot be done in an accurate way without the knowledge of these values. In this paper, we present three types of experiments which are used in our laboratory for determining elastic constants in polycrystalline thin films elaborated by ion beam sputtering: A vibrating reed device, X-ray tensile testing and AFM buckling geometry analysis. Results obtained for metallic 304L stainless steel thin films are given.

Molecular Dynamics Simulation of Mechanical Behaviors of a System Including Both a Crack and Grain Boundaries

Molecular Dynamics Simulation of Mechanical Behaviors of a System Including Both a Crack and Grain Boundaries

Global/Local Modelling of Structures with Local Heterogeneity.

For the numerical simulation of mechanical behaviors of structures with local heterogeneity, a global/local modelling technique using the finite element mesh superposition technique and shell-solid connection is proposed. Not only the global deformation but also three-dimensional stresses nearby the local heterogeneity can be analyzed precisely with less efforts than conventional methods. The finite element mesh superposition technique makes it possible to overlay local fine solid mesh which considers the local heterogeneity on global rough solid mesh which neglects the local heterogeneity. Aplate structure that contains dissimilar material in a local portion is analyzed by the proposed modelling technique. The results agreed well with those calculated using the conventional three-dimensional fine mesh model.

Numerical Simulation of Mechanical Behaviour of Textile Surfaces

AbstractThe paper presents a model which can be used for calculations of complex mechanical behaviour of textile surfaces e.g. surfaces obtained from a drapemeter. Fabric is treated an this model as a two‐dimensional continuum. As kinetic and kinematic measures are used these of the Cosserat continuum. Linear elastic, orthotropic constitutive equations which enable independent treatment of the in plane and out of plane deformations, describe material behaviour of the textile structure.

Mechanical behavior of strands in CIC conductor analyzed by Monte Carlo method

The computer simulation of mechanical behavior of strands in a cable-in-conduit (CIC) conductor analyzed by Monte Carlo method has been carried out for analyzing the stability of the CIC conductor. In the CIC conductor, the mechanical behavior of strands during energizing has not been evaluated sufficiently and hence the quantitative evaluation of the frictional heating, the contact stress between strands and the coupling losses that determine the stability of a CIC conductor hare not been clarified. A CIC conductor with 38% of void fraction were constructed in a computer by compressing the cable. In the Monte Carlo method, the position of strands which mere divided into mesh were changed to minimize the potential energy. It could simulate the strand motion induced by the Lorentz force and the change of the contact stress distribution between strands. The method developed in this work is also used to calculate the load-displacement curve of the cables and the position of strands. By using the method, it would be possible to estimate the stability of a CIC conductor.

Microscopic and Mesoscopic Evaluations of Materials. Hierarchical Modelling and Local Stress Analysis of Composite Materials and Structures.

In the numerical simulation of mechanical behaviors of composite materials and structures, a novel hierarchical modelling technique is proposed. Not only the global deformation but also the mesoscopic stresses are analyzed precisely with less human efforts than conventional methods. Four level hierarchy is defined for the textile composites, and the homogenization method and finite element mesh superposition technique are adopted. The latter technique makes it possible to overlay arbitrary local fine mesh on the global rough mesh. A panel with a rib made of knitted fabric composite material is analyzed by the proposed method. Three-dimensional modelling of the mesostructure of knitted fabric composite material is also shown. The validity of the proposed method was examined, and the mesoscopic stresses are calculated easily.

Finite Element Simulation of Mechanical Behaviors and Seal Performance of Oil Seal Plug.

A hydraulic machine is usually composed of many components. Oil seal plugs, which are used for preventing oil leakage, are one of the most important machine elements among them. Currently, it is sometimes reported that with increase of operating oil pressure, leakage occurs from the regions where oil seal plugs are attached. The configuration of oil seal plug is quite similar to that of ordinary hexagon bolt, except that the grip length and the height of head are particularly small. It is, therefore, anticipated that the specific shape of oil seal plug may yield characteristics significantly different from those of hexagon bolts. Despite its importance, however, it seems likely that mechanical behaviors of oil seal plug have not been investigated so far. In this paper, such fundamental characteristics of oil seal plug as the amounts of tightening torque required for desired clamping force and distributions of contact pressure relating to seal performance are analyzed using finite element method which deals with multi-body elastic contact problem. It is also examined how the rapid rising of oil pressure applied affects the variations of contact pressure with time and whether it might cause the oil leakage, using one-dimensional spring element together with the integration scheme proposed by Newmark.

Geometrically nonlinear bending of thin-walled shells and plates under creep-damage conditions

A phenomenological constitutive model for characterization of creep and damage processes in metals is applied to the simulation of mechanical behaviour of thin-walled shells and plates. Basic equations of the shell theory are formulated with geometrical nonlinearities at finite time-dependent deflections of shells and plates in moderate bending. Numerical solutions of initial/boundary-value problems have been obtained for rectangular thin plates (two-dimensional case) and axisymmetrically loaded shells of revolution (one-dimensional case). Based on the numerical examples for the two problems, the influence of geometrical nonlinearities on the creep deformation and damage evolution in shells and plates is discussed.

Finite Elements Simulation of Mechanical Behaviour of Shape Memory Alloys Coupled with a Non-Stationary Thermal Field

The main deformation mechanisms of shape memory alloys (SMA) are related to martensitic transformation and/or martensitic reorientation. These phenomena lead to heat production resulting from the transformation and/or from internal dissipation processes. As the SMA behaviour is strongly temperature dependent, its modelling has to take into account thermomechanical coupling. A 3-dimensional finite element code has been designed for that purpose. The quasi-static mechanical behaviour is described through the temperature dependent elastohysteresis model. Large displacements and large deformations are considered. The numerical problem is strongly non-linear and an implicit resolution scheme has been adopted. Two coupled thermomechanical calculations are presented. The first one deals with the one-way memory effect of a cantilever beam. The second one simulates the non-stationary thermal and mechanical fields of this beam during a near-adiabatic pseudoelastic bending.

Mechanical Behavior of Ceramic Granule Compact in Cold Isostatic Pressing. 2nd Report. Numerical Simulation of Mechanical Behavior.

A numerical simulation system is developed to estimate the mechanical behavior of a ceramic granule compact in cold isostatic pressing. In this system, a new yield criterion and constitutive equations proposed in the first report are used. Simulated results are compared with results of actually pressed <Al>2O3 compact. The agreement between calculated and the measured deformation of compact is relatively good.

Dynamic modelling of human articulating joints

Dynamic simulation of mechanical behavior and response of the total human body to external forces provide essential input for the injury prediction criteria and subsequent design and development of crash protection systems. The most sophisticated versions of the total-human-body models are articulated and multisegmented to simulate all the major articulating joints and segments of the human body. Effectiveness of the multisegmented models to predict accurately live human response depends heavily on the proper biomechanical description and simulation of the articulating joints. This paper is concerned with a mathematical modelling of an articulating joint defined by contact surfaces of two body segments which execute a relative dynamic motion within the constraints of ligament forces. Mathematical equations for the joint model are in the form of second-order nonlinear differential equations coupled with nonlinear algebraic constraint conditions. Differential equations of motion are reduced to a set of nonlinear simultaneous algebraic equations by applying the Newmark method of differential approximation. By subsequent application of Newton—Raphson iteration process the same equations are converted to a set of simultaneous linear algebraic equations. Iteration process is continued until a solution vector of unknowns satisfying a prescribed convergence criterion is obtained. The two-dimensional version of the mathematical joint model is applied to human knee joint for several dynamic loading conditions on tibia. Results for the ligament and contact forces, contact point locations between femur and tibia and the corresponding dynamic orientation of tibia with respect to femur are obtained.

Molecular dynamics simulation of mechanical behaviour

A molecular dynamics (MD) simulation of strain and failure of a crystal, the effect of environment on these processes, the interaction between the adsorption-active atoms and the environment walls, the effect of stress on mobility of interstitial admixtures, the formation and the failure of a contact between two crystals has been performed using a two-dimensional system consisting of Lennard-Jones atoms. The basic features of strain observed by means of MD included generation and motion of dislocations, various mechanisms of shear and brittle-to-ductile transition at low temperature. Environmentsensitive mechanical behaviour has been studied for the first time on an atomic scale. It is shown that rapid local processes whose unit act takes about 10−10 sec and involves several tens or a few hundred atoms may provide for environment-induced embrittlement. The features common to these microscopic processes are (1) pronounced interaction between the foreign atoms and the atoms of the solid, i.e. a sharp decrease in the surface energy of the solid in contact with the environment, and (2) direct participation of thermal fluctuations in the failure and rearrangement of interatomic bonds. By interacting with the crack walls, the environment atoms create a force compatible with the interatomic bond strength, which promotes crack propagation. Tensile stress causes appreciable acceleration of diffusion of interstitial admixtures in the direction normal to the strain axis and hinders diffusion along the axis. Under constant load the failure of interatomic bonds and sintering involve a thermal fluctuation mechanism.

金属材料の機械的挙動のシミュレーション

金属材料の機械的挙動のシミュレーション