Simulation Of Mechanical Response Research Articles

Simulation of Mechanical Response in Machining of Ti-6Al-4V Based on Finite Element Model and Visco-Plastic Self-Consistent Model

The predictions of mechanical responses (stress–strain variations) in the machining of Ti-6Al-4V alloy are important to analyze the deformation conditions of machining to optimize the machining parameters and investigate the generation of a machined surface. The selection of a constitutive model is an essential factor that determines the deformation behavior in the machining simulation model. In this paper, two constitutive models of a modified Johnson–Cook (JC) equation and visco-plastic self-consistent (VPSC) model were used to investigate the stress–strain evolutions in the machining process of Ti-6Al-4V. A finite element (FE) machining model was established, considering the influences of grain refinement and deformation twins, based on a modified JC equation. The VPSC model was fitted based on the macro-strain rate sensitivity of the JC equation. The prediction results of the stress–strain curves of two models were compared, and their validities were further proved. The results show that flow stress hardening and inhomogeneities are caused by multi-scale grain refinement during the machining process of Ti-6Al-4V. Five slip deformation modes and one compressive twinning mode were activated in the VPSC model to be consistent with the macro-deformation behavior predicted with the FE model. The validations show the effectiveness of the modified JC equation, considering microstructural changes and the fitted VPSC model, in predicting dynamic behavior in the machining process of Ti-6Al-4V. The results provide two aspects of macro-deformation and polycrystal plasticity to elucidate the stress variations that occur during the machining of Ti-6Al-4V.

Simulation of Mechanical Response in Nanoparticles

Morphology and mechanical resonse of copper nanoparticles with defects have been simulated by means of molecular dynamics simulation. The embedded atom method potential for copper was used to express the interaction of atoms. Four types of model samples were prepared and about 37,000 atoms were contained in each sample. Two of them are cubic shape with {100} surfaces, in which vacancies or interstitials are introduced. The other two samples are once melted and solidified particles with nearly spherical surfaces. The atomic structure is controlled by cooling rate, and crystalline and amorphous structures are realized. Shear and tetragonal strains are applied to the samples and stress-strain relations for the samples are derived. Mechanical damping and internal friction were evaluated from the free decaying oscillations by releasing static strains.

Simulation of mechanical response and internal friction by point defects

Structures and dynamical behaviors of atoms in crystals containing self-interstitials have been investigated by means of molecular dynamics simulations. Embedded atom method potential for copper was used in the simulation. Model crystals consist of 11,000 atoms and include several self-interstitials. Motions of interstitials at elevated temperatures are investigated by monitoring the trajectory of atoms. Simultaneous jumps of several atoms near the interstitial are observed. Motion of interstitial atoms under an elastic vibration of model crystals is also investigated. The internal friction is estimated from the decay of free oscillation of model crystals. The internal friction increases by the introduction of interstitials and the internal friction for one interstitial is estimated to be the order of 10 −4 at the frequency of 230 GHz.

Simulation of mechanical response of point defects in copper

A molecular dynamics simulation has been performed to investigate the dynamical nature and the mechanical response of self-interstitials in copper. The embedded-atom method potential developed by the present authors is adopted to express the atomic interaction in crystals. The static configuration and the interaction with the elastic vibration are simulated, and the internal friction by the interstitial is evaluated from the damping of elastic vibration. The motion of interstitial atoms in the vibrating crystal is analyzed through the trajectory of the motion of atoms. The trajectory for the thermal motion of interstitial atoms at elevated temperatures is also derived and the thermal migration of interstitials is investigated.

Simulation of mechanical response during polymer crystallization around rigid inclusions and voids: homogeneous crystallization

The mechanical effects of homogeneous polymer crystallization around single defects are studied, showing how crystallization can develop residual stresses, and change material moduli. Defects in the form of rigid inclusions or voids are considered, either having spherical or cylindrical geometry. Problems with spherical symmetry are considered in the case of a spherical defect, and plane strain problems with axial symmetry are considered in the case of a cylindrical defect. The predicted response is based on a constitutive model developed by Negahban et al. (1993, Int. J. Eng. Sci. 31(1), 93–113), and shows that large residual stresses develop, which may result in debonding or fracture.

Simulation of mechanical response in crystallizing polymers: crystallization under a constant shear force

The mechanical response of crystallizing polymers under shearing controlled by a constant load is simulated by the model developed by Negahban et al. [10]. It is shown that under a constant shear load the shear strain increases with crystallization. The history of this shear strain directly affects the residual shape of the material after unloading. The shear modulus and elastic moduli are calculated as functions of the shear load and the degree of crystallization. Comparison with simulations based on a constant shear strain shows that some material moduli have the same functional relations and others are different. Specific simulations based on parameters selected for natural rubber are presented and compared to the response under constant shear strain.

Simulation of mechanical response in crystallizing polymers: crystallization under constant shearing deformations

Using a model developed by Negahban et al. ((1993), Int. J. Eng. Sci. 31(1), 93–113), the mechanical response of crystallizing polymers under two different constant shearing deformations are simulated. Stress relaxation and mechanical moduli during the crystallization process are evaluated. Residual strains after unloading are calculated. Results are plotted for material constants representing natural rubber.

Simulation of mechanical response in polymer crystallization

The problem of following the mechanical response of a polymer during crystallization is studied using a theory developed by Negahban and Wineman [1]. Elastic modulus, shear modulus, and Poisson's ratio are defined in the context of polymer crystallization. For unconstrained crystallization and crystallization under constant uniaxial stretching, the values of elastic modulus, shear modulus, poisons ratio, and residual stretch are evaluated. The proposed model is fit to data available for natural rubber and the predictions of the model are discussed.