Mesoscopic Simulation Method Research Articles

Effects of solvent quality on the dynamics of polymer solutions simulated by dissipative particle dynamics

The rheology and configurational properties of dilute polymer solutions in steady shear flow are modeled by dissipative particle dynamics (DPD), a new mesoscopic simulation method. The simulations represent the polymer as a 10-bead chain of FENE connector springs and the solvent as a sea of free DPD particles. Thermodynamic interactions between the polymer and solvent are modeled by varying the strength of the repulsive forces acting between unlike particle species. Since DPD simulations model the full hydrodynamics of the polymer–solvent system, instantaneous hydrodynamic interactions among beads of the polymer chain emerge naturally from the simulations. The predicted rheological material functions include realistic features such as shear thinning of the viscosity and first normal stress coefficient, and negative values for the ratio Ψ2/Ψ1. The enhancement of η, Ψ1, and Ψ2 by means of chain expansion in good solvents is also realistically represented by the model predictions. The DPD simulations accurat...

Dynamics of liquid–liquid demixing: mesoscopic simulations of polymer solutions

In this article, the mesoscopic simulation method dissipative particle dynamics (DPD) is applied to study the dynamics of polymer–solvent liquid–liquid phase separation. It will be shown that the degree of branching has a pronounced effect on the radius of gyration and the centre of mass diffusion of the polymer. Based on the simulation results it can be concluded that the difference in chemical potential between the mixed and the demixed state is the main driving force behind the centre of mass diffusion (and thus phase separation), rather than the reduced radius of gyration due to to polymer chain collapse.

2-D Mesoscopic Simulation of Two-Phase Materials Containing Short Fibers.

The two-dimensional mesoscopic simulation method previously proposed by one of the authors for brittle microcracking solids is applied to the analysis of two-phase materials containing short fibers. Numerical results are presented to demonstrate validity of the proposed method. The effect of elastic property, slenderness, volume fraction, fiber-end cracks and orientation-distribution function of short fibers on overall elastic properties of two-phase materials has been studied. The microcracking behavior under tensile, shear and bending stress conditions accompanied by crack deflection, crack bridging and fiber pull-out has also been analyzed by the proposed mesoscopic simulation method.

2-D Mesoscopic Simulation of Two-Phase Materials Containing Microinclusions.

The microcracking behaviors of two-phase materials containing microinclusions with the various mismatch between mechanical properties of matrix and inclusions are analyzed by using the two-dimensional mesoscopic simulation method. The first mismatch considered is the one for Poisson's ratio. Under the condition of compressive stress, inclusions with higher or lower Poisson's ratio than the matrix cause different patterns of microcracking near the inclusion. The second mismatch is concerned with the stiffness and the strength against microcracking of matrix, inclusions and their interfaces. Parametric studies have been conducted for their influences on macro, stressstrain relations.

Dissipative particle dynamics: Bridging the gap between atomistic and mesoscopic simulation

We critically review dissipative particle dynamics (DPD) as a mesoscopic simulation method. We have established useful parameter ranges for simulations, and have made a link between these parameters and χ-parameters in Flory-Huggins-type models. This is possible because the equation of state of the DPD fluid is essentially quadratic in density. This link opens the way to do large scale simulations, effectively describing millions of atoms, by firstly performing simulations of molecular fragments retaining all atomistic details to derive χ-parameters, then secondly using these results as input to a DPD simulation to study the formation of micelles, networks, mesophases and so forth. As an example application, we have calculated the interfacial tension σ between homopolymer melts as a function of χ and N and have found a universal scaling collapse when σ/ρkBTχ0.4 is plotted against χN for N>1. We also discuss the use of DPD to simulate the dynamics of mesoscopic systems, and indicate a possible problem with the timescale separation between particle diffusion and momentum diffusion (viscosity).

Damage mechanics models for brittle microcracking solids based on three-dimensional mesoscopic simulations

Fracture behaviors of brittle polycrystalline solids such as ceramic materials are deeply related to microcracking. Continuum damage mechanics is considered a powerful theoretical framework to deal with brittle microcracking solids. However, it is fairly difficult to obtain analytically, as well as experimentally, evolution equations for microcracking and reduced elastic compliances of microcracked solids. In the present study, a three-dimensional mesoscopic simulation method using a discontinuum mechanics model is employed to obtain this information. Based on the results of mesoscopic simulations, improved damage mechanics models assuming anisotropy as well as isotropy are proposed. Some numerical studies have been conducted to confirm their validities.

Mesoscopic Simulation of Microcracking Behaviors of Brittle Polycrystalline Solids : 1st Report, Study of Isotropic Theory in Continuum Damage Mechanics

Fracture behaviors of brittle polycrystalline solids such as ceramic materials are deeply related to microcracking. Continuum damage mechanics is considered a powerful theoretical framework to deal with brittle microcracking solids. However, it is fairly difficult to obtain analytically, as well as experimentally, evolution equations for microcracking and reduced elastic compliances of microcracked solids. In the present study, a mesoscopic simulation method at grain scale using a discontinuum mechanics model is employed to obtain such information. The validity and limitations of the isotropic theory of continuum damage mechanics are studied here.

Computational damage mechanics models for brittle microcracking solids based on mesoscopic simulations

Fracture behavior of brittle polycrystalline solids such as ceramic materials is closely related to microcracking. Continuum damage mechanics is considered as a powerful theoretical framework within which to deal with brittle microcracking solids. However, it is fairly difficult to obtain analytically as well as experimentally evolution equations for microcracking and reduced elastic compliances of microcracked solids. In the present study, a mesoscopic simulation method using a discontinuum mechanics model is employed to obtain this information. Based on the results of mesoscopic simulations, improved damage mechanics models assuming anisotropy as well as isotropy are proposed and applied to the finite element analysis of microcracking near the macrocrack-tip in a compressive stress field.

Mesoscopic Simulation of Microcracking Behaviors of Brittle Polycrystalline Solids. 1st Report, Study of Isotropic Theory in Continuum Damage Mechanics.

Fracture behaviors of brittle polycrystalline solids such as ceramic materials are deeply related to microcracking. Continuum damage mechanics is considered a powerful theoretical framework to deal with brittle microcracking materials, however, it is fairly difficult to obtain analytically as well as experimentally evolution equations for microcracking and reduced elastic compliances of microcracked solids. In the present study, a mesoscopic (grain level) simulation method using a discontiuum mechanics model is proposed to solve these problems. The validity and limitations of the isotropic theory of continuum damage mechanics are studied in the first report.