iwan sahputra - Academia.edu (original) (raw)

Papers by iwan sahputra

ChemEngineering

LAMMPS is a powerful simulator originally developed for molecular dynamics that, today, also acco... more LAMMPS is a powerful simulator originally developed for molecular dynamics that, today, also accounts for other particle-based algorithms such as DEM, SPH, or Peridynamics. The versatility of this software is further enhanced by the fact that it is open-source and modifiable by users. This property suits particularly well Discrete Multiphysics and hybrid models that combine multiple particle methods in the same simulation. Modifying LAMMPS can be challenging for researchers with little coding experience. The available material explaining how to modify LAMMPS is either too basic or too advanced for the average researcher. In this work, we provide several examples, with increasing level of complexity, suitable for researchers and practitioners in physics and engineering, who are familiar with coding without been experts. For each feature, step by step instructions for implementing them in LAMMPS are shown to allow researchers to easily follow the procedure and compile a new version of...

ChemEngineering

Viscoelastic bonds intended for Discrete Multiphysics (DMP) models are developed to allow the stu... more Viscoelastic bonds intended for Discrete Multiphysics (DMP) models are developed to allow the study of viscoelastic particles with arbitrary shape and mechanical inhomogeneity that are relevant to the pharmaceutical sector and that have not been addressed by the Discrete Element Method (DEM). The model is applied to encapsulate particles with a soft outer shell due, for example, to the partial ingress of moisture. This was validated by the simulation of spherical homogeneous linear elastic and viscoelastic particles. The method is based on forming a particle from an assembly of beads connected by springs or springs and dashpots that allow the sub-surface stress fields to be computed, and hence an accurate description of the gross deformation. It is computationally more expensive than DEM, but could be used to define more effective interaction laws.

Qatar Foundation Annual Research Conference Proceedings Volume 2016 Issue 1

Journal of Polymer Science Part B: Polymer Physics

A hybrid molecular mechanics-molecular dynamics simulation method has been performed to study the... more A hybrid molecular mechanics-molecular dynamics simulation method has been performed to study the effects of moisture content on the mechanical properties of microcrystalline cellulose (MCC) and the mobility of the water molecules. The specific volume and diffusion coefficient of the water increase with increasing moisture content in the range studied of 1.8-25.5 w/w %, while the Young's modulus decreases. The simulation results are in close agreement with the published experimental data. Both the bound scission and free-volume mechanisms contribute to the plasticization of MCC by water. The Voronoi volume increases with increasing moisture content. It is related to the free volume and the increase enhances the mobility of the water molecules and thus increases the coefficient of diffusion of the water. Moreover, with increasing moisture content, the hydrogen bonding per water molecule between MCC-water molecules decreases, thus increasing the water mobility and number of free water molecules.

Molecular Simulation

Where a licence is displayed above, please note the terms and conditions of the licence govern yo... more Where a licence is displayed above, please note the terms and conditions of the licence govern your use of this document. When citing, please reference the published version. Take down policy While the University of Birmingham exercises care and attention in making items available there are rare occasions when an item has been uploaded in error or has been deemed to be commercially or otherwise sensitive.

Journal of physics. Condensed matter : an Institute of Physics journal, Jan 24, 2018

A hybrid molecular mechanics-molecular dynamics (MM-MD) method is proposed to calculate the Young... more A hybrid molecular mechanics-molecular dynamics (MM-MD) method is proposed to calculate the Young's modulus of polymers at various temperature. It overcomes the limitation that MD is restricted to extremely high strain rates. A case study based on poly-methyl-methacrylate demonstrates that, contrary to previous MD studies, the method is able to accurately reproduce the effect of temperature on the Young's modulus in close agreement with experimental data. The method can also predict a more clear transition between the glassy and rubbery states than previous MD studies.

physica status solidi (b)

The effects of temperature and strain rate on the deformation behaviour of Polycarbonate were inv... more The effects of temperature and strain rate on the deformation behaviour of Polycarbonate were investigated using Molecular Dynamics simulations. An all-atom model of Bisphenol A Polycarbonate based on the Dreiding force field was used containing 9902 atoms. Deformation processes were simulated at four different temperatures and four different strain rates. Results of the simulations were similar to experimental measurements performed by other researchers using much lower strain rates. This strain rate discrepancy will be discussed. Emphasis will be put on Young's modulus, Poisson's ratio and yield stress.

Macromolecular Theory and Simulations, 2014

ABSTRACT The creep-tensile fatigue relationship is investigated using MD simulations for amorphou... more ABSTRACT The creep-tensile fatigue relationship is investigated using MD simulations for amorphous polyethylene, by stepwise increasing the R-ratio from 0.3 for fatigue to an R-ratio = 1 for creep. The simulations can produce similar behavior as observed in experiments, for instances strain-softening behavior and hysteresis loops in the stress-strain curves. The simulations predict the molecular mechanisms of creep and fatigue are the same. Fatigue and creep cause significant changes of the van der Waals and dihedral potential energies. These changes are caused by movements of the polymer chains, creating more un-twisted dihedral angles and the unfolding of polymer chains along the loading direction.

Journal of Polymer Research, 2014

Fatigue of amorphous polyethylene under low strain was simulated using molecular dynamics. The un... more Fatigue of amorphous polyethylene under low strain was simulated using molecular dynamics. The united atom approach and the Dreiding force field were chosen to describe the interaction between monomers. Molecular dynamics simulations resembling strain-controlled loading fatigue tests in tension-tension mode were performed to study the effect of the R-ratio and mean strain on the mechanical responses. Laboratory fatigue experiments in strain/ displacement control were performed at room temperature, and the results were compared to the simulation results. The simulations are able to produce qualitatively similar behaviour to the experimental results, for instance, mean stress relaxation, hysteresis loops in the stress-strain curve, and change in the cyclic modulus. They also show that stress relaxation is enhanced by cyclic loading. The simulations show that cyclic loading changes the total potential energies of the system, especially the van der Waals potential. The changes in the van der Waals potential energy contribute significantly to the increasing of the stiffness of the system. Some changes in dihedral angles with lower energy configurations are observed; however, bond distances and angles do not change significantly. The chains tend to unfold slightly along the loading axis as the fatigue loading progresses.

2007 IEEE International Conference on Industrial Engineering and Engineering Management, 2007

Main objective of this paper is to discuss comparison the results of injection moulding process s... more Main objective of this paper is to discuss comparison the results of injection moulding process simulation analysis generated by particular software with those obtained in a small-scale industrial process. The samples were produced by 'Dasset' Injection moulding machine at laboratory. Component was modelled using Rhinoceros Computer Aided Design (CAD) software. Simulation analysis was performed using Moldflow Plastics Insight (MPI). Two different positions of gate were selected for simulation to investigate the accuracy of the software. Polyethylene (PE) and High Impact Polystyrene (HIPS) were selected for analysis and production. Comparison with the samples showed that MPI predict maximum pressure needed to fill the mould cavity accurate. MPI predicted flow path and weld lines graphically those were similar to the machine's process. SIMPOL does not provide such results. It was not possible to compare with the machine's result because of the machine's problem. In addition to these results, MPI generated more simulation analysis report of injection moulding process.

Modelling and Simulation in Materials Science and Engineering, 2013

Molecular dynamics simulations are used to investigate the effects of temperature and strain rate... more Molecular dynamics simulations are used to investigate the effects of temperature and strain rate on the deformation of amorphous polyethylene. The simulations predict the effects of temperature and strain rate on the stress-strain responses, Young's modulus and Poisson's ratio similar to those observed in laboratory experiments performed by other researchers. The time-temperature superposition principle is applied to the Young's modulus and Poisson's ratio to form a master curve to address the discrepancies in strain rates between the simulations and the experiments. Differences in the numbers of monomers and chains, the degree of crystallinity and molecular orientation lead to discrepancies in the Young's modulus and Poisson's ratio between simulations and experiments.

ChemEngineering

LAMMPS is a powerful simulator originally developed for molecular dynamics that, today, also acco... more LAMMPS is a powerful simulator originally developed for molecular dynamics that, today, also accounts for other particle-based algorithms such as DEM, SPH, or Peridynamics. The versatility of this software is further enhanced by the fact that it is open-source and modifiable by users. This property suits particularly well Discrete Multiphysics and hybrid models that combine multiple particle methods in the same simulation. Modifying LAMMPS can be challenging for researchers with little coding experience. The available material explaining how to modify LAMMPS is either too basic or too advanced for the average researcher. In this work, we provide several examples, with increasing level of complexity, suitable for researchers and practitioners in physics and engineering, who are familiar with coding without been experts. For each feature, step by step instructions for implementing them in LAMMPS are shown to allow researchers to easily follow the procedure and compile a new version of...

ChemEngineering

Viscoelastic bonds intended for Discrete Multiphysics (DMP) models are developed to allow the stu... more Viscoelastic bonds intended for Discrete Multiphysics (DMP) models are developed to allow the study of viscoelastic particles with arbitrary shape and mechanical inhomogeneity that are relevant to the pharmaceutical sector and that have not been addressed by the Discrete Element Method (DEM). The model is applied to encapsulate particles with a soft outer shell due, for example, to the partial ingress of moisture. This was validated by the simulation of spherical homogeneous linear elastic and viscoelastic particles. The method is based on forming a particle from an assembly of beads connected by springs or springs and dashpots that allow the sub-surface stress fields to be computed, and hence an accurate description of the gross deformation. It is computationally more expensive than DEM, but could be used to define more effective interaction laws.

Qatar Foundation Annual Research Conference Proceedings Volume 2016 Issue 1

Journal of Polymer Science Part B: Polymer Physics

A hybrid molecular mechanics-molecular dynamics simulation method has been performed to study the... more A hybrid molecular mechanics-molecular dynamics simulation method has been performed to study the effects of moisture content on the mechanical properties of microcrystalline cellulose (MCC) and the mobility of the water molecules. The specific volume and diffusion coefficient of the water increase with increasing moisture content in the range studied of 1.8-25.5 w/w %, while the Young's modulus decreases. The simulation results are in close agreement with the published experimental data. Both the bound scission and free-volume mechanisms contribute to the plasticization of MCC by water. The Voronoi volume increases with increasing moisture content. It is related to the free volume and the increase enhances the mobility of the water molecules and thus increases the coefficient of diffusion of the water. Moreover, with increasing moisture content, the hydrogen bonding per water molecule between MCC-water molecules decreases, thus increasing the water mobility and number of free water molecules.

Molecular Simulation

Where a licence is displayed above, please note the terms and conditions of the licence govern yo... more Where a licence is displayed above, please note the terms and conditions of the licence govern your use of this document. When citing, please reference the published version. Take down policy While the University of Birmingham exercises care and attention in making items available there are rare occasions when an item has been uploaded in error or has been deemed to be commercially or otherwise sensitive.

Journal of physics. Condensed matter : an Institute of Physics journal, Jan 24, 2018

A hybrid molecular mechanics-molecular dynamics (MM-MD) method is proposed to calculate the Young... more A hybrid molecular mechanics-molecular dynamics (MM-MD) method is proposed to calculate the Young's modulus of polymers at various temperature. It overcomes the limitation that MD is restricted to extremely high strain rates. A case study based on poly-methyl-methacrylate demonstrates that, contrary to previous MD studies, the method is able to accurately reproduce the effect of temperature on the Young's modulus in close agreement with experimental data. The method can also predict a more clear transition between the glassy and rubbery states than previous MD studies.

physica status solidi (b)

The effects of temperature and strain rate on the deformation behaviour of Polycarbonate were inv... more The effects of temperature and strain rate on the deformation behaviour of Polycarbonate were investigated using Molecular Dynamics simulations. An all-atom model of Bisphenol A Polycarbonate based on the Dreiding force field was used containing 9902 atoms. Deformation processes were simulated at four different temperatures and four different strain rates. Results of the simulations were similar to experimental measurements performed by other researchers using much lower strain rates. This strain rate discrepancy will be discussed. Emphasis will be put on Young's modulus, Poisson's ratio and yield stress.

Macromolecular Theory and Simulations, 2014

ABSTRACT The creep-tensile fatigue relationship is investigated using MD simulations for amorphou... more ABSTRACT The creep-tensile fatigue relationship is investigated using MD simulations for amorphous polyethylene, by stepwise increasing the R-ratio from 0.3 for fatigue to an R-ratio = 1 for creep. The simulations can produce similar behavior as observed in experiments, for instances strain-softening behavior and hysteresis loops in the stress-strain curves. The simulations predict the molecular mechanisms of creep and fatigue are the same. Fatigue and creep cause significant changes of the van der Waals and dihedral potential energies. These changes are caused by movements of the polymer chains, creating more un-twisted dihedral angles and the unfolding of polymer chains along the loading direction.

Journal of Polymer Research, 2014

Fatigue of amorphous polyethylene under low strain was simulated using molecular dynamics. The un... more Fatigue of amorphous polyethylene under low strain was simulated using molecular dynamics. The united atom approach and the Dreiding force field were chosen to describe the interaction between monomers. Molecular dynamics simulations resembling strain-controlled loading fatigue tests in tension-tension mode were performed to study the effect of the R-ratio and mean strain on the mechanical responses. Laboratory fatigue experiments in strain/ displacement control were performed at room temperature, and the results were compared to the simulation results. The simulations are able to produce qualitatively similar behaviour to the experimental results, for instance, mean stress relaxation, hysteresis loops in the stress-strain curve, and change in the cyclic modulus. They also show that stress relaxation is enhanced by cyclic loading. The simulations show that cyclic loading changes the total potential energies of the system, especially the van der Waals potential. The changes in the van der Waals potential energy contribute significantly to the increasing of the stiffness of the system. Some changes in dihedral angles with lower energy configurations are observed; however, bond distances and angles do not change significantly. The chains tend to unfold slightly along the loading axis as the fatigue loading progresses.

2007 IEEE International Conference on Industrial Engineering and Engineering Management, 2007

Main objective of this paper is to discuss comparison the results of injection moulding process s... more Main objective of this paper is to discuss comparison the results of injection moulding process simulation analysis generated by particular software with those obtained in a small-scale industrial process. The samples were produced by 'Dasset' Injection moulding machine at laboratory. Component was modelled using Rhinoceros Computer Aided Design (CAD) software. Simulation analysis was performed using Moldflow Plastics Insight (MPI). Two different positions of gate were selected for simulation to investigate the accuracy of the software. Polyethylene (PE) and High Impact Polystyrene (HIPS) were selected for analysis and production. Comparison with the samples showed that MPI predict maximum pressure needed to fill the mould cavity accurate. MPI predicted flow path and weld lines graphically those were similar to the machine's process. SIMPOL does not provide such results. It was not possible to compare with the machine's result because of the machine's problem. In addition to these results, MPI generated more simulation analysis report of injection moulding process.

Modelling and Simulation in Materials Science and Engineering, 2013

Molecular dynamics simulations are used to investigate the effects of temperature and strain rate... more Molecular dynamics simulations are used to investigate the effects of temperature and strain rate on the deformation of amorphous polyethylene. The simulations predict the effects of temperature and strain rate on the stress-strain responses, Young's modulus and Poisson's ratio similar to those observed in laboratory experiments performed by other researchers. The time-temperature superposition principle is applied to the Young's modulus and Poisson's ratio to form a master curve to address the discrepancies in strain rates between the simulations and the experiments. Differences in the numbers of monomers and chains, the degree of crystallinity and molecular orientation lead to discrepancies in the Young's modulus and Poisson's ratio between simulations and experiments.