Pub Date : 2022-02-11DOI: 10.1142/s242491302142011x
M. Salman, V. Guski, S. Schmauder
Shape memory polymers (SMPs) are introduced as polymers that have the ability to return to their early programmed shape after exposure to an external stimulus. Enhancement of the material with nano-clay filler has improved its thermomechanical properties and increased the range of its applications in many fields of industry. Due to the tiny size of filler and the heterogeneous nature of the material structure at different scale levels, characterizing the material’s thermomechanical flow using conventional experimental equipment is a far-fetched task. Furthermore, providing one numerical model that is able to simulate the material thermomechanical behavior by including all the effects of the lower scale material structure is also very hard. In this study, a two-scale modeling approach is developed by a combination of the numerical homogenization scheme, 3D Representative Volume Element (RVE) concept, and finite element method. The effects of the filler weight fractions on the overall effective elastic constants as well as the material flow under a finite deformation are investigated. The resulting elastic constants and the stress–strain curves show a fairly good agreement with the analytical results. Furthermore, all the investigated results provide a deep understanding of the material behavior and a starting point for the next higher scale level modeling approaches.
{"title":"Two-scale modeling of nano-clay-filled shape memory polymers","authors":"M. Salman, V. Guski, S. Schmauder","doi":"10.1142/s242491302142011x","DOIUrl":"https://doi.org/10.1142/s242491302142011x","url":null,"abstract":"Shape memory polymers (SMPs) are introduced as polymers that have the ability to return to their early programmed shape after exposure to an external stimulus. Enhancement of the material with nano-clay filler has improved its thermomechanical properties and increased the range of its applications in many fields of industry. Due to the tiny size of filler and the heterogeneous nature of the material structure at different scale levels, characterizing the material’s thermomechanical flow using conventional experimental equipment is a far-fetched task. Furthermore, providing one numerical model that is able to simulate the material thermomechanical behavior by including all the effects of the lower scale material structure is also very hard. In this study, a two-scale modeling approach is developed by a combination of the numerical homogenization scheme, 3D Representative Volume Element (RVE) concept, and finite element method. The effects of the filler weight fractions on the overall effective elastic constants as well as the material flow under a finite deformation are investigated. The resulting elastic constants and the stress–strain curves show a fairly good agreement with the analytical results. Furthermore, all the investigated results provide a deep understanding of the material behavior and a starting point for the next higher scale level modeling approaches.","PeriodicalId":36070,"journal":{"name":"Journal of Micromechanics and Molecular Physics","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-02-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47437546","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-02-11DOI: 10.1142/s2424913021420078
Flavien Ghiglione, S. Forest
Torsional loading of elastoplastic materials leads to size effects which are not captured by classical continuum mechanics and require the use of enriched models. In this work, an analytical solution for the torsion of isotropic perfectly plastic Cosserat cylindrical bars with circular cross-section is derived in the case of generalized von Mises plasticity accounting solely for the symmetric part of the deviatoric stress tensor. The influence of the characteristic length on the microrotation, stress and strain profiles as well as torsional size effects are then investigated. In particular, a size effect proportional to the inverse of the radius of the cylinder is found for the normalized torque. A similar analysis for an extended plasticity criterion accounting for both the couple-stress tensor and the skew-symmetric part of the stress tensor is performed by means of systematic finite element simulations. These numerical experiments predict size effects which are similar to those predicted by the analytical solution. Saturation effects and limit loads are found when the couple-stress tensor enters the yield function.
{"title":"On the torsion of isotropic elastoplastic Cosserat circular cylinders","authors":"Flavien Ghiglione, S. Forest","doi":"10.1142/s2424913021420078","DOIUrl":"https://doi.org/10.1142/s2424913021420078","url":null,"abstract":"Torsional loading of elastoplastic materials leads to size effects which are not captured by classical continuum mechanics and require the use of enriched models. In this work, an analytical solution for the torsion of isotropic perfectly plastic Cosserat cylindrical bars with circular cross-section is derived in the case of generalized von Mises plasticity accounting solely for the symmetric part of the deviatoric stress tensor. The influence of the characteristic length on the microrotation, stress and strain profiles as well as torsional size effects are then investigated. In particular, a size effect proportional to the inverse of the radius of the cylinder is found for the normalized torque. A similar analysis for an extended plasticity criterion accounting for both the couple-stress tensor and the skew-symmetric part of the stress tensor is performed by means of systematic finite element simulations. These numerical experiments predict size effects which are similar to those predicted by the analytical solution. Saturation effects and limit loads are found when the couple-stress tensor enters the yield function.","PeriodicalId":36070,"journal":{"name":"Journal of Micromechanics and Molecular Physics","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-02-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48966524","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-01-29DOI: 10.1142/s2424913021430049
Shoaib Anwer, Baosong Li, Shaohong Luo, T. Alkhidir, S. Mohamed, V. Chan, K. Liao
Two-dimensional (2D) materials have been developed intensively over the last decade, and combining different 2D materials to form heterogeneous 2D materials is anticipated to be more attractive with broader applications. The precise evaluation and prediction of interfacial properties of 2D heterostructures are critical for designing more robust heterostructures and developing advanced, engineered molecular devices. Here, we present a brief review on experimental (namely, atomic force microscopy (AFM), in situ peel test, double cantilever beam, pressurized blister test and sheet-on-bead method) and theoretical techniques (namely, molecular dynamics and density functional theory) for probing the adhesion/interaction energy of the interface of 2D heterogeneous materials and paving the way for future applications.
{"title":"Experimental and theoretical characterization of the interfacial adhesion of 2D heterogeneous materials: A review","authors":"Shoaib Anwer, Baosong Li, Shaohong Luo, T. Alkhidir, S. Mohamed, V. Chan, K. Liao","doi":"10.1142/s2424913021430049","DOIUrl":"https://doi.org/10.1142/s2424913021430049","url":null,"abstract":"Two-dimensional (2D) materials have been developed intensively over the last decade, and combining different 2D materials to form heterogeneous 2D materials is anticipated to be more attractive with broader applications. The precise evaluation and prediction of interfacial properties of 2D heterostructures are critical for designing more robust heterostructures and developing advanced, engineered molecular devices. Here, we present a brief review on experimental (namely, atomic force microscopy (AFM), in situ peel test, double cantilever beam, pressurized blister test and sheet-on-bead method) and theoretical techniques (namely, molecular dynamics and density functional theory) for probing the adhesion/interaction energy of the interface of 2D heterogeneous materials and paving the way for future applications.","PeriodicalId":36070,"journal":{"name":"Journal of Micromechanics and Molecular Physics","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42366937","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-01-27DOI: 10.1142/s242491302142008x
Basil J. Paudel, D. Conover, Jung‐Kun Lee, A. To
Sintering of binder jet 3D printed (BJ3DP) parts results in significant nonlinear distortion with typical shrinkage value of 5–20%, which makes design for BJ3DP and post-machining difficult. In this work, a computational modeling framework with calibration and validation procedure is developed to simulate distortion during sintering of BJ3DP parts accurately for the first time. The computational model employs the finite element analysis with a viscoplastic constitutive model that accounts for effects of gravity and friction. A calibration procedure is proposed to obtain values of different model parameters systematically through dilatometric, gravity bending, and grain growth experiments. For model validation, four bridges with different spans and a second part with a circular hole and two free overhangs are designed. The calibration procedure is applied to develop a computational model for sintered 316L stainless steel BJ3DP parts. The displacements at various locations on the sintered parts are simulated using the calibrated model and are found to have errors less than 3.5% compared to those obtained by experiment.
{"title":"A Computational Framework for Modeling Distortion During Sintering of Binder Jet Printed Parts","authors":"Basil J. Paudel, D. Conover, Jung‐Kun Lee, A. To","doi":"10.1142/s242491302142008x","DOIUrl":"https://doi.org/10.1142/s242491302142008x","url":null,"abstract":"Sintering of binder jet 3D printed (BJ3DP) parts results in significant nonlinear distortion with typical shrinkage value of 5–20%, which makes design for BJ3DP and post-machining difficult. In this work, a computational modeling framework with calibration and validation procedure is developed to simulate distortion during sintering of BJ3DP parts accurately for the first time. The computational model employs the finite element analysis with a viscoplastic constitutive model that accounts for effects of gravity and friction. A calibration procedure is proposed to obtain values of different model parameters systematically through dilatometric, gravity bending, and grain growth experiments. For model validation, four bridges with different spans and a second part with a circular hole and two free overhangs are designed. The calibration procedure is applied to develop a computational model for sintered 316L stainless steel BJ3DP parts. The displacements at various locations on the sintered parts are simulated using the calibrated model and are found to have errors less than 3.5% compared to those obtained by experiment.","PeriodicalId":36070,"journal":{"name":"Journal of Micromechanics and Molecular Physics","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48594755","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-01-22DOI: 10.1142/s2424913021420030
X. Xia, Yang Liu, Jacqueline J. Li, G. Weng
Over the past decade, we have witnessed a stream of research activities on the mechanical and functional properties of graphene- and carbon nanotube-based nanocomposites. In this paper, we outline some of the efforts the present authors have participated along the way. Closely related contributions from the other authors are also introduced. The focus here is on the development of homogenization models for the effective properties of these low-dimensional nanocomposites. A key issue involved is the interface effects which are responsible for many extraordinary properties of the nanocomposites. To pave the way for the presentation of various homogenization models, we first give a general introduction to various categories of interface effects for both mechanical and functional properties. Then, the mechanical properties, involving the complex viscoelastic characteristics and coupled elastoplastic-damage processes, and the functional properties, involving electrical conductivity, dielectric permittivity, thermal conductivity, electromagnetic interference shielding and energy storage, are presented. We conclude with some perspectives on topics that deserve closer investigation in the near future.
{"title":"Review and perspective on the calculations of mechanical and functional properties of low-dimensional nanocomposites","authors":"X. Xia, Yang Liu, Jacqueline J. Li, G. Weng","doi":"10.1142/s2424913021420030","DOIUrl":"https://doi.org/10.1142/s2424913021420030","url":null,"abstract":"Over the past decade, we have witnessed a stream of research activities on the mechanical and functional properties of graphene- and carbon nanotube-based nanocomposites. In this paper, we outline some of the efforts the present authors have participated along the way. Closely related contributions from the other authors are also introduced. The focus here is on the development of homogenization models for the effective properties of these low-dimensional nanocomposites. A key issue involved is the interface effects which are responsible for many extraordinary properties of the nanocomposites. To pave the way for the presentation of various homogenization models, we first give a general introduction to various categories of interface effects for both mechanical and functional properties. Then, the mechanical properties, involving the complex viscoelastic characteristics and coupled elastoplastic-damage processes, and the functional properties, involving electrical conductivity, dielectric permittivity, thermal conductivity, electromagnetic interference shielding and energy storage, are presented. We conclude with some perspectives on topics that deserve closer investigation in the near future.","PeriodicalId":36070,"journal":{"name":"Journal of Micromechanics and Molecular Physics","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43293713","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-01-22DOI: 10.1142/s2424913021430025
Juveiriah M. Ashraf, Jing Fu, K. Liao, V. Chan, R. Al-Rub
We have developed a novel, facile and architecturally versatile fabrication method for specially designed cellular graphene lattices using additively manufactured polymer-based gyroidal triply periodic minimal surface (TPMS) as the initial sacrificial scaffold. Three-dimensional (3D)-printed templates of the polymeric gyroid lattices were coated with a mixture of graphene oxide (GO) and hydrazine solution via the hydrothermal process, followed by drying and thermal etching of the polymer scaffold, which resulted in a neat reduced GO (rGO) lattice of the gyroidal TPMS structure. Scanning electron microscopy and micro-computed tomography were used to evaluate the morphology and size of the 3D rGO architectures, while a Raman response at 1360[Formula: see text]cm[Formula: see text] (D peak), 1589[Formula: see text]cm[Formula: see text] (G peak) and 2696[Formula: see text]cm[Formula: see text] (2D peak) verified the presence of rGO. Thermo–electro–mechanical properties of rGO gyroid lattices of different densities were characterized where the highest Young’s modulus recorded was 351[Formula: see text]kPa for a sample with a density of 45.9[Formula: see text]mg[Formula: see text][Formula: see text][Formula: see text]cm[Formula: see text]. The rGO gyroid lattice exhibits an electrical conductivity of 1.07[Formula: see text]S[Formula: see text][Formula: see text][Formula: see text]m[Formula: see text] and high thermal insulation property with a thermal conductivity of 0.102[Formula: see text]W[Formula: see text][Formula: see text][Formula: see text]m[Formula: see text][Formula: see text]K[Formula: see text]. It is demonstrated that the hydrothermal-assisted fabrication process is adaptable for different lattice architectures based on 3D-printed scaffolds and thus has wide functional applications.
{"title":"Scalable synthesis, characterization and testing of 3D architected gyroid graphene lattices from additively manufactured templates","authors":"Juveiriah M. Ashraf, Jing Fu, K. Liao, V. Chan, R. Al-Rub","doi":"10.1142/s2424913021430025","DOIUrl":"https://doi.org/10.1142/s2424913021430025","url":null,"abstract":"We have developed a novel, facile and architecturally versatile fabrication method for specially designed cellular graphene lattices using additively manufactured polymer-based gyroidal triply periodic minimal surface (TPMS) as the initial sacrificial scaffold. Three-dimensional (3D)-printed templates of the polymeric gyroid lattices were coated with a mixture of graphene oxide (GO) and hydrazine solution via the hydrothermal process, followed by drying and thermal etching of the polymer scaffold, which resulted in a neat reduced GO (rGO) lattice of the gyroidal TPMS structure. Scanning electron microscopy and micro-computed tomography were used to evaluate the morphology and size of the 3D rGO architectures, while a Raman response at 1360[Formula: see text]cm[Formula: see text] (D peak), 1589[Formula: see text]cm[Formula: see text] (G peak) and 2696[Formula: see text]cm[Formula: see text] (2D peak) verified the presence of rGO. Thermo–electro–mechanical properties of rGO gyroid lattices of different densities were characterized where the highest Young’s modulus recorded was 351[Formula: see text]kPa for a sample with a density of 45.9[Formula: see text]mg[Formula: see text][Formula: see text][Formula: see text]cm[Formula: see text]. The rGO gyroid lattice exhibits an electrical conductivity of 1.07[Formula: see text]S[Formula: see text][Formula: see text][Formula: see text]m[Formula: see text] and high thermal insulation property with a thermal conductivity of 0.102[Formula: see text]W[Formula: see text][Formula: see text][Formula: see text]m[Formula: see text][Formula: see text]K[Formula: see text]. It is demonstrated that the hydrothermal-assisted fabrication process is adaptable for different lattice architectures based on 3D-printed scaffolds and thus has wide functional applications.","PeriodicalId":36070,"journal":{"name":"Journal of Micromechanics and Molecular Physics","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46024844","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-01-21DOI: 10.1142/s242491302144001x
Shaoheng Li, Ning Liu, Matthew Becton, Xiaowei Zeng, Xianqiao Wang
Two-dimensional (2D) architectured cellular structures exhibit outstanding mechanical properties unmatched by their bulk counterparts and show promising outlooks in electronic applications. Understanding of the relationship between their mechanical properties and structure patterns has yet to be fully explored. Also, traditional design rules in 2D architectured structures requiring prior knowledge of geometric parameters impose fundamental challenges for achieving desired performance within a rapid optimization process. Here, by taking full advantage of unsupervised generative adversarial network-based transfer learning (TL) and high-performing coarse-grained molecular dynamics (CGMD), we propose an adaptive design strategy to predict the mechanical performance of 2D architectured cellular structures as well as unravel hidden design rules for maximizing specific tensile strength. Results indicate that the established TL model is accurate enough to predict the mechanical properties of graphene kirigami, in which [Formula: see text] is 0.994 and 0.985 for specific strength and yield strain, respectively. The proposed design method combining machine learning with CGMD extends the ability of physical simulation beyond performance prediction, optimizing fracture mechanical properties by screening through the entire geometric design space of the architected 2D structures. Overall, this work proves that the design method based on TL can effectively obtain the power of new physical insights for structure design and optimization of interest.
{"title":"Mechanics prediction of 2D architectured cellular structures using transfer learning","authors":"Shaoheng Li, Ning Liu, Matthew Becton, Xiaowei Zeng, Xianqiao Wang","doi":"10.1142/s242491302144001x","DOIUrl":"https://doi.org/10.1142/s242491302144001x","url":null,"abstract":"Two-dimensional (2D) architectured cellular structures exhibit outstanding mechanical properties unmatched by their bulk counterparts and show promising outlooks in electronic applications. Understanding of the relationship between their mechanical properties and structure patterns has yet to be fully explored. Also, traditional design rules in 2D architectured structures requiring prior knowledge of geometric parameters impose fundamental challenges for achieving desired performance within a rapid optimization process. Here, by taking full advantage of unsupervised generative adversarial network-based transfer learning (TL) and high-performing coarse-grained molecular dynamics (CGMD), we propose an adaptive design strategy to predict the mechanical performance of 2D architectured cellular structures as well as unravel hidden design rules for maximizing specific tensile strength. Results indicate that the established TL model is accurate enough to predict the mechanical properties of graphene kirigami, in which [Formula: see text] is 0.994 and 0.985 for specific strength and yield strain, respectively. The proposed design method combining machine learning with CGMD extends the ability of physical simulation beyond performance prediction, optimizing fracture mechanical properties by screening through the entire geometric design space of the architected 2D structures. Overall, this work proves that the design method based on TL can effectively obtain the power of new physical insights for structure design and optimization of interest.","PeriodicalId":36070,"journal":{"name":"Journal of Micromechanics and Molecular Physics","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43867737","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-01-08DOI: 10.1142/s2424913021420054
Leyu Wang, James D. Lee
The irreversibility, temperature, and entropy are identified for an atomic system of solid material. Thermodynamics second law is automatically satisfied in the time evolution of molecular dynamics (MD). The irreversibility caused by an atom spontaneously moves from a non-stable equilibrium position to a stable equilibrium position. The process is dynamic in nature associated with the conversion of potential energy to kinetic energy and the dissipation of kinetic energy to the entire system. The forward process is less sensitive to small variation of boundary condition than reverse process, causing the time symmetry to break. Different methods to define temperature in molecular system are revisited with paradox examples. It is seen that the temperature can only be rigorously defined on an atom knowing its time history of velocity vector. The velocity vector of an atom is the summation of the mechanical part and the thermal part, the mechanical velocity is related to the global motion (translation, rotation, acceleration, vibration, etc.), the thermal velocity is related to temperature and is assumed to follow the identical random Gaussian distribution for all of its [Formula: see text], [Formula: see text] and [Formula: see text] component. The [Formula: see text]-velocity (same for [Formula: see text] or [Formula: see text]) versus time obtained from MD simulation is treated as a signal (mechanical motion) corrupted with random Gaussian distribution noise (thermal motion). The noise is separated from signal with wavelet filter and used as the randomness measurement. The temperature is thus defined as the variance of the thermal velocity multiply the atom mass and divided by Boltzmann constant. The new definition is equivalent to the Nose–Hover thermostat for a stationary system. For system with macroscopic acceleration, rotation, vibration, etc., the new definition can predict the same temperature as the stationary system, while Nose–Hover thermostat predicts a much higher temperature. It is seen that the new definition of temperature is not influenced by the global motion, i.e., translation, rotation, acceleration, vibration, etc., of the system. The Gibbs entropy is calculated for each atom by knowing normal distribution as the probability density function. The relationship between entropy and temperature is established for solid material.
{"title":"Temperature and entropy in molecular system","authors":"Leyu Wang, James D. Lee","doi":"10.1142/s2424913021420054","DOIUrl":"https://doi.org/10.1142/s2424913021420054","url":null,"abstract":"The irreversibility, temperature, and entropy are identified for an atomic system of solid material. Thermodynamics second law is automatically satisfied in the time evolution of molecular dynamics (MD). The irreversibility caused by an atom spontaneously moves from a non-stable equilibrium position to a stable equilibrium position. The process is dynamic in nature associated with the conversion of potential energy to kinetic energy and the dissipation of kinetic energy to the entire system. The forward process is less sensitive to small variation of boundary condition than reverse process, causing the time symmetry to break. Different methods to define temperature in molecular system are revisited with paradox examples. It is seen that the temperature can only be rigorously defined on an atom knowing its time history of velocity vector. The velocity vector of an atom is the summation of the mechanical part and the thermal part, the mechanical velocity is related to the global motion (translation, rotation, acceleration, vibration, etc.), the thermal velocity is related to temperature and is assumed to follow the identical random Gaussian distribution for all of its [Formula: see text], [Formula: see text] and [Formula: see text] component. The [Formula: see text]-velocity (same for [Formula: see text] or [Formula: see text]) versus time obtained from MD simulation is treated as a signal (mechanical motion) corrupted with random Gaussian distribution noise (thermal motion). The noise is separated from signal with wavelet filter and used as the randomness measurement. The temperature is thus defined as the variance of the thermal velocity multiply the atom mass and divided by Boltzmann constant. The new definition is equivalent to the Nose–Hover thermostat for a stationary system. For system with macroscopic acceleration, rotation, vibration, etc., the new definition can predict the same temperature as the stationary system, while Nose–Hover thermostat predicts a much higher temperature. It is seen that the new definition of temperature is not influenced by the global motion, i.e., translation, rotation, acceleration, vibration, etc., of the system. The Gibbs entropy is calculated for each atom by knowing normal distribution as the probability density function. The relationship between entropy and temperature is established for solid material.","PeriodicalId":36070,"journal":{"name":"Journal of Micromechanics and Molecular Physics","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41348956","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-01-08DOI: 10.1142/s2424913021420042
Xuan Hu, Shaofan Li
Freshwater scarcity has emerged as a major challenge of our time. Under this context, the importance of an efficient and energy-saving water desalination method is highlighted. In recent years, carbon nanotube (CNT) membrane characterizing with high permeability has attracted much attention in research, and it is regarded as a promising alternative to the conventional reverse osmosis technology. This work aims at numerically investigating the water desalination ability of a novel type of CNT membrane structure, namely the double-walled carbon nanotube (DWCNT) with Moiré pattern. After establishing the physical CNT models and running the molecular dynamics (MD) simulation of the water desalination system, it is found that both the single-walled carbon nanotube (SWCNT) and DWCNT can desalinate the seawater successfully while the water permeability of DWCNT is at least 18.9% higher than that of SWCNT within the same time. As far as the Moiŕe pattern adopted in this study is concerned, the water permeability of DWCNT without Moiŕe pattern is 18.6% higher than that with Moiré pattern.
{"title":"Molecular dynamics modeling and simulation of water desalination through a double-walled carbon nanotube with moiré pattern","authors":"Xuan Hu, Shaofan Li","doi":"10.1142/s2424913021420042","DOIUrl":"https://doi.org/10.1142/s2424913021420042","url":null,"abstract":"Freshwater scarcity has emerged as a major challenge of our time. Under this context, the importance of an efficient and energy-saving water desalination method is highlighted. In recent years, carbon nanotube (CNT) membrane characterizing with high permeability has attracted much attention in research, and it is regarded as a promising alternative to the conventional reverse osmosis technology. This work aims at numerically investigating the water desalination ability of a novel type of CNT membrane structure, namely the double-walled carbon nanotube (DWCNT) with Moiré pattern. After establishing the physical CNT models and running the molecular dynamics (MD) simulation of the water desalination system, it is found that both the single-walled carbon nanotube (SWCNT) and DWCNT can desalinate the seawater successfully while the water permeability of DWCNT is at least 18.9% higher than that of SWCNT within the same time. As far as the Moiŕe pattern adopted in this study is concerned, the water permeability of DWCNT without Moiŕe pattern is 18.6% higher than that with Moiré pattern.","PeriodicalId":36070,"journal":{"name":"Journal of Micromechanics and Molecular Physics","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41791291","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-12-29DOI: 10.1142/s2424913021420029
Xianyang Yang, James D. Lee
This work developed the optimal and active control algorithms applicable to structural control for earthquake resistance. [Lewis, F. L., Vrabie, D. and Syrmos, V. L. [2012] Optimal Control (John Wiley & Sons)] developed a rigorous and comprehensive procedure for the derivation of an optimal control strategy based on the calculus of variation. This work is an application of Lewis’ formulation to the control of a structure for earthquake resistance. We developed a computer software which can be used to generate a dynamic model to simulate a planar structure and to construct the control law. This model also includes the tendon driven actuators, sensors and true history of earthquake excitation. The control law has two parts: (I) the feedback control which depends on the estimate state variables (Kalman filter) and (II) the record of the realistic earthquake excitation. The optimal control problem eventually leads to a two-point boundary value problem whose solution hinges on the knowledge of the entire history of the earthquake excitation. We employ true records of earthquake excitation as input. This approach enables one to solve the Riccati equations rigorously. Then, from the simulation results, one may study the relations between the control algorithm design and the characteristics (frequency, amplitude and duration) of earthquake excitation.
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