Pub Date : 2011-12-01DOI: 10.1061/(ASCE)NM.2153-5477.0000037
Dipanjan Sen, Andre P. Garcia, M. Buehler
Porous silica structures with intricate design patterns form the exoskeleton of diatoms, a large class of microscopic mineralized algae, whose structural features have been observed to exist down to nanoscale dimensions. Nanoscale patterned porous silica structures have also been manufactured for the use in optical systems, catalysts, and semiconductor nanolithography. The mechanical properties of these porous structures at the nanoscale are a subject of great interest for potential technological and biomimetic applications in the context of new classes of multifunctional materials. Previous studies have established the emergence of enhanced toughness and ductility in nanoporous crystalline silica structures over bulk silica. The authors undertake molecular dynamics simulations and theoretical size-scaling studies of elasticity and strength of a simple model of generic nanoporous silica structures, used to establish a theoretical model for the detailed mechanisms behind their improved properties, and show...
{"title":"Mechanics of Nano-Honeycomb Silica Structures: Size-Dependent Brittle-to-Ductile Transition","authors":"Dipanjan Sen, Andre P. Garcia, M. Buehler","doi":"10.1061/(ASCE)NM.2153-5477.0000037","DOIUrl":"https://doi.org/10.1061/(ASCE)NM.2153-5477.0000037","url":null,"abstract":"Porous silica structures with intricate design patterns form the exoskeleton of diatoms, a large class of microscopic mineralized algae, whose structural features have been observed to exist down to nanoscale dimensions. Nanoscale patterned porous silica structures have also been manufactured for the use in optical systems, catalysts, and semiconductor nanolithography. The mechanical properties of these porous structures at the nanoscale are a subject of great interest for potential technological and biomimetic applications in the context of new classes of multifunctional materials. Previous studies have established the emergence of enhanced toughness and ductility in nanoporous crystalline silica structures over bulk silica. The authors undertake molecular dynamics simulations and theoretical size-scaling studies of elasticity and strength of a simple model of generic nanoporous silica structures, used to establish a theoretical model for the detailed mechanisms behind their improved properties, and show...","PeriodicalId":90606,"journal":{"name":"Journal of nanomechanics & micromechanics","volume":"1 1","pages":"112-118"},"PeriodicalIF":0.0,"publicationDate":"2011-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1061/(ASCE)NM.2153-5477.0000037","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"58473966","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 : 2011-11-15DOI: 10.1061/(ASCE)NM.2153-5477.0000038
Hansung Kim, V. Tomar
Atomistic simulations have a unique capability to reveal the material deformation mechanisms and the corresponding deformation-based constitutive behavior. However, atomistic simulations are limited by the accessible length and time scales. In the present work, an equivalent crystal lattice method is used to analyze atomistic mechanical deformation of nanometer- to micrometer-sized polycrystalline silicon (Si) samples at accelerated time steps. The equivalent crystal lattice method’s validity is verified by the results of classical molecular dynamics (MD) simulations at MD strain rates. The method is then used to predict material behavior at subcontinuum length scales. An extrapolation of the thin film polycrystalline silicon stress-strain relationships to lower strain-rate values indicates that the thin film peak stress values at the experimental strain rates are in agreement with experimental values. Analyses reveal that the peak stress values in the case of polycrystalline Si follow inverse Hall-Petch ...
{"title":"Nanometer to Micron Scale Atomistic Mechanics of Silicon Using Atomistic Simulations at Accelerated Time Steps","authors":"Hansung Kim, V. Tomar","doi":"10.1061/(ASCE)NM.2153-5477.0000038","DOIUrl":"https://doi.org/10.1061/(ASCE)NM.2153-5477.0000038","url":null,"abstract":"Atomistic simulations have a unique capability to reveal the material deformation mechanisms and the corresponding deformation-based constitutive behavior. However, atomistic simulations are limited by the accessible length and time scales. In the present work, an equivalent crystal lattice method is used to analyze atomistic mechanical deformation of nanometer- to micrometer-sized polycrystalline silicon (Si) samples at accelerated time steps. The equivalent crystal lattice method’s validity is verified by the results of classical molecular dynamics (MD) simulations at MD strain rates. The method is then used to predict material behavior at subcontinuum length scales. An extrapolation of the thin film polycrystalline silicon stress-strain relationships to lower strain-rate values indicates that the thin film peak stress values at the experimental strain rates are in agreement with experimental values. Analyses reveal that the peak stress values in the case of polycrystalline Si follow inverse Hall-Petch ...","PeriodicalId":90606,"journal":{"name":"Journal of nanomechanics & micromechanics","volume":"1 1","pages":"134-141"},"PeriodicalIF":0.0,"publicationDate":"2011-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1061/(ASCE)NM.2153-5477.0000038","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"58474328","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 : 2011-06-10DOI: 10.1061/(ASCE)NM.2153-5477.0000036
G. Wang, A. Al-ostaz, A. Cheng
This paper presents a numerical method, known as hybrid lattice particle modeling (HLPM), for the study of the reinforcement potential for coating of three-layer functionally designed nonlinear response retrofitting structure on a linear response infrastructure. The three nonlinear materials behave with different strengths as members of the three-layer retrofitting structure. Different arrangements of these three materials are attempted to obtain a good understanding of the intrinsic mechanism to reach an optimal reinforcement performance to the infrastructure. The ultimate application is aimed at the retrofitting of failing infrastructure.
{"title":"Hybrid Lattice Particle Modeling of Retrofitting Infrastructure Design under a Blasting Load","authors":"G. Wang, A. Al-ostaz, A. Cheng","doi":"10.1061/(ASCE)NM.2153-5477.0000036","DOIUrl":"https://doi.org/10.1061/(ASCE)NM.2153-5477.0000036","url":null,"abstract":"This paper presents a numerical method, known as hybrid lattice particle modeling (HLPM), for the study of the reinforcement potential for coating of three-layer functionally designed nonlinear response retrofitting structure on a linear response infrastructure. The three nonlinear materials behave with different strengths as members of the three-layer retrofitting structure. Different arrangements of these three materials are attempted to obtain a good understanding of the intrinsic mechanism to reach an optimal reinforcement performance to the infrastructure. The ultimate application is aimed at the retrofitting of failing infrastructure.","PeriodicalId":90606,"journal":{"name":"Journal of nanomechanics & micromechanics","volume":"1 1","pages":"119-133"},"PeriodicalIF":0.0,"publicationDate":"2011-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1061/(ASCE)NM.2153-5477.0000036","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"58473849","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 : 2011-06-01DOI: 10.1061/(ASCE)NM.2153-5477.0000030
Yang Yang, W. Ching, A. Misra
Complex grain-boundary structures such as the 1–2 nm thick intergranular glassy films (IGF) play a prominent role in the failure behavior of nanophased ceramics. The IGF plays the role of an imperfection and serves as the location of strain localization and failure. This paper describes recently performed theoretical mechanical loading experiments on very large atomic models of IGF in silicon nitride using ab initio simulation to obtain their failure behavior. The ab initio simulations yield characteristic postpeak softening accompanied by strain localization zone. This paper applies microstructural granular mechanics-based higher-order continuum theory to model the failure behavior of these types of material systems. The results obtained from the ab initio simulations are compared with those predicted by the higher-order continuum theory.
{"title":"Higher-Order Continuum Theory Applied to Fracture Simulation of Nanoscale Intergranular Glassy Film","authors":"Yang Yang, W. Ching, A. Misra","doi":"10.1061/(ASCE)NM.2153-5477.0000030","DOIUrl":"https://doi.org/10.1061/(ASCE)NM.2153-5477.0000030","url":null,"abstract":"Complex grain-boundary structures such as the 1–2 nm thick intergranular glassy films (IGF) play a prominent role in the failure behavior of nanophased ceramics. The IGF plays the role of an imperfection and serves as the location of strain localization and failure. This paper describes recently performed theoretical mechanical loading experiments on very large atomic models of IGF in silicon nitride using ab initio simulation to obtain their failure behavior. The ab initio simulations yield characteristic postpeak softening accompanied by strain localization zone. This paper applies microstructural granular mechanics-based higher-order continuum theory to model the failure behavior of these types of material systems. The results obtained from the ab initio simulations are compared with those predicted by the higher-order continuum theory.","PeriodicalId":90606,"journal":{"name":"Journal of nanomechanics & micromechanics","volume":"1 1","pages":"60-71"},"PeriodicalIF":0.0,"publicationDate":"2011-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1061/(ASCE)NM.2153-5477.0000030","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"58473859","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 : 2011-05-16DOI: 10.1061/(ASCE)NM.2153-5477.0000026
Weidong Wu, A. Al-ostaz, A. Cheng, C. Song
There is a growing interest in relating nanostructures to the macro properties of engineering materials such as composites and cement materials. Better understanding of structure and elastic properties of nanoparticles in concrete by modeling and experiment could lead to nanoengineered concrete with much better performance and energy efficiency. In this study, the molecular dynamics (MD) atomistic simulation technique was applied to study the elastic properties of major portland cement compounds (i.e., alite, belite, and aluminate). Applicability of three commonly used force fields: COMPASS, Universal force field (UFF), and Dreiding were evaluated in the MD simulation. The combination of different simulation cell sizes and force fields was investigated. MD simulation results of cement were comparable to the experimental data. The results could be used as nanoparticle properties for multiscale modeling of concrete, cementitious composites, and aggregate.
将纳米结构与复合材料和水泥材料等工程材料的宏观性能联系起来的兴趣越来越大。通过模拟和实验，更好地了解混凝土中纳米颗粒的结构和弹性特性，可以使纳米工程混凝土具有更好的性能和能效。在本研究中，应用分子动力学(MD)原子模拟技术研究了主要硅酸盐水泥化合物(即阿利特、贝利特和铝酸盐)的弹性性能。在MD仿真中对COMPASS、Universal force field (UFF)和dreding三种常用力场的适用性进行了评估。研究了不同模拟单元尺寸和力场的组合。水泥的MD模拟结果与实验数据基本吻合。研究结果可用于混凝土、胶凝复合材料和骨料的纳米颗粒特性多尺度建模。
{"title":"Computation of Elastic Properties of Portland Cement Using Molecular Dynamics","authors":"Weidong Wu, A. Al-ostaz, A. Cheng, C. Song","doi":"10.1061/(ASCE)NM.2153-5477.0000026","DOIUrl":"https://doi.org/10.1061/(ASCE)NM.2153-5477.0000026","url":null,"abstract":"There is a growing interest in relating nanostructures to the macro properties of engineering materials such as composites and cement materials. Better understanding of structure and elastic properties of nanoparticles in concrete by modeling and experiment could lead to nanoengineered concrete with much better performance and energy efficiency. In this study, the molecular dynamics (MD) atomistic simulation technique was applied to study the elastic properties of major portland cement compounds (i.e., alite, belite, and aluminate). Applicability of three commonly used force fields: COMPASS, Universal force field (UFF), and Dreiding were evaluated in the MD simulation. The combination of different simulation cell sizes and force fields was investigated. MD simulation results of cement were comparable to the experimental data. The results could be used as nanoparticle properties for multiscale modeling of concrete, cementitious composites, and aggregate.","PeriodicalId":90606,"journal":{"name":"Journal of nanomechanics & micromechanics","volume":"1 1","pages":"84-90"},"PeriodicalIF":0.0,"publicationDate":"2011-05-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1061/(ASCE)NM.2153-5477.0000026","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"58473219","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 : 2011-05-16DOI: 10.1061/(ASCE)NM.2153-5477.0000029
I. Valero, F. Caner, Z. Guo
Theoretically, the polymers reinforced with long aligned single-walled carbon nanotubes (LASWCNTs) must have one order of magnitude larger stiffness and strength than the classical carbon fiber reinforced polymers. However, imperfections such as vacancy defects in the single-walled carbon nanotubes (SWCNTs), undulation, and clustering of SWCNTs in the polymer matrix are known to adversely affect the otherwise superior properties of LASWCNT-reinforced polymer composites. The determination of unbiased relative importance of various forms of imperfections is important to determine the most efficient strategies to produce polymers reinforced with LASWCNTs. An investigation of stochastic effects of imperfections in the form of vacancy defects in the nanotubes, undulation of nanotubes, and clustering of nanotubes on the initial elastic stiffness of LASWCNT-reinforced polymer composites is presented. To this end, first the effect of vacancy defects on axial elastic stiffness of imperfect LASWCNTS is determined b...
{"title":"Effect of Imperfections on Elastic Stiffness of Polymers Reinforced with Long Aligned Single-Walled Carbon Nanotubes","authors":"I. Valero, F. Caner, Z. Guo","doi":"10.1061/(ASCE)NM.2153-5477.0000029","DOIUrl":"https://doi.org/10.1061/(ASCE)NM.2153-5477.0000029","url":null,"abstract":"Theoretically, the polymers reinforced with long aligned single-walled carbon nanotubes (LASWCNTs) must have one order of magnitude larger stiffness and strength than the classical carbon fiber reinforced polymers. However, imperfections such as vacancy defects in the single-walled carbon nanotubes (SWCNTs), undulation, and clustering of SWCNTs in the polymer matrix are known to adversely affect the otherwise superior properties of LASWCNT-reinforced polymer composites. The determination of unbiased relative importance of various forms of imperfections is important to determine the most efficient strategies to produce polymers reinforced with LASWCNTs. An investigation of stochastic effects of imperfections in the form of vacancy defects in the nanotubes, undulation of nanotubes, and clustering of nanotubes on the initial elastic stiffness of LASWCNT-reinforced polymer composites is presented. To this end, first the effect of vacancy defects on axial elastic stiffness of imperfect LASWCNTS is determined b...","PeriodicalId":90606,"journal":{"name":"Journal of nanomechanics & micromechanics","volume":"1 1","pages":"51-59"},"PeriodicalIF":0.0,"publicationDate":"2011-05-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1061/(ASCE)NM.2153-5477.0000029","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"58473774","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 : 2011-04-15DOI: 10.1061/(ASCE)NM.2153-5477.0000035
S. Pradhan, D. Katti, K. Katti
Collagen is a fibrous protein that is responsible for structural integrity of various connective tissues such as bone, tendon, and skin. The mechanical properties of these hierarchical tissue structures are greatly influenced by presence of long and slender (~300 long and ~1.5 nm in diameter) collagen molecules that impart strength and elasticity. The current molecular dynamics studies of collagen are limited to the use of short collagen molecules that are approximately 8.5 nm in length. This study investigates the mechanical behavior of the full-length collagen molecule and the short collagen by using steered molecular dynamics. The simulations were carried out at various loading conditions corresponding to different rates of pulling and springs of different stiffness were used to pull collagen molecules. The underlying mechanisms with respect to unfolding of collagen molecules differ significantly between short and full-length molecules when stretched in molecular dynamics simulations. These differences...
{"title":"Steered Molecular Dynamics Study of Mechanical Response of Full Length and Short Collagen Molecules","authors":"S. Pradhan, D. Katti, K. Katti","doi":"10.1061/(ASCE)NM.2153-5477.0000035","DOIUrl":"https://doi.org/10.1061/(ASCE)NM.2153-5477.0000035","url":null,"abstract":"Collagen is a fibrous protein that is responsible for structural integrity of various connective tissues such as bone, tendon, and skin. The mechanical properties of these hierarchical tissue structures are greatly influenced by presence of long and slender (~300 long and ~1.5 nm in diameter) collagen molecules that impart strength and elasticity. The current molecular dynamics studies of collagen are limited to the use of short collagen molecules that are approximately 8.5 nm in length. This study investigates the mechanical behavior of the full-length collagen molecule and the short collagen by using steered molecular dynamics. The simulations were carried out at various loading conditions corresponding to different rates of pulling and springs of different stiffness were used to pull collagen molecules. The underlying mechanisms with respect to unfolding of collagen molecules differ significantly between short and full-length molecules when stretched in molecular dynamics simulations. These differences...","PeriodicalId":90606,"journal":{"name":"Journal of nanomechanics & micromechanics","volume":"1 1","pages":"104-110"},"PeriodicalIF":0.0,"publicationDate":"2011-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1061/(ASCE)NM.2153-5477.0000035","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"58473763","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 : 2011-03-01DOI: 10.1061/(ASCE)NM.2153-5477.0000027
G. Voyiadjis, D. Faghihi, Chengze Zhang
This work addresses the temperature and rate indentation size effects (TRISE) encountered in nanoindentation experiments and the corresponding material intrinsic length scales at different strain rates. The same value for the material length scale cannot be used for different rate, temperature, and accumulated plastic-strain conditions. A variable length scale is introduced in this work and used on two different face-centered cubic (FCC) metals. Indentation experiments are performed on copper and aluminum polycrystalline samples for different strain rates. To check the validity of the assumed concept for local hardening in nanoindentation, additional experiments are conducted on single-crystal materials. The existing theories describing the indentation size effects and length scales are reviewed, and a physically based model that depends on strain rate, accumulated plastic strain, and temperature that were scaled with hardness experiments results is proposed for length scales. Furthermore, numerical simul...
{"title":"Analytical and Experimental Determination of Rate- and Temperature-Dependent Length Scales Using Nanoindentation Experiments","authors":"G. Voyiadjis, D. Faghihi, Chengze Zhang","doi":"10.1061/(ASCE)NM.2153-5477.0000027","DOIUrl":"https://doi.org/10.1061/(ASCE)NM.2153-5477.0000027","url":null,"abstract":"This work addresses the temperature and rate indentation size effects (TRISE) encountered in nanoindentation experiments and the corresponding material intrinsic length scales at different strain rates. The same value for the material length scale cannot be used for different rate, temperature, and accumulated plastic-strain conditions. A variable length scale is introduced in this work and used on two different face-centered cubic (FCC) metals. Indentation experiments are performed on copper and aluminum polycrystalline samples for different strain rates. To check the validity of the assumed concept for local hardening in nanoindentation, additional experiments are conducted on single-crystal materials. The existing theories describing the indentation size effects and length scales are reviewed, and a physically based model that depends on strain rate, accumulated plastic strain, and temperature that were scaled with hardness experiments results is proposed for length scales. Furthermore, numerical simul...","PeriodicalId":90606,"journal":{"name":"Journal of nanomechanics & micromechanics","volume":"1 1","pages":"24-40"},"PeriodicalIF":0.0,"publicationDate":"2011-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1061/(ASCE)NM.2153-5477.0000027","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"58473166","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}
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