Strong thermal effect on microstructure and mechanical properties of Ti/Ni multilayer thin films was observed from in-situ heating during deposition and subsequent annealing. Films deposited at low-temperature show preferred crystallographic texture for both Ti and Ni layers, with columnar structure extending through the layers. The columnar structure become more distinct and complete with the increase of temperature up to 300°C, and meanwhile more atomic diffusion and intermixing occur along the Ti/Ni interfaces, promoting the formation of Ti-Ni intermetallic precipitates. High-temperature deposition causes disintegration of the layered structure. Columnar Ti-Ni alloys and further recrystallized alloys were detected with preferred crystallographic texture. For material strength, an increased hardness trend is observed with increasing deposition temperature even with much larger grain size compared to room temperature case. Furthermore, for multilayer system deposited under low temperature, post annealing results in higher hardness with minimal microstructure modification, with more strengthening observed in lower deposition temperature case.
{"title":"Deposition Temperature Induced Texture and Strengthening of Ti/Ni Multilayer Thin Films","authors":"Zhou Yang, Junlan Wang","doi":"10.1115/1.4062775","DOIUrl":"https://doi.org/10.1115/1.4062775","url":null,"abstract":"\u0000 Strong thermal effect on microstructure and mechanical properties of Ti/Ni multilayer thin films was observed from in-situ heating during deposition and subsequent annealing. Films deposited at low-temperature show preferred crystallographic texture for both Ti and Ni layers, with columnar structure extending through the layers. The columnar structure become more distinct and complete with the increase of temperature up to 300°C, and meanwhile more atomic diffusion and intermixing occur along the Ti/Ni interfaces, promoting the formation of Ti-Ni intermetallic precipitates. High-temperature deposition causes disintegration of the layered structure. Columnar Ti-Ni alloys and further recrystallized alloys were detected with preferred crystallographic texture. For material strength, an increased hardness trend is observed with increasing deposition temperature even with much larger grain size compared to room temperature case. Furthermore, for multilayer system deposited under low temperature, post annealing results in higher hardness with minimal microstructure modification, with more strengthening observed in lower deposition temperature case.","PeriodicalId":54880,"journal":{"name":"Journal of Applied Mechanics-Transactions of the Asme","volume":" ","pages":""},"PeriodicalIF":2.6,"publicationDate":"2023-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41430336","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Allen Kim, Lily Vu, Tony Chung, David Song, Junlan Wang
Additive manufacturing (AM) has emerged as a crucial technology in recent decades, particularly within aerospace industry. However, the thermally cyclic nature of these processes introduce significant variations and defects in microstructure, which can adversely affect final part performance and hinder the widespread adoption of the technology. Traditionally, characterization of AM parts has relied on conventional bulk testing methods, which involve analyzing many samples to gather sufficient data for statistical analysis. Unfortunately, these methods are unable to account for local nanoscale variations in material properties caused by the microstructure, as they measure a single averaged property for each tested sample. In this work, we use AM Inconel 718 as a model system in developing a novel approach to correlate nanomechanical properties obtained through nanoindentation with microstructure obtained through electron backscatter diffraction (EBSD). By associating mechanical properties obtained from each indent with the corresponding crystallographic direction measured with EBSD, we calculate the weighted average hardness and modulus for each orientation. This enables us to generate inverse property figure maps depicting the relationship between mechanical properties and crystallographic direction. Our method yields results in good agreement with literature when calculating the part modulus and hardness. Furthermore, it effectively captures nanoscale variations in properties across the microstructure. The key advantage of this methodology is its capability to rapidly test a single AM part and generate a large dataset for statistical analysis. Complementing existing macroscale characterization techniques, this method can help improve AM part performance prediction and contribute to the wider adoption of AM technologies.
{"title":"Correlation of Microstructure and Nanomechanical Properties of Additively Manufactured Inconel 718","authors":"Allen Kim, Lily Vu, Tony Chung, David Song, Junlan Wang","doi":"10.1115/1.4062776","DOIUrl":"https://doi.org/10.1115/1.4062776","url":null,"abstract":"\u0000 Additive manufacturing (AM) has emerged as a crucial technology in recent decades, particularly within aerospace industry. However, the thermally cyclic nature of these processes introduce significant variations and defects in microstructure, which can adversely affect final part performance and hinder the widespread adoption of the technology. Traditionally, characterization of AM parts has relied on conventional bulk testing methods, which involve analyzing many samples to gather sufficient data for statistical analysis. Unfortunately, these methods are unable to account for local nanoscale variations in material properties caused by the microstructure, as they measure a single averaged property for each tested sample. In this work, we use AM Inconel 718 as a model system in developing a novel approach to correlate nanomechanical properties obtained through nanoindentation with microstructure obtained through electron backscatter diffraction (EBSD). By associating mechanical properties obtained from each indent with the corresponding crystallographic direction measured with EBSD, we calculate the weighted average hardness and modulus for each orientation. This enables us to generate inverse property figure maps depicting the relationship between mechanical properties and crystallographic direction. Our method yields results in good agreement with literature when calculating the part modulus and hardness. Furthermore, it effectively captures nanoscale variations in properties across the microstructure. The key advantage of this methodology is its capability to rapidly test a single AM part and generate a large dataset for statistical analysis. Complementing existing macroscale characterization techniques, this method can help improve AM part performance prediction and contribute to the wider adoption of AM technologies.","PeriodicalId":54880,"journal":{"name":"Journal of Applied Mechanics-Transactions of the Asme","volume":" ","pages":""},"PeriodicalIF":2.6,"publicationDate":"2023-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49070496","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jennifer Xue, Zheren Baizhikova, R. Ballarini, Tian Chen
Thermomechanical buckling of slender and thin-walled structural components happens without warning and can lead to catastrophic failure. Similar phenomena are observed during plasmolysis (contraction of a plant cell’s protoplast) and rupture of viral capsids. Analytical formulas derived from stability analyses of elastic plates, cylinders, and shells that do not account for the effects of random geometric imperfections introduced during the manufacturing process or biological growth may vastly over-estimate buckling capacity. To ensure structural safety the formulas must therefore be combined with empirical data to define “knock down factors” which are in turn used to establish safety factors. Towards improved understanding of the role of imperfections on mechanical response, ingenious methods have been used to fabricate and test near-perfectly hemispherical shells and those containing dimple-like defects. However, a method of inducing imperfections in the form of randomly-shaped surfaces remains elusive. We introduce a protocol for realizing such imperfect shells and measuring the pressure required to buckle them. Silicone is poured onto an elastomeric mold under an acoustic excitation, which can be either random sound, or if desired the same as the modal frequency of the mold. Illustrative micro-Computed-Tomography images and buckling pressure experiments of a nearly-perfect shell and an imperfect one show that the method is effective in introducing randomly-shaped imperfections of significant magnitudes. This proof-of-concept study demonstrates that the experimental results when combined with computational simulations can lead to improved understanding of stochastic buckling phenomena.
{"title":"Creating Geometric Imperfections in Thin-Walled Structures using Acoustic Excitation","authors":"Jennifer Xue, Zheren Baizhikova, R. Ballarini, Tian Chen","doi":"10.1115/1.4062746","DOIUrl":"https://doi.org/10.1115/1.4062746","url":null,"abstract":"\u0000 Thermomechanical buckling of slender and thin-walled structural components happens without warning and can lead to catastrophic failure. Similar phenomena are observed during plasmolysis (contraction of a plant cell’s protoplast) and rupture of viral capsids. Analytical formulas derived from stability analyses of elastic plates, cylinders, and shells that do not account for the effects of random geometric imperfections introduced during the manufacturing process or biological growth may vastly over-estimate buckling capacity. To ensure structural safety the formulas must therefore be combined with empirical data to define “knock down factors” which are in turn used to establish safety factors. Towards improved understanding of the role of imperfections on mechanical response, ingenious methods have been used to fabricate and test near-perfectly hemispherical shells and those containing dimple-like defects. However, a method of inducing imperfections in the form of randomly-shaped surfaces remains elusive. We introduce a protocol for realizing such imperfect shells and measuring the pressure required to buckle them. Silicone is poured onto an elastomeric mold under an acoustic excitation, which can be either random sound, or if desired the same as the modal frequency of the mold. Illustrative micro-Computed-Tomography images and buckling pressure experiments of a nearly-perfect shell and an imperfect one show that the method is effective in introducing randomly-shaped imperfections of significant magnitudes. This proof-of-concept study demonstrates that the experimental results when combined with computational simulations can lead to improved understanding of stochastic buckling phenomena.","PeriodicalId":54880,"journal":{"name":"Journal of Applied Mechanics-Transactions of the Asme","volume":" ","pages":""},"PeriodicalIF":2.6,"publicationDate":"2023-06-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44386328","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract Combined systems, which are flexible structures carrying moving subsystems, are seen in various applications. Due to structure–subsystem interactions, the structure in a combined system encounters jump discontinuities in its internal forces (such as the bending moment and shear force of a beam). Accurate estimation of such jump discontinuities is important to the performance, safety, and longevity of a combined system. Because of the time-varying nature and complexity of structure–subsystem interactions, conventional series solution methods experience slow convergence, and the Gibbs phenomenon in computation and the improved series expansion methods are limited to certain proportionally damped continua under moving forces and moving oscillators. In this paper, a novel modified series expansion method (MSEM) is proposed to resolve the aforementioned issues with the existing series solution methods. Through the introduction of a jump influence function, the proposed method produces fast-convergent series solutions and accurately predicts the jump discontinuities without the Gibbs phenomenon. The MSEM is applicable to structures with nonproportional damping and subject to arbitrary boundary conditions, and it can easily manage general M-DOF moving subsystems having multiple contact points with a supporting structure. As an important result of this investigation, a mathematical proof of the convergence of the MSEM-based solutions is given for the first time. Additionally, two numerical examples are presented to demonstrate the accuracy, efficiency, and versatility of the proposed MSEM in modeling and analysis of combined systems.
{"title":"On Jump Discontinuities in Internal Forces of Flexible Structures Carrying Moving Subsystems","authors":"Bingen Yang, Hao Gao","doi":"10.1115/1.4062628","DOIUrl":"https://doi.org/10.1115/1.4062628","url":null,"abstract":"Abstract Combined systems, which are flexible structures carrying moving subsystems, are seen in various applications. Due to structure–subsystem interactions, the structure in a combined system encounters jump discontinuities in its internal forces (such as the bending moment and shear force of a beam). Accurate estimation of such jump discontinuities is important to the performance, safety, and longevity of a combined system. Because of the time-varying nature and complexity of structure–subsystem interactions, conventional series solution methods experience slow convergence, and the Gibbs phenomenon in computation and the improved series expansion methods are limited to certain proportionally damped continua under moving forces and moving oscillators. In this paper, a novel modified series expansion method (MSEM) is proposed to resolve the aforementioned issues with the existing series solution methods. Through the introduction of a jump influence function, the proposed method produces fast-convergent series solutions and accurately predicts the jump discontinuities without the Gibbs phenomenon. The MSEM is applicable to structures with nonproportional damping and subject to arbitrary boundary conditions, and it can easily manage general M-DOF moving subsystems having multiple contact points with a supporting structure. As an important result of this investigation, a mathematical proof of the convergence of the MSEM-based solutions is given for the first time. Additionally, two numerical examples are presented to demonstrate the accuracy, efficiency, and versatility of the proposed MSEM in modeling and analysis of combined systems.","PeriodicalId":54880,"journal":{"name":"Journal of Applied Mechanics-Transactions of the Asme","volume":"80 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134890883","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Deformation and fracture of metallic glasses are often modeled by stress-based criteria which often incorporate some sorts of pressure dependence. However, detailed mechanisms that are responsible for the shear band formation and the entire damage initiation and evolution process are complex and the origin of such a pressure dependence is obscure. Here we argue that the shear band formation results from the constitutive instability, so that the shear-band angle and arrangements can be easily related to the macroscopic constitutive parameters such as internal friction and dilatancy factor. This is one reason for the observed tension-compression asymmetry in metallic glasses. The free volume coalescence leads to precipitous formation of voids or cavities inside the shear bands, and the intrinsic “ductility” is therefore governed by the growth of these cavities. Based on a generalized Stokes-Hookean analogy, we can derive the critical shear-band failure strain with respect to the applied stress triaxiality, in which the cavity evolution scenarios are sharply different between tension-controlled and shear/compression-dominated conditions. This is another possible reason for the tension-compression asymmetry. It is noted that diffusive-controlled cavity growth could also be the rate-determining process, as suggested by the recent measurements of shear-band diffusivity and viscosity that turn out to satisfy the Stokes-Einstein relationship. This constitutes the third possible reason for the tension-compression asymmetry.
{"title":"A cavity-based micromechanical model for the shear band failure in metallic glasses under arbitrary stress states","authors":"Yanfei Gao","doi":"10.1115/1.4062724","DOIUrl":"https://doi.org/10.1115/1.4062724","url":null,"abstract":"\u0000 Deformation and fracture of metallic glasses are often modeled by stress-based criteria which often incorporate some sorts of pressure dependence. However, detailed mechanisms that are responsible for the shear band formation and the entire damage initiation and evolution process are complex and the origin of such a pressure dependence is obscure. Here we argue that the shear band formation results from the constitutive instability, so that the shear-band angle and arrangements can be easily related to the macroscopic constitutive parameters such as internal friction and dilatancy factor. This is one reason for the observed tension-compression asymmetry in metallic glasses. The free volume coalescence leads to precipitous formation of voids or cavities inside the shear bands, and the intrinsic “ductility” is therefore governed by the growth of these cavities. Based on a generalized Stokes-Hookean analogy, we can derive the critical shear-band failure strain with respect to the applied stress triaxiality, in which the cavity evolution scenarios are sharply different between tension-controlled and shear/compression-dominated conditions. This is another possible reason for the tension-compression asymmetry. It is noted that diffusive-controlled cavity growth could also be the rate-determining process, as suggested by the recent measurements of shear-band diffusivity and viscosity that turn out to satisfy the Stokes-Einstein relationship. This constitutes the third possible reason for the tension-compression asymmetry.","PeriodicalId":54880,"journal":{"name":"Journal of Applied Mechanics-Transactions of the Asme","volume":" ","pages":""},"PeriodicalIF":2.6,"publicationDate":"2023-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45189581","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Surface wrinkles have emerged as a promising avenue for the development of smart adhesives with dynamically tunable adhesion, finding applications in diverse fields, such as soft robots and medical devices. Despite intensive studies and great achievements, it is still challenging to model and simulate the tunable adhesion with surface wrinkles due to roughened surface topologies and pre-stress inside the materials. The lack of a mechanistic understanding hinders the rational design of these smart adhesives. Here we integrate a lattice model for nonlinear deformations of solids and nonlocal interaction potentials for adhesion in the framework of molecular dynamics to explore the roles of surface wrinkles on the adhesion behaviors. We validate the proposed model by comparing wrinkles in a neo-Hookean bilayer with benchmarked results and reproducing the analytical solution for cylindrical adhesion. We then systematically study the pull-off force of the wrinkled surface with varied compressive strains and adhesion energies. Our results reveal the competing effect between the adhesion induced contact and the roughness due to wrinkles on enhancing or weakening the adhesion. Such understanding provides guidance for tailoring material and geometry as well as loading of the wrinkled surfaces for different applications.
{"title":"Mechanics of tunable adhesion with surface wrinkles","authors":"Teng Zhang","doi":"10.1115/1.4062699","DOIUrl":"https://doi.org/10.1115/1.4062699","url":null,"abstract":"\u0000 Surface wrinkles have emerged as a promising avenue for the development of smart adhesives with dynamically tunable adhesion, finding applications in diverse fields, such as soft robots and medical devices. Despite intensive studies and great achievements, it is still challenging to model and simulate the tunable adhesion with surface wrinkles due to roughened surface topologies and pre-stress inside the materials. The lack of a mechanistic understanding hinders the rational design of these smart adhesives. Here we integrate a lattice model for nonlinear deformations of solids and nonlocal interaction potentials for adhesion in the framework of molecular dynamics to explore the roles of surface wrinkles on the adhesion behaviors. We validate the proposed model by comparing wrinkles in a neo-Hookean bilayer with benchmarked results and reproducing the analytical solution for cylindrical adhesion. We then systematically study the pull-off force of the wrinkled surface with varied compressive strains and adhesion energies. Our results reveal the competing effect between the adhesion induced contact and the roughness due to wrinkles on enhancing or weakening the adhesion. Such understanding provides guidance for tailoring material and geometry as well as loading of the wrinkled surfaces for different applications.","PeriodicalId":54880,"journal":{"name":"Journal of Applied Mechanics-Transactions of the Asme","volume":" ","pages":""},"PeriodicalIF":2.6,"publicationDate":"2023-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46329071","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Poisson's ratios of diamond-like structures, such as cubic C, Si, and Ge, have been widely explored because of their potential applications in solid-state devices. However, the theoretical bounds on the Poisson's ratios of diamond-like structures remain unknown. In this paper, we have derived analytical expressions for the minimum and maximum Poisson's ratios, as well as the Poisson's ratios averaged by three different schemes (i.e., Voigt, Reuss, and Hill averaging schemes). These expressions are based on the correlation between macroscopic elastic constants and microscopic force constants of diamond-like structures, and are solely a function of a dimensionless quantity (λ) that characterizes the ratio of mechanical resistances between angle bending and bond stretching. Based on these expressions, we have determined the bounds on the Poisson's ratios, as well as the minimum and maximum Poisson's ratios, and the Poisson's ratios averaged by the three schemes mentioned above. Specifically, these bounds are (−1, 4/5), (−1, 1/5), (0, 4/5), (−1, 1/2), (−1/3, 1/2), and (−2/3, 1/2), respectively. These results were well supported by atomistic simulations. Mechanism analyses demonstrated that the diverse Poisson's behaviors of diamond-like structures result from the interplay between two deformation modes (i.e., bond stretching and angle bending). This work provides the roadmap for finding interesting Poisson's behaviors of diamond-like structures.
{"title":"Bounds on the Poisson's ratios of diamond-like structures","authors":"Yi Liu, Chunbo Zhang, Hang Yang, Enlai Gao","doi":"10.1115/1.4062700","DOIUrl":"https://doi.org/10.1115/1.4062700","url":null,"abstract":"\u0000 Poisson's ratios of diamond-like structures, such as cubic C, Si, and Ge, have been widely explored because of their potential applications in solid-state devices. However, the theoretical bounds on the Poisson's ratios of diamond-like structures remain unknown. In this paper, we have derived analytical expressions for the minimum and maximum Poisson's ratios, as well as the Poisson's ratios averaged by three different schemes (i.e., Voigt, Reuss, and Hill averaging schemes). These expressions are based on the correlation between macroscopic elastic constants and microscopic force constants of diamond-like structures, and are solely a function of a dimensionless quantity (λ) that characterizes the ratio of mechanical resistances between angle bending and bond stretching. Based on these expressions, we have determined the bounds on the Poisson's ratios, as well as the minimum and maximum Poisson's ratios, and the Poisson's ratios averaged by the three schemes mentioned above. Specifically, these bounds are (−1, 4/5), (−1, 1/5), (0, 4/5), (−1, 1/2), (−1/3, 1/2), and (−2/3, 1/2), respectively. These results were well supported by atomistic simulations. Mechanism analyses demonstrated that the diverse Poisson's behaviors of diamond-like structures result from the interplay between two deformation modes (i.e., bond stretching and angle bending). This work provides the roadmap for finding interesting Poisson's behaviors of diamond-like structures.","PeriodicalId":54880,"journal":{"name":"Journal of Applied Mechanics-Transactions of the Asme","volume":" ","pages":""},"PeriodicalIF":2.6,"publicationDate":"2023-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49204152","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A previously proposed strain gradient plasticity theory is extended to incorporate a non-quadratic power law function of the plastic strain gradient in the free energy expression with an exponent of N + 1. The values of N are taken to vary from N = 1 to N = 0. A simple shear problem of a metal layer between rigid boundaries is analyzed. Two stages of plastic deformation are considered. In stage I, the plastic strain is taken to be zero at the boundaries. Stage I ends when a specified magnitude of the plastic strain gradient is attained at the boundaries. In stage II, the magnitude of the plastic strain gradient at the boundaries is fixed at the specified value. With N = 0, a critical plastic strain gradient cannot be specified at the boundaries because the plastic strain gradient is infinite at the boundaries. The theory with N = 0 predicts a constant plateau stress immediately after initial yield, and the dependence of the plateau stress on the layer thickness can fit experimentally observed plateau stress values. However, with N = 0, a stress gap occurs between the initial yield stress and the plateau stress. The theory with 0 < N = 1 and with stage II also can reproduce the experimentally observed dependence of the plateau stress on the layer thickness for any value of N in that range, with an appropriate value of critical plastic strain gradient at the boundaries. The solution for 0 < N = 1 includes that for N = 0 as a limiting case.
{"title":"Non-quadratic strain gradient plasticity theory and size effects in constrained shear","authors":"M. Kuroda, A. Needleman","doi":"10.1115/1.4062698","DOIUrl":"https://doi.org/10.1115/1.4062698","url":null,"abstract":"\u0000 A previously proposed strain gradient plasticity theory is extended to incorporate a non-quadratic power law function of the plastic strain gradient in the free energy expression with an exponent of N + 1. The values of N are taken to vary from N = 1 to N = 0. A simple shear problem of a metal layer between rigid boundaries is analyzed. Two stages of plastic deformation are considered. In stage I, the plastic strain is taken to be zero at the boundaries. Stage I ends when a specified magnitude of the plastic strain gradient is attained at the boundaries. In stage II, the magnitude of the plastic strain gradient at the boundaries is fixed at the specified value. With N = 0, a critical plastic strain gradient cannot be specified at the boundaries because the plastic strain gradient is infinite at the boundaries. The theory with N = 0 predicts a constant plateau stress immediately after initial yield, and the dependence of the plateau stress on the layer thickness can fit experimentally observed plateau stress values. However, with N = 0, a stress gap occurs between the initial yield stress and the plateau stress. The theory with 0 < N = 1 and with stage II also can reproduce the experimentally observed dependence of the plateau stress on the layer thickness for any value of N in that range, with an appropriate value of critical plastic strain gradient at the boundaries. The solution for 0 < N = 1 includes that for N = 0 as a limiting case.","PeriodicalId":54880,"journal":{"name":"Journal of Applied Mechanics-Transactions of the Asme","volume":" ","pages":""},"PeriodicalIF":2.6,"publicationDate":"2023-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44430720","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Fracture in solid solutions, such as electrodes for lithium-ion batteries and fuel cells, is mediated by intricate interactions between solid-state diffusion and crack propagation. In this work, we developed a composition-dependent cohesive zone model and integrated it with a chemo-mechanical coupling constitutive model to study the fracture mechanisms of solid solutions. The computational framework was used to investigate the effective fracture properties of chemo-mechanically coupled solid solutions over a wide range of crack growth velocities and compositional dependence of intrinsic fracture energy. The results revealed an important characteristic crack velocity, which is set by the ratio of the diffusivity to the intrinsic fracture energy and dictates the effective fracture resistance of the material. We also applied the model to study the fracture behavior of two-phase lithiated silicon (Si) and germanium (Ge) nanostructures as candidate high-capacity anodes for next-generation lithium-ion batteries, and showed that Ge nanostructures are more fracture resistant than their Si counterparts. The computational study presented here provides important insights for the rational design, operation, and mechanical testing of chemo-mechanically active material systems for their use in energy storage and conversion.
{"title":"Fracture Resistance of Chemo-mechanically Coupled Solid Solutions","authors":"Xueju Wang, Mu Lu, Min Zhou, S. Xia","doi":"10.1115/1.4062697","DOIUrl":"https://doi.org/10.1115/1.4062697","url":null,"abstract":"\u0000 Fracture in solid solutions, such as electrodes for lithium-ion batteries and fuel cells, is mediated by intricate interactions between solid-state diffusion and crack propagation. In this work, we developed a composition-dependent cohesive zone model and integrated it with a chemo-mechanical coupling constitutive model to study the fracture mechanisms of solid solutions. The computational framework was used to investigate the effective fracture properties of chemo-mechanically coupled solid solutions over a wide range of crack growth velocities and compositional dependence of intrinsic fracture energy. The results revealed an important characteristic crack velocity, which is set by the ratio of the diffusivity to the intrinsic fracture energy and dictates the effective fracture resistance of the material. We also applied the model to study the fracture behavior of two-phase lithiated silicon (Si) and germanium (Ge) nanostructures as candidate high-capacity anodes for next-generation lithium-ion batteries, and showed that Ge nanostructures are more fracture resistant than their Si counterparts. The computational study presented here provides important insights for the rational design, operation, and mechanical testing of chemo-mechanically active material systems for their use in energy storage and conversion.","PeriodicalId":54880,"journal":{"name":"Journal of Applied Mechanics-Transactions of the Asme","volume":" ","pages":""},"PeriodicalIF":2.6,"publicationDate":"2023-06-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45320373","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Natural defects such as nano inclusions and nanocracks are inevitable in dielectric materials. When materials are subjected to mechanical loading, the strain gradient around crack tips and inclusions would become large and induce significant flexoelectric fields. In contrast to classical crack-inclusion problems, the interactions between these flexoelectric fields may locally change the electromechanical behaviors of materials, and result in some interesting phenomena. To better understand the crack-inclusion interactions in flexoelectric solids, in this work, we use a collocation mixed finite element method to model and analyze the flexoelectric fields around the crack tip and inclusion. Based on the J-integral, we analyze how the flexoelectric effect affect the interactions energy between nanocracks and nearby nano inclusions. This work proposes a new coupling mechanism in crack-inclusion problems and may inspire future experiments in flexoelectric solids.
{"title":"Modeling the interaction between inclusions and nanocracks in flexoelectric solid","authors":"Mengkang Xu, Xinpeng Tian, Q. Deng, Qun Li","doi":"10.1115/1.4062659","DOIUrl":"https://doi.org/10.1115/1.4062659","url":null,"abstract":"\u0000 Natural defects such as nano inclusions and nanocracks are inevitable in dielectric materials. When materials are subjected to mechanical loading, the strain gradient around crack tips and inclusions would become large and induce significant flexoelectric fields. In contrast to classical crack-inclusion problems, the interactions between these flexoelectric fields may locally change the electromechanical behaviors of materials, and result in some interesting phenomena. To better understand the crack-inclusion interactions in flexoelectric solids, in this work, we use a collocation mixed finite element method to model and analyze the flexoelectric fields around the crack tip and inclusion. Based on the J-integral, we analyze how the flexoelectric effect affect the interactions energy between nanocracks and nearby nano inclusions. This work proposes a new coupling mechanism in crack-inclusion problems and may inspire future experiments in flexoelectric solids.","PeriodicalId":54880,"journal":{"name":"Journal of Applied Mechanics-Transactions of the Asme","volume":"1 1","pages":""},"PeriodicalIF":2.6,"publicationDate":"2023-06-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"63503969","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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