This paper is devoted to the microstructure geometric modeling and mechanical properties computation of cancellous bone.The microstructure of the cancellous bone determines its mechanical properties and a precise geom...This paper is devoted to the microstructure geometric modeling and mechanical properties computation of cancellous bone.The microstructure of the cancellous bone determines its mechanical properties and a precise geometric modeling of this structure is important to predict the material properties.Based on the microscopic observation,a new microstructural unit cell model is established by introducing the Schwarz surface in this paper.And this model is very close to the real microstructure and satisfies the main biological characteristics of cancellous bone.By using the unit cell model,the multiscale analysis method is newly applied to predict the mechanical properties of cancellous bone.The effective stiffness parameters are calculated by the up-scaling multi-scale analysis.And the distribution of microscopic stress in cancellous bone is determined through the down-scaling procedure.In addition,the effect of porosity on the stiffness parameters is also investigated.The predictive mechanical properties are in good agreement with the available experimental results,which verifies the applicability of the proposed unit cell model and the validness of the multiscale analysis method to predict the mechanical properties of cancellous bone.展开更多
In the present paper,the two-dimensional comprehensive model,which integrates the temperature model developed by the authors using finite difference methods and microstructural evolution model,has been developed.By us...In the present paper,the two-dimensional comprehensive model,which integrates the temperature model developed by the authors using finite difference methods and microstructural evolution model,has been developed.By using different microstructural evolution equations developed by Sellars,Senuma et al.and Easka et al.,the comparison studies have been made,which present that (1) the calculated γ-grain sizes show good agreements with the measured;(2) these equations show consistencies at the end of finishing stands.展开更多
In the present research, microstructure of akind of limnetic shell (Hyriopsis cumingii) is observed and measured by using the scanning electron microscopy, and mechanical behavior experiments of the shell nacre are ...In the present research, microstructure of akind of limnetic shell (Hyriopsis cumingii) is observed and measured by using the scanning electron microscopy, and mechanical behavior experiments of the shell nacre are carried out by using bending and tensile tests. The dependence of mechanical properties of the shell nacre on its microstructure is analyzed by using a modified shear-lag model, and the overall stress-strain relation is obtained. The experimental results reveal that the mechanical properties of shell nacre strongly depend on the water contents of the limnetic shell. Dry nacre shows a brittle behavior, whereas wetting nacre displays a strong ductility. Compared to the tensile test, the bending test overestimates the strength and underestimates the Young's modulus. The modified shear-lag model can characterize the deformation features of nacre effectively.展开更多
Two linked models have been developed to explore the relationship between the amount of porosity arising in service from both radiolytic oxidation and fast neutron damage that influences both the strength and the forc...Two linked models have been developed to explore the relationship between the amount of porosity arising in service from both radiolytic oxidation and fast neutron damage that influences both the strength and the force-displacement(load-displacement)behaviour and crack propagation in pile grade A graphite used as a nuclear reactor moderator material.Firstly models of the microstructure of the porous graphite for both unirradiated and irradiated graphite are created.These form the input for the second stage,simulating fracture in lattice-type finite element models,which predicts force(load)-displacement and crack propagation paths.Microstructures comprising aligned filler particles,typical of needle coke,in a porous matrix have been explored.The purpose was to isolate the contributions of filler particles and porosity to fracture strength and crack paths and consider their implications for the overall failure of reactor core graphite.展开更多
The damage models based on the eight-chain model and the affine full-chain network model are not adequate to describe the damage behaviors in double-network(DN)hydrogels.To overcome this limitation,we propose a combin...The damage models based on the eight-chain model and the affine full-chain network model are not adequate to describe the damage behaviors in double-network(DN)hydrogels.To overcome this limitation,we propose a combined chain stretch model with new damage flow rules.It is demonstrated that the new proposed micro-chain stretch is a reduced form of the complete representation for the transversely isotropic tensor function.As a result,the damage models based on the eight-chain model and the affine model are incorporated as special cases.The effects of chain affineness and network entangling are simultaneously involved in the new model,while only one of these two effects can be characterized in either the eight-chain model or the affine model.It is further shown that the new model can effectively capture the Mullins features of the DN hydrogels and achieve better agreement with the experimental data than the affine model and the eight-chain model.展开更多
To visually describe the sanding pattern,this study constructs a new particle-scale microstructure model of weakly consolidated formation,and develop the corresponding methodology to simulate the sanding process and p...To visually describe the sanding pattern,this study constructs a new particle-scale microstructure model of weakly consolidated formation,and develop the corresponding methodology to simulate the sanding process and predict sand cavity shape.The microstructure model is a particle-objective model,which focuses on the random sedimentation of every sand grain.In the microstructure,every particle has its own size,sphericity and inclination angle.It is used to simulate the actual structure of cemented granular materials,which considers the heterogeneity and randomness of reservoir properties,provides the initial status for subsequent sanding simulation.With the particle detachment criteria,the microscopic simulation of sanding can be visually implemented to investigate the pattern and cavity shapes caused by sand production.The results indicate that sanding always starts initially from the borehole border,and then extends along the weakly consolidated plane,showing obvious characteristic of randomness.Three typical microscopic sanding patterns,concerning pore liquefaction,pseudo wormhole and continuous collapse,are proposed to illustrate the sanding mechanism in weakly consolidated reservoirs.The nonuniformity of sanding performance depends on the heterogeneous distribution of reservoir properties,such as rock strength and particle size.Finally,the three sanding patterns are verified by visually experimental work.The proposed integrated methodology is capable of predicting and describing the sanding cavity shape of an oil well after long-term sanding production,and providing the focus objective of future sand control measure.展开更多
In the last three decades new stronger modified 9%Cr steels have been introduced in new power plants with steam parameters up to 300 bar(1 bar =10~5 Pa) and 600℃. In order to further increase the steam parameters of ...In the last three decades new stronger modified 9%Cr steels have been introduced in new power plants with steam parameters up to 300 bar(1 bar =10~5 Pa) and 600℃. In order to further increase the steam parameters of steel based power plants up to a target value of 650℃/ 325 bar it is necessary to double the creep strength compared with todays strongest 9%Cr steels,and at the same time the resistance against steam oxidation must be improved by adding 12%Cr to the steel. However,so far all attempts to make stronger 12%Cr steels have been unsuccessful because the high chromium content introduced severe microstructure instabilities in the tested steels.Recently,it was found that the microstructure instabilities in 11%- 12%Cr steels can be explained by the precipitation of coarse Cr(V,Nb)N Z-phases, which dissolve fine(V,Nb)N nitrides. A new possibility to use the Z-phase for strengthening of 12%Cr steels has been identified,and the development of stable strong martensitic 12%Cr steels based on this concept is expected to allow the construction of 325 bar/ 650℃steam power plants all based on steel.展开更多
Hydrogenated amorphous silicon (a-Si:H) films with high and same order of magnitude photosensitivity (-10^5) but different stability were prepared by using microwave electron cyclotron resonance chemical vapour d...Hydrogenated amorphous silicon (a-Si:H) films with high and same order of magnitude photosensitivity (-10^5) but different stability were prepared by using microwave electron cyclotron resonance chemical vapour deposition system under the different deposition conditions. It was proposed that there was no direct correlation between the photosensitivity and the hydrogen content (CH) as well as H-Si bonding configurations, but for the stability, they were the critical factors. The experimental results indicated that higher substrate temperature, hydrogen dilution ratio and lower deposition rate played an important role in improving the microstructure of a-Si:H films. We used hydrogen elimination model to explain our experimental results.展开更多
The evolution of the hydrate particle structure during growth and agglomeration under flowing condition affects the particle as well as flow characteristic,which plays an important role in the flow assurance as well a...The evolution of the hydrate particle structure during growth and agglomeration under flowing condition affects the particle as well as flow characteristic,which plays an important role in the flow assurance as well as heat transfer in refrigeration systems.Therefore,this article conducts experiments to study and observe the growth and agglomeration process in the main forming stage of hydrate.It was found that the growth of tetrahydrofuran hydrate was anisotropic and in a layered growth pattern.Single crystals generally transformed from octahedral structure to octahedral skeleton structure with growth,however some single crystals also deformed into plate type particles.The thickness of the plate type particles increased gradually during growth,and the edge part increased earlier than the middle part.During agglomeration,the hydrate particles contacted and sintered together.Sand as the impurity didn’t serve as the nucleation center but affected the agglomeration of hydrate particles by collisions.In addition,the effect increased as the sand size decreased.Finally,a microstructure model for hydrate growth and agglomeration was proposed,which showed the hydrate structure evolution in these processes and could lay a foundation for studying the flow assurance of hydrate slurry.展开更多
Micromechanics investigations of composites with fiber-shaped reinforcement are extensively applied in the engineering design and theoretical analysis of thermal composites in the aerospace engineering and high-tech i...Micromechanics investigations of composites with fiber-shaped reinforcement are extensively applied in the engineering design and theoretical analysis of thermal composites in the aerospace engineering and high-tech industry.In this paper,a critical review of various classical micromechanics approaches is provided based on the classification framework and the development of micromechanics tools.Several numerical micromechanics tools have been developed to overcome limitations through exactly/approximately solving the internal governing equations of microstructures.The connections and limitations of those models are also investigated and discussed,based on which three recently developed numerical or semi-analytical models are explained,including finite-element micromechanics,finite-volume direct averaging micromechanics,and locally exact homogenization theory,as well as machine learning tools.Since it is almost inevitable to mention the interfacial effects on thermal behavior of fibrous composites,we review the new mathematical relations that interrupt the original continuity conditions due to the existence of interphase/interface within unit cells.Generally speaking,the interphase/interface is demonstrated to play a significant role in influencing the effective coefficients and localized thermal fields.The present work also briefly reviews the application of micromechanics tools in emerging engineered woven composites,natural fibrous composites,and ablative thermal protection composites.It is demonstrated that sophisticated micromechanics tools are always demanded for investigating the effective and localized responses of thermal fibrous composites.展开更多
A modified cellular automaton model is developed to depict the interface evolution inside the cementite plus ferrite lamellar microstructures during the reaustenitization of a pearlite steel. In this model, migrations...A modified cellular automaton model is developed to depict the interface evolution inside the cementite plus ferrite lamellar microstructures during the reaustenitization of a pearlite steel. In this model, migrations of both the austenite- ferrite and austenite-cementite interfaces coupled with the carbon diffusion and redistribution are integrated. The capil- laxity effect derived from local interface curvatures is also carefully considered by involving the concentration given by the phase diagram modified by the Gibbs-Thomson effect. This allows the interface evolution from a transient state to a steady state under different annealing conditions and various interlamellar spacings to be simulated. The proposed cellular automaton approach could be readily used to describe the kinetics of austenite formation from the lamellar pearlites and virtually reveal the kinematics of the moving interfaces from the microstructural aspect.展开更多
Simulation technology for shape casting at macro-scale has been successfully put into engineer- ing application in a number of casting plants and as a result the quality of castings is assured, the research and deve...Simulation technology for shape casting at macro-scale has been successfully put into engineer- ing application in a number of casting plants and as a result the quality of castings is assured, the research and development time is shortened, and the manufacturing cost is greatly saved as well. In this paper, mod- eling and simulation technologies of solidification process of shape casting at microstructure-scale, espe- cially deterministic, cellular automaton, and phase field models are studied and reviewed.展开更多
The quantitative phase-field simulations were reviewed on the processes of solidification of pure metals and alloys.The quantitative phase-field equations were treated in a diffuse thin-interface limit,which enabled t...The quantitative phase-field simulations were reviewed on the processes of solidification of pure metals and alloys.The quantitative phase-field equations were treated in a diffuse thin-interface limit,which enabled the quantitative links between interface dynamics and model parameters in the quasi-equilibrium simulations.As a result,the quantitative modeling is more effective in dealing with microstructural pattern formation in the large scale simulations without any spurious kinetic effects.The development of the quantitative phase-field models in modeling the formation of microstructures such as dendritic structures,eutectic lamellas,seaweed morphologies,and grain boundaries in different solidified conditions was also reviewed with the purpose of guiding to find the new prospect of applications in the quantitative phase-field simulations.展开更多
The prediction of microstructure constituents and their morphologies is of great importance for the evaluation of material properties and design of advanced materials.There have been considerable efforts to model and ...The prediction of microstructure constituents and their morphologies is of great importance for the evaluation of material properties and design of advanced materials.There have been considerable efforts to model and simulate microstructure evolution using a wide spectrum of models and simulation approaches.This paper initially reviews the atomistic and mesoscale simulation approaches for microstructure evolution,emphasizing their advantages and disadvantages.Atomistic approaches,such as molecular dynamics,are restricted by the scale of the studied system because they are computationally expensive.Continuum mesoscale simulation approaches,such as phase field,cellular automata,and Monte Carlo,have inconsistent phenomenological equations,each of which only describes one aspect of microstructure evolution.To provide comprehensive insight into microstructure evolution,a unified model that is capable of equally evaluating the nucleation and growth processes is required.In this paper,a physics-based model is proposed that incorporates statistical mechanics,the energy conservation law,and the force equilibrium concept to include all aspects of microstructure evolution.A compatible simulation approach is also described to simulate microstructure evolution during thermomechanical treatments.Furthermore,the microstructure evolution of AISI 304 austenitic steel during isothermal heat treatment and fusion welding is simulated and discussed.The use of fundamental physical rules instead of phenomenological equations,together with the real spatial and temporal scales of the proposed model,facilitates the comparison of the simulation results with experimental results.To examine the accuracy of the proposed simulation approach,the isothermal heat treatment simulation results are compared with experimental data over a broad region of temperatures and time periods.展开更多
The reduction pretreatment process has been proposed to improve the center quality of large billet and reduce the rolling ratio.The microstructure evolution during the reduction pretreatment was further understood.The...The reduction pretreatment process has been proposed to improve the center quality of large billet and reduce the rolling ratio.The microstructure evolution during the reduction pretreatment was further understood.The austenite grains were refined after the reduction pretreatment experiment,especially those at the center of the billet.The effects of strain and strain rate on the average grain size were dependent on the deformation temperature.At a strain rate of 0.01 s-1 and 1200°C,the newly formed strain-free austenite grains grew very fast as the strain continued to increase,which resulted in the coarsening of austenite grains.The calculation results of the microstructure evolution model showed that at the same deformation temperature,the evolution curves of average grain size with different strain rates had the intersection points.With the increase in temperature,the position of intersection point moved to the downward direction of strain.The simulation results showed that when the reduction amount increased to 20%,the average grain size at the center was smaller than that near the surface.It could be inferred that when the reduction amount greatly exceeded 20%,the dynamic recrystallization at the center was mostly completed,and the austenite grain growth would become the main mechanism.展开更多
Temperature rise is a significant factor influencing microstructure during(α+β) deformation of TA15 titanium alloy.An experiment was designed to explore microstructure evolution induced by temperature rise due to...Temperature rise is a significant factor influencing microstructure during(α+β) deformation of TA15 titanium alloy.An experiment was designed to explore microstructure evolution induced by temperature rise due to deformation heat.The experiment was carried out in(α+β) phase field at typical temperature rise rates.The microstructures of the alloy under different temperature rise rates were observed by scanning electron microscopy(SEM).It is found that the dissolution rate of primary equiaxed a phase increases with the increase in both temperature and temperature rise rate.In the same temperature range,the higher the temperature rise rate is,the larger the final content and grain size of primary equiaxed a phase are due to less dissolution time.To quantitatively depict the evolution behavior of primary equiaxed a phase under any temperature rise rates,the dissolution kinetics of primary equiaxed a phase were well described by a diffusion model.The model predictions,including content and grain size of primary equiaxed a phase,are in good agreement with experimental observations.The work provides an important basis for the prediction and control of microstructure during hot working of titanium alloy.展开更多
基金This work is supported by the National Natural Science Foundation of China(11471262,11501449)Fundamental Research Funds for the Central Universities(3102017zy043)China Postdoctoral Science Foundation(2018M633569).
文摘This paper is devoted to the microstructure geometric modeling and mechanical properties computation of cancellous bone.The microstructure of the cancellous bone determines its mechanical properties and a precise geometric modeling of this structure is important to predict the material properties.Based on the microscopic observation,a new microstructural unit cell model is established by introducing the Schwarz surface in this paper.And this model is very close to the real microstructure and satisfies the main biological characteristics of cancellous bone.By using the unit cell model,the multiscale analysis method is newly applied to predict the mechanical properties of cancellous bone.The effective stiffness parameters are calculated by the up-scaling multi-scale analysis.And the distribution of microscopic stress in cancellous bone is determined through the down-scaling procedure.In addition,the effect of porosity on the stiffness parameters is also investigated.The predictive mechanical properties are in good agreement with the available experimental results,which verifies the applicability of the proposed unit cell model and the validness of the multiscale analysis method to predict the mechanical properties of cancellous bone.
文摘In the present paper,the two-dimensional comprehensive model,which integrates the temperature model developed by the authors using finite difference methods and microstructural evolution model,has been developed.By using different microstructural evolution equations developed by Sellars,Senuma et al.and Easka et al.,the comparison studies have been made,which present that (1) the calculated γ-grain sizes show good agreements with the measured;(2) these equations show consistencies at the end of finishing stands.
基金the National Natural Science Foundation of China (10432050,10428207 and 10672163)the Chinese Academy of Sciences (KJCX2-YW-M04)the Institute of Mechanics through Innovation Project
文摘In the present research, microstructure of akind of limnetic shell (Hyriopsis cumingii) is observed and measured by using the scanning electron microscopy, and mechanical behavior experiments of the shell nacre are carried out by using bending and tensile tests. The dependence of mechanical properties of the shell nacre on its microstructure is analyzed by using a modified shear-lag model, and the overall stress-strain relation is obtained. The experimental results reveal that the mechanical properties of shell nacre strongly depend on the water contents of the limnetic shell. Dry nacre shows a brittle behavior, whereas wetting nacre displays a strong ductility. Compared to the tensile test, the bending test overestimates the strength and underestimates the Young's modulus. The modified shear-lag model can characterize the deformation features of nacre effectively.
文摘Two linked models have been developed to explore the relationship between the amount of porosity arising in service from both radiolytic oxidation and fast neutron damage that influences both the strength and the force-displacement(load-displacement)behaviour and crack propagation in pile grade A graphite used as a nuclear reactor moderator material.Firstly models of the microstructure of the porous graphite for both unirradiated and irradiated graphite are created.These form the input for the second stage,simulating fracture in lattice-type finite element models,which predicts force(load)-displacement and crack propagation paths.Microstructures comprising aligned filler particles,typical of needle coke,in a porous matrix have been explored.The purpose was to isolate the contributions of filler particles and porosity to fracture strength and crack paths and consider their implications for the overall failure of reactor core graphite.
基金supported by the National Natural Science Foundation of China under Grant No.12022204,the Zhejiang Provincial Natural Science Foundation of China under Grant No.LD22A020001,and the Fundamental Research Funds for the Central Universities,China(Grant No.2021FZZX001-16).
文摘The damage models based on the eight-chain model and the affine full-chain network model are not adequate to describe the damage behaviors in double-network(DN)hydrogels.To overcome this limitation,we propose a combined chain stretch model with new damage flow rules.It is demonstrated that the new proposed micro-chain stretch is a reduced form of the complete representation for the transversely isotropic tensor function.As a result,the damage models based on the eight-chain model and the affine model are incorporated as special cases.The effects of chain affineness and network entangling are simultaneously involved in the new model,while only one of these two effects can be characterized in either the eight-chain model or the affine model.It is further shown that the new model can effectively capture the Mullins features of the DN hydrogels and achieve better agreement with the experimental data than the affine model and the eight-chain model.
基金financially supported by the National Natural Science Foundation of China(Grant No.51774307,52074331,42002182)partially supported by Major Special Projects of CNPC,China(ZD2019-184)。
文摘To visually describe the sanding pattern,this study constructs a new particle-scale microstructure model of weakly consolidated formation,and develop the corresponding methodology to simulate the sanding process and predict sand cavity shape.The microstructure model is a particle-objective model,which focuses on the random sedimentation of every sand grain.In the microstructure,every particle has its own size,sphericity and inclination angle.It is used to simulate the actual structure of cemented granular materials,which considers the heterogeneity and randomness of reservoir properties,provides the initial status for subsequent sanding simulation.With the particle detachment criteria,the microscopic simulation of sanding can be visually implemented to investigate the pattern and cavity shapes caused by sand production.The results indicate that sanding always starts initially from the borehole border,and then extends along the weakly consolidated plane,showing obvious characteristic of randomness.Three typical microscopic sanding patterns,concerning pore liquefaction,pseudo wormhole and continuous collapse,are proposed to illustrate the sanding mechanism in weakly consolidated reservoirs.The nonuniformity of sanding performance depends on the heterogeneous distribution of reservoir properties,such as rock strength and particle size.Finally,the three sanding patterns are verified by visually experimental work.The proposed integrated methodology is capable of predicting and describing the sanding cavity shape of an oil well after long-term sanding production,and providing the focus objective of future sand control measure.
文摘In the last three decades new stronger modified 9%Cr steels have been introduced in new power plants with steam parameters up to 300 bar(1 bar =10~5 Pa) and 600℃. In order to further increase the steam parameters of steel based power plants up to a target value of 650℃/ 325 bar it is necessary to double the creep strength compared with todays strongest 9%Cr steels,and at the same time the resistance against steam oxidation must be improved by adding 12%Cr to the steel. However,so far all attempts to make stronger 12%Cr steels have been unsuccessful because the high chromium content introduced severe microstructure instabilities in the tested steels.Recently,it was found that the microstructure instabilities in 11%- 12%Cr steels can be explained by the precipitation of coarse Cr(V,Nb)N Z-phases, which dissolve fine(V,Nb)N nitrides. A new possibility to use the Z-phase for strengthening of 12%Cr steels has been identified,and the development of stable strong martensitic 12%Cr steels based on this concept is expected to allow the construction of 325 bar/ 650℃steam power plants all based on steel.
文摘Hydrogenated amorphous silicon (a-Si:H) films with high and same order of magnitude photosensitivity (-10^5) but different stability were prepared by using microwave electron cyclotron resonance chemical vapour deposition system under the different deposition conditions. It was proposed that there was no direct correlation between the photosensitivity and the hydrogen content (CH) as well as H-Si bonding configurations, but for the stability, they were the critical factors. The experimental results indicated that higher substrate temperature, hydrogen dilution ratio and lower deposition rate played an important role in improving the microstructure of a-Si:H films. We used hydrogen elimination model to explain our experimental results.
基金supported by the National Natural Science Foundation of China(51991363(Major Program),51974349,U19B2012)State Key Laboratory of Natural Gas Hydrates(443CCL2020RCPS0225ZQN)。
文摘The evolution of the hydrate particle structure during growth and agglomeration under flowing condition affects the particle as well as flow characteristic,which plays an important role in the flow assurance as well as heat transfer in refrigeration systems.Therefore,this article conducts experiments to study and observe the growth and agglomeration process in the main forming stage of hydrate.It was found that the growth of tetrahydrofuran hydrate was anisotropic and in a layered growth pattern.Single crystals generally transformed from octahedral structure to octahedral skeleton structure with growth,however some single crystals also deformed into plate type particles.The thickness of the plate type particles increased gradually during growth,and the edge part increased earlier than the middle part.During agglomeration,the hydrate particles contacted and sintered together.Sand as the impurity didn’t serve as the nucleation center but affected the agglomeration of hydrate particles by collisions.In addition,the effect increased as the sand size decreased.Finally,a microstructure model for hydrate growth and agglomeration was proposed,which showed the hydrate structure evolution in these processes and could lay a foundation for studying the flow assurance of hydrate slurry.
基金supported by the National Key Research and Development Program of China(No.2020YFA0711700)the National Natural Science Foundation of China(No.12322206,U22A200531,and 12002303).
文摘Micromechanics investigations of composites with fiber-shaped reinforcement are extensively applied in the engineering design and theoretical analysis of thermal composites in the aerospace engineering and high-tech industry.In this paper,a critical review of various classical micromechanics approaches is provided based on the classification framework and the development of micromechanics tools.Several numerical micromechanics tools have been developed to overcome limitations through exactly/approximately solving the internal governing equations of microstructures.The connections and limitations of those models are also investigated and discussed,based on which three recently developed numerical or semi-analytical models are explained,including finite-element micromechanics,finite-volume direct averaging micromechanics,and locally exact homogenization theory,as well as machine learning tools.Since it is almost inevitable to mention the interfacial effects on thermal behavior of fibrous composites,we review the new mathematical relations that interrupt the original continuity conditions due to the existence of interphase/interface within unit cells.Generally speaking,the interphase/interface is demonstrated to play a significant role in influencing the effective coefficients and localized thermal fields.The present work also briefly reviews the application of micromechanics tools in emerging engineered woven composites,natural fibrous composites,and ablative thermal protection composites.It is demonstrated that sophisticated micromechanics tools are always demanded for investigating the effective and localized responses of thermal fibrous composites.
基金financially supported by the National Natural Science Foundation of China (Nos. 51371169 and 51401214)
文摘A modified cellular automaton model is developed to depict the interface evolution inside the cementite plus ferrite lamellar microstructures during the reaustenitization of a pearlite steel. In this model, migrations of both the austenite- ferrite and austenite-cementite interfaces coupled with the carbon diffusion and redistribution are integrated. The capil- laxity effect derived from local interface curvatures is also carefully considered by involving the concentration given by the phase diagram modified by the Gibbs-Thomson effect. This allows the interface evolution from a transient state to a steady state under different annealing conditions and various interlamellar spacings to be simulated. The proposed cellular automaton approach could be readily used to describe the kinetics of austenite formation from the lamellar pearlites and virtually reveal the kinematics of the moving interfaces from the microstructural aspect.
基金Supported by the National Key Basic Research and Development (973) Program of China (No. G20000672083)
文摘Simulation technology for shape casting at macro-scale has been successfully put into engineer- ing application in a number of casting plants and as a result the quality of castings is assured, the research and development time is shortened, and the manufacturing cost is greatly saved as well. In this paper, mod- eling and simulation technologies of solidification process of shape casting at microstructure-scale, espe- cially deterministic, cellular automaton, and phase field models are studied and reviewed.
基金supported by National Natural Science Foundation of China(No.51174177)the Fund of the State Key Solidification Laboratory of Solidification Processing in Northwestern Polytechnical University(No.SKLSP 201714)
文摘The quantitative phase-field simulations were reviewed on the processes of solidification of pure metals and alloys.The quantitative phase-field equations were treated in a diffuse thin-interface limit,which enabled the quantitative links between interface dynamics and model parameters in the quasi-equilibrium simulations.As a result,the quantitative modeling is more effective in dealing with microstructural pattern formation in the large scale simulations without any spurious kinetic effects.The development of the quantitative phase-field models in modeling the formation of microstructures such as dendritic structures,eutectic lamellas,seaweed morphologies,and grain boundaries in different solidified conditions was also reviewed with the purpose of guiding to find the new prospect of applications in the quantitative phase-field simulations.
文摘The prediction of microstructure constituents and their morphologies is of great importance for the evaluation of material properties and design of advanced materials.There have been considerable efforts to model and simulate microstructure evolution using a wide spectrum of models and simulation approaches.This paper initially reviews the atomistic and mesoscale simulation approaches for microstructure evolution,emphasizing their advantages and disadvantages.Atomistic approaches,such as molecular dynamics,are restricted by the scale of the studied system because they are computationally expensive.Continuum mesoscale simulation approaches,such as phase field,cellular automata,and Monte Carlo,have inconsistent phenomenological equations,each of which only describes one aspect of microstructure evolution.To provide comprehensive insight into microstructure evolution,a unified model that is capable of equally evaluating the nucleation and growth processes is required.In this paper,a physics-based model is proposed that incorporates statistical mechanics,the energy conservation law,and the force equilibrium concept to include all aspects of microstructure evolution.A compatible simulation approach is also described to simulate microstructure evolution during thermomechanical treatments.Furthermore,the microstructure evolution of AISI 304 austenitic steel during isothermal heat treatment and fusion welding is simulated and discussed.The use of fundamental physical rules instead of phenomenological equations,together with the real spatial and temporal scales of the proposed model,facilitates the comparison of the simulation results with experimental results.To examine the accuracy of the proposed simulation approach,the isothermal heat treatment simulation results are compared with experimental data over a broad region of temperatures and time periods.
基金funded by the National Key Research and Development Program of China(2021YFE0113200)the Fundamental Research Funds for the Central Universities(FRF-TP-20-104A1).
文摘The reduction pretreatment process has been proposed to improve the center quality of large billet and reduce the rolling ratio.The microstructure evolution during the reduction pretreatment was further understood.The austenite grains were refined after the reduction pretreatment experiment,especially those at the center of the billet.The effects of strain and strain rate on the average grain size were dependent on the deformation temperature.At a strain rate of 0.01 s-1 and 1200°C,the newly formed strain-free austenite grains grew very fast as the strain continued to increase,which resulted in the coarsening of austenite grains.The calculation results of the microstructure evolution model showed that at the same deformation temperature,the evolution curves of average grain size with different strain rates had the intersection points.With the increase in temperature,the position of intersection point moved to the downward direction of strain.The simulation results showed that when the reduction amount increased to 20%,the average grain size at the center was smaller than that near the surface.It could be inferred that when the reduction amount greatly exceeded 20%,the dynamic recrystallization at the center was mostly completed,and the austenite grain growth would become the main mechanism.
基金financially supported by the National Natural Science Foundation of China (Nos.51175427 and 51205317)the Open Fund of State Key Laboratory of Materials Processing and Die & Mould Technology of China (No.P2014-005)+1 种基金the Marie Curie International Research Staff Exchange Scheme within the 7th EC Framework Programme (FP7) (No.318968)the Programme of Introducing Talents of Discipline to Universities (No.B08040)
文摘Temperature rise is a significant factor influencing microstructure during(α+β) deformation of TA15 titanium alloy.An experiment was designed to explore microstructure evolution induced by temperature rise due to deformation heat.The experiment was carried out in(α+β) phase field at typical temperature rise rates.The microstructures of the alloy under different temperature rise rates were observed by scanning electron microscopy(SEM).It is found that the dissolution rate of primary equiaxed a phase increases with the increase in both temperature and temperature rise rate.In the same temperature range,the higher the temperature rise rate is,the larger the final content and grain size of primary equiaxed a phase are due to less dissolution time.To quantitatively depict the evolution behavior of primary equiaxed a phase under any temperature rise rates,the dissolution kinetics of primary equiaxed a phase were well described by a diffusion model.The model predictions,including content and grain size of primary equiaxed a phase,are in good agreement with experimental observations.The work provides an important basis for the prediction and control of microstructure during hot working of titanium alloy.