Because of the challenge of compounding lightweight,high-strength Ti/Al alloys due to their considerable disparity in properties,Al 6063 as intermediate layer was proposed to fabricate TC4/Al 6063/Al 7075 three-layer ...Because of the challenge of compounding lightweight,high-strength Ti/Al alloys due to their considerable disparity in properties,Al 6063 as intermediate layer was proposed to fabricate TC4/Al 6063/Al 7075 three-layer composite plate by explosive welding.The microscopic properties of each bonding interface were elucidated through field emission scanning electron microscope and electron backscattered diffraction(EBSD).A methodology combining finite element method-smoothed particle hydrodynamics(FEM-SPH)and molecular dynamics(MD)was proposed for the analysis of the forming and evolution characteristics of explosive welding interfaces at multi-scale.The results demonstrate that the bonding interface morphologies of TC4/Al 6063 and Al 6063/Al 7075 exhibit a flat and wavy configuration,without discernible defects or cracks.The phenomenon of grain refinement is observed in the vicinity of the two bonding interfaces.Furthermore,the degree of plastic deformation of TC4 and Al 7075 is more pronounced than that of Al 6063 in the intermediate layer.The interface morphology characteristics obtained by FEM-SPH simulation exhibit a high degree of similarity to the experimental results.MD simulations reveal that the diffusion of interfacial elements predominantly occurs during the unloading phase,and the simulated thickness of interfacial diffusion aligns well with experimental outcomes.The introduction of intermediate layer in the explosive welding process can effectively produce high-quality titanium/aluminum alloy composite plates.Furthermore,this approach offers a multi-scale simulation strategy for the study of explosive welding bonding interfaces.展开更多
A model of coupling macro finite volume method(FVM) and cellular automata(CA) is proposed in this paper to explore the columnar-to-equiaxed transition(CET) during selective laser melting(SLM) of rare earth magnesium a...A model of coupling macro finite volume method(FVM) and cellular automata(CA) is proposed in this paper to explore the columnar-to-equiaxed transition(CET) during selective laser melting(SLM) of rare earth magnesium alloy.Taking into account the impact of recoil pressure and Marangoni convection on the molten pool temperature field,the grain structure is simulated.As suggested by the simulation results,with the undissolved Zr serving as heterogeneous nucleation sites,the liquid undercooled layer under the combined action of forced cooling,the temperature gradient and the liquid solute concentration gradient leads to CET.While considering the dissolution of Zr in magnesium matrix,the results demonstrate that the dissolution of element Zr is effective in significantly inhibiting the growth of columnar crystals and ensuring the sufficient constitutional supercooling(CS) required for nucleation.In addition,to raise the preheating temperature contributes to enhancing the outcome of nucleation and incresing the grain size.Invoking the interdependence model(IM),with the cooling rate gradually increasing in the SLM process of magnesium alloy,the nucleation-free zone(NFZ) reduces by decreasing the solute diffusion layer in the front of the solid/liquid(SL) interface and the temperature gradient.The reduction in temperature gradient can promote undercooling for nucleation and facilitate the development of equiaxed crystals.The simulation results are qualitatively verified as highly consistent through experimentation.展开更多
The Secondary Air System(SAS)plays an important role in the safe operation and performance of aeroengines.The traditional 1D-3D coupling method loses information when used for secondary air systems,which affects the c...The Secondary Air System(SAS)plays an important role in the safe operation and performance of aeroengines.The traditional 1D-3D coupling method loses information when used for secondary air systems,which affects the calculation accuracy.In this paper,a Cross-dimensional Data Transmission method(CDT)from 3D to 1D is proposed by introducing flow field uniformity into the data transmission.First,a uniformity index was established to quantify the flow field parameter distribution characteristics,and a uniformity index prediction model based on the locally weighted regression method(Lowess)was established to quickly obtain the flow field information.Then,an information selection criterion in 3D to 1D data transmission was established based on the Spearman rank correlation coefficient between the uniformity index and the accuracy of coupling calculation,and the calculation method was automatically determined according to the established criterion.Finally,a modified function was obtained by fitting the ratio of the 3D mass-average parameters to the analytical solution,which are then used to modify the selected parameters at the 1D-3D interface.Taking a typical disk cavity air system as an example,the results show that the calculation accuracy of the CDT method is greatly improved by a relative 53.88%compared with the traditional 1D-3D coupling method.Furthermore,the CDT method achieves a speedup of 2 to 3 orders of magnitude compared to the 3D calculation.展开更多
Concentration distribution of the deterrent in single-base propellant during the process of firing plays an important role in the ballistic properties of gun propellant in weapons. However, the diffusion coefficient c...Concentration distribution of the deterrent in single-base propellant during the process of firing plays an important role in the ballistic properties of gun propellant in weapons. However, the diffusion coefficient calculated by molecular dynamics(MD) simulation is 6 orders of magnitude larger than the experimental values. Meanwhile, few simple and comprehensive theoretical models can explain the phenomenon and accurately predict the concentration distribution of the propellant. Herein, an onion model combining with MD simulation and finite element method of diffusion in propellants is introduced to bridge the gap between the experiments and simulations, and correctly predict the concentration distribution of deterrent. Furthermore, a new time scale is found to characterize the diffusion process. Finally, the time-and position-depended concentration distributions of dibutyl phthalate in nitrocellulose are measured by Raman spectroscopy to verify the correctness of the onion model. This work not only provides guidance for the design of the deterrent, but could be also extended to the diffusion of small molecules in polymer with different crystallinity.展开更多
In this study,a novel multi-physics multi-scale model with the dilute multicomponent phase-field method in three-dimensional(3D)space was developed to investigate the complex microstructure evolu-tion in the molten po...In this study,a novel multi-physics multi-scale model with the dilute multicomponent phase-field method in three-dimensional(3D)space was developed to investigate the complex microstructure evolu-tion in the molten pool during laser welding of Al-Li alloy.To accurately compute mass data within both two and three-dimensional computational domains,three efficient computing methods,including central processing unit parallel computing,adaptive mesh refinement,and moving-frame algorithm,were uti-lized.Emphasis was placed on the distinctive equiaxed-to-columnar-to-equiaxed transition phenomenon that occurs during the entire solidification process of Al-Li alloy laser welding.Simulation results indi-cated that the growth distance of columnar grains that epitaxially grew from the base metal(BM)de-creased as the nucleation rate increased.As the nucleation rate increased,the morphology of the newly formed grains near the fusion boundary(FB)changed from columnar to equiaxed,and newly formed equiaxed grains changed from having high-order dendrites to no obvious dendrite structure.When the nucleation rate was sufficiently high,non-dendritic equiaxed grains could directly form near the FB,and there was nearly no epitaxial growth from the BM.Additionally,simulation results illustrated the com-petition among multiple grains with varying orientations that grow in 3D space near the FB.Finally,how equiaxed grain bands develop was elucidated.The equiaxed band not only hindered the growth of early columnar grains but also some of its grains could grow epitaxially to form new columnar grains.These predicted results were in good agreement with experimental measurements and observations.展开更多
The existing research on continuous structure is usually analyzed with finite element method (FEM) and granular medium with discrete element method (DEM), but there are few researches on the coupling interaction betwe...The existing research on continuous structure is usually analyzed with finite element method (FEM) and granular medium with discrete element method (DEM), but there are few researches on the coupling interaction between continuous structure and discrete medium. To the issue of this coupling interaction, a multi-scale simulation method with coupled finite/discrete element model is put forward, in their respective domains of discrete and finite elements, the nodes follow force law and motion law of their own method, and on the their interaction interface, the touch type between discrete and finite elements is distinguished as two types: full touch and partial touch, the interaction force between them is calculated with linear elastic model. For full touch, the contact force is proportional to the overlap distance between discrete element and finite element patch. For partial touch, first the finite element patch is extended on all sides indefinitely to be a complete plane, the full contact force can be obtained with the touch type between discrete element and plane being viewed as full touch, then the full overlap area between them and the actual overlap area between discrete element and finite element patch are computed, the actual contact force is obtained by scaling the full contact force with a factor which is determined by the ratio of the actual overlap area to the full overlap area. The contact force is equivalent to the finite element nodes and the force and displacement on the nodes can be computed, so the ideal simulation results can be got. This method has been used to simulate the cutter disk of the earth pressure balance shield machine (EPBSM) made in North Heavy Industry (NHI) with its excavation diameter of 6.28 m cutting and digging the sandy clay layer. The simulation results show that as the gradual increase of excavating depth of the cutter head, the maximum stress occurs at the roots of cutters on the cutter head, while for the soil, the largest stress is distributed at the region which directly contacted with the cutters. The proposed research can provide good solutions for correct design and installation of cutters, and it is necessary to design mounting bracket to fix cutters on cutter head.展开更多
Computational simulation is an important technical means in research of nuclear fuel materials.Since nuclear fuel issues are inherently multi-scopic,it is imperative to study them with multi-scale simulation scheme.At...Computational simulation is an important technical means in research of nuclear fuel materials.Since nuclear fuel issues are inherently multi-scopic,it is imperative to study them with multi-scale simulation scheme.At present,the development of multi-scale simulation for nuclear fuel materials calls for a more systematic approach,in which lies the main purpose of this article.The most important thing in multi-scale simulation is to accurately formulate the goals to be achieved and the types of methods to be used.In this regard,we first summarize the basic principles and applicability of the simulation methods which are commonly used in nuclear fuel research and are based on different scales ranging from micro to macro,i.e.First-Principles(FP),Molecular Dynamics(MD),Kinetic Monte Carlo(KMC),Phase Field(PF),Rate Theory(RT),and Finite Element Method(FEM).And then we discuss the major material issues in this field,also ranging from micro-scale to macro-scale and covering both pellets and claddings,with emphasis on what simulation method would be most suitable for solving each of the issues.Finally,we give our prospective analysis and understanding about the feasible ways of multi-scale integration and relevant handicaps and challenges.展开更多
The head of nuclear pressure vessel is a key component to guarantee the safety of nuclear power plant, so it is necessary to improve its mechanical properties during manufacturing. In the practical production,due to t...The head of nuclear pressure vessel is a key component to guarantee the safety of nuclear power plant, so it is necessary to improve its mechanical properties during manufacturing. In the practical production,due to the huge size of the ingots from which the head is manufactured, coarse grains and voids are common defects existing in the material. Furthermore, cracks may appear in the forming process. It is highly demanded that the forming process must be properly designed with suitable parameters to compact the voids, to refine and homogenize the grains and to avoid cracks. Therefore, the research on the evolution of internal voids, grain size and cracks is very important to determine the forming process of huge components. SA508-3 steel is the material to manufacture the head of pressure vessel in the nuclear island. In the previous studies, we have separately built models to evaluate the evolution of internal voids, grain size and cracks during the hot forming process for SA508-3 steel. This study integrates the models for multi-scale simulation of the forging process of the head of nuclear pressure vessel in order to control the quality of the forgings. Through the software development, the models are integrated with a commercial finite element code DEFORM. Then, the extended forging and final forging processes of the head are investigated, and some appropriate deformation parameters are recommended.展开更多
We formulate a macroscopic particle modeling analysis of metallic materials (aluminum and copper, etc.) based on theoretical energy and atomic geome<span>tries derivable from their interatomic potential. In fact...We formulate a macroscopic particle modeling analysis of metallic materials (aluminum and copper, etc.) based on theoretical energy and atomic geome<span>tries derivable from their interatomic potential. In fact, particles in thi</span>s framework are presenting a large mass composed of huge collection of atoms and are interacting with each other. We can start from cohesive energy of metallic atoms and basic crystalline unit (e.g. face-centered cubic). Then, we can reach to interparticle (macroscopic) potential function which is presented by the analytical equation with terms of exponent of inter-particle distance, like a Lennard-Jones potential usually used in molecular dynamics simulation. Equation of motion for these macroscopic particles has dissipative term and fluctuation term, as well as the conservative term above, in order to express finite temperature condition. First, we determine the parameters needed in macroscopic potential function and check the reproduction of mechanical behavior in elastic regime. By using the present framework, we are able to carry out uniaxial loading simulation of aluminum rod. The method can also reproduce Young’s modulus and Poisson’s ratio as elastic behavior, though the result shows the dependency on division number of particles. Then, we proceed to try to include plasticity in this multi-scale framework. As a result, a realistic curve of stress-strain relation can be obtained for tensile and compressive loading and this new and simple framework of materials modeling has been confirmed to have certain effectiveness to be used in materials simulations. We also assess the effect of the order of loadings in opposite directions including yield and plastic states and find that an irreversible behavior depends on different response of the particle system between tensile and compressive loadings.展开更多
The multi-scale modeling combined with the cohesive zone model(CZM)and the molecular dynamics(MD)method were preformed to simulate the crack propagation in NiTi shape memory alloys(SMAs).The metallographic microscope ...The multi-scale modeling combined with the cohesive zone model(CZM)and the molecular dynamics(MD)method were preformed to simulate the crack propagation in NiTi shape memory alloys(SMAs).The metallographic microscope and image processing technology were employed to achieve a quantitative grain size distribution of NiTi alloys so as to provide experimental data for molecular dynamics modeling at the atomic scale.Considering the size effect of molecular dynamics model on material properties,a reasonable modeling size was provided by taking into account three characteristic dimensions from the perspective of macro,meso,and micro scales according to the Buckinghamπtheorem.Then,the corresponding MD simulation on deformation and fracture behavior was investigated to derive a parameterized traction-separation(T-S)law,and then it was embedded into cohesive elements of finite element software.Thus,the crack propagation behavior in NiTi alloys was reproduced by the finite element method(FEM).The experimental results show that the predicted initiation fracture toughness is in good agreement with experimental data.In addition,it is found that the dynamics initiation fracture toughness increases with decreasing grain size and increasing loading velocity.展开更多
Electronic packaging is an essential branch of electronic engineering that aims to protect electronic,microelec-tronic,and nanoelectronic systems from environmental conditions.The design of electronic packaging is hig...Electronic packaging is an essential branch of electronic engineering that aims to protect electronic,microelec-tronic,and nanoelectronic systems from environmental conditions.The design of electronic packaging is highly complex and requires the consideration of multi-physics phenomena,such as thermal transport,electromagnetic fields,and mechanical stress.This review presents a comprehensive overview of the multiphysics coupling of electric,magnetic,thermal,mechanical,and fluid fields,which are crucial for assessing the performance and reliability of electronic devices.The recent advancements in multi-scale simulation techniques are also system-atically summarized,such as finite element methods at the macroscopic scale,molecular dynamics and density functional theory at the microscopic scale,and particularly machine learning methods for bridging different scales.Additionally,we illustrate how these methods can be applied to study various aspects of electronic pack-aging,such as material properties,interfacial failure,thermal management,electromigration,and stress analysis.The challenges and the potential applications of multi-scale simulation techniques in electronic packaging are also highlighted.Further,some future directions for multi-scale simulation techniques in electronic packaging are concluded for further investigation.展开更多
Catalytic ozonation is regarded as a promising technology in the advanced treatment of refractory organic wastewater.Packed-bed reactors are widely used in practical applications due to simple structures,installation ...Catalytic ozonation is regarded as a promising technology in the advanced treatment of refractory organic wastewater.Packed-bed reactors are widely used in practical applications due to simple structures,installation and operation.However,mass transfer of packed-bed reactors is relatively restrained and amplified deviations usually occurred in scale-up application.Herein,a multi-scale packed-bed model of catalytic ozonation was established to guide pilot tests.First,a laboratory-scale test was conducted to obtain kinetic parameters needed for modeling.Then,a multi-scale packed-bed model was developed to research the effects of water distribution structure,catalyst particle size,and hydraulic retention time(HRT)on catalytic ozonation.It was found that the performance of packed bed reactor was increased with evenly distributed water inlet,HRT of 60 min,and catalyst diameter of about 3-7 mm.Last,an optimized reactor was manufactured and a pilot-scale test was conducted to treat kitchen wastewater using catalytic ozonation process.In the pilot-scale test with an ozone dosage of 50 mg/L and HRT of 60 min,the packed-bed reactor filled with catalysts I was able to reduce chemical oxygen demand(COD)from 117 to 59 mg/L.The performance of the catalytic ozonation process in the packed-bed reactor for the advanced treatment of actual kitchen wastewater was investigated via both multi-scale simulation and pilot-scale tests in this study,which provided a practical method for optimizing the reactors of treating refractory organic wastewater.展开更多
BACKGROUND Orthopaedic surgical education has traditionally depended on the apprenticeship model of“see one,do one,teach one”.However,reduced operative exposure,stricter work-hour regulations,medicolegal constraints...BACKGROUND Orthopaedic surgical education has traditionally depended on the apprenticeship model of“see one,do one,teach one”.However,reduced operative exposure,stricter work-hour regulations,medicolegal constraints,and patient safety concerns have constrained its practicality.Simulation-based training has become a reliable,safe,and cost-efficient alternative.Dry lab techniques,especially virtual and augmented reality,make up 78%of current dry lab research,whereas wet labs still set the standard for anatomical realism.AIM To evaluate the effectiveness,limitations,and future directions of wet and dry lab simulation in orthopaedic training.METHODS A scoping review was carried out across four databases-PubMed,Cochrane Library,Web of Science,and EBSCOhost-up to 2025.Medical Subject Headings included:"Orthopaedic Education","Wet Lab","Dry Lab","Simulation Training","Virtual Reality",and"Surgical Procedure".Eligible studies focused on orthopaedic or spinal surgical education,employed wet or dry lab techniques,and assessed training effectiveness.Exclusion criteria consisted of non-English publications,abstracts only,non-orthopaedic research,and studies unrelated to simulation.Two reviewers independently screened titles,abstracts,and full texts,resolving discrepancies with a third reviewer.RESULTS From 1851 records,101 studies met inclusion:78 on dry labs,7 on wet labs,4 on both.Virtual reality(VR)simulations were most common,with AI increasingly used for feedback and assessment.Cadaveric training remains the gold standard for accuracy and tactile feedback,while dry labs-especially VR-offer scalability,lower cost(40%-60%savings in five studies),and accessibility for novices.Senior residents prefer wet labs for complex tasks;juniors favour dry labs for basics.Challenges include limited transferability data,lack of standard outcome metrics,and ethical concerns about cadaver use and AI assessment.CONCLUSION Wet and dry labs each have unique strengths in orthopaedic training.A hybrid approach combining both,supported by standardised assessments and outcome studies,is most effective.Future efforts should aim for uniform reporting,integrating new technologies,and policy support for hybrid curricula to enhance skills and patient care.展开更多
The Regional Atmospheric Modeling System （RAMS） and the computational fluid dynamics （CFD） codes known as FLUENT are combinatorially applied in a multi-scale numerical simulation of the urban surface layer （USL）...The Regional Atmospheric Modeling System （RAMS） and the computational fluid dynamics （CFD） codes known as FLUENT are combinatorially applied in a multi-scale numerical simulation of the urban surface layer （USL）. RAMS and FLUENT are combined as a multi-scale numerical modeling system, in which the RAMS simulated data are delivered to the computational model for FLUENT simulation in an offline way. Numerical simulations are performed to present and preliminarily validate the capability of the multi-scale modeling system, and the results show that the modeling system can reasonably provide information on the meteorological elements in an urban area from the urban scale to the city-block scale, especially the details of the turbulent flows within the USL.展开更多
This study introduces a new ocean surface friction velocity scheme and a modified Thompson cloud microphysics parameterization scheme into the CMA-TYM model.The impact of these two parameterization schemes on the pred...This study introduces a new ocean surface friction velocity scheme and a modified Thompson cloud microphysics parameterization scheme into the CMA-TYM model.The impact of these two parameterization schemes on the prediction of the movement track and intensity of Typhoon Kompasu in 2021 is examined.Additionally,the possible reasons for their effects on tropical cyclone(TC)intensity prediction are analyzed.Statistical results show that both parameterization schemes improve the predictions of Typhoon Kompasu’s track and intensity.The influence on track prediction becomes evident after 60 h of model integration,while the significant positive impact on intensity prediction is observed after 66 h.Further analysis reveals that these two schemes affect the timing and magnitude of extreme TC intensity values by influencing the evolution of the TC’s warm-core structure.展开更多
Marine thin plates are susceptible to welding deformation owing to their low structural stiffness.Therefore,the efficient and accurate prediction of welding deformation is essential for improving welding quality.The t...Marine thin plates are susceptible to welding deformation owing to their low structural stiffness.Therefore,the efficient and accurate prediction of welding deformation is essential for improving welding quality.The traditional thermal elastic-plastic finite element method(TEP-FEM)can accurately predict welding deformation.However,its efficiency is low because of the complex nonlinear transient computation,making it difficult to meet the needs of rapid engineering evaluation.To address this challenge,this study proposes an efficient prediction method for welding deformation in marine thin plate butt welds.This method is based on the coupled temperature gradient-thermal strain method(TG-TSM)that integrates inherent strain theory with a shell element finite element model.The proposed method first extracts the distribution pattern and characteristic value of welding-induced inherent strain through TEP-FEM analysis.This strain is then converted into the equivalent thermal load applied to the shell element model for rapid computation.The proposed method-particularly,the gradual temperature gradient-thermal strain method(GTG-TSM)-achieved improved computational efficiency and consistent precision.Furthermore,the proposed method required much less computation time than the traditional TEP-FEM.Thus,this study lays the foundation for future prediction of welding deformation in more complex marine thin plates.展开更多
Analysis of the environmental and economic performance of fishing vessels has received limited attention compared with other ship types despite their notable contribution to global greenhouse gas(GHG)emissions.This st...Analysis of the environmental and economic performance of fishing vessels has received limited attention compared with other ship types despite their notable contribution to global greenhouse gas(GHG)emissions.This study evaluates the carbon footprint(CF)and economic viability of a liquefied natural gas(LNG)-fueled fishing vessel,using real engine operation simulations to provide precise and dynamic evaluation of fuel consumption and GHG emissions.Operational profiles are obtained through the utilization of onboard monitoring systems,whereas engine performance is simulated using the 1D/0D AVL Boost^(TM)model.Life cycle assessment(LCA)is conducted to quantify the environmental impact,whereas life cycle cost assessment(LCCA)is performed to analyze the profitability of LNG as an alternative fuel.The potential impact of the future fuel price uncertainties is addressed using Monte Carlo simulations.The LCA findings indicate that LNG has the potential to reduce the CF of the vessel by 14%to 16%,in comparison to a diesel power system configuration that serves as the baseline scenario.The LCCA results further indicate that the total cost of an LNG-powered ship is lower by 9.5%-13.8%,depending on the share of LNG and pilot fuels.This finding highlights the potential of LNG to produce considerable environmental benefits while addressing economic challenges under diverse operational and fuel price conditions.展开更多
The conventional digital core models are usually small in size and have difficulty in representing the complex structures of heterogeneous rocks;Therefore,the parameters of simulated rock physics are difficult to be r...The conventional digital core models are usually small in size and have difficulty in representing the complex structures of heterogeneous rocks;Therefore,the parameters of simulated rock physics are difficult to be referenced.In this study,we propose a feasible simulation method for obtaining multi-scale and multi-component digital cores based on three types of sandstone samples.In the proposed method,the plug and subplug samples are scanned via micro-computed tomography at different resolutions.Furthermore,the images are precisely registered using the proposed hybrid image registration method.In case of high-resolution images,the traditional segmentation method is used to segment the cores into pores and minerals.Subsequently,we established the relations between the gray values and the porosity/mineral content in case of the low-resolution images based on the registered domains and the relation curves were applied to the segmentation of the low-resolution images.The core images constitute the multi-scale and multi-component digital core models after segmentation.Further,the elastic properties of the three samples were simulated at both fine and coarse scales based on the multi-scale and multi-component digital core models,and four component models were considered.The results show that the multi-scale and multi-component digital core models can overcome the representative limits of the conventional digital core models and accurately characterize pores and minerals at different scales.The numerical results of the elastic modulus are more representative at large scales,and considerably reliable results can be obtained by appropriately considering the minerals.展开更多
Multi-scale finite element method is adopted to simulate wood compression behavior under axial and transverse loading. Representative volume elements (RVE) of wood microfibril and cell are proposed to analyze orthotro...Multi-scale finite element method is adopted to simulate wood compression behavior under axial and transverse loading. Representative volume elements (RVE) of wood microfibril and cell are proposed to analyze orthotropic mechanical behavior. Lignin, hemicellulose and crystalline-amorphous cellulose core of spruce are concerned in spruce nanoscale model. The equivalent elastic modulus and yield strength of the microfibril are gained by the RVE simulation. The anisotropism of the crystalline-amorphous cellulose core brings the microfibril buckling deformation during compression loading. The failure mechanism of the cell-wall under axial compression is related to the distribution of amorphous cellulose and crystalline cellulose. According to the spruce cell observation by scanning electron microscope, numerical model of spruce cell is established using simplified circular hole and regular hexagon arrangement respectively. Axial and transverse compression loadings are taken into account in the numerical simulations. It indicates that the compression stress-strain curves of the numerical simulation are consistent with the experimental results. The wood microstructure arrangement has an important effect on the stress plateau during compression process. Cell-wall buckling in axial compression induces the stress value drops rapidly. The wide stress plateau duration means wood is with large energy dissipation under a low stress level. The numerical results show that loading velocity affects greatly wood microstructure failure modes in axial loading. For low velocity axial compression, shear sliding is the main failure mode. For high velocity axial compression, wood occur fold and collapse. In transverse compression, wood deformation is gradual and uniform, which brings stable stress plateau.展开更多
Casting microstructure evolution is difficult to describe quantitatively by only a separate simulation of dendrite scale or grain scale, and the numerical simulation of these two scales is difficult to render compatib...Casting microstructure evolution is difficult to describe quantitatively by only a separate simulation of dendrite scale or grain scale, and the numerical simulation of these two scales is difficult to render compatible. A three-dimensional cellular automaton model couplling both dendritic scale and grain scale is developed to simulate the microstructure evolution of the nickel-based single crystal superalloy DD406. Besides, a macro–mesoscopic/microscopic coupling solution algorithm is proposed to improve computational efficiency. The simulation results of dendrite growth and grain growth of the alloy are obtained and compared with the results given in previous reports. The results show that the primary dendritic arm spacing and secondary dendritic arm spacing of the dendritic growth are consistent with the theoretical and experimental results. The mesoscopic grain simulation can be used to obtain results similar to those of microscopic dendrites simulation. It is indicated that the developed model is feasible and effective.展开更多
基金Opening Foundation of Key Laboratory of Explosive Energy Utilization and Control,Anhui Province(BP20240104)Graduate Innovation Program of China University of Mining and Technology(2024WLJCRCZL049)Postgraduate Research&Practice Innovation Program of Jiangsu Province(KYCX24_2701)。
文摘Because of the challenge of compounding lightweight,high-strength Ti/Al alloys due to their considerable disparity in properties,Al 6063 as intermediate layer was proposed to fabricate TC4/Al 6063/Al 7075 three-layer composite plate by explosive welding.The microscopic properties of each bonding interface were elucidated through field emission scanning electron microscope and electron backscattered diffraction(EBSD).A methodology combining finite element method-smoothed particle hydrodynamics(FEM-SPH)and molecular dynamics(MD)was proposed for the analysis of the forming and evolution characteristics of explosive welding interfaces at multi-scale.The results demonstrate that the bonding interface morphologies of TC4/Al 6063 and Al 6063/Al 7075 exhibit a flat and wavy configuration,without discernible defects or cracks.The phenomenon of grain refinement is observed in the vicinity of the two bonding interfaces.Furthermore,the degree of plastic deformation of TC4 and Al 7075 is more pronounced than that of Al 6063 in the intermediate layer.The interface morphology characteristics obtained by FEM-SPH simulation exhibit a high degree of similarity to the experimental results.MD simulations reveal that the diffusion of interfacial elements predominantly occurs during the unloading phase,and the simulated thickness of interfacial diffusion aligns well with experimental outcomes.The introduction of intermediate layer in the explosive welding process can effectively produce high-quality titanium/aluminum alloy composite plates.Furthermore,this approach offers a multi-scale simulation strategy for the study of explosive welding bonding interfaces.
基金the Key Research and Development Plan of Shaanxi Province (No. 2020GY-255)Scientific Research Plan Projects of Shaanxi Education Department (No. 20JC020)Scientific Research Plan Projects of Xi’an Technology Department (No. 2020KJRC0052)。
文摘A model of coupling macro finite volume method(FVM) and cellular automata(CA) is proposed in this paper to explore the columnar-to-equiaxed transition(CET) during selective laser melting(SLM) of rare earth magnesium alloy.Taking into account the impact of recoil pressure and Marangoni convection on the molten pool temperature field,the grain structure is simulated.As suggested by the simulation results,with the undissolved Zr serving as heterogeneous nucleation sites,the liquid undercooled layer under the combined action of forced cooling,the temperature gradient and the liquid solute concentration gradient leads to CET.While considering the dissolution of Zr in magnesium matrix,the results demonstrate that the dissolution of element Zr is effective in significantly inhibiting the growth of columnar crystals and ensuring the sufficient constitutional supercooling(CS) required for nucleation.In addition,to raise the preheating temperature contributes to enhancing the outcome of nucleation and incresing the grain size.Invoking the interdependence model(IM),with the cooling rate gradually increasing in the SLM process of magnesium alloy,the nucleation-free zone(NFZ) reduces by decreasing the solute diffusion layer in the front of the solid/liquid(SL) interface and the temperature gradient.The reduction in temperature gradient can promote undercooling for nucleation and facilitate the development of equiaxed crystals.The simulation results are qualitatively verified as highly consistent through experimentation.
基金supported by the National Science and Technology Major Project,China(No.2017-III-0010-0036).
文摘The Secondary Air System(SAS)plays an important role in the safe operation and performance of aeroengines.The traditional 1D-3D coupling method loses information when used for secondary air systems,which affects the calculation accuracy.In this paper,a Cross-dimensional Data Transmission method(CDT)from 3D to 1D is proposed by introducing flow field uniformity into the data transmission.First,a uniformity index was established to quantify the flow field parameter distribution characteristics,and a uniformity index prediction model based on the locally weighted regression method(Lowess)was established to quickly obtain the flow field information.Then,an information selection criterion in 3D to 1D data transmission was established based on the Spearman rank correlation coefficient between the uniformity index and the accuracy of coupling calculation,and the calculation method was automatically determined according to the established criterion.Finally,a modified function was obtained by fitting the ratio of the 3D mass-average parameters to the analytical solution,which are then used to modify the selected parameters at the 1D-3D interface.Taking a typical disk cavity air system as an example,the results show that the calculation accuracy of the CDT method is greatly improved by a relative 53.88%compared with the traditional 1D-3D coupling method.Furthermore,the CDT method achieves a speedup of 2 to 3 orders of magnitude compared to the 3D calculation.
基金sponsored by the National Natural Science Foundation of China (91834301, 22078088, 22005143)the National Natural Science Foundation of China for Innovative Research Groups (51621002)。
文摘Concentration distribution of the deterrent in single-base propellant during the process of firing plays an important role in the ballistic properties of gun propellant in weapons. However, the diffusion coefficient calculated by molecular dynamics(MD) simulation is 6 orders of magnitude larger than the experimental values. Meanwhile, few simple and comprehensive theoretical models can explain the phenomenon and accurately predict the concentration distribution of the propellant. Herein, an onion model combining with MD simulation and finite element method of diffusion in propellants is introduced to bridge the gap between the experiments and simulations, and correctly predict the concentration distribution of deterrent. Furthermore, a new time scale is found to characterize the diffusion process. Finally, the time-and position-depended concentration distributions of dibutyl phthalate in nitrocellulose are measured by Raman spectroscopy to verify the correctness of the onion model. This work not only provides guidance for the design of the deterrent, but could be also extended to the diffusion of small molecules in polymer with different crystallinity.
基金supported by the National Natural Science Foundation of China(Grant Nos.52075201,U22A20196,52188102)GuangDong Basic and Applied Basic Research Foundation(No.2023A1515010081).
文摘In this study,a novel multi-physics multi-scale model with the dilute multicomponent phase-field method in three-dimensional(3D)space was developed to investigate the complex microstructure evolu-tion in the molten pool during laser welding of Al-Li alloy.To accurately compute mass data within both two and three-dimensional computational domains,three efficient computing methods,including central processing unit parallel computing,adaptive mesh refinement,and moving-frame algorithm,were uti-lized.Emphasis was placed on the distinctive equiaxed-to-columnar-to-equiaxed transition phenomenon that occurs during the entire solidification process of Al-Li alloy laser welding.Simulation results indi-cated that the growth distance of columnar grains that epitaxially grew from the base metal(BM)de-creased as the nucleation rate increased.As the nucleation rate increased,the morphology of the newly formed grains near the fusion boundary(FB)changed from columnar to equiaxed,and newly formed equiaxed grains changed from having high-order dendrites to no obvious dendrite structure.When the nucleation rate was sufficiently high,non-dendritic equiaxed grains could directly form near the FB,and there was nearly no epitaxial growth from the BM.Additionally,simulation results illustrated the com-petition among multiple grains with varying orientations that grow in 3D space near the FB.Finally,how equiaxed grain bands develop was elucidated.The equiaxed band not only hindered the growth of early columnar grains but also some of its grains could grow epitaxially to form new columnar grains.These predicted results were in good agreement with experimental measurements and observations.
基金supported by National Basic Research Program of China (973 Program, Grant No. 2013CB035400)Science Fund for Creative Research Groups of NSFC of China (Grant No. 51221004)National Natural Science Foundation of China (Grant No. 51075357)
文摘The existing research on continuous structure is usually analyzed with finite element method (FEM) and granular medium with discrete element method (DEM), but there are few researches on the coupling interaction between continuous structure and discrete medium. To the issue of this coupling interaction, a multi-scale simulation method with coupled finite/discrete element model is put forward, in their respective domains of discrete and finite elements, the nodes follow force law and motion law of their own method, and on the their interaction interface, the touch type between discrete and finite elements is distinguished as two types: full touch and partial touch, the interaction force between them is calculated with linear elastic model. For full touch, the contact force is proportional to the overlap distance between discrete element and finite element patch. For partial touch, first the finite element patch is extended on all sides indefinitely to be a complete plane, the full contact force can be obtained with the touch type between discrete element and plane being viewed as full touch, then the full overlap area between them and the actual overlap area between discrete element and finite element patch are computed, the actual contact force is obtained by scaling the full contact force with a factor which is determined by the ratio of the actual overlap area to the full overlap area. The contact force is equivalent to the finite element nodes and the force and displacement on the nodes can be computed, so the ideal simulation results can be got. This method has been used to simulate the cutter disk of the earth pressure balance shield machine (EPBSM) made in North Heavy Industry (NHI) with its excavation diameter of 6.28 m cutting and digging the sandy clay layer. The simulation results show that as the gradual increase of excavating depth of the cutter head, the maximum stress occurs at the roots of cutters on the cutter head, while for the soil, the largest stress is distributed at the region which directly contacted with the cutters. The proposed research can provide good solutions for correct design and installation of cutters, and it is necessary to design mounting bracket to fix cutters on cutter head.
基金the financial support from the China National Natural Science Foundation project(11675126)Project of China Nuclear Power Innovation Center,China National Nuclear Corporation Science fund for talented young scholars(FY18000120)the National Science and Technology Major Project of the Ministry of Science and Technology of China(2019ZX06004009).
文摘Computational simulation is an important technical means in research of nuclear fuel materials.Since nuclear fuel issues are inherently multi-scopic,it is imperative to study them with multi-scale simulation scheme.At present,the development of multi-scale simulation for nuclear fuel materials calls for a more systematic approach,in which lies the main purpose of this article.The most important thing in multi-scale simulation is to accurately formulate the goals to be achieved and the types of methods to be used.In this regard,we first summarize the basic principles and applicability of the simulation methods which are commonly used in nuclear fuel research and are based on different scales ranging from micro to macro,i.e.First-Principles(FP),Molecular Dynamics(MD),Kinetic Monte Carlo(KMC),Phase Field(PF),Rate Theory(RT),and Finite Element Method(FEM).And then we discuss the major material issues in this field,also ranging from micro-scale to macro-scale and covering both pellets and claddings,with emphasis on what simulation method would be most suitable for solving each of the issues.Finally,we give our prospective analysis and understanding about the feasible ways of multi-scale integration and relevant handicaps and challenges.
基金the National Science and Technology Major Project of China(No.2012ZX04012-011)the National Natural Science Foundation of China(No.51675335)
文摘The head of nuclear pressure vessel is a key component to guarantee the safety of nuclear power plant, so it is necessary to improve its mechanical properties during manufacturing. In the practical production,due to the huge size of the ingots from which the head is manufactured, coarse grains and voids are common defects existing in the material. Furthermore, cracks may appear in the forming process. It is highly demanded that the forming process must be properly designed with suitable parameters to compact the voids, to refine and homogenize the grains and to avoid cracks. Therefore, the research on the evolution of internal voids, grain size and cracks is very important to determine the forming process of huge components. SA508-3 steel is the material to manufacture the head of pressure vessel in the nuclear island. In the previous studies, we have separately built models to evaluate the evolution of internal voids, grain size and cracks during the hot forming process for SA508-3 steel. This study integrates the models for multi-scale simulation of the forging process of the head of nuclear pressure vessel in order to control the quality of the forgings. Through the software development, the models are integrated with a commercial finite element code DEFORM. Then, the extended forging and final forging processes of the head are investigated, and some appropriate deformation parameters are recommended.
文摘We formulate a macroscopic particle modeling analysis of metallic materials (aluminum and copper, etc.) based on theoretical energy and atomic geome<span>tries derivable from their interatomic potential. In fact, particles in thi</span>s framework are presenting a large mass composed of huge collection of atoms and are interacting with each other. We can start from cohesive energy of metallic atoms and basic crystalline unit (e.g. face-centered cubic). Then, we can reach to interparticle (macroscopic) potential function which is presented by the analytical equation with terms of exponent of inter-particle distance, like a Lennard-Jones potential usually used in molecular dynamics simulation. Equation of motion for these macroscopic particles has dissipative term and fluctuation term, as well as the conservative term above, in order to express finite temperature condition. First, we determine the parameters needed in macroscopic potential function and check the reproduction of mechanical behavior in elastic regime. By using the present framework, we are able to carry out uniaxial loading simulation of aluminum rod. The method can also reproduce Young’s modulus and Poisson’s ratio as elastic behavior, though the result shows the dependency on division number of particles. Then, we proceed to try to include plasticity in this multi-scale framework. As a result, a realistic curve of stress-strain relation can be obtained for tensile and compressive loading and this new and simple framework of materials modeling has been confirmed to have certain effectiveness to be used in materials simulations. We also assess the effect of the order of loadings in opposite directions including yield and plastic states and find that an irreversible behavior depends on different response of the particle system between tensile and compressive loadings.
基金Funded by the National Natural Science Foundation of China Academy of Engineering Physics and Jointly Setup"NSAF"Joint Fund(No.U1430119)。
文摘The multi-scale modeling combined with the cohesive zone model(CZM)and the molecular dynamics(MD)method were preformed to simulate the crack propagation in NiTi shape memory alloys(SMAs).The metallographic microscope and image processing technology were employed to achieve a quantitative grain size distribution of NiTi alloys so as to provide experimental data for molecular dynamics modeling at the atomic scale.Considering the size effect of molecular dynamics model on material properties,a reasonable modeling size was provided by taking into account three characteristic dimensions from the perspective of macro,meso,and micro scales according to the Buckinghamπtheorem.Then,the corresponding MD simulation on deformation and fracture behavior was investigated to derive a parameterized traction-separation(T-S)law,and then it was embedded into cohesive elements of finite element software.Thus,the crack propagation behavior in NiTi alloys was reproduced by the finite element method(FEM).The experimental results show that the predicted initiation fracture toughness is in good agreement with experimental data.In addition,it is found that the dynamics initiation fracture toughness increases with decreasing grain size and increasing loading velocity.
基金supported by the National Natural Science Foundation of China(U2241244).
文摘Electronic packaging is an essential branch of electronic engineering that aims to protect electronic,microelec-tronic,and nanoelectronic systems from environmental conditions.The design of electronic packaging is highly complex and requires the consideration of multi-physics phenomena,such as thermal transport,electromagnetic fields,and mechanical stress.This review presents a comprehensive overview of the multiphysics coupling of electric,magnetic,thermal,mechanical,and fluid fields,which are crucial for assessing the performance and reliability of electronic devices.The recent advancements in multi-scale simulation techniques are also system-atically summarized,such as finite element methods at the macroscopic scale,molecular dynamics and density functional theory at the microscopic scale,and particularly machine learning methods for bridging different scales.Additionally,we illustrate how these methods can be applied to study various aspects of electronic pack-aging,such as material properties,interfacial failure,thermal management,electromigration,and stress analysis.The challenges and the potential applications of multi-scale simulation techniques in electronic packaging are also highlighted.Further,some future directions for multi-scale simulation techniques in electronic packaging are concluded for further investigation.
基金supported by the“Explorer 100”cluster system of Tsinghua HPC Platform.
文摘Catalytic ozonation is regarded as a promising technology in the advanced treatment of refractory organic wastewater.Packed-bed reactors are widely used in practical applications due to simple structures,installation and operation.However,mass transfer of packed-bed reactors is relatively restrained and amplified deviations usually occurred in scale-up application.Herein,a multi-scale packed-bed model of catalytic ozonation was established to guide pilot tests.First,a laboratory-scale test was conducted to obtain kinetic parameters needed for modeling.Then,a multi-scale packed-bed model was developed to research the effects of water distribution structure,catalyst particle size,and hydraulic retention time(HRT)on catalytic ozonation.It was found that the performance of packed bed reactor was increased with evenly distributed water inlet,HRT of 60 min,and catalyst diameter of about 3-7 mm.Last,an optimized reactor was manufactured and a pilot-scale test was conducted to treat kitchen wastewater using catalytic ozonation process.In the pilot-scale test with an ozone dosage of 50 mg/L and HRT of 60 min,the packed-bed reactor filled with catalysts I was able to reduce chemical oxygen demand(COD)from 117 to 59 mg/L.The performance of the catalytic ozonation process in the packed-bed reactor for the advanced treatment of actual kitchen wastewater was investigated via both multi-scale simulation and pilot-scale tests in this study,which provided a practical method for optimizing the reactors of treating refractory organic wastewater.
文摘BACKGROUND Orthopaedic surgical education has traditionally depended on the apprenticeship model of“see one,do one,teach one”.However,reduced operative exposure,stricter work-hour regulations,medicolegal constraints,and patient safety concerns have constrained its practicality.Simulation-based training has become a reliable,safe,and cost-efficient alternative.Dry lab techniques,especially virtual and augmented reality,make up 78%of current dry lab research,whereas wet labs still set the standard for anatomical realism.AIM To evaluate the effectiveness,limitations,and future directions of wet and dry lab simulation in orthopaedic training.METHODS A scoping review was carried out across four databases-PubMed,Cochrane Library,Web of Science,and EBSCOhost-up to 2025.Medical Subject Headings included:"Orthopaedic Education","Wet Lab","Dry Lab","Simulation Training","Virtual Reality",and"Surgical Procedure".Eligible studies focused on orthopaedic or spinal surgical education,employed wet or dry lab techniques,and assessed training effectiveness.Exclusion criteria consisted of non-English publications,abstracts only,non-orthopaedic research,and studies unrelated to simulation.Two reviewers independently screened titles,abstracts,and full texts,resolving discrepancies with a third reviewer.RESULTS From 1851 records,101 studies met inclusion:78 on dry labs,7 on wet labs,4 on both.Virtual reality(VR)simulations were most common,with AI increasingly used for feedback and assessment.Cadaveric training remains the gold standard for accuracy and tactile feedback,while dry labs-especially VR-offer scalability,lower cost(40%-60%savings in five studies),and accessibility for novices.Senior residents prefer wet labs for complex tasks;juniors favour dry labs for basics.Challenges include limited transferability data,lack of standard outcome metrics,and ethical concerns about cadaver use and AI assessment.CONCLUSION Wet and dry labs each have unique strengths in orthopaedic training.A hybrid approach combining both,supported by standardised assessments and outcome studies,is most effective.Future efforts should aim for uniform reporting,integrating new technologies,and policy support for hybrid curricula to enhance skills and patient care.
基金This study was supported by the National Natural Science Foundation of China （Grant Nos. 40233030, 40405004, 40405014）.
文摘The Regional Atmospheric Modeling System （RAMS） and the computational fluid dynamics （CFD） codes known as FLUENT are combinatorially applied in a multi-scale numerical simulation of the urban surface layer （USL）. RAMS and FLUENT are combined as a multi-scale numerical modeling system, in which the RAMS simulated data are delivered to the computational model for FLUENT simulation in an offline way. Numerical simulations are performed to present and preliminarily validate the capability of the multi-scale modeling system, and the results show that the modeling system can reasonably provide information on the meteorological elements in an urban area from the urban scale to the city-block scale, especially the details of the turbulent flows within the USL.
基金supported by the National Key R&D Program of China[grant number 2023YFC3008004]。
文摘This study introduces a new ocean surface friction velocity scheme and a modified Thompson cloud microphysics parameterization scheme into the CMA-TYM model.The impact of these two parameterization schemes on the prediction of the movement track and intensity of Typhoon Kompasu in 2021 is examined.Additionally,the possible reasons for their effects on tropical cyclone(TC)intensity prediction are analyzed.Statistical results show that both parameterization schemes improve the predictions of Typhoon Kompasu’s track and intensity.The influence on track prediction becomes evident after 60 h of model integration,while the significant positive impact on intensity prediction is observed after 66 h.Further analysis reveals that these two schemes affect the timing and magnitude of extreme TC intensity values by influencing the evolution of the TC’s warm-core structure.
基金Supported by the National Natural Science Foundation of China under Grant No.51975138the High-Tech Ship Scientific Research Project from the Ministry of Industry and Information Technology under Grant No.CJ05N20the National Defense Basic Research Project under Grant No.JCKY2023604C006.
文摘Marine thin plates are susceptible to welding deformation owing to their low structural stiffness.Therefore,the efficient and accurate prediction of welding deformation is essential for improving welding quality.The traditional thermal elastic-plastic finite element method(TEP-FEM)can accurately predict welding deformation.However,its efficiency is low because of the complex nonlinear transient computation,making it difficult to meet the needs of rapid engineering evaluation.To address this challenge,this study proposes an efficient prediction method for welding deformation in marine thin plate butt welds.This method is based on the coupled temperature gradient-thermal strain method(TG-TSM)that integrates inherent strain theory with a shell element finite element model.The proposed method first extracts the distribution pattern and characteristic value of welding-induced inherent strain through TEP-FEM analysis.This strain is then converted into the equivalent thermal load applied to the shell element model for rapid computation.The proposed method-particularly,the gradual temperature gradient-thermal strain method(GTG-TSM)-achieved improved computational efficiency and consistent precision.Furthermore,the proposed method required much less computation time than the traditional TEP-FEM.Thus,this study lays the foundation for future prediction of welding deformation in more complex marine thin plates.
文摘Analysis of the environmental and economic performance of fishing vessels has received limited attention compared with other ship types despite their notable contribution to global greenhouse gas(GHG)emissions.This study evaluates the carbon footprint(CF)and economic viability of a liquefied natural gas(LNG)-fueled fishing vessel,using real engine operation simulations to provide precise and dynamic evaluation of fuel consumption and GHG emissions.Operational profiles are obtained through the utilization of onboard monitoring systems,whereas engine performance is simulated using the 1D/0D AVL Boost^(TM)model.Life cycle assessment(LCA)is conducted to quantify the environmental impact,whereas life cycle cost assessment(LCCA)is performed to analyze the profitability of LNG as an alternative fuel.The potential impact of the future fuel price uncertainties is addressed using Monte Carlo simulations.The LCA findings indicate that LNG has the potential to reduce the CF of the vessel by 14%to 16%,in comparison to a diesel power system configuration that serves as the baseline scenario.The LCCA results further indicate that the total cost of an LNG-powered ship is lower by 9.5%-13.8%,depending on the share of LNG and pilot fuels.This finding highlights the potential of LNG to produce considerable environmental benefits while addressing economic challenges under diverse operational and fuel price conditions.
基金supported by the National Natural Science Foundation of China Research(Nos.41574122 and 41374124)National Science and Technology major Project(No.2016ZX05006002-004)。
文摘The conventional digital core models are usually small in size and have difficulty in representing the complex structures of heterogeneous rocks;Therefore,the parameters of simulated rock physics are difficult to be referenced.In this study,we propose a feasible simulation method for obtaining multi-scale and multi-component digital cores based on three types of sandstone samples.In the proposed method,the plug and subplug samples are scanned via micro-computed tomography at different resolutions.Furthermore,the images are precisely registered using the proposed hybrid image registration method.In case of high-resolution images,the traditional segmentation method is used to segment the cores into pores and minerals.Subsequently,we established the relations between the gray values and the porosity/mineral content in case of the low-resolution images based on the registered domains and the relation curves were applied to the segmentation of the low-resolution images.The core images constitute the multi-scale and multi-component digital core models after segmentation.Further,the elastic properties of the three samples were simulated at both fine and coarse scales based on the multi-scale and multi-component digital core models,and four component models were considered.The results show that the multi-scale and multi-component digital core models can overcome the representative limits of the conventional digital core models and accurately characterize pores and minerals at different scales.The numerical results of the elastic modulus are more representative at large scales,and considerably reliable results can be obtained by appropriately considering the minerals.
基金supported by the National Natural Science Foundation of China(Grants Nos 11302211,11390361,and 11572299).
文摘Multi-scale finite element method is adopted to simulate wood compression behavior under axial and transverse loading. Representative volume elements (RVE) of wood microfibril and cell are proposed to analyze orthotropic mechanical behavior. Lignin, hemicellulose and crystalline-amorphous cellulose core of spruce are concerned in spruce nanoscale model. The equivalent elastic modulus and yield strength of the microfibril are gained by the RVE simulation. The anisotropism of the crystalline-amorphous cellulose core brings the microfibril buckling deformation during compression loading. The failure mechanism of the cell-wall under axial compression is related to the distribution of amorphous cellulose and crystalline cellulose. According to the spruce cell observation by scanning electron microscope, numerical model of spruce cell is established using simplified circular hole and regular hexagon arrangement respectively. Axial and transverse compression loadings are taken into account in the numerical simulations. It indicates that the compression stress-strain curves of the numerical simulation are consistent with the experimental results. The wood microstructure arrangement has an important effect on the stress plateau during compression process. Cell-wall buckling in axial compression induces the stress value drops rapidly. The wide stress plateau duration means wood is with large energy dissipation under a low stress level. The numerical results show that loading velocity affects greatly wood microstructure failure modes in axial loading. For low velocity axial compression, shear sliding is the main failure mode. For high velocity axial compression, wood occur fold and collapse. In transverse compression, wood deformation is gradual and uniform, which brings stable stress plateau.
文摘Casting microstructure evolution is difficult to describe quantitatively by only a separate simulation of dendrite scale or grain scale, and the numerical simulation of these two scales is difficult to render compatible. A three-dimensional cellular automaton model couplling both dendritic scale and grain scale is developed to simulate the microstructure evolution of the nickel-based single crystal superalloy DD406. Besides, a macro–mesoscopic/microscopic coupling solution algorithm is proposed to improve computational efficiency. The simulation results of dendrite growth and grain growth of the alloy are obtained and compared with the results given in previous reports. The results show that the primary dendritic arm spacing and secondary dendritic arm spacing of the dendritic growth are consistent with the theoretical and experimental results. The mesoscopic grain simulation can be used to obtain results similar to those of microscopic dendrites simulation. It is indicated that the developed model is feasible and effective.
