Based on the TEM analysis of substructures of lower bainite in two steels containing Si,the lattice invariant shear elements were determined and a plastic accommodation double-shear model of phenomenological crystallo...Based on the TEM analysis of substructures of lower bainite in two steels containing Si,the lattice invariant shear elements were determined and a plastic accommodation double-shear model of phenomenological crystallography was proposed.The theoretical predictions about crystallography given by the model are in good agreement with the experimental data for the steels tested.展开更多
The establishment of the analogy theory between optimal control and computational structural mechanics is based on the linear quadratic control problem in optimal control and the substructural chain theory in structur...The establishment of the analogy theory between optimal control and computational structural mechanics is based on the linear quadratic control problem in optimal control and the substructural chain theory in structural mechanics.When the nonlinear optimal control problem is treated by the above theory, especially展开更多
Substructural type systems are designed from the insight inspired by the development of linear and substructural logics. Substructural type systems promise to control the usage of computational resources statically, t...Substructural type systems are designed from the insight inspired by the development of linear and substructural logics. Substructural type systems promise to control the usage of computational resources statically, thus detect more program errors at an early stage than traditional type systems do. In the past decade, substructural type systems have been deployed in the design of novel programming languages, such as Vault, etc. This paper presents a general typing theory for substructural type system. First, we define a universal semantic framework for substructural types by interpreting them as characteristic intervals composed of type qualifiers. Based on this framework, we present the design of a substructural calculus λSL with subtyping relations. After giving syntax, typing rules and operational semantics for λSL, we prove the type safety theorem. The new calculus λSL can guarantee many more safety invariants than traditional lambda calculus, which is demonstrated by showing that the ~.s, calculus can serve as an idealized type intermediate language, and defining a typepreserving translation from ordinary typed lambda calculus into λSL.展开更多
A data-driven model ofmultiple variable cutting(M-VCUT)level set-based substructure is proposed for the topology optimization of lattice structures.TheM-VCUTlevel setmethod is used to represent substructures,enriching...A data-driven model ofmultiple variable cutting(M-VCUT)level set-based substructure is proposed for the topology optimization of lattice structures.TheM-VCUTlevel setmethod is used to represent substructures,enriching their diversity of configuration while ensuring connectivity.To construct the data-driven model of substructure,a database is prepared by sampling the space of substructures spanned by several substructure prototypes.Then,for each substructure in this database,the stiffness matrix is condensed so that its degrees of freedomare reduced.Thereafter,the data-drivenmodel of substructures is constructed through interpolationwith compactly supported radial basis function(CS-RBF).The inputs of the data-driven model are the design variables of topology optimization,and the outputs are the condensed stiffness matrix and volume of substructures.During the optimization,this data-driven model is used,thus avoiding repeated static condensation that would requiremuch computation time.Several numerical examples are provided to verify the proposed method.展开更多
The spray-deposition was used to produce billets of Mg-4Al-1.5Zn-3Ca-1Nd(A alloy)and Mg-13Al-3Zn-3Ca-1Nd(B alloy),and evolution of deformation substructure and Mg_(x)Zn_(y)Ca_(z)metastable phase in fine-grained(3μm)M...The spray-deposition was used to produce billets of Mg-4Al-1.5Zn-3Ca-1Nd(A alloy)and Mg-13Al-3Zn-3Ca-1Nd(B alloy),and evolution of deformation substructure and Mg_(x)Zn_(y)Ca_(z)metastable phase in fine-grained(3μm)Mg alloys was investigated by scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),and electron backscattered diffraction(EBSD).It was found that different dislocation configurations were formed in A and B alloys.Redundant free dislocations(RFDs)and dislocation tangles were the ways to form deformation substructure in A alloy,no RFDs except dislocation tangles were found in B alloy.The interaction between nano-scale second phase particles(nano-scale C15 andβ-Mg_(17)(Al,Zn)_(12)phase)and different dislocation configurations had a significant effect on the deformation substructures formation.The mass transfer of Mg_(x)Zn_(y)Ca_(z)metastable phases and the stacking order of stacking faults were conducive to the Mg-Nd-Zn typed long period stacking ordered(LPSO)phases formation.Nano-scale C15 phases,Mg-Nd-Zn typed LPSO phases,c/a ratio,β-Mg_(17)(Al,Zn)_(12)phases were the key factors influencing the formation of textures.Different textures and grain boundary features(GB features)had a significant effect on k-value.The non-basal textures were the main factor affecting k-value in A alloy,while the high-angle grain boundary(HAGB)was the main factor affecting k-value in B alloy.展开更多
Based on the relationship between deformation microstructures and grain orientations,three characteristic Cu single crystals were used to investigate the opposite effects of ultrasonic superimposed high-strain-rate on...Based on the relationship between deformation microstructures and grain orientations,three characteristic Cu single crystals were used to investigate the opposite effects of ultrasonic superimposed high-strain-rate on the dislocation motion during ultrasonic welding(UW).The results revealed that equiaxed dislocation cells and discontinuous dynamic recrystallization(DRX)grains dominated in the joint microstructures.Three Cu single crystal joints exhibited an isotropic trend in grain orientation,welding quality,and microscopic mechanical properties.The preferred dislocation behaviors and DRX modes were further analyzed by modelling the stored energy difference,indicating that high mobility of intra-granular dislocations and homogeneous dislocation motion induced by the ultrasonic excitation were the intrinsic factors contributing to the formation of isotropic microstructures and welding quality.展开更多
In the present study,a single parameter governing the substructure and the strengthening for martensitic transformation was tentatively explored by detailing the microstructure and the strengthening of a Fe15 wt.%Cr b...In the present study,a single parameter governing the substructure and the strengthening for martensitic transformation was tentatively explored by detailing the microstructure and the strengthening of a Fe15 wt.%Cr binary alloy subjected to thermal cycle under high pressure(cooled at 10°C s-1 from 1050°C under hydrostatic pressure of 1.0-4.0 GPa).Experimental results show that high pressure makes martensitic transformation occur in a Fe-15Cr alloy that traditionally has no high-temperature austenite under atmospheric pressure.The phase transformation begins with the pairing of twinned variants,and the strengthening is solely dependent upon the density of dislocations and variants.The austenite strength at the transformation temperature governs the substructure and the induced strengthening by influencing:(1)The critical size below which twinned variants are solely allowed;(2)the orientation spreading of the pioneer twinned variants toward Bain pairs;(3)the variant thickness and in turn the strengthening extent.The present study sheds light on tuning the substructure and hardening during martensitic transformation via the austenite strength,showing potential scientific and technological importance.展开更多
Additive manufacturing(AM),laser powder bed fusion(L-PBF)in particular,enables the rapid creation of 316L stainless steel components with complex geometries,thereby overcoming the limitations associated with tradition...Additive manufacturing(AM),laser powder bed fusion(L-PBF)in particular,enables the rapid creation of 316L stainless steel components with complex geometries,thereby overcoming the limitations associated with traditional manufacturing methods.To further optimize the performance of these components,deep cryogenic treatment(DCT)—an extension of traditional heat treatment involving exposure to temperatures below 143 K—was employed to modify the microstructure of L-PBF fabricated 316L stainless steel.Experimental results showed that DCT with a duration below 15 min strengthened 316L stainless steel without obviously compromising ductility.Specifically,a 5-min DCT increased yield strength by 12.3% compared to the as-fabricated part.Microstructure analysis demonstrated that the strength enhancement was primarily attributed to the formation of nanotwins with thicknesses ranging from 20 to 30 nm.However,when DCT duration exceeded 15 min,softening rather than strengthening occurred.This softening was associated with a decrease in dislocation density,disruption of cellular substructure,and dissolution of nanoparticles,which are the key features of as L-PBF fabricated 316L stainless steel.Additionally,prolonged DCT caused the thickness of nanotwins to increase to sub-micron sizes,reducing their contribution to strengthening.展开更多
Facing the high demand for faster and heavier freight trains in Australia,researchers and practitioners are endeavouring to develop more innovative and resilient ballasted tracks.In recent years,many studies have been...Facing the high demand for faster and heavier freight trains in Australia,researchers and practitioners are endeavouring to develop more innovative and resilient ballasted tracks.In recent years,many studies have been conducted by the researchers from Transport Research Centre at the University of Technology Sydney(TRC-UTS)to examine the feasibility of incorporating recycled tyre/rubber into rail tracks.This paper reviews three innovative applications using recycled rubber products such as(1)a synthetic energy-absorbing layer for railway subballast using a composite of rubber crumbs and mining byproducts,(2)using rubber intermixed ballast stratum to replace conventional ballast,and(3)installing recycled rubber mat to mitigate ballast degradation under the impact loading.Comprehensive laboratory and field tests as well as numerical modelling have been conducted to examine the performance of rail tracks incorporating these innovative inclusions.The laboratory and field test results and numerical modelling reveal that incorporating these rubber products could increase the energy-absorbing capacity of the track,and mitigate the ballast breakage and settlement significantly,hence increasing the track stability.The research outcomes will facilitate a better understanding of the performance of ballast tracks incorporating these resilient waste tyre materials while promoting more economical and environmentally sustainable tracks for greater passenger comfort and increased safety.展开更多
Ti-Zr-Nb refractory multi-principal element alloys(RMPEAs)have attracted increased attention due to their excellent mechanical properties.In this study,(TiZr)_(80-x)Nb_(20)Mo_(x)(x=0,5 and 10)alloys were designed,and ...Ti-Zr-Nb refractory multi-principal element alloys(RMPEAs)have attracted increased attention due to their excellent mechanical properties.In this study,(TiZr)_(80-x)Nb_(20)Mo_(x)(x=0,5 and 10)alloys were designed,and the intrinsic conflicts between strength and ductility were overcome via composition optimization and recrystallization.The causes of the superior strength-ductility synergy were investigated in terms of their deformation mechanism and dislocation behavior.The results show that the strength improvement can be attributed to the deformation mechanism transition caused by local chemical fluctuations and lattice distortion.Specifically,the slip band widths decrease after Mo addition,and the measured slip traces in the fracture samples are associated with high-order{112}and{123}slip planes.Furthermore,the grain refinement achieved via recrystallization promotes multi-slip system activation and shortens the slip-band spacing,which reduces the stress concentration and inhibits crack source formation,thereby allowing the alloy to ensure sufficient ductility.Consequently,the Ti_(35)Zr_(35)Nb_(20)Mo_(10)alloy annealed at 900℃ exhibits high yield strength and elongation.These findings provide a new strategy for designing high-strength RMPEAs and addressing room-temperature brittleness.展开更多
The Al-9Zn-2.8Mg-2.5Cu-xZr-ySc alloys （x=0, 0.15%, 0.15%; y=0, 0.05%, 0.15%）, produced by low-frequent electromagnetic casting technology, were subjected to homogenization treatment, hot extrusion, solution and agin...The Al-9Zn-2.8Mg-2.5Cu-xZr-ySc alloys （x=0, 0.15%, 0.15%; y=0, 0.05%, 0.15%）, produced by low-frequent electromagnetic casting technology, were subjected to homogenization treatment, hot extrusion, solution and aging treatment. The effects of minor Sc and Zr addition on microstructure, recrystallization and properties of alloys were studied by optical microscopy （OM）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The results show that Sc and Zr addition can refine grains of the as-cast alloy by precipitation of primary Al3（Sc,Zr） particles formed during solidification as heterogeneous nuclei. Secondary Al3（Sc,Zr） precipitates formed during homogenization treatment strongly pin the movement of dislocation and subgrain boundaries, which can effectively inhibit the alloys recrystallization. Compared with the alloy without Sc and Zr addition, the Al-Zn-Mg-Cu-Zr alloy with 0.05%Sc and 0.15%Zr shows the increase in tensile strength and yield strength by 172 MPa and 218 MPa, respectively. Strengthening comes from the contributions of precipitation, substructure and grain refining.展开更多
In order to decrease model complexity of rice panicle for its complicated morphological structure,an interactive L-system based on substructure algorithm was proposed to model rice panicle in this study.Through the an...In order to decrease model complexity of rice panicle for its complicated morphological structure,an interactive L-system based on substructure algorithm was proposed to model rice panicle in this study.Through the analysis of panicle morphology,the geometrical structure models of panicle spikelet,axis and branch were constructed firstly.Based on that,an interactive panicle L-system model was developed by using substructure algorithm to optimize panicle geometrical models with the similar structure.Simulation results showed that the interactive L-system panicle model based on substructure algorithm could fast construct panicle morphological structure in reality.In addition,this method had the well reference value for other plants model research.展开更多
With the increment of the complexity of structural systems and the span of spatial structures, the interactions between parts of the structures, especially between some flexible substructures, become too complex to be...With the increment of the complexity of structural systems and the span of spatial structures, the interactions between parts of the structures, especially between some flexible substructures, become too complex to be analyzed clearly. In this paper, taking an actual gymnasium of a long-span spatial steel-cable-membrane hybrid structure as the calculation model, the static and dynamic analyses of the hybrid structures are performed by employing the global analysis of the whole hybrid structure and the substructural analysis of the truss arch substructure, the cable-membrane substructure, etc. In addition, the comparison of stresses and displacements of structural members in the global and substructural analyses is made. The numerical results show that serious errors exist in the substructural analysis of the hybrid structure, and the global analysis is necessary for the hybrid structure under the excitation of static loads and seismic loads.展开更多
Trabecular bone disconnection “hotspots” of real termini (ReTm) previously mapped as loci of weakness in the female aging spine and hip may be a source of free-floating cancellous segments found in the medullary spa...Trabecular bone disconnection “hotspots” of real termini (ReTm) previously mapped as loci of weakness in the female aging spine and hip may be a source of free-floating cancellous segments found in the medullary space using a bespoke, thick slice histological method for identifying ReTm. A factor in their origin is apparently microdamage proliferation (differentiated by en bloc silver staining) with occasional callus moderation. Validation of similar “floating segments” (FS) in the ex-breeder rat suggested a pilot model for a potentially common phenomenon. Following marrow elution and density fractionation of the isolated floating segments from the whole proximal rat femora, scanning electron microscopy (SEM) and elemental microanalysis (EDS) was performed. The eluent contained numbers of vertically truncated, laterally branched floating segments (acute severance of sequential tensile cross-struts, causing chronic compression overload of axial-struts, with ii) inadequate stabilising callus, facilitating ReTm stacking into predetermined, substructural “crumple zones” of force containment, spheroidal attrition and particulate dissociation. As a catabolic outcome of altered tensile and hormonal influence, FS number may add a novel variable to cancellous bone kinetics particularly in women of relevance to fracture predisposition.展开更多
The wave-shaped space truss is used as the roof of the natatorium in Tianjin University,which ingeniously displays the function of the building.In this paper,the wave-shaped space truss is analyzed and designed,consid...The wave-shaped space truss is used as the roof of the natatorium in Tianjin University,which ingeniously displays the function of the building.In this paper,the wave-shaped space truss is analyzed and designed,considering the substructure made of reinforced concrete rigid frame and the space truss working together.Also,the anti-seismic characteristic of the wave-shaped space truss is studied based on the integral model.展开更多
The method of inputting the seismic wave determines the accuracy of the simulation of soil-structure dynamic interaction. The wave method is a commonly used approach for seismic wave input, which converts the incident...The method of inputting the seismic wave determines the accuracy of the simulation of soil-structure dynamic interaction. The wave method is a commonly used approach for seismic wave input, which converts the incident wave into equivalent loads on the cutoff boundaries. The wave method has high precision, but the implementation is complicated, especially for three-dimensional models. By deducing another form of equivalent input seismic loads in the fi nite element model, a new seismic wave input method is proposed. In the new method, by imposing the displacements of the free wave fi eld on the nodes of the substructure composed of elements that contain artifi cial boundaries, the equivalent input seismic loads are obtained through dynamic analysis of the substructure. Subsequently, the equivalent input seismic loads are imposed on the artifi cial boundary nodes to complete the seismic wave input and perform seismic analysis of the soil-structure dynamic interaction model. Compared with the wave method, the new method is simplifi ed by avoiding the complex processes of calculating the equivalent input seismic loads. The validity of the new method is verifi ed by the dynamic analysis numerical examples of the homogeneous and layered half space under vertical and oblique incident seismic waves.展开更多
The morphology,microstructure and decomposition behavior of M2C carbides in high speed steels with different chemical compositions have been investigated by scanning electron microscopy,transmission electron microscop...The morphology,microstructure and decomposition behavior of M2C carbides in high speed steels with different chemical compositions have been investigated by scanning electron microscopy,transmission electron microscopy,electron backscatter diffraction and X-ray diffraction.The results show that the morphology and substructure of M2C carbides are very sensitive to chemical compositions of high speed steels.M2C carbides present the plate-like shape in tungsten-molybdenum steel and present the polycrystal orientation in the eutectic cell.In contrast,they show the fibrous shape in molybdenum-base steel and exhibit the monocrystal orientation.Plate-like and fibrous M2C carbides are both metastable and decompose into M6 C together with MC at high temperatures.MC nucleates inside the plate-like M2C while it is formed at the fibrous M2C/matrix interface during the decomposition process.Such differences are expected to arise from different compositions of plate-like and fibrous M2C carbides.展开更多
In order to analyze the influence of configuration parameters on dynamic characteristics of machine tools in the working space, the configuration parameters have been suggested based on the orthogonal experiment metho...In order to analyze the influence of configuration parameters on dynamic characteristics of machine tools in the working space, the configuration parameters have been suggested based on the orthogonal experiment method. Dynamic analysis of a milling machine, which is newly designed for producing turbine blades, has been conducted by utilizing the modal synthesis method. The finite element model is verified and updated by experimental modal analysis （EMA） of the machine tool. The result gained by modal synthesis method is compared with whole-model finite element method （FEM） result as well. According to the orthogonal experiment method, four configuration parameters of machine tool are considered as four factors for dynamic characteristics. The influence of configuration parameters on the first three natural frequencies is obtained by range analysis. It is pointed out that configuration parameter is the most important factor affecting the fundamental frequency of machine tools, and configuration parameter has less effect on lower-order modes of the system than others. The combination of configuration parameters which makes the fundamental frequency reach the maximum value is provided. Through demonstration, the conclusion can be drawn that the influence of configuration parameters on the natural frequencies of machine tools can be analyzed explicitly by the orthogonal experiment method, which offers a new method for estimating the dynamic characteristics of machine tools.展开更多
As a newly invented parallel kinematic machine（PKM）, Exechon has found its potential application in machining and assembling industries due to high rigidity and high dynamics. To guarantee the overall performance, t...As a newly invented parallel kinematic machine（PKM）, Exechon has found its potential application in machining and assembling industries due to high rigidity and high dynamics. To guarantee the overall performance, the loading conditions and deflections of the key components must be revealed to provide basic mechanic data for component design. For this purpose, a kinetostatic model is proposed with substructure synthesis technique. The Exechon is divided into a platform subsystem, a fixed base subsystem and three limb subsystems according to its structure. By modeling the limb assemblage as a spatial beam constrained by two sets of lumped virtual springs representing the compliances of revolute joint, universal joint and spherical joint, the equilibrium equations of limb subsystems are derived with finite element method（FEM）. The equilibrium equations of the platform are derived with Newton＇s 2nd law. By introducing deformation compatibility conditions between the platform and limb, the governing equilibrium equations of the system are derived to formulate an analytical expression for system＇s deflections. The platform＇s elastic displacements and joint reactions caused by the gravity are investigated to show a strong position-dependency and axis-symmetry due to its kinematic and structure features. The proposed kinetostatic model is a trade-off between the accuracy of FEM and concision of analytical method, thus can predict the kinetostatics throughout the workspace in a quick and succinct manner. The proposed modeling methodology and kinetostatic analysis can be further expanded to other PKMs with necessary modifications, providing useful information for kinematic calibration as well as component strength calculations.展开更多
Commercial grade rolled and electrodeposited copper foils from Japan and China were selected, and their mechanical properties and microstructure were investigated. It was observed that there are notable differences in...Commercial grade rolled and electrodeposited copper foils from Japan and China were selected, and their mechanical properties and microstructure were investigated. It was observed that there are notable differences in fracture strength, elongation at break and hydrophilicity between rol- led and electrodeposited copper foils. The rolled copper foils have higher tensile strength, lower ductility and larger static contact angle than electrodeposited copper foils. The rolled copper foils contain a [^-fiber texture, and the electrodeposited copper foils have random crystalline orientations. It was also observed that the rolled foils have packed grains, and elec- trodeposited foils have equiaxial grains. The uniform fine grain size and a few substructures of Japanese electrode- posited foils are major reasons for their higher elongation.展开更多
文摘Based on the TEM analysis of substructures of lower bainite in two steels containing Si,the lattice invariant shear elements were determined and a plastic accommodation double-shear model of phenomenological crystallography was proposed.The theoretical predictions about crystallography given by the model are in good agreement with the experimental data for the steels tested.
文摘The establishment of the analogy theory between optimal control and computational structural mechanics is based on the linear quadratic control problem in optimal control and the substructural chain theory in structural mechanics.When the nonlinear optimal control problem is treated by the above theory, especially
文摘Substructural type systems are designed from the insight inspired by the development of linear and substructural logics. Substructural type systems promise to control the usage of computational resources statically, thus detect more program errors at an early stage than traditional type systems do. In the past decade, substructural type systems have been deployed in the design of novel programming languages, such as Vault, etc. This paper presents a general typing theory for substructural type system. First, we define a universal semantic framework for substructural types by interpreting them as characteristic intervals composed of type qualifiers. Based on this framework, we present the design of a substructural calculus λSL with subtyping relations. After giving syntax, typing rules and operational semantics for λSL, we prove the type safety theorem. The new calculus λSL can guarantee many more safety invariants than traditional lambda calculus, which is demonstrated by showing that the ~.s, calculus can serve as an idealized type intermediate language, and defining a typepreserving translation from ordinary typed lambda calculus into λSL.
基金supported by the National Natural Science Foundation of China(Grant No.12272144).
文摘A data-driven model ofmultiple variable cutting(M-VCUT)level set-based substructure is proposed for the topology optimization of lattice structures.TheM-VCUTlevel setmethod is used to represent substructures,enriching their diversity of configuration while ensuring connectivity.To construct the data-driven model of substructure,a database is prepared by sampling the space of substructures spanned by several substructure prototypes.Then,for each substructure in this database,the stiffness matrix is condensed so that its degrees of freedomare reduced.Thereafter,the data-drivenmodel of substructures is constructed through interpolationwith compactly supported radial basis function(CS-RBF).The inputs of the data-driven model are the design variables of topology optimization,and the outputs are the condensed stiffness matrix and volume of substructures.During the optimization,this data-driven model is used,thus avoiding repeated static condensation that would requiremuch computation time.Several numerical examples are provided to verify the proposed method.
基金financial support by the National Natural Science Foundation of China(No.51364032)the Inner Mongolia Natural Science Foundation(No.2022MS05028)。
文摘The spray-deposition was used to produce billets of Mg-4Al-1.5Zn-3Ca-1Nd(A alloy)and Mg-13Al-3Zn-3Ca-1Nd(B alloy),and evolution of deformation substructure and Mg_(x)Zn_(y)Ca_(z)metastable phase in fine-grained(3μm)Mg alloys was investigated by scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),and electron backscattered diffraction(EBSD).It was found that different dislocation configurations were formed in A and B alloys.Redundant free dislocations(RFDs)and dislocation tangles were the ways to form deformation substructure in A alloy,no RFDs except dislocation tangles were found in B alloy.The interaction between nano-scale second phase particles(nano-scale C15 andβ-Mg_(17)(Al,Zn)_(12)phase)and different dislocation configurations had a significant effect on the deformation substructures formation.The mass transfer of Mg_(x)Zn_(y)Ca_(z)metastable phases and the stacking order of stacking faults were conducive to the Mg-Nd-Zn typed long period stacking ordered(LPSO)phases formation.Nano-scale C15 phases,Mg-Nd-Zn typed LPSO phases,c/a ratio,β-Mg_(17)(Al,Zn)_(12)phases were the key factors influencing the formation of textures.Different textures and grain boundary features(GB features)had a significant effect on k-value.The non-basal textures were the main factor affecting k-value in A alloy,while the high-angle grain boundary(HAGB)was the main factor affecting k-value in B alloy.
基金supported by the National Natural Science Foundation of China(Nos.52175310,52232004)the Launch Research Program of Fuzhou University,China(No.XRC-23083)+1 种基金the Education&Research Project of Fujian Province,China(No.JAT231003)the Open Test Fund for Valuable Instruments and Equipment of Fuzhou University,China(No.2024T036).
文摘Based on the relationship between deformation microstructures and grain orientations,three characteristic Cu single crystals were used to investigate the opposite effects of ultrasonic superimposed high-strain-rate on the dislocation motion during ultrasonic welding(UW).The results revealed that equiaxed dislocation cells and discontinuous dynamic recrystallization(DRX)grains dominated in the joint microstructures.Three Cu single crystal joints exhibited an isotropic trend in grain orientation,welding quality,and microscopic mechanical properties.The preferred dislocation behaviors and DRX modes were further analyzed by modelling the stored energy difference,indicating that high mobility of intra-granular dislocations and homogeneous dislocation motion induced by the ultrasonic excitation were the intrinsic factors contributing to the formation of isotropic microstructures and welding quality.
基金supported by the Hundred Outstanding Creative Talents Projects at Hebei University,China.The Natural Science Foundation-Steel and Iron Foundation of Hebei Province(No.E2021203051)One of the authors(Hongwang Zhang)would like to acknowledge Prof.Zhinan Yang from Yanshan University for the assistance in conducting the XRD experiment.We would like to thank the reviewers and editors for their valuable comments and suggestions.
文摘In the present study,a single parameter governing the substructure and the strengthening for martensitic transformation was tentatively explored by detailing the microstructure and the strengthening of a Fe15 wt.%Cr binary alloy subjected to thermal cycle under high pressure(cooled at 10°C s-1 from 1050°C under hydrostatic pressure of 1.0-4.0 GPa).Experimental results show that high pressure makes martensitic transformation occur in a Fe-15Cr alloy that traditionally has no high-temperature austenite under atmospheric pressure.The phase transformation begins with the pairing of twinned variants,and the strengthening is solely dependent upon the density of dislocations and variants.The austenite strength at the transformation temperature governs the substructure and the induced strengthening by influencing:(1)The critical size below which twinned variants are solely allowed;(2)the orientation spreading of the pioneer twinned variants toward Bain pairs;(3)the variant thickness and in turn the strengthening extent.The present study sheds light on tuning the substructure and hardening during martensitic transformation via the austenite strength,showing potential scientific and technological importance.
基金financially supported by the Natural Science Ba-sic Research Plan in Shaanxi Province of China(No.2024JC-ZDXM-33)the State Key Laboratory of Solidification Processing in NWPU(No.SKLSP202319)the Fundamental Research Funds for the Central Universities(No.G2023KY05103).
文摘Additive manufacturing(AM),laser powder bed fusion(L-PBF)in particular,enables the rapid creation of 316L stainless steel components with complex geometries,thereby overcoming the limitations associated with traditional manufacturing methods.To further optimize the performance of these components,deep cryogenic treatment(DCT)—an extension of traditional heat treatment involving exposure to temperatures below 143 K—was employed to modify the microstructure of L-PBF fabricated 316L stainless steel.Experimental results showed that DCT with a duration below 15 min strengthened 316L stainless steel without obviously compromising ductility.Specifically,a 5-min DCT increased yield strength by 12.3% compared to the as-fabricated part.Microstructure analysis demonstrated that the strength enhancement was primarily attributed to the formation of nanotwins with thicknesses ranging from 20 to 30 nm.However,when DCT duration exceeded 15 min,softening rather than strengthening occurred.This softening was associated with a decrease in dislocation density,disruption of cellular substructure,and dissolution of nanoparticles,which are the key features of as L-PBF fabricated 316L stainless steel.Additionally,prolonged DCT caused the thickness of nanotwins to increase to sub-micron sizes,reducing their contribution to strengthening.
基金financial support from the Australian Research Council for ARCLP200200915 and ARCDP220102862financial and technical support from industry partners including Sydney Trains,SMEC Australia Pty.
文摘Facing the high demand for faster and heavier freight trains in Australia,researchers and practitioners are endeavouring to develop more innovative and resilient ballasted tracks.In recent years,many studies have been conducted by the researchers from Transport Research Centre at the University of Technology Sydney(TRC-UTS)to examine the feasibility of incorporating recycled tyre/rubber into rail tracks.This paper reviews three innovative applications using recycled rubber products such as(1)a synthetic energy-absorbing layer for railway subballast using a composite of rubber crumbs and mining byproducts,(2)using rubber intermixed ballast stratum to replace conventional ballast,and(3)installing recycled rubber mat to mitigate ballast degradation under the impact loading.Comprehensive laboratory and field tests as well as numerical modelling have been conducted to examine the performance of rail tracks incorporating these innovative inclusions.The laboratory and field test results and numerical modelling reveal that incorporating these rubber products could increase the energy-absorbing capacity of the track,and mitigate the ballast breakage and settlement significantly,hence increasing the track stability.The research outcomes will facilitate a better understanding of the performance of ballast tracks incorporating these resilient waste tyre materials while promoting more economical and environmentally sustainable tracks for greater passenger comfort and increased safety.
基金supported by the National Key Research and Development Program of China(No.2022YFF0609000)the National Natural Science Foundation of China(Nos.52171034 and 52101037)the Postdoctoral Fellowship Program of CPSF(No.GZB20230944).
文摘Ti-Zr-Nb refractory multi-principal element alloys(RMPEAs)have attracted increased attention due to their excellent mechanical properties.In this study,(TiZr)_(80-x)Nb_(20)Mo_(x)(x=0,5 and 10)alloys were designed,and the intrinsic conflicts between strength and ductility were overcome via composition optimization and recrystallization.The causes of the superior strength-ductility synergy were investigated in terms of their deformation mechanism and dislocation behavior.The results show that the strength improvement can be attributed to the deformation mechanism transition caused by local chemical fluctuations and lattice distortion.Specifically,the slip band widths decrease after Mo addition,and the measured slip traces in the fracture samples are associated with high-order{112}and{123}slip planes.Furthermore,the grain refinement achieved via recrystallization promotes multi-slip system activation and shortens the slip-band spacing,which reduces the stress concentration and inhibits crack source formation,thereby allowing the alloy to ensure sufficient ductility.Consequently,the Ti_(35)Zr_(35)Nb_(20)Mo_(10)alloy annealed at 900℃ exhibits high yield strength and elongation.These findings provide a new strategy for designing high-strength RMPEAs and addressing room-temperature brittleness.
基金Project(0211002605132)supported by Institute of Multipurpose Utilization of Mineral Resources,Chinese Academy of Geological Sciences,ChinaProject(0211005303101)supported by the Fundamental Research Funds for the Central Universities,China+1 种基金Project(2010BB4074)supported by Natural Science Foundation Project of CQ CSTC,ChinaProject(2010ZD-02)supported by State Key Laboratory for Advanced Metals and Materials,China
文摘The Al-9Zn-2.8Mg-2.5Cu-xZr-ySc alloys （x=0, 0.15%, 0.15%; y=0, 0.05%, 0.15%）, produced by low-frequent electromagnetic casting technology, were subjected to homogenization treatment, hot extrusion, solution and aging treatment. The effects of minor Sc and Zr addition on microstructure, recrystallization and properties of alloys were studied by optical microscopy （OM）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The results show that Sc and Zr addition can refine grains of the as-cast alloy by precipitation of primary Al3（Sc,Zr） particles formed during solidification as heterogeneous nuclei. Secondary Al3（Sc,Zr） precipitates formed during homogenization treatment strongly pin the movement of dislocation and subgrain boundaries, which can effectively inhibit the alloys recrystallization. Compared with the alloy without Sc and Zr addition, the Al-Zn-Mg-Cu-Zr alloy with 0.05%Sc and 0.15%Zr shows the increase in tensile strength and yield strength by 172 MPa and 218 MPa, respectively. Strengthening comes from the contributions of precipitation, substructure and grain refining.
基金Supported by National Natural Science Foundation of China(60802040)Youth Fund in Southwest University of Science and Technology(10zx3106)~~
文摘In order to decrease model complexity of rice panicle for its complicated morphological structure,an interactive L-system based on substructure algorithm was proposed to model rice panicle in this study.Through the analysis of panicle morphology,the geometrical structure models of panicle spikelet,axis and branch were constructed firstly.Based on that,an interactive panicle L-system model was developed by using substructure algorithm to optimize panicle geometrical models with the similar structure.Simulation results showed that the interactive L-system panicle model based on substructure algorithm could fast construct panicle morphological structure in reality.In addition,this method had the well reference value for other plants model research.
文摘With the increment of the complexity of structural systems and the span of spatial structures, the interactions between parts of the structures, especially between some flexible substructures, become too complex to be analyzed clearly. In this paper, taking an actual gymnasium of a long-span spatial steel-cable-membrane hybrid structure as the calculation model, the static and dynamic analyses of the hybrid structures are performed by employing the global analysis of the whole hybrid structure and the substructural analysis of the truss arch substructure, the cable-membrane substructure, etc. In addition, the comparison of stresses and displacements of structural members in the global and substructural analyses is made. The numerical results show that serious errors exist in the substructural analysis of the hybrid structure, and the global analysis is necessary for the hybrid structure under the excitation of static loads and seismic loads.
文摘Trabecular bone disconnection “hotspots” of real termini (ReTm) previously mapped as loci of weakness in the female aging spine and hip may be a source of free-floating cancellous segments found in the medullary space using a bespoke, thick slice histological method for identifying ReTm. A factor in their origin is apparently microdamage proliferation (differentiated by en bloc silver staining) with occasional callus moderation. Validation of similar “floating segments” (FS) in the ex-breeder rat suggested a pilot model for a potentially common phenomenon. Following marrow elution and density fractionation of the isolated floating segments from the whole proximal rat femora, scanning electron microscopy (SEM) and elemental microanalysis (EDS) was performed. The eluent contained numbers of vertically truncated, laterally branched floating segments (acute severance of sequential tensile cross-struts, causing chronic compression overload of axial-struts, with ii) inadequate stabilising callus, facilitating ReTm stacking into predetermined, substructural “crumple zones” of force containment, spheroidal attrition and particulate dissociation. As a catabolic outcome of altered tensile and hormonal influence, FS number may add a novel variable to cancellous bone kinetics particularly in women of relevance to fracture predisposition.
文摘The wave-shaped space truss is used as the roof of the natatorium in Tianjin University,which ingeniously displays the function of the building.In this paper,the wave-shaped space truss is analyzed and designed,considering the substructure made of reinforced concrete rigid frame and the space truss working together.Also,the anti-seismic characteristic of the wave-shaped space truss is studied based on the integral model.
基金National Natural Science Foundation of China under Grant No.51478247National Key Research and Development Program of China under Grant No.2016YFC1402800
文摘The method of inputting the seismic wave determines the accuracy of the simulation of soil-structure dynamic interaction. The wave method is a commonly used approach for seismic wave input, which converts the incident wave into equivalent loads on the cutoff boundaries. The wave method has high precision, but the implementation is complicated, especially for three-dimensional models. By deducing another form of equivalent input seismic loads in the fi nite element model, a new seismic wave input method is proposed. In the new method, by imposing the displacements of the free wave fi eld on the nodes of the substructure composed of elements that contain artifi cial boundaries, the equivalent input seismic loads are obtained through dynamic analysis of the substructure. Subsequently, the equivalent input seismic loads are imposed on the artifi cial boundary nodes to complete the seismic wave input and perform seismic analysis of the soil-structure dynamic interaction model. Compared with the wave method, the new method is simplifi ed by avoiding the complex processes of calculating the equivalent input seismic loads. The validity of the new method is verifi ed by the dynamic analysis numerical examples of the homogeneous and layered half space under vertical and oblique incident seismic waves.
基金funded by National Natural Science Foundation of China(51301038,51371050)Industry-Academia-Research Program of Jiangsu Province of China(BY2014127-03)+2 种基金Natural Science Foundation of Jiangsu Province of China(BK20141306)Key Research Program of Jiangsu Province of China(BE2016154)Jiangsu Province Key Laboratory of High-end Structural Materials of China(hsm1404)
文摘The morphology,microstructure and decomposition behavior of M2C carbides in high speed steels with different chemical compositions have been investigated by scanning electron microscopy,transmission electron microscopy,electron backscatter diffraction and X-ray diffraction.The results show that the morphology and substructure of M2C carbides are very sensitive to chemical compositions of high speed steels.M2C carbides present the plate-like shape in tungsten-molybdenum steel and present the polycrystal orientation in the eutectic cell.In contrast,they show the fibrous shape in molybdenum-base steel and exhibit the monocrystal orientation.Plate-like and fibrous M2C carbides are both metastable and decompose into M6 C together with MC at high temperatures.MC nucleates inside the plate-like M2C while it is formed at the fibrous M2C/matrix interface during the decomposition process.Such differences are expected to arise from different compositions of plate-like and fibrous M2C carbides.
基金Important National Science & Technology Specific Projects (2009ZX04001-073)National Natural Science Foundation of China (51105025)
文摘In order to analyze the influence of configuration parameters on dynamic characteristics of machine tools in the working space, the configuration parameters have been suggested based on the orthogonal experiment method. Dynamic analysis of a milling machine, which is newly designed for producing turbine blades, has been conducted by utilizing the modal synthesis method. The finite element model is verified and updated by experimental modal analysis （EMA） of the machine tool. The result gained by modal synthesis method is compared with whole-model finite element method （FEM） result as well. According to the orthogonal experiment method, four configuration parameters of machine tool are considered as four factors for dynamic characteristics. The influence of configuration parameters on the first three natural frequencies is obtained by range analysis. It is pointed out that configuration parameter is the most important factor affecting the fundamental frequency of machine tools, and configuration parameter has less effect on lower-order modes of the system than others. The combination of configuration parameters which makes the fundamental frequency reach the maximum value is provided. Through demonstration, the conclusion can be drawn that the influence of configuration parameters on the natural frequencies of machine tools can be analyzed explicitly by the orthogonal experiment method, which offers a new method for estimating the dynamic characteristics of machine tools.
基金Supported by State Key Laboratory for Manufacturing Systems Engineering,Xi’an Jiaotong University(Grant No.sklms2015004)Open Research Fund of Key Laboratory of High Performance Complex Manufacturing,Central South University(Grant No.Kfkt2013-12)+2 种基金Open Fund of Shanghai Key Laboratory of Digital Manufacture for Thin-walled Structures(Grant No.2014001)Innovation Research Fund for Postgraduates of Anhui University of Technology(Grant No.2014054)Engineering and Physical Science Research Council in the United Kingdom(Grant No.EP/K004964/1)
文摘As a newly invented parallel kinematic machine（PKM）, Exechon has found its potential application in machining and assembling industries due to high rigidity and high dynamics. To guarantee the overall performance, the loading conditions and deflections of the key components must be revealed to provide basic mechanic data for component design. For this purpose, a kinetostatic model is proposed with substructure synthesis technique. The Exechon is divided into a platform subsystem, a fixed base subsystem and three limb subsystems according to its structure. By modeling the limb assemblage as a spatial beam constrained by two sets of lumped virtual springs representing the compliances of revolute joint, universal joint and spherical joint, the equilibrium equations of limb subsystems are derived with finite element method（FEM）. The equilibrium equations of the platform are derived with Newton＇s 2nd law. By introducing deformation compatibility conditions between the platform and limb, the governing equilibrium equations of the system are derived to formulate an analytical expression for system＇s deflections. The platform＇s elastic displacements and joint reactions caused by the gravity are investigated to show a strong position-dependency and axis-symmetry due to its kinematic and structure features. The proposed kinetostatic model is a trade-off between the accuracy of FEM and concision of analytical method, thus can predict the kinetostatics throughout the workspace in a quick and succinct manner. The proposed modeling methodology and kinetostatic analysis can be further expanded to other PKMs with necessary modifications, providing useful information for kinematic calibration as well as component strength calculations.
基金financially supported by the National Natural Science Foundation of China (No. 51344008)
文摘Commercial grade rolled and electrodeposited copper foils from Japan and China were selected, and their mechanical properties and microstructure were investigated. It was observed that there are notable differences in fracture strength, elongation at break and hydrophilicity between rol- led and electrodeposited copper foils. The rolled copper foils have higher tensile strength, lower ductility and larger static contact angle than electrodeposited copper foils. The rolled copper foils contain a [^-fiber texture, and the electrodeposited copper foils have random crystalline orientations. It was also observed that the rolled foils have packed grains, and elec- trodeposited foils have equiaxial grains. The uniform fine grain size and a few substructures of Japanese electrode- posited foils are major reasons for their higher elongation.
