In order to achieve the large-scale application of manufactured sand in railway high-strength concrete structure,a series of high-strength manufactured sand concrete(HMC)are prepared by taking the manufactured sand li...In order to achieve the large-scale application of manufactured sand in railway high-strength concrete structure,a series of high-strength manufactured sand concrete(HMC)are prepared by taking the manufactured sand lithology(tuff,limestone,basalt,granite),stone powder content(0,5%,10%,15%)and concrete strength grade(C60,C80,C100)as variables.The evolution of mechanical properties of HMC and the correlation between cubic compressive strength and other mechanical properties are studied.Compared to river sand,manufactured sand enhances the cubic compressive strength,axial compressive strength and elastic modulus of concrete,while its potential microcracks weaken the flexural strength and splitting tensile strength of concrete.Stone powder content displays both positive and negative effects on mechanical properties of HMC,and the stone powder content is suggested to be less than 10%.The empirical formulas between cubic compressive strength and other mechanical properties are proposed.展开更多
Al Si10Mg porous protective structure often produces different damage forms under compressive loading,and these damage modes affect its protective function.In order to well meet the service requirements,there is an ur...Al Si10Mg porous protective structure often produces different damage forms under compressive loading,and these damage modes affect its protective function.In order to well meet the service requirements,there is an urgent need to comprehensively understand the mechanical behavior and response mechanism of AlSi10Mg porous structures under compressive loading.In this paper,Al Si10Mg porous structures with three kinds of volume fractions are designed and optimized to meet the requirements of high-impact,strong-energy absorption,and lightweight characteristics.The mechanical behaviors of AlSi10Mg porous structures,including the stress-strain relationship,structural bearing state,deformation and damage modes,and energy absorption characteristics,were obtained through experimental studies at different loading rates.The damage pattern of the damage section indicates that AlSi10Mg porous structures have both ductile and brittle mechanical properties.Numerical simulation studies show that the AlSi10Mg porous structure undergoes shear damage due to relative misalignment along the diagonal cross-section,and the damage location is almost at 45°to the load direction,which is the most direct cause of its structural damage,revealing the damage mechanism of AlSi10Mg porous structures under the compressive load.The normalized energy absorption model constructed in the paper well interprets the energy absorption state of Al Si10Mg porous structures and gives the sensitive location of the structures,and the results of this paper provide important references for peers in structural design and optimization.展开更多
Wire-arc additive manufacture(WAAM)has great potential for manufacturing of Al-Cu components.However,inferior mechanical properties of WAAM deposited material restrict its industrial application.Inter-layer cold rolli...Wire-arc additive manufacture(WAAM)has great potential for manufacturing of Al-Cu components.However,inferior mechanical properties of WAAM deposited material restrict its industrial application.Inter-layer cold rolling and thermo-mechanical heat treatment(T8)with pre-stretching deformation between solution and aging treatment were adopted in this study.Their effects on hardness,mechanical properties and microstructure were analyzed and compared to the conventional heat treatment(T6).The results show that cold rolling increases the hardness and strengths,which further increase with T8 treatment.The ultimate tensile strength(UTS)of 513 MPa and yield stress(YS)of 413 MPa can be obtained in the inter-layer cold-rolled sample with T8 treatment,which is much higher than that in the as-deposited samples.The cold-rolled samples show higher elongation than that of as-deposited ones due to significant elimination of porosity in cold rolling;while both the T6 and T8 treatments decrease the elongation.The cold rolling and pre-stretching deformation both contribute to the formation of dense and dispersive precipitatedθ′phases,which inhibits the dislocation movement and enhances the strengths;as a result,T8 treatment shows better strengthening effect than the T6 treatment.The strengthening mechanism was analyzed and it was mainly related to work hardening and precipitation strengthening.展开更多
Customized heat treatment is essential for enhancing the mechanical properties of additively manufactured metallic materials,especially for alloys with complex phase constituents and heterogenous microstructure.Howeve...Customized heat treatment is essential for enhancing the mechanical properties of additively manufactured metallic materials,especially for alloys with complex phase constituents and heterogenous microstructure.However,the interrelated evolutions of different microstructure features make it difficult to establish optimal heat treatment processes.Herein,we proposed a method for customized heat treatment process exploration and establishment to overcome this challenge for such kind of alloys,and a wire arc additively manufactured(WAAM)Mg-Gd-Y-Zn-Zr alloy with layered heterostructure was used for feasibility verification.Through this method,the optimal microstructures(fine grain,controllable amount of long period stacking ordered(LPSO)structure and nano-scaleβ'precipitates)and the corresponding customized heat treatment processes(520°C/30 min+200°C/48 h)were obtained to achieve a good combination of a high strength of 364 MPa and a considerable elongation of 6.2%,which surpassed those of other state-of-the-art WAAM-processed Mg alloys.Furthermore,we evidenced that the favorable effect of the undeformed LPSO structures on the mechanical properties was emphasized only when the nano-scaleβ'precipitates were present.It is believed that the findings promote the application of magnesium alloy workpieces and help to establish customized heat treatment processes for additively manufactured materials.展开更多
Wire arc additive manufacturing offers advantages in producing large metal structures.The current research on GTA-based wire arc additive manufacturing(GTA-WAAM)of magnesium alloys is focused on deformed magnesium all...Wire arc additive manufacturing offers advantages in producing large metal structures.The current research on GTA-based wire arc additive manufacturing(GTA-WAAM)of magnesium alloys is focused on deformed magnesium alloys,mainly on the Mg-Al alloy system.However,there is little research on GTA-WAAM for casting magnesium alloy.This study investigates the microstructural characteristics and mechanical properties of AZ91D magnesium alloy(AZ91D-Mg)deposited by GTA-WAAM.Single-pass multilayer thin-walled components were successfully fabricated.The results show that equiaxed grains dominate the microstructure of the deposited samples.During the remelting process,the precipitated phases dissolve into the matrix,and they precipitate and grow from the matrix under the thermal effect of the subsequent thermal cycle.The mechanical properties in the vertical and horizontal directions are similar,showing higher overall mechanical properties than the casting parts.The average yield strength is 110.5 MPa,the ultimate tensile strength is 243.6 MPa,and the elongation is 11.7%.The overall hardness distribution in the deposited sample is relatively uniform,and the average microhardness is 59.6 HV_(0.2).展开更多
In the face of the increased global campaign to minimize the emission of greenhouse gases and the need for sustainability in manufacturing, there is a great deal of research focusing on environmentally benign and rene...In the face of the increased global campaign to minimize the emission of greenhouse gases and the need for sustainability in manufacturing, there is a great deal of research focusing on environmentally benign and renewable materials as a substitute for synthetic and petroleum-based products. Natural fiber-reinforced polymeric composites have recently been proposed as a viable alternative to synthetic materials. The current work investigates the suitability of coconut fiber-reinforced polypropylene as a structural material. The coconut fiber-reinforced polypropylene composites were developed. Samples of coconut fiber/polypropylene (PP) composites were prepared using Fused Filament Fabrication (FFF). Tests were then conducted on the mechanical properties of the composites for different proportions of coconut fibers. The results obtained indicate that the composites loaded with 2 wt% exhibited the highest tensile and flexural strength, while the ones loaded with 3 wt% had the highest compression strength. The ultimate tensile and flexural strength at 2 wt% were determined to be 34.13 MPa and 70.47 MPa respectively. The compression strength at 3 wt% was found to be 37.88 MPa. Compared to pure polypropylene, the addition of coconut fibers increased the tensile, flexural, and compression strength of the composite. In the study, an artificial neural network model was proposed to predict the mechanical properties of polymeric composites based on the proportion of fibers. The model was found to predict data with high accuracy.展开更多
In bone tissue engineering,good structural and forming qualities are prerequisites for the long-term implantation of scaffolds.To mitigate the stress-shielding effect between porous bone scaffolds and the human skelet...In bone tissue engineering,good structural and forming qualities are prerequisites for the long-term implantation of scaffolds.To mitigate the stress-shielding effect between porous bone scaffolds and the human skeleton,this study proposes a method for designing non-linear gradient gyroid porous structures with radial-axial hybrid gra-dients that are precisely controlled by multivariate polynomial functions to simulate human bone characteristics.The influence of the volumetric energy density on the forming quality of the porous structures was evaluated by characterizing the internal strut morphology and measuring the strut width and porosity.Finite element analysis combined with experimental observations revealed that during compression,the thin struts at the top and bottom of the hybrid-gradient porous structure deformed first,and the compressive stress and shear stress were gradually transferred from the thin struts at the upper and lower ends of the structure to the thicker struts in the middle.Compared with the axial gradient,the edge struts of the hybrid-gradient porous structures can withstand higher shear and compressive stresses.Furthermore,owing to the variation in the radial gradient,compared to struc-tures with 20%axial porosity variation,the hybrid-gradient porous structure with 40%radial porosity variation and 20%axial porosity variation exhibited an 18.10%increase in elastic modulus and a 4.29%increase in yield strength.Additionally,its effective energy absorption was 20.39%higher than that of the homogeneous structures.Compared to radial-gradient porous structures,the hybrid-gradient porous structure showed a lower sensitivity of the elastic modulus and yield strength to the volumetric energy density.展开更多
Recently,the application of wire-arc additive manufacturing(WAAM)for the production of metallic products is gaining traction.WAAM is associated with the direct energy deposition technique and therefore has a higher de...Recently,the application of wire-arc additive manufacturing(WAAM)for the production of metallic products is gaining traction.WAAM is associated with the direct energy deposition technique and therefore has a higher deposition rate(approximately 4 kg/h).For this reason,it is of greater interest than powder-based additive manufacturing techniques.Industrial applications such as marine and offshore structures and pressure vessels for space programs commonly utilize high-strength low-alloy(HSLA)steel.HSLA steel components produced by casting methods exhibit defects due to oxidation.Therefore,cold metal transfer(CMT)-WAAM was adopted in this study to fabricate HSLA steel components.The metallurgical properties were analyzed using microscopic and diffraction techniques.The effects of the evolved microstructures on mechanical properties,such as strength,microhardness,and elongation to fracture,were evaluated.To analyze and test the structure,two regions were selected,namely,top and bottom.Microstructural analyses revealed that both regions were primarily composed of acicular ferrite,polygonal ferrite,and bainitic structures.The bottom region exhibited superior mechanical properties compared with the top region.The improved strength at the bottom region can be ascribed to the formation of a high density of dislocations and finer grains.展开更多
Nickel-based superalloys, well-established in aeronautics, have recently gained significant traction in additive manufacturing. Inconel 939 is one of the alloys increasingly playing a vital role in this field. This pa...Nickel-based superalloys, well-established in aeronautics, have recently gained significant traction in additive manufacturing. Inconel 939 is one of the alloys increasingly playing a vital role in this field. This paper examines the development of the Portevin-Le Chatelier (PLC) effect in additively manufactured Inconel 939 in comparison with cast Inconel 939. A detailed analysis of tensile test characteristics was conducted, complemented by a high-resolution scanning electron microscopy (HR-SEM) investigation. The PLC region exhibited several properties during tensile testing, such as stress-strain behavior, cycle scale, and overall stress increase. The HR-SEM analysis of Gamma prime (γ') precipitates revealed distinct morphologies, which are suggested to be linked to the features of the PLC region. Samples with a high amount of γ' precipitates showed a less pronounced PLC region, while those with fewer γ' precipitates displayed a more distinct PLC effect. A mechanism for the cyclic drop-and-rise stress behavior, based on the work of Varvenne and La-Rose, was proposed, possibly induced by the varying morphologies of γ' precipitates in the IN939 alloy. Further study is needed to deepen the understanding of the relationship between the γ' micro-(nano) structure and the PLC phenomenon.展开更多
Vat photopolymerization additive manufacturing produces lightweight load-bearing ceramic lattice structures that have flexibility,time-efficiency,and high precision,compared to conventional technology.However,understa...Vat photopolymerization additive manufacturing produces lightweight load-bearing ceramic lattice structures that have flexibility,time-efficiency,and high precision,compared to conventional technology.However,understanding the compression behavior and failure mechanism of such structures under loading remains a challenge.In this study,considering the correlation between the strut angle and bearing capacity,body-centered tetragonal(BCT)lattice structures with varying angles are designed based on a body-centered cubic(BCC)structure.BCT Al_(2)O_(3) ceramic lattice structures with varying angles are fabricated by vat photopolymerization.The mechanical properties,deformation process,and failure mechanism of the Al_(2)O_(3) ceramic lattice structures are characterized through a combination of ex-and in-situ X-ray computed tomography(X-CT)compression testing and analyzed using a finite element method(FEM)at macro-and micro-levels.The results demonstrate that as the angle increases,the stress concentration gradually expands from the node to the strut,resulting in an increased loadbearing capacity.Additionally,the failure mode of the Al_(2)O_(3) ceramic lattice structures is identified as diagonal slip shear failure.These findings provide a greater understanding of ceramic lattice structure failures and design optimization approaches.展开更多
Aluminum–Lithium(Al–Li) alloy is a topic of great interest owing to its high strength and light weight, but there are only a few applications of Al–Li alloy in wire ss, a special AA2050 Al–Li alloy + arc additive ...Aluminum–Lithium(Al–Li) alloy is a topic of great interest owing to its high strength and light weight, but there are only a few applications of Al–Li alloy in wire ss, a special AA2050 Al–Li alloy + arc additive manufacturing(WAAM) process. To identify its feasibility in WAAM procewire was produced and employed in the production of straight-walled components, using a WAAM system based on variable polarity gas tungsten arc welding(VP-GTAW) process. The influence of post-deposited heat treatment on the microstructure and property of the deposit was investigated using optical micrographs(OM), scanning electron microscopy(SEM), X-ray diffraction(XRD), hardness and tensile properties tests. Results revealed that the microstructures of AA2050 aluminum deposits varied with their location layers. The upper layers consisted of fine equiaxed grains, while the bottom layer exhibited a coarse columnar structure. Mechanical properties witnessed a significant improvement after post-deposited heat treatment, with the average micro-hardness reaching 141 HV and the ultimate tensile strength exceeding 400 MPa. Fracture morphology exhibited a typical ductile fracture.展开更多
Wire arc additive manufacturing(WAAM)technology has been used to fabricate the multi-layer single-pass deposited wall of AZ80M magnesium(Mg)alloy by gas tungsten arc welding.The formability,thermal cycles,microstructu...Wire arc additive manufacturing(WAAM)technology has been used to fabricate the multi-layer single-pass deposited wall of AZ80M magnesium(Mg)alloy by gas tungsten arc welding.The formability,thermal cycles,microstructural evolution and mechanical properties of the WAAM AZ80M Mg alloy were investigated.The results show that there was significant difference in the temperature variation and the geometries between the original several layers and the subsequent deposited layers.Owing to the arc energy input,the interpass temperature rised rapidly and then stabilized at 150℃.As a result,the width of the deposited wall increased and then kept stable.There were obvious differences in the microstructure of the WAAM AZ80M Mg alloy among the top zone,intermediate zone and bottom zone of deposited wall.During the arc deposition process,theβphase of the WAAM AZ80M Mg alloy redissolved due to the cyclic heat accumulation,and then precipitated in the grain boundary.The cyclic heat accumulation also led to weakening of dendrite segregation.From the substrate to the top zone,the hardness of the deposited wall decreased gradually,and the intermediate zone which was the main body of deposited wall had relatively uniform hardness.The tensile properties of the WAAM AZ80M Mg alloy were different between the vertical direction and the horizontal direction.And the maximum ultimate tensile strength of the WAAM AZ80M Mg alloy was 308 MPa which was close to that of the as-extruded AZ80M Mg alloy.展开更多
Bio-inspired porous metallic scaffolds have tremendous potential to be used as artificial bone substitutes.In this work,a radially graded lattice structure (RGLS),which mimics the structures of natural human bones,was...Bio-inspired porous metallic scaffolds have tremendous potential to be used as artificial bone substitutes.In this work,a radially graded lattice structure (RGLS),which mimics the structures of natural human bones,was designed and processed by laser powder bed fusion of martensitic Ti-rich TiNi powder.The asymmetric tension-compression behaviour,where the compressive strength is significantly higher than the tensile strength,is observed in this Ti-rich TiNi material,which echoes the mechanical behaviour of bones.The morphologies,mechanical properties,deformation behaviour,and biological compatibility of RGLS samples were characterised and compared with those in the uniform lattice structure.Both the uniform and RGLS samples achieve a relative density higher than 99%.The graded porosities and pore sizes in the RGLS range from 40%-80% and 330-805 µm,respectively,from the centre to the edge.The chemical etching has significantly removed the harmful partially-melted residual powder particles on the lattice struts.The compressive yield strength of RGLS is 71.5 MPa,much higher than that of the uniform sample (46.5 MPa),despite having a similar relative density of about 46%.The calculated Gibson-Ashby equation and the deformation behaviour simulation by finite element suggest that the dense outer regions with high load-bearing capability could sustain high applied stress,improving the overall strength of RGLS significantly.The cell proliferation study suggests better biological compatibility of the RGLS than the uniform structures.The findings highlight a novel strategy to improve the performance of additively manufactured artificial implants by bio-inspiration.展开更多
Ti−Al−V−Nb alloys with the cluster formula,12[Al−Ti_(12)](AlTi_(2))+5[Al−Ti1_(4)](V,Nb)2Ti,were designed by replacing V with Nb based on the Ti−6Al−4V alloy.Single-track cladding layers and bulk samples of the alloys ...Ti−Al−V−Nb alloys with the cluster formula,12[Al−Ti_(12)](AlTi_(2))+5[Al−Ti1_(4)](V,Nb)2Ti,were designed by replacing V with Nb based on the Ti−6Al−4V alloy.Single-track cladding layers and bulk samples of the alloys with Nb contents ranging from 0 to 6.96 wt.%were prepared by laser additive manufacturing to examine their formability,microstructure,and mechanical properties.For single-track cladding layers,the addition of Nb increased the surface roughness slightly and decreased the molten pool height to improve its spreadability.The alloy,Ti−5.96Al−1.94V−3.54Nb(wt.%),exhibited better geometrical accuracy than the other alloys because its molten pool height was consistent with the spread layer thickness of the powder.The microstructures of the bulk samples contained similar columnar β-phase grains,regardless of Nb content.These grains grew epitaxially from the Ti substrate along the deposition direction,with basket-weaveα-phase laths within the columnar grains.Theα-phase size increased with increasing Nb contents,but its uniformity decreased.Along the deposition direction,the Vickers hardness increased from the substrate to the surface.The Ti−5.96Al−1.94V−3.54Nb alloy exhibited the highest Vickers hardness regardless of deposition position because of the optimal matching relationship between theα-phase size and its content among the designed alloys.展开更多
NiTi shape memory alloy(SMA)with nominal composition of Ni 50.8 at%and Ti 49.2 at%was additively manufactured(AM)by selective laser melting(SLM)and laser directed energy deposition(DED)for a comparison study,with emph...NiTi shape memory alloy(SMA)with nominal composition of Ni 50.8 at%and Ti 49.2 at%was additively manufactured(AM)by selective laser melting(SLM)and laser directed energy deposition(DED)for a comparison study,with emphasis on its phase composition,microstructure,mechanical property and deformation mechanism.The results show that the yield strength and ductility obtained by SLM are 100 MPa and 8%,respectively,which are remarkably different from DED result with 700 MPa and 2%.The load path of SLM sample presents shape memory effect,corresponding to martensite phase detected by XRD;while the load path of DED presents pseudo-elasticity with austenite phase.In SLM sample,fine grain and hole provide a uniform deformation during tensile test,resulting in a better elongation.Furthermore,the nonequilibrium solidification was studied by a temperature field simulation to understand the difference of the two 3D printing methods.Both temperature gradient G and growth rate R determine the microstructure and phase in the SLM sample and DED sample,which leads to similar grain morphologies because of similar G/R.While higher G×R of SLM leads to a finer grain size in SLM sample,providing enough driving force for martensite transition and subsequently changing texture compared to DED sample.展开更多
The microstructure, microhardness and tensile properties of laser additive manufactured (LAM) Ti?5Al?2Sn?2Zr?4Mo?4Cr alloy were investigated. The result shows that the microstructure evolution is strongly affected by ...The microstructure, microhardness and tensile properties of laser additive manufactured (LAM) Ti?5Al?2Sn?2Zr?4Mo?4Cr alloy were investigated. The result shows that the microstructure evolution is strongly affected by the thermal history of LAM process. Primary α (αp) with different morphologies, secondary α (αs) and martensite α' can be observed at different positions of the LAMed specimen. Annealing treatment can promote the precipitation of rib-like α phase or acicular α phase. As a result, it can increase or decrease the microhardness. The as-deposited L-direction and T-direction specimens contain the same phase constituent with different morphologies. The tensile properties of the as-deposited LAMed specimens are characterized of anisotropy. The L-direction specimen shows the character of low strength but high ductility when compared with the T-direction specimen. After annealing treatment, the strength of L-direction specimen increases significantly while the ductility reduces. The strength of the annealed T-direction specimen changes little, however, the ductility reduces nearly by 50%.展开更多
Multistable mechanical metamaterials are a type of mechanical metamaterials with special features,such as reusability,energy storage and absorption capabilities,rapid deformation,and amplified output forces.These meta...Multistable mechanical metamaterials are a type of mechanical metamaterials with special features,such as reusability,energy storage and absorption capabilities,rapid deformation,and amplified output forces.These metamaterials are usually realized by series and/or parallel of bistable units.They can exhibit multiple stable configurations under external loads and can be switched reversely among each other,thereby realizing the reusability of mechanical metamaterials and offering broad engineering applications.This paper reviews the latest research progress in the design strategy,manufacture and application of multistable mechanical metamaterials.We divide bistable structures into three categories based on their basic element types and provide the criterion of their bistability.Various manufacturing techniques to fabricate these multistable mechanical metamaterials are introduced,including mold casting,cutting,folding and three-dimensional/4D printing.Furthermore,the prospects of multistable mechanical metamaterials for applications in soft driving,mechanical computing,energy absorption and wave controlling are discussed.Finally,this paper highlights possible challenges and opportunities for future investigations.The review aims to provide insights into the research and development of multistable mechanical metamaterials.展开更多
Original equipment manufacturers(OEM) have never been so important and powerful as it is today in garment manufacturing industry.The OEMsupplier's production decisions always have a great impact on the market perf...Original equipment manufacturers(OEM) have never been so important and powerful as it is today in garment manufacturing industry.The OEMsupplier's production decisions always have a great impact on the market performance and the profits of a garment brand manufacturer.With constrained capacity and multiply buyers,howto make reasonable production decisions is an urgent problem for OEMsuppliers.A price discount model with a single OEMsupplier and two buyers is proposed to deal with the problem.Based on this model,the OEMsupplier could satisfy buyers' demands and guarantee their profits as well through adjusting price and delivery frequency.A numerical example validates the validity of the model.展开更多
Zibo Sangde Machinery Equipment Co., Ltd. is the first Manufacturer of Refractory Electric Screw Press in China, in the year of 2008, our company produced the first set 315T Refractory Electric Program-controlled Scre...Zibo Sangde Machinery Equipment Co., Ltd. is the first Manufacturer of Refractory Electric Screw Press in China, in the year of 2008, our company produced the first set 315T Refractory Electric Program-controlled Screw Press in China, which is no friction discs, simple structure, with PLC controlling the brick forming process, no need special operator. Once upon the Press was on the market, it achieved a strong interests and reputations from many Refractory Factories because of its Highefficient, Energy-saving（can save by 40-50% electricity comparing to the Friction Press）, manpower reduction and improving the quality of bricks.展开更多
ZTE Corporation announced on November 6, 2009 that the company has received the prestigious "World’s Best CDMA Equipment Manufacturer 2009" award from research and consulting firm Frost & Sullivan.
基金Funded by the National Natural Science Foundation of China(Nos.U1934206,52108260)China Academy of Railway Sciences Fund(No.2021YJ078)+1 种基金Railway Engineering Construction Standard Project(No.2023-BZWW-006)New Cornerstone Science Foundation through the XPLORER PRIZE。
文摘In order to achieve the large-scale application of manufactured sand in railway high-strength concrete structure,a series of high-strength manufactured sand concrete(HMC)are prepared by taking the manufactured sand lithology(tuff,limestone,basalt,granite),stone powder content(0,5%,10%,15%)and concrete strength grade(C60,C80,C100)as variables.The evolution of mechanical properties of HMC and the correlation between cubic compressive strength and other mechanical properties are studied.Compared to river sand,manufactured sand enhances the cubic compressive strength,axial compressive strength and elastic modulus of concrete,while its potential microcracks weaken the flexural strength and splitting tensile strength of concrete.Stone powder content displays both positive and negative effects on mechanical properties of HMC,and the stone powder content is suggested to be less than 10%.The empirical formulas between cubic compressive strength and other mechanical properties are proposed.
基金financially supported by the National Natural Science Foundation of China(Nos.12272356,12072326,and 12172337)the State Key Laboratory of Dynamic Measurement Technology,North University of China(No.2022-SYSJJ-03)。
文摘Al Si10Mg porous protective structure often produces different damage forms under compressive loading,and these damage modes affect its protective function.In order to well meet the service requirements,there is an urgent need to comprehensively understand the mechanical behavior and response mechanism of AlSi10Mg porous structures under compressive loading.In this paper,Al Si10Mg porous structures with three kinds of volume fractions are designed and optimized to meet the requirements of high-impact,strong-energy absorption,and lightweight characteristics.The mechanical behaviors of AlSi10Mg porous structures,including the stress-strain relationship,structural bearing state,deformation and damage modes,and energy absorption characteristics,were obtained through experimental studies at different loading rates.The damage pattern of the damage section indicates that AlSi10Mg porous structures have both ductile and brittle mechanical properties.Numerical simulation studies show that the AlSi10Mg porous structure undergoes shear damage due to relative misalignment along the diagonal cross-section,and the damage location is almost at 45°to the load direction,which is the most direct cause of its structural damage,revealing the damage mechanism of AlSi10Mg porous structures under the compressive load.The normalized energy absorption model constructed in the paper well interprets the energy absorption state of Al Si10Mg porous structures and gives the sensitive location of the structures,and the results of this paper provide important references for peers in structural design and optimization.
基金Project(ZZYJKT2024-08)supported by the State Key Laboratory of Precision Manufacturing for Extreme Service Performance,ChinaProject(2022JB11GX004)supported by Selection of the best Candidates to Undertake Key Research Projects by Dalian City,ChinaProject(201806835007)supported by China Scholarship Council。
文摘Wire-arc additive manufacture(WAAM)has great potential for manufacturing of Al-Cu components.However,inferior mechanical properties of WAAM deposited material restrict its industrial application.Inter-layer cold rolling and thermo-mechanical heat treatment(T8)with pre-stretching deformation between solution and aging treatment were adopted in this study.Their effects on hardness,mechanical properties and microstructure were analyzed and compared to the conventional heat treatment(T6).The results show that cold rolling increases the hardness and strengths,which further increase with T8 treatment.The ultimate tensile strength(UTS)of 513 MPa and yield stress(YS)of 413 MPa can be obtained in the inter-layer cold-rolled sample with T8 treatment,which is much higher than that in the as-deposited samples.The cold-rolled samples show higher elongation than that of as-deposited ones due to significant elimination of porosity in cold rolling;while both the T6 and T8 treatments decrease the elongation.The cold rolling and pre-stretching deformation both contribute to the formation of dense and dispersive precipitatedθ′phases,which inhibits the dislocation movement and enhances the strengths;as a result,T8 treatment shows better strengthening effect than the T6 treatment.The strengthening mechanism was analyzed and it was mainly related to work hardening and precipitation strengthening.
基金supported by the Projects of Major Scientific and Technological Achievements Local Transformation of Xi’an(2022JH-ZDZH-0039)International Science and Technology Cooperation Program of Shaanxi Province (2023-GHZD-50)+9 种基金Project of Qin Chuangyuan ‘Scientist+Engineer’team constructionKey R&D plan of Shaanxi Province (S2023-YF-QCYK-0001-237)Projects of Major Scientific and Technological Achievements Local Transformation of Xi’an (2022JH-ZDZH-0039)National Natural Science Foundation of China (52101134)Natural Science Foundation of Guangdong Province (2022A1515010275)Scientific Research Program Funded by Shaanxi Provincial Education Department (22JK0479)Doctoral Dissertations Innovation Fund of Xi’an University of Technology (101-252072305)Research Start-up Project of Xi’an University of Technology(101-256082204)Natural Science Foundation of Shaanxi Province (2023-JC-QN-0573)Natural Science Basic Research Program of Shaanxi(2023-JC-YB-412)
文摘Customized heat treatment is essential for enhancing the mechanical properties of additively manufactured metallic materials,especially for alloys with complex phase constituents and heterogenous microstructure.However,the interrelated evolutions of different microstructure features make it difficult to establish optimal heat treatment processes.Herein,we proposed a method for customized heat treatment process exploration and establishment to overcome this challenge for such kind of alloys,and a wire arc additively manufactured(WAAM)Mg-Gd-Y-Zn-Zr alloy with layered heterostructure was used for feasibility verification.Through this method,the optimal microstructures(fine grain,controllable amount of long period stacking ordered(LPSO)structure and nano-scaleβ'precipitates)and the corresponding customized heat treatment processes(520°C/30 min+200°C/48 h)were obtained to achieve a good combination of a high strength of 364 MPa and a considerable elongation of 6.2%,which surpassed those of other state-of-the-art WAAM-processed Mg alloys.Furthermore,we evidenced that the favorable effect of the undeformed LPSO structures on the mechanical properties was emphasized only when the nano-scaleβ'precipitates were present.It is believed that the findings promote the application of magnesium alloy workpieces and help to establish customized heat treatment processes for additively manufactured materials.
基金supported by the National Natural Science Foundation of China[Grant Nos.52275324 and 51975148]the Fundamental Research Funds for the Central Universities[Grant No.FRFCU5710051321].
文摘Wire arc additive manufacturing offers advantages in producing large metal structures.The current research on GTA-based wire arc additive manufacturing(GTA-WAAM)of magnesium alloys is focused on deformed magnesium alloys,mainly on the Mg-Al alloy system.However,there is little research on GTA-WAAM for casting magnesium alloy.This study investigates the microstructural characteristics and mechanical properties of AZ91D magnesium alloy(AZ91D-Mg)deposited by GTA-WAAM.Single-pass multilayer thin-walled components were successfully fabricated.The results show that equiaxed grains dominate the microstructure of the deposited samples.During the remelting process,the precipitated phases dissolve into the matrix,and they precipitate and grow from the matrix under the thermal effect of the subsequent thermal cycle.The mechanical properties in the vertical and horizontal directions are similar,showing higher overall mechanical properties than the casting parts.The average yield strength is 110.5 MPa,the ultimate tensile strength is 243.6 MPa,and the elongation is 11.7%.The overall hardness distribution in the deposited sample is relatively uniform,and the average microhardness is 59.6 HV_(0.2).
文摘In the face of the increased global campaign to minimize the emission of greenhouse gases and the need for sustainability in manufacturing, there is a great deal of research focusing on environmentally benign and renewable materials as a substitute for synthetic and petroleum-based products. Natural fiber-reinforced polymeric composites have recently been proposed as a viable alternative to synthetic materials. The current work investigates the suitability of coconut fiber-reinforced polypropylene as a structural material. The coconut fiber-reinforced polypropylene composites were developed. Samples of coconut fiber/polypropylene (PP) composites were prepared using Fused Filament Fabrication (FFF). Tests were then conducted on the mechanical properties of the composites for different proportions of coconut fibers. The results obtained indicate that the composites loaded with 2 wt% exhibited the highest tensile and flexural strength, while the ones loaded with 3 wt% had the highest compression strength. The ultimate tensile and flexural strength at 2 wt% were determined to be 34.13 MPa and 70.47 MPa respectively. The compression strength at 3 wt% was found to be 37.88 MPa. Compared to pure polypropylene, the addition of coconut fibers increased the tensile, flexural, and compression strength of the composite. In the study, an artificial neural network model was proposed to predict the mechanical properties of polymeric composites based on the proportion of fibers. The model was found to predict data with high accuracy.
基金supported by National Natural Science Foundation of China(Grant No.52175481)Postdoctoral Science Foundation of China(Grant No.2023M743539).
文摘In bone tissue engineering,good structural and forming qualities are prerequisites for the long-term implantation of scaffolds.To mitigate the stress-shielding effect between porous bone scaffolds and the human skeleton,this study proposes a method for designing non-linear gradient gyroid porous structures with radial-axial hybrid gra-dients that are precisely controlled by multivariate polynomial functions to simulate human bone characteristics.The influence of the volumetric energy density on the forming quality of the porous structures was evaluated by characterizing the internal strut morphology and measuring the strut width and porosity.Finite element analysis combined with experimental observations revealed that during compression,the thin struts at the top and bottom of the hybrid-gradient porous structure deformed first,and the compressive stress and shear stress were gradually transferred from the thin struts at the upper and lower ends of the structure to the thicker struts in the middle.Compared with the axial gradient,the edge struts of the hybrid-gradient porous structures can withstand higher shear and compressive stresses.Furthermore,owing to the variation in the radial gradient,compared to struc-tures with 20%axial porosity variation,the hybrid-gradient porous structure with 40%radial porosity variation and 20%axial porosity variation exhibited an 18.10%increase in elastic modulus and a 4.29%increase in yield strength.Additionally,its effective energy absorption was 20.39%higher than that of the homogeneous structures.Compared to radial-gradient porous structures,the hybrid-gradient porous structure showed a lower sensitivity of the elastic modulus and yield strength to the volumetric energy density.
文摘Recently,the application of wire-arc additive manufacturing(WAAM)for the production of metallic products is gaining traction.WAAM is associated with the direct energy deposition technique and therefore has a higher deposition rate(approximately 4 kg/h).For this reason,it is of greater interest than powder-based additive manufacturing techniques.Industrial applications such as marine and offshore structures and pressure vessels for space programs commonly utilize high-strength low-alloy(HSLA)steel.HSLA steel components produced by casting methods exhibit defects due to oxidation.Therefore,cold metal transfer(CMT)-WAAM was adopted in this study to fabricate HSLA steel components.The metallurgical properties were analyzed using microscopic and diffraction techniques.The effects of the evolved microstructures on mechanical properties,such as strength,microhardness,and elongation to fracture,were evaluated.To analyze and test the structure,two regions were selected,namely,top and bottom.Microstructural analyses revealed that both regions were primarily composed of acicular ferrite,polygonal ferrite,and bainitic structures.The bottom region exhibited superior mechanical properties compared with the top region.The improved strength at the bottom region can be ascribed to the formation of a high density of dislocations and finer grains.
文摘Nickel-based superalloys, well-established in aeronautics, have recently gained significant traction in additive manufacturing. Inconel 939 is one of the alloys increasingly playing a vital role in this field. This paper examines the development of the Portevin-Le Chatelier (PLC) effect in additively manufactured Inconel 939 in comparison with cast Inconel 939. A detailed analysis of tensile test characteristics was conducted, complemented by a high-resolution scanning electron microscopy (HR-SEM) investigation. The PLC region exhibited several properties during tensile testing, such as stress-strain behavior, cycle scale, and overall stress increase. The HR-SEM analysis of Gamma prime (γ') precipitates revealed distinct morphologies, which are suggested to be linked to the features of the PLC region. Samples with a high amount of γ' precipitates showed a less pronounced PLC region, while those with fewer γ' precipitates displayed a more distinct PLC effect. A mechanism for the cyclic drop-and-rise stress behavior, based on the work of Varvenne and La-Rose, was proposed, possibly induced by the varying morphologies of γ' precipitates in the IN939 alloy. Further study is needed to deepen the understanding of the relationship between the γ' micro-(nano) structure and the PLC phenomenon.
基金supported by National Natural Science Foundation of China(Grant Nos.52275310,52402084)the China Postdoctoral Science Foundation(Grant No.2024M751646).
文摘Vat photopolymerization additive manufacturing produces lightweight load-bearing ceramic lattice structures that have flexibility,time-efficiency,and high precision,compared to conventional technology.However,understanding the compression behavior and failure mechanism of such structures under loading remains a challenge.In this study,considering the correlation between the strut angle and bearing capacity,body-centered tetragonal(BCT)lattice structures with varying angles are designed based on a body-centered cubic(BCC)structure.BCT Al_(2)O_(3) ceramic lattice structures with varying angles are fabricated by vat photopolymerization.The mechanical properties,deformation process,and failure mechanism of the Al_(2)O_(3) ceramic lattice structures are characterized through a combination of ex-and in-situ X-ray computed tomography(X-CT)compression testing and analyzed using a finite element method(FEM)at macro-and micro-levels.The results demonstrate that as the angle increases,the stress concentration gradually expands from the node to the strut,resulting in an increased loadbearing capacity.Additionally,the failure mode of the Al_(2)O_(3) ceramic lattice structures is identified as diagonal slip shear failure.These findings provide a greater understanding of ceramic lattice structure failures and design optimization approaches.
基金Supported by National Natural Science Foundation of China(Grant No.51675031)Beijing Municipal Science and Technology Commission and Fundamental Research Funds for the Central Universities(Grant No.YWF-18-BJ-J-244,YWF-19-BJ-J-232)+1 种基金Beijing Natural Science Foundation(Grant No.3182020)the Academic Excellence Foundation of BUAA for PhD
文摘Aluminum–Lithium(Al–Li) alloy is a topic of great interest owing to its high strength and light weight, but there are only a few applications of Al–Li alloy in wire ss, a special AA2050 Al–Li alloy + arc additive manufacturing(WAAM) process. To identify its feasibility in WAAM procewire was produced and employed in the production of straight-walled components, using a WAAM system based on variable polarity gas tungsten arc welding(VP-GTAW) process. The influence of post-deposited heat treatment on the microstructure and property of the deposit was investigated using optical micrographs(OM), scanning electron microscopy(SEM), X-ray diffraction(XRD), hardness and tensile properties tests. Results revealed that the microstructures of AA2050 aluminum deposits varied with their location layers. The upper layers consisted of fine equiaxed grains, while the bottom layer exhibited a coarse columnar structure. Mechanical properties witnessed a significant improvement after post-deposited heat treatment, with the average micro-hardness reaching 141 HV and the ultimate tensile strength exceeding 400 MPa. Fracture morphology exhibited a typical ductile fracture.
基金This work was supported by the China Scholarship Coun-cil(No.201907000039)the national key research and devel-opment plan of China(grant number 2017YFB0305905)the Doctoral Innovation Fund Program of Southwest Jiaotong University(No.D-CX201830).
文摘Wire arc additive manufacturing(WAAM)technology has been used to fabricate the multi-layer single-pass deposited wall of AZ80M magnesium(Mg)alloy by gas tungsten arc welding.The formability,thermal cycles,microstructural evolution and mechanical properties of the WAAM AZ80M Mg alloy were investigated.The results show that there was significant difference in the temperature variation and the geometries between the original several layers and the subsequent deposited layers.Owing to the arc energy input,the interpass temperature rised rapidly and then stabilized at 150℃.As a result,the width of the deposited wall increased and then kept stable.There were obvious differences in the microstructure of the WAAM AZ80M Mg alloy among the top zone,intermediate zone and bottom zone of deposited wall.During the arc deposition process,theβphase of the WAAM AZ80M Mg alloy redissolved due to the cyclic heat accumulation,and then precipitated in the grain boundary.The cyclic heat accumulation also led to weakening of dendrite segregation.From the substrate to the top zone,the hardness of the deposited wall decreased gradually,and the intermediate zone which was the main body of deposited wall had relatively uniform hardness.The tensile properties of the WAAM AZ80M Mg alloy were different between the vertical direction and the horizontal direction.And the maximum ultimate tensile strength of the WAAM AZ80M Mg alloy was 308 MPa which was close to that of the as-extruded AZ80M Mg alloy.
基金financially supported by the National Natural Science Foundation of China(52005189)Guangdong Basic and Applied Basic Research Foundation(2019A1515110542 and 2020A1515110699)+1 种基金Guangzhou Foreign Cooperation Projects(2020B1212060049 and 201704030067)Guangdong Academy of Sciences and the University of Birmingham(Contract 17-0551).
文摘Bio-inspired porous metallic scaffolds have tremendous potential to be used as artificial bone substitutes.In this work,a radially graded lattice structure (RGLS),which mimics the structures of natural human bones,was designed and processed by laser powder bed fusion of martensitic Ti-rich TiNi powder.The asymmetric tension-compression behaviour,where the compressive strength is significantly higher than the tensile strength,is observed in this Ti-rich TiNi material,which echoes the mechanical behaviour of bones.The morphologies,mechanical properties,deformation behaviour,and biological compatibility of RGLS samples were characterised and compared with those in the uniform lattice structure.Both the uniform and RGLS samples achieve a relative density higher than 99%.The graded porosities and pore sizes in the RGLS range from 40%-80% and 330-805 µm,respectively,from the centre to the edge.The chemical etching has significantly removed the harmful partially-melted residual powder particles on the lattice struts.The compressive yield strength of RGLS is 71.5 MPa,much higher than that of the uniform sample (46.5 MPa),despite having a similar relative density of about 46%.The calculated Gibson-Ashby equation and the deformation behaviour simulation by finite element suggest that the dense outer regions with high load-bearing capability could sustain high applied stress,improving the overall strength of RGLS significantly.The cell proliferation study suggests better biological compatibility of the RGLS than the uniform structures.The findings highlight a novel strategy to improve the performance of additively manufactured artificial implants by bio-inspiration.
基金the National Key Research and Development Program of China(No.2016YFB1100103)。
文摘Ti−Al−V−Nb alloys with the cluster formula,12[Al−Ti_(12)](AlTi_(2))+5[Al−Ti1_(4)](V,Nb)2Ti,were designed by replacing V with Nb based on the Ti−6Al−4V alloy.Single-track cladding layers and bulk samples of the alloys with Nb contents ranging from 0 to 6.96 wt.%were prepared by laser additive manufacturing to examine their formability,microstructure,and mechanical properties.For single-track cladding layers,the addition of Nb increased the surface roughness slightly and decreased the molten pool height to improve its spreadability.The alloy,Ti−5.96Al−1.94V−3.54Nb(wt.%),exhibited better geometrical accuracy than the other alloys because its molten pool height was consistent with the spread layer thickness of the powder.The microstructures of the bulk samples contained similar columnar β-phase grains,regardless of Nb content.These grains grew epitaxially from the Ti substrate along the deposition direction,with basket-weaveα-phase laths within the columnar grains.Theα-phase size increased with increasing Nb contents,but its uniformity decreased.Along the deposition direction,the Vickers hardness increased from the substrate to the surface.The Ti−5.96Al−1.94V−3.54Nb alloy exhibited the highest Vickers hardness regardless of deposition position because of the optimal matching relationship between theα-phase size and its content among the designed alloys.
基金Project(2020JJ2046)supported by the Science Fund for Hunan Distinguished Young Scholars,ChinaProject(S2020GXKJGG0416)supported by the Special Project for Hunan Innovative Province Construction,China+1 种基金Project(2018RS3007)supported by the Huxiang Young Talents,ChinaProject(GuikeAB19050002)supported by the Science Project of Guangxi,China。
文摘NiTi shape memory alloy(SMA)with nominal composition of Ni 50.8 at%and Ti 49.2 at%was additively manufactured(AM)by selective laser melting(SLM)and laser directed energy deposition(DED)for a comparison study,with emphasis on its phase composition,microstructure,mechanical property and deformation mechanism.The results show that the yield strength and ductility obtained by SLM are 100 MPa and 8%,respectively,which are remarkably different from DED result with 700 MPa and 2%.The load path of SLM sample presents shape memory effect,corresponding to martensite phase detected by XRD;while the load path of DED presents pseudo-elasticity with austenite phase.In SLM sample,fine grain and hole provide a uniform deformation during tensile test,resulting in a better elongation.Furthermore,the nonequilibrium solidification was studied by a temperature field simulation to understand the difference of the two 3D printing methods.Both temperature gradient G and growth rate R determine the microstructure and phase in the SLM sample and DED sample,which leads to similar grain morphologies because of similar G/R.While higher G×R of SLM leads to a finer grain size in SLM sample,providing enough driving force for martensite transition and subsequently changing texture compared to DED sample.
基金Projects(51105311,51475380)supported by the National Natural Science Foundation of ChinaProject(2013AA031103)supported by the National High-Tech Research and Development Program of China
文摘The microstructure, microhardness and tensile properties of laser additive manufactured (LAM) Ti?5Al?2Sn?2Zr?4Mo?4Cr alloy were investigated. The result shows that the microstructure evolution is strongly affected by the thermal history of LAM process. Primary α (αp) with different morphologies, secondary α (αs) and martensite α' can be observed at different positions of the LAMed specimen. Annealing treatment can promote the precipitation of rib-like α phase or acicular α phase. As a result, it can increase or decrease the microhardness. The as-deposited L-direction and T-direction specimens contain the same phase constituent with different morphologies. The tensile properties of the as-deposited LAMed specimens are characterized of anisotropy. The L-direction specimen shows the character of low strength but high ductility when compared with the T-direction specimen. After annealing treatment, the strength of L-direction specimen increases significantly while the ductility reduces. The strength of the annealed T-direction specimen changes little, however, the ductility reduces nearly by 50%.
基金supported by the National Natural Science Foundation of China(Grant Nos.12172164,52250363)the National Key R&D Program of China(Grant Nos.2021YFB3801800,2018YFA0306200)。
文摘Multistable mechanical metamaterials are a type of mechanical metamaterials with special features,such as reusability,energy storage and absorption capabilities,rapid deformation,and amplified output forces.These metamaterials are usually realized by series and/or parallel of bistable units.They can exhibit multiple stable configurations under external loads and can be switched reversely among each other,thereby realizing the reusability of mechanical metamaterials and offering broad engineering applications.This paper reviews the latest research progress in the design strategy,manufacture and application of multistable mechanical metamaterials.We divide bistable structures into three categories based on their basic element types and provide the criterion of their bistability.Various manufacturing techniques to fabricate these multistable mechanical metamaterials are introduced,including mold casting,cutting,folding and three-dimensional/4D printing.Furthermore,the prospects of multistable mechanical metamaterials for applications in soft driving,mechanical computing,energy absorption and wave controlling are discussed.Finally,this paper highlights possible challenges and opportunities for future investigations.The review aims to provide insights into the research and development of multistable mechanical metamaterials.
基金Innovative Methods of Science and Technology of China(No.SQ2015IM3600021)Tianjin Planning Office of Philosophy and Social Science,China(No.TJGL16-019)
文摘Original equipment manufacturers(OEM) have never been so important and powerful as it is today in garment manufacturing industry.The OEMsupplier's production decisions always have a great impact on the market performance and the profits of a garment brand manufacturer.With constrained capacity and multiply buyers,howto make reasonable production decisions is an urgent problem for OEMsuppliers.A price discount model with a single OEMsupplier and two buyers is proposed to deal with the problem.Based on this model,the OEMsupplier could satisfy buyers' demands and guarantee their profits as well through adjusting price and delivery frequency.A numerical example validates the validity of the model.
文摘Zibo Sangde Machinery Equipment Co., Ltd. is the first Manufacturer of Refractory Electric Screw Press in China, in the year of 2008, our company produced the first set 315T Refractory Electric Program-controlled Screw Press in China, which is no friction discs, simple structure, with PLC controlling the brick forming process, no need special operator. Once upon the Press was on the market, it achieved a strong interests and reputations from many Refractory Factories because of its Highefficient, Energy-saving（can save by 40-50% electricity comparing to the Friction Press）, manpower reduction and improving the quality of bricks.
文摘ZTE Corporation announced on November 6, 2009 that the company has received the prestigious "World’s Best CDMA Equipment Manufacturer 2009" award from research and consulting firm Frost & Sullivan.
