The paper deals with the FEM(Finite Element Method)simulation of rotary swaging of Dievar alloy produced by additive manufacturing technology Selective Laser Melting and conventional process.Swaging was performed at a...The paper deals with the FEM(Finite Element Method)simulation of rotary swaging of Dievar alloy produced by additive manufacturing technology Selective Laser Melting and conventional process.Swaging was performed at a temperature of 900℃.True flow stress-strain curves were determined for 600℃–900℃and used to construct a Hensel-Spittel model for FEM simulation.The process parameters,i.e.,stress,temperature,imposed strain,and force,were investigation during the rotary swaging process.Firstly,the stresses induced during rotary swaging and the resistance of the material to deformation were investigated.The amount and distribution of imposed strain in the cross-section can serve as a valuable indicator of the reduction in porosity and the texture evolution of the material.The simulation revealed the force required to swag the Dievar alloy.It also showed the evolution of temperature,which is important for phase transformation during solidification.Furthermore,microstructure evolutionwas observed before and then after rotary swaging.Dievar alloy is a critical material in the manufacture of dies for high-pressure die casting,forging tools,and other equipment subjected to high temperatures and mechanical loads.Understanding its viscoelastoplastic behavior under rotary swaging conditions is essential to optimize its performance in these demanding industrial applications.展开更多
The effect of Ca addition on modification of primary Mg_(2)Si,hardness and wear behavior in Mg-5 wt.%Si hypereutectic alloy has been investigated.The results showed clearly that without Ca addition,most of primary Mg_...The effect of Ca addition on modification of primary Mg_(2)Si,hardness and wear behavior in Mg-5 wt.%Si hypereutectic alloy has been investigated.The results showed clearly that without Ca addition,most of primary Mg_(2)Si appeared as coarse dendritic morphology with average size of about 215μm.With the addition of 0.1 wt.%Ca,the average size of primary Mg_(2)Si decreased to about 98μm,but their morphologies did not significantly changed.As the addition level of Ca increased to 0.3 wt.%,the average size of primary Mg_(2)Si decreased significantly to about 50μm and their morphologies changed to polyhedral shape.However,with further increasing Ca addition to 0.6 wt.%and 1 wt.%,some needle-like and blocky CaMgSi particles formed and the average size of primary Mg_(2)Si increased slightly,which could described as over-modification.The present work showed that the optimal modification effect could be obtained when the Ca content in the investigated alloy reached 0.3 wt.%.The modification mechanism may be referred mainly due to poisoning effect resulting from the segregation of Ca atoms at the growth front of the Mg_(2)Si and the adsorption effect of some Ca atoms in the Mg_(2)Si crystal growth plane.The 0.3 wt.%Ca-added alloy has the highest hardness value and the best wear resistance among all other alloys.An excessive Ca addition resulted in the formation of some needle-like and blocky CaMgSi particles,which was detrimental to hardness and wear behavior of the 0.6 wt.%and 1 wt.%Ca-added alloys.The wear mechanism of investigated alloys is a mild abrasive oxidative wear with little adhesion.展开更多
Based on the special physical–chemical characteristics of optical crystal in the field of aeronautics,a new anhydrous based shear-thickening polishing(ASTP)method has been proposed to restrain deliquescence and to im...Based on the special physical–chemical characteristics of optical crystal in the field of aeronautics,a new anhydrous based shear-thickening polishing(ASTP)method has been proposed to restrain deliquescence and to improve physical properties for KDP machining.The ultraprecision polishing of KDP crystal is completed by ASTP.A kind of anhydrous based thickening polishing slurry(ATPS)was proposed in our work,and high-performance rheological properties were determined to achieve the ASTP of KDP crystal.A material removal model of ASTP in KDP machining is established,followed by the verification experiment of the prediction model.The maximum error of the predictive model is only 9.8%,which proves the validity of the material removal model for KDP polishing.The polishing experiments were carried out on the polishing platform developed by ourselves.The results show that the new polishing method can polish20 mm×20 mm×5 mm KDP crystal and obtain a super-smooth surface with a surface roughness of 1.37 nm and high shape accuracy.The surface accuracy of polished KDP crystal reaches up to0.68 k(RMS).The experimental results show that the ASTP is a potential ultra-precision machining method for KDP crystal.展开更多
Magnesium (Mg) and its alloys are one of a novel kind of biodegradable metallic implants which attracted much fundamental research to develop its clinical application. Nevertheless, it has more restrictions in biomedi...Magnesium (Mg) and its alloys are one of a novel kind of biodegradable metallic implants which attracted much fundamental research to develop its clinical application. Nevertheless, it has more restrictions in biomedical applications because it degrades too fast at the early stage after implantation, thus commonly leading to some problems such as early fast mechanical loss, hydric bubble aggregation, gap formation between the implants and the tissue. This work aims to study the effect of 0.5 wt% Sb addition on the microstructure, mechanical properties and degradation behavior of as cast Mg-4wt% Zn alloy. The evaluation process was conducted using optical and scanning electron microscopy, X-ray diffraction, tensile and compression tests, in addition to a corrosion study by immersing in simulated body fluid (SBF). Results showed that Sb refines the grain size of the base alloy and also enhances its mechanical properties and degradation rate as well. These were due to the formation of the secondary phase of Mg3Sb2. To get better degradation rate, the Mg-4wt% Zn and Mg-4wt% Zn-0.5wt% Sb alloys are coated with Ca-P using autocatalytic technique. The results demonstrated that the formed coat layer improves the degradation rate of samples under the condition of this study. The current study shows that Mg-4wt% Zn-0.5wt% Sb alloy has good mechanical properties and when it coated by Ca-P, it gave a better corrosion resistance that makes it ideal for biodegradable medical application.展开更多
Natural fibre reinforced polymer composite(NFRPC)materials are gaining popularity in the modern world due to their eco-friendliness,lightweight nature,life-cycle superiority,biodegradability,low cost,and noble mechani...Natural fibre reinforced polymer composite(NFRPC)materials are gaining popularity in the modern world due to their eco-friendliness,lightweight nature,life-cycle superiority,biodegradability,low cost,and noble mechanical properties.Due to the wide variety of materials available that have comparable attributes and satisfy the requirements of the product design specification,material selection has become a crucial component of design for engineers.This paper discusses the study’s findings in choosing the suitable thermoplastic matrices of Natural Fibre Composites for Cyclist Helmet utilising the DMAIC,and GRA approaches.The results are based on integrating two decision methods implemented utilising two distinct decision-making approaches:qualitative and quantitative.This study suggested thermoplastic polyethylene as a particularly ideal matrix in composite cyclist helmets during the selection process for the best thermoplastic matrices material using the 6σtechnique,with the decision based on the highest performance,the lightest weight,and the most environmentally friendly criteria.The DMAIC and GRA approach significantly influenced the material selection process by offering different tools for each phase.In the future study,selection technique may have been more exhaustive if more information from other factors had been added.展开更多
In this study, the characteristics of Graphite/Epoxy Composites (GECs) are evaluated from mechanical perspectives. Different weight percentages of graphite were used (0 - 7 wt%) for tensile and hardness experiments. T...In this study, the characteristics of Graphite/Epoxy Composites (GECs) are evaluated from mechanical perspectives. Different weight percentages of graphite were used (0 - 7 wt%) for tensile and hardness experiments. Then the findings were discussed to ascertain the optimum mixing ratio of the graphite with the epoxy. The primary finding of this study is that the graphite weight fraction has a substantial impact on the composites’ mechanical performance. At a low percentage (1 wt%), the graphite has little influence on the tensile behaviour. An intermediate weight percentage of the graphite is considered optimum for mechanical performance in the epoxy composites as it slightly reduces the tensile properties and significantly improves the hardness. Micrographs of the fractured surface of specimens showed many signs that clearly explained why fractures had occurred. For instance, when graphite/epoxy composite contained a low proportion of graphite, the cleavage failure was very easy to observe because there was no sign of aggregation or the detachment of fillers.展开更多
This paper reviews the machinability and mechanical properties of natural fiber-reinforced composites. Coupling agents, operating parameters, as well as chemical treatment effects on natural fiber-reinforced composite...This paper reviews the machinability and mechanical properties of natural fiber-reinforced composites. Coupling agents, operating parameters, as well as chemical treatment effects on natural fiber-reinforced composites’ machinability are also reviewed. Moreover, the impacts of fibers’ physical properties on the machinability of the composite are mentioned. Fiber volume fraction (V<sub>f</sub>), fiber orientation as well as chemical treatment effects on mechanical properties are also defined. Conclusively, the effect of fibers’ physical properties as well as mechanical properties is described. It was discovered that chemical treatment of natural fibers improved their compatibility with the matrix by removing their surface tissues, increasing the roughness average (Ra), and reducing moisture absorption. Also, the Orientation of the fiber plays an important role in controlling the mechanical properties of the composite. Moreover, some physical properties of the fibers, including quality of fiber distributed in the matrix;fiber size, length, and diameter;moisture absorption;porosity and the way fibers break during compounding with the matrix, were found to affect the mechanical properties of the composites formed.展开更多
The machining accuracy of the curved surfaces of integrated turbine blades directly determines the performance and service life of the turbojet engine system.In this paper,a non-contact on-machine measurement system i...The machining accuracy of the curved surfaces of integrated turbine blades directly determines the performance and service life of the turbojet engine system.In this paper,a non-contact on-machine measurement system is developed for precision milling of integrated turbines to reduce the impact of workpiece deformation,overcutting,tool chatter,and material work hardening.Milling with the on-machine measurement system obtained high-quality integrated turbine surfaces.The geometric accuracy error(PV)is below 3μm,and the surface roughness(Ra)is less than 2μm.The processed integrated turbine blade can achieve the accuracy requirements in the design and manufacturing and can be practically applied to the entire turbojet engine.展开更多
The wear profile analysis,obtained by different tribometers,is essential to characterise the wear mechanisms.However,most of the available methods did not take the stress distribution over the wear profile in consider...The wear profile analysis,obtained by different tribometers,is essential to characterise the wear mechanisms.However,most of the available methods did not take the stress distribution over the wear profile in consideration,which causes inaccurate analysis.In this study,the wear profile of polymer–metal contact,obtained by block-on-ring configuration under dry sliding conditions,was analysed using finite element modelling(FEM)and experimental investigation.Archard’s wear equation was integrated into a developed FORTRAN-UMESHMOTION code linked with Abaqus software.A varying wear coefficient(k)values covering both running-in and steady state regions,and a range of applied loads involving both mild and severe wear regions were measured and implemented in the FEM.The FEM was in good agreement with the experiments.The model reproduced the stress distribution profiles under variable testing conditions,while their values were affected by the sliding direction and maximum wear depth(hmax).The largest area of the wear profile,exposed to the average contact stresses,is defined as the normal zone.Whereas the critical zones were characterized by high stress concentrations reaching up to 10 times of that at the normal zone.The wear profile was mapped to identify the critical zone where the stress concentration is the key point in this definition.The surface features were examined in different regions using scanning electron microscope(SEM).Ultimately,SEM analysis showed severer damage features in the critical zone than that in the normal zone as proven by FEM.However,the literature data presented and considered the wear features the same at any point of the wear profile.In this study,the normal zone was determined at a stress value of about 0.5 MPa,whereas the critical zone was at about 5.5 MPa.The wear behaviour of these two zones showed totally different features from one another.展开更多
基金funded by the project SP2024/089 of the Specific Research of the VŠB-Technical University of Ostrava and realized within the framework of the Johannes Amos Comenius Program,Materials and Technologies for Sustainable Development-MATUR,No.CZ.02.01.01/00/22_008/0004631Brno University of Technology project No.FSI-S-23-8231“Investigation of Dynamic Deformation Behavior ofMetallicMaterials Prepared via Alternative Production Methods”.
文摘The paper deals with the FEM(Finite Element Method)simulation of rotary swaging of Dievar alloy produced by additive manufacturing technology Selective Laser Melting and conventional process.Swaging was performed at a temperature of 900℃.True flow stress-strain curves were determined for 600℃–900℃and used to construct a Hensel-Spittel model for FEM simulation.The process parameters,i.e.,stress,temperature,imposed strain,and force,were investigation during the rotary swaging process.Firstly,the stresses induced during rotary swaging and the resistance of the material to deformation were investigated.The amount and distribution of imposed strain in the cross-section can serve as a valuable indicator of the reduction in porosity and the texture evolution of the material.The simulation revealed the force required to swag the Dievar alloy.It also showed the evolution of temperature,which is important for phase transformation during solidification.Furthermore,microstructure evolutionwas observed before and then after rotary swaging.Dievar alloy is a critical material in the manufacture of dies for high-pressure die casting,forging tools,and other equipment subjected to high temperatures and mechanical loads.Understanding its viscoelastoplastic behavior under rotary swaging conditions is essential to optimize its performance in these demanding industrial applications.
文摘The effect of Ca addition on modification of primary Mg_(2)Si,hardness and wear behavior in Mg-5 wt.%Si hypereutectic alloy has been investigated.The results showed clearly that without Ca addition,most of primary Mg_(2)Si appeared as coarse dendritic morphology with average size of about 215μm.With the addition of 0.1 wt.%Ca,the average size of primary Mg_(2)Si decreased to about 98μm,but their morphologies did not significantly changed.As the addition level of Ca increased to 0.3 wt.%,the average size of primary Mg_(2)Si decreased significantly to about 50μm and their morphologies changed to polyhedral shape.However,with further increasing Ca addition to 0.6 wt.%and 1 wt.%,some needle-like and blocky CaMgSi particles formed and the average size of primary Mg_(2)Si increased slightly,which could described as over-modification.The present work showed that the optimal modification effect could be obtained when the Ca content in the investigated alloy reached 0.3 wt.%.The modification mechanism may be referred mainly due to poisoning effect resulting from the segregation of Ca atoms at the growth front of the Mg_(2)Si and the adsorption effect of some Ca atoms in the Mg_(2)Si crystal growth plane.The 0.3 wt.%Ca-added alloy has the highest hardness value and the best wear resistance among all other alloys.An excessive Ca addition resulted in the formation of some needle-like and blocky CaMgSi particles,which was detrimental to hardness and wear behavior of the 0.6 wt.%and 1 wt.%Ca-added alloys.The wear mechanism of investigated alloys is a mild abrasive oxidative wear with little adhesion.
基金the National Natural Science Foundation of China(No.51605163)Alexander von Humboldt Foundation of Germany(2019)+1 种基金Hunan Provincial Key R&D Project(No.GK2050)Zhejiang Provincial Natural Science Foundation(No.LR17E050002)。
文摘Based on the special physical–chemical characteristics of optical crystal in the field of aeronautics,a new anhydrous based shear-thickening polishing(ASTP)method has been proposed to restrain deliquescence and to improve physical properties for KDP machining.The ultraprecision polishing of KDP crystal is completed by ASTP.A kind of anhydrous based thickening polishing slurry(ATPS)was proposed in our work,and high-performance rheological properties were determined to achieve the ASTP of KDP crystal.A material removal model of ASTP in KDP machining is established,followed by the verification experiment of the prediction model.The maximum error of the predictive model is only 9.8%,which proves the validity of the material removal model for KDP polishing.The polishing experiments were carried out on the polishing platform developed by ourselves.The results show that the new polishing method can polish20 mm×20 mm×5 mm KDP crystal and obtain a super-smooth surface with a surface roughness of 1.37 nm and high shape accuracy.The surface accuracy of polished KDP crystal reaches up to0.68 k(RMS).The experimental results show that the ASTP is a potential ultra-precision machining method for KDP crystal.
文摘Magnesium (Mg) and its alloys are one of a novel kind of biodegradable metallic implants which attracted much fundamental research to develop its clinical application. Nevertheless, it has more restrictions in biomedical applications because it degrades too fast at the early stage after implantation, thus commonly leading to some problems such as early fast mechanical loss, hydric bubble aggregation, gap formation between the implants and the tissue. This work aims to study the effect of 0.5 wt% Sb addition on the microstructure, mechanical properties and degradation behavior of as cast Mg-4wt% Zn alloy. The evaluation process was conducted using optical and scanning electron microscopy, X-ray diffraction, tensile and compression tests, in addition to a corrosion study by immersing in simulated body fluid (SBF). Results showed that Sb refines the grain size of the base alloy and also enhances its mechanical properties and degradation rate as well. These were due to the formation of the secondary phase of Mg3Sb2. To get better degradation rate, the Mg-4wt% Zn and Mg-4wt% Zn-0.5wt% Sb alloys are coated with Ca-P using autocatalytic technique. The results demonstrated that the formed coat layer improves the degradation rate of samples under the condition of this study. The current study shows that Mg-4wt% Zn-0.5wt% Sb alloy has good mechanical properties and when it coated by Ca-P, it gave a better corrosion resistance that makes it ideal for biodegradable medical application.
文摘Natural fibre reinforced polymer composite(NFRPC)materials are gaining popularity in the modern world due to their eco-friendliness,lightweight nature,life-cycle superiority,biodegradability,low cost,and noble mechanical properties.Due to the wide variety of materials available that have comparable attributes and satisfy the requirements of the product design specification,material selection has become a crucial component of design for engineers.This paper discusses the study’s findings in choosing the suitable thermoplastic matrices of Natural Fibre Composites for Cyclist Helmet utilising the DMAIC,and GRA approaches.The results are based on integrating two decision methods implemented utilising two distinct decision-making approaches:qualitative and quantitative.This study suggested thermoplastic polyethylene as a particularly ideal matrix in composite cyclist helmets during the selection process for the best thermoplastic matrices material using the 6σtechnique,with the decision based on the highest performance,the lightest weight,and the most environmentally friendly criteria.The DMAIC and GRA approach significantly influenced the material selection process by offering different tools for each phase.In the future study,selection technique may have been more exhaustive if more information from other factors had been added.
文摘In this study, the characteristics of Graphite/Epoxy Composites (GECs) are evaluated from mechanical perspectives. Different weight percentages of graphite were used (0 - 7 wt%) for tensile and hardness experiments. Then the findings were discussed to ascertain the optimum mixing ratio of the graphite with the epoxy. The primary finding of this study is that the graphite weight fraction has a substantial impact on the composites’ mechanical performance. At a low percentage (1 wt%), the graphite has little influence on the tensile behaviour. An intermediate weight percentage of the graphite is considered optimum for mechanical performance in the epoxy composites as it slightly reduces the tensile properties and significantly improves the hardness. Micrographs of the fractured surface of specimens showed many signs that clearly explained why fractures had occurred. For instance, when graphite/epoxy composite contained a low proportion of graphite, the cleavage failure was very easy to observe because there was no sign of aggregation or the detachment of fillers.
文摘This paper reviews the machinability and mechanical properties of natural fiber-reinforced composites. Coupling agents, operating parameters, as well as chemical treatment effects on natural fiber-reinforced composites’ machinability are also reviewed. Moreover, the impacts of fibers’ physical properties on the machinability of the composite are mentioned. Fiber volume fraction (V<sub>f</sub>), fiber orientation as well as chemical treatment effects on mechanical properties are also defined. Conclusively, the effect of fibers’ physical properties as well as mechanical properties is described. It was discovered that chemical treatment of natural fibers improved their compatibility with the matrix by removing their surface tissues, increasing the roughness average (Ra), and reducing moisture absorption. Also, the Orientation of the fiber plays an important role in controlling the mechanical properties of the composite. Moreover, some physical properties of the fibers, including quality of fiber distributed in the matrix;fiber size, length, and diameter;moisture absorption;porosity and the way fibers break during compounding with the matrix, were found to affect the mechanical properties of the composites formed.
基金the financial support from National Natural Science Foundation of China(Nos.51775046&51875043&52005040)Beijing Municipal Natural Science Foundation(No.JQ20014).
文摘The machining accuracy of the curved surfaces of integrated turbine blades directly determines the performance and service life of the turbojet engine system.In this paper,a non-contact on-machine measurement system is developed for precision milling of integrated turbines to reduce the impact of workpiece deformation,overcutting,tool chatter,and material work hardening.Milling with the on-machine measurement system obtained high-quality integrated turbine surfaces.The geometric accuracy error(PV)is below 3μm,and the surface roughness(Ra)is less than 2μm.The processed integrated turbine blade can achieve the accuracy requirements in the design and manufacturing and can be practically applied to the entire turbojet engine.
文摘The wear profile analysis,obtained by different tribometers,is essential to characterise the wear mechanisms.However,most of the available methods did not take the stress distribution over the wear profile in consideration,which causes inaccurate analysis.In this study,the wear profile of polymer–metal contact,obtained by block-on-ring configuration under dry sliding conditions,was analysed using finite element modelling(FEM)and experimental investigation.Archard’s wear equation was integrated into a developed FORTRAN-UMESHMOTION code linked with Abaqus software.A varying wear coefficient(k)values covering both running-in and steady state regions,and a range of applied loads involving both mild and severe wear regions were measured and implemented in the FEM.The FEM was in good agreement with the experiments.The model reproduced the stress distribution profiles under variable testing conditions,while their values were affected by the sliding direction and maximum wear depth(hmax).The largest area of the wear profile,exposed to the average contact stresses,is defined as the normal zone.Whereas the critical zones were characterized by high stress concentrations reaching up to 10 times of that at the normal zone.The wear profile was mapped to identify the critical zone where the stress concentration is the key point in this definition.The surface features were examined in different regions using scanning electron microscope(SEM).Ultimately,SEM analysis showed severer damage features in the critical zone than that in the normal zone as proven by FEM.However,the literature data presented and considered the wear features the same at any point of the wear profile.In this study,the normal zone was determined at a stress value of about 0.5 MPa,whereas the critical zone was at about 5.5 MPa.The wear behaviour of these two zones showed totally different features from one another.
