New research and development(R&D)institutions are an important part of the national innovation system,playing an important role in promoting the transformation of scientific and technological achievements.In recen...New research and development(R&D)institutions are an important part of the national innovation system,playing an important role in promoting the transformation of scientific and technological achievements.In recent years,new R&D institutions have gradually become the driving force of innovation-driven development in China.Taking new R&D institutions in Zhejiang Province as the research object,this paper studies the internal talent training path and performance evaluation mechanism of new R&D institutions in Zhejiang Province by using the literature research method,comparison method,case verification method,and other methods.The investigation results show that there are problems such as lack of material and spiritual support and neglect of the absorption of local talents in the internal talent training,and there are problems such as unclear standards,insufficient data,and opaque processes in the performance evaluation mechanism,which greatly affect the establishment and improvement of the performance evaluation mechanism.Given the above problems,this paper puts forward a forward-looking,oriented,flexible,and compatible talent training path and performance evaluation mechanism,hoping to optimize the effective internal talent training path of new R&D institutions,improve the evaluation performance,and promote healthy development of new R&D institutions in Zhejiang Province.展开更多
One dimensional(1D) and three dimensional(3D) ultrasound sources were applied to the solidification process of Mg_(71.5)Zn_(26.1)Y_(2.4) alloy.The acoustic spectra were in-situ measured, based on which the cavitation ...One dimensional(1D) and three dimensional(3D) ultrasound sources were applied to the solidification process of Mg_(71.5)Zn_(26.1)Y_(2.4) alloy.The acoustic spectra were in-situ measured, based on which the cavitation intensities and dynamic solidification mechanism were further investigated. With the increase of ultrasonic dimension and amplitude, the primary Mg_(3)Zn_(6)Y phase was significantly refined from petals to nearly pentagonal shape. The sound field measurements showed that the transient cavitation played a decisive role in generating a high local undercooling, which facilitated the formation of icosahedral clusters and promoted the nucleation of primary Mg_(3)Zn_(6)Y phase. The morphological transition of(α-Mg+Mg_(3)Zn_(6)Y) eutectic from lamellar to anomalous structure occurred under 3D ultrasonic condition. The stable cavitation took the main responsibility because the high pressure excited by nonlinearly oscillating bubbles induced the preferential nucleation of α-Mg phase rather than Mg_(3)Zn_(6)Y phase. As compared with its static values, the tensile strength and compression plasticity of this alloy were increased by the factors of 1.9 and 2.1, and its corrosion resistance was also improved with the corrosion current density decreased by one order of magnitude.展开更多
The landing buffer is an important problem in the research on bionic locust jumping robots, and the different modes of landing and buffering can affect the dynamic performance of the buffering process significantly. B...The landing buffer is an important problem in the research on bionic locust jumping robots, and the different modes of landing and buffering can affect the dynamic performance of the buffering process significantly. Based on an experimental observation, the different modes of landing and buffering are determined, which include the different numbers of landing legs and different motion modes of legs in the buffering process. Then a bionic locust mechanism is established, and the springs are used to replace the leg muscles to achieve a buffering effect. To reveal the dynamic performance in the buffering process of the bionic locust mechanism, a dynamic model is established with different modes of landing and buffering. In particular, to analyze the buffering process conveniently, an equivalent vibration dynamic model of the bionic locust mechanism is proposed.Given the support forces of the ground to the leg links, which can be obtained from the dynamic model, the spring forces of the legs and the impact resistance of each leg are the important parameters affecting buffering performance, and evaluation principles for buffering performance are proposed according to the aforementioned parameters. Based on the dynamic model and these evaluation principles, the buffering performances are analyzed and compared in different modes of landing and buffering on a horizontal plane and an inclined plane. The results show that the mechanism with the ends of the legs sliding can obtain a better dynamic performance. This study offers primary theories for buffering dynamics and an evaluation of landing buffer performance,and it establishes a theoretical basis for studies and engineering applications.展开更多
In the induction heating of airport pavement to remove snow and ice,soft magnetic geopolymer composite(SMGC)can be used to gather the dissipated electromagnetic energy,thus enhancing the energy utilization efficiency....In the induction heating of airport pavement to remove snow and ice,soft magnetic geopolymer composite(SMGC)can be used to gather the dissipated electromagnetic energy,thus enhancing the energy utilization efficiency.The aim of this work is to analyze the influence mechanism of iron powder content on the electromagnetic and mechanical performance of SMGC,so as to provide theoretical guidance for the design of soft magnetic layer within airport pavement structure.The results show that the increase of iron powder content reduces the resistance and magnetoresistance of SMGC by decreasing the content of non-magnetic phases between iron powder.However,the reduction of iron powder spacing also provides a shorter transmission path for the inter-particle eddy currents in the SMGC specimen,which enhances the exchange coupling between iron powder,thus increasing the electromagnetic loss.Therefore,the compatibility between magnetic permeability and electromagnetic loss should be considered comprehensively in the mix design of SMGC.In addition,although iron powder can enhance the mechanical properties of SMGC by improving the density of geopolymer matrix,the excessive amount of iron powder can lead to a weak interfacial transition zone between geopolymer matrix and iron powder.According to the induction heating results,optimized SMGC can improve the energy transfer efficiency of induction heating by 24.03%.展开更多
Vocational education is an effective way to achieve accurate poverty alleviation and get rid of intergenerational poverty.Vocational education is mainly to train skilled talents,not only to provide academic education ...Vocational education is an effective way to achieve accurate poverty alleviation and get rid of intergenerational poverty.Vocational education is mainly to train skilled talents,not only to provide academic education for the children of poor families,but also to use a skill to achieve employment.It is of great necessity to implement accurate poverty alleviation in vocational education,and performance assessment is a very important part of the accurate poverty alleviation work of vocational education.This paper mainly analyzes the predicament of accurate poverty alleviation in vocational education and the problems in the construction of performance assessment system for accurate poverty alleviation in vocational education,and puts forward measures to improve the accurate poverty alleviation assessment system for vocational education and strengthen the accurate of vocational education.展开更多
The composites were prepared by modifying silicon carbide fiber with particles of zirconium carbide(ZrC)and boron carbide(B_(4)C)and incorporating them into a phenolic resin matrix.The influence of ZrC and B_(4)C on t...The composites were prepared by modifying silicon carbide fiber with particles of zirconium carbide(ZrC)and boron carbide(B_(4)C)and incorporating them into a phenolic resin matrix.The influence of ZrC and B_(4)C on the mechanical performance of SiCf/phenolic composites after high-temperature pyrolysis was studied through flexural performance test.The results show that the composite material has good thermal stability and high-temperature mechanical properties.After static ablation at 1400℃ for 15 minutes,the flexural strength of the composite material reaches 286 MPa,which is still 7.3%higher than at room temperature,indicating that the composite material still has good mechanical properties even after heat treatment at 1400℃.展开更多
In this paper,the influence of NaCl freeze-thaw(F-T)cycles and dry-wet(D-W)alternations on theflexural,com-pressive and bonding strengths of alkali-activatedfly ash(FA)and a blast furnace slag powder(BFS)is investi-gated...In this paper,the influence of NaCl freeze-thaw(F-T)cycles and dry-wet(D-W)alternations on theflexural,com-pressive and bonding strengths of alkali-activatedfly ash(FA)and a blast furnace slag powder(BFS)is investi-gated.The considered NaCl concentration is 3%.The effect of polypropylenefibers on the mechanical strengths is also examined.Scanning electron microscopy(SEM),thermogravimetry(TG)and X-ray diffraction(XRD)are selected to discern the mechanisms underpinning the NaCl-induced erosion.The obtained results indicate that the best results in terms of material resistance are obtained with admixtures containing 60%BFS and 40%FA in terms of mass ratio and 3%polypropylenefibers in terms of volume ratio.The maximum rates of decrease of theflexural,compressive and bonding strengths after 300 NaCl F-T cycles are 21.5%,20.3%and 22.6%,respec-tively.The corresponding rates of decrease due to NaCl D-W alternations are 28.1%,26.1%and 31.5%,respec-tively.The TG curves show that the alkali-activating activity of BFS is higher than that of FA.Moreover,in thefirst case,the microstructure of the hydration products is more compact.The results also show that NaCl F-T cycles lead to increasing cracks in the alkali-activated BFS.展开更多
Biomedical magnesium(Mg)alloys have garnered significant attention because of their unique biodegradability,favorable biocompatibility,and suitable mechanical properties.The incorporation of rare earth(RE)elements,wit...Biomedical magnesium(Mg)alloys have garnered significant attention because of their unique biodegradability,favorable biocompatibility,and suitable mechanical properties.The incorporation of rare earth(RE)elements,with their distinct physical and chemical properties,has greatly contributed to enhancing the mechanical performance,degradation behavior,and biological performance of biomedical Mg alloys.Currently,a series of RE-Mg alloys are being designed and investigated for orthopedic implants and cardiovascular stents,achieving substantial and encouraging research progress.In this work,a comprehensive summary of the state-of-the-art in biomedical RE-Mg alloys is provided.The physiological effects and design standards of RE elements in biomedical Mg alloys are discussed.Particularly,the degradation behavior and mechanical properties,including their underlying action are studied in-depth.Furthermore,the preparation techniques and current application status of RE-Mg alloys are reviewed.Finally,we address the ongoing challenges and propose future prospects to guide the development of high-performance biomedical Mg-RE alloys.展开更多
Magnesium(Mg)alloys are considered to be a new generation of revolutionary medical metals.Laser-beam powder bed fusion(PBF-LB)is suitable for fabricating metal implants withpersonalized and complicated structures.Howe...Magnesium(Mg)alloys are considered to be a new generation of revolutionary medical metals.Laser-beam powder bed fusion(PBF-LB)is suitable for fabricating metal implants withpersonalized and complicated structures.However,the as-built part usually exhibits undesirable microstructure and unsatisfactory performance.In this work,WE43 parts were firstly fabricated by PBF-LB and then subjected to heat treatment.Although a high densification rate of 99.91%was achieved using suitable processes,the as-built parts exhibited anisotropic and layeredmicrostructure with heterogeneously precipitated Nd-rich intermetallic.After heat treatment,fine and nano-scaled Mg24Y5particles were precipitated.Meanwhile,theα-Mg grainsunderwent recrystallization and turned coarsened slightly,which effectively weakened thetexture intensity and reduced the anisotropy.As a consequence,the yield strength and ultimate tensile strength were significantly improved to(250.2±3.5)MPa and(312±3.7)MPa,respectively,while the elongation was still maintained at a high level of 15.2%.Furthermore,the homogenized microstructure reduced the tendency of localized corrosion and favoredthe development of uniform passivation film.Thus,the degradation rate of WE43 parts was decreased by an order of magnitude.Besides,in-vitro cell experiments proved their favorable biocompatibility.展开更多
The effect of rare earth element Ce on mechanical performance and electrical conductivity of aluminum rod for electrical purpose were studied under industrial production condition. Using optical microscope, SEM, TEM, ...The effect of rare earth element Ce on mechanical performance and electrical conductivity of aluminum rod for electrical purpose were studied under industrial production condition. Using optical microscope, SEM, TEM, EDS and X-ray diffractometer, the microstructure and phase composition of aluminum rod were measured and analyzed. The results indicate that the content of rare earth element Ce is between 0.05% -0.16% in the aluminum rod for electrical purpose. Its tensile strength is enhanced to some extent. The research also discovers that the tensile strength is enhanced remarkably with impurity element Si content increases. Because influence of Si is big to the conductivity, the Si content should be controlled continuously strictly in the aluminum for electrical purpose. Adding rare earth element Ce reduces the solid solubility of Si in the aluminum matrix, and the negative effect of Si on the aluminum conductor reduces effectively. So the limit of in Si content in aluminum rod for electrical purpose can be relaxed moderately.展开更多
Rare earth -containing PSBR sheet was prepared by reaction of rare earth alkoxide with quaternary ammonium salt of pyridine modified SBR (PSBR) latex, and then it was blended with natural rubber (NR) to produce rare e...Rare earth -containing PSBR sheet was prepared by reaction of rare earth alkoxide with quaternary ammonium salt of pyridine modified SBR (PSBR) latex, and then it was blended with natural rubber (NR) to produce rare earth - containing composite elastomer. It is found that mechanical performance can be improved remarkably. Analyzed by infrared spectrometry (IR), differential scanning calorimetry (DSC) and cross-linking densitometry, the relationship between structure and performance was discussed.展开更多
It is essential to design economic and efficient tougheners to prepare high-performance epoxy resin;however,this has remained a huge challenge.Herein,an eco-friendly,low-cost,and facile-fabricated bio-based hyperbranc...It is essential to design economic and efficient tougheners to prepare high-performance epoxy resin;however,this has remained a huge challenge.Herein,an eco-friendly,low-cost,and facile-fabricated bio-based hyperbranched toughener,carboxylic acid-functionalized tannic acid(CATA),was successfully prepared and applicated to the preparation of solvent-free epoxy resins.The mechanical performance,morphology,structural characterization,and thermal characterization of toughened epoxy resin system were studied.The toughened epoxy resin system with only 1.0wt%CATA reached the highest impact strength,111%higher than the neat epoxy resin system.Notably,the tensile strength and elongation at break of toughened epoxy resin systems increased moderately with increasing CATA loading.Nonphase-separated hybrids with significant toughening effect were obtained.Additionally,the thermal stabilities of toughened epoxy resin systems decreased with increasing CATA loading.This study provides an eco-friendly,cost-effective,and facile approach for the preparation of high-performance,solvent-free epoxy resins with potential for practical applications in sealing integrated circuits and electrical devices fields.展开更多
The aim of this study is to provide the quantificational change laws of strength,stiffness,and deformation capacity of frost-damaged concrete relating to a united index,the data were obtained by different researchers....The aim of this study is to provide the quantificational change laws of strength,stiffness,and deformation capacity of frost-damaged concrete relating to a united index,the data were obtained by different researchers.Then the index of relative compressive strength(RCS) was introduced as the indicator of frost damage and a large number of mechanical performance testing data of frost-damaged concrete were collected and analyzed.By curve fitting,the correlations between RCS and the initial elastic modulus,the strain at peak compressive stress,and biaxial compressive strength,and tensile strength,and the strain at peak tensile stress were established.Thereafter,the analytical stress-strain response of frost-damaged concrete under monotonic loading was presented using RCS and compared with that of the experimental data.Moreover,an isotropic elastoplastic damage model of frost-damaged concrete subjected to repeated loading was established.Finally,we can systematically estimate the effects of frost-damage on the mechanical performance of concrete,which can be provided for the numerical simulation of frost-damaged concrete structures.展开更多
Nitrogen doped diamond-like carbon (DLC:N) films were prepared by electron cyclotron resonance chemical vapor deposition (ECR-CVD) on polycrystalline Si chips. Film thickness is about 50 nm. Auger electron spectr...Nitrogen doped diamond-like carbon (DLC:N) films were prepared by electron cyclotron resonance chemical vapor deposition (ECR-CVD) on polycrystalline Si chips. Film thickness is about 50 nm. Auger electron spectroscopy (AES) was used to evaluate nitrogen content, and increasing N2 flow improved N content from 0 to 7.6%. Raman and X-ray photoelectron spectroscopy (XPS) analysis results reveal CN-sp^3C and N-sp^2C structure. With increasing the N2 flow, sp^3C decreases from 73.74% down to 42.66%, and so does N-sp^3C from 68.04% down to 20.23%. The hardness decreases from 29.18 GPa down to 19.74 GPa, and the Young's modulus from 193.03 GPa down to 144.52 GPa.展开更多
On the basis of test, nonlinear finite element analysis of reinforcedconcrete (R. C) short-limb shear walls under monotonic horizontal load are carried out by ANSYSprogram in order to understand the evolution of crack...On the basis of test, nonlinear finite element analysis of reinforcedconcrete (R. C) short-limb shear walls under monotonic horizontal load are carried out by ANSYSprogram in order to understand the evolution of cracking, deformation and failure course of thespecimens. At the same time, the results of numerical calculation are compared with the results oftest. The results indicate that, under monotonic horizontal load the failures of the specimens withflange wall and without flange wall all occur at the intersections of lintel bottom and limb ofwall, the failures also occur at the bottom of limb; the load-displacement curve of wall withoutflange is steeper than that of wall with flange, and the ductility is worse than that of wall withflange; the results, such as cracking, deformation, yield load and so on of finite element analysisagree well with the results of test. These results provide theoretical basis of study andapplication of R. C short-limb shear wall.展开更多
The two kinds of rigid polyurethane(PU) foams were prepared with respectively adding the refined alkali lignin and alkali lignin modified by 3-chloro-1,2-epoxypropane to be instead of 15% of the polyether glycol in we...The two kinds of rigid polyurethane(PU) foams were prepared with respectively adding the refined alkali lignin and alkali lignin modified by 3-chloro-1,2-epoxypropane to be instead of 15% of the polyether glycol in weight.The indexes of mechanical performance, apparent density, thermal stability and aging resistance were separately tested for the prepared PU foams.The results show that the mechanical property, thermal insulation and thermal stability for PU foam with modified alkali lignin are excellent among two kinds of PU foams and control samples.The additions of the refined alkali lignin and modified alkali lignin to PU foam have little effect on the natural aging or heat aging resistance except for decreasing hot alkali resistance apparently.Additionally, the thermal conductivity of modified alkali lignin PU foam is lowest among two kinds of PU foams and control samples.The alkali lignin PU foam modified by 3-chloro-1,2-epoxypropane could be applied in the heat preservation field.展开更多
An advanced ceramic cutting tool material Al2O3/TiC/TiN (LTN) is developed by incorporation and dispersion of micro-scale TiC particle and nano-scale TiN particle in alumina matrix. With the optimal dispersing and f...An advanced ceramic cutting tool material Al2O3/TiC/TiN (LTN) is developed by incorporation and dispersion of micro-scale TiC particle and nano-scale TiN particle in alumina matrix. With the optimal dispersing and fabricating technology, this multi-scale and multi-phase nanocomposite ceramic tool material can get both higher flexural strength and fracture toughness than that of A1203/TiC (LZ) ceramic tool material without nano-scale TiN particle, especially the fracture toughness can reach to 7.8 MPa . m^0.5. The nano-scale TiN can lead to the grain fining effect and promote the sintering process to get a higher density. The coexisting transgranular and intergranular fracture mode induced by micro-scale TiC and nano-scale TiN, and the homogeneous and densified microstructure can result in a remarkable strengthening and toughening effect. The cutting performance and wear mechanisms of the advanced multi-scale and multi-phase nanocomposite ceramic cutting tool are researched.展开更多
The multi-impact characteristics and failure mechanism of two kinds of automotive engine chain made in China are studied through engine assembly and road-drive tests. The worn surface morphologies of rubbing area betw...The multi-impact characteristics and failure mechanism of two kinds of automotive engine chain made in China are studied through engine assembly and road-drive tests. The worn surface morphologies of rubbing area between pin, bush and roller are also analyzed based on scanning electron microscope. The results show that the main wear mechanism of automotive engine chain is fatigue wear, and its failure mechanism is the forming, extending and flaking of cracks on top layer of pin and bush. In addition, the material, hot-treatment method and shaping technique for roller have a great influence upon the resistance to multi-impact. Ensuring sufficient strength and plasticity of roller, as well as adopting suitable shaping technique are the effective method to increase its resistance to multi-impact.展开更多
Motivated by the huge practical engineering demand for the fundamental understanding of mechanical characteristics of high-speed railway infrastructure,a fullscale multi-functional test platform for high-speed railway...Motivated by the huge practical engineering demand for the fundamental understanding of mechanical characteristics of high-speed railway infrastructure,a fullscale multi-functional test platform for high-speed railway track–subgrade system is developed in this paper,and its main functions for investigating the mechanical performance of track–subgrade systems are elaborated with three typical experimental examples.Comprising the full-scale subgrade structure and all the five types of track structures adopted in Chinese high-speed railways,namely the CRTS I,the CRTS II and the CRTS III ballastless tracks,the double-block ballastless track and the ballasted track,the test platform is established strictly according to the construction standard of Chinese high-speed railways.Three kinds of effective loading methods are employed,including the real bogie loading,multi-point loading and the impact loading.Various types of sensors are adopted in different components of the five types of track–subgrade systems to measure the displacement,acceleration,pressure,structural strain and deformation,etc.Utilizing this test platform,both dynamic characteristics and long-term performance evolution of high-speed railway track–subgrade systems can be investigated,being able to satisfy the actual demand for large-scale operation of Chinese high-speed railways.As examples,three typical experimental studies are presented to elucidate the comprehensive functionalities of the full-scale multi-functional test platform for exploring the dynamic performance and its long-term evolution of ballastless track systems and for studying the long-term accumulative settlement of the ballasted track–subgrade system in high-speed railways.Some interesting phenomena and meaningful results are captured by the developed test platform,which provide a useful guidance for the scientific operation and maintenance of high-speed railway infrastructure.展开更多
Continuous CNT fibers have been directly fabricated in a speed of 50 m/h-400 m/h,based on an improved chemical vapor deposition method.As-prepared fibers are further post-treated by acid.According to the SEM images an...Continuous CNT fibers have been directly fabricated in a speed of 50 m/h-400 m/h,based on an improved chemical vapor deposition method.As-prepared fibers are further post-treated by acid.According to the SEM images and Raman spectra,the acid treatment results in the compaction and surface modification of the CNTs in fibers,which are beneficial for the electron and load transfer.Compared to the HNO3 treatment,HClSO_3 or H_2SO_4 treatment is more effective for the improvement of the fibers' properties.After HCISO_3 treatment for 2 h,the fibers' strength and electrical conductivity reach up to-2 GPa and-4.3 MS/m,which are promoted by-200%and almost one order of magnitude than those without acid treatment,respectively.The load-bearing status of the CNT fibers are analyzed based on the downshifts of the G' band and the strain transfer factor of the fibers under tension.The results reveal that acid treatment could greatly enhance the load transfer and inter-bundle strength.With the HCISO3 treatment,the strain transfer factor is enhanced from-3.9%to-53.6%.展开更多
文摘New research and development(R&D)institutions are an important part of the national innovation system,playing an important role in promoting the transformation of scientific and technological achievements.In recent years,new R&D institutions have gradually become the driving force of innovation-driven development in China.Taking new R&D institutions in Zhejiang Province as the research object,this paper studies the internal talent training path and performance evaluation mechanism of new R&D institutions in Zhejiang Province by using the literature research method,comparison method,case verification method,and other methods.The investigation results show that there are problems such as lack of material and spiritual support and neglect of the absorption of local talents in the internal talent training,and there are problems such as unclear standards,insufficient data,and opaque processes in the performance evaluation mechanism,which greatly affect the establishment and improvement of the performance evaluation mechanism.Given the above problems,this paper puts forward a forward-looking,oriented,flexible,and compatible talent training path and performance evaluation mechanism,hoping to optimize the effective internal talent training path of new R&D institutions,improve the evaluation performance,and promote healthy development of new R&D institutions in Zhejiang Province.
基金financially supported by National Natural Science Foundation of China (nos.52088101 and 52130405)Basic Research Project of Shaanxi Natural Science Foundation (no: 2021JCW-09 and 2023-JC-JQ-28)Key R&D Plan of Shaanxi Province-Key Industrial Innovation Chain Project (no: 2020ZDLGY13-03)。
文摘One dimensional(1D) and three dimensional(3D) ultrasound sources were applied to the solidification process of Mg_(71.5)Zn_(26.1)Y_(2.4) alloy.The acoustic spectra were in-situ measured, based on which the cavitation intensities and dynamic solidification mechanism were further investigated. With the increase of ultrasonic dimension and amplitude, the primary Mg_(3)Zn_(6)Y phase was significantly refined from petals to nearly pentagonal shape. The sound field measurements showed that the transient cavitation played a decisive role in generating a high local undercooling, which facilitated the formation of icosahedral clusters and promoted the nucleation of primary Mg_(3)Zn_(6)Y phase. The morphological transition of(α-Mg+Mg_(3)Zn_(6)Y) eutectic from lamellar to anomalous structure occurred under 3D ultrasonic condition. The stable cavitation took the main responsibility because the high pressure excited by nonlinearly oscillating bubbles induced the preferential nucleation of α-Mg phase rather than Mg_(3)Zn_(6)Y phase. As compared with its static values, the tensile strength and compression plasticity of this alloy were increased by the factors of 1.9 and 2.1, and its corrosion resistance was also improved with the corrosion current density decreased by one order of magnitude.
基金supported by the National Natural Science Foundation of China (Grant 51375035)the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant 20121102110021)
文摘The landing buffer is an important problem in the research on bionic locust jumping robots, and the different modes of landing and buffering can affect the dynamic performance of the buffering process significantly. Based on an experimental observation, the different modes of landing and buffering are determined, which include the different numbers of landing legs and different motion modes of legs in the buffering process. Then a bionic locust mechanism is established, and the springs are used to replace the leg muscles to achieve a buffering effect. To reveal the dynamic performance in the buffering process of the bionic locust mechanism, a dynamic model is established with different modes of landing and buffering. In particular, to analyze the buffering process conveniently, an equivalent vibration dynamic model of the bionic locust mechanism is proposed.Given the support forces of the ground to the leg links, which can be obtained from the dynamic model, the spring forces of the legs and the impact resistance of each leg are the important parameters affecting buffering performance, and evaluation principles for buffering performance are proposed according to the aforementioned parameters. Based on the dynamic model and these evaluation principles, the buffering performances are analyzed and compared in different modes of landing and buffering on a horizontal plane and an inclined plane. The results show that the mechanism with the ends of the legs sliding can obtain a better dynamic performance. This study offers primary theories for buffering dynamics and an evaluation of landing buffer performance,and it establishes a theoretical basis for studies and engineering applications.
基金This work was supported by National Key Research and Development Project(2020YFB1600102,2020YFA0714302)National Natural Science Foundation of China(51878164,51922030,52208430)+2 种基金Fundamental Research Funds for the Central Universities of China(2242022R10059)Natural Science Foundation of Jiangsu Province(SBK2021042206)Southeast University“Zhongying Young Scholars”Project,and Shuangchuang Program of Jiangsu Province(JSSCBS20210058).
文摘In the induction heating of airport pavement to remove snow and ice,soft magnetic geopolymer composite(SMGC)can be used to gather the dissipated electromagnetic energy,thus enhancing the energy utilization efficiency.The aim of this work is to analyze the influence mechanism of iron powder content on the electromagnetic and mechanical performance of SMGC,so as to provide theoretical guidance for the design of soft magnetic layer within airport pavement structure.The results show that the increase of iron powder content reduces the resistance and magnetoresistance of SMGC by decreasing the content of non-magnetic phases between iron powder.However,the reduction of iron powder spacing also provides a shorter transmission path for the inter-particle eddy currents in the SMGC specimen,which enhances the exchange coupling between iron powder,thus increasing the electromagnetic loss.Therefore,the compatibility between magnetic permeability and electromagnetic loss should be considered comprehensively in the mix design of SMGC.In addition,although iron powder can enhance the mechanical properties of SMGC by improving the density of geopolymer matrix,the excessive amount of iron powder can lead to a weak interfacial transition zone between geopolymer matrix and iron powder.According to the induction heating results,optimized SMGC can improve the energy transfer efficiency of induction heating by 24.03%.
文摘Vocational education is an effective way to achieve accurate poverty alleviation and get rid of intergenerational poverty.Vocational education is mainly to train skilled talents,not only to provide academic education for the children of poor families,but also to use a skill to achieve employment.It is of great necessity to implement accurate poverty alleviation in vocational education,and performance assessment is a very important part of the accurate poverty alleviation work of vocational education.This paper mainly analyzes the predicament of accurate poverty alleviation in vocational education and the problems in the construction of performance assessment system for accurate poverty alleviation in vocational education,and puts forward measures to improve the accurate poverty alleviation assessment system for vocational education and strengthen the accurate of vocational education.
基金Funded by the Joint Fund of Ministry of Education for Equipment Pre-research(No.6141A02022250)the Fundamental Research Funds for the Central Universities,China(No.WUT:2021III003XZ)。
文摘The composites were prepared by modifying silicon carbide fiber with particles of zirconium carbide(ZrC)and boron carbide(B_(4)C)and incorporating them into a phenolic resin matrix.The influence of ZrC and B_(4)C on the mechanical performance of SiCf/phenolic composites after high-temperature pyrolysis was studied through flexural performance test.The results show that the composite material has good thermal stability and high-temperature mechanical properties.After static ablation at 1400℃ for 15 minutes,the flexural strength of the composite material reaches 286 MPa,which is still 7.3%higher than at room temperature,indicating that the composite material still has good mechanical properties even after heat treatment at 1400℃.
基金supported by 2023 University-Level Scientific Research Project of Ningbo Polytechnic(NZ23002)the First Batch of Ningbo Construction Scientific Research Projects in 2023(20230106).
文摘In this paper,the influence of NaCl freeze-thaw(F-T)cycles and dry-wet(D-W)alternations on theflexural,com-pressive and bonding strengths of alkali-activatedfly ash(FA)and a blast furnace slag powder(BFS)is investi-gated.The considered NaCl concentration is 3%.The effect of polypropylenefibers on the mechanical strengths is also examined.Scanning electron microscopy(SEM),thermogravimetry(TG)and X-ray diffraction(XRD)are selected to discern the mechanisms underpinning the NaCl-induced erosion.The obtained results indicate that the best results in terms of material resistance are obtained with admixtures containing 60%BFS and 40%FA in terms of mass ratio and 3%polypropylenefibers in terms of volume ratio.The maximum rates of decrease of theflexural,compressive and bonding strengths after 300 NaCl F-T cycles are 21.5%,20.3%and 22.6%,respec-tively.The corresponding rates of decrease due to NaCl D-W alternations are 28.1%,26.1%and 31.5%,respec-tively.The TG curves show that the alkali-activating activity of BFS is higher than that of FA.Moreover,in thefirst case,the microstructure of the hydration products is more compact.The results also show that NaCl F-T cycles lead to increasing cracks in the alkali-activated BFS.
基金supported by National Key Research and Development Program of China[2023YFB4605800]National Natural Science Foundation of China[51935014,52165043]+3 种基金JiangXi Provincial Natural Science Foundation of China[20224ACB204013,20224ACB214008]Jiangxi Provincial Cultivation Program for Academic and Technical Leaders of Major Subjects[20225BCJ23008]Anhui Provincial Natural Science Foundation[2308085ME171]The University Synergy Innovation Program of Anhui Province[GXXT-2023-025,GXXT-2023-026].
文摘Biomedical magnesium(Mg)alloys have garnered significant attention because of their unique biodegradability,favorable biocompatibility,and suitable mechanical properties.The incorporation of rare earth(RE)elements,with their distinct physical and chemical properties,has greatly contributed to enhancing the mechanical performance,degradation behavior,and biological performance of biomedical Mg alloys.Currently,a series of RE-Mg alloys are being designed and investigated for orthopedic implants and cardiovascular stents,achieving substantial and encouraging research progress.In this work,a comprehensive summary of the state-of-the-art in biomedical RE-Mg alloys is provided.The physiological effects and design standards of RE elements in biomedical Mg alloys are discussed.Particularly,the degradation behavior and mechanical properties,including their underlying action are studied in-depth.Furthermore,the preparation techniques and current application status of RE-Mg alloys are reviewed.Finally,we address the ongoing challenges and propose future prospects to guide the development of high-performance biomedical Mg-RE alloys.
基金supported by the following funds:National Natural Science Foundation of China(51935014,52165043)Jiangxi Provincial Cultivation Program for Academic and Technical Leaders of Major Subjects(20225BCJ23008)+1 种基金Jiangxi Provincial Natural Science Foundation(20224ACB204013,20224ACB214008)Scientific Research Project of Anhui Universities(KJ2021A1106)。
文摘Magnesium(Mg)alloys are considered to be a new generation of revolutionary medical metals.Laser-beam powder bed fusion(PBF-LB)is suitable for fabricating metal implants withpersonalized and complicated structures.However,the as-built part usually exhibits undesirable microstructure and unsatisfactory performance.In this work,WE43 parts were firstly fabricated by PBF-LB and then subjected to heat treatment.Although a high densification rate of 99.91%was achieved using suitable processes,the as-built parts exhibited anisotropic and layeredmicrostructure with heterogeneously precipitated Nd-rich intermetallic.After heat treatment,fine and nano-scaled Mg24Y5particles were precipitated.Meanwhile,theα-Mg grainsunderwent recrystallization and turned coarsened slightly,which effectively weakened thetexture intensity and reduced the anisotropy.As a consequence,the yield strength and ultimate tensile strength were significantly improved to(250.2±3.5)MPa and(312±3.7)MPa,respectively,while the elongation was still maintained at a high level of 15.2%.Furthermore,the homogenized microstructure reduced the tendency of localized corrosion and favoredthe development of uniform passivation film.Thus,the degradation rate of WE43 parts was decreased by an order of magnitude.Besides,in-vitro cell experiments proved their favorable biocompatibility.
基金Project supported by the Baotou Aluminum Co. Ltd.
文摘The effect of rare earth element Ce on mechanical performance and electrical conductivity of aluminum rod for electrical purpose were studied under industrial production condition. Using optical microscope, SEM, TEM, EDS and X-ray diffractometer, the microstructure and phase composition of aluminum rod were measured and analyzed. The results indicate that the content of rare earth element Ce is between 0.05% -0.16% in the aluminum rod for electrical purpose. Its tensile strength is enhanced to some extent. The research also discovers that the tensile strength is enhanced remarkably with impurity element Si content increases. Because influence of Si is big to the conductivity, the Si content should be controlled continuously strictly in the aluminum for electrical purpose. Adding rare earth element Ce reduces the solid solubility of Si in the aluminum matrix, and the negative effect of Si on the aluminum conductor reduces effectively. So the limit of in Si content in aluminum rod for electrical purpose can be relaxed moderately.
文摘Rare earth -containing PSBR sheet was prepared by reaction of rare earth alkoxide with quaternary ammonium salt of pyridine modified SBR (PSBR) latex, and then it was blended with natural rubber (NR) to produce rare earth - containing composite elastomer. It is found that mechanical performance can be improved remarkably. Analyzed by infrared spectrometry (IR), differential scanning calorimetry (DSC) and cross-linking densitometry, the relationship between structure and performance was discussed.
基金from the Special Fund for the Program for Zhejiang Provincial Natural Science Foundation of China(LZ16C160001)National Key Research and Development Program(2017YFD0601105),the National Natural Science Foundation of China(Grant No.21806142)the Zhejiang Provincial Natural Science Foundation of China(Grant No.LY20B070002).
文摘It is essential to design economic and efficient tougheners to prepare high-performance epoxy resin;however,this has remained a huge challenge.Herein,an eco-friendly,low-cost,and facile-fabricated bio-based hyperbranched toughener,carboxylic acid-functionalized tannic acid(CATA),was successfully prepared and applicated to the preparation of solvent-free epoxy resins.The mechanical performance,morphology,structural characterization,and thermal characterization of toughened epoxy resin system were studied.The toughened epoxy resin system with only 1.0wt%CATA reached the highest impact strength,111%higher than the neat epoxy resin system.Notably,the tensile strength and elongation at break of toughened epoxy resin systems increased moderately with increasing CATA loading.Nonphase-separated hybrids with significant toughening effect were obtained.Additionally,the thermal stabilities of toughened epoxy resin systems decreased with increasing CATA loading.This study provides an eco-friendly,cost-effective,and facile approach for the preparation of high-performance,solvent-free epoxy resins with potential for practical applications in sealing integrated circuits and electrical devices fields.
基金Funded by the Program of Innovative Team of the Ministry of Education of China(No.IRT13089)the National Natural Science Foundation of China(No.51078307)
文摘The aim of this study is to provide the quantificational change laws of strength,stiffness,and deformation capacity of frost-damaged concrete relating to a united index,the data were obtained by different researchers.Then the index of relative compressive strength(RCS) was introduced as the indicator of frost damage and a large number of mechanical performance testing data of frost-damaged concrete were collected and analyzed.By curve fitting,the correlations between RCS and the initial elastic modulus,the strain at peak compressive stress,and biaxial compressive strength,and tensile strength,and the strain at peak tensile stress were established.Thereafter,the analytical stress-strain response of frost-damaged concrete under monotonic loading was presented using RCS and compared with that of the experimental data.Moreover,an isotropic elastoplastic damage model of frost-damaged concrete subjected to repeated loading was established.Finally,we can systematically estimate the effects of frost-damage on the mechanical performance of concrete,which can be provided for the numerical simulation of frost-damaged concrete structures.
文摘Nitrogen doped diamond-like carbon (DLC:N) films were prepared by electron cyclotron resonance chemical vapor deposition (ECR-CVD) on polycrystalline Si chips. Film thickness is about 50 nm. Auger electron spectroscopy (AES) was used to evaluate nitrogen content, and increasing N2 flow improved N content from 0 to 7.6%. Raman and X-ray photoelectron spectroscopy (XPS) analysis results reveal CN-sp^3C and N-sp^2C structure. With increasing the N2 flow, sp^3C decreases from 73.74% down to 42.66%, and so does N-sp^3C from 68.04% down to 20.23%. The hardness decreases from 29.18 GPa down to 19.74 GPa, and the Young's modulus from 193.03 GPa down to 144.52 GPa.
文摘On the basis of test, nonlinear finite element analysis of reinforcedconcrete (R. C) short-limb shear walls under monotonic horizontal load are carried out by ANSYSprogram in order to understand the evolution of cracking, deformation and failure course of thespecimens. At the same time, the results of numerical calculation are compared with the results oftest. The results indicate that, under monotonic horizontal load the failures of the specimens withflange wall and without flange wall all occur at the intersections of lintel bottom and limb ofwall, the failures also occur at the bottom of limb; the load-displacement curve of wall withoutflange is steeper than that of wall with flange, and the ductility is worse than that of wall withflange; the results, such as cracking, deformation, yield load and so on of finite element analysisagree well with the results of test. These results provide theoretical basis of study andapplication of R. C short-limb shear wall.
基金The key project of "11th Five-Year Plan" in Heilongjiang Province (No. GB06B501-3)
文摘The two kinds of rigid polyurethane(PU) foams were prepared with respectively adding the refined alkali lignin and alkali lignin modified by 3-chloro-1,2-epoxypropane to be instead of 15% of the polyether glycol in weight.The indexes of mechanical performance, apparent density, thermal stability and aging resistance were separately tested for the prepared PU foams.The results show that the mechanical property, thermal insulation and thermal stability for PU foam with modified alkali lignin are excellent among two kinds of PU foams and control samples.The additions of the refined alkali lignin and modified alkali lignin to PU foam have little effect on the natural aging or heat aging resistance except for decreasing hot alkali resistance apparently.Additionally, the thermal conductivity of modified alkali lignin PU foam is lowest among two kinds of PU foams and control samples.The alkali lignin PU foam modified by 3-chloro-1,2-epoxypropane could be applied in the heat preservation field.
基金Selected from Proceedings of the 7th International Conference on Frontiers of DesignManufacturing(ICFDM'2006)This project is supported by National Natural Science Foundation of China(No.50275086)the University of New South Wales Visiting Professorship Scheme,Australia.
文摘An advanced ceramic cutting tool material Al2O3/TiC/TiN (LTN) is developed by incorporation and dispersion of micro-scale TiC particle and nano-scale TiN particle in alumina matrix. With the optimal dispersing and fabricating technology, this multi-scale and multi-phase nanocomposite ceramic tool material can get both higher flexural strength and fracture toughness than that of A1203/TiC (LZ) ceramic tool material without nano-scale TiN particle, especially the fracture toughness can reach to 7.8 MPa . m^0.5. The nano-scale TiN can lead to the grain fining effect and promote the sintering process to get a higher density. The coexisting transgranular and intergranular fracture mode induced by micro-scale TiC and nano-scale TiN, and the homogeneous and densified microstructure can result in a remarkable strengthening and toughening effect. The cutting performance and wear mechanisms of the advanced multi-scale and multi-phase nanocomposite ceramic cutting tool are researched.
基金This project is supported by National Innovation Foundation for TechnologyBased Firms, China (No.01C26213300872).
文摘The multi-impact characteristics and failure mechanism of two kinds of automotive engine chain made in China are studied through engine assembly and road-drive tests. The worn surface morphologies of rubbing area between pin, bush and roller are also analyzed based on scanning electron microscope. The results show that the main wear mechanism of automotive engine chain is fatigue wear, and its failure mechanism is the forming, extending and flaking of cracks on top layer of pin and bush. In addition, the material, hot-treatment method and shaping technique for roller have a great influence upon the resistance to multi-impact. Ensuring sufficient strength and plasticity of roller, as well as adopting suitable shaping technique are the effective method to increase its resistance to multi-impact.
基金This work was supported by the National Natural Science Foundation of China[Grant Nos.11790283,51978587,51708457]the Program of Introducing Talents of Discipline to Universities(111 Project)[Grant No.B16041].
文摘Motivated by the huge practical engineering demand for the fundamental understanding of mechanical characteristics of high-speed railway infrastructure,a fullscale multi-functional test platform for high-speed railway track–subgrade system is developed in this paper,and its main functions for investigating the mechanical performance of track–subgrade systems are elaborated with three typical experimental examples.Comprising the full-scale subgrade structure and all the five types of track structures adopted in Chinese high-speed railways,namely the CRTS I,the CRTS II and the CRTS III ballastless tracks,the double-block ballastless track and the ballasted track,the test platform is established strictly according to the construction standard of Chinese high-speed railways.Three kinds of effective loading methods are employed,including the real bogie loading,multi-point loading and the impact loading.Various types of sensors are adopted in different components of the five types of track–subgrade systems to measure the displacement,acceleration,pressure,structural strain and deformation,etc.Utilizing this test platform,both dynamic characteristics and long-term performance evolution of high-speed railway track–subgrade systems can be investigated,being able to satisfy the actual demand for large-scale operation of Chinese high-speed railways.As examples,three typical experimental studies are presented to elucidate the comprehensive functionalities of the full-scale multi-functional test platform for exploring the dynamic performance and its long-term evolution of ballastless track systems and for studying the long-term accumulative settlement of the ballasted track–subgrade system in high-speed railways.Some interesting phenomena and meaningful results are captured by the developed test platform,which provide a useful guidance for the scientific operation and maintenance of high-speed railway infrastructure.
基金Project supported by the National Basic Research Program of China(Grant No.2012CB932302)the National Natural Science Foundation of China(Grant Nos.11634014,51172271,51372269,and 51472264)the“Strategic Priority Research Program”of the Chinese Academy of Sciences(Grant No.XDA09040202)
文摘Continuous CNT fibers have been directly fabricated in a speed of 50 m/h-400 m/h,based on an improved chemical vapor deposition method.As-prepared fibers are further post-treated by acid.According to the SEM images and Raman spectra,the acid treatment results in the compaction and surface modification of the CNTs in fibers,which are beneficial for the electron and load transfer.Compared to the HNO3 treatment,HClSO_3 or H_2SO_4 treatment is more effective for the improvement of the fibers' properties.After HCISO_3 treatment for 2 h,the fibers' strength and electrical conductivity reach up to-2 GPa and-4.3 MS/m,which are promoted by-200%and almost one order of magnitude than those without acid treatment,respectively.The load-bearing status of the CNT fibers are analyzed based on the downshifts of the G' band and the strain transfer factor of the fibers under tension.The results reveal that acid treatment could greatly enhance the load transfer and inter-bundle strength.With the HCISO3 treatment,the strain transfer factor is enhanced from-3.9%to-53.6%.