Aground firing test of the Chang'e 3 lander was conducted recently to check the mechanical performance of the spacecraft. The test was vital before the propulsion system test of the Chang'e 3 lander and was al...Aground firing test of the Chang'e 3 lander was conducted recently to check the mechanical performance of the spacecraft. The test was vital before the propulsion system test of the Chang'e 3 lander and was also a very important precondition to verify whether the propulsion system design could meet the requirements for in-orbit operation.展开更多
The aim of this study is to address the issues associated with traditional magnetorheological fluid(MRF)dampers,such as insufficient damping force after power failure and susceptibility to settlement.In order to achie...The aim of this study is to address the issues associated with traditional magnetorheological fluid(MRF)dampers,such as insufficient damping force after power failure and susceptibility to settlement.In order to achieve this,a bidirectional adjustable MRF damper was designed and developed.Magnetic field simulation analysis was conducted on the damper,along with simulation analysis on its dynamic characteristics.The dynamic characteristics were ultimately validated through experimental testing on the material testing machine,thereby corroborating the theoretical simulation results.Concurrently,this process generated valuable test data for subsequent implementation of the semi-active vibration control system.The simulation and test results demonstrate that the integrated permanent magnet effectively accomplishes bidirectional regulation.The magnetic induction intensity of the damping channel is 0.2 T in the absence of current,increases to 0.5 T when a maximum forward current of 4 A is applied,and becomes 0 T when a maximum reverse current of 3.8 A is applied.When the excitation amplitude is 8 mm and the frequency is 2 Hz,with the applied currents varying,the maximum damping force reaches 8 kN,while the minimum damping force measures at 511 N.Additionally,at zero current,the damping force stands at 2 kN,which aligns closely with simulation results.The present paper can serve as a valuable reference for the design and research of semi-active MRF dampers.展开更多
Characterizing the architecture of tree root systems is essential to advance the development of root-inspired anchorage in engineered systems.This study explores the structural root architectures of orchard trees to u...Characterizing the architecture of tree root systems is essential to advance the development of root-inspired anchorage in engineered systems.This study explores the structural root architectures of orchard trees to understand the interplays between the mechanical behavior of roots and the root architecture.Full three-dimensional(3D)models of natural tree root systems,Lovell,Marianna,and Myrobalan,that were extracted from the ground by vertical pullout are reconstructed through photogrammetry and later skeletonized as nodes and root branch segments.Combined analyses of the full 3D models and skeletonized models enable a detailed examination of basic bulk properties and quantification of architectural parameters.While the root segments are divided into three categories,trunk root,main lateral root,and remaining roots,the patterns in branching and diameter distributions show significant differences between the trunk and main laterals versus the remaining lateral roots.In general,the branching angle decreases over the sequence of bifurcations.The main lateral roots near the trunk show significant spreading while the lateral roots near the ends grow roughly parallel to the parent root.For branch length,the roots bifurcate more frequently near the trunk and later they grow longer.Local thickness analysis confirms that the root diameter decays at a higher rate near the trunk than in the remaining lateral roots,while the total cross-sectional area across a bifurcation node remains mostly conserved.The histograms of branching angle,and branch length and thickness gradient can be described using lognormal and exponential distributions,respectively.This unique study presents data to characterize mechanically important structural roots,which may help link root architecture to the mechanical behaviors of root structures.展开更多
In-situ transmission electron microscopy(TEM)has been demonstrated to be a powerful method in resolving challenging problems such as interactions among various defects.To take advantage of the atomic resolution of adv...In-situ transmission electron microscopy(TEM)has been demonstrated to be a powerful method in resolving challenging problems such as interactions among various defects.To take advantage of the atomic resolution of advanced TEMs,a compact five-degree-of-freedom nanomanipulator was integrated with an indenter that was made of nanotwinned diamonds,for both the in-situ mechanical testing and double tilting of TEM samples.As a demonstration,in-situ bending tests were performed on the?111?,?110?and?100?single-crystal diamond needles.The tests revealed the{111}cleavage to be the dominant failure mode.The in-situ indentation on a diamond nanoplate led to curved cracks consisting of nanometer-scale steps,which were identified to be atomic flat{111}facets.The atomic-scale observation of the deformation and failure of diamonds demonstrated the stability of the entire system and the durability of the indenter.We expect that more delicate research can be carried out by means of this holder in the near future,including in-situ stimulation,atomic characterization,and tomography.展开更多
Mechanical properties of silicon nanobeams are of prime importance in nanoelectromechanical system applications. A numerical experimental method of determining resonant frequencies and Young＇s modulus of nanobeams by...Mechanical properties of silicon nanobeams are of prime importance in nanoelectromechanical system applications. A numerical experimental method of determining resonant frequencies and Young＇s modulus of nanobeams by combining finite element analysis and frequency response tests based on an electrostatic excitation and visual detection by using a laser Doppler vibrometer is presented in this paper. Silicon nanobeam test structures are fabricated from silicon-oninsulator wafers by using a standard lithography and anisotropic wet etching release process, which inevitably generates the undercut of the nanobeam clamping. In conjunction with three-dimensional finite element numerical simulations incorporating the geometric undercut, dynamic resonance tests reveal that the undercut significantly reduces resonant frequencies of nanobeams due to the fact that it effectively increases the nanobeam length by a correct value △L, which is a key parameter that is correlated with deviations in the resonant frequencies predicted from the ideal Euler-Bernoulli beam theory and experimentally measured data. By using a least-square fit expression including △L, we finally extract Young＇s modulus from the measured resonance frequency versus effective length dependency and find that Young＇s modulus of a silicon nanobeam with 200-nm thickness is close to that of bulk silicon. This result supports that the finite size effect due to the surface effect does not play a role in the mechanical elastic behaviour of silicon nanobeams with thickness larger than 200 nm.展开更多
In order to study how to improve the overall performance of the operational metal bolt, based on the production process of an ordinary metal bolt used in understructure engineering, this paper focused on the existing ...In order to study how to improve the overall performance of the operational metal bolt, based on the production process of an ordinary metal bolt used in understructure engineering, this paper focused on the existing problems of ordinary metal bolts identified by some survey and analysis. The results show that the structure of operational metal bolts is so unrea- sonable that the bolt tail is easily fractured by low load capacity. Furthermore, a new type of strong big-end metal bolt and its heat treatment and roughing processing technology were introduced. Through bolt tensile and metallographic tests, the property of the new big-end bolt was analyzed. The new findings indicate that after a special processing, the overall strength and plasticity of the bolt is greatly improved, and the grain of the bolt tail structure is refined, which would help build up favorable working conditions for bolt tails.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
Mechanical properties of silicon nanobeams are of prime importance in nanoelectromechanical system applications.A numerical experimental method of determining resonant frequencies and Young’s modulus of nanobeams by ...Mechanical properties of silicon nanobeams are of prime importance in nanoelectromechanical system applications.A numerical experimental method of determining resonant frequencies and Young’s modulus of nanobeams by combining finite element analysis and frequency response tests based on an electrostatic excitation and visual detection by using a laser Doppler vibrometer is presented in this paper.Silicon nanobeam test structures are fabricated from silicon-oninsulator wafers by using a standard lithography and anisotropic wet etching release process,which inevitably generates the undercut of the nanobeam clamping.In conjunction with three-dimensional finite element numerical simulations incorporating the geometric undercut,dynamic resonance tests reveal that the undercut significantly reduces resonant frequencies of nanobeams due to the fact that it effectively increases the nanobeam length by a correct value △L,which is a key parameter that is correlated with deviations in the resonant frequencies predicted from the ideal Euler-Bernoulli beam theory and experimentally measured data.By using a least-square fit expression including △L,we finally extract Young’s modulus from the measured resonance frequency versus effective length dependency and find that Young’s modulus of a silicon nanobeam with 200-nm thickness is close to that of bulk silicon.This result supports that the finite size effect due to the surface effect does not play a role in the mechanical elastic behaviour of silicon nanobeams with thickness larger than 200 nm.展开更多
Mechanical soil aeration is a simple, effective, and low-cost soil remediation technology that is suitable for sites contaminated with volatile chlorinated hydrocarbons（VCHs）. Conventionally, this technique is used ...Mechanical soil aeration is a simple, effective, and low-cost soil remediation technology that is suitable for sites contaminated with volatile chlorinated hydrocarbons（VCHs）. Conventionally, this technique is used to treat the mixed soil of a site without considering the diversity and treatability of different soils within the site. A laboratory test was conducted to evaluate the effectiveness of mechanical soil aeration for remediating soils of different textures（silty,clayey, and sandy soils） along a vertical profile at an abandoned chloro-alkali chemical site in China. The collected soils were artificially contaminated with chloroform（TCM） and trichloroethylene（TCE）. Mechanical soil aeration was effective for remediating VCHs（removal efficiency 〉 98%）. The volatilization process was described by an exponential kinetic function.In the early stage of treatment（0–7 hr）, rapid contaminant volatilization followed a pseudofirst order kinetic model. VCH concentrations decreased to low levels and showed a tailing phenomenon with very slow contaminant release after 8 hr. Compared with silty and sandy soils, clayey soil has high organic-matter content, a large specific surface area, a high clay fraction, and a complex pore structure. These characteristics substantially influenced the removal process, making it less efficient, more time consuming, and consequently more expensive. Our findings provide a potential basis for optimizing soil remediation strategy in a cost-effective manner.展开更多
The limited metal-polymer interlaminar property is a significant obstacle to the advancement of Ti/Carbon Fiber(CF)/Polyether Ether Ketone(PEEK)hybrid laminates.We report for the first time a novel method by utilizing...The limited metal-polymer interlaminar property is a significant obstacle to the advancement of Ti/Carbon Fiber(CF)/Polyether Ether Ketone(PEEK)hybrid laminates.We report for the first time a novel method by utilizing the mussel-inspired Polydopamine(PDA)to introduce a strong chemical-physical bonding between titanium and PEEK.The enhanced Fiber-Metal Laminate(FML)exhibits a significant 48.82%enhancement in Interlaminar Shear Strength(ILSS).In addition,it alters the failure mode of the FML from single metal-resin interlaminar delamination to a multi-mechanism,including debonding,delamination of different composite layers,leading to a 28.57%improvement in maximum displacement.展开更多
In this study, to meet the development and application requirements for high-strength and hightoughness energetic structural materials, a representative volume element of a TA15 matrix embedded with a TaZrNb sphere wa...In this study, to meet the development and application requirements for high-strength and hightoughness energetic structural materials, a representative volume element of a TA15 matrix embedded with a TaZrNb sphere was designed and fabricated via diffusion bonding. The mechanisms of the microstructural evolution of the TaZrNb/TA15 interface were investigated via SEM, EBSD, EDS, and XRD.Interface mechanical property tests and in-situ tensile tests were conducted on the sphere-containing structure, and an equivalent tensile-strength model was established for the structure. The results revealed that the TA15 titanium alloy and joint had high density and no pores or cracks. The thickness of the planar joint was approximately 50-60 μm. The average tensile and shear strengths were 767 MPa and 608 MPa, respectively. The thickness of the spherical joint was approximately 60 μm. The Zr and Nb elements in the joint diffused uniformly and formed strong bonds with Ti without forming intermetallic compounds. The interface exhibited submicron grain refinement and a concave-convex interlocking structure. The tensile fracture surface primarily exhibited intergranular fracture combined with some transgranular fracture, which constituted a quasi-brittle fracture mode. The shear fracture surface exhibited brittle fracture with regular arrangements of furrows. Internal fracture occurred along the spherical interface, as revealed by advanced in-situ X-ray microcomputed tomography. The experimental results agreed well with the theoretical predictions, indicating that the high-strength interface contributes to the overall strength and toughness of the sphere-containing structure.展开更多
The small punch test technique facilitates the convenient acquisition of the mechanical properties of in-service equipment materials and the assessment of their remaining service life through sampling.However,the weld...The small punch test technique facilitates the convenient acquisition of the mechanical properties of in-service equipment materials and the assessment of their remaining service life through sampling.However,the weldability of components with thin walls after small punch sampling,such as ethylene cracking furnace tubes,requires further investigation.Therefore,the weldability of in-service ethylene cracking furnace tubes following small punch sampling was investigated through nondestructive testing,microstructural characterization,and mechanical testing.Additionally,the impact of small punch sampling size and residual stress on the creep performance of the specimens was studied using an improved ductility exhaustion model.The results indicate that both the surface and interior of the weld repair areas on new furnace tubes and service-exposed furnace tubes after small-punch sampling are defect-free,exhibiting good weld quality.The strength of the specimens after weld repair was higher than that before sampling,whereas toughness decreased.Weld repair following small punch sampling of furnace tubes is both feasible and necessary.Furthermore,a linear relationship was observed between specimen thickness,diameter,and creep fracture time.The residual stress of welding affects the creep performance of the specimen under different stresses.展开更多
In industrial application,unintentional manufacturing line troubles often consequence in heating raw materials excessively,in terms of either time or temperature.One of the effects of such occurrence is a product with...In industrial application,unintentional manufacturing line troubles often consequence in heating raw materials excessively,in terms of either time or temperature.One of the effects of such occurrence is a product with a variation of prior austenite grain size,even if after the heat treatment the end result is the same,martensite.The variation of the prior austenite grain size is believed to vary the end results of the martensite.This undesirable variation includes the variation of fatigue resistance,impact strength,yield strength,hardness,etc.This research studies the effect of the prior austenite grain size on the morphology of the martensite microstructure.The results show that within the typical industrial application of temperature and holding time set up,as holding time or the temperature increases,the prior austenite average diameter increases.The block and packet sizes in the martensite also increase.The variation of mechanical property dependence on the grain size is indeed due to the different characteristics reflected in the martensite morphology.With respect to the same area,smaller grain has more blocks and packets,which agrees with higher dislocation density verified with transmission electron microscopic evaluation.展开更多
Toarcian claystone such as that of the Callovo-Oxfordian is a qualified multiphase material. The claystone samples tested in this study are composed of four main mineral phases: silicates(clay minerals, quartz,feldspa...Toarcian claystone such as that of the Callovo-Oxfordian is a qualified multiphase material. The claystone samples tested in this study are composed of four main mineral phases: silicates(clay minerals, quartz,feldspars, micas)(z86%), sulphides(pyrite)(z3%), carbonates(calcite, dolomite)(z10%) and organic kerogen(z1%). Three sets of measurements of the modulus of deformability were compared as determined in(i) nanoindentation tests with a constant indentation depth of 2 mm,(ii) micro-indentation tests with a constant indentation depth of 20 mm, and(iii) meso-compression tests with a constant displacement of 200 mm. These three experimental methods have already been validated in earlier studies. The main objective of this study is to demonstrate the influence of the scaling effect on the modulus of deformability of the material. Different frequency distributions of the modulus of deformability were obtained at the different sample scales:(i) in nano-indentation tests, the distribution was spread between 15 GPa and 90 GPa and contained one peak at34 GPa and another at 51 GPa;(ii) in the micro-indentation tests, the distribution was spread between 25 GPa and 60 GPa and displayed peaks at 26 GPa and 37 GPa; and(iii) in the meso-compression tests, a narrow frequency distribution was obtained, ranging from 25 GPa to 50 GPa and with a maximum at around 35 GPa.展开更多
Titanium matrix composite reinforced by graphene nanoplatelets(GNPs)was fabricated via powder metallurgy route.Hot isostatic pressing and hot extrusion were used to consolidate the mixed powder of GNPs and TC4 titaniu...Titanium matrix composite reinforced by graphene nanoplatelets(GNPs)was fabricated via powder metallurgy route.Hot isostatic pressing and hot extrusion were used to consolidate the mixed powder of GNPs and TC4 titanium(Ti)alloy.The microstructures,mechanical properties and sliding wear performance of Ti/GNPs composite had been researched to evaluate the rein forcing effect of GNPs on tita nium matrix.Microstructure observation indicates that GNPs could restrain grai n growth slightly in titanium matrix.Titanium matrix and graphene exhibit a clean and firm interface formed by means of metallurgical bonding on atomic scale.Compared with the monolithic titanium alloy,the composite with 1.2 vol.%GNPs exhibits significantly improved elastic modulus and strength.The sliding wear test shows that there is an obvious enhancement in the tribological performance of Ti/GNPs composite with 1.2 vol.%GNPs.The results of this work indicate that GNP is an efficient reinforcenient material in titanium matrix.The strengthening mechanism including precipitates strengthening,load transfer and grain refinement mechanism of GNPs in titanium matrix was discussed.A modified shear-lag model was used to analyze the reinforcement contribution of the stress transfer mechanism.The calculation shows that the stress load mechanism constitutes the main strengthening mechanism in Ti/GNPs composite.展开更多
Natural fiber-reinforced hybrid composites can be a better replacement for plastic composites since these plastic composites pose a serious threat to the environment.The aim of this study is to analyze the effect of s...Natural fiber-reinforced hybrid composites can be a better replacement for plastic composites since these plastic composites pose a serious threat to the environment.The aim of this study is to analyze the effect of surface modification of the natural fibers on the mechanical,thermal,hygrothermal,and water absorption behaviors of flax,sisal,and glass fiber-reinforced epoxy hybrid composites.The mechanical properties of alkaline treated sisal and flax fibers were found to increase considerably.Tensile,flexural and impact strength of glass/flax-fiber-reinforced hybrid samples improved by 58%,36%,and 51%,respectively,after surface alkaline treatment.In addition,the hygrothermal analysis and water absorption capacity are studied and also the Interfacial bonding properties were analyzed using Scanning Electron Microscopic images.The thermal analysis using thermogravimetric analyzer reveals that the decomposition temperature for hybrid fiber reinforced composites are between 306 and 312℃.In conclusion,surface treatment improves the performance of natural fiber in hybrid fiber-reinforced composites,particularly flax fiber.展开更多
In this work,the microstructural and mechanical properties of the certain magnesium-based alloys were investigated.The alloys were produced under a controlled atmosphere by a squeeze-casting process and characterized ...In this work,the microstructural and mechanical properties of the certain magnesium-based alloys were investigated.The alloys were produced under a controlled atmosphere by a squeeze-casting process and characterized by optical microscopy(OM),scanning electron microscopy(SEM),an energy-dispersive spectrometer(EDS)and X-ray diffraction(XRD)analysis.The results indicated that the addition of strontium element modified the structure and refined the grain size.The hardness and yield strength of the alloys increased continuously with increasing strontium content,while the elongation was gradually decreased.Also,the tensile strength value of the based alloy was increased by adding Sr up to 1 wt.%.After more addition of Sr,the tensile strength starts to diminish.展开更多
In order to verify the influence of different block proportions S/B on the effect of SBS modified asphalt,the dynamic mechanical performance test and static loading test were performed on the samples composed of diffe...In order to verify the influence of different block proportions S/B on the effect of SBS modified asphalt,the dynamic mechanical performance test and static loading test were performed on the samples composed of different kinds of SBS with base asphalt. It is found that different S/B values fix on different modified effects and different viscoelastic mechanical behaviors,due to biphasic separate fabric of polybutadiene and polystyrene in SBS. In low-speed running pavement,the modified asphalt with lower S/B value shows better pavement performance,while in high-speed running pavement,the modified asphalt with higher S/B value shows better pavement performance. As far as SBS modified asphalt itself is concerned,mixing proportion impacts on resisting displacement and block proportion S/B ratio impacts on strain recovery capacity. In the case that the conditions are the same,SBS modified asphalt with different S/B values can be used for different travelling speed pavement construction demands to get an intelligent use.展开更多
A newly proposed rapid fracture test in four-point bending was used to evaluate the effect of tempering on the hydrogen embrittlement(HE)susceptibility of an AISI 4135 steel,where it was tempered to four different str...A newly proposed rapid fracture test in four-point bending was used to evaluate the effect of tempering on the hydrogen embrittlement(HE)susceptibility of an AISI 4135 steel,where it was tempered to four different strength(or hardness)levels.It was observed that HE susceptibility increases with the increase in hardness.It was shown that there will be minimal impact of hydrogen(H)on the fracture of materials with hardness 37 HRC and below,even if they are completely saturated with H.On the other hand,H will have similar detrimental effect on fracture properties of quench and tempered(Q and T)steels having hardness higher than 45 HRC.Ductile to brittle transition behavior was observed for a critical hardness(or strength)range as well as for a critical concentration level of H.Additionally,a critical H concentration was observed to exist for each of the strength levels.Fractography was performed in addition to microstructural characterization using transmission electron microscopy(TEM).A very good correlation was observed between the fast fracture test results and fractography.The fast fracture test was further compared with a conventional incremental step load(ISL)test for the evaluation of HE susceptibility.The ISL test results and fracture surface characteristics corroborate very well with the observations from the fast fracture test.This study successfully establishes the fast fracture test as a novel technique to study HE susceptibility and mechanism(s).展开更多
The in-soil biodegradation of Stipa tenacissima(alfa)leaves was examined.Non-linear mechanical testing was performed at various biodegradation stages.Tensile strength,loading and unloading Young’s moduli and dissipat...The in-soil biodegradation of Stipa tenacissima(alfa)leaves was examined.Non-linear mechanical testing was performed at various biodegradation stages.Tensile strength,loading and unloading Young’s moduli and dissipation energy decreased with the burial time,whereas plasticity increased.Field-emission scanning electron microscopy(FE-SEM)showed that the fracture cracks propagated in the longitudinal direction in the raw material,resulting in a fracture mode consisting of a mixture of middle lamella delamination and fiber pull-out.In contrast,the cracks were perpendicular to the stem axis in the biodegraded material,demonstrating an important strength loss of the load-bearing fibers.This strength loss was correlated with rapid cellulose degradation.A novel X-ray diffraction(XRD)model was implemented in order to take into account anisotropic size broadening.For the first time,XRD demonstrated the action of biodegradation on unrefined plant tissues under quasi in-situ conditions.Biodegradation induced a progressive loss of crystalline cellulose accompanied with anisotropic crystallite thinning.展开更多
文摘Aground firing test of the Chang'e 3 lander was conducted recently to check the mechanical performance of the spacecraft. The test was vital before the propulsion system test of the Chang'e 3 lander and was also a very important precondition to verify whether the propulsion system design could meet the requirements for in-orbit operation.
文摘The aim of this study is to address the issues associated with traditional magnetorheological fluid(MRF)dampers,such as insufficient damping force after power failure and susceptibility to settlement.In order to achieve this,a bidirectional adjustable MRF damper was designed and developed.Magnetic field simulation analysis was conducted on the damper,along with simulation analysis on its dynamic characteristics.The dynamic characteristics were ultimately validated through experimental testing on the material testing machine,thereby corroborating the theoretical simulation results.Concurrently,this process generated valuable test data for subsequent implementation of the semi-active vibration control system.The simulation and test results demonstrate that the integrated permanent magnet effectively accomplishes bidirectional regulation.The magnetic induction intensity of the damping channel is 0.2 T in the absence of current,increases to 0.5 T when a maximum forward current of 4 A is applied,and becomes 0 T when a maximum reverse current of 3.8 A is applied.When the excitation amplitude is 8 mm and the frequency is 2 Hz,with the applied currents varying,the maximum damping force reaches 8 kN,while the minimum damping force measures at 511 N.Additionally,at zero current,the damping force stands at 2 kN,which aligns closely with simulation results.The present paper can serve as a valuable reference for the design and research of semi-active MRF dampers.
基金supported by the National Research Foundation of Korea(NRF)grant funded by the Korean government(MSIT)(RS-2024-00340851)the Engineering Research Center Program of the National Science Foundation(NSF)under NSF Cooperative Agreement EEC-1449501.
文摘Characterizing the architecture of tree root systems is essential to advance the development of root-inspired anchorage in engineered systems.This study explores the structural root architectures of orchard trees to understand the interplays between the mechanical behavior of roots and the root architecture.Full three-dimensional(3D)models of natural tree root systems,Lovell,Marianna,and Myrobalan,that were extracted from the ground by vertical pullout are reconstructed through photogrammetry and later skeletonized as nodes and root branch segments.Combined analyses of the full 3D models and skeletonized models enable a detailed examination of basic bulk properties and quantification of architectural parameters.While the root segments are divided into three categories,trunk root,main lateral root,and remaining roots,the patterns in branching and diameter distributions show significant differences between the trunk and main laterals versus the remaining lateral roots.In general,the branching angle decreases over the sequence of bifurcations.The main lateral roots near the trunk show significant spreading while the lateral roots near the ends grow roughly parallel to the parent root.For branch length,the roots bifurcate more frequently near the trunk and later they grow longer.Local thickness analysis confirms that the root diameter decays at a higher rate near the trunk than in the remaining lateral roots,while the total cross-sectional area across a bifurcation node remains mostly conserved.The histograms of branching angle,and branch length and thickness gradient can be described using lognormal and exponential distributions,respectively.This unique study presents data to characterize mechanically important structural roots,which may help link root architecture to the mechanical behaviors of root structures.
基金supported by the National Natural Science Foundation of China(11725210,11672355 and 11702165)the National Key R&D Program of China(2018YFA0703400)。
文摘In-situ transmission electron microscopy(TEM)has been demonstrated to be a powerful method in resolving challenging problems such as interactions among various defects.To take advantage of the atomic resolution of advanced TEMs,a compact five-degree-of-freedom nanomanipulator was integrated with an indenter that was made of nanotwinned diamonds,for both the in-situ mechanical testing and double tilting of TEM samples.As a demonstration,in-situ bending tests were performed on the?111?,?110?and?100?single-crystal diamond needles.The tests revealed the{111}cleavage to be the dominant failure mode.The in-situ indentation on a diamond nanoplate led to curved cracks consisting of nanometer-scale steps,which were identified to be atomic flat{111}facets.The atomic-scale observation of the deformation and failure of diamonds demonstrated the stability of the entire system and the durability of the indenter.We expect that more delicate research can be carried out by means of this holder in the near future,including in-situ stimulation,atomic characterization,and tomography.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 41075026 and 61001044)the Open Re-search Fund of Key Laboratory of Microelectromechanical System of Ministry of Education,Southeast University,China (Grant Nos. 2009-03 and 2010-02)+1 种基金the Special Fund for Meteorology Research in the Public Interest,China (Grant No. GYHY200906037)the Priority Academic Program Development of Sensor Networks and Modern Meteorological Equipment of Jiangsu Provincial Higher Education Institutions
文摘Mechanical properties of silicon nanobeams are of prime importance in nanoelectromechanical system applications. A numerical experimental method of determining resonant frequencies and Young＇s modulus of nanobeams by combining finite element analysis and frequency response tests based on an electrostatic excitation and visual detection by using a laser Doppler vibrometer is presented in this paper. Silicon nanobeam test structures are fabricated from silicon-oninsulator wafers by using a standard lithography and anisotropic wet etching release process, which inevitably generates the undercut of the nanobeam clamping. In conjunction with three-dimensional finite element numerical simulations incorporating the geometric undercut, dynamic resonance tests reveal that the undercut significantly reduces resonant frequencies of nanobeams due to the fact that it effectively increases the nanobeam length by a correct value △L, which is a key parameter that is correlated with deviations in the resonant frequencies predicted from the ideal Euler-Bernoulli beam theory and experimentally measured data. By using a least-square fit expression including △L, we finally extract Young＇s modulus from the measured resonance frequency versus effective length dependency and find that Young＇s modulus of a silicon nanobeam with 200-nm thickness is close to that of bulk silicon. This result supports that the finite size effect due to the surface effect does not play a role in the mechanical elastic behaviour of silicon nanobeams with thickness larger than 200 nm.
文摘In order to study how to improve the overall performance of the operational metal bolt, based on the production process of an ordinary metal bolt used in understructure engineering, this paper focused on the existing problems of ordinary metal bolts identified by some survey and analysis. The results show that the structure of operational metal bolts is so unrea- sonable that the bolt tail is easily fractured by low load capacity. Furthermore, a new type of strong big-end metal bolt and its heat treatment and roughing processing technology were introduced. Through bolt tensile and metallographic tests, the property of the new big-end bolt was analyzed. The new findings indicate that after a special processing, the overall strength and plasticity of the bolt is greatly improved, and the grain of the bolt tail structure is refined, which would help build up favorable working conditions for bolt tails.
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.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 41075026 and 61001044)the Open Re-search Fund of Key Laboratory of Microelectromechanical System of Ministry of Education,Southeast University,China (Grant Nos. 2009-03 and 2010-02)+1 种基金the Special Fund for Meteorology Research in the Public Interest,China (Grant No. GYHY200906037)the Priority Academic Program Development of Sensor Networks and Modern Meteorological Equipment of Jiangsu Provincial Higher Education Institutions
文摘Mechanical properties of silicon nanobeams are of prime importance in nanoelectromechanical system applications.A numerical experimental method of determining resonant frequencies and Young’s modulus of nanobeams by combining finite element analysis and frequency response tests based on an electrostatic excitation and visual detection by using a laser Doppler vibrometer is presented in this paper.Silicon nanobeam test structures are fabricated from silicon-oninsulator wafers by using a standard lithography and anisotropic wet etching release process,which inevitably generates the undercut of the nanobeam clamping.In conjunction with three-dimensional finite element numerical simulations incorporating the geometric undercut,dynamic resonance tests reveal that the undercut significantly reduces resonant frequencies of nanobeams due to the fact that it effectively increases the nanobeam length by a correct value △L,which is a key parameter that is correlated with deviations in the resonant frequencies predicted from the ideal Euler-Bernoulli beam theory and experimentally measured data.By using a least-square fit expression including △L,we finally extract Young’s modulus from the measured resonance frequency versus effective length dependency and find that Young’s modulus of a silicon nanobeam with 200-nm thickness is close to that of bulk silicon.This result supports that the finite size effect due to the surface effect does not play a role in the mechanical elastic behaviour of silicon nanobeams with thickness larger than 200 nm.
基金supported by the National Environmental Protection Public Welfare projects(Nos.201409047 and 201109017)the “13th Five-Year Plan” National Key Research and Development Program of China(No.2016YFC0501108)+1 种基金the Fundamental Research Funds for the Central Universities(No.2016QH02)Beijing Natural Science Foundation(No.8152025)
文摘Mechanical soil aeration is a simple, effective, and low-cost soil remediation technology that is suitable for sites contaminated with volatile chlorinated hydrocarbons（VCHs）. Conventionally, this technique is used to treat the mixed soil of a site without considering the diversity and treatability of different soils within the site. A laboratory test was conducted to evaluate the effectiveness of mechanical soil aeration for remediating soils of different textures（silty,clayey, and sandy soils） along a vertical profile at an abandoned chloro-alkali chemical site in China. The collected soils were artificially contaminated with chloroform（TCM） and trichloroethylene（TCE）. Mechanical soil aeration was effective for remediating VCHs（removal efficiency 〉 98%）. The volatilization process was described by an exponential kinetic function.In the early stage of treatment（0–7 hr）, rapid contaminant volatilization followed a pseudofirst order kinetic model. VCH concentrations decreased to low levels and showed a tailing phenomenon with very slow contaminant release after 8 hr. Compared with silty and sandy soils, clayey soil has high organic-matter content, a large specific surface area, a high clay fraction, and a complex pore structure. These characteristics substantially influenced the removal process, making it less efficient, more time consuming, and consequently more expensive. Our findings provide a potential basis for optimizing soil remediation strategy in a cost-effective manner.
基金the financial supports of Fundamental Research Funds for the Central Universities,China(Nos.YWF-23-L-1012,YWF-22-L-1017)。
文摘The limited metal-polymer interlaminar property is a significant obstacle to the advancement of Ti/Carbon Fiber(CF)/Polyether Ether Ketone(PEEK)hybrid laminates.We report for the first time a novel method by utilizing the mussel-inspired Polydopamine(PDA)to introduce a strong chemical-physical bonding between titanium and PEEK.The enhanced Fiber-Metal Laminate(FML)exhibits a significant 48.82%enhancement in Interlaminar Shear Strength(ILSS).In addition,it alters the failure mode of the FML from single metal-resin interlaminar delamination to a multi-mechanism,including debonding,delamination of different composite layers,leading to a 28.57%improvement in maximum displacement.
基金supported by the National Natural Science Foundation of China(Grant No.12372351).
文摘In this study, to meet the development and application requirements for high-strength and hightoughness energetic structural materials, a representative volume element of a TA15 matrix embedded with a TaZrNb sphere was designed and fabricated via diffusion bonding. The mechanisms of the microstructural evolution of the TaZrNb/TA15 interface were investigated via SEM, EBSD, EDS, and XRD.Interface mechanical property tests and in-situ tensile tests were conducted on the sphere-containing structure, and an equivalent tensile-strength model was established for the structure. The results revealed that the TA15 titanium alloy and joint had high density and no pores or cracks. The thickness of the planar joint was approximately 50-60 μm. The average tensile and shear strengths were 767 MPa and 608 MPa, respectively. The thickness of the spherical joint was approximately 60 μm. The Zr and Nb elements in the joint diffused uniformly and formed strong bonds with Ti without forming intermetallic compounds. The interface exhibited submicron grain refinement and a concave-convex interlocking structure. The tensile fracture surface primarily exhibited intergranular fracture combined with some transgranular fracture, which constituted a quasi-brittle fracture mode. The shear fracture surface exhibited brittle fracture with regular arrangements of furrows. Internal fracture occurred along the spherical interface, as revealed by advanced in-situ X-ray microcomputed tomography. The experimental results agreed well with the theoretical predictions, indicating that the high-strength interface contributes to the overall strength and toughness of the sphere-containing structure.
基金supports provided by the National Natural Science Foundation of China(No.52372330).
文摘The small punch test technique facilitates the convenient acquisition of the mechanical properties of in-service equipment materials and the assessment of their remaining service life through sampling.However,the weldability of components with thin walls after small punch sampling,such as ethylene cracking furnace tubes,requires further investigation.Therefore,the weldability of in-service ethylene cracking furnace tubes following small punch sampling was investigated through nondestructive testing,microstructural characterization,and mechanical testing.Additionally,the impact of small punch sampling size and residual stress on the creep performance of the specimens was studied using an improved ductility exhaustion model.The results indicate that both the surface and interior of the weld repair areas on new furnace tubes and service-exposed furnace tubes after small-punch sampling are defect-free,exhibiting good weld quality.The strength of the specimens after weld repair was higher than that before sampling,whereas toughness decreased.Weld repair following small punch sampling of furnace tubes is both feasible and necessary.Furthermore,a linear relationship was observed between specimen thickness,diameter,and creep fracture time.The residual stress of welding affects the creep performance of the specimen under different stresses.
文摘In industrial application,unintentional manufacturing line troubles often consequence in heating raw materials excessively,in terms of either time or temperature.One of the effects of such occurrence is a product with a variation of prior austenite grain size,even if after the heat treatment the end result is the same,martensite.The variation of the prior austenite grain size is believed to vary the end results of the martensite.This undesirable variation includes the variation of fatigue resistance,impact strength,yield strength,hardness,etc.This research studies the effect of the prior austenite grain size on the morphology of the martensite microstructure.The results show that within the typical industrial application of temperature and holding time set up,as holding time or the temperature increases,the prior austenite average diameter increases.The block and packet sizes in the martensite also increase.The variation of mechanical property dependence on the grain size is indeed due to the different characteristics reflected in the martensite morphology.With respect to the same area,smaller grain has more blocks and packets,which agrees with higher dislocation density verified with transmission electron microscopic evaluation.
文摘Toarcian claystone such as that of the Callovo-Oxfordian is a qualified multiphase material. The claystone samples tested in this study are composed of four main mineral phases: silicates(clay minerals, quartz,feldspars, micas)(z86%), sulphides(pyrite)(z3%), carbonates(calcite, dolomite)(z10%) and organic kerogen(z1%). Three sets of measurements of the modulus of deformability were compared as determined in(i) nanoindentation tests with a constant indentation depth of 2 mm,(ii) micro-indentation tests with a constant indentation depth of 20 mm, and(iii) meso-compression tests with a constant displacement of 200 mm. These three experimental methods have already been validated in earlier studies. The main objective of this study is to demonstrate the influence of the scaling effect on the modulus of deformability of the material. Different frequency distributions of the modulus of deformability were obtained at the different sample scales:(i) in nano-indentation tests, the distribution was spread between 15 GPa and 90 GPa and contained one peak at34 GPa and another at 51 GPa;(ii) in the micro-indentation tests, the distribution was spread between 25 GPa and 60 GPa and displayed peaks at 26 GPa and 37 GPa; and(iii) in the meso-compression tests, a narrow frequency distribution was obtained, ranging from 25 GPa to 50 GPa and with a maximum at around 35 GPa.
基金National Natural Science Foundation of China(51802296)Beijing Municipal Science and Technology Commission(Z171100002017016,Z191100005619006).
文摘Titanium matrix composite reinforced by graphene nanoplatelets(GNPs)was fabricated via powder metallurgy route.Hot isostatic pressing and hot extrusion were used to consolidate the mixed powder of GNPs and TC4 titanium(Ti)alloy.The microstructures,mechanical properties and sliding wear performance of Ti/GNPs composite had been researched to evaluate the rein forcing effect of GNPs on tita nium matrix.Microstructure observation indicates that GNPs could restrain grai n growth slightly in titanium matrix.Titanium matrix and graphene exhibit a clean and firm interface formed by means of metallurgical bonding on atomic scale.Compared with the monolithic titanium alloy,the composite with 1.2 vol.%GNPs exhibits significantly improved elastic modulus and strength.The sliding wear test shows that there is an obvious enhancement in the tribological performance of Ti/GNPs composite with 1.2 vol.%GNPs.The results of this work indicate that GNP is an efficient reinforcenient material in titanium matrix.The strengthening mechanism including precipitates strengthening,load transfer and grain refinement mechanism of GNPs in titanium matrix was discussed.A modified shear-lag model was used to analyze the reinforcement contribution of the stress transfer mechanism.The calculation shows that the stress load mechanism constitutes the main strengthening mechanism in Ti/GNPs composite.
文摘Natural fiber-reinforced hybrid composites can be a better replacement for plastic composites since these plastic composites pose a serious threat to the environment.The aim of this study is to analyze the effect of surface modification of the natural fibers on the mechanical,thermal,hygrothermal,and water absorption behaviors of flax,sisal,and glass fiber-reinforced epoxy hybrid composites.The mechanical properties of alkaline treated sisal and flax fibers were found to increase considerably.Tensile,flexural and impact strength of glass/flax-fiber-reinforced hybrid samples improved by 58%,36%,and 51%,respectively,after surface alkaline treatment.In addition,the hygrothermal analysis and water absorption capacity are studied and also the Interfacial bonding properties were analyzed using Scanning Electron Microscopic images.The thermal analysis using thermogravimetric analyzer reveals that the decomposition temperature for hybrid fiber reinforced composites are between 306 and 312℃.In conclusion,surface treatment improves the performance of natural fiber in hybrid fiber-reinforced composites,particularly flax fiber.
基金The authors wish to thank The Scientific and Technical Research Council of Turkey-TUBITAK(grant number:106M122)for financial support in this study.The authors also would like to thank Mr.Metin GUNAY for his technical support.
文摘In this work,the microstructural and mechanical properties of the certain magnesium-based alloys were investigated.The alloys were produced under a controlled atmosphere by a squeeze-casting process and characterized by optical microscopy(OM),scanning electron microscopy(SEM),an energy-dispersive spectrometer(EDS)and X-ray diffraction(XRD)analysis.The results indicated that the addition of strontium element modified the structure and refined the grain size.The hardness and yield strength of the alloys increased continuously with increasing strontium content,while the elongation was gradually decreased.Also,the tensile strength value of the based alloy was increased by adding Sr up to 1 wt.%.After more addition of Sr,the tensile strength starts to diminish.
基金Sponsored by the National Natural Science Foundation of China (Grant No. 50008005)
文摘In order to verify the influence of different block proportions S/B on the effect of SBS modified asphalt,the dynamic mechanical performance test and static loading test were performed on the samples composed of different kinds of SBS with base asphalt. It is found that different S/B values fix on different modified effects and different viscoelastic mechanical behaviors,due to biphasic separate fabric of polybutadiene and polystyrene in SBS. In low-speed running pavement,the modified asphalt with lower S/B value shows better pavement performance,while in high-speed running pavement,the modified asphalt with higher S/B value shows better pavement performance. As far as SBS modified asphalt itself is concerned,mixing proportion impacts on resisting displacement and block proportion S/B ratio impacts on strain recovery capacity. In the case that the conditions are the same,SBS modified asphalt with different S/B values can be used for different travelling speed pavement construction demands to get an intelligent use.
基金This work was financially supported by the Government of Canada through Natural Sciences and Engineering Research Council(NSERC),and the industrial collaborators led by Industrial Fasteners Institute(USA),Canadian Fasteners Institute(CFI),Boeing Company(USA),Infasco(Canada)and the Research Council on Structural Connections(RCSC).
文摘A newly proposed rapid fracture test in four-point bending was used to evaluate the effect of tempering on the hydrogen embrittlement(HE)susceptibility of an AISI 4135 steel,where it was tempered to four different strength(or hardness)levels.It was observed that HE susceptibility increases with the increase in hardness.It was shown that there will be minimal impact of hydrogen(H)on the fracture of materials with hardness 37 HRC and below,even if they are completely saturated with H.On the other hand,H will have similar detrimental effect on fracture properties of quench and tempered(Q and T)steels having hardness higher than 45 HRC.Ductile to brittle transition behavior was observed for a critical hardness(or strength)range as well as for a critical concentration level of H.Additionally,a critical H concentration was observed to exist for each of the strength levels.Fractography was performed in addition to microstructural characterization using transmission electron microscopy(TEM).A very good correlation was observed between the fast fracture test results and fractography.The fast fracture test was further compared with a conventional incremental step load(ISL)test for the evaluation of HE susceptibility.The ISL test results and fracture surface characteristics corroborate very well with the observations from the fast fracture test.This study successfully establishes the fast fracture test as a novel technique to study HE susceptibility and mechanism(s).
文摘The in-soil biodegradation of Stipa tenacissima(alfa)leaves was examined.Non-linear mechanical testing was performed at various biodegradation stages.Tensile strength,loading and unloading Young’s moduli and dissipation energy decreased with the burial time,whereas plasticity increased.Field-emission scanning electron microscopy(FE-SEM)showed that the fracture cracks propagated in the longitudinal direction in the raw material,resulting in a fracture mode consisting of a mixture of middle lamella delamination and fiber pull-out.In contrast,the cracks were perpendicular to the stem axis in the biodegraded material,demonstrating an important strength loss of the load-bearing fibers.This strength loss was correlated with rapid cellulose degradation.A novel X-ray diffraction(XRD)model was implemented in order to take into account anisotropic size broadening.For the first time,XRD demonstrated the action of biodegradation on unrefined plant tissues under quasi in-situ conditions.Biodegradation induced a progressive loss of crystalline cellulose accompanied with anisotropic crystallite thinning.
