Driver distraction is a leading cause of traffic accidents,with fatigue being a significant contributor.This paper introduces a novel method for detecting driver distraction by analyzing facial features using machine ...Driver distraction is a leading cause of traffic accidents,with fatigue being a significant contributor.This paper introduces a novel method for detecting driver distraction by analyzing facial features using machine deep learning and 68 face model.The proposed system assesses driver tiredness by measuring the distance between key facial landmarks,such as the distance between the eyes and the angle of the mouth,to evaluate signs of drowsiness or disengagement.Real-time video feed analysis allows for continuous monitoring of the driver’s face,enabling the system to detect behavioral cues associated with distraction,such as eye closures or changes in facial expressions.The effectiveness of this method is demonstrated through a series of experiments on a dataset of driver videos,which proves that the approach can accurately assess tiredness and distraction levels under various driving conditions.By focusing on facial landmarks,the system is computationally efficient and capable of operating in real-time,making it a practical solution for in-vehicle safety systems.This paper discusses the system’s performance,limitations,and potential for future enhancements,including integration with other in-vehicle technologies to provide comprehensive driver monitoring.展开更多
It is well known that coarse-grained super-elastic NiTi shape memory alloys(SMAs)exhibit localized rather than homogeneous martensite transformation(MT),which,however,can be strongly influenced by either internal size...It is well known that coarse-grained super-elastic NiTi shape memory alloys(SMAs)exhibit localized rather than homogeneous martensite transformation(MT),which,however,can be strongly influenced by either internal size(grain size,GS)or the external size(geometric size).The coupled effect of GS and geometric size on the functional properties has not been clearly understood yet.In this work,the super-elasticity,one-way,and stress-assisted two-way shape memory effects of the polycrystalline NiTi SMAs with different aspect ratios(length/width for the gauge section)and different GSs are investigated based on the phase field method.The coupled effect of the aspect ratio and GS on the functional properties is adequately revealed.The simulated results indicate that when the aspect ratio is lower than about 4:1,the stress biaxiality and stress heterogeneity in the gauge section of the sample become more and more obvious with decreasing the aspect ratio,which can significantly influence the microstructure evolution in the process involving external stress.Therefore,the corresponding functional property is strongly dependent on the aspect ratio.With decreasing the GS and the aspect ratio(to be lower than 4:1),both the aspect ratio and GS can affect the MT or martensite reorientation in each grain and the interaction among grains.Thus,due to the strong internal constraint(i.e.,the constraint of grain boundary)and the external constraint(i.e.,the constraint of geometric boundary),the capabilities of the functional properties of NiTi SMAs are gradually weakened and highly dependent on these two factors.展开更多
Flow characteristics around a wall-mounted square cylinder have been numerically simulated at aspect ratios (AR) ranging from 4 to 7 at Re =10 000. Four turbulence models have been compared in terms of drag coefficien...Flow characteristics around a wall-mounted square cylinder have been numerically simulated at aspect ratios (AR) ranging from 4 to 7 at Re =10 000. Four turbulence models have been compared in terms of drag coefficient (C_D). The closest result has been provided by two turbulence models, namely, k-ε Realizable and k ?ω Shear Stress Transport (SST). Hence, these models were utilized to present the flow patterns of pressure distributions, turbulent kinetic energy values, velocity magnitude values with streamlines, streamwise velocity components, crossstream velocity components and spanwise velocity components on different planes. Flow stagnation has been attained in front of the cylinder. Pressure values peaked for the upstream region. Over the cylinders, the tip vortex structure was dominant owing to the influence of the free end. Flow separation from the top front edge of the body has been obtained. The dividing streamline affected by the flow separation was highly effective in the wake region and moved nearer to the body when the aspect ratio was decreased;the reason was the wake shrinkage owing to the decreasing aspect ratio. Upwash and downwash have been seen in the cylinder wake. These two models presented similar flow patterns and drag coefficients. These drag coefficients are in good agreement with those in previous studies.展开更多
Streamlined box girders serve as a prevalent choice for the primary structural elements in large-span suspension bridge designs.With the increase in traffic demands,the design of such girders is evolving towards wider...Streamlined box girders serve as a prevalent choice for the primary structural elements in large-span suspension bridge designs.With the increase in traffic demands,the design of such girders is evolving towards wider bridge decks and larger aspect ratios(B/D).To obtain more effective and aerodynamic design shapes for streamlined box girders,it is essential to investigate the impact of B/D on their aerodynamic performance.Accordingly,in this study we investigate the buffeting responses of large-span suspension bridges using girders of varying aspect ratios(B/D of 7.5,9.3,and 12.7).First,the aerodynamic coefficients of these girders are estimated using computational fluid dynamics(CFD)simulations.Subsequently,spatial finite element(FE)models of three long-span suspension bridges with different girders(B/D of 7.5,9.3,and 12.7)are established in Ansys software,and the dynamic characteristics of these bridges are obtained.Then,the time-domain buffeting analysis is performed by simulating the fluctuating wind fields acting on the bridge through the spectral representation method.Ultimately,the buffeting responses are computed using Ansys software,and the impact of B/D on these responses is assessed.The results reveal that the root mean square(RMS)values of the main girder’s buffeting displacement are highest at the midspan position and are lowest at the ends of the bridge.A decrease in B/D of the main girder leads to a more severe buffeting response because both the range and the effective value of the displacement increase with the decreasing B/D.Comparing the buffeting displacements in three directions,B/D plays a significant role in the vertical buffeting displacement,moderately impacts the torsional displacement,and has the least effect on the lateral displacement.The findings of this study may help wind resistance analysis and design optimization for bridges.展开更多
To clarify the deformation behavior of MnS inclusions in a non-quenched and tempered steel at three different positions (edge, 1/2 radius and center) in the cross-section of the billet in the course of hot rolling, is...To clarify the deformation behavior of MnS inclusions in a non-quenched and tempered steel at three different positions (edge, 1/2 radius and center) in the cross-section of the billet in the course of hot rolling, isothermal compression experiments were performed under the deformation temperature range from 1073 to 1473 K, the reduction rates from 25% to 75% and the strain rates from 0.01 to 10 s^(−1). The variations of deformability features (i.e., aspect ratios, size distributions, and morphologies) of MnS inclusions with those isothermal compression parameters were revealed. The evaluation of the probable maximum aspect ratio of MnS inclusions at the three different positions in the cross-section of the billet after hot rolling was examined using the statistical analysis of extreme values. Results showed that the number densities of MnS inclusions at three different positions (edge, 1/2 radius and center) in the cross-section of the steel billet only fluctuated slightly when the deformation parameters varied in the isothermal compression, while the average inclusion aspect ratios in all cases generally have a negative correlation with the deformation temperature and positive correlations with the reduction ratio and the strain rate. Statistical analysis reveals that larger inclusions deform more easily during hot rolling. The effect of rolling temperature on the extreme value of the aspect ratio of inclusions is the smallest, while the effects of initial size, reduction ratio and strain rate are more significant.展开更多
The aspect ratio of the structure has a significant impact on the overall stability of the ultra high-rise building. A large aspect ratio of the structure increases the risk of overturning and reduces the lateral stif...The aspect ratio of the structure has a significant impact on the overall stability of the ultra high-rise building. A large aspect ratio of the structure increases the risk of overturning and reduces the lateral stiffness of the structure, leading to significant tensile and compressive stresses in the isolated bearings. To study the effect of aspect ratio on the seismic response and overturning resistance of a new staggered story isolated structure, three models with different aspect ratios were established. Nonlinear time-history analysis of the three models was conducted using ETABS finite element software. The results indicate that the overturning moment and overturning resistance moment of the superstructure in the new staggered story isolated structure increase with an increasing aspect ratio. However, the increase in the overturning moment of the superstructure is much greater than the increase in the overturning resistance moment, resulting in a decrease in the overturning resistance ratio of the superstructure with an increasing aspect ratio. The overturning moment and overturning resistance moment of the substructure in the new staggered story isolated structure decrease with an increasing aspect ratio. However, the decrease in the overturning moment of the substructure is greater than the decrease in the overturning resistance moment, leading to an increase in the overturning resistance ratio of the substructure with an increasing aspect ratio. The decrease in the overturning resistance ratio of the superstructure in the new staggered story isolated structure is much greater than the increase in the overturning resistance ratio of the substructure. Therefore, as the aspect ratio of the overall structure increases, the overturning resistance ratio of the superstructure and the entire structure decreases.展开更多
Room-temperature mechanical properties of Cu50Zr40Ti10-xNix（0≤x≤4,mole fraction,%） bulk metallic glasses （BMG） with aspect ratios in the range of 1：1-2.5：1 and loading rates in the range of1×10^-5-1×...Room-temperature mechanical properties of Cu50Zr40Ti10-xNix（0≤x≤4,mole fraction,%） bulk metallic glasses （BMG） with aspect ratios in the range of 1：1-2.5：1 and loading rates in the range of1×10^-5-1×10^-2s^-1were systematically investigated by room-temperatureuniaxialcompression test.In the condition of an aspect ratio of 1：1, the superplasticity can be clearly observed for Cu50Zr40Ti10BMG when the loading rate is1×10^-4s^-1, while for Cu50Zr40Ti10-xNix（x=1-3, mole fraction, %） BMGs when the loading rate is1×10^-2s^-1. The plastic strain （εp）, yielding strength （σy） and fracture strength （σf） of the studied Cu-based BMGs significantly depend on the aspect ratio and the loading rate. In addition, theσyof the studied Cu-based BMGs with an aspect ratio of 1：1 is close to the σfof those with the other aspect ratios when the loading rate is1×10^-2s^-1. The mechanism for the mechanical response to the loading rate and the aspect ratiowas also discussed.展开更多
The shales of the Qiongzhusi Formation and Wufeng-Longmaxi Formations at Sichuan Basin and surrounding areas are presently the most important stratigraphic horizons for shale gas exploration and development in China. ...The shales of the Qiongzhusi Formation and Wufeng-Longmaxi Formations at Sichuan Basin and surrounding areas are presently the most important stratigraphic horizons for shale gas exploration and development in China. However, the regional characteristics of the seismic elastic properties need to be better determined. The ultrasonic velocities of shale samples were measured under dry conditions and the relations between elastic properties and petrology were systemically analyzed. The results suggest that 1） the effective porosity is positively correlated with clay content but negatively correlated with brittle minerals, 2） the dry shale matrix consists of clays, quartz, feldspars, and carbonates, and 3） organic matter and pyrite are in the pore spaces, weakly coupled with the shale matrix. Thus, by assuming that all connected pores are only present in the clay minerals and using the Gassmann substitution method to calculate the elastic effect of organic matter and pyrite in the pores, a relatively simple rock-physics model was constructed by combining the self-consistent approximation （SCA）, the differential effective medium （DEM）, and Gassmann＇s equation. In addition, the effective pore aspect ratio was adopted from the sample averages or estimated from the carbonate content. The proposed model was used to predict the P-wave velocities and generally matched the ultrasonic measurements very well.展开更多
In modern gas turbines, rim seal located between the stator-disc and rotor-disc is used to prevent hot-gas ingestion into the inner stage-gap of high pressure turbine. However, the purge flow supplied to the cavity th...In modern gas turbines, rim seal located between the stator-disc and rotor-disc is used to prevent hot-gas ingestion into the inner stage-gap of high pressure turbine. However, the purge flow supplied to the cavity through the rim seal interacts with the main flow, producing additional aerodynamic loss due to the mixing process which plays a significant role in the formation, development and evolution of downstream secondary flow. In this paper, a set of cascade representative of low aspect ratio turbine is selected to numerically investigate the influence of upstream cavity purge flow on the hub secondary flow structure and aerodynamic loss. Cascade with/without upstream cavity and four different purge mass flow rates are all taken into account in this simulation. Then, a deep insight into the loss mechanism of interaction between purge flow and main flow is gained. The results show that the presence of cavity and purge flow has a significant impact on the main flow which not only changes the vortex structure in both the passage and upstream cavity, but also alters the cascade exit flow angle distribution along the spanwise. Moreover, aerodynamic loss in the cascade rises with the increase of purge flow rate while the sealing effect is also enhanced. Therefore, the effect of upstream cavity purge flow must be considered in the process of turbine aerodynamic design. What is more, it is necessary to minimize the purge flow rate in order to reduce aerodynamic loss on the premise of satisfying cooling requirements.展开更多
A photochemistry coupled computational fluid dynamics （CFD） based numerical model has been developed to model the reactive pollutant dispersion within urban street canyons, particularly integrating the interrelation...A photochemistry coupled computational fluid dynamics （CFD） based numerical model has been developed to model the reactive pollutant dispersion within urban street canyons, particularly integrating the interrelationship among diurnal heating scenario （solar radiation affections in nighttime, daytime, and sun-rise/set）, wind speed, building aspect ratio （building-height-to-street-width）, and dispersion of reactive gases, specifically nitric oxide （NO）, nitrogen dioxide （NO2） and ozone （O3） such that a higher standard of air quality in metropolitan cities can be achieved. Validation has been done with both experimental and numerical results on flow and temperature fields in a street canyon with bottom heating, which justifies the accuracy of the current model. The model was applied to idealized street canyons of different aspect ratios from 0.5 to 8 with two different ambient wind speeds under different diurnal heating scenarios to estimate the influences of different aforementioned parameters on the chemical evolution of NO, NO2 and 03. Detailed analyses of vertical profiles of pollutant concentrations showed that different diurnal heating scenarios could substantially affect the reactive gases exchange between the street canyon and air aloft, followed by respective dispersion and reaction. Higher building aspect ratio and stronger ambient wind speed were revealed to be, in general, responsible for enhanced entrainment of 03 concentrations into the street canyons along windward walls under all diurnal heating scenarios. Comparatively, particular attention can be paid on the windward wall heating and nighttime uniform surface heating scenarios.展开更多
The complete stress-strain characteristics of sandstone specimens were investigated in a series of quasistatic monotonic uniaxial compression tests.Strain patterns development during pre-and post-peak behaviours in sp...The complete stress-strain characteristics of sandstone specimens were investigated in a series of quasistatic monotonic uniaxial compression tests.Strain patterns development during pre-and post-peak behaviours in specimens with different aspect ratios was also examined.Peak stress,post-peak portion of stress-strain,brittleness,characteristics of progressive localisation and field strain patterns development were affected at different extents by specimen aspect ratio.Strain patterns of the rocks were obtained by applying three-dimensional(3D) digital image correlation(DIC) technique.Unlike conventional strain measurement using strain gauges attached to specimen,3D DIC allowed not only measuring large strains,but more importantly,mapping the development of field strain throughout the compression test,i.e.in pre-and post-peak regimes.Field strain development in the surface of rock specimen suggests that strain starts localising progressively and develops at a lower rate in pre-peak regime.However,in post-peak regime,strains increase at different rates as local deformations take place at different extents in the vicinity and outside the localised zone.The extent of localised strains together with the rate of strain localisation is associated with the increase in rate of strength degradation.Strain localisation and local inelastic unloading outside the localised zone both feature post-peak regime.展开更多
In current guidelines, the free air blast loads(overpressure and impulse) are determined by spherical charges, although most of ordnance devices are more nearly cylindrical than spherical in geometry. This may result ...In current guidelines, the free air blast loads(overpressure and impulse) are determined by spherical charges, although most of ordnance devices are more nearly cylindrical than spherical in geometry. This may result in a great underestimation of blast loads in the near field and lead to an unsafe design.However, there is still a lack of systematic quantitative analysis of the blast loads generated from cylindrical charges. In this study, a numerical model is developed by using the hydrocode AUTODYN to investigate the influences of aspect ratio and orientation on the free air blast loads generated from center-initiated cylindrical charges. This is done by examining the pressure contours, the peak overpressures and impulses for various aspect ratios ranged from 1 to 8 and arbitrary orientation monitored along every azimuth angle with an interval of 5°. To characterize the distribution patterns of blast loads,three regions, i.e., the axial region, the vertex region and the radial region are identified, and the propagation of blast waves in each region is analyzed in detail. The complexity of blast loads of cylindrical charges is found to result from the bridge wave and its interaction with primary waves. Several empirical formulas are presented based on curve-fitting the numerical data, including the orientation where the maximum peak overpressure emerges, the critical scaled distance beyond which the charge shape effect could be neglected and blast loads with varied aspect ratio in arbitrary orientation, all of which are useful for blast-resistant design.展开更多
Severe tool wear and poor surface quality are the main problems during micro machining of cemented carbide.In this work,an innovative hybrid process of laser-induced oxidation assisted micro milling(LOMM)was proposed ...Severe tool wear and poor surface quality are the main problems during micro machining of cemented carbide.In this work,an innovative hybrid process of laser-induced oxidation assisted micro milling(LOMM)was proposed to solve the problems.A nanosecond laser was utilized to induce oxidation of the WC-20%Co material,producing loose oxide which was easy to remove.The micro machinability of the material was improved by laser-induced oxidation.The oxidation mechanisms of cemented carbide were studied.A microgroove with a depth of 2.5 mm and aspect ratio of 5 was fabricated successfully.The milling force,surface quality and tool wear mechanisms were investigated.For comparison,a microgroove was also fabricated with conventional micro milling(COMM)using identical milling parameters.Results revealed that in LOMM the milling force and tool wear rate were extremely low during removing the oxide.The machined surface quality and dimensional accuracy achieved by LOMM were superior to those obtained by COMM.The surface roughness Saof the microgroove bottom reached 88 nm in LOMM,while the cross-sectional geometry of the microgroove was a trapezoid.Perpendicularity of the microgroove sidewall machined by LOMM was better than that by COMM.The tool wear forms in LOMM were coating spalling and slight tool nose breakage.Compared with COMM,the tool life in LOMM was prolonged significantly.It indicates that the proposed hybrid process is an effective and efficient way to fabricate high aspect ratio micro-features with high dimensional accuracy.展开更多
In order to produceα-calcium sulfate hemihydrate(α-CaSO4·0.5H2O)whiskers with high aspect ratios,a minor amount of CuCl2·2H2O was used as the modifying agent in the process of hydrothermal treatment of cal...In order to produceα-calcium sulfate hemihydrate(α-CaSO4·0.5H2O)whiskers with high aspect ratios,a minor amount of CuCl2·2H2O was used as the modifying agent in the process of hydrothermal treatment of calcium sulfate dihydrate(CaSO4·2H2O)precursor.The presence of 2.60×10–3 mol/L CuCl2·2H2O resulted in the increase of the aspect ratios ofα-CaSO4·0.5H2O whiskers from 81 to 253.The preferential adsorption of Cu2+on the negative{110}and{100}facets ofα-CaSO4·0.5H2O crystal structures was confirmed by EDS and XPS.And ATR-FTIR demonstrated the ligand adsorption of Cu2+on the surface ofα-CaSO4·0.5H2O whiskers.The experimental results reveal that the whiskers with high aspect ratios are attributed to the adsorption of Cu2+,which promotes the 1-D growth ofα-CaSO4·0.5H2O whiskers along the c axis.展开更多
A theoretical nonlinear aeroelastic response analysis for a flexible high-aspect ratio wing excited by harmonic gust load is presented along with a companion wind tunnel test. A multidisci- plinary coupled numerical c...A theoretical nonlinear aeroelastic response analysis for a flexible high-aspect ratio wing excited by harmonic gust load is presented along with a companion wind tunnel test. A multidisci- plinary coupled numerical calculation is developed to simulate the flexible model wing undergoing gust load in the time domain via discrete nonlinear finite element structural dynamic analysis and nonplanar unsteady vortex lattice aerodynamic computation. A dynamic perturbation analysis about a nonlinear static equilibrium is also used to determine the small perturbation flutter bound- ary. A novel noncontact 3-D camera measurement analysis system is firstly used in the wind tunnel test to obtain the spatial large deformation and responses. The responses of the flexible wing under different static equilibrium states and frequency gust loads are discussed. The fair to good quanti- tative agreements between the theoretical and experimental results demonstrate that the presented analysis method is an acceptable way to predict the geometrically nonlinear gust response for flex- ible wings.展开更多
Eucalyptus is a major fast-grown species in South China,which has the potential for producing structural wood products such as cross-laminated timber(CLT).Aspect ratio(board width vs.board thickness)of eucalyptus lumb...Eucalyptus is a major fast-grown species in South China,which has the potential for producing structural wood products such as cross-laminated timber(CLT).Aspect ratio(board width vs.board thickness)of eucalyptus lumbers is small due to the small diameter of fast-grown eucalyptus wood.To evaluate its rolling shear modulus and strength for potential CLT applications,three-layer hybrid CLT shear block specimens with different aspect ratios(2,4,6),were tested by planar shear test method.Digital image correlation(DIC)was employed to measure the rolling shear strain distribution and development during the planar shear tests.The mean values of rolling shear modulus and strength of eucalyptus lamination were 260.3%and 88.2%higher than those of SPF(Spruce-pine-fir)lamination with the same aspect ratio of 4,respectively.The rolling shear properties of eucalyptus laminations increased as the aspect ratio increased.Aspect ratio had a significant influence on rolling shear modulus compared to rolling shear strength.The high shear strain regions were primarily found around the gaps between segments of cross layer.The quantity of high shear strain regions increased as the aspect ratio of lamination decreased.Other high shear strain regions also occurred around the pith and along the glue line.The sudden failure of specimen occurred in the high strain region.In conclusion,the rolling shear strength and modulus of fast-grown eucalyptus laminations exceed the respective characteristic values for softwoods in the current standard by roughly factors of 3 and 8,indicating great potential for fast-grown eucalyptus wood cross-layers in CLT.展开更多
Morphology as well as kinematics is a critical determinant of performance in flapping flight.To understand the effects of the structural traits on aerodynamics of bioflyers,three rectangular wings with aspect ratios...Morphology as well as kinematics is a critical determinant of performance in flapping flight.To understand the effects of the structural traits on aerodynamics of bioflyers,three rectangular wings with aspect ratios（AR）of1,2,and 4 performing hovering-like sinusoidal kinematics at wingtip based Reynolds number of 5 300 are experimentally investigated.Flow structures on sectional cuts along the wing span are compared.Stronger K-H instability is found on the leading edge vortex of wings with higher aspect ratios.Vortex bursting only appears on the outer spanwise locations of high-aspect-ratio wings.The vortex bursting on high-aspect-ratio wings is perhaps one of the reasons why bio-flyers normally have low-aspect-ratio wings.Quantitative analysis exhibits larger dimensionless circulation of the leading edge vortex（LEV）over higher aspect ratio wings except when vortex bursting happens.The average dimensionless circulation of AR1 and AR2 along the span almost equals the dimensionless circulation at the 50%span.The flow structure and the circulation analysis show that the sinusoidal kinematics suppresses breakdown of the LEV compared with simplified flapping kinematics used in similar studies.The Reynolds number effect results on AR4 show that in the current Re range,the overall flow structure is not sensitive to Reynolds number.展开更多
Quasi-static and compressive fatigue tests on the closed cell Al-Si-Ca alloy foam specimens with three different aspect ratios were performed. It turned out that the onset of cyclic shortening of foam with a lower asp...Quasi-static and compressive fatigue tests on the closed cell Al-Si-Ca alloy foam specimens with three different aspect ratios were performed. It turned out that the onset of cyclic shortening of foam with a lower aspect ratio took place earlier and the fatigue strength was lower compared with the specimen with a higher aspect ratio, although all the dimensions of specimen satisfied the seven times the cell size criterion, while the quasi-static stress-strain curves were almost same having same Young＇s modulus, yield stress and plateau stress. Therefore, the seven times the cell size criterion for the quasi-static compression behavior was not applicable to the fatigue analysis of Al-Si-Ca alloy foam.展开更多
Conventionally,flexible barriers are rated based on their ability to resist a free-falling boulder with a particular input energy.However,there is still no well-accepted approach for evaluating performance of flexible...Conventionally,flexible barriers are rated based on their ability to resist a free-falling boulder with a particular input energy.However,there is still no well-accepted approach for evaluating performance of flexible barrier under debris flow impact.In this study,a large-nonlinear finite-element model was used to back-analyze centrifuge tests to discern the effects of impact material type,barrier stiffness,and flow aspect ratio(flow height to flow length)on the reaction force between the impacting medium and flexible barrier.Results show that,in contrast to flexible barriers for resisting rockfall,the normal impact force induced by the highly frictional and viscous debris is insensitive to barrier stiffness.This is because the elongated distributions of kinetic energy are mainly dissipated by the internal and boundary shearing,and only a small portion is forwarded to the barrier.Furthermore,a new stiffness number is proposed to characterize the equivalent stiffness between a debris flow or a boulder,and a flexible barrier.Under the circumstance of an extremely elongated debris flow event,i.e.,low aspect ratio,the load on a barrier is dominated by the static component and thus not sensitive to the barrier stiffness.展开更多
Microcasting is one of the significant technologies for the production of metallic micro parts with high aspect ratio(ratio of flow length to diameter).A micro precision casting technology based on investment casting ...Microcasting is one of the significant technologies for the production of metallic micro parts with high aspect ratio(ratio of flow length to diameter).A micro precision casting technology based on investment casting using centrifugal method was investigated.The micro parts of Zn-4%Al alloy with an aspect ratio up to 200 was produced at the centrifugal speed of 1 500 r/min and the mold temperature of 270℃.The investigations on the relationship between flow length and rotational speed were carried out. For microcasting,the flow length is not only dependent on the centrifugal speed under the constant centrifugal radius,but also on the preheating temperature of mold.The flow length increases as the rotational speed and the mold temperature increase,and is much higher at a mold temperature of 270 ℃thanat other mold temperatures.展开更多
文摘Driver distraction is a leading cause of traffic accidents,with fatigue being a significant contributor.This paper introduces a novel method for detecting driver distraction by analyzing facial features using machine deep learning and 68 face model.The proposed system assesses driver tiredness by measuring the distance between key facial landmarks,such as the distance between the eyes and the angle of the mouth,to evaluate signs of drowsiness or disengagement.Real-time video feed analysis allows for continuous monitoring of the driver’s face,enabling the system to detect behavioral cues associated with distraction,such as eye closures or changes in facial expressions.The effectiveness of this method is demonstrated through a series of experiments on a dataset of driver videos,which proves that the approach can accurately assess tiredness and distraction levels under various driving conditions.By focusing on facial landmarks,the system is computationally efficient and capable of operating in real-time,making it a practical solution for in-vehicle safety systems.This paper discusses the system’s performance,limitations,and potential for future enhancements,including integration with other in-vehicle technologies to provide comprehensive driver monitoring.
基金supported by the National Natural Science Foundation of China (Grant Nos.12202294 and 12022208)the Project funded by China Postdoctoral Science Foundation (Grant No.2022M712243)the Fundamental Research Funds for the Central Universities (Grant No.2023SCU12098).
文摘It is well known that coarse-grained super-elastic NiTi shape memory alloys(SMAs)exhibit localized rather than homogeneous martensite transformation(MT),which,however,can be strongly influenced by either internal size(grain size,GS)or the external size(geometric size).The coupled effect of GS and geometric size on the functional properties has not been clearly understood yet.In this work,the super-elasticity,one-way,and stress-assisted two-way shape memory effects of the polycrystalline NiTi SMAs with different aspect ratios(length/width for the gauge section)and different GSs are investigated based on the phase field method.The coupled effect of the aspect ratio and GS on the functional properties is adequately revealed.The simulated results indicate that when the aspect ratio is lower than about 4:1,the stress biaxiality and stress heterogeneity in the gauge section of the sample become more and more obvious with decreasing the aspect ratio,which can significantly influence the microstructure evolution in the process involving external stress.Therefore,the corresponding functional property is strongly dependent on the aspect ratio.With decreasing the GS and the aspect ratio(to be lower than 4:1),both the aspect ratio and GS can affect the MT or martensite reorientation in each grain and the interaction among grains.Thus,due to the strong internal constraint(i.e.,the constraint of grain boundary)and the external constraint(i.e.,the constraint of geometric boundary),the capabilities of the functional properties of NiTi SMAs are gradually weakened and highly dependent on these two factors.
文摘Flow characteristics around a wall-mounted square cylinder have been numerically simulated at aspect ratios (AR) ranging from 4 to 7 at Re =10 000. Four turbulence models have been compared in terms of drag coefficient (C_D). The closest result has been provided by two turbulence models, namely, k-ε Realizable and k ?ω Shear Stress Transport (SST). Hence, these models were utilized to present the flow patterns of pressure distributions, turbulent kinetic energy values, velocity magnitude values with streamlines, streamwise velocity components, crossstream velocity components and spanwise velocity components on different planes. Flow stagnation has been attained in front of the cylinder. Pressure values peaked for the upstream region. Over the cylinders, the tip vortex structure was dominant owing to the influence of the free end. Flow separation from the top front edge of the body has been obtained. The dividing streamline affected by the flow separation was highly effective in the wake region and moved nearer to the body when the aspect ratio was decreased;the reason was the wake shrinkage owing to the decreasing aspect ratio. Upwash and downwash have been seen in the cylinder wake. These two models presented similar flow patterns and drag coefficients. These drag coefficients are in good agreement with those in previous studies.
基金funded by the National Natural Science Foundation of China(Grant No.52108435)the Science and Technology Research Program of Chongqing Municipal Education Commission(Grant No.KJQN202404320)+1 种基金Chongqing Jiaotong University Postgraduate Research and Innovation Project(2024S0013)Chongqing Jiaotong University Undergraduate Innovation and Entrepreneurship Project(S202410618019).
文摘Streamlined box girders serve as a prevalent choice for the primary structural elements in large-span suspension bridge designs.With the increase in traffic demands,the design of such girders is evolving towards wider bridge decks and larger aspect ratios(B/D).To obtain more effective and aerodynamic design shapes for streamlined box girders,it is essential to investigate the impact of B/D on their aerodynamic performance.Accordingly,in this study we investigate the buffeting responses of large-span suspension bridges using girders of varying aspect ratios(B/D of 7.5,9.3,and 12.7).First,the aerodynamic coefficients of these girders are estimated using computational fluid dynamics(CFD)simulations.Subsequently,spatial finite element(FE)models of three long-span suspension bridges with different girders(B/D of 7.5,9.3,and 12.7)are established in Ansys software,and the dynamic characteristics of these bridges are obtained.Then,the time-domain buffeting analysis is performed by simulating the fluctuating wind fields acting on the bridge through the spectral representation method.Ultimately,the buffeting responses are computed using Ansys software,and the impact of B/D on these responses is assessed.The results reveal that the root mean square(RMS)values of the main girder’s buffeting displacement are highest at the midspan position and are lowest at the ends of the bridge.A decrease in B/D of the main girder leads to a more severe buffeting response because both the range and the effective value of the displacement increase with the decreasing B/D.Comparing the buffeting displacements in three directions,B/D plays a significant role in the vertical buffeting displacement,moderately impacts the torsional displacement,and has the least effect on the lateral displacement.The findings of this study may help wind resistance analysis and design optimization for bridges.
基金supported by the National Natural Science Foundation of China(Grant Nos.52074198,52374342 and U21A20113)also supported by the Department of Science and Technology of Hubei Province(Grant No.2023AFB603 and No.2023DJC140).
文摘To clarify the deformation behavior of MnS inclusions in a non-quenched and tempered steel at three different positions (edge, 1/2 radius and center) in the cross-section of the billet in the course of hot rolling, isothermal compression experiments were performed under the deformation temperature range from 1073 to 1473 K, the reduction rates from 25% to 75% and the strain rates from 0.01 to 10 s^(−1). The variations of deformability features (i.e., aspect ratios, size distributions, and morphologies) of MnS inclusions with those isothermal compression parameters were revealed. The evaluation of the probable maximum aspect ratio of MnS inclusions at the three different positions in the cross-section of the billet after hot rolling was examined using the statistical analysis of extreme values. Results showed that the number densities of MnS inclusions at three different positions (edge, 1/2 radius and center) in the cross-section of the steel billet only fluctuated slightly when the deformation parameters varied in the isothermal compression, while the average inclusion aspect ratios in all cases generally have a negative correlation with the deformation temperature and positive correlations with the reduction ratio and the strain rate. Statistical analysis reveals that larger inclusions deform more easily during hot rolling. The effect of rolling temperature on the extreme value of the aspect ratio of inclusions is the smallest, while the effects of initial size, reduction ratio and strain rate are more significant.
文摘The aspect ratio of the structure has a significant impact on the overall stability of the ultra high-rise building. A large aspect ratio of the structure increases the risk of overturning and reduces the lateral stiffness of the structure, leading to significant tensile and compressive stresses in the isolated bearings. To study the effect of aspect ratio on the seismic response and overturning resistance of a new staggered story isolated structure, three models with different aspect ratios were established. Nonlinear time-history analysis of the three models was conducted using ETABS finite element software. The results indicate that the overturning moment and overturning resistance moment of the superstructure in the new staggered story isolated structure increase with an increasing aspect ratio. However, the increase in the overturning moment of the superstructure is much greater than the increase in the overturning resistance moment, resulting in a decrease in the overturning resistance ratio of the superstructure with an increasing aspect ratio. The overturning moment and overturning resistance moment of the substructure in the new staggered story isolated structure decrease with an increasing aspect ratio. However, the decrease in the overturning moment of the substructure is greater than the decrease in the overturning resistance moment, leading to an increase in the overturning resistance ratio of the substructure with an increasing aspect ratio. The decrease in the overturning resistance ratio of the superstructure in the new staggered story isolated structure is much greater than the increase in the overturning resistance ratio of the substructure. Therefore, as the aspect ratio of the overall structure increases, the overturning resistance ratio of the superstructure and the entire structure decreases.
基金Projects(50874045,51301194)supported by the National Natural Science Foundation of ChinaProject(2144057)supported by the Beijing Natural Science Foundation,China
文摘Room-temperature mechanical properties of Cu50Zr40Ti10-xNix（0≤x≤4,mole fraction,%） bulk metallic glasses （BMG） with aspect ratios in the range of 1：1-2.5：1 and loading rates in the range of1×10^-5-1×10^-2s^-1were systematically investigated by room-temperatureuniaxialcompression test.In the condition of an aspect ratio of 1：1, the superplasticity can be clearly observed for Cu50Zr40Ti10BMG when the loading rate is1×10^-4s^-1, while for Cu50Zr40Ti10-xNix（x=1-3, mole fraction, %） BMGs when the loading rate is1×10^-2s^-1. The plastic strain （εp）, yielding strength （σy） and fracture strength （σf） of the studied Cu-based BMGs significantly depend on the aspect ratio and the loading rate. In addition, theσyof the studied Cu-based BMGs with an aspect ratio of 1：1 is close to the σfof those with the other aspect ratios when the loading rate is1×10^-2s^-1. The mechanism for the mechanical response to the loading rate and the aspect ratiowas also discussed.
基金sponsored by the National Natural Science Foundation of China(No.41274185 and 41676032)
文摘The shales of the Qiongzhusi Formation and Wufeng-Longmaxi Formations at Sichuan Basin and surrounding areas are presently the most important stratigraphic horizons for shale gas exploration and development in China. However, the regional characteristics of the seismic elastic properties need to be better determined. The ultrasonic velocities of shale samples were measured under dry conditions and the relations between elastic properties and petrology were systemically analyzed. The results suggest that 1） the effective porosity is positively correlated with clay content but negatively correlated with brittle minerals, 2） the dry shale matrix consists of clays, quartz, feldspars, and carbonates, and 3） organic matter and pyrite are in the pore spaces, weakly coupled with the shale matrix. Thus, by assuming that all connected pores are only present in the clay minerals and using the Gassmann substitution method to calculate the elastic effect of organic matter and pyrite in the pores, a relatively simple rock-physics model was constructed by combining the self-consistent approximation （SCA）, the differential effective medium （DEM）, and Gassmann＇s equation. In addition, the effective pore aspect ratio was adopted from the sample averages or estimated from the carbonate content. The proposed model was used to predict the P-wave velocities and generally matched the ultrasonic measurements very well.
基金Key Laboratory Foundation (9140C4103091003C) for funding this work
文摘In modern gas turbines, rim seal located between the stator-disc and rotor-disc is used to prevent hot-gas ingestion into the inner stage-gap of high pressure turbine. However, the purge flow supplied to the cavity through the rim seal interacts with the main flow, producing additional aerodynamic loss due to the mixing process which plays a significant role in the formation, development and evolution of downstream secondary flow. In this paper, a set of cascade representative of low aspect ratio turbine is selected to numerically investigate the influence of upstream cavity purge flow on the hub secondary flow structure and aerodynamic loss. Cascade with/without upstream cavity and four different purge mass flow rates are all taken into account in this simulation. Then, a deep insight into the loss mechanism of interaction between purge flow and main flow is gained. The results show that the presence of cavity and purge flow has a significant impact on the main flow which not only changes the vortex structure in both the passage and upstream cavity, but also alters the cascade exit flow angle distribution along the spanwise. Moreover, aerodynamic loss in the cascade rises with the increase of purge flow rate while the sealing effect is also enhanced. Therefore, the effect of upstream cavity purge flow must be considered in the process of turbine aerodynamic design. What is more, it is necessary to minimize the purge flow rate in order to reduce aerodynamic loss on the premise of satisfying cooling requirements.
基金supported by the ICEE of the University of Hong Kong and the Hong Kong Research Grant Council(Project HKU7146/06E)
文摘A photochemistry coupled computational fluid dynamics （CFD） based numerical model has been developed to model the reactive pollutant dispersion within urban street canyons, particularly integrating the interrelationship among diurnal heating scenario （solar radiation affections in nighttime, daytime, and sun-rise/set）, wind speed, building aspect ratio （building-height-to-street-width）, and dispersion of reactive gases, specifically nitric oxide （NO）, nitrogen dioxide （NO2） and ozone （O3） such that a higher standard of air quality in metropolitan cities can be achieved. Validation has been done with both experimental and numerical results on flow and temperature fields in a street canyon with bottom heating, which justifies the accuracy of the current model. The model was applied to idealized street canyons of different aspect ratios from 0.5 to 8 with two different ambient wind speeds under different diurnal heating scenarios to estimate the influences of different aforementioned parameters on the chemical evolution of NO, NO2 and 03. Detailed analyses of vertical profiles of pollutant concentrations showed that different diurnal heating scenarios could substantially affect the reactive gases exchange between the street canyon and air aloft, followed by respective dispersion and reaction. Higher building aspect ratio and stronger ambient wind speed were revealed to be, in general, responsible for enhanced entrainment of 03 concentrations into the street canyons along windward walls under all diurnal heating scenarios. Comparatively, particular attention can be paid on the windward wall heating and nighttime uniform surface heating scenarios.
基金supported by the Deep Exploration Technologies Cooperative Research Centre whose activities are funded by the Australian Government's Cooperative Research Centre Programme.This is DET CRC Document 2017/954
文摘The complete stress-strain characteristics of sandstone specimens were investigated in a series of quasistatic monotonic uniaxial compression tests.Strain patterns development during pre-and post-peak behaviours in specimens with different aspect ratios was also examined.Peak stress,post-peak portion of stress-strain,brittleness,characteristics of progressive localisation and field strain patterns development were affected at different extents by specimen aspect ratio.Strain patterns of the rocks were obtained by applying three-dimensional(3D) digital image correlation(DIC) technique.Unlike conventional strain measurement using strain gauges attached to specimen,3D DIC allowed not only measuring large strains,but more importantly,mapping the development of field strain throughout the compression test,i.e.in pre-and post-peak regimes.Field strain development in the surface of rock specimen suggests that strain starts localising progressively and develops at a lower rate in pre-peak regime.However,in post-peak regime,strains increase at different rates as local deformations take place at different extents in the vicinity and outside the localised zone.The extent of localised strains together with the rate of strain localisation is associated with the increase in rate of strength degradation.Strain localisation and local inelastic unloading outside the localised zone both feature post-peak regime.
基金supported by the National Natural Science Foundations of China (51808550, 52078133)the China Postdoctoral Science Foundation (2020M671296)。
文摘In current guidelines, the free air blast loads(overpressure and impulse) are determined by spherical charges, although most of ordnance devices are more nearly cylindrical than spherical in geometry. This may result in a great underestimation of blast loads in the near field and lead to an unsafe design.However, there is still a lack of systematic quantitative analysis of the blast loads generated from cylindrical charges. In this study, a numerical model is developed by using the hydrocode AUTODYN to investigate the influences of aspect ratio and orientation on the free air blast loads generated from center-initiated cylindrical charges. This is done by examining the pressure contours, the peak overpressures and impulses for various aspect ratios ranged from 1 to 8 and arbitrary orientation monitored along every azimuth angle with an interval of 5°. To characterize the distribution patterns of blast loads,three regions, i.e., the axial region, the vertex region and the radial region are identified, and the propagation of blast waves in each region is analyzed in detail. The complexity of blast loads of cylindrical charges is found to result from the bridge wave and its interaction with primary waves. Several empirical formulas are presented based on curve-fitting the numerical data, including the orientation where the maximum peak overpressure emerges, the critical scaled distance beyond which the charge shape effect could be neglected and blast loads with varied aspect ratio in arbitrary orientation, all of which are useful for blast-resistant design.
基金the National Natural Science Foundation of China(No.51705249)the China Postdoctoral Science Foundation(No.2019M661823)+1 种基金the Aeronautical Science Foundation of China(No.2017ZE52047)the 111 Project on Key Technology in Sustainable Manufacturing(No.B16024)。
文摘Severe tool wear and poor surface quality are the main problems during micro machining of cemented carbide.In this work,an innovative hybrid process of laser-induced oxidation assisted micro milling(LOMM)was proposed to solve the problems.A nanosecond laser was utilized to induce oxidation of the WC-20%Co material,producing loose oxide which was easy to remove.The micro machinability of the material was improved by laser-induced oxidation.The oxidation mechanisms of cemented carbide were studied.A microgroove with a depth of 2.5 mm and aspect ratio of 5 was fabricated successfully.The milling force,surface quality and tool wear mechanisms were investigated.For comparison,a microgroove was also fabricated with conventional micro milling(COMM)using identical milling parameters.Results revealed that in LOMM the milling force and tool wear rate were extremely low during removing the oxide.The machined surface quality and dimensional accuracy achieved by LOMM were superior to those obtained by COMM.The surface roughness Saof the microgroove bottom reached 88 nm in LOMM,while the cross-sectional geometry of the microgroove was a trapezoid.Perpendicularity of the microgroove sidewall machined by LOMM was better than that by COMM.The tool wear forms in LOMM were coating spalling and slight tool nose breakage.Compared with COMM,the tool life in LOMM was prolonged significantly.It indicates that the proposed hybrid process is an effective and efficient way to fabricate high aspect ratio micro-features with high dimensional accuracy.
基金Project(B14034)supported by the National 111 Project,ChinaProject(2015CX005)supported by the Innovation Driven Plan of Central South University,ChinaProject(2016zzts104)supported by the Fundamental Research Funds for the Central Universities,China
文摘In order to produceα-calcium sulfate hemihydrate(α-CaSO4·0.5H2O)whiskers with high aspect ratios,a minor amount of CuCl2·2H2O was used as the modifying agent in the process of hydrothermal treatment of calcium sulfate dihydrate(CaSO4·2H2O)precursor.The presence of 2.60×10–3 mol/L CuCl2·2H2O resulted in the increase of the aspect ratios ofα-CaSO4·0.5H2O whiskers from 81 to 253.The preferential adsorption of Cu2+on the negative{110}and{100}facets ofα-CaSO4·0.5H2O crystal structures was confirmed by EDS and XPS.And ATR-FTIR demonstrated the ligand adsorption of Cu2+on the surface ofα-CaSO4·0.5H2O whiskers.The experimental results reveal that the whiskers with high aspect ratios are attributed to the adsorption of Cu2+,which promotes the 1-D growth ofα-CaSO4·0.5H2O whiskers along the c axis.
基金supported by the National Natural Science Foundation of China(Nos.11302011,11172025)the National Natural Science Foundation for Youth of China(No.11402013)
文摘A theoretical nonlinear aeroelastic response analysis for a flexible high-aspect ratio wing excited by harmonic gust load is presented along with a companion wind tunnel test. A multidisci- plinary coupled numerical calculation is developed to simulate the flexible model wing undergoing gust load in the time domain via discrete nonlinear finite element structural dynamic analysis and nonplanar unsteady vortex lattice aerodynamic computation. A dynamic perturbation analysis about a nonlinear static equilibrium is also used to determine the small perturbation flutter bound- ary. A novel noncontact 3-D camera measurement analysis system is firstly used in the wind tunnel test to obtain the spatial large deformation and responses. The responses of the flexible wing under different static equilibrium states and frequency gust loads are discussed. The fair to good quanti- tative agreements between the theoretical and experimental results demonstrate that the presented analysis method is an acceptable way to predict the geometrically nonlinear gust response for flex- ible wings.
基金the National Natural Science Foundation of China(Grant No.31570559 and No.51808293)Natural Science Foundation of Jiangsu Province,China(Grant No.BK20180778).
文摘Eucalyptus is a major fast-grown species in South China,which has the potential for producing structural wood products such as cross-laminated timber(CLT).Aspect ratio(board width vs.board thickness)of eucalyptus lumbers is small due to the small diameter of fast-grown eucalyptus wood.To evaluate its rolling shear modulus and strength for potential CLT applications,three-layer hybrid CLT shear block specimens with different aspect ratios(2,4,6),were tested by planar shear test method.Digital image correlation(DIC)was employed to measure the rolling shear strain distribution and development during the planar shear tests.The mean values of rolling shear modulus and strength of eucalyptus lamination were 260.3%and 88.2%higher than those of SPF(Spruce-pine-fir)lamination with the same aspect ratio of 4,respectively.The rolling shear properties of eucalyptus laminations increased as the aspect ratio increased.Aspect ratio had a significant influence on rolling shear modulus compared to rolling shear strength.The high shear strain regions were primarily found around the gaps between segments of cross layer.The quantity of high shear strain regions increased as the aspect ratio of lamination decreased.Other high shear strain regions also occurred around the pith and along the glue line.The sudden failure of specimen occurred in the high strain region.In conclusion,the rolling shear strength and modulus of fast-grown eucalyptus laminations exceed the respective characteristic values for softwoods in the current standard by roughly factors of 3 and 8,indicating great potential for fast-grown eucalyptus wood cross-layers in CLT.
基金supported by the Innovation Technology Commission(ITC)of the Government of the Hong Kong Special Administrative Region(HKSAR)with Project(ITS/115/13FP)Hong Kong Ph.D.Fellowship Scheme from the Research Grants Council(RGC)
文摘Morphology as well as kinematics is a critical determinant of performance in flapping flight.To understand the effects of the structural traits on aerodynamics of bioflyers,three rectangular wings with aspect ratios（AR）of1,2,and 4 performing hovering-like sinusoidal kinematics at wingtip based Reynolds number of 5 300 are experimentally investigated.Flow structures on sectional cuts along the wing span are compared.Stronger K-H instability is found on the leading edge vortex of wings with higher aspect ratios.Vortex bursting only appears on the outer spanwise locations of high-aspect-ratio wings.The vortex bursting on high-aspect-ratio wings is perhaps one of the reasons why bio-flyers normally have low-aspect-ratio wings.Quantitative analysis exhibits larger dimensionless circulation of the leading edge vortex（LEV）over higher aspect ratio wings except when vortex bursting happens.The average dimensionless circulation of AR1 and AR2 along the span almost equals the dimensionless circulation at the 50%span.The flow structure and the circulation analysis show that the sinusoidal kinematics suppresses breakdown of the LEV compared with simplified flapping kinematics used in similar studies.The Reynolds number effect results on AR4 show that in the current Re range,the overall flow structure is not sensitive to Reynolds number.
基金supported by Chungnam Automotive Technology Education Center(NURI)and BK 21.
文摘Quasi-static and compressive fatigue tests on the closed cell Al-Si-Ca alloy foam specimens with three different aspect ratios were performed. It turned out that the onset of cyclic shortening of foam with a lower aspect ratio took place earlier and the fatigue strength was lower compared with the specimen with a higher aspect ratio, although all the dimensions of specimen satisfied the seven times the cell size criterion, while the quasi-static stress-strain curves were almost same having same Young＇s modulus, yield stress and plateau stress. Therefore, the seven times the cell size criterion for the quasi-static compression behavior was not applicable to the fatigue analysis of Al-Si-Ca alloy foam.
基金support from the National Natural Science Foundation of China(Grant Nos.51809261,11672318,and 51709052)financial support from the Theme-based Research Grant T22-603/15N+1 种基金the General Research Fund 16209717 provided by the Research Grants Council of the Government of Hong Kong SAR,Chinafinancial support by the Hong Kong Jockey Club Disaster Preparedness and Response Institute(HKJCDPRI18EG01)
文摘Conventionally,flexible barriers are rated based on their ability to resist a free-falling boulder with a particular input energy.However,there is still no well-accepted approach for evaluating performance of flexible barrier under debris flow impact.In this study,a large-nonlinear finite-element model was used to back-analyze centrifuge tests to discern the effects of impact material type,barrier stiffness,and flow aspect ratio(flow height to flow length)on the reaction force between the impacting medium and flexible barrier.Results show that,in contrast to flexible barriers for resisting rockfall,the normal impact force induced by the highly frictional and viscous debris is insensitive to barrier stiffness.This is because the elongated distributions of kinetic energy are mainly dissipated by the internal and boundary shearing,and only a small portion is forwarded to the barrier.Furthermore,a new stiffness number is proposed to characterize the equivalent stiffness between a debris flow or a boulder,and a flexible barrier.Under the circumstance of an extremely elongated debris flow event,i.e.,low aspect ratio,the load on a barrier is dominated by the static component and thus not sensitive to the barrier stiffness.
文摘Microcasting is one of the significant technologies for the production of metallic micro parts with high aspect ratio(ratio of flow length to diameter).A micro precision casting technology based on investment casting using centrifugal method was investigated.The micro parts of Zn-4%Al alloy with an aspect ratio up to 200 was produced at the centrifugal speed of 1 500 r/min and the mold temperature of 270℃.The investigations on the relationship between flow length and rotational speed were carried out. For microcasting,the flow length is not only dependent on the centrifugal speed under the constant centrifugal radius,but also on the preheating temperature of mold.The flow length increases as the rotational speed and the mold temperature increase,and is much higher at a mold temperature of 270 ℃thanat other mold temperatures.
