Al/Mg bimetal was prepared by lost foam solid-liquid compound casting,and the effects of mechanical vibration on the filling and solidification behavior,microstructure and performance of the bimetal were investigated....Al/Mg bimetal was prepared by lost foam solid-liquid compound casting,and the effects of mechanical vibration on the filling and solidification behavior,microstructure and performance of the bimetal were investigated.Results show that the mechanical vibration has a remarkable influence on the filling and solidification processes.It is found that after mechanical vibration,the filling rate increases and the filling rate at different times is more uniform than that without vibration.In addition,the mechanical vibration also increases the wettability between liquid AZ91D and A356 inlays.The mechanical vibration reduces the horizontal and vertical temperature gradient of the casting and makes the temperature distribution of the whole casting more uniform.Compared to the Al/Mg bimetal without vibration,the shear strength is improved by 39.76%after the mechanical vibration is applied,due to the decrease of the inclusions and Al_(12)Mg_(17) dendrites,and the refinement and uniform distribution of the Mg_(2)Si particles in the interface of the Al/Mg bimetal.展开更多
A mechanical vibration technique to refine solidified microstructure was reported. Vibration energy was directly introduced into a molten alloy by a vibrating horn, and the vibrating horn was melted during vibration. ...A mechanical vibration technique to refine solidified microstructure was reported. Vibration energy was directly introduced into a molten alloy by a vibrating horn, and the vibrating horn was melted during vibration. Effects of vibration acceleration and mass ratio on the microstructure of Al-5% Cu alloy were investigated. Results show that the present mechanical vibration could provide localized cooling by extracting heat from the interior of molten alloy, and the cooling rate is strongly dependent on vibration acceleration. It is difficult to refine the solidified microstructure when the treated alloy keeps full liquid state within the entire vibrating duration. Significantly refined microstructure was obtained by applying mechanical vibration during the initial stage of solidification. Moreover, mechanisms of grain refinement were discussed.展开更多
The burst feeding behavior of ZL205 A casting under mechanical vibration and low pressure was investigated by casting experiment and physical model. Experimental results indicated that the burst feeding appeared repea...The burst feeding behavior of ZL205 A casting under mechanical vibration and low pressure was investigated by casting experiment and physical model. Experimental results indicated that the burst feeding appeared repeatedly during solidification and left a shrinkage cavity with layered structure under mechanical vibration. The castings with less shrinkage and higher density could be achieved through the vibration. The calculation results of physical model showed that the burst feeding could perform spontaneously under vibration while difficultly without vibration in low-pressure die casting. The obstruction of a casting could be broken and the grains could be rearranged by the vibration. And the obstruction could be carried away due to the inner and outer pressure difference, causing a burst feeding.展开更多
Mechanical vibration was applied to the solidification of a lost foam cast(LFC) 356 aluminum alloy.Effects of mechanical vibration,with different peak acceleration,on the size and morphology of α-Al phase,and also on...Mechanical vibration was applied to the solidification of a lost foam cast(LFC) 356 aluminum alloy.Effects of mechanical vibration,with different peak acceleration,on the size and morphology of α-Al phase,and also on the mechanical properties of the castings were studied.Results indicated that α-Al dendrites gradually grow into equiaxed grains as the peak acceleration of vibration is increased.When the peak acceleration is between about 1 to 4 g,α-Al phase distribution is uniform and is refined obviously.α-Al dendrites are reduced and the mechanical properties of the castings are improved significantly when compared to those of the castings that are produced without vibration.However,when the peak acceleration is higher than 4 g,strong vibration will lead to defects formation,such as sand adhesion,while the amount and size of pores will be increased.And due to the turbulent flow that caused by strong vibration,the chance of forming large pores in the matrix has been increased significantly.The increase in defects will result in the deterioration of mechanical properties.展开更多
As an alternative power solution for low-power devices, harvesting energy from the ambient mechanical vibration has received increasing research interest in recent years. In this paper we study the transient dynamic c...As an alternative power solution for low-power devices, harvesting energy from the ambient mechanical vibration has received increasing research interest in recent years. In this paper we study the transient dynamic characteristics of a piezoelectric energy harvesting system including a piezoelectric energy harvester, a bridge rectifier, and a storage capacitor. To accomplish this, this energy harvesting system is modeled, and the charging process of the storage capacitor is investigated by employing the in-phase assumption The results indicate that the charging voltage across the storage capacitor and the gathered power increase gradually as the charging process proceeds, whereas the charging rate slows down over time as the charging voltage approaches to the peak value of the piezoelectric voltage across the piezoelectric materials. In addition, due to the added electrical damping and the change of the system natural frequency when the charging process is initiated, a sudden drop in the vibration amplitude is observed, which in turn affects the charging rate. However, the vibration amplitude begins to increase as the charging process continues, which is caused by the decrease in the electrical damping (i.e., the decrease in the energy removed from the mechanical vibration). This electromechanical coupling characteristic is also revealed by the variation of the vibration amplitude with the charging voltage.展开更多
This study investigated the microstructure,physical,and mechanical properties of die-cast A308 alloy subjected to mechanical vibration during solidification.Different frequencies(0,20,30,40,and 50 Hz)at constant ampli...This study investigated the microstructure,physical,and mechanical properties of die-cast A308 alloy subjected to mechanical vibration during solidification.Different frequencies(0,20,30,40,and 50 Hz)at constant amplitude(31μm)were employed using a power amplifier as the power input device.X-ray diffraction,optical microscopy,and scanning electron microscopy were used to examine the morphological changes in the cast samples under stationary and vibratory conditions.Metallurgical features of the castings were evaluated using Image J software.The average values of metallurgical features,including primaryα-Al grain size,dendrite arm spacing,average area of eutectic silicon,aspect ratio,and percentage porosity,reduced by 34%,59%,56%,22%,and 62%,respectively,at 30 Hz frequency compared with stationary casting.Mechanical tests of the cast samples showed that the yield strength(YS),ultimate tensile strength(UTS),percentage elongation(%EL),and microhardness(HV)increased by 8%,13%,17%,and 16%,respectively,at 30 Hz frequency compared with stationary casting.The fractured surface of the tensile specimens exhibited mixed-mode fracture behavior because of brittle facets,cleavage facets,ductile tearing,and dimple morphologies.The presence of small dimples showed that plastic deformation occurred before fracture.展开更多
Energy preservation is one of the key components in developing eco-friendly machines.In industry,the majority of machines lose a considerable amount of energy through mechanical vibrations.However,the wasted energy th...Energy preservation is one of the key components in developing eco-friendly machines.In industry,the majority of machines lose a considerable amount of energy through mechanical vibrations.However,the wasted energy through vibration can be utilized as a renewable energy source to compensate for the overall energy loss.The research work presented in this paper discusses the ability to design a linear power generator utilizing Nd Fe-B magnets,which can generate energy through mechanical vibrations.A pilot model was developed and simulated to understand the efficiency and limitation.The results showed that the model could reduce 14% rotor bulk with a marginal impact on the current generation.展开更多
Al2O3/YSZ composite ceramics was fabricated with combustion synthesis technology, and the influences of mechanical vibration on its microstructures and properties were investigated. It is found that under the mechanic...Al2O3/YSZ composite ceramics was fabricated with combustion synthesis technology, and the influences of mechanical vibration on its microstructures and properties were investigated. It is found that under the mechanical vibration of ever-increasing frequency, increasing combustion temperature, accelerating ceramics/metal liquid-liquid separation and quickening ceramic solidification could not only reduce the average diameter and the size distribution of aligned ZrO2 nano-micron fibers in rod-shaped Al2O3 matrix grains, but also make the randomly-oriented rod-shaped grains finer and increase their aspect ratios. As a result, a remarkable increase in flexural strength and fracture toughness of the ceramics can be observed.展开更多
To refine the microstructure and improve the mechanical properties of AZ91 D alloy by expendable pattern shell casting(EPSC),the mechanical vibration method was applied in the solidification process of the alloy.The e...To refine the microstructure and improve the mechanical properties of AZ91 D alloy by expendable pattern shell casting(EPSC),the mechanical vibration method was applied in the solidification process of the alloy.The effects of amplitude and pouring temperature on microstructure and mechanical properties of AZ91 D magnesium alloy were studied.The results indicated that the mechanical vibration remarkably improved the sizes,morphologies and distributions of the primaryα-Mg phase andβ-Mg17 Al12 phase,and the densification and tensile properties of the AZ91 D alloy.With an increase in amplitude,the microstructures were gradually refined,resulting in a continuous increase in mechanical properties of the AZ91 D alloy.While,with the increase of pouring temperature,the microstructures were continuously coarsened,leading to an obvious decrease of the mechanical properties.The tensile strength and yield strength of the AZ91 D alloy with a vibration amplitude of 1.0 mm and a pouring temperature of 730℃were 60%and 38%higher than those of the alloy without vibration,respectively.展开更多
This paper presents the result of an experimental study on the compression of mechanical vibration signals. The signals are collected from both rotating and reciprocating machineries by the accelerometers and a data a...This paper presents the result of an experimental study on the compression of mechanical vibration signals. The signals are collected from both rotating and reciprocating machineries by the accelerometers and a data acquisition (DAQ) system. Four optimal sparse representation methods for compression have been considered including the method of frames ( MOF), best orthogonal basis ( BOB), matching pursuit (MP) and basis pursuit (BP). Furthermore, several indicators including compression ratio (CR), mean square error (MSE), energy retained (ER) and Kurtosis are taken to evaluate the performance of the above methods. Experimental results show that MP outperforms other three methods.展开更多
The root development of Actinidia chinensis planUets was studied in exposure to environmental stress of mechanical vibration at respectively 1 Hz, 2 Hz, 3 Hz, 4 Hz and 5 Hz. The plantlets exposed to vibration stimuli ...The root development of Actinidia chinensis planUets was studied in exposure to environmental stress of mechanical vibration at respectively 1 Hz, 2 Hz, 3 Hz, 4 Hz and 5 Hz. The plantlets exposed to vibration stimuli at all those frequencies have a larger total number and a larger total length of roots and a smaller permeability of root plasma-membrane, compared with those cultivated in an environment without vibration stress. Vibration at respectively 1 Hz, 2 Hz, 3 Hz and 4 Hz enhances root activity and the 3 Hz vibration is the most favorable. There is an obvious negative correlation between root activity and permeability of root plasma-membrane. The effects may be explained by the likelihood that mechanical Vibration at an appropriate frequency facilitates roots' absorbing water and minerals which are indispensable to inducing and synthesizing in roots some active substances favorable to growth. Nevertheless, overstress damages the integrity of root plasm-membrane, increases the permeability, and results in the disability of protecting root cells.展开更多
When material properties, geometry parameters and applied loads are assumed to be stochastic, the vibration equation of a system is transformed to static problem by using Newmark method. In order to improve the comput...When material properties, geometry parameters and applied loads are assumed to be stochastic, the vibration equation of a system is transformed to static problem by using Newmark method. In order to improve the computational efficiency and to save storage, the Conjugate Gradient (CG) method is presented. The CG is an effective method for solving a large system of linear equations and belongs to the method of iteration with rapid convergence and high precision. An example is given and calculated results are compared to validate the proposed methods.展开更多
Effects of ultrasonic vibration(UV)and mechanical vibration(MV)on the Mn-rich phase modification and mechanical properties of Al−12Si−4Cu−1Ni−1Mg−2Mn piston alloys were investigated.The results show that the UV and UV...Effects of ultrasonic vibration(UV)and mechanical vibration(MV)on the Mn-rich phase modification and mechanical properties of Al−12Si−4Cu−1Ni−1Mg−2Mn piston alloys were investigated.The results show that the UV and UV+MV treatments can significantly refine and fragmentize the microstructures.In addition,UV treatment can significantly passivate the primary Mn-rich Al15Mn3Si2 intermetallics.The formation mechanisms of refinement and passivation of the grains and non-dendrite particles were discussed.Compared with the gravity die-cast alloys,the UV and UV+MV treated alloys exhibit improved tensile and creep resistance at room and elevated temperatures.These results can be attributed to the refinement of theα(Al)grains and the secondary intermetallics,the increased proportion of refined heat-resistant precipitates,and the formation of nano-sized Si particles.The ultimate tensile strength of the UV treated alloys at 350℃ exceeds that of commercial piston alloys.This indicates the high application potential of the developed piston alloys in density diesel engines.展开更多
Objective: To investigate the curative effect of the self-made mechanical vibration massage instrument for treatment of brachial plexus injury in rats and to explore its mechanism. Methods: Brachial plexus injury mode...Objective: To investigate the curative effect of the self-made mechanical vibration massage instrument for treatment of brachial plexus injury in rats and to explore its mechanism. Methods: Brachial plexus injury models were made in 144 Wistar rats and one week after natural healing of the wound, they were randomly divided into 3 groups, mechanical vibration treatment group (MV group), nerve growth factor treatment group (NGF group) and model group, 48 rats in each group. Then again, the each group was randomly divided into 4 subgroups, 7-day group, 14-day group, 21-day group and 28-day group, 12 rats in each subgroup. The MV group were treated by mechanical vibration at acupoints on three-yang and three-yin channels of the hand with the mechanical vibration massage instrument; The NGF group were treated with injection of NGF into musculus pectoralis major on the affected side; And the model group were normally fed with no treatment. After treatment for 7, 14, 21 and 28 days, the diameter of both forelimbs were measured, the electrophysiological examination on the brachial plexus in vitro and the ultrastructure observation with electron microscope on the affected side were carried out, the motor nerve conduction velocity (MNCV) and motor nerve action potential (MNAP) of the brachial plexus on the affected side, NGF content of submaxillary gland as well as muscular Na+, K+-ATPase activity were determined respectively. Results: The different rates of the forelimb diameter in the MV group and the NGV group on the 14th d, 21st d and 28th d were better than those in the model group (P<0.05 or P<0.001), and in the MV group were better than those in the NGF group on the 21st d and the 28th d (P<0.05). MNCV in the MV group and the NGV group on the 21st d and 28th d was better than that in the model group (P<0.05 or P<0.001), and in the MV group was better than that in the NGF group on the 28th d (P<0.05). MNAP in the MV group and the NGV group on the 14th d, 21st d and 28th d was better than that in the model group (P<0.05 or P<0.001), and in the MV group was better than that in the NGF group on the 21st d and 28th d (P<0.05). The NGF mean gray index of submaxillary gland in the model group was higher than that in the MV group and the NGF group on the 7th d (P<0.05); in the NGF group and the model group was higher than that in the MV group on the 14th d (P<0.05); and in the NGF group and the MV group was higher than that in the model group on the 21st d and 28th d (P<0.05). Na+, K+-ATPase activity in the model group and the MV group was higher than that in the NGF group (P<0.05) on the 14th d, and in the MV group was higher than that in the model group on the 28th d (P<0.05). Conclusion: As compared with the NGF group and the model group, mechanical vibration treatment can effectively accelerate repair of injured brachial plexus, slow down atrophy of skeletal muscle, and promote secretion of NGF in submaxillary gland.展开更多
Batteries often show the coupling change of multiple physical field characteristic parameters in the charging or discharging processes.Conventional battery modeling and characterization methods mainly focus on electri...Batteries often show the coupling change of multiple physical field characteristic parameters in the charging or discharging processes.Conventional battery modeling and characterization methods mainly focus on electrical or thermal parameters.Considering that battery state change can cause a change in the mechanical structure,research on the vibration characteristic modeling and characterization of a plastic-cased lithium-ion battery is carried out.By analyzing the mechanical structure of the battery,the first principles modeling method is selected to model the battery's mechanical performance.The vibration data in the process of battery charging and discharging are measured by a laser Doppler vibrometer(LDV).The obtained experimental data are used to identify the mechanical parameters of the battery.Based on the experimentael results,the root mean square error(RMSE)of the frequency domain amplitude fitting result of the model is less than 11.36%.The effectiveness of the battery mechanical vibration model is verified.The model and the characterization method provide tools for nondestructive battery state evaluation.展开更多
Immunomagnetic bead(IMB)-based detection has great potential for biomedical applications.Passive and active strategies,including microfluidics and magnetic actuation methods,have been developed to mix IMBs and analyte...Immunomagnetic bead(IMB)-based detection has great potential for biomedical applications.Passive and active strategies,including microfluidics and magnetic actuation methods,have been developed to mix IMBs and analytes efficiently.However,cost-effective on-site detection using a simple microfluidic chip is challenging,and miniaturization of the magnetic driving device is imperative for portability.In this study,we propose a novel mixing method for an on-chip IMB swarm via magnetic actuation and mechanical vibration.A microfluidic chip system coupled with double spiral magnetic coils and a vibration motor was fabricated.The aggregation behavior of IMBs under magnetic fields and the diffusion behavior of the IMB swarm under mechanical vibration were analyzed in detail.Based on the synergetic effects of magnetic actuation and mechanical vibration,we achieved the highly efficient capturing of Vibrio parahaemolyticus DNA and goat anti-human immunoglobulin G by mixing the IMB swarm with the microfluidic chip.In this case,the antigen detection rate could reach~94.4%.Given its fascinating features,such IMB-microfluidic detection demonstrates significant potential for biomedical applications.展开更多
The present work investigates the mechanically forced vibration of the hydro-elasto-piezoelectric system consisting of a two-layer plate“elastic+PZT”,a compressible viscous fluid,and a rigid wall.It is assumed that ...The present work investigates the mechanically forced vibration of the hydro-elasto-piezoelectric system consisting of a two-layer plate“elastic+PZT”,a compressible viscous fluid,and a rigid wall.It is assumed that the PZT(piezoelectric)layer of the plate is in contact with the fluid and time-harmonic linear forces act on the free surface of the elastic-metallic layer.This study is valuable because it considers for the first time the mechanical vibration of the metal+piezoelectric bilayer plate in contact with a fluid.It is also the first time that the influence of the volumetric concentration of the constituents on the vibration of the hydro-elasto-piezoelectric system is studied.Another value of the present work is the use of the exact equations and relations of elasto-electrodynamics for elastic and piezoelectric materials to describe the motion of the plate layers within the framework of the piecewise homogeneous body model and the use of the linearized Navier-Stokes equations to describe the flow of the compressible viscous fluid.The plane-strain state in the plate and the plane flow in the fluid take place.For the solution of the corresponding boundary-value problem,the Fourier transform is used with respect to the spatial coordinate on the axis along the laying direction of the plate.The analytical expressions of the Fourier transform of all the sought values of each component of the system are determined.The origins of the searched values are determined numerically,after which numerical results on the stress on the fluid and plate interface planes are presented and discussed.These results are obtained for the case where PZT-2 is chosen as the piezoelectric material,steel and aluminum as the elastic metal materials,and Glycerin as the fluid.Analysis of these results allows conclusions to be drawn about the character of the problem parameters on the frequency response of the interfacial stress.In particular,it was found that after a certain value of the vibration frequency,the presence of the metal layer in the two-layer plate led to an increase in the absolute values of the above interfacial stress.展开更多
Nickel-based alloys exhibit excellent high-temperature stxengtfi and oxidation resistance; however, because of coarse grains and severe segregation in daeir welding joints, these alloys exhibit increased susceptibilit...Nickel-based alloys exhibit excellent high-temperature stxengtfi and oxidation resistance; however, because of coarse grains and severe segregation in daeir welding joints, these alloys exhibit increased susceptibility to hot cracking. In this paper, to improve the hot-cracking resistance and mechaxtical properties ofinckel-based alloy welded joints, sodium daiosulfate was used to simulate crystallization, enabling the nucleation mechanism under mechaxtical vibration to be investigated. On the basis of the results, the grain refinement mechan- ism during the gas tungsten arc welding (GTAW) of Inconel 601H alloy under wxious vibration modes and parameters was investigated. Compared witfi the GTAW process, the low-frequency mechanical vibration processes resulted in substantial grain refinement effects in the welds; thus, a higher haxdness distxibution was also achieved under the vibration conditions. In addition, the 7' phase exhibited a dispersed distribution and segregation was improved in the welded joints witfi vibration assistance. The results demonstxated that the generation of free crystals caused by vibration in the nucleation stage was the main mechaxtism of grain refinement. Also, free equiaxed grains and a dispersed 7' phase were found to improve the grain-boundary strength and reduce the segregation, contributing to preventing the initiation of welding hot cracking in nickel-based alloys.展开更多
EN-GJS-450-10 ductile cast iron was produced with and without vibration to evaluate microstructural features. To investigate the effect of vibration, a reference, and two different castings having amplitudes of 0.9 mm...EN-GJS-450-10 ductile cast iron was produced with and without vibration to evaluate microstructural features. To investigate the effect of vibration, a reference, and two different castings having amplitudes of 0.9 mm and 1.8 mm were cast with a fixed vibration frequency of 50 Hz. The nodule count (density), form (type), size distribution, nodularity, and the fraction of graphite, percentages of both ferrite and pearlite phases, length of ferrite shell, and pore, were evaluated via optical microscopy using an image analysis software. It is observed that the microstructure of the cast iron is more uniform by vibrational casting than that by non-vibrational casting. Additionally, mechanical vibration enhances nodule count and nodularity, also, more ferritic matrix could be obtained after the application of vibration. Nodule count and nodularity of vibrational casting with 1.8 mm amplitude increased from 226 nodule per mm2 and 80% to 311 nodule per mm2 and 86.5% of non-vibrational casting. Percentages of ferrite and graphite area dramatically improved from 24% and 16.5% for non-vibrational casting to 57% and 22.3% for vibrational casting with 1.8 mm amplitude, whereas the percentages of pearlite and pores decreased significantly from 56.1% and 5% to 20% and 1%, respectively.展开更多
The vibration of machines due to rotating parts unbalance disturbs the machine functioning and shortens the lifetime of its parts. A dynamic vibration absorber is a favorite solution to suppress the machine vibration ...The vibration of machines due to rotating parts unbalance disturbs the machine functioning and shortens the lifetime of its parts. A dynamic vibration absorber is a favorite solution to suppress the machine vibration since its implementation does not require any modification neither on the machine nor on its installation. The paper considers an unbalanced machine to which a lumped mass dynamic vibration absorber is attached. Firstly, the machine equipped with the absorber is modeled, and the vibration expressions are extracted. Secondly, an original approach to optimize the absorber parameters is presented, and simulation results are advanced, when the absorber is undamped and damped. Thirdly, the absorber optimal parameters allowing the best vibration reduction of the machine are identified, showing bow the absorber should be designed, when the disturbance frequency is stable or unstable. The results are a significant contribution in the vibration control of unbalanced machines.展开更多
基金This work was funded by the National Natural Science Foundation of China(Nos.52075198,52271102 and 52205359)the China Postdoctoral Science Foundation(No.2021M691112).
文摘Al/Mg bimetal was prepared by lost foam solid-liquid compound casting,and the effects of mechanical vibration on the filling and solidification behavior,microstructure and performance of the bimetal were investigated.Results show that the mechanical vibration has a remarkable influence on the filling and solidification processes.It is found that after mechanical vibration,the filling rate increases and the filling rate at different times is more uniform than that without vibration.In addition,the mechanical vibration also increases the wettability between liquid AZ91D and A356 inlays.The mechanical vibration reduces the horizontal and vertical temperature gradient of the casting and makes the temperature distribution of the whole casting more uniform.Compared to the Al/Mg bimetal without vibration,the shear strength is improved by 39.76%after the mechanical vibration is applied,due to the decrease of the inclusions and Al_(12)Mg_(17) dendrites,and the refinement and uniform distribution of the Mg_(2)Si particles in the interface of the Al/Mg bimetal.
基金Project(50804023)supported by the National Natural Science Foundation of ChinaProject(GJJ12032)supported by the Education Department of Jiangxi Province,China+1 种基金Project(20122BAB206021)supported by the Natural Science Foundation of Jiangxi Province,ChinaProject(20122BCB23001)supported by the Jiangxi Province Young Scientists Cultivating Programs,China
文摘A mechanical vibration technique to refine solidified microstructure was reported. Vibration energy was directly introduced into a molten alloy by a vibrating horn, and the vibrating horn was melted during vibration. Effects of vibration acceleration and mass ratio on the microstructure of Al-5% Cu alloy were investigated. Results show that the present mechanical vibration could provide localized cooling by extracting heat from the interior of molten alloy, and the cooling rate is strongly dependent on vibration acceleration. It is difficult to refine the solidified microstructure when the treated alloy keeps full liquid state within the entire vibrating duration. Significantly refined microstructure was obtained by applying mechanical vibration during the initial stage of solidification. Moreover, mechanisms of grain refinement were discussed.
基金Projects(51475120,U1537201) supported by the National Natural Science Foundation of China
文摘The burst feeding behavior of ZL205 A casting under mechanical vibration and low pressure was investigated by casting experiment and physical model. Experimental results indicated that the burst feeding appeared repeatedly during solidification and left a shrinkage cavity with layered structure under mechanical vibration. The castings with less shrinkage and higher density could be achieved through the vibration. The calculation results of physical model showed that the burst feeding could perform spontaneously under vibration while difficultly without vibration in low-pressure die casting. The obstruction of a casting could be broken and the grains could be rearranged by the vibration. And the obstruction could be carried away due to the inner and outer pressure difference, causing a burst feeding.
基金supported by the National High Technology Research and Development Program of China (Grant No.2007AA03Z113)The National Natural Science Foundation of China (Grant No.50775085)
文摘Mechanical vibration was applied to the solidification of a lost foam cast(LFC) 356 aluminum alloy.Effects of mechanical vibration,with different peak acceleration,on the size and morphology of α-Al phase,and also on the mechanical properties of the castings were studied.Results indicated that α-Al dendrites gradually grow into equiaxed grains as the peak acceleration of vibration is increased.When the peak acceleration is between about 1 to 4 g,α-Al phase distribution is uniform and is refined obviously.α-Al dendrites are reduced and the mechanical properties of the castings are improved significantly when compared to those of the castings that are produced without vibration.However,when the peak acceleration is higher than 4 g,strong vibration will lead to defects formation,such as sand adhesion,while the amount and size of pores will be increased.And due to the turbulent flow that caused by strong vibration,the chance of forming large pores in the matrix has been increased significantly.The increase in defects will result in the deterioration of mechanical properties.
基金Project supported by the National Natural Science Foundation of China(Grant No.10476019)the Fundamental Research Funds for the Central Universities(Grant No.K5051304011)
文摘As an alternative power solution for low-power devices, harvesting energy from the ambient mechanical vibration has received increasing research interest in recent years. In this paper we study the transient dynamic characteristics of a piezoelectric energy harvesting system including a piezoelectric energy harvester, a bridge rectifier, and a storage capacitor. To accomplish this, this energy harvesting system is modeled, and the charging process of the storage capacitor is investigated by employing the in-phase assumption The results indicate that the charging voltage across the storage capacitor and the gathered power increase gradually as the charging process proceeds, whereas the charging rate slows down over time as the charging voltage approaches to the peak value of the piezoelectric voltage across the piezoelectric materials. In addition, due to the added electrical damping and the change of the system natural frequency when the charging process is initiated, a sudden drop in the vibration amplitude is observed, which in turn affects the charging rate. However, the vibration amplitude begins to increase as the charging process continues, which is caused by the decrease in the electrical damping (i.e., the decrease in the energy removed from the mechanical vibration). This electromechanical coupling characteristic is also revealed by the variation of the vibration amplitude with the charging voltage.
文摘This study investigated the microstructure,physical,and mechanical properties of die-cast A308 alloy subjected to mechanical vibration during solidification.Different frequencies(0,20,30,40,and 50 Hz)at constant amplitude(31μm)were employed using a power amplifier as the power input device.X-ray diffraction,optical microscopy,and scanning electron microscopy were used to examine the morphological changes in the cast samples under stationary and vibratory conditions.Metallurgical features of the castings were evaluated using Image J software.The average values of metallurgical features,including primaryα-Al grain size,dendrite arm spacing,average area of eutectic silicon,aspect ratio,and percentage porosity,reduced by 34%,59%,56%,22%,and 62%,respectively,at 30 Hz frequency compared with stationary casting.Mechanical tests of the cast samples showed that the yield strength(YS),ultimate tensile strength(UTS),percentage elongation(%EL),and microhardness(HV)increased by 8%,13%,17%,and 16%,respectively,at 30 Hz frequency compared with stationary casting.The fractured surface of the tensile specimens exhibited mixed-mode fracture behavior because of brittle facets,cleavage facets,ductile tearing,and dimple morphologies.The presence of small dimples showed that plastic deformation occurred before fracture.
文摘Energy preservation is one of the key components in developing eco-friendly machines.In industry,the majority of machines lose a considerable amount of energy through mechanical vibrations.However,the wasted energy through vibration can be utilized as a renewable energy source to compensate for the overall energy loss.The research work presented in this paper discusses the ability to design a linear power generator utilizing Nd Fe-B magnets,which can generate energy through mechanical vibrations.A pilot model was developed and simulated to understand the efficiency and limitation.The results showed that the model could reduce 14% rotor bulk with a marginal impact on the current generation.
基金National Natural Science Foundation of China (50672131)
文摘Al2O3/YSZ composite ceramics was fabricated with combustion synthesis technology, and the influences of mechanical vibration on its microstructures and properties were investigated. It is found that under the mechanical vibration of ever-increasing frequency, increasing combustion temperature, accelerating ceramics/metal liquid-liquid separation and quickening ceramic solidification could not only reduce the average diameter and the size distribution of aligned ZrO2 nano-micron fibers in rod-shaped Al2O3 matrix grains, but also make the randomly-oriented rod-shaped grains finer and increase their aspect ratios. As a result, a remarkable increase in flexural strength and fracture toughness of the ceramics can be observed.
基金the financial support from the State Key Laboratory of Materials Processing and Die&Mould Technology,Huazhong University of Science and Technology(P2020-05)。
文摘To refine the microstructure and improve the mechanical properties of AZ91 D alloy by expendable pattern shell casting(EPSC),the mechanical vibration method was applied in the solidification process of the alloy.The effects of amplitude and pouring temperature on microstructure and mechanical properties of AZ91 D magnesium alloy were studied.The results indicated that the mechanical vibration remarkably improved the sizes,morphologies and distributions of the primaryα-Mg phase andβ-Mg17 Al12 phase,and the densification and tensile properties of the AZ91 D alloy.With an increase in amplitude,the microstructures were gradually refined,resulting in a continuous increase in mechanical properties of the AZ91 D alloy.While,with the increase of pouring temperature,the microstructures were continuously coarsened,leading to an obvious decrease of the mechanical properties.The tensile strength and yield strength of the AZ91 D alloy with a vibration amplitude of 1.0 mm and a pouring temperature of 730℃were 60%and 38%higher than those of the alloy without vibration,respectively.
基金Supported by the National Natural Science Foundation of China (No. 50635010).
文摘This paper presents the result of an experimental study on the compression of mechanical vibration signals. The signals are collected from both rotating and reciprocating machineries by the accelerometers and a data acquisition (DAQ) system. Four optimal sparse representation methods for compression have been considered including the method of frames ( MOF), best orthogonal basis ( BOB), matching pursuit (MP) and basis pursuit (BP). Furthermore, several indicators including compression ratio (CR), mean square error (MSE), energy retained (ER) and Kurtosis are taken to evaluate the performance of the above methods. Experimental results show that MP outperforms other three methods.
基金Funded by the Natural Science Foundation of China (No. 39770206).
文摘The root development of Actinidia chinensis planUets was studied in exposure to environmental stress of mechanical vibration at respectively 1 Hz, 2 Hz, 3 Hz, 4 Hz and 5 Hz. The plantlets exposed to vibration stimuli at all those frequencies have a larger total number and a larger total length of roots and a smaller permeability of root plasma-membrane, compared with those cultivated in an environment without vibration stress. Vibration at respectively 1 Hz, 2 Hz, 3 Hz and 4 Hz enhances root activity and the 3 Hz vibration is the most favorable. There is an obvious negative correlation between root activity and permeability of root plasma-membrane. The effects may be explained by the likelihood that mechanical Vibration at an appropriate frequency facilitates roots' absorbing water and minerals which are indispensable to inducing and synthesizing in roots some active substances favorable to growth. Nevertheless, overstress damages the integrity of root plasm-membrane, increases the permeability, and results in the disability of protecting root cells.
文摘When material properties, geometry parameters and applied loads are assumed to be stochastic, the vibration equation of a system is transformed to static problem by using Newmark method. In order to improve the computational efficiency and to save storage, the Conjugate Gradient (CG) method is presented. The CG is an effective method for solving a large system of linear equations and belongs to the method of iteration with rapid convergence and high precision. An example is given and calculated results are compared to validate the proposed methods.
基金the National Natural Science Foundation of China(No.52265043)Science and Technology Plan,Guizhou Province,China(No.ZK2021(267))+2 种基金Technology Achievements Application and Industrialization Project,Guizhou Province,China(No.2021(067))Cultivation Project of Guizhou University,China(No.2019(23))Lastly,we thank the Shanghai Synchrotron Radiation Facility(SSRF)for providing the synchrotron radiation beamtime.
文摘Effects of ultrasonic vibration(UV)and mechanical vibration(MV)on the Mn-rich phase modification and mechanical properties of Al−12Si−4Cu−1Ni−1Mg−2Mn piston alloys were investigated.The results show that the UV and UV+MV treatments can significantly refine and fragmentize the microstructures.In addition,UV treatment can significantly passivate the primary Mn-rich Al15Mn3Si2 intermetallics.The formation mechanisms of refinement and passivation of the grains and non-dendrite particles were discussed.Compared with the gravity die-cast alloys,the UV and UV+MV treated alloys exhibit improved tensile and creep resistance at room and elevated temperatures.These results can be attributed to the refinement of theα(Al)grains and the secondary intermetallics,the increased proportion of refined heat-resistant precipitates,and the formation of nano-sized Si particles.The ultimate tensile strength of the UV treated alloys at 350℃ exceeds that of commercial piston alloys.This indicates the high application potential of the developed piston alloys in density diesel engines.
文摘Objective: To investigate the curative effect of the self-made mechanical vibration massage instrument for treatment of brachial plexus injury in rats and to explore its mechanism. Methods: Brachial plexus injury models were made in 144 Wistar rats and one week after natural healing of the wound, they were randomly divided into 3 groups, mechanical vibration treatment group (MV group), nerve growth factor treatment group (NGF group) and model group, 48 rats in each group. Then again, the each group was randomly divided into 4 subgroups, 7-day group, 14-day group, 21-day group and 28-day group, 12 rats in each subgroup. The MV group were treated by mechanical vibration at acupoints on three-yang and three-yin channels of the hand with the mechanical vibration massage instrument; The NGF group were treated with injection of NGF into musculus pectoralis major on the affected side; And the model group were normally fed with no treatment. After treatment for 7, 14, 21 and 28 days, the diameter of both forelimbs were measured, the electrophysiological examination on the brachial plexus in vitro and the ultrastructure observation with electron microscope on the affected side were carried out, the motor nerve conduction velocity (MNCV) and motor nerve action potential (MNAP) of the brachial plexus on the affected side, NGF content of submaxillary gland as well as muscular Na+, K+-ATPase activity were determined respectively. Results: The different rates of the forelimb diameter in the MV group and the NGV group on the 14th d, 21st d and 28th d were better than those in the model group (P<0.05 or P<0.001), and in the MV group were better than those in the NGF group on the 21st d and the 28th d (P<0.05). MNCV in the MV group and the NGV group on the 21st d and 28th d was better than that in the model group (P<0.05 or P<0.001), and in the MV group was better than that in the NGF group on the 28th d (P<0.05). MNAP in the MV group and the NGV group on the 14th d, 21st d and 28th d was better than that in the model group (P<0.05 or P<0.001), and in the MV group was better than that in the NGF group on the 21st d and 28th d (P<0.05). The NGF mean gray index of submaxillary gland in the model group was higher than that in the MV group and the NGF group on the 7th d (P<0.05); in the NGF group and the model group was higher than that in the MV group on the 14th d (P<0.05); and in the NGF group and the MV group was higher than that in the model group on the 21st d and 28th d (P<0.05). Na+, K+-ATPase activity in the model group and the MV group was higher than that in the NGF group (P<0.05) on the 14th d, and in the MV group was higher than that in the model group on the 28th d (P<0.05). Conclusion: As compared with the NGF group and the model group, mechanical vibration treatment can effectively accelerate repair of injured brachial plexus, slow down atrophy of skeletal muscle, and promote secretion of NGF in submaxillary gland.
基金National Natural Science Foundation of China(No.52177219)Natural Science Foundation of Guangdong Province(2021A1515010525).
文摘Batteries often show the coupling change of multiple physical field characteristic parameters in the charging or discharging processes.Conventional battery modeling and characterization methods mainly focus on electrical or thermal parameters.Considering that battery state change can cause a change in the mechanical structure,research on the vibration characteristic modeling and characterization of a plastic-cased lithium-ion battery is carried out.By analyzing the mechanical structure of the battery,the first principles modeling method is selected to model the battery's mechanical performance.The vibration data in the process of battery charging and discharging are measured by a laser Doppler vibrometer(LDV).The obtained experimental data are used to identify the mechanical parameters of the battery.Based on the experimentael results,the root mean square error(RMSE)of the frequency domain amplitude fitting result of the model is less than 11.36%.The effectiveness of the battery mechanical vibration model is verified.The model and the characterization method provide tools for nondestructive battery state evaluation.
基金supported by the National Natural Science Foundation of China(Grant No.51975574)the Fundamental Research Funds for the Central Universities(Grant No.2020TC017)。
文摘Immunomagnetic bead(IMB)-based detection has great potential for biomedical applications.Passive and active strategies,including microfluidics and magnetic actuation methods,have been developed to mix IMBs and analytes efficiently.However,cost-effective on-site detection using a simple microfluidic chip is challenging,and miniaturization of the magnetic driving device is imperative for portability.In this study,we propose a novel mixing method for an on-chip IMB swarm via magnetic actuation and mechanical vibration.A microfluidic chip system coupled with double spiral magnetic coils and a vibration motor was fabricated.The aggregation behavior of IMBs under magnetic fields and the diffusion behavior of the IMB swarm under mechanical vibration were analyzed in detail.Based on the synergetic effects of magnetic actuation and mechanical vibration,we achieved the highly efficient capturing of Vibrio parahaemolyticus DNA and goat anti-human immunoglobulin G by mixing the IMB swarm with the microfluidic chip.In this case,the antigen detection rate could reach~94.4%.Given its fascinating features,such IMB-microfluidic detection demonstrates significant potential for biomedical applications.
文摘The present work investigates the mechanically forced vibration of the hydro-elasto-piezoelectric system consisting of a two-layer plate“elastic+PZT”,a compressible viscous fluid,and a rigid wall.It is assumed that the PZT(piezoelectric)layer of the plate is in contact with the fluid and time-harmonic linear forces act on the free surface of the elastic-metallic layer.This study is valuable because it considers for the first time the mechanical vibration of the metal+piezoelectric bilayer plate in contact with a fluid.It is also the first time that the influence of the volumetric concentration of the constituents on the vibration of the hydro-elasto-piezoelectric system is studied.Another value of the present work is the use of the exact equations and relations of elasto-electrodynamics for elastic and piezoelectric materials to describe the motion of the plate layers within the framework of the piecewise homogeneous body model and the use of the linearized Navier-Stokes equations to describe the flow of the compressible viscous fluid.The plane-strain state in the plate and the plane flow in the fluid take place.For the solution of the corresponding boundary-value problem,the Fourier transform is used with respect to the spatial coordinate on the axis along the laying direction of the plate.The analytical expressions of the Fourier transform of all the sought values of each component of the system are determined.The origins of the searched values are determined numerically,after which numerical results on the stress on the fluid and plate interface planes are presented and discussed.These results are obtained for the case where PZT-2 is chosen as the piezoelectric material,steel and aluminum as the elastic metal materials,and Glycerin as the fluid.Analysis of these results allows conclusions to be drawn about the character of the problem parameters on the frequency response of the interfacial stress.In particular,it was found that after a certain value of the vibration frequency,the presence of the metal layer in the two-layer plate led to an increase in the absolute values of the above interfacial stress.
基金the financial supported by the Natural Science Foundation of Hebei Province,China(No.E2017202011)
文摘Nickel-based alloys exhibit excellent high-temperature stxengtfi and oxidation resistance; however, because of coarse grains and severe segregation in daeir welding joints, these alloys exhibit increased susceptibility to hot cracking. In this paper, to improve the hot-cracking resistance and mechaxtical properties ofinckel-based alloy welded joints, sodium daiosulfate was used to simulate crystallization, enabling the nucleation mechanism under mechaxtical vibration to be investigated. On the basis of the results, the grain refinement mechan- ism during the gas tungsten arc welding (GTAW) of Inconel 601H alloy under wxious vibration modes and parameters was investigated. Compared witfi the GTAW process, the low-frequency mechanical vibration processes resulted in substantial grain refinement effects in the welds; thus, a higher haxdness distxibution was also achieved under the vibration conditions. In addition, the 7' phase exhibited a dispersed distribution and segregation was improved in the welded joints witfi vibration assistance. The results demonstxated that the generation of free crystals caused by vibration in the nucleation stage was the main mechaxtism of grain refinement. Also, free equiaxed grains and a dispersed 7' phase were found to improve the grain-boundary strength and reduce the segregation, contributing to preventing the initiation of welding hot cracking in nickel-based alloys.
文摘EN-GJS-450-10 ductile cast iron was produced with and without vibration to evaluate microstructural features. To investigate the effect of vibration, a reference, and two different castings having amplitudes of 0.9 mm and 1.8 mm were cast with a fixed vibration frequency of 50 Hz. The nodule count (density), form (type), size distribution, nodularity, and the fraction of graphite, percentages of both ferrite and pearlite phases, length of ferrite shell, and pore, were evaluated via optical microscopy using an image analysis software. It is observed that the microstructure of the cast iron is more uniform by vibrational casting than that by non-vibrational casting. Additionally, mechanical vibration enhances nodule count and nodularity, also, more ferritic matrix could be obtained after the application of vibration. Nodule count and nodularity of vibrational casting with 1.8 mm amplitude increased from 226 nodule per mm2 and 80% to 311 nodule per mm2 and 86.5% of non-vibrational casting. Percentages of ferrite and graphite area dramatically improved from 24% and 16.5% for non-vibrational casting to 57% and 22.3% for vibrational casting with 1.8 mm amplitude, whereas the percentages of pearlite and pores decreased significantly from 56.1% and 5% to 20% and 1%, respectively.
文摘The vibration of machines due to rotating parts unbalance disturbs the machine functioning and shortens the lifetime of its parts. A dynamic vibration absorber is a favorite solution to suppress the machine vibration since its implementation does not require any modification neither on the machine nor on its installation. The paper considers an unbalanced machine to which a lumped mass dynamic vibration absorber is attached. Firstly, the machine equipped with the absorber is modeled, and the vibration expressions are extracted. Secondly, an original approach to optimize the absorber parameters is presented, and simulation results are advanced, when the absorber is undamped and damped. Thirdly, the absorber optimal parameters allowing the best vibration reduction of the machine are identified, showing bow the absorber should be designed, when the disturbance frequency is stable or unstable. The results are a significant contribution in the vibration control of unbalanced machines.