Increasing Vibration Frequency Research Articles

Método ultrassônico de detecção de microvibração: Desenvolvimento da técnica

Many investigations have been devoted, during the last years, to implement an ultrasonic method able to generate shear waves and to detect the microvibrations caused by the wave propagation in biological tissues. Applications of such method include measuring rheological parameters for tissue characterization. Considering the potential to use shear wave propagation, this work presents an ultrasonic method able to detect microvibrations (UDmV), which is based on Kalman filtering to estimate the medium vibrations from a signal contaminated with noise. The UDmV was tested employing a speaker to generate microvibrations on a membrane and a pulse-echo ultrasonic system, operating at a center frequency of 4.96 MHz, to detect the membrane microvibrations. The UDmV demonstrated promising future potential, being able to detect the vibration frequency and amplitude with the same order of magnitude as presented in the literature (≈10 mm). Moreover, the method implemented in the present work confirmed previous results, from the literature, related with a reduction of the estimated vibration amplitude as the vibration frequency increases. The method developed in the present work can be employed to estimate the phase velocity and the attenuation coefficient of a shear wave propagating in a viscoelastic medium.

Enhanced nanoflow behaviors of polymer melts using dispersed nanoparticles and ultrasonic vibration

In the micro/nano fabrication of polymer nanostructures, a key factor is the favorable nanoflow behavior of polymer melts. Compared with the fluidic hydrodynamics of simple liquids through micro- or macrochannels, the nanoflow behavior of polymer melts, however, is affected much more by nanoscale effects and surface interactions. Therefore, achieving a favorable nanoflow of polymer melts in nanochannels is the key to fabricate high quality polymer nanoproducts. In this paper, the improved nanoflow behaviors of polystyrene melts in ordered porous alumina templates with the addition of nanoparticles and ultrasonic vibration were reported for the first time. Compared with bulk polystyrene (PS), the nanoflow rate of PS melts was enhanced when nanoparticles, such as surface-modified nano-silica (nano-SiO(2)) or β-cyclodextrin (β-CD), were added in a dispersed phase into a polystyrene matrix due to the decrease of the melts' viscosity caused by interactions between nanoparticles and PS segments. The enhancement action of β-CD was observed to be more significant than that of nano-SiO(2) based on the adsorption and the supramolecular self-assembly interactions between PS segments and β-CD. The enhanced nanoflow rate has shown to be more pronounced under ultrasonic vibration than those of the static condition and the low frequency vibration attributed to the synergetic effects of mechanical vibration and ultrasonic oscillation. The nanoflow rate of polymer melts increases with the gradual increase of vibration frequency. The optimal nanoflow behavior can be obtained by simultaneously adding β-CD as dispersed phase into PS matrix and applying ultrasonic vibration in one nanoflow system. These new findings will help the preparation of polymer-based functional nanocomposites, ultrasonic vibration-assisted nanofluidics, and micro/nano injection molding etc.

Real time observation of nucleation and detachment of crystal from chilling surface Part I – effects of vibration

The nucleation and detachment of grains from a chilling surface were observed in real time in a model NH4Cl solution system. The effects of vibration frequency and amplitude on the detachment behaviour and crystallographic morphology of grains were also studied. The results show that partial dendrite arms were broken off under low frequency vibration, whereas the entire dendrite was broken off at its root under high frequency vibration. The higher the frequency and amplitude, the thinner the detached grains. The effect of frequency on the morphology of grains is much greater than that of amplitude, thus increasing vibration frequency is effective in forming fine granular grains, but not amplitude. The amount of detached grains increases with increasing vibration frequency and amplitude up to 1200 Hz and 80 μm; further increase in vibration frequency or amplitude reduced the amount of detached grains.

Study on the Morphology and Properties of PP/HDPE Blend Prepared by Vibration Injection Molding

A self-designed pressure vibration injection molding device was used to study the effect of vibration frequency and vibration pressure on tensile strength and impact strength of PP/HDPE (70/30) samples prepared by vibration injection molding. Furthermore, DSC and scanning electron microscopy (SEM) observations were conducted. The tensile strength and impact strength increase with increasing vibration frequency and vibration pressure. SEM micrographs show that the orientation degree of the vibration sample obtained at 190°C obviously increases compared with the static sample, and the clusters of lamellae are stretched along the flow direction, whereas their lateral sizes decrease correspondingly. There is no evident orientation in the core layer of the vibration sample obtained at 230°C. DSC testing results show that the degree of crystallinity of vibration samples are higher than those of static samples.

A molecular dynamics simulation of segregation behaviours of horizontally vibrated binary granular mixture

This paper performs the two-dimensional, soft-sphere molecular dynamics simulations to study the granular segregation in a binary granular mixture with the same size but different density in the container with the sawtooth base under horizontal vibration. The segregation phase diagram is presented in the acceleration-frequency space. When the acceleration is high enough to result in relative motions of the particles, the system can be in various states (mixed state, vertical and horizontal segregation state), which depend on both acceleration and frequency. Due to the sawtooth base there is stratified flow effect besides density effect. The density effect raises the light particles. The stratified flow drives the particles in the upper levels to the right and the particles in the lower particles to the left, resulting in the appearance of the left segregation state. The left segregation state can be changed to the right segregation by changing the shape of the sawtooth. As the vibration frequency increases, the stratified flow effect becomes weaker and weaker, so at high vibration frequencies the vertical segregation state appears instead of the left segregation state.

Effect of Viscosity on Vibration-Induced Motion of a Spherical Particle Suspended in a Fluid Cell

Production of protein and semi-conductor crystals with advanced quality and properties is possible under microgravity conditions due to the suppression of convection effects. However, aboard space platforms, g-jitter induced motions of solid particles can cause unsteady convection that may result in degradation of the properties of crystals produced. There are different effects of g-jitter on small particles suspended in a fluid cell which are not fully understood. To investigate these small vibration effects, ground experiments were conducted by suspending a spherical particle with a thin wire in a rectangular fluid cell and subjecting the cell and particle to horizontal vibrations with different frequencies and amplitudes. The fluid viscosity was varied to investigate the attraction or repulsion force induced in the direction normal to the direction of the vibration. The force was found to change from attraction to repulsion with an increase in the fluid viscosity and increase with the increasing vibration frequency and amplitude.

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The frictional behavior of mild steel under horizontal vibration

The present paper investigates experimentally the effect of external horizontal vibration on friction property of mild steel. To do so, a pin-on-disc apparatus having facility of vibrating the test samples in horizontal direction was designed and fabricated. Horizontal vibration is created along the sliding direction of vibration and perpendicular to the direction of vibration. The experimental setup has the facility to vary the amplitudes and frequencies of vibration while velocity of vibration is kept constant. During the experiment, the frequency and amplitude of vibration were varied from 0 to 500 Hz and 0 to 200 μm, respectively. Results show that the friction coefficient increases with the increase in amplitude and frequency of vibration for mild steel. The horizontal vibration can be of two types: one along the direction of sliding (longitudinal direction) and the other along the perpendicular direction of sliding (transverse direction). For both the cases, test sample slides horizontally. It is found that the magnitude of friction coefficient for longitudinal vibration is less than that for under transverse vibration. These results are analyzed by dimensional analysis to correlate the friction coefficient with sliding velocity, frequency and amplitude of vibration. The experimental results are also compared with those available in literature and simple physical explanations are provided.

Effects of Mechanical Vibration on Macrostructure and Mechanical Properties of AC4C Aluminum Alloy Castings

The gravity die casting of the AC4C aluminum alloy was conducted when mechanical vibration was incorporated. The specimen with a specification of 25 mm in diameter and 210 mm in length were solidified at various vibration frequencies so as to examine the effect of the vibration on the grain size, the casting defect distribution, and mechanical properties. In comparison with the grains formed in the as-cast state without vibration, the grains in the inner area of a specimen became finer after mechanical vibration. The columnar structure remained in its outer region under all vibration frequency. The average density of specimen increased by imposition the mechanical vibration. The casting defects involved in the specimen reduced and became smaller with the increase of vibration frequency. The scattering in mechanical properties of specimens cast with mechanical vibration decreased because of the decrease in casting defects. [doi:10.2320/matertrans.F-M2009822]

The Effect of Melt Vibration on Polystyrene Melt Flowing Behavior During Extrusion

Vibration extrusion (VE) is achieved by superimposing a mechanical vibration on the flowing melt during extrusion. The effect of melt vibration on the melt flow behavior of polystyrene (PS) was studied. The melt flow behavior during conventional extrusion (CE) was studied for comparison. With the application of the melt vibration technology, the melt flow behavior of PS was greatly improved. The melt viscosity during the VE strongly depends on the vibration frequency and vibration amplitude. Extruded at constant vibration amplitude, the melt viscosity decreases sharply with increasing vibration frequency and also does so for increasing vibration amplitude when extruded at a constant vibration frequency. The improved melt flow property is explained in terms of shear-thinning criteria. The effect of melt vibration on the melt flow behavior is also related to the melt temperature and extrusion pressure; the greatest decease in viscosity is obtained at low temperature and low extrusion pressure.

Effects of vibration and grain refiner on microstructure of semisolid slurry of hypoeutectic Al-Si alloy

The effects of vibration and grain refiner on the microstructure of semisolid slurry of hypoeutectic Al-Si alloy were studied. The impact of vibration on the convection of liquid was conducted by using a system of water-particle tracer. The 356 melt at temperature of 630–660 °C with or without grain refiner Al-5%Ti-1%B was poured into a metal cup as the vibrating vessel, then it was cooled to 590–610 °C in the semisolid zone and kept for some time, subsequently vibration with different frequencies was applied. The results show that the primary α(Al) particles become finer and rounder with the increase of vibration frequency. The slurry with primary α(Al) equivalent particle diameter(EPD) of about 90 μm and average shape coefficient(ASC) of about 0.5 can be prepared under vibration of 20 Hz. With the combined action of vibration and grain refiner Al-5Ti-B, even smaller and rounder spheroids with EPD of about 85 μm and ASC of about 0.6 are obtained.

Melt Vibration Improved Melt Flow Behavior and Mechanical Properties of High Density Polyethylene

A pulse pressure was superimposed on the melt flow resulting in melt vibration. With application of the melt vibration technology, the melt flow behavior and mechanical properties of high‐density polyethylene were studied. For vibration‐assisted extrusion (VAE) at constant vibration pressure amplitude, the viscosity decreases sharply with increasing vibration frequency, and also does so when increasing vibration pressure amplitude for VAE at constant vibration frequency. The effect of vibration field on melt rheological behavior is also related to the melt temperature; a large decease in viscosity is obtained at low melt temperature. Compared with the mechanical properties obtained by conventional injection molding (CIM), the mechanical properties for vibration‐assisted injection molding (VAIM) samples were improved by changing the vibration frequency and vibration pressure amplitude. Injected at constant low vibration pressure amplitude, the VAIM sample prepared at high vibration frequency shows large elongation at break; injected at constant low vibration frequency, the VAIM sample prepared at high vibration pressure amplitude shows greatly improved yield strength. The above two VAIM processing routes produce different VAIM samples with different fracture behaviors; a distinct layered structure for VAIM samples was observed by SEM.

Improving the mechanical properties of polypropylene via melt vibration

AbstractThe effect of melt vibration on the mechanical properties of polypropylene prepared by low‐frequency vibration‐assisted injection molding (VAIM) has been investigated. With the application of melt vibration technology, the mechanical properties of polypropylene are improved. The yield strength increases with the increment of the vibration frequency, and a peak stands at a special frequency for VAIM; the elongation at break decreases first and then increases with increasing vibration frequency, and a valley stands at a special frequency. The tensile properties increase sharply at an enlarged vibration pressure amplitude with sharply decreased elongation at break. The Young's modulus and impact strength also increase with the vibration frequency and pressure vibration amplitude. When it is prepared at 59.4 MPa and 0.7 Hz, the maximal yield strength is approximately 40 MPa versus 33.7 MPa for a conventional sample; an 18.7% increase in the tensile strength is produced. Self‐reinforcing and self‐toughening polypropylene molded parts have been found to be prepared at a high vibration frequency or at a large pressure vibration amplitude. Scanning electron micrographs have shown that, in the vibration field, the enhancement of the mechanical properties is attributable to more pronounced spherulite orientation and increased crystallinity in comparison with conventional injection moldings. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Effects of vibration force field on the interfacial interaction and morphology of polystyrene/poly(methyl methacrylate) blends

Immiscible polystyrene (PS)/poly(methyl methacrylate) (PMMA) blends were extruded using an electromagnetic dynamic plasticating extruder. Effects of vibration force field on the interfacial interaction and morphology of PS/PMMA blends were studied by differential scanning calorimetry (DSC), IR spectra, scanning electron microscope (SEM) and small angle X-ray scattering (SAXS). Results show that the introduction of a vibration force field into the extrusion process increases the solubility of the two components of PS/PMMA blends, which seems to be a physical compatibilization as indicated by the IR spectra. The enhanced interfacial interaction and the increased shear effect caused by vibration improve the dispersion of the dispersed phase. With application of vibration, the PS/PMMA blends exhibit a smaller drop size and a narrower particle size distribution. The morphologies of PS/PMMA blends with different compositions have a different response to vibration forces; the mean domain size of 25/75 PS/PMMA blends has a higher speed of decrease with increase of vibration amplitude or frequency. The Porod invariant data as determined by SAXS indicate that introduction of vibration improves the homogeneity of the PS/PMMA system.

The Dynamic Apparent Viscosity of Polymer Melts During Pulsatile Extrusion Flow with Vibration Force Field

Abstract The dynamic apparent viscosity of polymer melts during pulsatile extruding flow with a vibration force field was studied on a self-made dynamic capillary rheometer (DCR). A theory that could reflect the vibration influence on the dynamic apparent viscosity was proposed. Due to the superposition of the vibration force field upon the steady shear flow, the phase difference between the shear stress and the shear rate could be chosen as a parameter to reflect the effect of vibration on the dynamic apparent viscosity. According to this theory, the average shear rate during pulsatile extrusion increased because of the existence of the phase difference, which caused the decrease of the dynamic apparent viscosity. The experimental results proved that the phase difference was reduced with the increase of vibration frequency, which resulted in a decrease in the dynamic apparent viscosity during the pulsatile extrusion.

Research on Dynamic Characteristic of Concrete Box-girder with Corrugated Steel Webs

AbstractAn interspaced calculation model of a concrete box-girder with corrugated steel webs was built by sap2000, and the applicability of FEM was proved according to the comparison between the test value and FEM value of concrete box-girder with corrugated steel webs. The influence of structural parameters of corrugated steel webs on dynamic characteristic was analyzed. The results of the research indicates that vibration frequency of box-girder especially torsion vibration frequency can be improved by the augment of corrugated steel webs’ thickness to some extent; vertical and transverse vibration frequency of box-girder is affected less than torsion vibration frequency by the augment of corrugated steel webs’ folded angle; vertical, transverse and torsion vibration frequency increase and then decrease under the change of horizontal face plate width of corrugated steel webs, so the best horizontal face plate width of corrugated steel webs do exist but not too big.

Mechanical Property, Thermal Property and Crystal Structure of Isotactic Polypropylene Samples Prepared by Vibration Injection Molding

A self-designed pressure vibration injection device was used to study the effect of vibration frequency and vibration pressure on tensile strength and impact strength of iPP F401 vibration injection molding samples. Furthermore, vicat softening temperature, WAXD measurements and polarized microscopic observation were conducted. According to the results, tensile strength and impact strength increase with increasing vibration frequency and vibration pressure. The maximum increment of tensile strength is 26.1%. Under certain process conditions, there is a transition of the impact strength, whose maximum increment is 85%. The vicat softening temperatures have a significant increase of 6∼8 °C for the samples obtained at high vibration frequencies compared with that of static samples. According to pole figures, α-PP of vibration samples orientates much stronger than that of static samples. PM micrograghs show that vibration changes the crystal structure of samples and enhances their orientation.

The Effect of Vibration on Mechanical Properties of Blends of EPDM/PP in a Tri-screw Dynamic Mixing Extruder

The effects of vibration force field on mechanical properties of blends of EPDM/PP during process of plastics in tri-screw dynamic mixing extruders were investigated experimentally. It was found that vibration force field enhanced mechanical properties of blends of EPDM/PP, and the amplitude of enhancement varied as EPDM content varying. The yangs modulus, the impact strength and the tensile strength were improved the maximum 17, 28, and 17.3%, respectively under dynamic conditions than that under steady conditions. Mechanical properties of blends of EPDM/PP represented a tendency of a rising followed by a fall with the increase of vibration frequency and amplitude.

Rheological behavior of a polymer melt under the impact of a vibration force field

AbstractA model for the molecular motion of a polymer melt under the impact of a vibration force field was developed. From complicated theory deduction, an expression of the relaxation time and dynamic apparent viscosity were obtained. The effect of a vibration frequency and amplitude on the melt's dynamic apparent viscosity is explained in terms of shear‐thinning and untie‐tangle criteria. The model is supplemented by a calculation sample and experiment, which show that dynamic apparent viscosity of a melt will tend to decrease as the vibration frequency or amplitude increases. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Effect of Electromagnetic Vibration Frequency and Temperature Gradient on Grain Refinement of Pure Aluminum

The electromagnetic vibrations are applied to grain refinement of pure aluminum (99.7 mass%) and the effects of electromagnetic vibration frequency and temperature gradient on grain refinement are investigated. As the pure aluminum melt has been subjected to electromagnetic vibrations with a frequency range from 150 to 500 Hz, crystal grain has become small with increase of vibration frequency. To the contrary, the effect of refinement has become weak at the vibration frequency more than 1 kHz and this microstructure is similar to one of nonvibrated state. When the longitudinal temperature gradient in the specimen becomes gradual, refined area is remarkably extends. It is assumed that refinement by the electromagnetic vibrations is significantly affected by the temperature gradient.