Effect Of Acoustic Energy Research Articles

Achievement of high-quality joints and regulation of intermetallic compounds in ultrasonic vibration enhanced friction stir lap welding of aluminum/steel

The lap joints of 6061-T6 aluminum alloy/Q235 steel were obtained by conventional friction stir welding (FSW) and ultrasonic vibration enhanced friction stir welding (UVeFSW). The weld forming characteristics and microstructure differences of the joints with or without ultrasonic were compared and analyzed, and the effects of acoustic energy on the mechanical properties and intermetallic compounds (IMCs) layer of the joints were revealed. The results showed that ultrasonic vibrations could effectively improve the weld surface forming quality, increase the volume of plastic flow materials, significantly improve the welding speed of defect-free joints and expand the welding process window. The additional ultrasonic vibration can refine the grain structure of the weld nugget zone and the thermo-mechanically affected zone, improve the mechanical properties of the lap joints, and change the joint's fracture position and fracture mechanism. The assistance of acoustic can significantly enhance the mechanical interlocking ability of the center of the lap interface and change the type and thickness of the IMCs layer.

Acoustic effect on the joint quality and process of friction stir lap welding of aluminum to steel

To gain a high strength-to-weight ratio and economic viability for multiple industrial applications, the Al and steel need to be joined successfully. In the present work, we used conventional friction stir welding (FSW) and ultrasonic vibration enhanced friction stir welding (UVeFSW) techniques to obtain high-strength industrial-grade dissimilar joints of Al and steel. The effects of acoustic energy on the joint quality and welding process were investigated. Macrographs of the joints revealed that ultrasonic vibrations could effectively promote the material flow and increase the mixing degree and width of the Al/steel interface. Steel strips' fragmentation and intermixing with the Al substrate were enhanced under ultrasonic effects. The tool torque, axial force, and spindle power were significantly decreased with ultrasonic vibration. Acoustic assistance was found beneficial to increase the joints’ failure load and change the fracture mechanism. The microhardness of acoustically treated regions was found to be higher compared to its counterparts. The thinning of the brittle intermetallic compounds (IMCs) layer at the interface of the UVeFSW joint was caused by decreased peak temperature during welding. In UVeFSW, when the welding speed was 50 mm/min, the maximum failure load of the joint was obtained under the joint action of the macro interlocks (interface zone), the thinner IMCs layer, and the micro interlocks (laminated structure). When the welding speed was 100 mm/min, the failure load of the joint was improved by 25.8% compared with conventional FSW.

Effect of acoustic energy on onset of fire propagation phenomenon

Scholars and scientists have been making efforts to discover ways to control and lessen the resonance of concurrent fires such as forest fires, and various space fires; however, no potential solutions have been concluded from their studies so far. The origin of these types of fires concerns the unstable nature of the flames and the considerable unpredictability associated with them. This work led us to do proper experimentation for the effect of sound on the spreading of the flames. Sound energy as a wave is always accompanied by compression and rarefaction. As an external effect, sound in the immediate vicinity of spreading flame can affect the flame spread rates. Appreciable work had been carried out however; the effect of sound on flames in a purely natural convective environment is an aspect yet to be thoroughly understood. Flame spread rate is a direct indication of forwarding heat transfer from burning to non-burning region. Formation of localized pressure and velocity fields occurs around the pilot fuel by the presence of sound waves. Change in heat transfer may results in increment or decrement in spread rates, when compared with one without sound. The present work attempts physical insight into the effect of sound frequency of intermediate range (3500 Hz to 7500Hz) on the spreading of flames in different configurations coupled with external sources. Results advocate the noteworthy impact of acoustics on the fire propagation phenomenon in distinct modes. Experimentation have revealed that acoustics has a critical influence on fire propagation, reducing the spread rate by 100 percent in a unilateral configuration.

Observation of selective optical manipulation of particles in acoustic levitation.

Acoustic Radiation Force is commonly used to create stable large-scale aggregates of particles in levitation (so-called "acoustic levitation") in a micro-cavity. The authors show in the following work that this well-known and well-controlled aggregation process can be reversed without contact or external flow if the aggregated particles are enlightened with the proper optical wavelength. This coupled optics and acoustics effect has been observed with various kinds of particles and different optic wavelengths, showing high reproducibility. The phenomenon is studied using fluorescent micro-metric polystyrene particles without flow, and the effects of acoustic energy and illumination power have been quantitatively assessed. It is then exploited to separate a mix of particles with identical mechanical properties based on their different optic absorption. If the phenomenon is not well understood, some possible mechanisms are proposed and discussed that could be responsible for the rapid ejection of the objects in levitation from the illuminated area. Since it is a tag free phenomenon that does not need high energies to happen and since it works with biological objects such as algae, red blood cells, and bacteria, it may open the way to a broad range of applications.

Effects of ultrasonic vibration on filling behaviours in micro-embossing processes

To improve the quality of patterning used in optical system and biological detection, a serial of ultrasonic assisted micro-embossing experiments were carried out at room temperature using silicon moulds with different groove widths. Effects of acoustic energy and application time were investigated. The filling ratio increases with the increasing of acoustic energy, however, it decreases after 55%. And, filling ratio at room temperature with ultrasonic vibration is bigger than that of hot embossing without vibration when the groove width is bigger than 80μm. This means that ultrasonic vibration is helpful for increasing the filling ratio under a suitable condition.

Effect of Acoustic Energy on Fluidization of Ultra-Fine Particle

Achieving fine particles to fluidize are very difficult with conventional methods, due to strong inter particle attraction. The difficulty of putting these powders in suspension in the fluidizing gas is related to the cohesive structure and, interparticular force, to the physical forces between the primary particles. Large inter particle forces lead to bed cracking, slugging and channeling, and cause the powder not to fluidize consistently. In this study the fluidization behavior of fume silica and talc of micronic diameter belonging to the group C of Geldart’s classification has been investigated. The basic aim of this research work is to improve the quality of fluidization of fume silica (dp=45μm) and talc (dp=10-75 μm) by applying external source in terms of acoustic field. In addition, effect of acoustic field and variation of frequency on minimum fluidization velocity (Umf) and on minimum bubbling velocity has been found out. It was observed that Umf decreases in presence of acoustic field with homogenous fluidization. The best effect observed at 145dB and 120Hz.Fluidization under acoustic field allows to partly overcoming the adhesive forces between powders. The fluidization behavior has been improved for the highest sound intensity.

Effect of acoustic energy on contact angle measurements

Effect of acoustic energy on contact angle measurements

Laboratory Simulation of Sonic Boom and Its Effects on Sleep and Human Performance

As a part of a larger program concerned with the effects of acoustic energy on sleep and human performance, an electromechanical sonic boom simulator has been designed and constructed. The operational characteristics and performance of the simulator will be discussed. Preliminary results on the effect that the sound stimulus has on sleep and performance will be described and compared with other research investigations. [NASA Langley Research Center is acknowledged for support of this work.]

The kinetics and the mechanism of acoustic drying of capillaryporous materials

We present the results of an experimental investigation into the kinetics of acoustic drying of silica gel and felt at a frequency of 500 cps; we examine the mechanism of the intensifying effect of acoustic energy on the drying process.