Investigation on Deformation Behavior in the Surface of Metal foil with Ultrasonic Vibration-Assisted Micro-Forging

Excitation of the acoustic field leading to the Blaha effect affects the plasticity of the material significantly in ultrasonic vibration-assisted forming. In a micro-forming field, the effects are more significant in the deformation in surface of materials [1]-[3], in which reduction of the surface roughness based on the increasing of plastic deformation of surface asperity was effective [4]. On the other hand, the effect on deformation behavior of the bulk region indicted reduction in the yield stress of materials, and not only acoustic effect [5], but also impact effect is found to generate a large amount of dislocation and produce plastic deformation [6][7]. However, the effect on the bulk is more significant as that on the surface. Differences in the effect on the surface and the bulk are not clarified. In this study, the mechanism of the deformation in the surface of the material with ultrasonic vibration assistance is investigated and compared with that in the bulk. Forging tests using a newly developed ultrasonic vibrator were carried out on pure Cu foils with various process conditions. The longitudinal vibration frequency of the ultrasonic transducer is 60∓2kHz, and the vibration amplitude is in an adjustable range of 0~10μm. Forging test was carried out at different initial stress, specimen size and amplitude. The difference in acoustic softening and impact effects on the surface and the bulk was discussed.

THEORETICAL SUBSTANTIATION OF THE PHYSICAL MECHANISM OF ULTRASONIC CAVITATION DESTRUCTION OF MACROMOLECULES

Многообещающее направление исследований, которое потенциально может служить базой для создания эффективной технологии управления свойствами полимеров – воздействие механическими колебательными возмущениями на высокомолекулярную среду. В реальных неотверждённых полимерах механические колебательные возмущения, как правило, представляют собой кавитационно-акустическое воздействие, т.е. линейные синусоидальные колебания, создаваемые в среде, инициируют вторичное явление – кавитационные пузырьки. Пузырьки при кавитационно-акустическом воздействии периодически расширяются и схлопываются, формируя микроударные волны. Таким образом, механические колебательные возмущения имеют две составляющие – линейная синусоидальная и нелинейная ударно-волновая. Основное воздействие на структуру полимеров оказывает ударно-волновая составляющая. Для реализации данного процесса с максимальной энергетической эффективностью необходимо выявить оптимальные режимы воздействия. Для выявления оптимальных режимов воздействия в статье теоретически обоснован физический механизм разрушения макромолекул, основанный на их соударении со скоростью, превышающей критическую за счёт формирования экстремальных условий по температуре и давлению в окрестности схлопывающегося кавитационного пузырька. A promising area of research that can potentially serve as a basis for creating an effective technology for controlling the properties of polymers is the effect of mechanical oscillatory disturbances on a high–molecular medium. In real uncured polymers, mechanical oscillatory disturbances, as a rule, represent a cavitation-acoustic effect, i.e. linear sinusoidal vibrations created in the medium initiate a secondary phenomenon - cavitation bubbles. Bubbles under cavitation-acoustic action periodically expand and collapse, forming micro-shock waves. Thus, mechanical oscillatory disturbances have two components – linear sinusoidal and nonlinear shock wave. The main effect on the structure of polymers has a shock-wave component. To implement this process with maximum energy efficiency, it is necessary to identify optimal exposure modes. In order to identify optimal exposure modes, the article theoretically substantiates the physical mechanism of destruction of macromolecules based on their collision with a velocity exceeding the critical one due to the formation of extreme conditions for temperature and pressure in the vicinity of a collapsing cavitation bubble.

Experiments with Pyrotechnic Compositions Based on a Mathematical Model—Part I Evaluation of the Applicability of Mathematical Models in Developing Pyrotechnic Compositions Producing an Acoustic Effect

This paper presents research on the development of pyrotechnic compositions producing an acoustic effect. These types of compositions are used in firecrackers to imitate a cannon shot—they are most frequently used during military exercises. The research was based on a mathematical model of an experiment. For environmental reasons, the replacement of the harmful oxidant Ba(NO3)2 by KClO4 and NH4ClO4 was modelled. The compositions were tested for reliability and evaluated in terms of friction sensitivity and burning rate. This allowed for the verification of the effectiveness of the modelling carried out. Optimum compositions were selected for further research.

Investigation in characteristics of belt conveyors and their idler rollers for coal-fired power plants

Belt conveyors are highly efficient systems used in mining and other industries to transport bulk materials, mainly brown coal and overburden, over distances ranging from short distances to several kilometres. For technical reasons, their operation is associated with noise emissions. During inspections and maintenance this can lead to increased noise exposure of employees. In the vicinity of residential buildings or in areas needing protection, exceeding the emission limits can lead to a temporary restriction of the operation of these high performance installations. Measures are required to reduce the noise impact primarily at the source or in the immediate vicinity. The acoustic and mechanical parameters are investigated on a test bench at the Technical University of Brandenburg (BTU) Cottbus-Senftenberg as part of the drive assembly tests in cooperation with LEAG. The stages of these tests are: Run-up test. In this test the supporting roller is accelerated under test load to a circumferential speed of 10 m/s and the sound pressure level is recorded. This makes it possible to calculate the sound emission as a function of the peripheral speed; Recording the geometry of the idler gear. An accurate description of the geometry of the idler housing allows conclusions to be drawn about the possible causes of excitation. The defined characteristics serve to quantify the acoustic effect of the driven rollers and derive specifications for use in belt conveyor systems. Based on the special requirements to the planned belt conveyor system, an adapted selection of low-noise idler rollers can be made at an early stage on the basis of specified parameters and confirmed test results.

Numerical calculation of intermolecular bonds under the action of ultrasonic cavitation

The linear model of macromolecules was proposed. Expression for probability of macromolecules breakup under ultrasonic cavitation action was obtained. The fractional composition and viscosity of uncured polymer were calculated. As a result of the calculations, it was evaluated that the cavitation-acoustic effect for a time of no more than 1 min at an vibration intensity of at least 6 W/cm2 and an initial viscosity of 0.2 Pa· s reduces the viscosity of polymers by at least 8 times. At the same time, it was theoretically revealed that the cavitation-acoustic effect is also capable of reducing the viscosity of polymers with an initial viscosity of more than 1 Pa·s up to 4 times.

Sub-array equalization technique for the parametric array loudspeaker to reduce nonlinear distortion

The parametric array loudspeaker (PAL) is a directional loudspeaker which uses the nonlinear acoustic effect, namely the parametric array, to produce an audio beam from narrow ultrasonic beams. The PAL can efficiently deliver audible information, without generating noise to the surroundings. One significant drawback of the PAL is the nonlinear distortion. Therefore, many sophisticated methods have been proposed to preprocess the input signal of the PAL. However, those methods usually request a flat frequency response of the ultrasonic transducer array (UTA). In the past, equalization has been tried out for the whole UTA, but the performance was sometimes not satisfactory due to the inconsistent productions of ultrasonic transducers. This paper proposes to group the ultrasonic transducers by their impedances. Several sub-arrays are thereafter formed and equalized individually. The comparison results demonstrate that the propose sub-array equalization technique can suppress the nonlinear distortion of the PAL more effectively than the previous method.

Evaluation of additively manufactured stacks for thermo-acoustic devices

The thermo-acoustic effect provides a means to convert acoustic energy to heat and vice versa without the need for moving parts. This is especially useful to construct mechanically-simple and robust energy harvesting devices, although there are limitations to the power-to-volume ratio achievable. The mechanical and thermal properties as well as geometry of the porous stack that forms a set of acoustic waveguides in thermo-acoustic devices are key to its performance. In this study, we evaluate various additively manufactured polymer stacks against more conventional ceramic stacks using a benchtop thermos-acoustic refrigerator rig that uses air at ambient pressure as its working fluid. Influence of stack parameters such as material, length, location, porosity and pore geometry are examined using experiments and correlated to simulations using DeltaEC, a software tool based on Rott's linear approximation. Structure-performance relationships are established by extracting scaling laws for power-to-volume ratio and frequency-thermal gradient dependencies. It is found that additively manufactured stacks can deliver performance comparable to ceramic stacks while being more affordable and customizable for thermo-acoustic transduction applications.

Review of up-to-date approaches for extinguishing oil and petroleum products

The paper provides a review of up-to-date approaches for extinguishing oil and petroleum products. The variability of extinguishing methods and fire extinguishing agents is noted. Fire extinguishing agents used in extinguishing petroleum products are considered in more detailed way, and their environmental characteristics are discussed. The ambiguity of using various foams for extinguishing the fire is shown. A new method for extinguishing oil and petroleum products, based on the acoustic effect, and the capabilities of acoustic fire extinguishers for preventing and eliminating the combustible hydrocarbon fires, and their identification are analyzed. The further development of known approaches and the simultaneous emergence of innovative methods for extinguishing oil and petroleum products are shown. Keywords: oil; petroleum products; extinguishing agent; environmental characteristics; extinguishing foam; acoustic method.