Investigation of Impact Loads Caused by Ultrasonic Cavitation Bubbles in Small Gaps

Ultrasonic cavitation shows a great potential in various industrial applications such as sonochemistry, food processing, ultrasonic cleaning, and surface treatments. These applications have the advantages of high temperatures or high pressure due to the collapse of cavitation bubbles. In surface treatments, the collapse of bubbles occurs near workpiece surfaces and creates micro-jets which lead to high impact forces. As one of these surface treatment processes, ultrasonic cavitation peening requires a small gap between the vibration source and the treated surface to obtain the maximum impact force. Due to these small gaps, the growth and collapse of cavitation bubbles are affected, which result in the changes of impact forces. Therefore, the investigation of the impact loads caused by ultrasonic cavitation bubbles in small gaps is the focus of this contribution. A theoretical model taking into consideration bubble interactions is utilized to estimate the optimal standoff distance at which the largest impact forces occur. Then, experimental investigations are carried out. A piezoelectric sensor with a titanium alloy cover is used to record the number of impacts and their amplitudes. The recorded signals are then processed in time and frequency domains. The experimental results show that large impact loads are generated when the gap width is in the range of 0.5-0.8 mm. It is also found that the maximum working efficiency occurs in this range

Novel Traveling Wave Sandwich Piezoelectric Transducer with Single Phase Drive: Theoretical Modeling, Experimental Validation, and Application Investigation

Most of traditional traveling wave piezoelectric transducers are driven by two phase different excitation signals, leading to a complex control system and seriously limiting their applications in industry. To overcome these issues, a novel traveling wave sandwich piezoelectric transducer with a single-phase drive is proposed in this study. Traveling waves are produced in two driving rings of the transducer while the longitudinal vibration is excited in its sandwich composite beam, due to the coupling property of the combined structure. This results in the production of elliptical motions in the two driving rings to achieve the drive function. An analytical model is firstly developed using the transfer matrix method to analyze the dynamic behavior of the proposed transducer. Its vibration characteristics are measured and compared with computational results to validate the effectiveness of the proposed analytical model. Besides, the driving concept of the transducer is investigated by computing the motion trajectory of surface points of the driving ring and the quality of traveling wave of the driving ring. Additionally, application example investigations on the driving effect of the proposed transducer are carried out by constructing and assembling a tracked mobile system. Experimental results indicated that 1) the assembled tracked mobile system moved in the driving frequency of 19410 Hz corresponding to its maximum mean velocity through frequency sensitivity experiments; 2) motion characteristic and traction performance measurements of the system prototype presented its maximum mean velocity with 59 mm/s and its maximum stalling traction force with 1.65 N, at the excitation voltage of 500 VRMS. These experimental results demonstrate the feasibility of the proposed traveling wave sandwich piezoelectric transducer

Experimental investigation of peening cylindrical workpieces utilizing a transducer with ring sonotrode

In industrial applications, the shafting components with high stress are easily damaged due to cyclic loads if there is no surface treatment. With the use of ultrasonic cavitation peening, the residual compressive stress and the surface hardness of these components can be improved. While tradi-tional longitudinal vibration transducers are used to treat cylindrical workpieces, the treated areas are limited, and the treatment period is relatively long. To solve these problems, we designed a novel configuration of the piezoelectric transducer as a type of the combination of rod and ring. During ultrasonic cavitation peening, we placed the cylindrical workpieces in the ring tool to improve the limitation. However, the treated surface properties were largely influenced by the input parameters (driving voltage and rod diameters). In this investigation, the cylindrical workpieces, which were covered with aluminum foils, were first treated by ultrasonic cavitation peening to detect the intensity and distribution of the cavitation bubbles on the treated surface. Then, the sonochemiluminescence method was utilized as an additional way to find the optimal operation parameters (190 V and 16 mm). Finally, the ultrasonic cavitation process was conducted with the optimal parameters. The treatment results showed that the surface hardness increased by about 36% without significant increase of the surface roughness. © 2020 by the authors. Licensee MDPI, Basel, Switzerland

A heterozygous moth genome provides insights into herbivory and detoxification

How an insect evolves to become a successful herbivore is of profound biological and practical importance. Herbivores are often adapted to feed on a specific group of evolutionarily and biochemically related host plants1, but the genetic and molecular bases for adaptation to plant defense compounds remain poorly understood2. We report the first whole-genome sequence of a basal lepidopteran species, Plutella xylostella, which contains 18,071 protein-coding and 1,412 unique genes with an expansion of gene families associated with perception and the detoxification of plant defense compounds. A recent expansion of retrotransposons near detoxification-related genes and a wider system used in the metabolism of plant defense compounds are shown to also be involved in the development of insecticide resistance. This work shows the genetic and molecular bases for the evolutionary success of this worldwide herbivore and offers wider insights into insect adaptation to plant feeding, as well as opening avenues for more sustainable pest management.Minsheng You … Simon W Baxter … et al

Experimental Investigation of Peening Cylindrical Workpieces Utilizing a Transducer with Ring Sonotrode

In industrial applications, the shafting components with high stress are easily damaged due to cyclic loads if there is no surface treatment. With the use of ultrasonic cavitation peening, the residual compressive stress and the surface hardness of these components can be improved. While traditional longitudinal vibration transducers are used to treat cylindrical workpieces, the treated areas are limited, and the treatment period is relatively long. To solve these problems, we designed a novel configuration of the piezoelectric transducer as a type of the combination of rod and ring. During ultrasonic cavitation peening, we placed the cylindrical workpieces in the ring tool to improve the limitation. However, the treated surface properties were largely influenced by the input parameters (driving voltage and rod diameters). In this investigation, the cylindrical workpieces, which were covered with aluminum foils, were first treated by ultrasonic cavitation peening to detect the intensity and distribution of the cavitation bubbles on the treated surface. Then, the sonochemiluminescence method was utilized as an additional way to find the optimal operation parameters (190 V and 16 mm). Finally, the ultrasonic cavitation process was conducted with the optimal parameters. The treatment results showed that the surface hardness increased by about 36% without significant increase of the surface roughness

Investigation of the effect of ultrasonic cavitation in small gaps on surface properties

Ultrasonic cavitation can be used to improve surface properties of workpieces in industrial applications. During this surface enhancement process, a small gap is required to generate high impact forces on the workpiece surfaces. The distribution of cavitation bubbles, the optimal gap width and the process time highly affect the treated surface properties. In this thesis, the distribution of sound fields in the small gaps and the optimal standoff distance are simulated with the consideration of bubble interactions. Then, sonochemiluminescence and surface volume variation experiments are carried out. Additionally, a piezoelectric force sensor is designed to detect impact forces. Finally, plastic deformation volume is studied to more accurately identify the optimal process time. The simulation and experimental results show good agreements

A Novel Ultrasonic Cavitation Peening Approach Assisted by Water Jet

Ultrasonic cavitation peening is an environmentally friendly technology to improve surface properties. In the traditional ultrasonic cavitation peening process, specimens have to be immersed in a liquid and temperature control is required, which limits the wide usage of this technology due to the geometry and complicated setup. In order to improve this process, water is slowly jetted (75 mL/min) into the gap between the sonotrode tip and specimen surface. The water jet makes the gap full of water. Thus, cavitation bubbles can be generated in the gap as the traditional ultrasonic cavitation peening process. In this case, the water container and temperature control are no longer necessary. The goal of this contribution is to evaluate the treatment effectiveness of this novel approach by the impact loads, the volume loss, the surface roughness, the microhardness and the microstructure of the specimen surface. The results indicate that a higher input power is beneficial and there would be an optimal gap width for this novel ultrasonic cavitation peening process

The formation mechanism and morphology of the nickel particles by the ultrasound-aided spark discharge in different liquid media

Spark discharge is widely applied in the fabrication process of the particles with very small sizes. The ultrasound-aided spark discharge process is based on the electrical discharge in the liquid media of the electrical discharge machining (EDM). In this paper, the morphology, element composition, and crystal structure of the Nickle particles produced by the ultrasound-aided spark discharge were observed and analyzed by SEM, EDS and XRD respectively. The EDS and XRD indicated that the purity of the nickel particles generated in pure water is higher than that in kerosene. Meanwhile the effects of dielectric media on the size distribution were also investigated. It was found that the size distribution of the particles in pure water is narrower than that in kerosene, but when the ultrasound was introduced into the generating process, the size distributions of the particles in both media have remarkable improvements (both became narrower). Based on the attaching and entrapping processes, the formation mechanism of different structural particles was also presented. Following the study on the changes of the effective densities and the ratios of the closed hollow particles in different experiments (with and without ultrasound), we found that, with the aid of ultrasound, the ratio of the closed hollow particles increased about 10–15%. In overall, the results in this paper provide a foundation for the some future research, such as the study on the control of the particle properties (in size and morphology) by improving the experimental conditions