A Comparison of the Effects of Ultrasonic Cavitation on the Surfaces of 45 and 40Kh Steels

The ultrasonic treatment of metal products in liquid is used mainly to remove various kinds of contaminants from surfaces. The effects of ultrasound not only separate and remove contaminants, they also significantly impact the physical–mechanical and geometric properties of the surfaces of products if there is enough time for treatment. The aim of this study was to compare the dynamics of ultrasonic cavitation effects on the surface properties of 45 (ASTM M1044; DIN C45; GB 45) and 40Kh (AISI 5140; DIN 41Cr4; GB 40Cr) structural steels. During the study, changes in the structure, roughness, sub-roughness, and microhardness values of these materials were observed. The results showed significant changes in the considered characteristics. It was found that the process of cavitation erosion involves at least 3 stages. In the first stage, the geometric properties of the surface slightly change with the accumulation of internal stresses and an increase in microhardness. The second stage is characterized by structure refinement, increased roughness and sub-microroughness, and the development of surface erosion. In the third stage, when a certain limiting state is reached, there are no noticeable changes in the surface properties. The lengths of these stages and the quantitative characteristics of erosion for the considered materials differ significantly. It was found that the time required to reach the limiting state was longer for carbon steel than for alloy steel. The results can be used to improve the cleaning process, as well as to form the required surface properties of structural steels.

NUMERICAL STUDY OF THE EFFECT OF MUTUAL ORIENTATION OF OLIGOMER MACROMOLECULES ON THEIR DESTRUCTION UNDER ULTRASONIC CAVITATION

Исследование механизма разрушения макромолекул под действием ультразвуковой кавитации представляет собой важную задачу. На сегодняшний день известен механизм разрушения макромолекул, основанный на том, что в условиях ультразвуковой кавитации создаются микроскопические зоны экстремально высоких давлений, в которых повышается вероятность актов разрыва макромолекулы. Разрыв происходит тогда и только тогда, когда относительная скорость при соударении макромолекул между собой превышает критическое значение. За счёт кавитации доля макромолекул, относительная скорость которых превышает критическое значение, увеличивается. В статье описана предложенная численная модель, которая предназначена для выявления молекулярных весов образуемых фрагментов при соударении. Предложен способ уменьшения количества неизвестных функций в 4 раза по сравнению с полной системой уравнений механики мономерных звеньев, основанный на симметрии в предлагаемой постановке задачи. Численно исследовано влияние взаимной ориентации макромолекул олигомеров на количество образуемых фрагментов. Полученные результаты могут служить ориентиром для развития макроскопической кинетической модели эволюции фракционного состава мономерных звеньев (эволюции концентраций мономерных звеньев различных типовых весов). The study of the mechanism of destruction of macromolecules under the action of ultrasonic cavitation is an important task. To date, the mechanism of destruction of macromolecules is known, based on the fact that microscopic zones of extremely high pressures are created in the conditions of ultrasonic cavitation, in which the probability of acts of rupture of the macromolecule increases. A rupture occurs if and only if the relative velocity when macromolecules collide with each other exceeds a critical value. Due to cavitation, the proportion of macromolecules whose relative velocity exceeds the critical value increases. The article describes the proposed numerical model, which is designed to identify the molecular weights of the fragments formed during collision. A method is proposed to reduce the number of unknown functions by 4 times compared to the complete system of equations of mechanics of monomeric links, based on symmetry in the proposed formulation of the problem. The effect of the mutual orientation of oligomer macromolecules on the number of fragments formed has been numerically investigated. The results obtained can serve as a guideline for the development of a macroscopic kinetic model of the evolution of the fractional composition of monomeric units (the evolution of concentrations of monomeric units of various typical weights).

RBF Model for the Mass Loss of a Brass in Cavitation Field

This article aims at presenting the model of the mass loss of a brass sample in ultrasonic cavitation field in saline water. The experiments done for data collecting was performed in three scenarios. In the first one, the high frequency generator worked at three power levels - 80 W, at the second one - at 120 W, and in the third one - at 180 W. The Model has been built using the series of the mass loss on surface.

3D printing-directed flexible strain sensors of accordion-like architecture to achieve ultrastretchability with the assist of ultrasonic cavitation treatment

A new class of accordion-like cellular architecture with sinusoidal struts is designed to enhance the planar stretchability of cellular solids, aiming to fabricate flexible strain sensors with ultrastretchability. The combination manufacturing process of fused deposition modeling (FDM) 3D printing technique and ultrasonic cavitation-enabled treatment was introduced into the fabrication of flexible strain sensors made of thermoplastic polyurethane (TPU) substrate and carbon nanotubes (CNTs). A negative Poisson’s ratio (NPR) architecture made of TPU was firstly 3D-printed by FDM. The ultrasonic cavitation treatment was then conducted on the soft auxetic structure immersing in CNTs liquid, aiming to embed the CNTs into the surface layer of the flexible TPU substrate with NPR configurations. Instead of 3D printing the TPU matrix composite after hybridization inside the matrix material, the hybrid manufacturing procedure can ensure that the intrinsic excellent mechanical properties of TPU are not embrittled. Besides, the sinusoidal struts in accordion-like cellular architectures offer a design route to extend the material property chart to achieve ultrahigh stretchability in lightweight 3D printable flexible polymers for the applications that require combined stretchability, lightweight, and energy absorption such as soft robotics, stretchable electronics, and wearable protection shields.

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.