Tribological properties of an ultra￾sonic drill with beating for planetary soil drilling.

Abstract

This article examines practical and theoretical issues regarding the improvement of the operational characteristics of an ultrasonic drill designed for planetary soil drilling on celestial bodies. A distinctive feature of the drill's design is the presence of interconnected friction zones between its mating elements; depending on operating conditions, one type of friction can transition into another, thereby altering operational parameters – such as the frequency range of the working tool's oscillations (beating). The study aims to investigate the tribological properties of the ultrasonic drill and assess their impact on the device's operational performance, including its frequency characteristics. Technical solutions proposed by both domestic and foreign authors were reviewed, and a prototype was selected. An analysis of existing research on ultrasonic drills revealed a lack of data regarding their tribological properties. The theoretical section of the article employs mathematical models based on the hydrodynamic theory of sliding-bearing lubrication and the vibro-rheological behavior of friction bodies. Methods from mathematical physics, fluid mechanics, classical mechanics, and similarity theory were utilized. The study presents the tribological characteristics of the ultrasonic drill, which also reveal its frequency characteristics. It is demonstrated that the design of the ultrasonic drill is essentially identical to that of a vibration-supported gas suspension system, with their operating frequency ranges lying in close proximity. A parametric study was conducted to derive the device's integral tribological characteristics. It is shown that a frequency parameter (a similarity criterion for the problem) allows for the determination of the frequency boundary between the suspension and beating regimes based on medium parameters within the layer – such as density, viscosity, and vibration frequency. An analytical condition is proposed for the transition from the suspension regime to the working body's beating regime; this condition depends significantly on the vibration mode of the working tip. The uniform, umbrella-like, and single-nodal-circle vibration modes of a T-shaped tip have been investigated, demonstrating the effectiveness of umbrella-like vibrations. A gas content characteristic – continuously describing the medium's state from liquid to pure gas – has been incorporated into the suspension model. The influence of the planetary atmosphere is accounted for via this gas content parameter; calculations show that as the liquid component increases, the suspension's integral characteristics and frequency parameter rise significantly, thereby affecting the drill's operating performance.