Model of Wear of Working Attachments of Earth Digging Machines upon Interaction with a Soil Mass

This article describes the development of a physical and mathematical model aimed at analysis of the physical essence of surface wear of working attachments of earth digging machines on the basis of soil cutting as well as at quantitative and qualitative assessment of this process allowing us to expand the understanding of the very essence of wear. The presented model exemplified by a ripper tip allows us not only to study the mechanics of soil destruction and to assess its quantitatively, but also to reveal physical phenomena of changes in friction forces and adhesion upon contact of the working attachment surface with soil. It has been established that the lower edge of the ripper tip is exposed to the highest wear and the forces of soil moving over it are 1.6 times higher than those occurring at the upper edge of the working attachment. The model development is based on the fact that in the zone of soil compression existing for 0.8 s the motion of the working attachment towards the motion direction of the machine is insignificant, and the cutting forces increase to the level of excess of ultimate soil strength from the acting traction force of the working attachment. Then, in the course of soil dispersion for 1.8-2 s the motion speed of the working attachment in soil increases, which results in wear increase, since exactly at this time the working attachment contacts directly with soil. The performed studies allowed to take into account the issue of influence of adhesive and cohesive properties of soil during its excavation and the influence of these forces on wear of working attachments of earth digging machines.