Motion and forces at a point of contact

Abstract

Frame of reference This book is concerned with the stresses and deformation which arise when the surfaces of two solid bodies are brought into contact. We distinguish between conforming and non-conforming contacts. A contact is said to be conforming if the surfaces of the two bodies ‘fit’ exactly or even closely together without deformation. Flat slider bearings and journal bearings are examples of conforming contact. Bodies which have dissimilar profiles are said to be non-conforming. When brought into contact without deformation they will touch first at a point – ‘point contact’ – or along a line – ‘line contact’ For example, in a ball-bearing the ball makes point contact with the races, whereas in a roller bearing the roller makes line contact. Line contact arises when the profiles of the bodies are conforming in one direction and nonconforming in the perpendicular direction. The contact area between nonconforming bodies is generally small compared with the dimensions of the bodies themselves; the stresses are highly concentrated in the region close to the contact zone and are not greatly influenced by the shape of the bodies at a distance from the contact area. These are the circumstances with which we shall be mainly concerned in this book. The points of surface contact which are found in engineering practice frequently execute complex motions and are called upon to transmit both forces and moments.