International Journal of Innovations in Engineering and Technology (IJIET) http://dx.doi.org/10.21172/ijiet.93.03 Volume 9 Issue 3 February 2018 014 ISSN: 2319-1058 Mechanisms of friction and their correlation to bond strength of friction welded Ti-6Al-4V similar welds, Low Carbon steel-Stainless steel and Aluminium-Copper dissimilar welds. D. Ananthapadmanaban Associate Professor, Department of Mechanical Engineering, SSN College of Engineering Abstract- There have been various mechanisms used to explain the phenomenon known as friction. This paper studies these mechanisms and identifies the correct mechanism/combination of mechanisms for the case of friction welding of Low Carbon steel-Stainless steel combination, Aluminium to Copper and similar Ti-6Al4V welds. It tries to correlate bonding based on tensile strength obtained based on the mechanisms which are predominant in each of these friction welded combinations. Keywords- Mechanisms of friction, recrystallization, Upset pressure, Bond unsaturation I. INTRODUCTION Friction is probably due to various mechanisms that may appear in different proportions under different circumstances. The word friction is generally used to describe the gradual loss of kinetic energy in many situations where bodies move relative to one another. ”internal friction‟ dampens vibrations of solids. This type of friction is due to the interactions that happen at the atomic or molecular level. Viscous friction slows the internal motion of liquids. Skin friction acts between a moving aeroplane and the surrounding air.” Solid friction is the friction between two solid bodies that move relative to each other. The need to control friction is the driving force behind this study. In many cases, low friction is desired( bearings, gears, materials processing operations) and sometimes high friction is the goal(brakes, clutches, screw threads, road surfaces, friction welding, friction stir welding and friction surfacing). II. THEORIES OF FRICTION A. Early theories Amontons saw the cause of friction as collision of surface irregularities. He determined the two main laws of friction, often called Amontons‟ laws which are:  The friction force is proportional to the applied load.  The friction force is independent of the apparent area of contact. The same relationships had been observed by Leonardo da Vinci 200 years earlier. Euler (1707) a Swiss physicist said that friction was due to hypothetical surface ratchets as shown in Figure 1.In friction welding, ratchets or unevenness of the surface is may have a very negligible contribution to the bond strength because the frictional force and the upset force are high and the unevenness evens out very soon. Figure 1 Shows Surface Ratchets