Friction, Lubrication, and Wear

Abstract

Friction is the force between interacting surfaces that resists or hinders their relative movement. Wear is defined as the progressive loss of material from a body caused by contact and relative movement of a contacting solid, liquid or gas. The aim of lubrication is to reduce friction between surfaces and minimize wear. Today the research field of friction, lubrication and wear is called "tribology". This word is derived from the ancient Greek word "tribein" (meaning rubbing) and was first used in 1966 in a publication titled, The Jost Report: Lubrication (Tribology) Education and Research published by Her Majesty's Stationery Office (HMSO) in the United Kingdom. Since then it became the common term to describe the science of friction, wear, and lubrication. Introductions to this field are Refs. [452, 453].In spite of the strong economic importance of friction and wear and the resulting scientific effort, our understanding of the fundamental processes is still rudimentary. This results from the complexity of these topics. In addition, this complexity demands a multi-disciplinary approach to tribology. In recent years the development of new experimental methods such as the surface forces apparatus, the atomic force microscope, and the quartz microbalance made it possible to study friction and lubrication at the molecular scale. However, this new wealth of information does not alter the fact, that there are no fundamental equations to describe wear or calculate friction coefficients. Engineers still have to rely largely on their empirical knowledge and their extensive experience.

Rheological and tribological characteristics of mung bean-rice porridge and its impact on sensory evaluation

“…From transition point T 2 , the friction curves increased linearly in conjunction with speed, i.e., s 3 was positive, indicating hydrodynamic lubrication. [32] As the mung bean level increased, the entrainment speed (transition point T 1 and T 2 ) of porridge shifted to higher values, which was possibly due to less gelatinized starch with the addition of mung beans. Gelatinized starch particles are softer and more deformable due to the absorption of water, as well as the partial loss of their crystalline structure.…”

“…The friction is governed by the internal friction (or the viscosity of fluid) and increases linearly with speed. [32,34] However, the friction curves (Figure 8) of the mung bean-rice porridge did not resemble the traditional Stribeck curve but instead followed the schematic diagram in Figure 7. The difference between the friction curve of the mung bean-rice porridge and the traditional Stribeck curve lies in the boundary regime.…”

“…this curve is divided into three regimes: boundary, mixed, and hydrodynamic. [31] In the boundary regime, the sample has to adsorb and form a lubrication film between the surfaces [32] and, therefore, the friction remains constant. In the mixed regime, the friction coefficient decreases together with an increase in speed.…”