Selim Tevfik İLKER, 030060028, 11th week

Stress Relaxation: Stress relaxation is the time and temperature dependent decrease of stress in a solid due to the conversation of elastic into inelastic strain. Stress relaxation data can be used to develop stress-relief heat treatments for reducing residual stresses and for the design of such mechanical elements as joints, gaskets and springs. Stress relaxation data are also an important tool for evaluating the constitutive relations governing a material' s inelastic behavior.

(Stress Relaxation Testing: A Symposium, Alfred Fox,American Society for Testing and Materials, pg. 1 )

Viscosity: Viscosity is a fundemental characteristic property of all liquids. When a liquid flows, it has an internal resistance to flow. Viscosity is a measure of this resistance to flow or shear. Viscosity can also be termed as a drag force and is a measure of the frictional properties of the liquid. Viscosity is a funtion of temperature and pressure. Although the viscosities of both liquids and gases change with temperature and pressure, they effect the viscosity in a different manner.

(Viscosity of liquids: theory, estimation, experiment and data, Dabir S. Viswanath, pg. 1)

Tribology: Tribology has been defined as the science practice of an interacting surfaces in relative motion and the practices related there to.

Elements of Tribology:

(a) Friction

(b) Wear

(c) Lubrication

The subject "Tribology" generally deals with the technology lubrication, friction control and wear prevention of surface having relative motion under load. However, the surface interaction phenomena are so closely related to all above disciplines. This makes the study of tribology a multi-disciplinary concept. Thus, tribology is truely an interdisciplinary science and is very useful for its practitioners.

(Tribology, H.G. Phakatkar, R.R. Ghorpade, pg. 1.1)

Lubrication: The principal of supporting a sliding load on a friction reducing film is known as lubrication. The substance of the which film is composed as a lubricant and to apply it is to lubricate. These are not new concepts, nor, in their essence, particularly involved ones.

Moden machinery has many times more complicated and the demands placed upon the lubricant have become propotionally more exacitng. Though the basic principle still prevails - the prevention of metal to metla contact by means of an intervening layer of fluid or fluid like material- modern lubrication have become a complex study.

Basically, lubrication is governed by one of two principles: hydrodynamic and boundary lubrications. In the former, a continious full-fluid film seperates the sliding surfaces. In the latter, the oil film is not sufficient to prevent metal to metal contact.

(Practical Lubrication for Industrial Facilities, Heinz P. Bloch, pg. 1, 3)