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The subject of this paper, namely stress, strain, strass-strain relation & Hooke's law is a very extensive one. Neverthcles$, I am going to try to collect and present the most Important informatlon. I will start with the very foundation of the subject by laying out definitions of both stress and strain, subsequently I will discuss the matter of stress-strain relation after which I will finish presentlng Hooke's law.

Stress. The concept of stress originated from the study of strength and failurc of sollds. In continuum mechanics, stress is a meosure of the Internal forccs acting within a deformable body. The stress field Is the distribution of internal "tractions" that balance a given set of external tractions and body forces. Quantitatlvely, It is a measure of the average force per unit area of a surface within the body on which Internal forces act. Specifically, it shows the intensity of the Internal forces acting between the particles in the deformable body across imaginary internal surfaces. Thesc Internal forces arise as a reaction to external forces applied on the body that cause it to deform. Bcyond certain limits of materiaÅ‚ strength, this can lead to a permanent shape change or structural failure. External forces are either surface forces or body forces. The stresses considered in continuum mechanics are only those produced during the application of external forces and the consequent deformation of the body. Bccause the loaded deformable body Is assumed to behavc as a continuum, these internal forces are distributed continuously within the volume of the materiaÅ‚ body. The stress distribution in the body Is expressed as a piecewise continuous function of space and time. A body is considered stress-free if the only forces present are those intcr-atomic forces (ionic, metallic, and van der Waals forces) requlred to hoÅ‚d the body together and to keep its shape in the absence of all external influences, induding gravitational attraction. The dimension of stress is that of pressure, and therefore the SI unit for stress is the pascal (symbol Pa), which is equivalent to one newton (force) per square meter (unit area), that is N/m^J. Stress can be a tension, compression, shear, torsion or any combination.

Stresses occur in any materiaÅ‚ that is subject to a load or any applied force. There are many types of stresses, but they can all be generally classified in one of slx categories: residual stresses, structural stresses, pressure stresses, flow stresses, thermal stresses, and fatigue stresses.

Residual Stress

Residual stresses are due to the manufacturing processes that leave stresses in a materiał. Welding leaves residual stresses in the metals welded.

Structural Stress

Structural stresses are stresses produced in structural members because of the weights they support. The weights provido the loadings. These stresses are found in building foundations and frameworks, as well as in machinery parts.

Pressure Stress

Pressure stresses are stresses Induced in vessels containing pressurized materials. The loading is provided by the same force producing the pressure.

Flow Stress

Flow stresses occur when a mass of flowing fluid induces a dynamie pressure on a conduit wali. The force of the fluid striking the wali acts as the load. This type of stress may be applied In an unsteady fashion when flow rates fluctuate. Water hammer is an example of a transient flow stress.