Stress and Strain are fundamentals of the Civil Engineering discipline and are not to be confused
Solid Mechanics look into various material's motion and deformation under the action of forces.
STRESS
Stress is the ratio of applied force F to a cross-section area - defined as "force per unit area".
The idea of stress could be used to describe the state of affairs at any point inside a solid in a much more general way. Also, stress could be used to predict when the material will break.
"Stress tells us how hard- that is, with how much force - the atoms at any point in a solid are being pulled apart"
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Different types/names of stress exist such as normal tensile stress which acts perpendicular to the surface and shear stress which acts in a parallel to the surface.
Stress units are usually MN/m2 ( MEGANEWTONS PER SQUARE METRE) in SI units and p.s.i ( POUNDS PER SQUARE INCH) which is mostly used in America.
STRAIN
Strain which is not to be confused with stress is a completely different thing. Strain tells us how far the atoms at any point in a solid are being pulled apart.
Strain is a ratio of the extended length divided by the original length therefore, does have units and hence it is expressed as a percentage.
Strain in association with stress is used to analyse and better understand material properties such as stiffness, strength and much more concepts are based on these two basic and principle concepts.
