Behavior of materials under loading is an essential study for structural analysis. This field of study is known by many headings including strength of materials. Study of rigid bodies is called mechanics, and deformable bodies is called mechanics of deformable bodies. The solid bodies considered here is axially loaded members, shafts in torsion , beams and columns, as well as structures that are assemblies of these components. The objectives of this analysis will be to find stress, strain and deflections, produced by the loads. Stress is force/area, strain is elongation /original length, stress/strain is a constant up to certain load and this load is called elastic limit. This law is known as Hooks law.

The above quantities can be founded up to failure load, then this will give a complete picture of the behavior of the body. The complete understanding of mechanical behavior is essential for the design of all structures. Including buildings and bridges , machines and motors ships airplane etc. Here it is examining the stresses and strains occur inside real bodies that deform under loading.

Theoretical analysis and experimental results are equally important in the study of mechanics of materials. Because of many practical problems in engineering cannot be handled efficiently by theory alone so experimental measurement is a necessity. The development of mechanics of materials is a blend of both theory and experiment. In certain instants theory is useful but in some others experiment gives good result. Leonardo da Vinci (1452-1519) and Galileo Galilei (1564-1642) held experiments to find strength of wires, bars, and beams, but they did not propose any theory. The famous mathematician Euler developed theory of column and calculated critical load of columns in 1744. This theory is used today.

This study can be done in 2 parts 1st understanding the logical development of concepts and 2nd apply this to practical situations. We must solve numerical problems and familiar with quantities for example allowable stress. Specific units of measurements must be thorough.

Ultimate or maximum load taken by a bar can be found and divide it by a factor of safety, which is the allowable load. There is tensile and compressive force, a stretching force is called tensile force and if shortening is occurred by compressive force. Force by perpendicular cross sectional area is called normal stress and there is tensile stress and compressive stress. Stress is considered because we can design area. When a sign convention is required take tensile stress as positive and compressive stress as negative. We can determine theoretically a load that can brake a bar by bending moment concept.

Steel is elastic that means the strain by a load is disappeared completely when the load is removed. Steel is more elastic than rubber because if rubber is stretched and the force is removed some stretch will not disappear. Testing of specimens can be done in laboratory, it’s a kind of quality control. Stress –strain diagram is prepared and elastic limit shall be found from this graph which is a load.