Strength of materials is the science which deals with the relations between externally applied loads and their internal effects on bodies.
The bodies are not assumed to be rigid, and the deformation, however small are of major interest.
Or,
we can say that, When an external force act on a body. The body tends to undergoes some deformation. Due to cohesion between the molecules, the body resists deformation. This resistance by which material of the body oppose the deformation is known as strength of material, with in a certain limit (in the elastic stage). The resistance offered by the materials is proportional to the deformation brought out on the material by the external force.
So we conclude that the subject of strength of materials is basically a study of
(i) The behaviour of materials under various types of load and moment.
(ii) The action of forces and their effects on structural and machine elements such as angle iron, circular bars and beams etc.
Certain assumption are made for analysis the problems of strength of materials such as:
(i) The material of the body is homogeneous and isotropic,
(ii) There are no internal stresses present in the material before the application of loads.
