Mechanical Properties of Solids – Notes
Elastic behaviour of solids
When a force acts on a body, it accelerates in the direction of the net force.
When a set of equal and opposite forces acts on a body, there is no net force on the body but it gets deformed, changing its size or shape or both.
The deformation of the body changes the intermolecular separation, and gives rise to intermolecular forces.
In some materials, when deforming forces are removed, the intermolecular forces try to restore the body to its original shape and size. Materials such as these are called elastic and this property of a body is called elasticity.
Some materials display little or no tendency to return to their original size and shape even when deforming forces are removed. Such materials are called plastic and this property is called plasticity.
Deforming forces may change the length, volume or shape of a body on which they act.
Stress strain and Hooke’s law
Stress is the sum total of restoring intermolecular forces per unit area within a deformed body. It is measured as the external deforming force per unit area.
Strain is defined as the fractional deformation produced in the body by external deforming forces.
Longitudinal stress is equal to the deforming force per unit area.