The mechanical properties of a material are concerned with its behavior under the action of the
external forces, a matter of importance to engineers when selecting a material for a particular job.
Four important mechanical properties are strength, stiffness, ductility and toughness.
Strength deals with how great an applied force a material can withstand before breaking.
Stiffness tells us about the opposition a material sets up to being distorted by having its shape or
size, or both, changed. A stiff material is not flexible.
Ductility or workability relates to the ability of the material to be hammered, pressed, bent, rolled
cut or stretched into useful shapes.
A tough material is one which is not brittle, i.e. it does not crack readily.
When an external force acts on a body, the body tends to undergo some deformation. Due to
cohesion between the molecules, the body resists deformation. This resistance by which material
of the body opposes the deformation is known as strength of material. Within a certain limit (i.e.,
in the elastic stage) the resistance offered by the material is proportional to the deformation brought
by the external force. Also between this limit the resistance is equal to the external force (or applied
load). But beyond the elastic stage, the resistance offered by the material is less than the applied
load. In such case, the deformation continues, until failure takes place. Within elastic stage, the
resisting force equals the applied load. This resisting force per unit area is called stress or intensity
of stress.
- Teacher: Gaspard Bizimungu