The important properties of material are:
1. Physical properties:
It includes luster, color, size and shape, density, elastic and thermal conductivity, and melting point.
2. Chemical properties:
It includes chemical composition, structure, etc.
3. Mechanical properties:
The mechanical properties of materials are the properties which describe the behavior of the material under the action of external forces. They usually relate to elastic and plastic behavior of the materials. Some mechanical properties are as follows:
A. Strength: It is the ability of material to resist the externally applied force without breaking or yielding. It is expressed as tensile strength, a compressive strength or shear strength.
B. Stiffness: It is the ability of material to resist the deformation under stress.
C. Elasticity: It is defined as the ability of the material to regain its original shape and size after the deformation, when the external forces are removed. All engineering metals are elastic but the degree of elasticity varies from metal to metal. Steel is perfectly elastic within elastic limit. This property is desirable for materials used in tools and machines.
D. Plasticity: It is defined as the ability of of the material to retain the deformation produced under the load on permanent basis. It is necessary for forgings, in stamping images on coins and ornamental work.
E. Resilience: The ability of a material to absorb energy within its elastic limit without any permanent deformation is called Resilience. It is measured by a quantity called modulus & resilience. It is essential for spring material.
F. Toughness: It is defined as the ability of the material to absorb the energy before fracture has taken place
OR It is the property of the material to resist fracture due to high impact loads like hammer blow. The toughness of a material decreases when it is heated. This property is desirable in parts subjected to shock and impact loads. The toughness is measured by quantity called modulus of toughness.
G. Ductility: It is the property of a material enabling it to be drawn into wire with the application of a tensile force. Ductility is a measured in units of percentage elongation or percentage reduction in area in tension test. E. g. Mild steel, copper, Al, nickel, zinc, tin, etc.
H. Malleability: It is a special case of ductility which permits materials to be rolled or hammered into thin sheet. E.g. wrought iron, soft steel, lead, copper etc.
I. Brittleness: It is that property of material which shows negligible plastic deformation before fracture takes place. E.g. Cast Iron.
J. Hardness: It is the ability of a material to resist penetration, plastic deformation, abrasion or scratching.
K. Machinability: It refers to a relative ease with which a material can be cut. E.g. Brass can be easily machined as compare to steel.
L. Creep: When a part is subjected to a constant stress at high temperature for a long period of time, it will undergo a slow and permanent deformation called creep. It is useful in designing IC engines, boilers and turbines.
M. Fatigue: When a material is subjected to a repeated stresses, it fails at stress below the Yield point stresses. Such type of failure of a material called fatigue. It is used in designing of shafts, connecting rods, springs, gears, etc.