IMPORTANT MECHANICAL PROPERTIES
Following are the important mechanical properties of the materials :
1) Strength :
The capacity of material to withstand load is called strength.
- The strength of material is it’s ability to withstand loads without undue distortion, rupture or collapse.
- A material should have adequate strength in tension, compression, shear, bending or torsion.
- The maximum load that any material can withstand is known as ultimate strength.
2) Toughness :
Capacity of a material to absorb energy before rupture is called toughness.
Work required to cause rupture, under static load is called toughness.
Toughness of a material is the ability to withstand large stresses and strains without fracture.
- Mild steel, Wrought iron, Manganese steel etc. have good toughness property.
- Toughness is the highly desirable quality in materials for structural and machine parts subjected to shocks and vibrations.
3) Hardness :
It is the ability of a material to resist to permanent shape change due to external stress.
There are various measure of hardness – Scratch Hardness, Indentation Hardness and Rebound Hardness.
Scratch Hardness :
Scratch Hardness is the ability of materials to the oppose the scratches to outer surface layer due to external force.
Indentation Hardness :
It is the ability of materials to oppose the dent due to punch of external hard and sharp objects.
Rebound Hardness :
Rebound hardness is also called as dynamic hardness. It is determined by the height of
bounce of a diamond tipped hammer dropped from a fixed height on the material.
4) Stiffness :
Resistance to deformation or strain is called stiffness.
Force required to produce unit deformation in a material is called stiffness.
- The stiffness of a material is measured by its ‘Modulus of Elasticity (E)’. The higher the value of E, the more is stiffness.
- Steel is considered as a stiffer material.
5) Elasticity :
It is the property of a material to regain its original shape after deformation when the external forces are removed.
- The elastic properties of a material are of great importance to a design engineer since materials loaded beyond their elastic limit develop a permanent deformation or strain.
- It may be noted that steel is more elastic than rubber.
6) Plasticity :
Plasticity is a property of a material which retains the deformation produced under load permanently.
- The material does not regain it’s original shape, on the removal of the external load.
- This property of the material is necessary for forgings, in stamping images on coins and in ornamental work.
7) Ductility :
Ductility is the property of a material enabling it to be drawn into a wire with the application of a tensile force.
- A ductile material must be both strong and plastic.
- The ductility is usually measured by the terms, percentage elongation and percentage reduction in area.
- The ductile material commonly used in engineering practice are mild steel, copper, aluminum, wrought-iron, nickel, zinc, tin and lead.
- Materials having elongation more than 15% are ductile.
8) Brittleness :
It is the property of breaking of a material with little permanent distortion. Brittleness of a material is opposite to ductility property.
- Brittle materials are withstanding compression load.
- When subjected to tensile loads snap off without giving any sensible elongation.
- Examples of Brittle materials are : Cast iron, Glass, Concrete, Brick, China-ware
- Materials having elongation less than 5% are considered as brittle.
9) Malleability :
It is a special case of ductility which permits materials to be rolled or hammered into thin sheets, making wire.
- A malleable material should be plastic but it is not essential to be so strong.
- Examples of malleable materials are : Gold, Silver, Copper, Lead, steel and aluminum.
10) Machinability :
It is the property of a material which refers to a relative ease with which a material can be cut.
- The machinability of a material can be measured in a number of ways such as comparing the tool life for cutting different materials or thrust required to remove the material at some given rate or the energy required to remove a unit volume of the material.
- For example, that brass can be easily machined than steel. That means the machinability property of brass is high when compare to steel.
11) Resilience :
It is the property of a material to absorb energy and to resist shock and impact loads.
- It is measured by the amount of energy absorbed per unit volume within elastic limit.
- This property is essential for designing the spring materials.
12) Creep :
Inelastic Deformation due to sustained load is known as Creep
13) Fatigue Strength :
Fatigue is the state of a material when it is subjected to repeated loading.
Fatigue Strength is the maximum stress that a material can withstand under repeated stress cycles without breaking.