MECHANICAL PROPERTIES OF MATERIALS

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.

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