Simple Stresses in Machine Parts : Machine Design

Simple Stresses in Machine Parts :

The machine parts are subjected to a various forces which is due to energy transmitted , weight of machine , frictional resistance , Inertia of reciprocating parts , change of temperature and lack of balance of moving parts .

Load :

Load is the external force acting upon a machine part .

Dead or steady load
Live or variable load
Suddenly applied or Shock loads
Impact load

Dead load is means ' does not change magnitude or direction '. When change of magnitude or direction is continuously then it is live load . When load is suddenly applied or removed then load is called suddenly applied or Shock loads .When applied some initial velocity then load is impact load .

Stress :

When external forces or loads act on a body , the internal stress resist the external forces . This internal force per unit area at section is known as unit stress or stress . Stress is denoted as ( sigma ) .The unit of stress is N/mm2 or Pascal ( Pa ) .

Where -

P = Load acting on body .

A = Cross Section area .

Strain :

The ratio of change in length and original length of body is known as Strain . Strain is deformation of body when loads act on a body . Strain is denoted as ( epsilon ) . The unit of strain is unitless .

Where -

Tensile Stress and Strain :

Two equal and opposite axial pull ( tensile load ) is acting on a body then stress is known as tensile Stress . The ratio of increasing in length to original length is known as tensile strain .

Tensile Stress -

Tensile Strain -

Compressive Stress and Strain :

Two equal and opposite axial pushes ( Compressive load ) is acting on a body then stress is known as compressive Stress . The ratio of decreasing in length to original length is known as compressive strain .

Compressive Stress -

Compressive Strain -

Young's Modulus or Modulus of Elasticity :

According to Hooke's law , stress is directly proportional to Strain .

Where E is a constant of proportionality , which is known as young modulus or Modulus of elasticity . The unit of modulus of elasticity is GPa .

Shear Stresses in Machine Parts :

Two equal and opposite forces is acting on tangential section then stress is known as Shear Stress . Due to this stress , strain is called Shear Strain . Shear stress is denoted as tau and shear strain is denoted as phi .