Stress Strain Curve for Mild Steel
OA is Proportionality limit
• OB is Elastic limit but OB is
Non linear
• The slippage of the carbon
atom within a molecular
mass leads to drop down of
stress marginally from C to C’
• C is upper yield point
• C’ is lower yield point (also
known as Yield Stress f y )
• For exp Fe-250 =>
f y =250N/mm 2
• C’D is constant stress region
called Yield Plateau
DE is Strain Hardening region,
material starts offering
resistance against deformation
• EF is Necking region where
drop down of stresses occur
upto Failure point
• Necking region exists only in
ductile material
• In mild steel, ABC are closer to
each other, therefore it is
known as Linear Elastic Metal,
and Yield stress and elastic
stress is taken as 250N/mm 2
• The Fracture or Failure in mild
steel depends upon
Percentage of carbon present
in a steel
The strain at yield stress is
about 0.00125 or 0.125%
• CD represents plastic
Yielding i.e. it is the strain
which occurs after the
yield point with no
increase in stress
• The strain at point D is
about 0.015 or 1.5%
• The strain in the range CD
lies between 10 to 15
times the strain at yield
point
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