Stress Vs. Strain Diagram for Ductile Materials Video Lecture | Design of Machine Elements - Mechanical Engineering

Hello Friends here in this video we will
see the Stress Strain graph for ductile
materials and for that purpose I have
drawn the diagram here in this diagram
we have on y-axis stress and on x-axis
we have strain so this video will show us
stress-strain graph for ductile
materials now as I have drawn this graph
here we can see some lines which I have
drawn in red this is the origin o now
when we look fro in this graph
there are various points from O to A as
we can see here we have an inclined line
and this is we can say that a sense it
is an inclined line it is not a curve so
here we are getting a linear
relationship between stress and strain
and I can see that your o to a it is
called as proportional limit now when we
say that from o to a it is proportional
limit it means if we go on increasing
stress strain will also increase means
their relation is directly proportional
so in proportional limit I can say that
therefore stress is directly
proportional to strain so now as we can
see in this stress all day I have
denoted it by Sigma strain it is denoted
by letter E if I remove this
proportionality sign I have a constant
here called as capital e I will say that
where capital e it is called as Young's
modulus
or modulus of elasticity its unit is
Newton per mm square so as we have seen
in this graph from zero to a it is
proportional limit now when we reach
point a that is if we are increasing the
stress and we reach up to point a then
we are getting a strain value as well
here there will be stress and here we
are getting strain now the moment we
remove the load from point A it means
stress becomes zero so if I remove the
load this object will return back to its
original shape it means it behaves in an
elastic manner so within this zero to a
region the material behaves in an
elastic manner that is when the load is
removed it will regain its original
shape next we see point A to B that is I
will write it down here on the next page
from A to B it is called as elastic
limit now when I talk about the elastic
limit from A to B again as we can see
here that I have when we have reached
point B from A to B it is a curve now
from zero to a the relation between
stress and strain was linear from A to B
the relation is it is a curve so the
relation is not linear like it was from
zero to a but even at point B if we are
removing the load the material will
regain its original shape
so from A to B it is elastic limit now
when we go from point B to C the change
in stress is not very much as we can see
there is very little difference between
B to C so I can say that
b2c it is called as here I'll say that
point C is called upper yield point is
called as upper yield point it means at
Point C the yielding has started
yielding means change in shape so once
the material crosses point B it reaches
in the region between B to C where it
will be permanently deformed that is if
we remove the load from Point C then the
material won't regain its original shape
it means at Point C it has deformed
permanently so this B to C region it is
also called as permanent set now when we
are from region C to D as we can see in
this diagram now compared to Point C
Point D is below it means the stress at
Point D it is less compared to Point C
but the material is deforming wood as we
can see at Point C the strain is less
strain means the physical deformation
and at Point D the strain is more but
stress value is less so here I can say
that C to D Point D is called lower yell
point
and strain is more at point d then point
c next as we can see in this diagram D
to e here again stress is increasing in
a tremendously high manner as we can see
here we can look at the diagram the
stress at Point E it is the highest
point in this graph so here we are
getting maximum stress so I will say
that point from the region D to e here
point E is called yield point and stress
is maximum at the yield point now up to
point a the stress is maximum then if we
go from E to F the stress will go on
reducing as we can see the graph is
falling so your stress decreases and
from E to F we can say that stress
decreases but strain increases
as it is very much clear from the
diagram from e2f the stress is falling
whereas the strain is increasing here we
can look at this and finally at point F
er I've mark star the material will be
breaking and this is called as breaking
point so I will say that at point F the
material breaks hence it is called as
breaking point so now it is very much
clear from this stress-strain diagram
that this is for ductile material and
ductile material will be flowing like
this that is it shows the strain
variation and strain is nothing but
physical deformation which we can see
and we can see the material flowing and
finally it will break and this breaking
point is just after the material has
reached maximum stress so we can say
that if the material is having maximum
stress after that it can break at any
given point so in this video we have
seen stress strain graph for ductile
materials