We
want to study how a wire behaves when we apply the force continuously on
the body. By increasing the stress on the body continuously the corresponding
strain is noted down and a graph is drawn between the stress and strain as
shown. Here the stress is taken and y-axis and the strain is taken on x-axis.
When
we do not apply any force on the body there is no stress and hence there is no
strain. With the increase of the stress the strain also increases
proportionately up to certain extent and the point up to where it happens is
called as elastic limit. Many times this limit is also called as proportionality
limit, it meant to say that for many bodies proportionality limit and the elastic
limit coincides with each other.
When
the stress is applied about this point the stress is not exactly directly
proportional to strain but the particle will still have elastic nature. That
means if you revert back the stress that we have applied strain also comes back
and the graph retraces back to the origin.
Once
if this elastic limit is crossed ,with respect to the increase of the stress
the strain also increases but the proportionality is no more there. From
this point we cannot retrace the graph which mean to say that when you decrease
the stress strain is not going to completely disappear rather a small portion
of the strain will exists forever. This kind of the arrangement is called permanent set. We can calculate the value of the permanent set has the product of
the original length of the wire and the shift of the graph. This point is
generally called as yielding point.
If
the force is applied beyond the yielding point there will be a increase of the
strain even when the stress is not increases significantly and the wire start
becoming thin. This can happen up to some extend and finally at a particular
point the wire will break .This point where the wire breaks is called as breaking
point.
If
there is a good gap between the yielding point and breaking point, that kind of
the material is called ductile materials
and there are very much useful in making thin and long wires. Gold and copper
are simple examples of this kind of the materials.
If
there is no big gap between yielding point and the breaking point they cannot
be molded into wires and this kind of the material is called as brittle
materials. Glasses a typical example of a brittle material.
Related Posts
No comments:
Post a Comment