2. • Damping can give information on the orgin of
defects such as the formation of quenching
cracks.
• When a solid specimen vibrates, its free
oscillations decay when isolated from their
environment. some of the energy is always
convert into heat.
3. • The various mechanisms by which this transfer
of energy occurs are collectively termed as
internal friction.
• For EXAMPLE: An increase in damping was
found in a steel specimen which had been
quenched . with cylindrical pieces it is possible
to determine the position of a crack in the
piece .
4. • The method of determining the damping factor
consists of finding the time for amplitude to
decrease by a specific fraction, the ratio
between the amplitudes of successive free
oscillations is constant .
• The natural log of this ratio delta, called the
logarithmic decrement is taken as a measure of
the internal friction.
5. The figure shows the damping factor varies in the case of a sound
specimen and for a cracked specimen.
6. • Using torsional vibrations, sensitivity with which
flaws can be detected is least, when they are
situated in the centre of the bar.
• High strain damping is sensitive to the presence
of cracks and this fact has been applied
successfully in the routine detention of season
cracks in brass catridge cases.