A test specimen, usually of square crossed
section is notched and held between a pair of
jaws, to be broken by a swinging or falling
weight. When the pendulum of the Izod testing
machine is released it swings with a downward
movement and when it reaches the vertical the
hammer makes contact with the specimen
which is broken by the force of the blow. The
hammer continues its upward motion but the
energy absorbed in breaking the test piece
reduces its momentum. A graduated scale
enables a reading to be taken of the energy
used to fracture the test piece. To obtain a
representative result the average of three tests
is used and to ensure that the results conform
to those of the steel specification the test
specimens should meet the standard
dimensions laid down in BS 131.