Charpy impact test

The Charpy impact test measures the energy a material absorbs when fractured by a sudden blow, and so gives its toughness and notch brittleness.

Specimen

A standard bar 10 × 10 × 55 mm with a 2 mm deep V-notch (or U-notch) at the middle.

Apparatus

A pendulum hammer of known mass raised to a fixed height, an anvil with two supports 40 mm apart, and a scale to read the energy.

        pivot
          o
          |\
          | \ hammer
   h1 ....|..O
          |
   =======+=====  <- specimen
   |__ ___|__ __|
   supports (anvil), notch faces away from the hammer

Procedure

1. The specimen is placed simply supported on the anvil with the notch on the side opposite to the striking edge.
2. The pendulum is released from the initial height $h_1$.
3. It strikes the specimen behind the notch, breaks it and swings up to a lower height $h_2$.
4. The energy absorbed is

$$E = m\,g\,(h_1 - h_2)$$

It is read directly from the dial in joules.

Use

The test is repeated at different temperatures to find the ductile-brittle transition temperature. A tough material absorbs high energy; a brittle one absorbs little.