Charpy Impact Testing

CHARPY IMPACT TESTING 

The impact test requires a rectangular sample which is machined out either a welded plate or from a piece of material to be investigated.  A notch is cut out of the sample and then it is placed in the machine.  A hammer is applied to the sample in the area of the notch, and the sample fractures.  The energy required to cause fracture is measured.

Tests are conducted at different temperatures from room temperature up to as low as -100°C.  This is because steels can become brittle at low temperatures.  After welding, brittle phases may be present in the weld.  A test at low temperature will reveal if these phases are present.

The impact test is also used to re-grade material and is not only used for weld procedure qualification (WPQ) records.

The appearance of the fracture surface after impact gives a wealth of information about the material.  A brittle material shows a flat smooth fracture surface compared to a ductile surface which has shear lips and is distorted.

We can also use charpy impact testing to identify other brittle failure mechanisms like hydrogen embrittlement for example.