charpy impact test low temperature

charpy impact test low temperature

The Izod Test and Charpy Impact Test have similarities, but there are a few differences between the tests too. Both impact tests entail striking notched specimens with a swinging weight or pendulum at a series of temperatures to show the relationship of ductile to brittle transition in absorbed energy. Where they differ is in the dimensions of the specimens and the positioning of the specimens in the test machine.

Several machined bar specimens, sized at 1cm x 1cm x 5.5cm with a 2mm deep U-shaped notch at the middle of a specified flat surface, are required to perform the Charpy Test. The Charpy V-notch Test is very common and requires a specimen with a V-shaped notch. The notch on the ASTM Izod Impact test specimen is also V-shaped.
The impact specimens are tested at a series of specified temperatures (e.g. -20ºC, -10ºC, 0ºC, +10ºC, +20ºC) in the range of -452ºF to 500ºF. Low temperature charpy testing involves placing the specimens in a chamber bath of propylene glycol and dry ice until a calibrated thermocouple records the temperature required for the test.
Once a specimen reaches the precise temperature, it is quickly placed into a special holder in the test machine. The Charpy specimen is placed horizontally with the notch facing away from the pendulum or striker and is supported on two sides, while the Izod specimen is supported from one side and the notch is oriented vertically and toward the origin of impact.

The specimen is struck by a “tup” attached to the swinging pendulum of specific design and weight. The specimen breaks at its notched cross-section upon impact, and the upward swing of the pendulum is used to determine the amount of energy absorbed (notch toughness) in the process. Energy absorption is directly related to the brittleness of the material.