Charpy

The Charpy impact test, named after French metallurgist Georges Charpy, is a standardized method used to measure the notch toughness of materials. It determines how much energy a material can absorb when fractured by a single, high-rate impact. The test is commonly performed on metallic materials to assess behavior under sudden loading and to evaluate the effect of temperature on toughness.

Specimens are small, usually rectangular bars with a notch, most commonly a V-shaped notch. The specimen is mounted horizontally in a pendulum-type impact machine and positioned so the notch lies in the path of the falling hammer. Charpy specimens are typically described by their standard cross-section and length, with the notch located at the center of the gauge section. The exact dimensions and notch geometry are defined by the applicable standard.

During testing, a pendulum hammer is released from a fixed height to strike the specimen at the notch. The energy absorbed by the specimen to fracture is inferred from the difference between the pendulum’s energy before and after impact, and is reported as the impact energy in joules. The test can be conducted at various temperatures to observe how toughness changes with temperature.

Interpreting results involves comparing impact energy values to assess notch toughness. Higher energies indicate tougher, more ductile behavior, while lower energies indicate brittle behavior. Many materials exhibit a ductile-to-brittle transition as temperature decreases, which Charpy testing helps characterize. The method is widely used for material selection, quality control, and evaluating the effects of heat treatment or welding.

Standards for Charpy testing include ASTM E23 and ISO 148, which specify specimen geometry, testing procedure, temperature control, and reporting.