Reliability of fracture appearance measurement in the Charpy test

Despite conventional wisdom, the Charpy fracture appearance transition curve does not always coincide with the energy transition curve. Furthermore, unlike Charpy energy, fracture appearance tells how a specimen failed. It can therefore be used meaningfully to relate the results of Charpy testing to results of other toughness tests which may employ different geometries and loading rates. It may also validly be used to compare charpy test results to real service failures. As a part of this work, fracture appearance curves were compared to energy impact curves for the Charpy test and a similar test, the Schnadt K[sub o] test, which uses a sharp impressed notch. It was found that energy and fracture appearance transition may differ by as much as 50 C (90 F) in the Charpy test, while the two curves coincided in the Schnadt test. In a series of toughness tests on 132 steels, the average difference between Charpy energy transition and Schnadt K[sub o] energy transition was about 27 C (49 F). This is believed to represent the difference in toughness between blunt and sharp notches in Charpy size specimens.