Percent shear area determination in charpy impact testing

The Charpy test is used throughout the world in a wide range of industries because of its low cost and the fact that notching and dynamic loading produces a crack tip stress field that is conservative for many applications. As a result of its widespread use, there is a compelling motivation to extract as much data as possible from the Charpy test. In a Charpy impact test, three key measurements are typically made: total absorbed energy, lateral expansion, and percent shear fracture area. At present, the measurements of absorbed energy and lateral expansion are quantitative and well defined, but the methods used by most laboratories in the measurement of percent shear are qualitative at best. This is ironic for a 100-year-old test because, as discussed in this paper, it can be reasonably argued that percent shear is the most fundamental and physically meaningful of the three Charpy parameters for brittle fracture characterization. Digital image analysis for shear fracture area is shown to have low uncertainty and be both repeatable and easy to use on a routine basis. Recommendations for changes to the ASTM E23 standard are provided.