Charpy Impact Toughness
Charpy Impact Toughness
The Charpy V-notch test swings a pendulum into a small notched bar and measures how much energy the specimen absorbs before fracturing — a quick, inexpensive way to screen materials (especially steels) for brittle-fracture risk, particularly at low temperature. Reporting the raw absorbed energy alone makes it hard to compare specimens of different sizes, so dividing by the fractured ligament area gives an impact toughness value that is more directly comparable across specimen geometries — this test is also the classic tool for finding a material's ductile-to-brittle transition temperature by repeating it across a temperature range.
Charpy impact toughness is IT = E/A, absorbed impact energy divided by the fractured ligament area. where E_impact is the energy absorbed during fracture and A_lig is the cross-sectional area of the fractured ligament beneath the notch.
Inputs
E_impact := 45 J=45 Nm
A_lig := 80 mm^2=8e-05 m^2
Normalizing the absorbed energy by the ligament area converts a raw test result into an intensive toughness property that does not depend on the exact specimen size.
IT_charpy := E_impact/A_lig=562500 kg/s^2
Results
This result falls in a range typical of a tough, ductile steel at or above its transition temperature; a sharp drop in this same measurement as test temperature decreases is exactly what identifies the ductile-to-brittle transition. A material intended for a cold environment (piping, pressure vessels, structural steel in arctic service) must retain adequate impact toughness at its lowest expected service temperature, not just at room temperature.
Assumptions & limitations
- Standard Charpy V-notch geometry and pendulum test method assumed.
- Single test result shown — real practice averages multiple specimens.
- Result is temperature-dependent; the temperature of this test is not itself modeled here.
- Impact toughness (energy/area) is a comparative index, not a direct fracture-mechanics property like Kc.