Charpy V-Notch Impact Energy
Turn pendulum release and rise angles into absorbed impact energy — J, ft·lbf, and J/cm² over the notch ligament per ASTM E23.
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The engineering
The Charpy machine is a bookkeeping device for potential energy: the hammer falls from release angle α, breaks the notched specimen at the bottom of the swing, and rises to β. Whatever height it fails to recover went into the specimen. This card runs that ledger — absorbed energy in J and ft·lbf, plus energy normalized over the standard 10 × 8 mm V-notch ligament (0.8 cm²) so you can compare sub-size specimens.
Two sanity checks before you trust a number: ASTM E23 wants impact velocity between 3 and 6 m/s (shown on the card), and results above about 80% of machine capacity are suspect because the hammer decelerates too much for a clean strike. Also remember the specification game — many steel specs read in ft·lbf (e.g. 20 ft·lbf ≈ 27 J minimum at temperature), so keep the units straight before signing off a heat lot.
Absorbed energy is not a design property — it is a quality-control and transition-temperature screening number. To rank steels for low-temperature service, run a temperature series and find where the energy (and shear fracture appearance) falls off the upper shelf.
Where this math comes from
The pendulum impact test was proposed by American engineer S. B. Russell in 1898, but it was French metallurgist Georges Charpy who, in 1901, standardized the notched-bar specimen and the machine geometry, arguing that a notch was needed to expose brittleness that slow tensile tests missed. His paper to the French mechanical engineering society gave the test its enduring form — and his name.
The test's career-making moment came in World War II, when welded Liberty ships cracked in half at dockside in cold water. Cambridge metallurgist Constance Tipper used Charpy data to show the steel itself crossed a ductile-to-brittle transition temperature — the plates were fine in summer and glass in winter. Charpy energy at temperature has been a mandatory acceptance test for structural and pressure-vessel steel ever since, codified in ASTM E23.
- 1898S. B. RussellProposes measuring impact energy of metals with a swinging pendulum.
- 1901Georges CharpyStandardizes the notched-bar pendulum test — specimen, anvil, and energy bookkeeping.
- 1933ASTMFirst issues E23, the standard test method for notched-bar impact testing of metallic materials.
- 1945Constance TipperTies Liberty ship brittle fractures to the ductile-to-brittle transition, measured by Charpy energy.
- 2000ISOPublishes ISO 14556 for instrumented Charpy testing, adding load-time traces to the classic energy number.
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