Charpy & Izod impact calculator

Mod 1 — Absorbed energy from pendulum angles

Inputs: hammer mass m (kg), pendulum length L (m), release angle θᵢ (°), exit angle θf (°), optional energy loss Ek (J).

Formula:

E = mgL(cos θf − cos θᵢ) − Ek

where g = 9.80665 m/s². Angles are measured from the vertical (down) rest position.

Output: absorbed energy E (J), reported as KV, KU, or Izod depending on test type.

Alternatively, enable machine-reported energy and enter E directly from the display.

Mod 2 — Machine capacity

Formula:

Emax = mgL(1 − cos θᵢ)

Output: maximum potential energy (J) at the selected release angle.

Mod 4 — Impact strength

Inputs: absorbed energy E (J), specimen width b (mm), ligament height h (mm).

Cross-section area A = b × h (mm²).

Charpy (metals):

aCU = 1000E / (b·h) → kJ/m²

Izod (plastics, ASTM D256 style):

Impact strength = 1000E / b → J/m

Worked example (ISO Charpy Type A)

Parameter	Value
Specimen	10 × 10 mm, 2 mm V-notch
Ligament h	8 mm
Area A	80 mm²
Energy E	120 J

aCU = (120 × 1000) / 80 = 1500 kJ/m²

Charpy vs Izod

Charpy: bar rests horizontally on anvils; striker hits the face opposite the notch. Common symbols: KV, KU, aCU (kJ/m²).

Izod: bar clamped vertically; striker hits on the notch side. Plastics often report energy per unit width (J/m).

Both methods share the same absorbed-energy physics; reporting units and specimen orientation differ.

Applicable standards

Metals: ISO 148-1, ASTM E23, ISO 148-2 (machine verification).

Plastics & composites: ISO 179-1 (Charpy), ISO 180 (Izod), ASTM D256 (Izod plastics).

Treat calculator outputs as auxiliary checks; confirm machine calibration, friction corrections, and reporting rules in the official standard text.