Impact Test Calculator — Charpy & Izod Absorbed Energy
Compute the energy absorbed during a Charpy or Izod pendulum impact test from the initial and final swing angles, and derive impact toughness by dividing by the notch cross-section area.
Test type
kg
m
°
°
mm²
Absorbed energy = initial pendulum energy minus energy remaining after fracture
- 1
Initial drop height
0.8 × (1 − cos 140°) = 1.4128Height of pendulum centre above the lowest point of its arc - 2
Final swing height
0.8 × (1 − cos 90°) = 0.8 - 3
Initial pendulum energy
20 × 9.80665 × 1.4128 = 277.104 - 4
Remaining energy after fracture
20 × 9.80665 × 0.8 = 156.906 - 5
Energy absorbed by specimen
277.104 − 156.906 = 120.20
How does this calculator work?
Charpy/Izod absorbed energy = m·g·R·(cos θ_f − cos θ_i). The pendulum stores E_i = m·g·R·(1−cos θ_i) before release; after fracture the remaining energy E_f leaves the difference absorbed by the specimen. Divide by notch area (mm²) to get impact toughness in J/mm² (= kJ/m²).
Formula
How this is calculated
In a pendulum impact test a heavy hammer is raised to a fixed angle (θ_i from vertical) and released. The potential energy stored is E_i = m·g·R·(1 − cos θ_i), where R is the arm length. The hammer strikes and fractures the notched specimen, then continues swinging to a final angle θ_f. The remaining potential energy is E_f = m·g·R·(1 − cos θ_f). The energy absorbed by the specimen is E_abs = E_i − E_f. Because a higher final angle means more energy was retained by the pendulum, a tougher material causes a lower final angle.
The Charpy test (standardised in ISO 148 / ASTM E23) places the specimen horizontally, supported at both ends, with the notch facing away from the hammer. The Izod test clamps the specimen vertically with the notch facing the striker. Both yield absorbed energy in joules. Impact toughness (notch toughness, K) is E_abs divided by the cross-sectional area at the notch in mm², giving J/mm² (= MJ/m²), or equivalently kJ/m² when multiplied by 1 000.
Impact toughness is sensitive to temperature (especially in steel — the ductile-to-brittle transition), strain rate, notch geometry, and specimen size. Standard specimens are 55 × 10 × 10 mm with a 2 mm-deep notch, giving a 10 × 8 = 80 mm² cross-section at the notch. Non-standard specimens require size-correction factors.
Frequently asked questions
Both use a swinging pendulum; the difference is specimen orientation and support. Charpy specimens are horizontal, notch-away from the striker, and supported at both ends. Izod specimens are vertical, notch facing the striker, and clamped at one end. Charpy is more common for metals; Izod is often used for plastics.
Impact toughness from a pendulum test (J or J/mm²) is an empirical, high-strain-rate measure of absorbed energy. Fracture toughness K_Ic is a linear-elastic fracture mechanics property (MPa·√m) describing resistance to crack propagation. They correlate roughly but are not interchangeable.
Temperature is the most important factor for metals: ferritic steels undergo a ductile-to-brittle transition at low temperatures, dropping absorbed energy dramatically. Notch sharpness, specimen size, loading rate, and material microstructure all influence the result.
Also known as
TG we-Calculate Editorial Team. (2026). Impact Test Calculator — Charpy & Izod Absorbed Energy [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/impact-test-calculator
TG we-Calculate Editorial Team. "Impact Test Calculator — Charpy & Izod Absorbed Energy." TG we-Calculate. 2026. https://we-calculate.com/calculator/impact-test-calculator.
TG we-Calculate Editorial Team, "Impact Test Calculator — Charpy & Izod Absorbed Energy," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/impact-test-calculator
@misc{wecalculate_impact_test_calculator, title = {Impact Test Calculator — Charpy & Izod Absorbed Energy}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/impact-test-calculator}}, year = {2026}, note = {TG we-Calculate} }
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