Impact Test Calculator

Related Calculators

Test method: The specimen setup. Charpy is usually a simply supported bar, and Izod is usually a cantilever specimen [1].

Calculation mode: The set of inputs used to find energy: pendulum angles, pendulum heights, or striker mass and impact speed.

Absorbed impact energy: The energy lost by the pendulum during the impact event. In this calculator it is reported in J or ft-lbf.

Available impact energy before strike: The energy the striker has just before impact, based on the starting height or the mass-and-speed shortcut.

Impact strength: Absorbed energy divided by specimen area, often reported as kJ/m^2 or J/cm^2 [2].

Section area used for normalization: The area used in the impact-strength calculation. It can be the gross area or the net area after notch depth is subtracted.

Net area after notch: Width times remaining thickness, using thickness minus notch depth.

Height difference across impact: Initial striker height minus final striker height. A larger positive value means more energy was absorbed.

Method note: A short result message that explains assumptions, nonphysical inputs, or why impact strength is unavailable.

Mistake: Entering a Final rise angle after impact (deg) that is larger than Initial release angle from vertical (deg) in angle mode.
Fix: Use angles measured from the downward vertical, and make sure final angle is less than or equal to the initial angle.

Mistake: Typing Initial striker height above lowest point (m) and Final striker height above lowest point (m) in mm or cm instead of meters.
Fix: Convert to meters before calculating, such as 1866 mm to 1.866 m.

Mistake: Using a negative or zero value for Striker or pendulum mass (kg) , Pendulum length to striker center (m) , Specimen width (mm) , or Specimen thickness (mm) .
Fix: Enter positive real values only; these dimensions and masses must be greater than zero for valid energy or strength results.

Mistake: Setting Notch depth (mm) equal to or larger than Specimen thickness (mm) while using Impact strength area basis set to net area.
Fix: Reduce notch depth, increase thickness, or switch the area basis to gross area before notch if that matches your reporting convention.

Mistake: Comparing Impact strength values from different specimens without checking Impact strength area basis .
Fix: Keep the same area basis for all comparisons and read Section area used for normalization to confirm the exact area used.

Mistake: Confusing Absorbed impact energy with Available impact energy before strike in mass-and-speed mode.
Fix: In that mode the simplified model treats them as the same starting energy, so use the Method note to remember this is an estimate rather than a corrected machine reading.

• This calculator uses a simplified pendulum-energy model. The main energy result is based on change in potential energy or on 0.5 x mass x speed squared, not on a full machine correction method.
• Charpy and Izod mainly change the test context and interpretation note here. The core energy math is the same if the same pendulum-energy quantities are used.
• Angle mode assumes angles are measured from the downward vertical direction and must satisfy 0 <= final angle <= initial angle < 180 deg for a physically meaningful absorbed-energy result.
• Height mode assumes both striker heights are measured from the same lowest reference point and must satisfy initial height >= final height >= 0.
• Mass-and-speed mode gives available pre-impact energy from striker mass and impact speed. It is useful as a shortcut, but it does not include machine friction, windage, or correction factors.
• Impact strength depends strongly on the chosen area basis. Gross area and net area after notch can give different values, so only compare specimens when the same basis is used.
• If specimen inputs are missing or invalid, the calculator can still show energy results when possible, but impact strength will be shown as not available until the area inputs are fixed.
• Very small negative energy caused only by rounding can be treated as zero, but clearly negative energy or a final state above the initial energy state means the inputs are inconsistent.

Core calculation steps

The calculator first finds the striker energy before impact and after impact using the mode you choose. The absorbed energy is the loss in pendulum energy during the event. Then, if specimen dimensions are valid, it divides that absorbed energy by the selected specimen area to get impact strength.

Formulas used

E_abs = m x g x (h_i - h_f)

h = L x (1 - cos(θ))

E_abs = m x g x L x (cos(θ_f) - cos(θ_i))

E_avail = 0.5 x m x v^2

IS = E_abs / A

What each term means

E_abs is absorbed impact energy, E_avail is available impact energy before strike, m is striker mass, g is gravity, h_i and h_f are initial and final striker heights above the lowest point, L is pendulum length to striker center, θ is angle from the downward vertical, v is impact speed, and A is the selected specimen area.

Area basis for impact strength

If Impact strength area basis is gross, the calculator uses the full specimen area.

A_gross = width x thickness

If the area basis is net, the calculator subtracts notch depth from thickness before forming area.

A_net = width x (thickness - notch depth)

Area is kept in mm^2 for the area output, then converted for the selected strength unit. For kJ/m^2, the calculator converts mm^2 to m^2 and J to kJ. For J/cm^2, it converts mm^2 to cm^2.

Unit conversions

1 J = 0.737562149 ft-lbf

1 mm^2 = 1e-6 m^2

1 mm^2 = 0.01 cm^2

1 kJ = 1000 J

The default gravity is 9.80665 m/s^2.

Worked mini-example

Suppose you choose angle mode with striker mass 22 kg, pendulum length 1.0 m, initial angle 150 deg, final angle 100 deg, width 10 mm, thickness 10 mm, notch depth 2 mm, and net area basis. Using gravity 9.80665 m/s^2, the absorbed energy is about 149.38 J and the available impact energy before strike is about 402.59 J. The net area is 10 x (10 - 2) = 80 mm^2, so the impact strength is about 1867.22 kJ/m^2.

How to interpret the results

A higher Absorbed impact energy usually means the specimen took more energy to fracture or deform under that setup. A higher Impact strength helps compare specimens of different sizes more fairly, but only when the same area basis and similar test conditions are used [2].

Assumptions used by this calculator

This page uses the basic pendulum-energy approach commonly associated with Charpy and Izod style impact testing [1][3]. It does not apply machine-specific correction factors, so real instrument readings can differ from the simplified value. The method note warns when your input order is nonphysical or when the strength part cannot be computed from the specimen dimensions you entered.