Impact Test Calculator
The impact test calculator will help you determine the energy absorbed by a notched material specimen during a pendulum impact test. We perform impact tests to understand material failure behavior under dynamic conditions.
Structures for transportation, military, and space applications undergo extreme loads while operating. The materials for such structures must be tested for their fracture toughness and failure behavior to understand how they deform and ultimately break under dynamic conditions such as impact or shock loads. Some examples of impact loads are an object falling on the ground, a vehicle crash, or a bird strike on a windshield. Typical impact tests are pendulum-based tests like the Charpy and Izod impact tests, which follow different standards for plastics, metals, composites, and concrete.
What is an impact test?
An impact test consists of a striker hitting a test specimen to transfer a large force in a very short time. You can use a drop tower or a pendulum tester to achieve such large forces. In a drop tower test, a striker is dropped vertically from a height and uses gravity to reach the necessary impact energy. In a pendulum test, the striker is fixed to an arm that swings like a pendulum. There are two common pendulum tests: the Izod and the Charpy impact tests.
The test begins with the arm set to a high position at the angle of fall, β. Upon release, the pendulum travels from a height h and swings to make contact with the notched specimen. When the moving striker stops suddenly due to the collision, it transfers its kinetic energy to the material specimen. The sample deforms upon impact, generating a stress wave, and the striker rises again to the angle of rise, α.
Impact test formula
For a pendulum arm of length S and a striker mass m, the initial drop height and the height of rise are:
hfall = S · (1 − cos β) hrise = S · (1 − cos α)
The energy absorbed by the specimen is the loss in potential energy of the striker between the fall and the rise:
E = m · g · (hfall − hrise) = m · g · S · (cos α − cos β)
where g is the acceleration due to gravity (9.80665 m/s²). The impact velocity at the lowest point of the swing is v = √(2·g·hfall).
What is the Izod test?
In the Izod impact test, the notched specimen is clamped vertically as a cantilever, with the notch facing the striker. The pendulum strikes the upper free end of the specimen. The Izod test is widely used for plastics and is described by standards such as ASTM D256.
What is the Charpy test?
In the Charpy impact test, the specimen is placed horizontally as a simply supported beam, with the notch on the face opposite to the point of impact. The pendulum strikes the middle of the specimen behind the notch. The Charpy test is the most common impact test for metals and is described by standards such as ASTM E23 and ISO 148.
Using the impact test calculator
- Choose your unit system — Metric (SI) or American/Imperial.
- Enter the striker mass (m) and the pendulum arm length (S), i.e. the distance from the pivot to the center of mass of the striker.
- Enter the angle of fall (β) — the release angle measured from the bottom of the swing — and the angle of rise (α) reached after breaking the specimen. The angle of fall must be greater than the angle of rise.
- Optionally, enter the notch cross-section area to obtain the impact strength (absorbed energy per unit area).
- Read off the energy absorbed, the impact strength, the impact velocity, and the drop and rise heights.
FAQs
What is the energy absorbed for m = 20 kg, S = 0.75 m, β = 150°, α = 60°?
Using E = m·g·S·(cos α − cos β): E = 20 · 9.80665 · 0.75 · (cos 60° − cos 150°) = 147.1 · (0.5 − (−0.866)) ≈ 201 J.
Why must the angle of fall be larger than the angle of rise?
Some of the striker's energy is absorbed by the specimen, so the striker cannot rise as high as it started. If the angle of rise equals or exceeds the angle of fall, no energy was absorbed, which is physically impossible for a real impact test — so the calculator reports an error.
What is impact strength?
Impact strength (or notch toughness) is the absorbed energy divided by the cross-sectional area at the notch. It is reported in kJ/m² (metric) or ft·lbf/in² (imperial) and lets you compare specimens of different sizes.
Can I use imperial units?
Yes. Select the American/Imperial system to enter mass in pounds (lb), arm length in feet (ft), and area in square inches (in²). The absorbed energy is then returned in ft·lbf.