Impact Tests
An impact test is a type of accelerated stress test designed to determine a material’s toughness and its ability to absorb energy. It is a destructive test, meaning that it can cause permanent damage to the material being tested. Impact tests can be used to test elastomers, plastics, composites, metals, and ceramics.
Impact testing is used mostly when testing materials for use in safety-critical applications. For example, an automotive manufacturer will use an impact test to determine if the materials used in the frame, seatbelts and airbags will be able to withstand an impact in the event of a crash. The test also helps the manufacturer determine what load a material can withstand before failing.
Types of Impact Tests
Drop weight impact test: This test is used to determine how much energy a material can absorb. The test sample is held in a jig and dropped from a certain height onto a target. The energy absorbed by the material is measured upon impact.
Dynamic impact test: This test is used to determine a material’s dynamic properties such as modulus, resilience and fatigue resistance. The test sample is tensioned between two rods and an impactor is used to repeatedly strike the sample and measure its response.
Charpy impact test: This test is used to determine a material’s toughness, which is its ability to absorb energy until the specimen fractures. The Charpy test uses a pendulum which strikes a test sample, causing it to fracture. The absorbed energy is measured and used to calculate toughness.
Izod impact test: This test is similar to the Charpy test, but here the test sample is struck on the side with an impactor. The absorbed energy is used to calculate toughness.
Impact Testing Equipment
Impact testing requires specialized equipment, such as impact hammers, pendulums, jigs, fixtures and instrumented impact test machines. The most common type of machine is the Charpy impact testing machine. It consists of a machine frame, clamping device for the test sample and a pendulum. The pendulum is used to deliver the impact and is equipped with strain gauges to measure the force.
Conclusion
Impact testing is a destructive test and is used mainly to determine a material’s ability to absorb energy and its toughness. The most common types of impact tests are drop weight, dynamic, Charpy, and Izod tests. These tests require specialized equipment, such as impact hammers, pendulums, fixtures, and instrumented impact test machines.