Impact tests are performed to measure the response of a material to dynamic loading. The most common laboratory test configurations are the Pendulum Machine and the Drop Tower. However, other test geometries and loading configurations can be used (see our Beverage Can Tester and Double Pendulum Dynamic Tear web pages).
Types of Test Machines
MPM manufactures several impact test systems which can perform a wide variety of impact tests including:
- Charpy pendulum and drop tower impact testing (ASTM E23)
- Drop tower nil-ductility transition temperature (NDTT) impact testing (ASTM E208)
- Drop weight tear (DWT) impact testing (ASTM E 436)
- Dynamic tear (DT) impact testing (ASTM E604)
- Plastic Charpy impact testing (ASTM D256)
- Miniature Charpy pendulum impact testing (ASTM E2248)
- Beverage can impact testing
The impact test equipment can be provided with several options:
- Optical encoder for velocity and energy measurement (pendulum machines only)
- Instrumented striker system
- Automatic pendulum return system (pendulum machines)
- Automatic rail cart positioning system (drop tower machines)
- In-situ heating & cooling system
- Automatic specimen transfer system
- Image analysis system for percent shear determination
Energy And Impact Velocity
Energy and impact velocity are two key measurements made during an impact test. These measurements can be made using various technologies depending on the type of test machine. Drop tower test machines measure energy using an instrumented striker system (see the Instrumented Impact Testing page). The impact velocity is obtained using an infrared detector mounted to the test machine frame.
MPM pendulum impact test machines measure the energy absorbed in fracturing a test specimen using an optical encoder with 36,000 divisions per revolution. This is the finest division encoder ever used in Charpy testing and is capable of resolving energy to a much finer resolution than can be achieved with a dial. For example, the MPM encoder resolves energy to within 0.03 ft-lbs on 400 ft-lb pendulum machines. Experience at MPM has shown that it is not possible to resolve a dial indicator to within better than about 0.25 ft-lbs. Therefore, the 100 year-old dial has been eliminated from the MPM test machines. The encoder data is acquired by the ImpactTM v 4.3 software and used to determine the absorbed energy by calculating the height of the striker contact point before release and the maximum height attained after impact. In addition, the velocity of the striker is recorded from release up to termination of the impact event. Therefore, the exact velocity at impact is recorded in the test record for each test. The software provides a printed test record which includes key information such as the test specimen ID, the date of the test, name of the operator, test temperature, impact velocity, measured energy, etc. A sample output is shown in the Figure below.