Impact Test

Impact testing is used to determine material behavior at higher deformation speeds. Classical pendulum impact testers determine the impact energy absorbed by a standardized specimen up to break by measuring the height of rise of the pendulum hammer after impact. Several test methods are commonly employed: 

• Charpy  (ISO 179-1, ASTM D 6110)
• Izod (ISO 180, ASTM D 256, ASTM D 4508) plus 'unnotched cantilever beam impact' (ASTM D 4812)
• Impact tensile tests (ISO 8256 und ASTM D 1822)
• Dynstat impact bending test (DIN 53435)

For the single characteristic value Standard ISO 10350-1, Charpy to ISO 179-1 is the preferred test method. For this the test is normally performed on unnotched specimens with impact on the narrow face (1eU). If the specimen does not break in this configuration, the test is performed with notched specimens, although the test results are not directly comparable. If specimen break is still not achieved the impact tensile method is employed. 

For ASTM Standards the Izod test method  to ASTM D 256 is usually employed. Here notched specimens are always used for testing. A seldom-used method is the 'unnotched cantilever beam impact' described in ASTM D 4812, which is similar to the Izod method, but is performed with unnotched specimens. If it is only possible to produce small specimens the 'chip-impact' method to ASTM D 4508 can be used. 

The Charpy method has a broad range of applications and is better suited to tests on materials displaying interlaminar shear fractures or surface effects. In addition the Charpy method offers other advantages when testing at low temperatures as the specimen support is farther away from the notch and thus rapid heat transfer to the critical area of the specimen is avoided. 

Some German automobile manufacturers use the Dynstat impact bending method to test small specimens. This method is only described in DIN.  

When testing to ISO, each pendulum hammer may be used in the range from 10 % to 80 % of its nominal initial potential energy. ASTM permits use up to 85%. 

A fundamental diffference between ISO and ASTM concerns the choice of pendulum size. According to ISO the largest possible pendulm hammer must be used, although the overlaps between pendulum sizes are often very small. This requirement is based on the consideration that speed decay during specimen penetration should be kept as low as possible. With ASTM the standard pendulum hanner has a rated initial potential energy of 2.7 joules and all further sizes are arrived at by doubling. Here the smallest possible hammer in the range is to be used for testing. 

Zwick pendulum impact testers in the 5102 and 5113 ranges and the new HIT range are constructed strictly to DIN, ISO and ASTM Standards. 

Typical products for these applications: