To the present day there is no common standardized process for testing the toughness and hardenability of case-hardened steel. Decades ago, the Zahnradfabrik (ZF) Friedrichshafen developed a process with which these parameters were tested for the release of the corresponding molten masses. This test, which is used by many manufacturers and users of case-hardened steels, is known in the steel business as the “Brugger test”.
An impact flexure test is performed to determine the toughness. A special specimen with lobed ends (which can be interpreted as realistic models of a cogwheel) is mounted so that the impact fin strikes the broad surface of the fin at an angle less than 30 degrees. This simulates the impact loading of a cog.
The dynamic force at break is the characteristic parameter for impact toughness. It is the maximum force of the recorded force-time characteristic for an impact test. The instrumented pendulum impact tester RKP 450 from Zwick, Ulm, which is designed for a maximum impact energy of 450 Joules, is optimally suited for this test. The specimen is gripped in a special 2-screw clamping shell which allows reactionless clamping. A special baseplate for exchangeable grips as well as the pendulum’s interchangeable impact fins makes it possible to use the impact pendulum tester for the Brugger Test as well as for the usual impact bending tests to Charpy.
The impact fin with its applied strain measurement strips (SMS) is highly stressed during this test. For that reason it is manufactured from high-strength steel. A special heat treatment makes it particularly resistant to wear. It is easily removed for reworking or exchange.
The force-time characteristic during the test is acquired, processed, and evaluated with a high measurement frequency and a resolution of more than 65,000 measurement points. The underlying hardware and software package applied for this is, of course, testXpert® from Zwick.