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Kappa SS-CF for Thermo-Mechanical Fatigue Testing on Turbine and Motor Materials

For the design and construction of thermal and simultaneously mechanical cyclic loaded components for gas turbines or combustion engines for example, reliable characteristic values for the prediction of the fatigue life and the cyclic deformation behavior under existing operating conditions must be available. In thermo-mechanical fatigue testing, the required material characteristics are determined through the in-phase or out-of-phase combination of cyclic thermal and mechanical loads.

For this particular application, ZwickRoell in Fürstenfeld in close collaboration with the Karlsruhe Institute of Technology (KIT) developed a new electromechanical testing system. The proven Kappa 100 SS-CF was equipped with an induction heating system for a temperature range of 50°C up to 1,200°C and an air cooling system. Depending on the test material and specimen geometry, this combination allows for maximum heating rates and maximum cooling rates of 25 K per second. With the use of specimen-specific inductors, even temperature distribution along the specimen is ensured, and precise and standard-compliant specimen temperature with a maximum temperature deviation of < 10K or < ± 2% of ∆T is guaranteed. Temperature measurement can be carried out with calibrated ribbon thermo-couples (i.e. type K) in the center of the specimen measurement travel.

To safely grip the metal specimen, water-cooled mechanical or hydraulic specimen grips are used. A contact extensometer in accuracy class 0.5 to ISO 9513 is used for the specimen strain measurement.

For control of the induction heating system and active cooling, and the synchronization of mechanical and thermal cycles, a real-time control system specifically developed for this purpose is used. Parameterization and operation, as well as saving of measured data and the evaluation of results take place via the well-known ZwickRoell testing software, testXpert III.

The new testing solution for thermo-mechanical fatigue testing meets all requirements of the European Code of Practice for thermo-mechanical fatigue testing, as well as those of ASTM E2368 and ISO 12111.