Multi-axis thermomechanical testing system
The test system developed at the Institute for Materials Research enables, in addition to time-varying mechanical and thermal loads, a high thermal gradient across the sample wall. The thermal gradient is established in hollow samples by simultaneously heating the outer wall with a concentrating radiation oven and cooling the inner wall with compressed air. After the heating phase of the test load cycle, a stationary temperature gradient sets in across the sample wall.
Multiaxial stress states arise in cooled components due to the temperature gradient that occurs across the component wall. With internal cooling, e.g. in the blades of the first stage of an engine turbine, the thermally induced stresses cannot be reduced by macroscopic deformations. The compression of the component creates multi-axial compressive stresses on the heated side and multi-axial tensile stresses on the cooled side. These stress states cannot be generated in conventional thermomechanical laboratory tests with homogeneous temperature distribution.
The high power density of the radiation furnace enables high heating rates, comparable to those in an aircraft engine. High cooling rates are achieved with an air shower. During the cooling phase of a load cycle, the sample is enclosed in two half-shells using a slider technique and is simultaneously blown with cold compressed air.
The realistic thermomechanical testing offers the advantage that the data from the laboratory test can be transferred to operating conditions. Another key advantage of the test facility presented here is the extremely short load cycle times - e.g. the fatigue stress that occurs in the turbine blade during a flight mission can be simulated in 3 to 5 minutes.
Characteristics:
The heating output of the system is 16 kW. For a cylindrical hollow sample made of nickel-based superalloy, for example, the following test data is achieved: heating from 100°C to 1000°C in approx. 20 seconds, cooling from 1000°C to 100°C in approx. 15 seconds, stationary temperature gradient of 100°C per mm. The maximum mechanical load is 25kN.