Temperature gradients in TMF specimens. Measurement and influence on TMF life

Axial stress components caused by radial temperature gradients in TMF specimens lead to local control deviations in temperature and mechanical strain. Measurements and simulations have been carried out in order to estimate the level of control deviation in non-isothermal heated TMF specimens. Thermal cycle tests were carried out with a variety of specimen coil configurations which cause different radial temperature profiles. Temperature gradients were measured by means of instrumented specimens under different heating and cooling rates. In order to calculate the resulting stresses, model parameters of a thermal–mechanical FE-analysis (e.g., coefficient of convection, emissivity and heat transfer) were fitted on the basis of the measured temperature distribution. TMF tests have been carried out on Ni90 specimens with two induction coil configurations and with two different heating and cooling rates. The experimental results were reported and discussed on the basis of the measured and simulated results.