Affordable TMF testing supported by FE simulations

The predictive capability of cyclic life assessment methodology for gas hot parts of turbines is analysed and improved. The main finding is that standard test data is seldom sufficient to guide the modelling,or to calibrate the resulting model when one aims for predictive capability under component conditions. We therefore focus on improved testing as a basis for improved modelling. Constitutive characterisation tests have been performed and modem state variable models are evaluated. We find that there are models that can be used with some modifications, for particle strengthened blades and vane materials such as IM792, but no adequate models for solution-strengthened combustor materials such as Haynes 230. Constitutive models for IN792 are being developed and calibrated using creep data and step relaxation tests tailor made for robust parameter estimation of back stress evolution models. Blades such as IN792 have high temperature strength, but must be coated to survive the corrosive environment. For base metal/coating aggregates, it has been recognised that TMF tests are needed, i.e. tests in which strain and temperature aresimultaneously varied. The current TMF test methodology is toprovide a standard LCF test rig with a variable temperature oven. However, the resulting test rig becomes difficult to handle and the difference between test and component conditions is in many cases still too large. Work is on-going to develop an easy-to-handle TMF test rig which allow one to obtain realistic conditions. The method require extensive FE simulations to compute material parameters and evaluate results.