A Simplified Thermal Mechanical Fatigue (TMF) Test Method

Abstract

The thermal fatigue environment of gas turbine engine airfoils is severe and is often a life-limiting mode of failure. Alloy and coating system evaluation and accurate service life predictions for advanced turbine blades and vanes are dependent upon realistic laboratory simulation of the engine service environment. Engine conditions are best simulated in the laboratory by mechanical testing capable of imposing simultaneous, independently controlled temperature and strain cycles, or thermal mechanical fatigue (TMF) tests. Historically, TMF tests are expensive and usually require computer-controlled laboratory equipment. Consequently the cost of TMF testing has been prohibitively expensive for airfoil material and coating system evaluation. A simplified, low-cost TMF test method has been developed which is useful for alloy/coating system research and screening. This method, referred to as “load-adjusted TMF” (LATMF), uses load and temperature as the primary test control parameters. Test results using the simplified TMF test method show good correlation (within a factor of two) with the full computer-automated strain control TMF test results.