Efficient test method for determining the thermomechanical fatigue lifetime of additively manufactured combustion chamber tiles under component-related conditions

Combustion chamber tiles of aircraft engines are subject to locally high thermomechanical fatigue (TMF) loading during flight operations. The TMF loading in these components results in a cyclic bending load over the wall thickness. Additional stress concentrations occur at geometric features such as fillets or effusion cooling holes. Thus complex loading conditions arise that cannot be reliably assessed using conventional material database and computational design methods. In the context of this article, a new test method is presented that consists of a bending test rig for applying component-related loading conditions to corresponding specimens, here called subelements, that represent significant geometric, lifetime-limiting features of the component. In various test series on additively manufactured subelements, geometric, manufacturing, thermal, mechanical and time-dependent parameters are investigated concerning their influence on fatigue crack growth and lifetime. The results from these tests are compiled in a database, which is used to validate an advanced computational assessment approach for crack growth and lifetime accounting for stress gradients in the depth direction due to the bending and along the surface due to possible geometric features. The method can be applied to component geometries such as combustion chamber tiles using a mechanical finite element analysis (FEA) followed by postprocessing steps to increase reliability of lifetime predictions.