The combustion chamber of aeronautical turbomachines, made from thin sheets of the cobalt-based superalloy Haynes 188 (Ha188), is subjected to cyclic loads caused by repeated engine ignitions, extremely high temperatures from the high-pressure turbine flame, and significant temperature gradients induced by the cooling systems. The inner walls, located in the flame zone, are coated with thermal barriers coatings (TBC), which help protect the walls from high temperatures and increase their thermomechanical resistance. However, these thermal gradients result in severe mechanical stresses. Combined with cyclic loading, they lead to damage in the form of cracks. The development of these cracks is one of the main factors determining the lifetime of the component. Through this study, Safran aims to improve its lifetime prediction models by focusing on a damage-tolerance approach for the coated combustion chamber. The aim of the work is to examine the propagation and evolution of pre-existing cracks to assess the durability of combustion chambers, particularly in the presence of TBC.

The component is subjected to complex thermo-mechanical loads, consisting of variable-amplitude cycles with significant temperature gradients, which can lead to extensive plastic deformation. Furthermore, the presence of a TBC, composed of a NiCrAlY bond coat layer and a yttria-stabilized zirconia ceramic layer applied by APS (Air Plasma Spraying), adds further complexity. The mechanisms of crack propagation under these conditions are not well understood. The challenge of this study is to develop experimental and numerical techniques that accurately represent the loads experienced by the component and replicate the crack propagation observed in coated chambers. Consequently, an experimental test series has been launched to understand the role of each coating layer in crack propagation, using image correlation techniques and infrared thermography. In parallel, finite element numerical methods, informed by experimentally measured fields, are being used to analyze the driving forces that lead to crack propagation. In particular, a phase field approach is implemented to analyze the damage field. This approach is valuable because it can predict the interactions, directions, and paths of multiple cracks from an initial network of experimentally observed micro-cracks, allowing for a detailed analysis of damage mechanisms. New criteria can then be established and applied in remeshing-based methods, facilitating the transition from laboratory results to the length scale of industrial components.