Patching is a high-tech repair procedure that is very adequate for compressor blisks with larger damages. This repair concept has the advantage that the added patch provides the same mechanical strength as the parent material of the blade and the initial aerodynamic contour of the blade is fully restored. However, the welding process locally induces stresses in the heat affected zone at the patch-to-blisk interface. These welding residual stresses influence the fatigue life of the repaired blade and have to be considered during the design phase of patch repairs.
In this work, we contribute to the design of patch repairs by introducing a numerical simulation to predict weld-induced stresses in repaired compressor blades. Therefore, a finite element model is developed that includes sequential thermal and mechanical analyses of blisk blades. The temperature field caused by the welding torch is determined by performing a transient heat transfer analysis. The model also reflects the changes in the geometry due to the additional patch material and subsequent re-contoured patch. Different patch geometries are evaluated and compared in terms of their resulting stress levels. Basically, two kinds of patch geometries with long and short welding seams are studied. The stationary stress distribution of the repaired blade results from the superposition of residual stresses with steady stresses due to rotational and pressure forces.
Thus, we provide the basis for a new fatigue assessment of the repaired blade considering the residual stress level in the patch-to-blisk interface.