Multiobjective Approach Toward Optimized Patch Repairs of Blisk Blades

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Multiobjective Approach Toward Optimized Patch Repairs of Blisk Blades

Berger, Ricarda / Quaak, Guido / Hofmeister, Benedikt / Gebhardt, Cristian G. / Rolfes, Raimund

Patching is a high-technology repair to preserve damaged jet engine blisks instead of replacing them. The damaged portion of the blade is restored by welding a patch to the blade. Since the extent of defects varies, the optimal repair is initially unknown. This work contributes to the design of patch repairs by employing multiobjective optimization. A multiobjective function is formulated, maximizing high cycle fatigue strength and minimizing the length of the weld. An inequality constraint equation ensures the complete removal of the damaged blade area. The geometry of the patch and the position of the defect are described using parametric models. Optimization results are presented for an exemplary damage scenario. The set of Pareto optimal alternatives is computed using nondominated sorting genetic algorithm II and imposing constraints by using a linear penalty approach. The results demonstrate that designs are found by the optimization that would not intuitively be recognized as optimal by maintenance technicians. Individual designs from the Pareto frontier are selected, and the welding process is analyzed in more detail using thermomechanical simulations. The distribution of residual stresses in the repaired blade is computed, and the influence on fatigue strength is determined. The multiobjective optimization and the finite element simulations implemented in the presented approach thus enable a systematic evaluation of design alternatives and support informed engineering decisions in the repair process.