Robust optimal positioning of strain gages on blades

This paper focuses on the formulation and validation of an automatic strategy for the selection of the locations and directions of strain gages to capture at best the modal response of a blade in a series of modes. These locations and directions are selected to render the strain measurements as robust as possible with respect to random mispositioning of the gages and gage failures. The approach relies on the evaluation of the signal-to-noise ratios of the gage measurements from finite element strain data and includes the effects of gage size. A genetic algorithm is used to find the strain gage locations-directions that lead to the largest possible value of the smallest modal strain signal-to-noise ratio, in the absence of gage failure, or of its expected value when gage failure is possible. A fan blade is used to exemplify the applicability of the proposed methodology and to demonstrate the effects of the essential parameters of the problem, i.e., the mispositioning level, the probability of gage failure, and the number of gages.