Analysis of nonlinear vibrations of a blade with dovetail attachment using DIC and the Smoothed Harmonics Analysis

This paper focuses on the experimental investigation of the effects of blade-root contact on turbine blade dynamics. Since under operating conditions the blade supports both cyclic loads and centrifugal loads, the nonlinear response of a dummy blade is investigated by means of a specially designed test rig, which allows tuning normal load and high-frequency excitation acting on the sample. To avoid interfering with the measurements, it is essential to avoid adding damping and external masses by attaching measuring instruments to the vibrating blade. Accordingly, Stereo Digital Image Correlation (Stereo-DIC) was used in this work to obtain full-field, non-contact measurements of specimen deformation. In this work, tests are performed exciting at a frequency higher than the maximum frame rate of the high-resolution cameras employed, and then a down-sampling technique, called Smoothed Harmonics Analysis (SHA), is implemented to avoid aliasing error in the detection of displacement signals.