Investigation of Rotating Structures’ Modal Response by Using DIC

Modal analysis of rotating structures is a challenging field of structural analysis research. In the case of a rotating structure, the major difficulty is applying a known excitation to the system, which is crucial for frequency domain modal analysis. Another obstacle is installing and connecting enough sensors (such as strain gauges or accelerometers) to the rotating blades in order to fully characterize the system. Slip rings are used to transmit electrical signals between the rotating and non-rotating frames, complicating the installation. They can also change the actual response by shifting the natural frequencies and introducing external damping. As a result, the number of experimental modal analyses of rotating structures under operating conditions is limited. DIC and other optical methods are appealing for measuring deformations because they do not require electrical wiring or slip rings and can be easily configured to measure large test articles. While setting up an experimental setup with DIC is easier than setting up a contact measurement test setup, there are several challenges to overcome when using DIC with rotating structures. The main challenge is compensating for rigid body motion caused by structure rotation motion to evaluate deformation displacements rather than absolute displacements. This chapter uses DIC to measure deformations on a rotating structure to characterize its modal behavior in operational conditions.