Modal Validation of Academic Bladed Disk Using Digital Image Correlation

Determining the modal response of integrally bladed rotors (IBRs), or bladed disks (blisks), is critical within the aerospace industry. Specifically for gas turbine engines, experimentally measuring the modal response of a physical IBR is a critical step in determining optimal operating conditions and maintenance schedules. Currently, traveling wave excitation (TWE) is a state of the art experimental method which enables the measurement of the modal response of IBRs and blisks. The experimental method is performed with the component laying at rest on a flat surface and each individual blade excited, with amplitudes on the order of 10^-6 meters, typically via electromagnetically or acoustically. In the current state of the experimental method, a scanning laser vibrometer (SLV) measures the resulting velocity of key locations on the component during frequency sweeps over multiple engine orders. Therefore, TWE is highly advantageous as the method has exceedingly low risk of damaging the component, instrumentation of the component, surrounding facility, or personnel. However, the SLV can measure only a single point at a time and significantly increases the required testing time. This is because the experimental test time of a TWE test campaign can be determined by the product of key locations (often hundreds), over multiple engine orders, and the time to sweep across a large frequency range. Thus, the purpose of the work presented in this paper validates the use of digital image correlation (DIC), an optical measurement technique and capable of measuring displacement field information, by measuring the modal response of an academic finger disc with a single point excitation source with both DIC and SLV. Then the mode shapes measured with DIC are quantitatively compared to SLV using a modal assurance criterion (MAC) analysis and found to be in good agreement. The MAC analysis of DIC to SLV data demonstrates how DIC is an accurate and effective alternative method to SLV and is able to replace SLV to significantly reduce the experimental testing time of TWE.