Optical measurement of the dynamic strain field of a fan blade using a 3D scanning vibrometer

Understanding the origin of the stress and strain distribution is crucial to increase the durability of components under dynamic loading. Numerical simulations based on finite element (FE) models help with this understanding but must be validated by real measured data. Updating the FE model using the measured data is often the next step in the design process. In this paper the recently developed 3D-scanning laser doppler vibrometer (3D-SLDV) is used to measure the 3D-displacement of a fan blade, which is then used to calculate the dynamic strain distributions. The measurement principle and experimental setup are discussed thoroughly. The experimental results are validated by using a FE model on the one hand and strain gage measurements on the other. It is shown that this technique is capable of measuring normal strain far below 1 microstrain. This technique has the potential to fill in the gap of accurately measuring small (full-field) normal and shear strains at both low and high frequencies, where other optical techniques (and strain gages) would certainly fail.

Research highlights
► Measurement of dynamic strain using a 3D-Scanning Laser Doppler Vibrometer (3D-SLDV).
► Detailed comparison between 3D-SLDV, strain gages and a Finite Element model.
► The 3D-SLDV accurately measures small (full-field) normal and shear strains at both low and high frequencies.