Modal Analysis Using a Virtual Speckle Pattern Based Digital Image Correlation Method: An Application for an Artificial Flapping Wing

Background A conventional three-dimensional digital image correlation (DIC) based on painted speckle patterns has been used widely as a non-contact measurement method to study modal analysis of various structures. Surface treatment using painted speckle patterns might change the structural properties of flexible and lightweight structures such as artificial wings of flapping micro air vehicles. Furthermore, if materials and structures are being serviced, it is essential that their surfaces not be contaminated. Objective We propose a new DIC method that is capable of preventing effects of painted speckle patterns on thin flexible structures during vibration measurement. Methods We project a virtual speckle pattern onto the surface of structures instead of using painted speckle patterns. For a benchmark test, we demonstrate the effectiveness of the proposed virtual speckle pattern DIC method for measuring the structural characteristics of a cantilever beam. We then apply the proposed DIC method to the vibration measurement of an artificial flapping wing. Finite element analysis (FEA) of the artificial wing is performed in ABAQUS (TM) to obtain natural frequencies and mode shapes. Results The natural frequencies at the first three modes of the artificial wing obtained from the proposed method are higher than those obtained from the conventional 3D DIC because of the smaller weight of the unpainted wing. The results of the mass compensation, laser sensor, and finite element analysis prove the effectiveness of the proposed virtual speckle pattern DIC method. Conclusion The proposed DIC method achieves high accuracy and prevents the effect of painted speckle patterns on the dynamic vibration measurement of a thin flexible structure such as an artificial flapping wing.

Automated summary

This study introduces a new DIC method to prevent the effects of painted speckle patterns on thin flexible structures during vibration measurement. By projecting virtual speckle patterns onto the surfaces of structures, higher natural frequencies are obtained, proving the effectiveness of the proposed method.