The use of a Digital Image Correlation method with a low-speed camera to obtain characteristics of surface velocity and sound radiation for automotive-type panels

The perceived quality of a vehicle is highly influenced by the driver s experience of the vehicle interior noise. Significant research has been carried out all over the world in order to characterize structural and acoustic characteristics, to control and minimize the vibration and noise from entering or emitted to vehicles. Designers require tools to inform them whether the design changes are positive or negative in terms of the noise and vibration, and to help validate numerical finite element models of complicated structures. This research explores the use of Digital Image Correlation (DIC) equipment and methods by using a relatively inexpensive low speed camera to investigate the structural-acoustics characteristics applied to automotive-type panels, where otherwise a highly expensive and sensitive scanning laser Doppler vibrometer would be required. Experimental measurements based on Noise Path Analysis (NPA) have been carried out and theoretical and numerical predictions on sound radiation behaviour have been developed. The prediction values have been evaluated and validated with experimental measurements. Using a DIC measurement method to obtain spatially averaged surface velocities, averaged over several cycles through phase locking, the results for the sound power predictions for the selected mode shape and the resonance frequencies provided a good estimation when comparing with the experiment. For mode (1, 1), the sound power prediction was 80.9 dB while the measured one was 77.2 dB with a difference of 3.7.while the other selected modes showed a difference not more than 3.7 dB. It was within the range suggested by considering the mathematical simplification approach during the prediction development stage. To conclude, it was found that the prediction of sound power throughout the vibrating structure can provide a good accuracy by using the DIC method Therefore, it can be an alternative technique to evaluate the sound radiation for characterizing one of the structural propertie

Evaluation of the digital image correlation method for the measurement of vibration mode shapes

Digital Image Correlation (DIC) is a modern non-contact, full-field optical technique that is being used for the measurement of static and dynamic displacement problems, material testing and fracture mechanics. In particular, three dimensional DIC is able to measure the out-of-plane vibration mode shapes and deformation of a vibrating structure. Thus, this technique can potentially provide an important validation tool between measured and predicted results. This paper presents some preliminary evaluation results from using the DIC measurement approach. The DIC method was implemented using two low-speed charge-couple device cameras and a phase-locked measurement technique synchronised to the excitation. A 1.2mm thick steel plate with clamped boundary conditions was chosen as the test sample. Resonant frequencies and mode shapes were compared to predictions made using a Finite Element analysis and the experimental Chladni method of visualizing vibrating mode patterns. This comparison reveals some of the advantages and limitations of the DIC method for vibration mode shape analysi