4 Full-Field Strain Shape Estimation from 3D SLDV 45 4.7 Conclusions Several methods for determining full-field modal strain shapes from 3D SLDV data were evaluated. The Direct Modal method was found to work reasonably well, does not require a FEM, and provides improvements over the Direct ODS Method, which is considered as the current standard ODS strain shape measurement method. The use of direct measurements (ODS or modal) without some manner of filtering to smooth the displacements is not recommended due to the sensitivity to measurement noise in the strain estimation process. The Transformation ODS Method provides a means to convert ODS strain shapes to modal quantities, also without use of a FEM. However, if starting from nothing, the Direct Modal Method provided similar, if not better, results with less processing effort but potentially longer test times. Further, the SEREP smoothing using (noisy) ODS may not provide enough smoothing by itself, driving the need to use a spatial filter in addition. The test article used in this work was observed to exhibit nonlinear behavior, which is believed to have caused a reduction in the ODS methods’ effectiveness. Finally, the Transformation Modal Method was shown to work very well; it is robust against measurement noise, avoids spatial filter edge effects, results are obtained in full n-space, and either surface or volume strains can be estimated. The primary drawback is that a FEM is required. Acknowledgements This manuscript has been authored by National Technology and Engineering Solutions of Sandia, LLC. under Contract No. DE-NA0003525 with the U.S. Department of Energy/National Nuclear Security Administration. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. References 1. Cazzolato, B., Wildy, S., Codrington, J., et al.: Scanning laser vibrometer for non-contact three-dimensional displacement and strain measurements. In: Proceedings of ACOUSTICS, Geelong, 24–26 Nov 2008 2. Weisbecker, H., Cazzolato, B., Wildy, S., et al.: Surface strain measurements using a 3D scanning laser vibrometer. Exp. Mech. 52(7), 805–815 (2012) 3. Reyes, J., Avitabile, P.: Use of 3D scanning laser vibrometer for full field strain measurements. In: De Clerck, J. (ed.) Experimental Techniques, Rotating Machinery, and Acoustics, Volume 8 Conference Proceedings of the Society for Experimental Mechanics Series. Orlando, Springer (2015) 4. O’Callahan, J., Avitabile, P., Riemer, R.: System Equivalent Reduction Expansion Process (SEREP). In: Proceedings of the 7th International Modal Analysis Conference, Las Vegas, 1989 5. Rohe, D., Schoenherr, T., Skousen, T., et al.: Testing summary for the box and removable component structure. In: Proceedings of the 37th International Modal Analysis Conference, Orlando, Jan 2019 6. Hensley, D., Mayes, R.: Extending SMAC to multiple references. In: Proceedings of the 24th International Modal Analysis Conference, St. Louis, pp. 220–230, Feb 2006 7. Felippa, C.: Introduction to Finite Element Methods (2004), Chapter 17. Department of Aerospace Engineering Sciences, University of Colorado at Boulder. https://www.colorado.edu/engineering/CAS/courses.d/IFEM.d/. Accessed online 2018
RkJQdWJsaXNoZXIy MTMzNzEzMQ==