Chapter23 Strain-Based Dynamic Measurements and Modal Testing Fábio Luis Marques dos Santos, Bart Peeters, Marco Menchicchi, Jenny Lau, Ludo Gielen, Wim Desmet, and Luiz Carlos Sandoval Góes Abstract The most common and established way of performing experimental modal analysis is to use acceleration or velocity based transducers that lead to the calculation of the displacement mode shapes. However, there are applications where the use of strain measurements makes for a more attractive and interesting option. For instance, since strain measurements are more directly related to stress, fatigue and failure, strain-based measurement methods can be a good option for structural health monitoring methods and monitoring systems. Moreover, applications where sensor size and placement might be critical are also good candidates for strain-based methods. Helicopters, wind turbines and gas turbines are a good example where strain gauges are more suited for vibration measurements. Additionally, any sort of system that uses strain gauges for static testing can also use the same sensors for dynamic testing without incurring additional sensor costs, which can be very useful in some situations. Some application cases of dynamic strain measurements and dynamic strain modal analysis are shown in this work, with test subjects such as a composite helicopter blade, a small wind turbine blade and a composite beam. Different types of sensors and excitation methods were also used as well as correlation with a computational model. Keywords Strain modal analysis • Dynamic strain • Strain field • Modal analysis • Mode shape 23.1 Introduction Modal testing has been, for a long time, associated with the use of displacement responses (or their derivatives with respect to time). The use of strain sensors for modal testing [1, 2], on the other hand, has been less accentuated, with the difficulties of using strain gauges slowing down the advent of strain modal analysis. But the increased interest from both industry and academia on assessing and evaluating structural integrity on design prototype stages and also monitoring in real-time (with structural health monitoring systems (SHM)), has led to an increase in the number of dynamic strain applications, to the development of improved identification and measurement techniques, as well as to improved sensor technology [3, 4]. F.L.M. dos Santos ( ) LMS, A Siemens Business, Interleuvenlaan 68, 3001 Leuven, Belgium Katholieke Universiteit Leuven (KUL), Division PMA, Celestijnenlaan 300B, 3001 Heverlee, Belgium Instituto Tecnológico de Aeronáutica (ITA), Praça Marechal Eduardo Gomes, 50 - Vila das Acácias CEP 12.228-900, São José dos Campos - SP, Brazil e-mail: fabio.santos@lmsintl.com B. Peeters • M. Menchicchi • J. Lau • L. Gielen LMS, A Siemens Business, Interleuvenlaan 68, 3001 Leuven, Belgium W. Desmet Katholieke Universiteit Leuven (KUL), Division PMA, Celestijnenlaan 300B, 3001 Heverlee, Belgium L.C.S. Góes Instituto Tecnológico de Aeronáutica (ITA), Praça Marechal Eduardo Gomes, 50 - Vila das Acácias CEP 12.228-900, São José dos Campos - SP, Brazil R. Allemang (ed.), Topics in Modal Analysis II, Volume 8: Proceedings of the 32nd IMAC, A Conference and Exposition on Structural Dynamics, 2014, Conference Proceedings of the Society for Experimental Mechanics Series, DOI 10.1007/978-3-319-04774-4__23, © The Society for Experimental Mechanics, Inc. 2014 233
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