Detection of Sources of Nonlinearity in Multiple Bolted Joints by Use of Laser Vibrometer
The use of non-contact measurement methods for detecting and locating sources of nonlinearities can be potentially a break-through in the nowadays experimental modal analysis. The primary goal is to define more effective test strategies, whereby contact s
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Detection of Sources of Nonlinearity in Multiple Bolted Joints by Use of Laser Vibrometer Arnaldo delli Carri, Sante Campanelli, and Dario Di Maio
Abstract The use of non-contact measurement methods for detecting and locating sources of nonlinearities can be potentially a break-through in the nowadays experimental modal analysis. The primary goal is to define more effective test strategies, whereby contact sensors will measure the nonlinear vibration responses at the best location possible. Jointed structures are a typical example where a large number of the joint can pose the question of where what and how to measure the nonlinear response. Upon the identification of one, or more, nonlinear response mode the objective is to determine where is the source of such nonlinear vibration. Nonlinearity can be characterised when its source is well defined and can be adequately tested. This paper will attempt to detect and locate the source of nonlinearity from a multi-beam jointed assembly. The approach will be carried out by using both contact and non-contact measurement methods, the results of which will be compared and evaluated. The operator to detect the source of nonlinearity will be the coherence function applied to random response data. Keywords SLDV · Bolted joints · Nonlinear vibration testing
1.1 Introduction This paper attempts to exploit the potential of the scanning LDV system to measure vibration nonlinear response at a much greater number of locations, than it can be done by using setup based on contact sensors. The objective is to use such denser measurement grid to identify one, or more, sources of nonlinearity. It is not intended to replace the accelerometer for the characterization and quantification of a source of nonlinearity. The localization of nonlinearities is fundamental when such sources are discrete as for bolted structures. It is notorious that structures with a high number of interfaces will exhibit nonlinear responses when subjected to high amplitude of excitation forces. From a model validation viewpoint, the accurate localization, characterization and quantification of the nonlinearity can make the modelling work more effective and time efficient. Resources can be dedicated to improving the model where it is needed by inclusion of the nonlinear physics. The localization of nonlinearities was usefully carried out in [1]. It was demonstrated that by setting up a good number of accelerometers on a structure the localization can be done with a good level of accuracy. However, it looked clear that such a method of localization depends on the setup of the contact sensors, and when an engineering judgment is not based on the identification of nonlinearity it might be possible that nonlinearities stay hidden to the sensors. Following the methodology applied to locate the source of nonlinearity (explained in the following sections), it become interesting to use a different technology which would enable much denser measurement grind than offered by contact sensors. Three research works addressed t
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