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Vibration analysis of cracked aluminium plates

Israr, Asif (2008) Vibration analysis of cracked aluminium plates. PhD thesis, University of Glasgow.

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Abstract

This research is concerned with analytical modelling of the effects of cracks in structural plates and panels within aerospace systems such as aeroplane fuselage, wing, and tail-plane structures, and, as such, is part of a larger body of research into damage detection methodologies in such systems. This study is based on generating a so-called reduced order analytical model of the behaviour of the plate panel, within which a crack with some arbitrary characteristics is present, and which is subjected to a force that causes it to vibrate. In practice such a scenario is potentially extremely dangerous as it can lead to failure, with obvious consequences. The equation that is obtained is in the form of the classical Duffing equation, in this case, the coefficients within the equation contain information about the geometrical and mass properties of the plate, the loading and boundary conditions, and the geometry, location, and potentially the orientation of the crack. This equation has been known for just over a century and has in the last few decades received very considerable attention from both the analytical dynamics community and also from the dynamical systems researchers, in particular the work of Ueda, Thompson, in the 1970s and 1980s, and Thomsen in the 1990s and beyond. An approximate analytical solution is obtained by means of the perturbation method of multiple scales. This powerful method was popularized in the 1970s by Ali H.Nayfeh, and discussed in his famous books, ‘Perturbation Methods’ (1974) and ‘Nonlinear Oscillations’ (1979, with D.T.Mook), and also by J.Murdock (1990), and M.P.Cartmell et al. (2003) and has been shown to be immensely useful for a wide range of nonlinear vibration problems. In this work it is shown that different boundary conditions can be admitted for the plate and that the modal natural frequencies are sensitive to the crack geometry. Bifurcatory behaviour of the cracked plate has then been examined numerically, for a range of parameters. The model has been tested against experimental work and against a Finite Element model, with good corroboration from both. In all events, this is a significant new result in the field and one that if implemented within a larger damage detection strategy, could be of considerable practical use.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Analytical Modelling, Plates, Crack, Boundary conditions, Galerkin's method, Duffing equation, Loading, Linear, Nonlinearity, Numerical integration, Finite element analysis, bifurcation, Lyapunov exponent, Poincare maps,
Subjects: T Technology > TJ Mechanical engineering and machinery
Colleges/Schools: College of Science and Engineering > School of Engineering
Supervisor's Name: Cartmell, Professor Matthew
Date of Award: 2008
Depositing User: Mr Asif Israr
Unique ID: glathesis:2008-261
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 12 Jun 2008
Last Modified: 10 Dec 2012 13:17
URI: http://theses.gla.ac.uk/id/eprint/261

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