The static and dynamic structural bulk properties of fibrous media

Shin, Ho-Chul

February 2004

Thesis or dissertation

© 2004 Ho-Chul Shin. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.

The structural bulk properties of fibrous materials are investigated. Theoretical models are developed and their predictions are compared to measured data. The properties under both static loading and dynamic excitation are studied.

Macro-scale experimental models are constructed to represent the idealised microscopic structure and to investigate its static behaviour under compression. As a result, the dominant mechanisms of deflection and nonlinearity are respectively identified as bending and the increase in the number of inter-fibre contacts under compression. Exploratory investigations concerning friction and electric contact resistance are conducted on macro-scale models.

As an effective means of representing its structural characteristic, a transversely isotropic structure of stacked cylinders is employed to model a bulk fibrous material. Based on this, static bending models are formulated to describe the structural nonlinear stress-strain behaviour of bulk fibrous media under static compression. In these models, the increase in the number of inter-fibre contacts is related to the shortening of fibre links, and is also further examined in terms of "connectivity'' inside a medium. Similarities to, and differences from, percolation theory are noted.

The dynamic structural bulk properties of fibrous materials are also investigated. Their nonlinear behaviour is dealt with mainly in terms of dependence on the amplitude of excitation, and is characterised by shifts in the measured transmissibility and the corresponding complex Young's modulus.

As in the case of the static properties, the dynamic behaviour of a fibrous material is also investigated by means of idealised models, which show that the nonlinear mechanism is similar to that in the static case.

A novel method is proposed to improve the efficacy in measuring the dynamic properties of a bulk fibrous material. The new method combines the advantages of two conventional techniques, the transfer function method and the mechanical impedance method.

Finally, a nonlinear governing partial differential equation is derived for the dynamic behaviour of a bulk fibrous material. Its analogy to nonlinear equations in other types of media is observed. And the nonlinear behaviour, especially regarding the occurrence of harmonic components, is predicted in the theory as well as being confirmed by experiment.

Department of Engineering, The University of Hull
Cummings, Alan
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Engineering and Physical Sciences Research Council
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