whole_ZouRongDar1994_thesis.pdf (10.9 MB)
Stability studies on cellular-walled circular cylindrical shells
thesisposted on 2023-05-27, 12:54 authored by Zou, Rong Dar
The present study deals with the stability behaviour of cellular-walled cylindrical shells subjected to simultaneous loading of axial compression and external pressure. In particular, the effect of high fluid pressure within the cells on the buckling behaviour of the shell is considered. The form of cellular-walled shell originated from a consideration of fossil shell remains belonging to the Nautiloid Cephalopod group. These extinct animals (relatives to the modern day pearly nautilus) grew to about 300mm in length and had an exoskeleton in the form of a conical shell with a small apex angle. However, the unique feature of the shell of this fish was that it contained small closely spaced holes running longitudinally in the shell wall. Interest 'in these fossil shells originated from discussions with Dr. M.R. Banks, a paleontologist at the University of Tasmania. Dr. Banks was interested to discover why the shellfish should want to build its shell in such a particular form. Other than for the obvious conclusion that a cellular wall has better bending stiffness than a solid wall of the same mass, there appeared to be no particular reason for the specific form of this shell. From a strength point of view, there appears to be no advantage in the shell having longitudinal holes over circumferential or spiral holes, and spiral holes would be easier for the shell fish to manufacture. This study showed both theoretically and experimentally that a possible answer lies in the stability behaviour of this particular form of shell. The cellular-walled cylindrical shell can be characterized as a pseudo-orthotropic cylindrical shell with the principal directions axially and circumferentially oriented. Different effective Young's moduli had to be used for tension and bending. A theoretical analysis, based on Flugge's linear buckling theory, resulted in simple interaction formulas for buckling under external pressure, axial compression and cell pressure. Cellular-walled model shells have been made out of epoxy by an adaptation of the spin casting process developed by Tennyson. These shells have 360 longitudinal holes each of 0.7mm diameter, shell internal diameter 153mm, wall thickness 1.2mm and length 245mm. The tests of the model shells were carried out on a rigid test machine with parallel platens. Since the shells are cast with a free surface on the inside they are internally reflective. An optical system making use of the reflective surface was used to monitor buckling and prebuckling deformations. Test data was logged into a PC. Southwell plots were then employed to predict axial buckling loads. Because of the likelihood of the shell shattering on buckling, actual collapse loads were the final values obtained. Test data confirmed the theoretical predictions. Both theoretical and experimental results showed that shells of this type with pressurized cells exhibit significantly improved stability, hence they appear to have potential in engineering applications, particularly in marine situations.
Rights statementCopyright 1993 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s). Includes bibliographical references (p. 178-190). Thesis (Ph.D.)--University of Tasmania, 1994