Secondary ion mass spectrometry (SIMS) has been used in conjunction with isotopic labeling to determine
the extent and rate of passive film hydration on aluminum. The rates at which oxygen- and hydrogen-containing
species migrate through the film have been determined as a function of temperature and applied potential
(cathodic and anodic polarization). The results suggest that defects such as hydroxide ions are prevalent and
mobile in the oxide film, influencing the kinetics and mechanisms of corrosion and pitting processes.
This paper describes an experimental and an analytical and numerical investigation into
the buckling behaviour of cylindrical composite tubes under external hydrostatic pressure. The
investigations concentrated on fibre reinforced plastic tube specimens made from a mixture of three
carbon and two E-glass fibre layers. The lay-up was 0°/90°/0°/90°/0; the carbon fibres were laid
lengthwise (0°) and the E-glass fibres circumferentially (90°). The theoretical investigations were
carried out using a simple solution for isotropic materials, namely a well-known formula by “von
Mises” and also by finite element analyses using ANSYS.
The experimental investigations showed that the composite specimens behaved similarly to
isotropic materials tested by various other researchers. The specimens failed by the common modes
associated with this study, namely due to elastic buckling, inelastic buckling and axisymmetric
yield failure. Furthermore it was discovered that the specimens failed at changes of the composite
lay-up due to the manufacturing process of these specimens. These changes seem to be the weak
points of the specimens.
For the theoretical investigations two different types of material properties were used to analyse the
composite. These were calculated properties derived from the properties of the single layers given
by the manufacturer and experimentally obtained properties.
Two different approaches were chosen for the investigation of the theoretical buckling pressure, a
program called “MisesNP”, based on a well-known formula by von Mises for single layer isotropic
materials, and two finite element analyses using the famous computer package called “ANSYS”.
This latter analyses simulated the composite with a single layer orthotropic element (Shell93) and
also with a multi layer element (Shell99). It was found out that the results obtained with ANSYS
predicted questionable buckling pressures that could not be reproduced logically.
Nevertheless this report provides Design Charts for all approaches and material types. These Design
Charts allow the possibility of obtaining a ‘plastic knockdown factor’. The theoretical buckling
pressures obtained using MisesNP or ANSYS can then be divided by the plastic knockdown factor,
to give predicted buckling pressures. This method can be used for the design of full-scale vessels.
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