The behaviour of damage tolerant hat-stiffened composite panels loaded in uniaxial compression

Damage tolerant hat-stiffened thin-skinned composite panels with and without a centrally located circular cutout, under uniaxial compression loading, were investigated experimentally and analytically. These panels incorporated a highly postbuckling design characterised by two integral stiffeners separated by a large skin bay with a high width to skin-thickness ratio. In both configurations, the skin initially buckled into three half-wavelengths and underwent two mode-shape changes; the first a gradual mode change characterised by a central deformation with double curvature and the second a dynamic snap to five half-wavelengths. The use of standard path-following non-linear finite element analysis did not consistently capture the dynamic mode change and an approximate solution for the prediction of mode-changes using a Marguerre-type Rayleigh-Ritz energy method is presented. Shortcomings with both methods of analysis are discussed and improvements suggested. The panels failed catastrophically and their strength was limited by the local buckling strength of the hat stiffeners. (C) 2001 Elsevier Science Ltd. All rights reserved.

Buckling mode transition in hat-stiffened composite panels loaded in uniaxial compression

A combined experimental and analytical study of a hat-stiffened carbon-fibre composite panel loaded in uniaxial compression was investigated. A buckling mode transition was observed in the panel's skin bay which was not captured using non-linear finite-element analysis. Good correlation between experimental and numerical strain and displacement results was achieved in the prebuckling and initial postbuckling region of the loading history. A Marguerre-type Rayleigh-Ritz energy method was applied to the skin bay using representative displacement functions of permissible mode shapes to explain the mode transition phenomenon. The central criterion of this method was based on the assumption that a change in mode shape occurred such that the total potential energy of the structure was maintained at a minimum. The ultimate strength of the panel was limited by the column buckling strength of the hat-stiffeners.

Environmental forensic investigations: The potential use of a novel heavy metal sensor and novel taggants

This chapter presents a novel hand-held instrument capable of real-time in situ detection and identification of heavy metals, along with the potential use of novel taggants in environmental forensic investigations. The proposed system provides the facilities found in a traditional laboratory-based instrument but in a hand held design, without the need for an associated computer. The electrochemical instrument uses anodic stripping voltammetry, which is a precise and sensitive analytical method with excellent limits of detection. The sensors comprise a small disposable plastic strip of screen-printed electrodes rather than the more common glassy carbon disc and gold electrodes. The system is designed for use by a surveyor on site, allowing them to locate hotspots, thus avoiding the expense and time delay of prior laboratory analysis. This is particularly important in environmental forensic analysis when a site may have been released back to the owner and samples could be compromised on return visits. The system can be used in a variety of situations in environmental assessments, the data acquired from which provide a metals fingerprint suitable for input to a database. The proposed novel taggant tracers, based on narrow-band atomic fluorescence, are under development for potential deployment as forensic environmental tracers. The use of discrete fluorescent species in an environmentally stable host has been investigated to replace existing toxic, broadband molecular dye tracers. The narrow band emission signals offer the potential for tracing a large number of signals in the same environment. This will give increased data accuracy and allow multiple source environmental monitoring of environmental parameters.

Commission 15: Physical Studies of Comets and Minor Planets

This report of the business meeting of Commission 15 at the 2009 IAU GA is based on notes provided by Walter Huebner, past president, and on the minutes taken by Daniel Boice, secretary of Commission 15 in the triennium 2006 to 2009, with additional notes from the current secretary, Daniel Hestroffer. The business meeting was split into two sessions, the first held on 5 August and the second held on 11 August. This report presents the minutes of the two Commission 15 business-meeting sessions held during General Assembly XXVII.