Web-assisted first-year undergraduate teaching in engineering

A software system, recently developed by the authors for the efficient capturing, editing, and delivery of audio-visual web lectures, was used to create a series of lectures for a first-year undergraduate course in Dynamics. These web lectures were developed to serve as an extra study resource for students attending lectures and not as a replacement. A questionnaire was produced to obtain feedback from students. The overall response was very favorable and numerous requests were made for other lecturers to adopt this technology. Despite the students' approval of this added resource, there was no significant improvement in overall examination performance

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.

Buckling and Postbuckling of Stiffened Composite Structures

Postbuckling Behaviour of Hat Stiffened Thin Skinned Carbon Fibre Composite Panels

The results of a combined experimental and numerical study of hat-stiffened co-cured carbon-fibre composite panels loaded in uniaxial compression are presented. All panels consisted of two integrated stiffeners separated by an eight-ply thick skin bay of lay-up [*45/0190], . The effects of a 100 mm circular cutout in the skin was also investigated. The ultimate strength of all panels was governed by the load carrying capacity of the stiffeners. A change in the skin's buckling mode-shape was also observed for all panels loaded deep in the postbuckling region. The strains induced at the interior free-edge were not found to be critical. Non-linear finite element results correlated well with the prebuckling and initial postbuckling strain and displacements results obtained by experiment.

Effect of offset web holes on web crippling strength of cold-formed steel channel sections under end-two-flange loading condition

A combination of experiments and non-linear finite element analyses are used to investigate the effect of offset web holes on the web crippling strength of cold-formed steel channel sections under the end-two-flange (ETF) loading condition; the cases of both flanges fastened and unfastened to the support are considered. The web holes are located at the mid-depth of the sections, with a horizontal clear distance of the web holes to the near edge of the bearing plate. Finite element analysis results are compared against the laboratory test results; good agreement was obtained in terms of both strength and failure modes. A parametric study was then undertaken to investigate both the effect of the position of holes in the web and the cross-section sizes on the web crippling strength of the channel sections. It was demonstrated that the main factors influencing the web crippling strength are the ratio of the hole depth to the depth of the web, and the ratio of the distance from the edge of the bearing to the flat depth of the web. Design recommendations in the form of web crippling strength reduction factors are proposed in this study.