Buckling analysis of stiffened variable angle tow panels

Variable angle tow (VAT) laminates have previously shown enhanced buckling performance compared to conventional straight fibre laminates. In this study, an analytical method is developed for the buckling analysis of a novel blade stiffened VAT panel to allow this potential to be more fully exploited. The prebuckling and buckling analysis, performed on a representative section of a blade stiffened VAT panel, are based on a generalised Rayleigh–Ritz procedure. The buckling analysis includes a first order shear deformation theory by introducing additional shape functions for transverse shear and is therefore applicable to structures with thick skins relative to characteristic length. Modelling of the stiffener is achieved with two approaches; idealisation as a beam attached to the skin’s midplane and as a rigidly attached plate. Comparing results with finite element analysis (Abaqus) for selected case studies, local buckling errors for the beam model and plate model were found to be less than 3% and 2% respectively, whilst the beam model error for global buckling was between 3% and 10%. The analytical model provides an accurate alternative to the computationally expensive finite element analysis and is therefore suitable for future work on the design and optimisation of stiffened VAT panels

Lethality and Developmental Delay in Drosophila melanogaster Larvae after Ingestion of Selected Pseudomonas fluorescens Strains

The fruit fly, Drosophila melanogaster, is a well-established model organism for probing the molecular and cellular basis of physiological and immune system responses of adults or late stage larvae to bacterial challenge. However, very little is known about the consequences of bacterial infections that occur in earlier stages of development. We have infected mid-second instar larvae with strains of Pseudomonas fluorescens to determine how infection alters the ability of larvae to survive and complete development.We mimicked natural routes of infection using a non-invasive feeding procedure to study the toxicity of the three sequenced P. fluorescens strains (Pf0-1, SBW25, and Pf-5) to Drosophila melanogaster. Larvae fed with the three strains of P. fluorescens showed distinct differences in developmental trajectory and survival. Treatment with SBW25 caused a subset of insects to die concomitant with a systemic melanization reaction at larval, pupal or adult stages. Larvae fed with Pf-5 died in a dose-dependent manner with adult survivors showing eye and wing morphological defects. In addition, larvae in the Pf-5 treatment groups showed a dose-dependent delay in the onset of metamorphosis relative to control-, Pf0-1-, and SBW25-treated larvae. A functional gacA gene is required for the toxic properties of wild-type Pf-5 bacteria.These experiments are the first to demonstrate that ingestion of P. fluorescens bacteria by D. melanogaster larvae causes both lethal and non-lethal phenotypes, including delay in the onset of metamorphosis and morphological defects in surviving adult flies, which can be decoupled

Buckling analysis and optimization of blade stiffened variable stiffness panels

A rapid and robust semi-analytical model is developed based on the Rayleigh-Ritz energy method for the buckling analysis of blade stiffened variable stiffness panels. The method includes the often neglected, yet important, stiffener ange in the analysis by not only accounting for the local increase in stiffness but, for the first time in a Rayleigh-Ritz method, allowing the structure to respond in a discontinuous manner at the location of the stiffness discontinuity. This is achieved by discretizing the panel at locations of discontinuities such as ange edges and assigning each region individual shape functions thus preventing a global C1-continuous response in the buckled mode shape. The model is shown to be in excellent agreement with, and computationally efficient when compared to, a commercial FEA package. The model is then used in a genetic algorithm optimization study to design blade stiffened variables stiffness panels by applying practical design and failure constraints. Results are compared with optimized conventional stiffened panels and for the case considered, mass savings over 6% are shown to be achievable when utilising variable stiffness laminates as the skin on stiffened panels

Tristability of an orthotropic doubly curved shell

In this work, the structural response of a doubly curved orthotropic shell is tailored to achieve tristable geometries. This is done by varying both material properties and the Gaussian curvature of the surface profile. Tristability is predicted analytically, verified with finite element analysis and, for the first time, demonstrated experimentally. Predicted geometries of the tristable states are shown to compare well with experiment