Martyn John Hucker

Experimental evaluation of unidirectional hollow glass fibre/epoxy composites under compressive loading

Abstract The use of hollow fibres has been proposed as a way of improving the mechanical performance of fibre reinforced composite materials under compressive loading. The relative magnitudes of compression strength for hollow glass fibre and nominally identical solid fibre composite specimens were measured using a bespoke method. A considerable degree of scatter was observed for the compression strengths of the various fibre geometrys investigated. However, the results overall suggest that fibre hollow fractions around 20–25% may offer significant improvements in specific compressive strength for otherwise identical test specimens.

Investigation into the behaviour of hollow glass fibre bundles under compressive loading

Abstract In this study the behaviour of small epoxy resin-bonded hollow glass fibre (HGF) tows, in a range of fibre hollow fractions and external diameters, was investigated under axial compressive loading. The relative magnitudes of compression strength for HGF tows and nominally identical bundles of solid fibres of the same external diameter (D) were measured. The interactions between fibres in a micro-tow replicated the conditions found in unidirectional composite materials. A significant degree of scatter in compression strengths were observed. However, experimental and calculated compression strengths for the range of specimens tested show a strong dependence on fibre geometry. Large fibre D and fibre hollow fraction (K2) appears to give higher experimental strength values relative to the equivalent solid fibre specimens. Conversely, strength values calculated using actual glass cross-sectional area indicate that smaller D, high K2 fibres should offer the best compressive performance. It would appear from these findings that the arrangement of the fibres within the bundle (i.e. alignment, spacing, etc.) rather than the individual fibre property has an overriding effect on subsequent compression performance.

Development of MEMS Hot-film Sensors for use in the Integrated Wing Project

As part of a large UK project called “Integrated Wing, Flight Physics, Technology Validation Programme”, BAE Systems have been further developing their hot-film sensors constructed using silicon manufacturing techniques with the ultimate aim of making them capable of being certified for flight. Primarily, this has involved looking at aspects of the sensor design, such as the robustness of the sensors to impacts and their resistance to environmental degradation. Tests done to date have shown that provided the sensors have a thin protective coating of a few microns thickness and are not installed close to the leading-edge of a wing they should be capable of being certified for flight.

Development of MEMS Hot-Film Sensors

BAE Systems have been developing hot-film sensors for the detection and monitoring of laminar/turbulent flow on a wing. The sensors are constructed using silicon manufacturing techniques, with the ultimate aim of making them capable of being certified for flight. Primarily, this has involved looking at aspects of the sensor design, such as the robustness of the sensors to raindrop impacts and their resistance to environmental degradation. Tests done to date have shown that provided the sensors have a thin protective coating of a few microns thickness and are not installed close to the leading-edge of a wing they should be capable of being certified for flight.

Development of a MEMS based Integrated Hot-film Flow Sensor

Previous research at BAE Systems has developed a MEMS based hot-film sensor that can be flush mounted into a surface with sub-surface connections. The work described in this paper covers the development of a device that integrates this MEMS sensor, with an integrated, miniaturized constant temperature anemometer circuit, and a miniaturized laminar/turbulent flow detection circuit. Attention has also been paid to addressing how this might be incorporated into an aircraft structure and systems. The ultimate aim is a flightworthy sensor that includes all the necessary components into a single package of the order of a few cm 3 , which only requires three wires - power, earth and data, and which can easily be integrated into an aircraft structure.

High Breakdown Strength, High Dielectric Constant Composites for High Frequency Applications

Dielectric materials used for high power applications currently tend to be based upon either bulk ceramics or liquids such as ethylene glycol-water mixtures. Both of these approaches suffer problems in use; ceramics have limited strength and are brittle, whilst liquid based materials have chemical compatibility and environmental issues and cannot be used in applications that require a solid-state solution. This paper outlines the design and fabrication of material systems that allow the achievement of high breakdown strength, high dielectric constant, low dielectric losses and good mechanical strength and toughness. The approach that has been taken to achieve this involves the use of novel proprietary methods to fabricate composite structures of sizes ranging from microns to several hundred millimetres. Control of the electrical properties is complex as it is necessary to tailor the dielectric constant, the breakdown strength and the loss component, which inherently have conflicting requirements, and the situation is exacerbated in the high frequency region of interest for our application in the MHz-GHz range. The properties obtained with these materials, on a large scale, have resulted in the achievement of significant increases in the available energy density. Breakdown strengths that were previously only seen in thin-film structures are now possible in large scale bulk structures. This paper gives an overview of the development and recent advances that have been made through the use of different ceramic/matrix combinations and the effect of microstructure and morphology on the electrical properties.