The effect of cure cycle heating rate on the fibre/matrix interface

Development of civil aerospace composites is key to future “greener” aircraft. Aircraft manufacturers must improve efficiency of their product and manufacturing processes to remain viable. The aerospace industry is undergoing a materials revolution in the design and manufacture of composite airframes. The Airbus A350 and Boeing 787 (both due to enter service in the latter part of this decade) will push utilisation levels of  composite materials beyond 50% of the total airframe by weight. This  change requires massive investment in materials technology, manufacturing capability and skills development. The Quickstep process provides the ability to rapidly cure aerospace standard composite materials whilst providing enhanced mechanical properties. Utilising fluid to transfer heat to the   composite component during the curing process allows far higher heat rates than with conventional cure techniques. The rapid heat-up rates reduce the viscosity of the resin system greatly to provide a longer processing window introducing greater flexibility and removing the need for high pressure during cure. Interlaminar fracture toughness (Mode I) and Interfacial Shear Strength of aerospace standard materials cured using Quickstep have been    compared to autoclave cured laminates. Results suggest an improvement in fibre-matrix adhesion.

Corrosion of magnesium alloy ZE41 – The role of microstructural features

Magnesium alloy ZE41, used extensively in the aerospace industry, possesses excellent mechanical properties albeit poor corrosion resistance. This paper investigates the mechanism of corrosion and the interaction between the grain boundary intermetallic phases, the Zr-rich regions within the grains and the bulk Mg-rich matrix. The results of optical and scanning electron microscopy (SEM) together with energy-dispersive X-ray (EDX) and atomic force microscopy (AFM) potential map measurements have shown the importance of the microstructure in the initiation and propagation of corrosion in an aqueous environment, indicating that the Zr-rich regions play a distinct role in the early stages of corrosion in this alloy.

Study of phase transformation and work hardening phenomenon during drilling of Ti-5553 and Ti-64

Titanium 5553 is a recently developed modification of Russian near-β titanium alloy VT-22 which has applications and potential particularly in the aerospace industry for such key components as landing gear. However, indications are that Ti-5553 has poorer machinability characteristics than other Ti alloys and a comprehensive and far-reaching analysis is a necessary research imperative. This paper presents the result of phase transformation and work hardening during drilling of Ti-5553 compared with Ti-64. The aim of this research work is to optimise the machining condition for Ti-5553, in which the β to a phase transformation, together with material work hardening could be fully understood. Analysis of machinability indicators, such as subsurface micrograph and hardness of drilled samples and drilling forces and torques, demonstrated that Ti-5553 generally has poorer machinability characteristics than Ti-64 and to some extent this variation has been quantified to allow for further and more detailed investigation.

Deformation induced phase transformation during machining of Ti-5553

Ti-5553 is a relatively new titanium alloy with applications particularly in the aerospace industry for such key structural components as landing gear. However, during machining of Ti-5553, the elevated temperature and high strain at tool-workpiece interface may alter workpiece microstructure and result in ß to a phase transformation. During phase transformation, some intermediated phase such as w phase may form which is brittle and hard to machine, and it could reduce the fatigue life of machined components. The aim of this research work is to optimize the machining condition for Ti-5553, in which its hot deformation behavior in terms of ß to a phase transformation could be fully understood. Analysis of variables such as micrographs of phase components and cutting zone temperature demonstrates that the cutting temperature governs the formation of final phase components and to some extent this variation has been quantified to allow for further and more detailed investigation.

An integrated approach to shape and topology optimisation of mechanical structures

In mechanical engineering, simulation and optimisation methods have become indispensable. The thesis looks into a novel way to combine shape and topology optimisation approaches. The proposed method - named IST for Integrated Shape And Topology Optimisation - proves to be beneficial for many application in the automotive and aerospace industry.

Corrosion of mg alloy ZE41 and its mitigation using ionic liquids

Magnesium alloy ZE41 (Mg-Zn-RE-Zr), which is used extensively in the aerospace industry, possesses excellent mechanical properties albeit poor corrosion resistance. This work investigates the mechanism of corrosion, and the interaction between the grain boundary intermetallic phases, the zirconium (Zr)-rich regions within the grains and the bulk Mg rich matrix in both the as-cast and heat-treated conditions. The results of optical and scanning electron microscopy (SEM) show the importance of the microstructure in the initiation and propagation of corrosion in an aqueous environment. The Zr-rich regions play a distinct role in the early stages of corrosion with this alloy. The second part of this work investigates the interaction of two different ionic liquids (ILs) with the surface of the ZE41 alloy. ILs based on trihexyltetradecylphosphonium (P 6,6,6,14) coupled with either diphenylphosphate (DPP) or bis(trifluoromethanesulfonyl) amide (Tf 2N) have been shown to react with Mg alloy surfaces, leading to the formation of a surface film that can improve the corrosion resistance of the alloy. The interaction of the ILs with the ZE41 surface has been investigated by optical microscopy and SEM. Surface characterization has been performed using Time of Flight-Secondary Ion Mass Spectrometry (ToF-SIMS) and X-ray Photoelectron Spectroscopy (XPS). The surface characterization and microscopy revealed the preferential interaction with the grain boundaries and grain boundary phases. Thus the morphology and microstructure of the Mg surface seems critical in determining the nature of the interaction with the IL. The corrosion protection of the IL films formed on the ZE41 surface was investigated by SEM and potentiodynamic polarisation.

A preliminary assessment of machinability of titanium alloy Ti 6Al 4V during thin wall machining using trochoidal milling

Titanium alloys are of great demand in the aerospace and biomedical industries. Most the titanium products are either cast or sintered to required shape and finish machined to get the appropriate surface texture to meet the design requirements. Ti-6Al-4V is often referred as work horse among the titanium alloys due to its heavy use in the aerospace industry. This paper is an attempt to investigate and improve the machining performance of Ti-6Al-4V. Thin wall machining is an advance machining technique especially used in machining turbine blades which can be done both in a conventional way and using a special technique known as trochoidal milling. The experimental design consists of conducting trials using combination of cutting parameters such as cutting speed (vc), 90 and 120 m/min; feed/tooth (fz) of 0.25 and 0.35 mm/min; step over (ae) 0.3 and 0.2; at constant depth of cut (ap) 20mm and using coolant. A preliminary assessment of machinability of Ti-6Al-4V during thin wall machining using trochoidal milling is done. A correlation established using cutting force, surface texture and dimensional accuracy.

Forming behaviour analysis and constitutive modelling of Ti-6Al-4V at room temperature.

 A constitutive model was proposed in this thesis and a promising approach for accurate prediction of forming behaviour of high strength titanium alloy sheet metal forming at room temperature is presented. Outcomes showed a potential solution of cold roll forming of this material for aerospace and automotive structural applications.

Shape morphing in fibre reinforced composite beams containing NiTi

The present research investigates the design, activation and modelling of a new generation of hybrid materials; called shape memory alloy-composites. These hybrid materials exhibit reversible bending motion with a temperature change and have the potential to be employed in aerospace, automotive and robotic application.

Investigation of corrosion inhibition mechanisms of rare-earth mercaptoacetate inhibitors on AA2024-T3

 Corrosion inhibition mechanisms on the aerospace alloy, AA2024-T3, was investigated for the inhibitor combination of rare earth metals and mercaptoacetate. The inhibitor demonstrated synergistic protection for AA2024-T3 from localised corrosion. It is intended to be a more environmentally friendly alternative to toxic chromate-based inhibitors.

Microstructure and corrosion of AA2024

AA2024-Tx is one of the most common high-strength aluminium alloys used in the aerospace industry. This article reviews current understanding of the microstructure of sheet AA2024-T3 and chronicles the emergence of new compositions for constituent particles as well as reviews older literature to understand the source of the original compositions. The review goes on to summarise older and more recent studies on corrosion of AA2024-T3, drawing attention to areas of corrosion initiation and propagation. It pays particular attention to modern approaches to corrosion characterisation as obtained through microelectrochemical techniques and physicochemical characterisation, which provide statistical assessment of factors that contribute to corrosion of AA2024. These approaches are also relevant to other alloys.