Direct processing of structural thermoplastic composites using rapid isothermal stamp forming

A novel rapid isothermal stamp forming process is proposed which enables the rapid manufacture of structural thermoplastic composite laminate parts directly from multilayer hybrid fabrics comprising stitched unidirectional carbon fibre-thermoplastic polymer veil. The process employs rapid-response variothermal tooling, allowing macro-scale (fabric forming/draping) and micro-scale (fibre wetting/laminate consolidation) composite material transformation processes to occur isothermally above the constituent polymer matrix melt temperature (Tm), thus manufacturing a composite component directly from a hybrid dry fabric in a single press cycle in a relatively short overall cycle time. The proposed rapid isothermal stamp forming (RISF) concept is presented, and details of the process are given along with some considerations made throughout the formulation of the process. As a result of the RISF process development work, candidate manufacturing parameters were derived, delivering parts that exhibit acceptable composite laminate microstructure and mechanical performance within a press station cycle time of 330 s

Strain mapping and nanocrystallite size determination by neutron diffraction in an aluminum alloy (AA5083) severely plastically deformed through equal channel angular pressing

Six specimens of an aluminum alloy (AA-5083) extruded by Equal Channel Angular Pressing following two different routes plus a blank sample were examined with a neutron radiation of 1.5448 Å. Macrostrain maps from the (311) reflection were obtained. A clear difference about accumulated macrostrain with the extrusion cycles between the two routes is shown. The diffraction data of annealed specimens did permit to estimate crystallite sizes that range between 89 nm and 115 nm depending on the routes

Enhancement of reliability in condition monitoring techniques in wind turbines

The majority of electrical failures in wind turbines occur in the semiconductor components (IGBTs) of converters. To increase reliability and decrease the maintenance costs associated with this component, several health-monitoring methods have been proposed in the literature. Many laboratory-based tests have been conducted to detect the failure mechanisms of the IGBT in their early stages through monitoring the variations of thermo-sensitive electrical parameters. The methods are generally proposed and validated with a single-phase converter with an air-cored inductive or resistive load. However, limited work has been carried out considering limitations associated with measurement and processing of these parameters in a three-phase converter. Furthermore, looking at just variations of the module junction temperature will most likely lead to unreliable health monitoring as different failure mechanisms have their own individual effects on temperature variations of some, or all, of the electrical parameters. A reliable health monitoring system is necessary to determine whether the temperature variations are due to the presence of a premature failure or from normal converter operation. To address this issue, a temperature measurement approach should be independent from the failure mechanisms. In this paper, temperature is estimated by monitoring an electrical parameter particularly affected by different failure types. Early bond wire lift-off is detected by another electrical parameter that is sensitive to the progress of the failure. Considering two separate electrical parameters, one for estimation of temperature (switching off time) and another to detect the premature bond wire lift-off (collector emitter on-state voltage) enhance the reliability of an IGBT could increase the accuracy of the temperature estimation as well as premature failure detection

Inkjet printed TiO2 nanoparticles from aqueous solutions for dye sensitized solar cells (DSSCs)

This is the accepted version of the following article: Cherrington, R., Hughes, D. J., Senthilarasu, S. and Goodship, V. (2015), Inkjet-Printed TiO2 Nanoparticles from Aqueous Solutions for Dye-Sensitized Solar Cells (DSSCs). Energy Technology., which has been published in final form at http://dx.doi.org/10.1002/ente.201500096This work reports on the formulation of suitable ink for inkjet printing of TiO2 by investigating the critical parame- ters of particle size, pH, viscosity, and stability. Aqueous sus- pensions of TiO2 nanoparticles (Degussa, P25) were pre- pared with the addition of 25 wt % polyethylene glycol 400 as a humectant to minimize drying at the printer nozzles and reduce the likelihood of nozzle blockage. The inkjet-printed TiO2 layers were assembled into dye-sensitized solar cells. The current–voltage (I–V) characteristics were measured under one sun (air mass 1.5, 100 mW cm 2) using a source meter (Model 2400, Keithley Instrument, Inc.), and the active area of the cell was 0.25 cm2. The inkjet-printed TiO2 photoanode produced a device with a short-circuit current (Isc) of 9.42 mA cm 2, an open-circuit voltage (Voc) of 0.76 V, and a fill factor (FF) of 0.49, resulting in a power conversion efficiency (PCE) of 3.50 %.Engineering and Physical Sciences Research Council (EPSRC

The formation of a nanohybrid shish-kebab (NHSK) structure in melt-processed composites of poly (ethylene terephthalate) (PET) and multi-walled carbon nanotubes (MWCNTs)

The combination of synchrotron Small- and Wide-Angle X-ray scattering (SAXS/WAXS), and thermal analysis was used to follow the evolution of crystalline morphology and crystallization kinetics in a series of melt-processed composites of poly(ethylene terephthalate) (PET) and multiwall carbon nanotubes (MWCNT). The as-extruded PET-MWCNT composites underwent both hot and cold isothermal crystallizations where a final oriented nanohybrid shish-kebab (NHSK) crystalline structure was observed. An oriented NHSK structure was seen to persist even after melting and recrystallization of the composites. From the scattering data, we propose a model whereby the oriented MWCNTs act as heterogeneous nucleation surfaces (shish) and the polymer chains wrap around them and the crystallites (kebabs) grow epitaxially outwards during crystallization. However, depending on crystallization temperature, unoriented crystallites also grow in the polymer matrix, resulting in a combination of a NHSK and lamellar morphology. In contrast, the neat PET homopolymer showed the sporadic nucleation of a classic unoriented lamellar structure under the same isothermal crystallization conditions. These results provide a valuable insight into the distinctive modification of the crystalline morphology of melt-processed polymer-MWCNT composites prior to any secondary processing, having a significant impact on the use of MWCNTs as fillers in the processing and modification of the physical and mechanical properties of engineering polymers

Automotive to rail : can technologies cross the gap?

There are significant drivers of change in the automotive industry today. Not only is legislation forcing manufacturers to meet ever more stringent emissions standards (particularly in terms of CO2), but customers are also demanding more efficient, safer and more electronically advanced vehicles (both in terms of performance features and interfaces). Manufacturers have responded with dramatic improvements in engine and powertrain efficiencies which have helped address legislative requirements to date. Furthermore they have rapidly moved away from standard steel bodies to multi-material solutions including various advanced grades of steel, aluminium, magnesium and polymer-based materials. Indeed there is currently significant research in the field of composite use for automotive bodies where there are pressing questions about manufacturing times for high volume production, costs and recyclability. The rail industry faces similar pressures as those seen in the automotive sector, driven by needs for lower costs, increased capacities, reduced carbon emissions and higher customer expectations. This paper will discuss the current state-of-the-art in automotive technologies and consider if and how they can be translated into the rail sector. It will consider current research within the WMG High Value Manufacturing Catapult towards implementation of automotive-style technologies in a light rail context

Development of a very light rail vehicle

The collaborative very light rail project involves the development of a novel railcar designed to revolutionise the rail industry: a self-powered, Very Light Rail (VLR) vehicle. Each of the two bogies contains a complete diesel-electric series-hybrid drive system, whilst the whole vehicle has undergone significant lightweighting activity to realise a target weight of less than 18 tonnes, or 1 tonne per linear meter. The target cost is £500,000, which is to be achieved through the use of standardised, modular components, and appropriate materials and structural design methodologies. The research covers several aspects of the GB Rail Technical Strategy (RTS) chapter relating to Rolling Stock. Lightweighting leads to a reduction in the propulsion requirements and reduces the infrastructure installation and maintenance costs. The use of higher efficiency drive systems achieved through on-board energy systems enables a reduction in carbon emissions. These hybridisation activities improve the passenger experience through quieter operation, decreased vibration and the possible elimination of exhaust emissions in stations. Combining new drive systems with modular lightweight structures will lead to lower life-cycle costs and thus could enable the economical reopening of lines

Evolution of residual stresses in linear deposition wire-based cladding of Ti-6Al-4V

Neutron diffraction and curvature measurements were conducted to investigate the residual stresses associated with Plasma Transferred Arc Cladding (PTA) of Ti-6Al-4V on a substrate of the same material. The wire-feed PTA coupled with 3-axis CNC machine was used as an Additive Manufacturing (AM) technique to build parts. A combination of the process parameters was chosen to investigate their effects on residual stress evolution. Neutron Diffraction (ND) measurements of residual strains were performed on the SALSA instrument at the Institut Laue-Langevin (ILL), Grenoble, France. Longitudinal stresses were also inferred by using a Coordinate Measurement Machine (CMM) and Euler-Bernoulli beam theorem. Furthermore, Optical Microscopy (OM) of the cross section of the parts was used to analyse the microstructural evolution. The results show the effect of shorter and longer ‘dwell time’ between layers on the evolution of residual stresses

Investigation of adhesive joining strategies for the application of a multi-material light rail vehicle

To meet the high demand for lightweight energy-efficient and safe structures for transport applications, a current state-of-the-art light rail vehicle structure is under development that adopts a multi-material design strategy. This strategy creates the need for advanced multi-material joining technologies. The compatibility of the adhesive with a wide range of material types and the possibility of joining multi-material structures is also a key advantage to its success. In this paper, the feasibility of using either epoxy or polyurethane adhesive joining techniques applied to the multi-material vehicle structure is investigated. Importantly, consideration is given to the effect of variation in bond thickness for both families of structural adhesives. Multi-material adhesively bonded single lap joints with different adhesives of controlled bond thicknesses were manufactured and tested in order to experimentally assess the shear strength and stiffness. The torsional stiffness and natural frequency of the vehicle were modelled using a global two-dimensional finite element model (FEM) with different adhesive properties, and the obtained vehicle performances were further explained by the coupon-level experimental tests. The results showed that the vehicle using polyurethane adhesive with a target bond thickness of 1.0 mm allowed for optimal modal frequency and weight reduction

Structure evolution in poly(ethylene terephthalate) (PET) - Multi-walled carbon nanotube (MWCNT) composite films during <i>in-situ</i> uniaxial deformation

Combined small- and wide-angle X-ray scattering (SAXS/WAXS), mechanical and thermal techniques have been used to follow the morphology evolution in a series of poly(ethylene terephthalate) (PET) multiwall carbon nanotube (MWCNT) composite films during quasi solid-state uniaxial deformation at low strain rates. Uniaxially deformed PET-MWCNT films displayed improved mechanical properties compared with unfilled PET films. SAXS/WAXS data revealed a well oriented lamellar structure for unfilled PET films. In contrast, the PET-MWCNT composites revealed a nanohybrid shish-kebab (NHSK) morphology, with reduced orientation and crystallinity. Mechanistically, this morphology development is attributed to the MWCNTs acting as shish for the epitaxial growth of PET crystallites. Furthermore, nucleation and crystal growth occurs in the PET matrix, but MWCNTs ultimately inhibit crystallite development and hinder a final lamellar structure developing. The results show unequivocally the role MWCNTs play as nanofillers, in the morphology development, thermal and mechanical properties in composite polymer films