Percorrer por autor "Kamma-Lorger, Christina S."
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- Multi-scale computer simulations of multi-tubular components manufactured by water-assisted injection mouldingPublication . Pascoal-Faria, Paula; Alves, Nuno; Kamma-Lorger, Christina S.; Marques, Rita; Gomes, Marta; Venkat, Anurag; Silva, Rui; Bastos, Lourenço; Carneiro, Filipa; Cunha, Jorge; Mateus, Artur; Mitchell, Geoffrey R.Water assisted injection moulding is a recent development in the manufacturing technology associated with injection moulding. Injection moulding involved the high pressure injection of molten plastic in to a preformed metal mould which defines the exterior of the shape of the object. Water assisted injection moulding is a variant with an addition step in which water is injected into the mould after its has been filled with molten plastic. The water jet sweeps out the molten plastic in its path to leave a hollow tube in which the interior of the part is defined by the water jet. This technology is used for preparing tubular components for use in the automotive industry and for domestic appliances. We have been developing the technology to prepare parts with branches in the tubing. We have used fine-element simulations to explore the relationship between the process parameters and the subsequent final part. Of course such simulations only serve to define the exterior and interior of the tubular part. It is clear from the outline of the technology above that the molten plastic is subjected to a complex pressure and temperature variation with time which vary across the part and its location within the mould. The specification of the part is in most cases is limited to the geometry and the materials which is used in its preparation, in this case polyamide6 with 30% glass fibre. From the development of plastic processes over the last 50 years we have learnt that the properties of plastic part depend critically on the processing pathway and in particular the timescale for the transformation from molten material to the semi-crystalline solid state. We know from the use of small-angle and wide-angle scattering mapping of the structure and morphology of the multi-tubular components that the level of crystallinity and the extent of preferred orientation varies throughout the part and this may lead to warpage and other geometrical changes in the part during its service life. We have set out to explore how we can use the temperature and pressure variation from the finite element modelling to predict the structure and morphology at different regions in the part in order to be able to establish the parameters which yield a geometrically correct part which is also homogenous in its structure and morphology and hence properties. This paper describes the approach we have taken to make progress with this complex matter of simulations on multiple scales and the application of this technique to realistic automotive tubular components.
- Multiscale Structure Evolution in Electrically Conductive Nanocomposites Studied by SAXSPublication . Khan, Imran; Mohan, Saeed D.; Belbut, Miguel; Kamma-Lorger, Christina S.; Mateus, Artur; Mitchell, Geoffrey R.The successful introduction of nanostructured materials is hampered by the lack of a quantitative and qualitative understanding of the structure–property relationship within the nanocomposites. Variation in the electrical conductivity of nanocomposite materials depends on the structure evolution of the nanoscale fillers within the polymer phase. This article pertains to the small angle x-ray scattering study of electrically conductive nanocomposites to understand the structure-property relationship. The nanocomposites in this study are comprised of thermoset polyurethane as the matrix material with carbon nanotubes as the filler material. A percolation threshold of 0.5% wt/wt was observed along with substantial changes in the electrical conductivity of the nanocomposites. The small angle x-ray scattering data exhibits mass and surface fractal regimes indicating multiple structure evolution in the nanocomposites. Moreover, the data is interpreted using the crossovers of the scaling laws and sizes are measured to characterize the microstructure with a possible explanation for structural development.
- The Exploitation of Polymer Based Nanocomposites for Additive Manufacturing: A Prospective ReviewPublication . Khan, Imran; Kamma-Lorger, Christina S.; Mohan, Saeed D.; Mateus, Artur; Mitchell, GeoffreyAdditive manufacturing (AM) is a well-known technology for making real three dimensional objects, based on metal, ceramic and plastic material used for various applications. The aim of this review is to explore and offer an insight in to the state of the art polymer based nanocomposites in to additive manufacturing applications. In context to this, the developing efforts and trends in nanocomposites development particularly for additive manufacturing processes were studied and summed up. The scope and limitations of nanocomposites into Stereolithography, selective laser sintering and fused deposition modeling was explored and highlighted. The review highlights widely accepted nanoparticles for range of applications including mechanical, electrical, flame retardance and crossing over into more biological with the use of polymer matrices. Acquisition of functional parts with limitations in regard to printing is highlighted. Overall, the review highlights successes, limitations and opportunities that the union of AM and polymer based nanocomposites can bring to science and technology.
- Time resolved strain dependent morphological study of electrically conducting nanocompositesPublication . Khan, Imran; Mitchell, Geoffrey; Mateus, Artur; Kamma-Lorger, Christina S.An efficient and reliable method is introduced to understand the network behaviour of nano-fillers in a polymeric matrix under uniaxial strain coupled with small angle x-ray scattering measurements. The nanoparticles (carbon nanotubes) are conductive and the particles form a percolating network that becomes apparent source of electrical conduction and consequently the samples behave as a bulk conductor. Polyurethane based nanocomposites containing 2% w/w multiwall carbon nanotubes are studied. The electrical conductivity of the nanocomposite was (3.28×10-5s/m).The sample was able to be extended to an extension ratio of 1.7 before fracture. A slight variation in the electrical conductivity is observed under uniaxial strain which we attribute to the disturbance of conductive pathways. Further, this work is coupled with in- situ time resolved small angle x-ray scattering measurements using a synchrotron beam line to enable its measurements to be made during the deformation cycle. We use a multiscale structure to model the small angle x-ray data. The results of the analysis are interpreted as the presence of aggregates which would also go some way towards understanding why there is no alignment of the carbon nanotubes.
- Tools to define and evaluate morphology mapping, a route to complex structures using direct digital manufacturingPublication . Pinheiro, João; Abdulghani Oliveira da Silva, Saba; Pascoal-Faria, Paula; Sousa, Dora; Carreira, Pedro; Viana, Tânia; Kamma-Lorger, Christina S.; Mitchell, GeoffreyDirect Digital Manufacturing is a new set of technologies which allow objects to be printed directly from a digital definition. Such technologies allow us to manufacture any self-supporting shape, but simply replicating shape is not sufficient for the production of many parts especially those with specific function. We need to be able to generate complex multiscale structures similar to those we observe in nature. Direct digital manufacturing can be seen as method for achieving this, as we can deposit materials with different compositions and different structures in selected volumes and thereby generate a complex structure. This manuscript addresses the challenges of achieving this concept and the tools needed to characterize the parts produced and the variation in the composition and structure. We conclude by discussing how we might design such complex parts.