48 results for Kelly, Piaras, Conference item

  • Design of brazed or diffusion bonded joints between ceramic components

    Kelly, Piaras; Hills, DA; Nowell, D (1991)

    Conference item
    The University of Auckland Library

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  • The Numerical Solution of Singular Integral Equations arising in certain Fracture Mechanics Problems

    Kelly, Piaras (2000)

    Conference item
    The University of Auckland Library

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  • Numerical Simulation of the RTM Light Manufacturing Process

    Timms, J; Bickerton, Simon; Kelly, Piaras (2011)

    Conference item
    The University of Auckland Library

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  • Application of a Complete Tooling Force Analysis for Simulation of Liquid Composite Moulding Processes

    Bickerton, Simon; Kelly, Piaras (2006)

    Conference item
    The University of Auckland Library

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  • Transverse compression properties of textile materials, International conference on textile engineering and materials

    Kelly, Piaras; Bickerton, Simon; Cheng, Jonathan (2011)

    Conference item
    The University of Auckland Library

    The response of textile materials to transverse compression is of great importance in many applications. In this paper is discussed the mechanical properties of textile materials when subjected to transverse compression. The response of a textile to load is very non-linear and inelastic. The response is viscoelastic (there are rate effects) and plastic (there are permanent deformations). It is shown that energy is stored in a textile when it is loaded, and that some of this energy is not released when the material is unloaded, but instead is locked into its structure. This locked energy cannot be released unless the structure is placed in tension. A thermomechanical framework is introduced which incorporates the textile locked energy. Models are developed which predict well the response of textiles to load.

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  • A 2.5 Simulation of the Resin Infusion Process addressing complex reinforcement compaction response

    Verleye, B; Kelly, Piaras; Bickerton, Simon (2010)

    Conference item
    The University of Auckland Library

    The simulation of composite manufacturing processes is a great aid to obtaining efficient production and high quality parts. The mould and process design must allow for fast filling times as well as dry-spot free parts. In previous work we presented our software SimLCM for the simulation of force and velocity controlled Resin Transfer Moulding (RTM) and Compression RTM. These are two examples of the general Liquid Composite Moulding (LCM) group of processes. Another recently popular subclass is Resin Infusion (RI), also know as Vacuum Assisted RTM. The simulation of RI adds an extra difficulty to the simulation process, as the height of the preform will change locally because of the filling. In contrast to CRTM, this change of height is not imposed, and thus not known beforehand. This paper describes the extension of SimLCM to the simulation of RI processes. The results of the simulations are compared with results from other programs that use different techniques, and also with experimentally obtained data found in literature. The comparison between simulation and experiment is found to be excellent.

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  • Simulation and tooling forces exerted on rigid non-planar LCM tools

    Walbran, W; Verleye, B; Bickerton, Simon; Kelly, Piaras (2010)

    Conference item
    The University of Auckland Library

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  • A Rate-independent thermomechanical Constitutive Model for Fibrous Reinforcements

    Cheng, Jonathan; Kelly, Piaras; Bickerton, Simon (2010)

    Conference item
    The University of Auckland Library

    In Liquid Composite Moulding (LCM) processes, the constitutive behaviour of fibrous reinforcements has a strong bearing on the choice of manufacturing parameters and final part properties. In many LCM processes, the fibrous preform is subjected to loading and unloading, the latter also occurring during filling and post-filling phases of the manufacturing process. Fibrous materials display inelastic behaviour with rate-dependent and rate-independent components and this must be modelled accurately over several load-unload cycles in order to accurately simulate such processes. An important feature of the material behaviour is its unchanging response to successive load cycles once a large number of load cycles have been applied. Inelastic effects such as fibre-fibre frictional sliding occur during loading as well as unloading and the inelastic deformation remaining after successive cycles appears unchanged. The model presented is developed within a thermomechanical framework and reproduces such behaviour using a single internal variable to account for inelasticity. It is compared to cyclic loading experiments and serves as a starting point for the incorporation of effects such as cyclic softening and rate-effects through additional internal variables.

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  • Observations from the filling and post-filling stages of axisymmetric liquid composite moulding with flexible tooling

    Timms, J; Govignon, Quentin; Bickerton, Simon; Kelly, Piaras (2010)

    Conference item
    The University of Auckland Library

    This paper presents experimental observations from the filling and postfilling stages of 1D axisymmetric Resin Infusion (VARTM) and RTM Light. A series of experiments have been performed to investigate the influence of mould flexural stiffness and fill mode on fluid pressure, cavity thickness, filling stage time, and postfilling stage time. Observations are also made on the effect of those parameters on the repeatability of nominally identical experiments.

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  • Neural network versus Kriging, surrogate models for LCM process optimisation

    Gupta, A; Kelly, Piaras; Ehrgott, Matthias; Bickerton, Simon (2012-07-09)

    Conference item
    The University of Auckland Library

    In Liquid Composite Moulding (LCM) processes an optimal combination of a variety of manufacturing design variables must be chosen in order to minimize cycle time while keeping equipment, layout and running costs low. Such black-box function optimization can be achieved by integrating the process simulation algorithm with a metaheuristic, such as a genetic algorithm (GA). However, the large number of function evaluations required by a GA combined with the computational expense of the simulations often makes this approach unaffordable. This issue is further emphasized when the filling and curing phases are coupled and an iterative optimization strategy becomes necessary. The use of a surrogate model, as a substitute to the expensive simulation algorithm, is a common technique for reducing the run-time of an optimization algorithm. Choosing such a model that suitably duplicates all the features and trends of the objective functions over the design space, is an important task. In this paper we compare two popular surrogate models, namely the artificial neural network (specifically the Cascade-Correlation Learning Architecture Neural Network) and kriging, and discuss their performance in terms of prediction accuracy and the run-time of the resultant optimization algorithm.

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  • Automated Geometric Characterisation of Woven Reinforcing Textiles using Image Analysis Techniques

    Swery, Elinor; Kelly, Piaras; Sharma, Rajnish; Bickerton, Simon (2013-09-02)

    Conference item
    The University of Auckland Library

    An automated geometric characterisation tool for woven reinforcement textiles has been developed and is presented. This tool is used to obtain the in-plane geometry of woven textiles. The image of the textile is captured using a standard office scanner, eliminating the need for complex set up and specialised equipment. The controlled lighting provided by the scanner also enables any fibre material to be analysed, and examples of glass and carbon textiles are presented. The steps used in the processing technique are discussed, along with the resulting geometric information for the materials studied. The extracted information can be used to provide a better understanding of the reinforcing material properties, for example, compaction response and permeability. A study has been conducted, which shows how the geometric characteristics can be used to predict the fabric permeability.

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  • Numerical Permeability Prediction of Woven Textiles at Different Compaction Levels

    Swery, Elinor; Kelly, Piaras; Walbran, WA; Bickerton, Simon (2013-09-19)

    Conference item
    The University of Auckland Library

    The permeability behaviour of woven textiles at different compaction levels is predicted using textile modelling techniques. Unit cell geometries, reflecting the textile structure are created from data obtained through image analysis on scanned images of the textile. These unit cells are then used to create voxel meshes representing the volume which the fluid (resin) fills. By executing flow simulations on these meshes, the permeability characteristics may be obtained, and results for uncompacted textile are in good agreement with results obtained through experiments. A number of different methods used to account for the change in textile architecture due to applied compaction are integrated into the existing automated prediction process (executed through the Matlab environment). The resulting permeability predictions of single layer textiles are compared to experimental results. For most methods, the change in permeability behaviour due to compaction is captured at lower compaction levels, however further modelling will need to be integrated in order to capture the change in behaviour at higher compaction levels.

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  • A 2.5D simulation of the filling and post-filling stages of the Resin Infusion process

    Govignon, Q; Maes, L; Verleye, B; Bickerton, Simon; Kelly, Piaras (2012-07-09)

    Conference item
    The University of Auckland Library

    The Resin Infusion process (RI, also known as VARTM) is a subclass of the Liquid Composite Moulding (LCM) collective, which is increasingly applied in industry. As opposed to the other LCM processes, RI utilises only one rigid mould half, the upper mould half of the mould being a flexible plastic bag. This greatly reduces tooling costs, and makes the process suitable for medium to very large sized parts. However, the interaction between a flexible bag and the infusion of the laminate within, presents a significant challenge to model and understand. The University of Auckland LCM research group is developing SimLCM as a generic LCM mould filling simulation. SimLCM has recently been extended to simulate RI, focusing on resin flow and laminate thickness predictions throughout the process. To accurately predict filling times, and the evolution of fluid pressure and laminate thickness during filling and post-filling phases, a detailed knowledge is required of the complex compaction response of the fibre reinforcement. While significant research has been published on modelling of the filling in RI, the post-filling period has received much less attention. This phase is, however, significant as spatial variations in laminate thickness are removed, preferably before the infused resin gels. Extending on previous work on rectilinear filling, this paper will present a program of RI experiments in a range of 2D flow geometries and the results will be compared to the predictions made using SimLCM. Special attention is given to the post-filling stage, and the validation of the new models developed for SimLCM. A selection of radial, peripheral and more complex filling situations have been addressed.

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  • Modelling Forces Acting on Rigid, Non-planar Liquid Composite Moulding Tools

    Bickerton, Simon; Kelly, Piaras (2005)

    Conference item
    The University of Auckland Library

    The term Liquid Composite Molding (LCM) encompasses a growing list of composite manufacturing processes, including Resin Transfer Molding (RTM), Injection/Compression Molding (I/CM), and Vacuum Assisted RTM (VARTM). The RTM and I/CM processes utilise two-piece rigid moulds, which are subject to force components due to reinforcement compaction and internally generated resin pressure. The focus of this paper is prediction of tooling forces for RTM, which will allow efficient structural design of moulds, and selection of cost effective process parameters. Previous experimental work has demonstrated the influence of reinforcement compaction behaviour, which is strongly non-elastic. A viscoelastic compaction model has been developed which addresses both dry and wet response, and is implemented in RTM simulations of simple flat parts. Non-planar geometries introduce a tangential stress acting on mould surfaces, due to shear of the reinforcement. The tooling force analysis is extended to complex parts using an existing RTM filling simulation, LIMS, which has been developed at the University of Delaware.

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  • The analysis of surface-breaking interface cracks

    Kelly, Piaras; Hills, DA; Nowell, D (1992)

    Conference item
    The University of Auckland Library

    This paper discusses the analysis of a crack along an interface between two dissimilar elastic quarter planes for cases where the crack breaks the free surface. A dislocation density method of analysis is employed and the appropriate dislocation solution and far-field stress expressions are highlighted. Models for crack tip behaviour are discussed and it is shown that a simplified quadrature can be used to extract the crack extension force. Sample results for an interface crack loaded by constant crack face pressure are given.

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  • Compaction of Dry and Wet Fibrous Materials during Infusion Processes

    Kelly, Piaras; Umer, Rehan; Bickerton, Simon (2004)

    Conference item
    The University of Auckland Library

    The objective of this study was to investigate the response of fibrous materials to compaction, since this response can affect significantly a number of important parameters, e.g. required tooling forces and fill-times, for some resin infusion manufacturing processes. A series of compression tests were carried out on both dry and wet (resin-impregnated) samples, at a number of different compaction speeds and to various final volume fraction levels. The materials were seen to exhibit a significant viscoelastic (stress relaxation) response, which changed according to whether the fibers were dry or wet. A thermomechanical model of fibrous material deformation was developed, incorporating the observed non-linear viscoelastic response, and the wet-dry change in response. The model is appropriate for the simple fibre compaction deformation which occurs during many of the liquid composite molding (LCM) processes. The model gives reasonably good results over a range of fiber volume fractions and compression speeds.

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  • Towards a Complete Tooling Force Analysis of Liquid Composite Moulding Processes

    Bickerton, Simon; Kelly, Piaras (2007)

    Conference item
    The University of Auckland Library

    The term Liquid Composite Moulding (LCM) encompasses a growing list of composite manufacturing processes. Resin Transfer Moulding (RTM) and Injection/Compression Moulding (I/CM) utilise two-piece, rigid mould tools, and are the focus of this paper. Moulds used in these processes must supply forces to compact fibre reinforcement, and to balance resin pressures generated within the cavity. An RTM and I/CM simulation is presented, for which a complete tooling force analysis has been incorporated. Complex geometries require the consideration of both the normal and shear stress components acting on mould surfaces. Our previous experimental work has demonstrated the complex time dependency of tooling forces, due to non-elastic compaction behaviour of fibre reinforcements. A combination of elastic models is applied here, modeling phenomena such as stress relaxation and fluid lubrication of the reinforcement in a simple manner. A simple friction based model is included, allowing consideration of complex non-planar part geometries. Two industrial components are used to demonstrate the benefits of a complete tooling analysis. Such analyses are required as the application of the filling simulation is extended to processes within flexible and semi-rigid moulds.

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  • Predicting Stress Distributions Exerted on LCM Tools using Visco-elastic Compaction Models

    Walbran, William; Bickerton, Simon; Kelly, Piaras (2007)

    Conference item
    The University of Auckland Library

    Mould tools used for LCM processes such as Resin Transfer Moulding (RTM) and Injection/Compression Moulding (I/CM) must withstand the forces applied during compaction of the preform and injection of the resin. A simulation package has been developed at the University of Auckland to predict the forces applied to moulds during these processes. This will allow cost effective mould design and process selection. The simulation package utilizes a viscoelastic compaction model, which has been characterized for a glass-fibre chopped strand mat. Several RTM and I/CM experiments have been carried out, the local stress distribution being monitored throughout, as well as the total clamping force applied to the mould. The influence of the fluid pressure on the total stress experienced by the mould is shown to be a function of both the fibre volume fraction and the injection pressure, the latter being more pronounced at low volume fractions. The stresses observed during I/CM are significantly higher than during RTM, however the process times for I/CM are considerably lower. These experiments have been compared to initial calculations performed with the LCM simulation, and good agreement has been shown for the normal stress distributions and total clamping force evolutions recorded.

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  • Simulation of Resin Infusion Processes

    Kelly, Piaras; Johnson, C (2007)

    Conference item
    The University of Auckland Library

    This study is concerned with Resin Infusion Liquid Composite Molding processes such as Vacuum Assisted Resin Transfer Molding. The Resin Infusion process has been effectively simulated using two models, one based on the conventional Darcy's Law and one based on a height-averaged modified version of Darcy's Law. The finite elements themselves are used as control volumes and a mass conservation technique is applied to improve the accuracy of fluid flux evaluation. Elements at the flow front are temporarily subdivided to allow for convergence of the numerical scheme. It is found that the temporal height derivative is important and cannot be neglected if one is interested in an accurate simulation. Neglecting this term to form the quasi-static forms of the full governing equations significantly increases the mass balance error and can greatly reduce the mold fill time.

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  • A Fibre Compaction Model for Liquid Composite Moulding

    Kelly, Piaras (2007)

    Conference item
    The University of Auckland Library

    Liquid Composite Moulding (LCM) processes such as Resin Transfer Moulding (RTM) are widely-used to manufacture composite material components. The evaluation of resin fluid pressures and time to manufacture in these processes have been the study of many previous investigations. This study focuses on the forces which arise in LCM processes. A knowledge of these forces is of practical importance because they give the necessary tooling forces and also they help predict part thicknesses where force and thickness are coupled in complex processes such as Vacuum Assisted Resin Transfer moulding (VARTM). A phenomenological model is developed which predicts the forces required to compact certain fibrous materials in rigid moulds over a range of compaction velocities and volume fractions. Stress relaxation is accounted for. The model parameters can be obtained from a limited number of tests. The model is used to predict the stresses in dry and wet compacted fibrous materials, and the tooling forces in a complete LCM process. The model results agree well with experimental results.

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