49 results for Kelly, Piaras, Conference item

  • 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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  • The Mechanics of Osteoarthritis: The Fracture Mechanisms of Rapidly Loaded Cartilage

    Kelly, Piaras; Oconnor, JJ (1996-01-01)

    Conference item
    The University of Auckland Library

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  • 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 RTM-Light Manufacturing Process: Experimentation and Modelling

    MacLaren, O; Gan, Jia; Hickey, Christopher; Bickerton, Simon; Kelly, Piaras (2009)

    Conference item
    The University of Auckland Library

    An initial study was carried out to investigate key aspects of the RTM-Light process, in particular the effect of mould flexibility on process times, cavity thickness and pressure distributions. Radial and peripheral injection experiments have been performed, utilising mould platens of varied flexural stiffness. A simulation of these RTM-Light experiments was developed using an iterative coupling procedure to solve the fluid-mould interaction problem. Initial comparisons of experimental and numerical results are presented.

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  • Why incongruous knee replacements do not fail early

    Kelly, Piaras; O'Connor, JJ

    Conference item
    The University of Auckland Library

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  • A 2.5D Model of the Resin Infusion Process, Experiments and Simulation

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

    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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  • A Thermomechanical Constitutive Model for Fibrous Reinforcements

    Cheng, Jonathan; Kelly, Piaras; Bickerton, Simon (2009)

    Conference item
    The University of Auckland Library

    In Liquid Composite Moulding processes, many important manufacturing parameters and final properties of the part are influenced by the constitutive behaviour of fibrous reinforcements. A thermomechanical model for the response of fibrous materials to compaction is presented. Rate-dependent and rate-independent features observed in experimental data are reproduced by the model.

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  • Stresses and cracks in a theoretical model of a metal-backed tibial knee replacement component

    Kelly, Piaras; O'Connor, JJ (1996)

    Conference item
    The University of Auckland Library

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  • Stress distributions within rapidly loaded cartilage - possible contributions to arthrosis

    O'Connor, JJ; Kelly, Piaras (1994)

    Conference item
    The University of Auckland Library

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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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  • Mechanical design of joints incorporating metal interlayers

    Kelly, Piaras; Hills, DA; Nowell, D (1989)

    Conference item
    The University of Auckland Library

    We undertake a theoretical study of the strength of a joint modelled as two rigid blocks (ceramic components) bonded by a thin, comparatively soft metal interlayer, loaded in tension. Slip-line field theory and the upper bound theorem enables us to suggest firm guidelines for the maximum thickness of the interlayer which enables the full strength of the ceramic to be achieved, by exploiting the constraint implicit in a thin layer. We go on to investigate the influence of flaws (poorly bonded regions) and show how a comparatively small region of poor adhesion (~5% debonding) can significantly reduce the strength of the joint. Quantitative information about the amount of de-bonding which can be tolerated in a particular configuration without loss of strength will be presented.

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  • The quasi-static approximation for cracked interfaces in layered systems

    Pecorari, C; Kelly, Piaras (1999)

    Conference item
    The University of Auckland Library

    For the last two decades the quasi-static approximation (QSA) has been the most commonly used approach for describing the interaction of ultrasonic waves with imperfect interfaces. The QSA is a low-frequency approximation and it can be used when the thickness of the interface is much smaller than the wavelength of the waves used to inspect the interface. Its most complete formulation has been presented by Baik and Thompson [1], and models the real interfacial imperfections as continuous, uniform distributions of springs and masses along the interface plane (see Fig 1).

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  • Nonconforming elements for liquid composite molding process simulations

    Kelly, Piaras; Jennings, S (2006)

    Conference item
    The University of Auckland Library

    Liquid Composite Molding (LCM) processes are now a prevalent group of manufacturing methods for advanced composite materials. They offer many advantages over more traditional manufacturing methods, such as the ability to deal with large and complex shapes. Numerical simulations can lead to better predictions of process parameters. The standard procedure for the simulation of these processes is to use a Control Volume (CV) method. One problem with the CV method is that resin mass is not conserved on an element level, and this has consequences for accuracy. An attractive alternative to the CV method is to use a single grid of non-conforming finite elements. Such non-conforming elements encompass essential mass conservation properties. In this study it is shown how the standard non-conforming triangular element can be adjusted to ensure mass conservation on the element level and to ensure continuity of the fluid flux across inter-element boundaries. Numerical experiments are carried out which show that single grids of such elements, and nonconforming quadrilateral elements, produce accurate results in the case of the Injection Compression Molding process.

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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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  • Numerical Simulation of Liquid Composite Molding Processes

    Kelly, Piaras; Bickerton, Simon (2005)

    Conference item
    The University of Auckland Library

    Liquid Composite Molding (LCM) includes a range of composite materials manufacturing processes, for example Resin Transfer Molding (RTM), Injection Compression Molding (I/CM) and flexile-bag processes such as Vacuum Assisted Resin Transfer Molding (RTM). In these processes, resin is injected under pressure into a fully or partially-compacted fibrous preform before final cure. Mathematical models and numerical simulations of these manufacturing processes lead to better predictions of the filling times and preform final thicknesses, and of the optimal position of inlet gate location and inlet pressures. In this study, the governing equations of LCM are solved using a number of different variants of the Finite Element Method. In particular, a single fixed grid scheme which conserves fluid mass on the element level, and which ensures continuity of fluid flux across inter-element boundaries, is used and is shown to give accurate results.

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  • Modeling the viscoelastic behaviour of fibre reinforcing fabrics

    Kelly, Piaras; Umer, RA (2004)

    Conference item
    The University of Auckland Library

    The deformation of fibrous materials plays an important role in the Liquid Composite Molding (LCM) processes. These materials display markedly non-linear viscoelastic characteristics. A model of fibrous material deformation is developed, incorporating this non-linear viscoelastic response, with a view to being used in simulations of LCM processes. The model is one-dimensional and is appropriate for the simple fibre compaction deformation which occurs during LCM processes. A limited number of compaction experiments were carried out to determine the model parameters for a continuous filament mat. These included a rapid compaction (100mm/min), a number of slower compactions to the same final volume fraction, and then a number of tests at a constant compaction speed to different final volume fractions. The model gives reasonably good results over a range of compaction speeds and volume fractions.

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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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  • 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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