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 resin flow, mould deflection and reinforcement deformation in RTM Light processing

    Timms, J; Bickerton, Simon; Kelly, Piaras (2012)

    Conference item
    The University of Auckland Library

    A numerical simulation of the RTM Light manufacturing process must capture the interactions between resin flow, preform deformation and mould deflection that occur during filling and post-filling. From a numerical solution perspective, RTM Light is similar to the fluid-structure interaction (FSI) class of problems, where the ‘fluid’ is a saturating deformable porous media and the structure is a compliant mould. Previous implementations of RTM Light simulations have been based on a partitioned solution procedure, using independent solvers for the flow and structure modules and a fixed point iteration coupling method. While this type of coupling has been successfully implemented in the solution of a number of FSI problems, it is prone to instability when coupling between the subdomains is strong, as is the case in RTM Light. This paper presents the development of a finite element RTM light simulation and compares performance of a number of partitioned and monolithic solution approaches for solving the coupled structural and flow problem. The flexibility of the code is demonstrated by simulating the limiting cases of zero mould compliance (i.e. RTM) and complete compliance (i.e. Resin Infusion/VARTM), along with the intermediate case of RTM Light.

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  • Deviation from Darcy's Law During the Post-filling Stage of Resin Infusion

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

    Conference item
    The University of Auckland Library

    To allow for a better control of the quality of parts produced through the resin infusion process, it is necessary to understand the phenomenon happening during the post-filling stage of the process. This paper investigates the causes of the residual pressure gradient that can be observed at the end of the post-filling stage of the resin infusion and RTMLight processes. A modified formulation of Darcy’s law is presented along with experimental evidence in an attempt to verify and quantify the existence of a threshold pressure gradient in the case of flow through porous media.

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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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  • 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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  • Challenges for Modelling Filling during Liquid Composite Moulding Processes

    Bickerton, Simon; Buntain, MJ; Kelly, Piaras (2003)

    Conference item
    The University of Auckland Library

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  • Modelling the Viscoelastic Compression Behaviour of Fibrous Reinforcing Fabrics

    Bickerton, Simon; Kelly, Piaras; Buntain, MJ (2002)

    Conference item
    The University of Auckland Library

    The majority of fiber reinforced plastic manufacturing processes involve compressive deformation of the reinforcing material to be included in the product. The development of accurate process simulations will in many cases be dependent on our ability to provide good models for the deformation of these reinforcing structures. The viscoelastic behavior of preform materials in the absence of any matrix has been investigated, and the implications for Liquid Composite Molding (LCM) processes considered. Extending existing Resin Transfer Molding simulations to predict local and total tooling forces will require the development of viscoelastic preform deformation models. For other LCM processes that involve cavity thickness changes during mould filling, an accurate preform deformation model is essential in order to simulate mould filling. An experimental study is presented demonstrating the strong time dependent viscoelastic compression behavior of common LCM preform materials. A nonlinear viscoelastic model has been developed for constant speed preform compaction. The required empirical parameters have been derived from a series of characterization experiments performed on the preform materials studied.

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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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  • 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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  • 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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