Browsing by Author "Ronda, Jacek"

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    A computational implementation of design sensitivity analysis and structural optimisation
    (1996) Bothma, André Smith; Ronda, Jacek
    In the field of computational mechanics, increases in computing power and enhancements in material and kinematic models have enhanced the feasibility of performing structural design optimisation for a wide range of applications. The work presented here was motivated by the current groundswell of research effort in computational optimisation. Design Sensitivity Analysis (DSA) crucially underpins much of structural optimisation and, as such, is focussed on more intently than the optimisation theory itself: various approaches to the Direct Differentiation Method (DDM) DSA procedure are investigated and computationally implemented. The procedures implemented were chosen so as to involve a range of important issues in computational sensitivity analysis, particularly * Shape and non-shape sensitivity analysis, * Total and Updated Lagrange-based DSA, * DSA of displacement and non-displacement based response functionals, * Multiparameter DSA. * DSA for large strain behaviour The primary objectives of this thesis are: I. Development of a design sensitivity formulation which, when discretised, resembles the standard displacement based kinematic element formulation, thus enabling the implementation of design sensitivity analysis in established Finite Element Analysis (FEA) codes as a 'pseudo'-element routine. II. lmplemention of several design sensitivity formulations and structural optimisation into the FEA code ABAQUS as a verification of the first objective. Numerical results provided in this work demonstrate the successful completion of the above-mentioned objectives. The discretised DSA formulations presented, as well as the 'pseudo'-element approach adopted, particularly in the case of shape DSA are entirely original. To the best of the author's knowledge, DSA and DSA-based structural optimisation had never before been attempted with ABAQUS. The research conducted here lays the foundation for potentially very fruitful future work.
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    Friction models in the solution of nonstationary contact problems
    (1993) Colville, Kevin William; Ronda, Jacek
    In most implementations of the finite element method for the solution of contact problems the model of friction used is the classic Amontons-Coulomb. This dissertation is an attempt to rectify the current situation by considering four more advanced friction models, and coding them in FORTRAN for use with the finite element program ABAQUS. The new models are: a quasi-steady-state sliding model proposed by Zhang, Moslehy and Rice; a nonlinear pressure-dependent model proposed by Wriggers, vu Van and Stein; and a model that includes a film of lubricant proposed by Wilson, Hsu and Huang. The friction models are described in detail, including the algorithmic implementation. The contact problem is then formulated in the Total Lagrangian and Updated Lagrangian formulations for contact between an elastic-plastic (Mises plasticity) body and a rigid tool. The variational (weak) form of the formulation is given and this is then discretised by the finite element method. To test and compare the models three common metal forming processes are simulated: hemispherical punching of a disk, two-dimensional plane strain and three-dimensional cold rolling of a strip, and axisymmetric cup deep-drawing. The results are presented in the form of contour plots of the second invariant of stress (Mises), and the plastic yield and maximum stress. Also graphs for the thickness strain are given. These results are presented for each combination of friction model and process to allow easy comparison of frictional behaviour.
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    Improvement of solid phase transition simulations, by developing the supporting database
    (2000) Phaswana, Arthur K; Ronda, Jacek
    The modern approach to modelling of welding leads to the phenomenological description of the complex thermo-mechano-metallurgical (TMM) process and finite element (FE) solution of this problem. The TMM process requires four groups of data that define material properties, welding control variables, boundary and initial conditions and finite element approximation. To assure the better control of this simulation with the very large number of data an interactive database was developed. The development of the database has been one of the major tasks of this M.Sc. thesis.
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    Large plastic deformation and shear localization of crystals
    (2000) Abu-Saman, Awni; Ronda, Jacek
    Bibliography: leaves 87-94.
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    Modelling of welding with various constitutive models for steel
    (1994) Oliver, Graeme John; Ronda, Jacek
    This dissertation is an attempt at the quality analysis of constitutive modelling of welding as a coupled thermo-mechanical or thermo-mechanical-metallurgical problem. Three types of inelastic theories of continua: unified viscoplasticity based on dislocation density theory, unified viscoplasticity based on potential theory, and transformation induced plasticity have been chosen for quantitative investigation. Material models proposed by Anand, Estrin and Mecking, Estrin, Robinson, and Leblond et.al. have been implemented into the finite element program ABAQUS. Specific subroutines have been written specifically for each constitutive equation. The material model implementation is based on the implicit solution of stress-strain relations and the derivation of associated constitutive tangent moduli necessary for the Nonlinear Finite Element solution procedures. Material model comparisons are based on numerical results obtained for the welding of thick plates; that is the bench mark problem considered in this thesis.