Cranfield Institute of Technology - PhD, EngD, MSc, MSc by research theses, (CIT)

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Browsing Cranfield Institute of Technology - PhD, EngD, MSc, MSc by research theses, (CIT) by Supervisor "El-Zafrany, A."

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    Design of an interactive finite element computer package for the analysis of the ride of a generalised off-road vehicle
    (1987-02) Kamar, Elsayed Abdrabboh; Cookson, R. A.; El-Zafrany, A.
    A versatile computer package, to evaluate ground vehicle ride comfort has been designed. Wheeled, tracked, and semitracked vehicles have been modelled. The emphasis has been placed upon the tracked vehicle suspension systems with the neatly ”standard" torsion bar arrangement operating with either telescopic or rotary-vane dampers. Substantial investigation of the four-bar linkage, associated with the rotary-vane damper, has been carried out and is presented here.The package includes linear ,nonlinear ,[2-V) ,and I3-Vj vehicle models. A new technique employing the finite element method (FEM) fat suspension system modelling has been developed. Several methods of numerical integration are available in the package .A new evident scheme based on a hypetosculatory Hermitian weighted residual of the second order for the solution of the system of differential equations which simulate the vehicle has been derived. Whenever necessary the error developed during the integration process was limited. The graphic display facility of digital computers has been used extensively in the present code. As an example, the damped eigen-value problem has been solved graphically. The graphical solution is simple, direct, and tellable compared to the analytical solution. The terrain configuration might be of either harmonic or atbitrary shape function. Two tolerence critetia have been employed fat tide comfort evaluation ,namely, the absorbed power critetion and the international standard organization ISO 2631 critetion.The two critetia are fully integrated into the package and operate automatically. All individual subroutines have been tested successfully for the purpose intended. Complete sectors have been validated by running various case studies. The results obtained from the package agree reasonably well with the analytical or experimental results. The package allows updating in response to new vehicle and vehicle-terrain technology and can be run on both time-skating or batch processing computer machines. The main package structute is independent of computer type.
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    Experimental and theoretical studies into the fatigue crack propagation behaviour of the 7075 aluminium-zinc alloy under constant and variable amplitude loading
    (1991-03) Kyriacou, S. A; El-Zafrany, A.
    This thesis describes both theoretical and experimental work performed in order to study the fatigue- crack propagation behaviour of the 7075 T7351 Aluminium - Zinc alloy, under constant and variable amplitude loading. For the theoretical aspects of the work. Static, Elastic and Elastic-Plastic Finite Element methods were utilised for the evaluation of residual stresses in the vicinity of the crack tip caused by overloading. The results have demonstrated that the plasticity caused by the loading part of the load cycle induces compressive residual stresses in the vicinity of the crack upon partial and/or full unloading. The experimental work has been carried out aiming to ascertain the constant load amplitude fatigue crack growth behaviour. It has been established that the material does not exhibit a sigmoidal crack growth curve but, one of parabolic like shape. A n empirical crack growth law has been derived to describe the constant load amplitude behaviour. It has been established that overloads cause substantial extension of the total life to failure due to delays caused by overloading. The observed delay increases if block overloads are introduced, and crack arrest is possible to occur . Finally, it is concluded that crack closure is responsible for the observed crack growth rate reductions.
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    Finite element and boundary element methods for elasto-plastic stress analysis of two-dimensional and axisymmetric problems
    (1989-07) Husain, Imad Ahmed; El-Zafrany, A.; Cookson, A.
    This work dealt with elasto-plastic analysis of 2-dimensional and axisymmetric problems using the finite-element and boundary-element techniques. The analysis is based upon a vide range of yield criteria and hardening rules so as to be suitable for most engineering materials. Many accuracy measures have been employed with the boundary-integral equation derivations, such as isoparametric boundary elements, singular quadrature, corner models, finite-difference schemes for internal stress evaluation, high-order integration cells, and the use of boundary-integral expressions for domain loading terms. A programming package has been developed vith its own mesh generator and results plotter. The package has been validated using several case studies including a benchmark test case recommended by NAFEMS. The finite-element analysis of elasto-plastic problems proved to be more stable and reliable than the corresponding boundary-element analysis.