Browsing by Author "El-Zafrany, A."
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Item Open Access An advanced finite element system for static and dynamic analysis-with application to the design of radial impellers(Cranfield University, 1987-07) Al-Azzawi, Mohammad Mousa; Cookson, R. A.; El-Zafrany, A.An advanced finite-element package, tailored to the static and dynamic analysis of radial impellers has been produced. Two families of new elements, one for thin and thick plates and the other for thin and thick shells, have been derived and proved to perform very well within a wide range of structural thicknesses. Static and dynamic economical solvers, two- and three-dimensional mesh generation and plotting, sectorial symmetric analysis, steady state response, transient response, and other programs are part of the large number of facilities available in the package. The finite-element package has been validated by solving a large number of simple case studies and comparing the package results with those obtained from analytical solutions. Two different radial impeller, experimental validation tests have been carried out, the first being the dynamic analysis of a radial impeller using the time averaged holographic technique, and the second the measurement of the steady-state stresses by means of a strain-gauge/slip ring assembly for a rotating impeller. The experimental results have been shown to be in good agreement with those obtained from the package.Item Open Access The coupling of the FEM and the BEM for the solution of elastoplacticity and contact problems(Cranfield University, 1998-03) Landenberger, Axel; El-Zafrany, A.This thesis introduces a method for the coupling of the elastic Boundary Element Method (BEM) and the elastoplastic Finite Element Method (FEM) and the extension of this method to contact problems by using gap finite elements. A method for the coupling of BEM subregions and FEM subregions is derived which limits the transformation of nodal forces into nodal traction to the interface degrees of freedom. This method is also capable of modelling body forces. Then the coupling procedure is extended to allow for elastoplastic material models in the FEM parts of the structure. Additionally contact conditions are included by defining an extra artificial subregion which consists of gap finite elements. Incremental iterative algorithms are used to overcome the present nonlinearities resulting from plasticity, non-conforming contact and friction. A computer program based on the developed methods and algorithms was coded in FORTRAN77 and tested on PCs. Patch tests and case studies were run in order to validate the developed package against known analytical solutions or the commercial finite element package ABAQUS. It can be concluded that all the original ideas and methods developed in this work are successful. The coupled FEM/BEM is as accurate and reliable as the pure FEM for elastoplastic analysis, with FEM/BEM having the advantage of ininimising the modelling effort. The use of gap elements in an artificial subregion was found to be an ideal and accurate way of including contact conditions into the environment of the elastoplastic coupled FEM/BEM.Item Open Access 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.Item Open Access 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.Item Open Access Finite element analysis of fatigue damage of composite laminated structures(Cranfield University, 2002-02) Hegaze, Moutaz Mohamed Ebrahim; El-Zafrany, A.; Mba, DavidComposite materials are increasingly believed to be the materials of the future with potential for application in high perfon-nance structures. One of the reasons for that is the indication that composite materials have a rather good rating with regard to life time in fatigue. Fatigue of composite materials is a quite complex phenomenon, and the fatigue behaviour of these heterogeneous materials is fundamentally different from the behaviour of metals. Finite element method is a powerful numerical technique for the solution of such complex problems. The present work comprises theoretical and experimental research into the implementation of composite materials in structure applications. A new finite element derivation was carried out based on a high-order shear deformation theory, which is accurate for a wide range of thickness. The geometric nonlinearity effect was considered in the derivation of the element. The force increment method was also introduced to improve the accuracy of nonlinear analysis. Experimental measurements were carried out with two different types of composite materials, carbon/epoxy and glass/epoxy, in order to obtain fatigue life diagrams (S/N diagrams) to be used for the fatigue damage assessment.F atigue damage assessmentsw ere developed to predict the fatigue behaviour of laminated plates and shells based on two aspects; damage by initiation and damage by crack growth. A computer package was built based on the proposed finite element theory to carry out the previous analyses. Several finite element solvers and eigenproblem solvers are available to users of the package to choose the suitable one for their applications. The validation of the developed package for some analyses such as stress analysis, natural frequency analysis, stability analysis and fatigue analysis was successfully achieved using a number of composite case studies. A parametric study was also carried out to illustrate the potential of the package to be used as a good optimization tool. Fatigue life assessment by damage growth has been achieved by a single run of the package, thus saving enormous user effort and computer resources, compared with the use of commercial finite element packages.Item Open Access 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.Item Open Access Nonlinear static and dynamic analysis of composite layered plates and shells using finite strip methods(Cranfield University, 2003-10) Razzaq, Raja Javed; El-Zafrany, A.In this thesis, a new concept of finite strip elements is introduced. Lagrangian, Hermitian and spline-type interpolations have been used independently along the two axes of the plate mid-plane. Different plate-bending theories; Mindlin, Reissner and Kirchhoff theories have been applied in the derivations of the new finitestrip elements, for isotropic and composite materials. The new elements have also been extended to work as faceted shell elements for the analysis of cylindrical shells, folded plates and stiffened plates. An efficient modular programming package based on those elements was designed, and it is capable of performing linear and non-linear stress analysis, buckling analysis and natural frequency analysis. The modular package, which was coded in FORTRAN has different solvers and a built-in mesh generator for different types of plate structures. A number of case studies have been employed for the validation of the package and testing its different capabilities. The package has proved to be an efficient tool for numerical modelling of plates, cylindrical shells, folded plates and stiffened plates made of isotropic and composite layered materials.Item Open Access The numerical modelling of elastomers(Cranfield University, 2003) Bayliss, Martin T.; El-Zafrany, A.This thesis reports onreview and research work carried out on the numerical analysis of elastomers. The two numerical techniques investigated for this purpose are the finite and boundary element methods. The finite element method is studied so that existing theory is used to develop a finite element code both to review the finite element method as applied to the stress analysis of elastomers and to provide a comparison of results and numerical approach with the boundary element method. The research work supported on in this thesis covers the application of the boundary element method to the stress analysis of elastomers. To this end a simplified regularization approach is discussed for the removal of strong and hypersingularities generated in the system on non-linear boundary integral equations. The necessary programming details for the implementation of the boundary element method are discussed based on the code developed for this research. Both the finite and boundary element codes developed for this research use the Mooney-Rivlin material model as the strain energy based constitutive stress strain function. For validation purposes four test cases are investigated. These are the uni-axial patch test, pressurized thick wall cylinder, centrifugal loading of a rotating disk and the J-Integral evaluation for a centrally cracked plate. For the patch test and pressurized cylinder, both plane stress and strain have been investigated. For the centrifugal loading and centrally cracked plate test cases only plane stress has been investigated. For each test case the equivalent results for an equivalent FEM program mesh have been presented. The test results included in this thesis prove that the FE and BE derivations detailed in this work are correct. Specifically the simplified domain integral singular and hyper-singular regularization approach was shown to lead to accurate results for the test cases detailed. Various algorithm findings specific to the BEM implementation of the theory are also discussed.Item Open Access Numerical modelling of elastomers using the boundary element method(Wiley, 2004-08-18) Bayliss, Martin T.; El-Zafrany, A.The FEM analysis of hyper elastic, elastomeric materials has been formulated and implemented for various material models (strain energy functions) over the years. More recently, the analysis of elastomeric materials has been attempted in the boundary element method. This has been achieved by the addition of non-linear domain terms to the basic linear boundary element equation. These non-linear domain terms require the evaluation of the displacement derivative components directly from displacement derivative boundary integral equations. In the solution to the boundary problem it is required to regularize the different types of singularities occurring in the system of non-linear boundary integral equations. This paper discusses the necessary theory for the boundary element method as applied to elastomers and presents a comparison between semi-analytical and numerical solutions for various test cases.Item Open Access Progressive damage analysis of composite layered plates and shells using finite strip methods(2005-04) Zahari, Rizal; El-Zafrany, A.As far as design of composite structures is concerned, it is important that we are able to accurately determine the failure modes and damage progression of structures made of composite materials. This will in turn, aid structural designers to develop reliable and safe designs which will exploit the advantages offered by composite materials. With the development of numerical analysis strategies towards non-linear progressive failure algorithms and the increase in computing capacity, it has now become possible to replace the existing experimental data with numerical results. Verified numerical models offer a practical method for exploring parametric study. Hence, it is essential to devise a reliable progressive damage scheme in order to predict the damage propagation in composite laminated structures using efficient computational tools such as the finite strip method. In this thesis, a new finite strip method, for non-linear stress analysis based on the tangential stiffness matrix has been developed using the new concept of polynomial and spline-type finite strip elements, with Mindlin and Reissner plate-bending theories for composite plates and shells. A progressive damage methodology and algorithm for composite laminates was successfully developed for the new finite strip methods using stress-based failure criteria. A finite strip analysis programming package which is capable of performing nonlinear progressive damage analysis for composite plates and facetted shells, has also been developed with Mindlin and Reissner plate bending elements. Validation of the developed finite strip package has been successfully carried out by comparing the results with corresponding results obtained with the finite element analysis using ABAQUS and with some published experimental results. Good comparison with the finite element results and experimental results were observed through various test cases, confirming the accuracy and reliability of the new derivations and the programming package.Item Open Access Stress analysis of thin and thick plates on elastic foundations using boundary and finite element methods(Cranfield University, 1991-04) Al-Hosani, Khaleel Ibrahim Abdulla; El-Zafrany, A.In this work an attempt has been made to derive a full finite element and boundary element theory for the analysis of thin and thick plates on elastic foundations. A new high order shear finite element capable of the analysis of thin thick plates has been derived using Hermitian and Lagrangian shape functions. Different new boundary element derivations for the analysis of thin plates on elastic foundations are introduced using 3 degrees-of-freedom per node. A full new derivation of boundary elements for thick plates on elastic foundations using complex Bessel functions is presented. Fourier and Hankel integral transforms have been employed for the derivation of different fundamental solutions required for boundary element analysis. Several techniques for dealing with singular and divergent integrals encountered with boundary integral equations were developed including the use of "Modified Kelvin Functions" and fictitious boundary concept. some case studies with different loading and boundary conditions were tested and proved that the new derivations presented in this work are correct and reliable for the analysis of thin and thick plates on elastic foundations.Item Open Access Structural integrity of engineering components made of functionally graded materials(Cranfield University, 2008) Oyekoya, Oyedele O.; Mba, David; El-Zafrany, A.Functionally graded materials (FGM) are composite materials with microstructure gradation optimized for the functioning of engineering components. For the case of fibrous composites, the fibre density is varied spatially, leading to variable material properties tailored to specific optimization requirements. There is an increasing demand for the use of such intelligent materials in space and aircraft industries. The current preferred methods to study engineering components made of FGM are mainly modelling particularly those that are finite element (FE) based as experimental methods have not yet sufficiently matured. Hence this thesis reports the development of a new Mindlin-type element and new Reissner-type element for the FE modelling of functionally graded composite (FGC) structures subjected to various loadings such as tensile loading, in-plane bending and out-of-plane bending, buckling and free vibration. The Mindlin-type element formulation is based on averaging of transverse shear distribution over plate thickness using Lagrangian interpolation. Two types of Mindlintype element were developed in this report. The properties of the first Mindlin-type element (i.e. Average Mindlin-type element) are computed by using an average fibre distribution technique which averages the macro-mechanical properties over each element. The properties of the second Mindlin-type element (i.e. Smooth Mindlin-type element) are computed by using a smooth fibre distribution technique, which directly uses the macro-mechanical properties at Gaussian quadrature points of each element. The Reissner-type element formulation is based on parabolic transverse shear distribution over plate thickness using Lagrangian and Hermitian interpolation. Two types of Reissner-type element were developed in this report, which include the Average and Smooth Reissner-type elements. There were two types of non-linearity considered in the modelling of the composite structures, which include finite strain and material degradation. The composite structures considered in this paper are functionally graded in a single direction only, but the FE code developed is capable of analysing composite structures with multidirectional functional gradation. This study was able to show that the structural integrity enhancement and strength maximisation of composite structures are achievable through functional gradation of material properties over the composite structures.Item Open Access Structural Integrity of Functionally Graded Composite Structure using Mindlin-Type Finite Elements.(Tech Science Press, 2008-03-01T00:00:00Z) Oyekoya, Oyedele O.; Mba, David; El-Zafrany, A.In this paper, two new Mindlin-type plate bending elements have been derived for the modelling of functionally graded plate subjected to various loading conditions such as tensile loading, in-plane bending and out-of-plane bending. The properties of the first Mindlin-type element (i.e. Average Mindlin element) are computed by using an average fibre distribution technique which averages the macro-mechanical properties over each element. The properties of the second Mindlin-type element (i.e. Smooth Mindlin element) are computed by using a smooth fibre distribution technique, which directly uses the macro-mechanical properties at Gaussian quadrature points of each element. There were two types of non-linearity considered in the modelling of the plate, which include finite strain and material degradation. The composite plate considered in this paper is functionally graded in the longitudinal direction only, but the FE code developed is capable of analysing composite plates with functional gradation in transverse and radial direction as well. This study was able to show that the structural integrity enhancement and strength maximisation of composite structures are achievable through functional gradation of material properties over the structure.