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A numerical evaluation of nonlinear material behaviour and geometric imperfections on the behaviour of #CR12 hot-rolled columns

  • Authors: Kruger, Sunita
  • Date: 2012-09-10
  • Subjects: Strength of materials , Buckling (Mechanics) , Columns, Iron and steel , Steel, Stainless , Corrosion resistant alloys , Finite element method
  • Type: Mini-Dissertation
  • Identifier: uj:9895 , http://hdl.handle.net/10210/7294
  • Description: M.Ing. , 3CR12 is corrosion-resisting steel containing 12% chrome. The corrosion-resisting characteristics of 3CR12 are between those of carbon steel and existing stainless steels. Since the material properties of 3CR12 differ from carbon steel, the current SABS code of practice cannot be utilized in the design of hot-rolled components. A numerical investigation into the effect of gradual yielding material behaviour on the buckling strength of 3CR12 columns is presented. The columns under investigation was hot-rolled channel (152 x 76 x 18) sections. The influence of material and geometric non-linearities were investigated numerically. The effect of residual stresses was also investigated. Material data for the Finite Element Model was obtained experimentally via compression tests. The magnitude and distribution of the residual stresses were obtained experimentally by using the sectioning method. The results obtained from the Finite Element Analysis are compared to the buckling load predictions of the South African Code of Practice (SABS 0162-1:1993). Conclusions are made regarding the applicability to hot-rolled 3CR12 sections.
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A numerical investigation into the behaviour of cracks in uPVC pipes under pressure

  • Authors: Cassa, Amanda Marilu
  • Date: 2012-07-19
  • Subjects: Pipe - Fluid dynamics , Numerical analysis , Piping , Finite element method
  • Type: Thesis
  • Identifier: uj:8843 , http://hdl.handle.net/10210/5255
  • Description: D.Ing. , This study is a numerical investigation into the behaviour of cracks in uPVC pipes under pressure. This study is a continuation of a Masters dissertation which showed that leakage exponents vary significantly from the theoretical orifice exponent of 0.5 for cracks in pipes for different materials. This study looks at the behaviour of cracks in more detail and specifically with regard to the parameters of the pipe and crack. Using Finite Element Analysis the relationship between the pressure head and the leak area in pipes with longitudinal, spiral and circumferential cracks was investigated. It was found that the longitudinal, spiral and circumferential crack areas increase linearly with pressure. The slope of this linear relationship depends on various parameters, including loading state, pipe dimensions and pipe material properties. The effect that the individual pipe parameters had on the pressure-area slope was investigated. These parameters included the material properties of the pipe (Young’s modulus, Poisson’s ratio and longitudinal stress), the geometry of the pipe (internal diameter and wall thickness) as well as the geometry of the crack (length of the crack and the width of the crack). Once the effect of the pressure-area slope m is known, the link between the conventional leakage exponent N1 and the pressure-area slope m was further investigated and the effect of each parameter on the leakage exponent N1 was found. Using various data techniques the above data was combined and processed to find mathematical relationships that give reasonable descriptions of the pressure-area slopes of longitudinal, spiral and circumferential cracks. Once these equations for the pressure-area slopes were determined it was possible to obtain three new relationships for leakage from longitudinal, spiral and circumferential cracks.
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An experimental and numerical evaluation of an interbody spinal fusion device

  • Authors: Rossouw, M.M.
  • Date: 2013-11-25
  • Subjects: Interbody spinal fusion device , Finite element method , Spinal implants , Spine - Mechanical properties
  • Type: Thesis
  • Identifier: http://ujcontent.uj.ac.za8080/10210/380854 , uj:7801 , http://hdl.handle.net/10210/8696
  • Description: M.Ing. (Mechanical Engineering) , A stand-alone anterior lumbar interbody fusion device is used to stabilise the spine and restore the disc space height without any other instrumentation. The stand-alone anterior lumbar interbody device is fixed to the adjacent vertebrae using titanium screws. In this research an experimental and numerical investigation on the structural strength of the SASCATM stand-alone anterior lumbar interbody fusion device are presented. The outcome of the investigation will be used as part of the device validation documentation necessary for market approval. The SASCATM device is manufactured from PEEK (a high strength polymer). Tensile and compressive testing was conducted to determine the appropriate mechanical properties of PEEK. The structural integrity of the SASCA device was evaluated by conducting full scale compression testing on a limited number of different design revisions. Comparisons as regards to their loaddisplacement behaviour were made. All specimens were visually inspected. The Finite Element Analysis (FEA) method was used in the numerical investigation of the SASCATM stand-alone anterior lumbar interbody device. Three studies were conducted. The first study aimed at comparing the full scale experimental compressive testing results with the FEA simulation. Although the desired results weren’t achieved, the model gave a fair representation of the initial region of the experimental setup in the sense that it had a similar slope. It was concluded that the nominal stress (4.1 MPa) fell within the proportional limit (35 MPa) as measured during the materials testing. The second study was aimed at determining the displacement at a worst-case load determined from the literature (2.7 kN). The study showed that the maximum Von Mises stress does not exceed the yield strength of the material. The third and final (parametric) study aimed at geometric optimisation of the cages. The motivation for the changes was based on the literature and customer suggestions for improvement. The geometric optimisation intended to show whether a desired increase in graft hole size would have an effect on the structural integrity of the device. The suggestion to move the screw holes of the threehole version closer to the center of the cage was also assessed. It was shown that enlarging the two graft holes does have an effect on the compressive strength. Higher stresses were presented in all but one case. Combining the holes also had an effect on the compressive strength. Movement of the screw holes more medially did have an impact on the compressive strength of the cages. The effect was significant. The closer the holes were to the center of the cage, the higher the Von Mises stress was. This change should therefore be considered before implementation. The results showed that different shapes and sizes of the graft holes do have an impact on the stress of this particular cage. None of the models exceeded the compressive yield strength of the material. The proposed graft hole opening design changes are therefore not warranted for the current SASCATM stand-alone anterior lumbar interbody device.
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Characterization of Bragg grating pressure sensor using finite element analysis theory and experimental results

  • Authors: Van Niekerk, Wynand F.
  • Date: 2010-10-04T08:55:31Z
  • Subjects: Bragg gratings , Fiber optics , Pressure transducers , Finite element method
  • Type: Thesis
  • Identifier: uj:6925 , http://hdl.handle.net/10210/3435
  • Description: M.Ing. , Optical fibre Bragg gratings are a periodic variation of the refractive index in the core of an optical fibre andmay be formed by exposure to intense UV laser light under specific conditions. Light at a certain wavelength, called the Bragg wavelength, is reflected back when illuminating the grating with a light source. Bragg gratings can relatively easily be employed as strain and temperature sensors, but have small sensitivity for pressure. Special transducers are required to increase the sensitivity. A pressure sensor was manufactured by coating a fibre Bragg grating with a polymer. The polymer coating converts transverse pressure into longitudinal strain through the Poisson effect inside the polymer coating. This thesis investigates the sensitivity of themanufactured Bragg grating pressure sensor, by using the method of finite element analysis. An account of the experimental setup, whereby the Bragg grating is written with a frequency tripled Nd:YAG laser, is given. The process whereby the fibre is coated with the polymer is described. The sensor is characterized through experimental results and a comparison is made between theoretical and experimental results. Uses for this sensor and ways with which the sensitivity may be increased are suggested as future work.
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Combined analytical and numerical method for magnetic component design

  • Authors: Odendaal, Willem Gerhardus
  • Date: 2015-09-08
  • Subjects: Magnetic devices , Finite element method , Semiconductor switches
  • Type: Thesis
  • Identifier: uj:14067 , http://hdl.handle.net/10210/14483
  • Description: M.Ing. , High frequency magnetic components have significant advantages related to cost and physical size compared to their low frequency counterparts. The advent of high frequency power switch technology made the transformer frequency a variable and recent advances in this field have been ever pushing the switching frequency of higher power converters. Although high frequency inductors and transformers have been used and applied extensively to an increasingly broad range of applications over recent decades, analysis and design of these devices involves certain difficulties, related to extra losses due to eddy currents as well as smaller cooling surfaces,..
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Dynamic modelling of an induced draft fan

  • Authors: Henning, Petrus Francois Joubert
  • Date: 2012-01-24
  • Subjects: Fans (Machinery) , Finite element method , Strains and stresses , Statics , Fossil fuel power plants
  • Type: Thesis
  • Identifier: uj:1934 , http://hdl.handle.net/10210/4294
  • Description: M.Ing. , The performance and reliability of induced draft fans are of ever growing concarn in industry, especially in the power generation industry. The reliability and plant efficiency depend on the design conditions of all plant components. Induced draft fans handle high temperature flyash-laden flue gas, and are often plagued by mass-flow deficiencies and excessive vibration in fossil fuel powerplants [1]. In this research an existing induced-draft fan is analysed to investigate the occurrence of high stresses forming on the impeller, as these stresses lead to cracks appearing on the centre plate of the impeller. The basic approach used to address this problem is implementing the Finite Element Method starting with different cantilever beam configurations to simulate the connection of the blade with the centre plate. Geometries are kept constant to facilitate in the practical set-up implementation stage of the dissertation. The practical set-up is used to verify the results obtained from the Finite Element Method program, and it serves as a benchmark test for evaluating the further use of the chosen Finite Element Method program. A simplified Finite Element Method model is presented for the induced draft fan. Static and frequency analyses are done to determine the characteristics of the fan structure. Lastly an advanced dynamic analysis is done on the specific fan. Different ramp force functions are used to simulate different start-up curves for the fan. A conclusion will be drawn from the dissertation, and recommendations will be made for similar future research work.
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Effect of clay-concrete lining on canal seepage towards the drainage region – an analysis using Finite-Element method

  • Authors: Solomon, Fitsum , Ekolu, Stephen
  • Date: 2014
  • Subjects: Canals , Seepage , Drainage , Finite element method , Canals - Linings
  • Type: Book chapter
  • Identifier: uj:5049 , http://hdl.handle.net/10210/13588
  • Description: For proper design of a drainage system that utilizes lined canals, knowledge of the seepage into a soil substrate/drainage region is necessary so that the drainage blanket and /or filter type and thickness, and the size of collector pipes can all be designed. The work presented in this paper is based on the problem of steady-state seepage from a hypothetical irrigation canal into the substrate/drainage region towards asymmetrical trapezoidal concrete-lined canal. The problem is solved using a finite element based software program to determine the flow volume into the drainage region. Typical values of soil permeability coefficients of single and two-layer subsoil from literature are used along with experimental results of a laboratory study done for the design seepage coefficient of clay-cement concrete as lining material. The water flow effect of canal seepage discharge analyzed shows that the effectiveness of canal lining in reducing seepage is less when drainage distance is large. This study may contribute towards a better understanding on design of hydraulic conductivity under hydraulic structures. It will systematically enumerate the many, often straightforward factors that determine coefficient of permeability for compliance purposes. This could also involve a re-estimation of the values of the permeability coefficient and the factors on which the coefficient depends.
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Effect of constitutive modeling during finite element analysis of machining-induced residual stresses in Ti6Al4V

  • Authors: Oosthuizen, Gert A. , Laubscher, Rudolph F. , Styger, Gary
  • Date: 2014
  • Subjects: Residual stresses , Titanium alloys , Finite element method , Machining
  • Type: Article
  • Identifier: uj:5028 , http://hdl.handle.net/10210/13547
  • Description: Residual stress is an important surface integrity descriptor that may have a marked effect on the functional performance of machined alloy parts. This paper describes a finite element evaluation of the effect of different constitutive models on machining induced residual stresses for Ti6Al4V titanium alloy. A two dimensional orthogonal turning process is modelled and the results compared to experimental data. Residual stress is evaluated with respect to different elastic-viscoplastic constitutive models at certain cutting speeds and feeds. The general-purpose finite element code MSC Marc@ was used with comparisons with experimental data made relative to residual stress, cutting force and temperature. The magnitude and extent (depth) of the residual stress field is evaluated with regards to the different material models and compared with experimental data.
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Evaluation of rotor design parameters for minimising torque ripple on a synchronous reluctance machine using multifactor ANOVA

Evaluering van dieptrekbaarheid van aluminiumplaat

  • Authors: Kruger, Martin J.
  • Date: 2015-09-08
  • Subjects: Finite element method , Aluminum , Sheet-metal work
  • Type: Thesis
  • Identifier: uj:14063 , http://hdl.handle.net/10210/14479
  • Description: M.Ing. , To investigate the effect of plastic anisotropy in 1200H14 Aluminium sheet, simulations of the Swift Cupping Test were carried out using the finite element program ABAQUS. Anisotropy was built into all simulations based on the plastic strain ratio which was calculated from tensile tests on specimen cut in three directions in the plane of the sheet. Deep drawing tests were carried out using a punch and die sub-assembly as described by the Swift Cupping Test. Holder loads were kept constant while the punch load and displacement were recorded. Punch force-punch displacement curve and the formation of ears were compared with experimental results.
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Method of lines based on finite element technique to analyse electromagnetic problems

  • Authors: Mushiri, Tawanda , Mbohwa, Charles
  • Date: 2015-03-03
  • Subjects: Method of lines , Computational electromagnetics , Variational analysis , Finite element method
  • Type: Article
  • Identifier: uj:5159 , http://hdl.handle.net/10210/14291
  • Description: A hybrid scheme called finite element method of lines is described and proposed for modelling and analysis of generalized computational electromagnetic problems with emphasis on a number of irregular waveguide. This finite element based method of lines is developed by combining finite element method and the method of lines, so that it not only has high flexibility to treat geometrically and compositionally complex problems but also maintains high accuracy of semi-analytical technique. Analytical and numerical algorithmic building blocks of this new scheme are discussed such as geometry discretization, element mapping, element trial functions, reformulation and computational issues of non-linear ordinary differential equations. The results therefore show that this new technique is able to efficiently solve complex problems as compared with the conventional method of lines. MATLAB was used to compute the solutions of various problems.
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Modelling of heat flow rate in cylindrical geometry based varistor arresters using finite element analysis

Nonlinear finite element program for reinforced concrete structural control

Structural integrity assessment of a low pressure turbine with transverse cracking

  • Authors: Nel, Willem Petrus
  • Date: 2009-02-26T12:21:22Z
  • Subjects: Fracture mechanics , Elasticity , Continuum mechanics , Stress corrosion , Finite element method , Steam turbines corrosion
  • Type: Thesis
  • Identifier: uj:8170 , http://hdl.handle.net/10210/2175
  • Description: M.Ing. , This dissertation deals with the structural integrity analysis of a low pressure (LP) turbine with transverse cracking. Cracks are initiated in the centre ring keyway of the shaft by a fretting mechanism and propagate during barring operation. The cracks arrest during normal operation when they are still relatively shallow. The aim of the calculations is to predict the transition where cracks start propagating by high cycle fatigue during normal operation of the shaft. Most influencing factors, including continuum mechanics, mathematical modelling, material behaviour, service loads and industry experience, are studied in detail as a precursor to the case study. The calculated results show that the case study is an example where the application of fracture mechanics on the crack-free stress field leads to erroneous results. There is a significant redistribution of stress in the presence of the crack so that the actual stress ratio, as calculated from three dimensional cracked models, varies significantly compared to the crack-free model. Calculated results, together with carefully researched material properties, confirm the postulated crack growth during barring operation and predict limiting crack sizes where high cycle fatigue would ensue during normal operation. The case study concludes that the shaft has a significant remaining life and that it can be returned to service with periodic non-destructive examinations.
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The calibration of a finite element model by means of field tests

The dynamic analysis of a curved composite bridge deck

  • Authors: Steyn, Johannes Daniel
  • Date: 2014-02-11
  • Subjects: Finite element method , Bridges - Design and construction
  • Type: Thesis
  • Identifier: uj:3861 , http://hdl.handle.net/10210/9229
  • Description: M.Ing. (Civil Engineering) , Bridge design/analysis in South Africa is seldom done from the dynamic point of view, and then only .in most exceptional cases. The topic of dynamic behavior of bridges is fairly complex and not always well understood by the average design engineer. Until the advent of 3-D finite element packages, dynamic design was usually done by assuming behaviour of simplebeams and/orplatesandequating these to the real life situation. Thesevaluescan be found in standard designbooks and tables drawnup as a result of empirical studies and analyses done in the past The author felt that there was a need for a better understanding of the dynamic behavior of bridges and to develop skills in finite element modelling and analysis. He therefore undertook to investigate and study the dynamic behavior of the Bothasfontein interchange bridge. An empirical evaluation of the composite deck was developed using Finite Element Analysis, and the results compared with the actual behavior of the bridge. Good correlation between the model and the measured values was obtained.
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The finite element method and its' link to the finite difference method for Poisson's equation

The modelling and characterization of flexible shaft couplings

  • Authors: De Wet, D.H.
  • Date: 2014-09-11
  • Subjects: Couplings, Flexible , Rubber - Analysis , Finite element method
  • Type: Thesis
  • Identifier: uj:12265 , http://hdl.handle.net/10210/12029
  • Description: M.Ing. (Mechanical Engineering) , This dissertation evaluates the suitability of the finite element method as a tool for the design and analysis of elastomeric materials in general and flexible shaft couplings in particular. The theoretical background covers numerous aspects that are essential to the comprehension of the functioning of elastomeric materials and the difficulties inherent to the numerical modelling of such materials. These aspects include the properties of rubber, the functioning and selection of flexible couplings and some details regarding linear -, non-linear - 'and dynamic finite element analysis. The problems investigated for the purposes of this study may be divided into three categories: • The capabilities of the finite element method to compare different variations of a flexible coupling design parametrically is investigated. • Uni-axial tensile - and compressive material tests are numerically simulated to assess the ability of the finite element method to predict the response of materials subjected to large-scale nonlinear deformation. The numerical results are also verified by means of physical material tests. • Based on the modelling methods that were optimized in the first two categories, a numerical model of a flexible coupling in start up mode is developed. The accuracy of predictions is evaluated by comparison with physically measured results.
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