Mechanical Engineering

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Analysis and design optimization of laminated composite structures using symbolic computation.
(1994) Summers, Evan.; Adali, Sarp.; Verijenko, Viktor.
The present study involves the analysis and design optimization of thin and thick laminated composite structures using symbolic computation. The fibre angle and wall thickness of balanced and unbalanced thin composite pressure vessels are optimized subject to a strength criterion in order to maximise internal pressure or minimise weight, and the effects of axial and torsional forces on the optimum design are investigated. Special purpose symbolic computation routines are developed in the C programming language for the transformation of coordinate axes, failure analysis and the calculation of design sensitivities. In the study of thin-walled laminated structures, the analytical expression for the thickness of a laminate under in-plane loading and its sensitivity with respect to the fibre orientation are determined in terms of the fibre orientation using symbolic computation. In the design optimization of thin composite pressure vessels, the computational efficiency of the optimization algorithm is improved via symbolic computation. A new higher-order theory which includes the effects of transverse shear and normal deformation is developed for the analysis of laminated composite plates and shells with transversely isotropic layers. The Mathematica symbolic computation package is employed for obtaining analytical and numerical results on the basis of the higher-order theory. It is observed that these numerical results are in excellent agreement with exact three-dimensional elasticity solutions. The computational efficiency of optimization algorithms is important and therefore special purpose symbolic computation routines are developed in the C programming language for the design optimization of thick laminated structures based on the higher-order theory. Three optimal design problems for thick laminated sandwich plates are considered, namely, the minimum weight, minimum deflection and minimum stress design. In the minimum weight problem, the core thickness and the fibre content of the surface layers are optimally determined by using equations of micromechanics to express the elastic constants. In the minimum deflection problem, the thicknesses of the surface layers are chosen as the design variables. In the minimum stress problem, the relative thicknesses of the layers are computed such that the maximum normal stress will be minimized. It is shown that this design analysis cannot be performed using a classical or shear-deformable theory for the thick panels under consideration due to the substantial effect of normal deformation on the design variables.
Analysis of residual stresses and distortions resulting from multi-pass welding of nozzles to cylindrical pressure vessels.
(2012) Zondi, Mthobisi Clyde.; Adali, Sarp.
The purpose of the present study is to obtain insight into the formation, behaviour and magnitude of welding-induced residual stresses and distortions resulting from welding nozzles onto cylindrical pressure vessels. A hybrid methodology that comprises numerical analysis, experimental measurements and empirical calculations is used in the present study. The welding process induces a high thermal gradient on the material due to non-uniform temperature distribution; thereby causing the portion of the material that is exposed to high temperatures to expand. However, the relatively cooler material portion that is away from the weld pool resists such expansion, thereby subjecting the structure to stresses and distortions around the fusion zone (FZ) and the heat-affected zone (HAZ). Over the last two decades a number of studies have been done in an effort to predict the effect of welding-induced residual stresses on the integrity of welded structures. However, to this end, such studies have focussed on analysing residual stresses on bead-on-plate, plate-to-plate and [to a less extent] on pipe-to-pipe weld joints. Fewer studies have looked at nozzle-cylinder joints of pressure vessels as is the case in this study. The second chapter gives a detailed review of applicable literature. The constitutive model described in the third chapter includes a two-phase sequentially-coupled thermo-mechanical analysis, which incorporates metallurgical effects. The non-linear transient problem is solved using an axisymmetric 2D model with ‘element birth’ technique, developed on ABAQUS. The first phase comprises the thermal analysis based on Goldak’s moving heat source model that is used to determine temperature histories. The second phase is a sequel stress/strain analysis wherein the temperature fields are used as input loads. The results discussed in chapters three and four show that there is a high concentration of residual stresses close to the weld centre-line, and these die down as distance away from centre-line increases. It is also shown that the inside surface is under tensile stresses, while the outer surface is under compressive stress, whose magnitude approaches yield strength of the material. Axial deflections of up to 0.384mm and radial shrinkage of 0.0237mm are observed. Distortion decreases as distance away from weld centre-line increases. Minimum axial shrinkage, which is close to zero, is observed at the restrained end. The analytical results show adequate corroboration and agreement with the experimental measurements. A number of mitigation techniques are suggested in order to alleviate the impact of residual stress and distortions on fatigue performance of welded structures.
Buckling of short, thin-walled cylinders, as applied to storage tanks.
(2001) Du Poujol, Geraldine Touche.; Bodger, Robert.; Adali, Sarp.
This is an investigation of the buckling characteristics of short, thin-walled cylinders. This study was required as large storage tanks, which were converted from Boating roof to fixed roofed tanks, were found to buckle when severe atmospheric temperature drops and thus pressure differentials occurred. These severe ambient temperature changes are characteristic of the Highveld in South Africa where the tanks in question are situated. Since this modification is an uncommon procedure, codes of practice for storage vessels do not cover this type of cylinder. For the same reason, research performed in this field is limited. Buckling due to axial loading, lateral external pressure, hydrostatic pressure and a combination of axial loading and hydrostatic pressure are explored in this study. To compare with and verify theory, existing research for each case is examined, and the Finite Element Analysis package MSC Nastran used to determine trends. In some cases, to the best of the author's knowledge, no research exists and numerical analysis is performed to establish the relationships present in those cases. The study is extended to include the design of imperfect cylinders, as defined in the tank code AD Merkblatter where it is stated as being dependant on the major and minor diameters of the imperfect section . The study is also extended to the case of variable wall thickness cylinders, where the thickness variation is symmetrical about the axis of the cylinder.
Buckling of woven fibre and graphene platelet reinforced nanocomposite laminates.
(2021) Sewnath, Kiren.; Adali, Sarp.; Drosopoulos, Georgios A.
Composite materials are known for exhibiting high specific stiffness, strength and light weight. Their properties can be optimized by designers for a specific application. They currently have many applications in various industries such as aerospace, automotive and building industries. Fibre reinforced polymer composites are a large portion of the composite material market. The use of such materials has many advantages. Recently, nanosized reinforcements such as carbon nanotubes and graphene nanoplatelets have also been used as filler materials in composites. Graphene is one of the strongest materials available today and exhibits excellent mechanical properties. The study presented here is an investigation into the buckling of a woven glass fibre and graphene nanoplatelet reinforced epoxy composite. A laminate analogy is utilised. The analytical equations governing these types of laminates are presented and incorporated into Matlab, a computer simulation software that makes use of matrix implementations. The programme is then used to investigate the effects of various design parameters on the buckling load, by generating 2D and 3D graphs. In this study, a laminate analogy is used for the woven glass fibres whereby undulation of the fibres is neglected, and the composite is regarded as an assembly of cross-ply laminates with woven fibres orientated at 90° to each other. The Halpin-Tsai equations are used to incorporate the graphene nanoplatelets into the epoxy matrix. The laminate that is investigated consists of 4 plies, each reinforced by woven glass fibres and graphene nanoplatelets. The laminate is symmetric about its midpoint, such that the two outer layers are identical, and the two middle layers are identical. Layer thicknesses are non-uniform and the reinforcements are distributed non-uniformly in the layers. The thickness ratio of the laminate is defined as the ratio of the total width of the outer layers to the entire laminate thickness. The governing equations of classical laminate theory for buckling of a simply-supported rectangular plate under biaxial loading are used to predict the critical buckling load of the laminate. The bending-twisting coupling terms are neglected. The results generated display the influence of various design parameters on the buckling load. The design parameters investigated are the woven glass fibre volume fraction, woven glass fibre orientation, woven glass fibre balancing coefficient, graphene platelet weight fraction, laminate thickness ratio and laminate aspect ratio. The results show that the graphene nanoplatelets have a greater effect on the buckling load than the woven glass fibres. High graphene content can obscure the effect of the woven fibre orientation and laminate aspect ratio on the buckling load. At low graphene contents, a more concentrated fibre distribution in a single direction (warp or weft) is preferred for the buckling load. At higher graphene content, a more evenly balanced distribution is preferred. Furthermore, for high thickness ratios, more focus must be placed in the reinforcements in the outer layer of the laminate for a cost-effective design.
A comparative study on the effects of internal vs external pressure for a pressure vessel subjected to piping loads at the shell-to-nozzle junction.
(2003) Maharaj, Ashveer.; Adali, Sarp.; Von Klemperer, Christopher Julian.
This investigation seeks to perform a comparative study between the combined effects of internal pressure and piping loads versus external pressure and piping loads on a pressure vessel. There are currently several well-known and widely-used procedures for predicting the stress situation and the structural stability of pressure vessels under internal pressure when external piping loads (due to thermal expansion, weight, pressure, etc.) are applied at the nozzles. This project familiarises one with several international pressure vessel design Codes and standards, including AS ME (American Society of Mechanical Engineers) pressure vessel code sections and WRC (Welding Research Council) bulletins. It has been found that many vessels are designed to operate under normal or steam-out conditions (in vacuum). The combined effect of the external atmospheric pressure and the piping loads at the nozzle could be catastrophic if not addressed properly - especially when the stability of the structure is a crucial consideration, i.e. when buckling is a concern. The above-mentioned codes and standards do not directly address procedures or provide acceptance criteria for external loads during vacuum conditions. The approach to the study was, firstly, to investigate the effects of internal pressure and piping loads at the shell-to-nozzle junction. Theoretical stresses were compared with Finite Element results generated using the software package MSC PATRAN. Finite Element Methods provide a more realistic approach to the design of pressure vessels as compared to theoretical methods. It was necessary to determine if the theoretical procedures currently used were adequate in predicting the structural situation of a pressure vessel. Secondly, the buckling effects of vessels subjected to external atmospheric pressure and piping loads were also investigated. Buckling of the shell-to-nozzle region was explored with the aid of Finite Element software. The results gained were used to develop appropriate procedures for the design of vessels under external atmospheric pressure and piping loads. The design is such that it indicates if buckling will occur at the shell-to-nozzle junction. These design procedures form the basis for future exploration in this regard.
Computational and analytical modelling of composite structures based on exact and higher order theories.
(1995) Tabakov, Pavel.; Adali, Sarp.; Verijenko, Viktor.
The objective of the present study is the computational and analytical modelling of a stress and strain state of the composite laminated structures. The exact three dimensional solution is derived for laminated anisotropic thick cylinders with both constant and variable material properties through the thickness of a layer. The governing differential equations are derived in a such form that to satisfy the stress functions and are given for layered cylindrical shell with open ends. The solution then extended to the laminated cylindrical shells with closed ends, that is to pressure vessels. Based on the accurate three-dimensional stress analysis an approach for the optimal design of the thick pressure vessels is formulated. Cylindrical pressure vessels are optimised taking the fibre angle as a design variable to maximise the burst pressure. The effect of the axial force on the optimal design is investigated. Numerical results are given for both single and laminated (up to five layers) cylindrical shells. The maximum burst pressure is computed using the three-dimensional interactive Tsai-: Wu failure criterion, which takes into account the influence of all stress components to the failure. Design optimisation of multilayered composite pressure vessels are based on the use of robust multidimensional methods which give fast convergence. Transverse shear and normal deformation higher-order theory for the solution of dynamic problems of laminated plates and shells is studied. The theory developed is based on the kinematic hypotheses which are derived using iterative technique. Dynamic effects, such as forces of inertia and the direct influence of external loading on the stress and strain components are included at the initial stage of derivation where kinematic hypotheses are formulated. The proposed theory and solution methods provide a basis for theoretical and applied studies in the field of dynamics and statics of the laminated shells, plates and their systems, particularly for investigation of dynamic processes related to the highest vibration forms and wave propagation, for optimal design etc. Geometrically nonlinear higher-order theory of laminated plates and shells with shear and normal deformation is derived. The theory takes into account both transverse shear and normal deformations. The number of numerical results are obtained based on the nonlinear theory developed. The results illustrate importance of the influence of geometrical nonlinearity, especially, at high levels of loading and in case when the laminae exhibit significant differences in their elastic properties.
Design and optimisation of a composite space frame chassis including experimental and computational analysis.
(2017) Narsai, Mikhail.; Adali, Sarp.; Padayachee, Jared.; Veale, Kirsty Lynn.
Composites are used in lightweight structural designs. In this dissertation, a robust carbon fibre reinforced polymer (CFRP) space frame chassis for a lightweight electric tricycle is produced. In large, most composite research is directed toward flat laminates rather than closed sections. This dissertation addresses the complexities of stresses at joints and buckling (local and global). The space frame design consists of two segments of iterations. The second and more important segment is based on optimisation using NX Nastran finite element analysis (FEA). The final design incorporates the use of steel sleeves to address stress concentrations at joins and local buckling. The design and execution of a new test method was developed to validate FEA results. The test method involves applying compressive stress on tubes fabricated using unidirectional (UD) fibre set at 35°, to induce compressive and shear stresses along the primary fibres. In this way, four major failure criteria were compared: Tsai-Wu, Hoffman, Hill and Maximum Strain. The Hoffman and Tsai-Wu criteria were shown to be accurate and conservative. The Hill criteria showed inaccuracy by having incorrectly high strength ratios, while the Maximum Strain criteria had the highest strength ratio, proving to be the least conservative and most inaccurate. This dissertation shows that certain failure criteria may be used confidently in applications such as filament winding and continuous pulComposites are used in lightweight structural designs. In this dissertation, a robust carbon fibre reinforced polymer (CFRP) space frame chassis for a lightweight electric tricycle is produced. In large, most composite research is directed toward flat laminates rather than closed sections. This dissertation addresses the complexities of stresses at joints and buckling (local and global). The space frame design consists of two segments of iterations. The second and more important segment is based on optimisation using NX Nastran finite element analysis (FEA). The final design incorporates the use of steel sleeves to address stress concentrations at joins and local buckling. The design and execution of a new test method was developed to validate FEA results. The test method involves applying compressive stress on tubes fabricated using unidirectional (UD) fibre set at 35°, to induce compressive and shear stresses along the primary fibres. In this way, four major failure criteria were compared: Tsai-Wu, Hoffman, Hill and Maximum Strain. The Hoffman and Tsai-Wu criteria were shown to be accurate and conservative. The Hill criteria showed inaccuracy by having incorrectly high strength ratios, while the Maximum Strain criteria had the highest strength ratio, proving to be the least conservative and most inaccurate. This dissertation shows that certain failure criteria may be used confidently in applications such as filament winding and continuous pultrusion methods, which are widely used in producing closed sections.trusion methods, which are widely used in producing closed sections.
Design and testing of a composite material for modelling wind turbine blade structures in tropical region.
(2018) Tefera, Getahun Akulu.; Adali, Sarp.; Bright, Glen.; Davidson, Innocent Ewean.
Currently large wind turbine blades have been installed in several offshore and onshore wind farms around the world, particularly in the desert areas of North East Africa where wind turbine blades and nacelles are affected by elevated temperatures. The aim of this study is to investigate the effect of temperature variation on the mechanical behaviour of composite wind turbine blades installed in tropical wind farms. The blades are constructed from unidirectional carbon fibre/epoxy, glass fibre/epoxy and hybrids of these two composite materials. ASTM standards were taken into account when the composite specimens were manufactured for testing purposes. Short Beam Shear (SBS), Dynamic Mechanical Analysis (DMA) and tensile tests were conducted under increasing temperatures to investigate the mechanical behaviour of composite materials when used for structural modelling of wind turbine blades. Experimental findings revealed that the strength and stiffness properties of composite specimens were reduced when temperatures increased. Betz’s element momentum theory and Glauert’s modelling methods were used to investigate the characteristics of composite wind turbine blades measuring 54m and generating 2MW power. Flap-wise loading was taken into account along the length of the wind turbine blades when they were analysed using the Blade Element Momentum (BEM) theory. The wind turbine blades were developed using carbon fibre/epoxy, glass fibre/epoxy, glass-carbon fibre/epoxy and carbon-glass fibre/epoxy composite materials. The tip deflection of the blades was analysed allowing for different flap-wise and thermal loadings. Simulation results indicated that a glass/epoxy blade has the highest and a carbon/epoxy blade the lowest tip deflection. The values for the tip deflections of the blades show minimal change under thermal loading. To study the mechanical behaviour of the blades under thermal loading, an element-wise approach was developed and the failure index for different composite materials was computed. Tsai-Wu failure criterion was employed to determine the failure index of each composite material under thermal and mechanical loadings. Blades failed when the thermal loading was above 40ºC irrespective of the flap-wise loading. This finding was similar to the experimental results mentioned above. Carbon/epoxy showed non-linear behaviour when the test temperature approached 40ºC. Generally, experimental and numerical results are comparable and can be considered valid. To conclude carbon-glass fibre/epoxy composite wind turbine blades are observed to be a better option for tropical wind farms based on experimental and simulation results. Iqoqa Njengamanje sekufakwe ophephela bomoya abakhulu emapulazini amaningi omoya asolwandle nasezweni emhlabeni jikelele, ikakhulukazi ezindaweni eziwugwadule zaseMpumalangantshonalanga Afrika lapho amazinga okushisa aphakeme enomthelela kophephela bomoya nakuzembozo zezihambisiphephela. Inhloso yalolu cwaningo ngukuhlola umthelela wokuguquguquka kwamazinga okushisa endleleni okusebenza ngayo ophephela bomoya abafakwe emapulazini asezindaweni ezishisa kakhulu. Ophephela bakhiwe ngomabhekanxazonke befayibha yekhabhoni/ ephoksi, ifayibha yengilazi/ephoksi, Kucatshangelwe amazinga e-ASTM ngenkathi kwakhiwa amasampula ayindidiyela ngenhloso yokuhlola. Kwenziwe uhlelo lwe-Short Beam Shear (SBS), Dynamic Mechanical Analysis (DMA) nokuhlola kwamathensayili ngaphansi kwamazinga okushisa anyukayo, ukuhlola indlela ezisebenza ngayo izakhi eziyindidiyela uma zisetshenziselwa ukubona ukuthi singama kanjani isakhiwo sophephela bomoya. Imiphumela yokuhlola iveze ukuthi amazinga amandla nokuqina kwamasampula ayindidiyela kwehlile uma kunyuswa amazinga okushisa. Kusetshenziswe injulalwazi ka-Betz yomthamosivinini kanye nezindlela zika-Glauret zesibonelokulinga ukuhlola izimpawu zophephela bomoya abayindidiyela, abanesikalo esingu-54m futhi esiphehla amandla angu-2MW. Kucatshangelwe isisindo sokuthwala uma ophephela bebheke phansi noma phezulu ngokunjalo nobude bophephela bomoya ngenkathi behlaziywa, kusetshenziswa injulalalwazi i-Blade Element Momentum (BEM). Ophephela bomoya benziwe kusetshenziswa izakhi eziyindidiyela zefayibha yekhabhoni/ ephoksi, ifayibha yengilazi/ ephoksi nefayibha yekhabhoni-ngilazi/ ephoksi. Impebezo yezihloko zophephela ihlaziywe kuvunyelwa okuhlukahlukene kwesisindo sokuthwala netemali, uma ophephela bebheke phansi noma phezulu. Imiphumela yokulingisa ikhombise ukuthi uphephela wengilazi/ ephoksi unempebezo yesihloko ephakene kanti uphephela wekhabhoni/ ephoksi unempebezo yesihloko ephansi. Amavelu empebezo yezihloko zophephela akhombisa uguquko olusesilinganisweni esincane, ngaphansi kokulayishwa kwetemali. Ukucwaninga okwenziwa ngophephela okuphathelene nokusebenza kwemishini uma kulayishwe itemali, kwenziwe ngokuqamba indlela evuna i-elementi, kwase kwenziwa uhlelo lokubala ngekhompyutha inkomba kwehluleka yezakhi eziyindidiyela ezihlukahlukene. Kuthathwe indlelakukhetha kuhluleka kaTsai-Wu ukubona inkomba kuhluleka yesakhi ngasinye esiyindidiyela uma kulayishwe itemali nokusebenza ngemishini. Ophephela behlulekile uma umthamo wetemali ungaphezu kuka-40ºC kungakhathaliseki izinga kulayisha elivuna ukubheka phansi noma phezulu kophephela. Okutholakele bekufana nemiphumela yokuhlola ebalulwe ngenhla. Ikhabhoni/ ephoksi ikhombise indlela okwenza ngayo ophephela engaqondile uma amazinga okushisa okuhlola esondela ku-40ºC. Ezimweni eziningi, imiphumela yokulinga neyezibalo iyaqhathaniseka futhi ingase ibhekwe njengekholakalayo. Ukuphetha, ophephela bomoya abayindidiyela yefayibha yekhabhoningilazi/ ephoksi babonakala beyisu elingalunga kahle emapulazini omoya uma kuthathelwa emiphumeleni yokuhlola nokufanisa.
A design methodology investigation and the design of a material handling system.
(2000) Govender, Daryl Sebastian.; Adali, Sarp.; Verijenko, Viktor.
This dissertation is undertaken under the auspices of both the CSIR, Division of Mining Technology and the University of Natal, School of Mechanical Engineering. The CSIR have outlined two fundamental objectives of the dissertation. Firstly, the need for competent design engineers has become increasingly evident. To this end, an evaluation and research into the science of design methodology has been conducted and regarded as a significant component of the thesis. The rationale behind this aim is that the subject of design has been practiced for thousands of years, but an understanding of the process is comparably in its infancy. The importance of the steps involved in the mechanical design process can in no uncertain terms be overemphasized as the adherence there to results in designs that are least likely prone to failure as well as the attainment of highly efficient product design time scales. This is vitally important more especially when the drive towards multifunctional multidisciplinary teams is rapidly developing in the global market place. Secondly, the CSIR, having done the appropriate market research, have defined the need for the design of a timber handling system to be implemented in a deep level mining environment. It is the authors expressed intent not to separate the theory from the design at hand but rather to allow this thesis to become, for the reader, forum where a holistic and integrated approach to design can be presented.
Development of a design methodology of a composite monocoque chassis.
(2018) Denny, Jason Andrew.; Adali, Sarp.; Veale, Kirsty Lynn.; Leverone, Fiona Kay.
The concept of the composite monocoque chassis has been implemented in many vehicle designs; however, there is little open-access literature defining the primary considerations when simulating one. The purpose of this research is to develop a methodology for determining the structural integrity of a composite monocoque chassis, through finite element analysis, with the intention of developing a lightweight solar powered vehicle. Factors that influence this methodology include; the definition of the vehicle loading conditions, failure criteria, and important design parameters, chief among which is the torsional stiffness. Chassis design specifications were developed from the 2017 Bridgestone World Solar Challenge rules and regulations as these are the most common and complete specifications for this particular type of vehicle. The primary design criteria considered is the torsional stiffness, which was determined from the application requirements and literature, and resulted in a suitable value of 4000 Nm/deg. Siemens NX Nastran was used to develop a torsional stiffness model, which uses the torsional loading condition, to determine the torsional stiffness value. The design methodology then follows an iterative process where various geometry and layup modifications were considered, under the same loading conditions, with the aim of increasing the torsional stiffness to achieve the required value. Aerodynamic properties were adapted from existing UKZN solar vehicle knowledge; however, this research does not consider the optimisation of the aerodynamic properties of a monocoque chassis. Only a structural simulation was conducted. The ultimate strength of the material was also considered throughout the simulation process, however in all cases the model failed to meet the required torsional stiffness parameter before material failure modes. The door recesses had the most significant effect on the torsional stiffness. By compacting the door recesses the torsional stiffness was increased by 29.04 %. A final torsional stiffness was of 4097 Nm/deg was attained with the implementation of an aluminium honeycomb core. Additionally; an analysis of the mounting points was conducted to ensure that the layup can withstand the concentrated loads at the suspension mounts. This analysis is concerned with the principal stresses, where the principal stresses give insight into the most suitable orientation of the layup. The torsional stiffness model resulted in a maximum principal stress of 81.68 MPa, below the 464.4 MPa tensile strength of the reinforcement material orientated in the direction of the fibres. To verify the significance of the torsional stiffness failure criterion, vertical and lateral bending analyses were conducted. A vertical bending model was developed where the chassis is modelled as a simply supported beam, simulating the squatting and diving of a chassis under acceleration and deceleration respectively. The maximum deflection was 5.28 mm, which is below the vi maximum allowable deflection of 12.29 mm, determined from a maximum deflection ratio of 1/360th of chassis length. A lateral bending model modelled the chassis as a simply supported beam with the maximum stress being analysed. The maximum stress experienced by the chassis under this loading condition was 18.73 MPa, which was 75.8 % less when compared to the maximum stress exhibited by the chassis under the torsional loading condition. Flexural bending tests were conducted on various laminate sandwich structures used in the finite element analysis to validate the simulation material properties. The peak load and mid-span deflection of each specimen was recorded to determine the maximum flexural stress and flexural modulus of elasticity. The flexural stress at specific midspan deflections was compared, under the same loading conditions, to that of the bending stress exhibited by a flexural bend test model finite element analysis conducted in Siemen’s NX Nastran. Graphs of the stress versus midspan deflection were plotted for each specimen layup type and the curves of the simulated and experimental results were compared. In each laminate sandwich structure case, the simulation curve exhibited a linear relationship between the midspan deflection and flexural bend stress and the experimental curve exhibited a linear relationship until the elastic limit of the specimens was reached. Thereafter the curve exhibited an exponential relationship as plastic deformation occurs until the specimen failure. An iterative finite element analysis design methodology was used to develop a composite monocoque chassis. The design process of a composite monocoque chassis is simplified by using finite element analysis to iterate through many different configurations, such as core thicknesses, layup orientations, and geometry features, to customise the properties of the structure. With these properties, it is possible to determine chassis performance. The finite element analysis results illustrated that geometry modifications, such as compacting door recesses, and applying strategic layup orientations, such as implementing a honeycomb core, significantly affected the torsional stiffness of a chassis. In addition, a chassis with sufficient torsional stiffness exhibits sufficient bending stiffness. The methodology presented in this research stands to be supportive in designing a fully composite monocoque chassis for lightweight race vehicle applications.
Dynamic stability and buckling of viscoelastic plates and nanobeams subjected to distributed axial forces.
(2016) Robinson, Mouafo Teifouet Armand.; Adali, Sarp.
Plates and beams are typical examples of structures that must be analyzed and understood. Buckling and vibration represent for such structures a potential source of fatigue and damage. Damage and fatigue are often caused by axial forces. The current research uses differential quadrature method to study the stability of viscoelastic plate subjected to follower forces in one hand, and the Rayleigh-Ritz method to analyze the buckling of Carbone nanotubes subjected to point and axial load in other hand. For plate, the 3D relation of viscoelastic is used to derive the equation of vibration of viscoelastic rectangular plate subjected to follower force. This equation is solved numerically by differential quadrature method, then the dynamic stability analysis is done by plotting the eigenvalues versus the follower force. We employ the Euler Bernoulli beam theory and the nonlocal theory to derive the equation of equilibrium of Carbone nanotubes subjected to point and axial loads. Rayleigh-Ritz method is used to calculate buckling loads, and the effects of equation's parameters on that buckling loads are analysed properly. Frequencies of vibration of viscoelastic plates and critical load obtained by using differential quadrature method are compared to other results with good satisfaction. The same satisfaction is observed when the buckling load values of Carbone nanotubes obtained using the Rayleigh-Ritz methods are compared to those existing in the literature. The cantilever viscoelastic plate undergoes flutter instability only and the delay time appears to influence that instability more than other parameters. The SFSF plate undergoes divergence instability only. The both types of instability are observed CSCS plate subjected to uniformly follower load but the flutter instability disappears in presence of triangular follower load. The values of the mentioned critical loads increase with triangular follower load for all boundary conditions. The aspect ratio has a large influence on the divergence and flutter critical load values and little influence on the instability quality. The laminar friction coefficient of the flowing fluid increases the critical fluid velocity but its effect on the stability of viscoelastic plate behavior is minor. The nonlocal parameter appears to decrease buckling load considerably. Buckling is more sensitive to the magnitude of the tip load for the clamped-free boundary conditions. The application of the present theory to a non-uniform nanocone shows that the buckling loads increases with radius ratio and decreases with small scale constants.
Effect of displacement feedback control on the frequencies of cantilevered beams with tip mass and axial load using piezo actuators.
(2014) Moutlana, Malesela K.; Adali, Sarp.
This work provides a study of the natural frequencies of a cantilevered beam with tip mass and axial load. Displacement feedback control is applied using piezo actuators attached to the top and bottom of the beam. The center of gravity of the mass and its rotary inertia are accounted for in the solution. The analysis of flexible components is essential to provide for the successful design of various engineering structures. This study provides an analytical solution to the dynamic behavior of a cantilevered beam carrying a mass at the free end, while being subjected to constant axial load. The structure is modeled using the Euler-Bernoulli theory and the contributions of the mass, thickness and stiffness of the piezoelectric actuators to the structure are taken into account. The effects of the piezo input voltage polarity is also taken into account. The natural frequencies of the beam can be altered by applying a voltage in the desired polarity and thereby causing an extension or contraction in the piezo actuator. This mechanical response alters the frequencies of the piezoelectric beam. The piezoelectric effect causes a compression or extension strain when a voltage is applied along the direction of polarization. The strain in the piezoelectric beam causes a moment at the free end, which directly affects the natural frequencies. By applying a voltage in the same or opposite direction of the poling of the piezo, the result is a compression or extension perpendicular to the poling. An applied voltage in the same direction can be considered positive and reduces the frequencies, whilst in the opposite direction negative and increases the natural frequencies. In this investigation the piezo layer thickness is varied, which in turn allows for a variable voltage input. For a thicker layer, the voltage can be increased and the actuation strain increased. The frequency content of the dynamically varying forces applied to a structure has the potential to excite the structure at one or more of its natural frequencies. Using piezo actuators, the natural frequencies and the natural frequency gaps can be maximized. Maximizing the natural frequencies is useful to avoid resonance when the external excitation frequency is less than the natural frequency.
Effect of flexible supports on the frequencies of nanobeams with tip mass and axial load for applications in atomic force microscopy (AFM)
(2020) Moutlana, Malesela Kenneth.; Adali, Sarp.
This aim of this investigation is to describe the mechanical performance of a beam (probe) used in dynamic atomic force microscopy (dAFM) which can be utilized in scanning the topographical features of biological samples or "pliable" samples in general. These nanobeams can also be used to modify samples by using high frequency oscillating contact forces to remove material or shape nano structures. A nanobeam with arbitrary boundary conditions is studied to investigate different configurations and the effects of the relevant parameters on the natural frequencies. The nano structure is modelled using the Euler-Bernoulli theory and Eringen's theory of nonlocal continuum or first order stress-gradient theory is incorporated to simulate the dynamics of the system. This theory is effective at nanoscale because it considers the small-scale effects on the mechanical properties of the material. The theory of Nonlocal continuum is based on the assumption that the stress at a single point in the material is influenced by the strains at all the points in the material. This theory is widely applied to the vibration modelling of carbon nanotubes in several studies. The system is modelled as a beam with a torsional spring boundary condition that is rigidly restrained in the transverse direction at one end. The torsional boundary condition can be tuned, by changing the torsional spring stiffness, such that the compliance of the system matches that of the sample to prevent mechanical damage of both the probe tip and the sample. When the torsional spring stiffness is zero, the beam is pinned and when the stiffness is infinite, the beam is a cantilever. In the first case, a mass is attached to the tip and a linear transverse spring is attached to the nanobeam. The mass and spring model the probe tip and contact force, respectively. In the second case, at the free end is a transverse linear spring attached to the tip. The other end of the spring is attached to a mass, resulting in a single degree of freedom spring-mass system. When the linear spring constant is infinite, the free end behaves as a beam with a concentrated tip mass. When the mass is infinite, the boundary condition is that of a linear spring. When the tip mass is zero, the configuration is that of a torsionally restrained cantilever beam. When tip of the nanobeam vibrates, the system behaves like a hammer and chisel. The motion of the tip of the beam and tip mass can be investigated to observe the tip frequency response, force, acceleration, velocity and displacement. The combined frequencies of the beam and spring-mass systems contain information about the maximum displacement amplitude and therefore the sample penetration depth.
Finite element and analytical solutions for the optimal design of laminated composites.
(1996) Reiss, Talmon.; Adali, Sarp.; Walker, Mark.
The present study involves the analysis and design optimisation of composite structures using analytical and numerical methods. Five different problems are considered. The first problem considers the design of laminated plates subject to non-uniform temperature distributions. The plates are optimised for maximum buckling temperature using the fibre angle as the optimising variable. The method of solution involves the finite element method based on Mindlin theory for thin laminated plates and shells, and numerical optimisation. A computational approach is developed which involves successive stages of solution for temperature distribution, buckling temperature and optimal fibre angle. Three different temperature loadings are considered and various combinations of simply supported and clamped boundary conditions are studied. The effect of plate aspect ratio on the optimal fibre angle and the maximum buckling temperature is investigated. The influence of bending-twisting coupling on the optimum design is studied by considering plates with increasing number of layers. The second problem concerns the optimal design of composite pressure vessels. Finite element solutions are presented for the design of hemispherically and flat capped symmetrically laminated pressure vessels subjected to external pressure. The effect of vessel length, radius and wall thickness, as well as bending-twisting coupling and hybridisation on the optimal ply angle and buckling pressure are numerically studied. Comparisons of the optimal fibre angles and maximum buckling pressures for various vessel geometries are made with those for hybrid pressure vessels. In the third problem, the multiobjective design of a symmetrically laminated shell is obtained with the objectives defined as the maximisation of the axial and torsional buckling loads. The ply angle is taken as the optimising variable and the performance index is formulated as the weighted sum of individual objectives in order to obtain Pareto optimal solutions of the design problem. Single objective design results are obtained and compared with the multiobjective design. The effect of weighting factors on the optimal design is investigated. Results are given illustrating the dependence of the optimal fibre angle and performance index on the cylinder length, radius and wall thickness. In the fourth problem, the optimal layup with least weight or cost for a symmetrically laminated plate subject to a buckling load is determined using a hybrid composite construction. A hybrid construction provides further tailoring capabilities and can meet the weight, cost and strength constraints while a non-hybrid construction may fail to satisfy the design requirements. The objective of the optimisation is to minimise either the weight or cost of the plate using the ply angles, layer thicknesses and material combinations as design variables. As the optimisation problem contains a large number of continuous (ply angles and thicknesses) and discrete (material combinations) design variables, a sequential solution procedure is devised in which the optimal variables are computed in different stages. The proposed design method is illustrated using graphite, kevlar and glass epoxy combinations and the efficiency of the hybrid designs over the non-hybrid ones are computed. Finally, the minimum deflection and weight designs of laminated composite plates are given in the fifth and last problem. The finite element method is used in conjunction with optimisation routines in order to obtain the optimal designs, as was the procedure in the first problem. Various boundary conditions are considered and results are given for varying aspect ratios and for different loading types.
Finite element modelling of smart TRIP steel sensors and systems.
(2003) Jonson, David.; Verijenko, Viktor.; Adali, Sarp.
Transformation Induced Plasticity (TRIP) steels undergo a phase transformation when subjected to high levels of mechanical strain. This transformation from a paramagnetic austenitic parent phase to a ferromagnetic martensitic phase is irreversible and the resultant magnetic properties may therefore be used as a measure of strain history. The transformation behaviour of TRIP steels has been recognised as a potential smart characteristic and various proposals have appeared aimed at producing a structure that performs its primary structural function as well a strain sensing function simultaneously. However the strain induced nature of the transformation implies that transformation will occur in areas of high stress concentration and therefore engineered stress concentration features will be required to provide a consistent measure of the changes in the magnetic properties of the material as a function of applied load. In order to predict the performance of smart TRIP steel sensors, an analysis method capable of quantifying the effectiveness of a component in its dual role as structure and sensor is needed. The thesis addresses the development of a methodology for correlating the changing magnetic permeability of TRIP steel sensors and structures with martensitic transformation behaviour. The prediction of the deformation behaviour including transformation is implemented by considering a mechanical analysis based on the finite element method and a constitutive model incorporating strain-induced martensitic transformation kinetics. .Extensions to the model which allow for a wide range of deformation rates and temperatures are also discussed. In order to demonstrate the application of the methodology, an analysis of a simple tensile element used in strain measurement applications is presented. The analysis also includes the effect of temperature on the performance of the sensor. An analysis of a design proposal for a smart aircraft bolt is also included to investigate the effects of geometry, particularly engineered stress concentrations, and sensor placement.
Finite element solutions of optimization problems with stability constraints involving columns and laminated composites.
(2006) Cagdas, Izzet Ufuk.; Adali, Sarp.
The primary aim of this study is to assess the applicability and performance of the finite element method (FEM) in solving structural optimization problems with stability constraints. In order to reach this goal, several optimization problems are solved using FEM which are briefly described as follows: The strongest column problem is one of the oldest optimization problems for which analytical solutions exist only for some special cases. Here, both unimodal and bimodal optimization of columns under concentrated and/or distributed compressive loads with several different boundary conditions and constraints are performed using an iterative method based on finite elements. The analytical solutions available in the literature for columns under concentrated loads and an analytical solution derived for simply supported columns under distributed loads are used for verification purposes. Optimization results are presented for fibre-reinforced composite rectangular plates under inplane loads. The non-uniformity of the in-plane stresses due to stress diffusion and/or in-plane boundary conditions is taken into account, and its influence on optimal buckling load is investigated. It is shown that the exclusion of the in-plane restraints may lead to errors in stability calculations and consequently in optimal design. The influences of the panel aspect ratio, stacking sequence, panel thickness, and the rotational edge restraints on the optimal axially compressed cylindrical and non-cylindrical curved panels are investigated, where the optimal panel is the one with the highest failure load. The prebuckling and the first-ply failure loads of the panels are calculated and minimum of these two is selected as the failure load. The results show that there are distinct differences between the behaviour of cylindrical and non-cylindrical panels. The formulations of the finite elements which are used throughout the study are given and several verification problems are solved to verify the accuracy of the methodology. The computer codes written in Matlab are also given in the appendix sections accompanied with the selected codes used for optimization purposes.
Hybrid nanoshell reinforced plant fiber biocomposite.
(2020) Gbadeyan, Oluwatoyin Joseph.; Adali, Sarp.; Glen, Bright.; Sithole, Bishop Bruce.
Abstract available in PDF.
Influence of wagon structure on the vertical response of freight.
(2002) Loubser, Richard Clive.; Kaczmarczyk, Stefan.; Adali, Sarp.
Historically, wagons have been designed according to the American Association of Railroads specifications. These require that wagons be designed to withstand a static load between the couplers of 350 tons. This implies that the structure has a certain stiffness. In order to improve load to tare ratio, there has been talk of reducing the end load specifications. This implies that the stiffness of the wagon will reduce. Using more flexible wagons implies that the freight will probably be exposed to a harsher dynamic environment. There is a trade off between the cost of packaging and the cost of protection devices installed in the vehicle. If handling damage can be prevented then an understanding of the dynamic environment will assist in reducing the packaging requirement. This research looked at the dynamic characteristics of an existing design of wagon using modal analysis. The results from the modal analysis were extended to be inputs to the time domain freight model. Various analytical models of the freight were developed depending on the configuration and dynamic properties. Special consideration was given to a cylinder with its axis transverse to the wagon. The modal model was modified to accommodate the change in mass imposed by the freight. The various sources of dynamic excitation were explored, namely inputs from the coupler and from the bogie. Data from shunting yard simulations were used to generate spectra as input to the wagon model. The objective was to use modal techniques to be able to take individual components, form them into a complete model and make informed decisions about the suitability of a certain configuration for traffic.
Investigation and design of wet-mill equipment and process technology.
(2003) Smith, Lisa Noelle.; Bodger, Robert.; Adali, Sarp.
need to dry-mill the wheat into flour, and as a result, the total cost of conversion from wheat to bread is reduced. The resulting product has been perceived as being more filling than normal bread and it is also more nutritious and more affordable. The wet-mill concept was developed in a laboratory environment and no process methodology or equipment has existed to enable the technology to be used in a real bakery environment. The focus of this research was to design the particular equipment required for a medium plant-bakery production facility based on the wet-mill technology. Due to severe overcapacity in the bread-making industry, the research focuses on how best to integrate this equipment into an existing production facility. Three broad areas are investigated: • Product Development • Process Design • Machine Design The aim of the Product Development phase was to create a recipe that would withstand the rigours of the plant bakery environment, while at the same time satisfying consumer demand for taste and texture. The Process Design phase ensured that any new equipment had the capacity to match the throughput rate of the rest of the plant bakery, so that wet-mill dough could seamlessly continue downstream. Process control variables were examined to ensure that a consistent quality product was delivered. Inbound material handling was also investigated and designed to ensure safe and uncontaminated delivery of perishable raw material. Since the end product is edible, hygiene design requirements were also considered by completing a HACCP study to ensure a consumer-safe product. The Machine Design phase involves the development and design of a completely new food machine: a vertical wet-mill cutter. Many ideas are evaluated and a prototype machine, based on the optimal design, was built to test the concept. This prototype was then used to define process and design constraints for a scaled, large plantbakery machine. The final detailed design of a plant bakery wet-mill cutter was then completed. It includes drive, belt, bearing and pneumatic cylinder selection, and shaft and blade design. Safety considerations were an important part of the design process and production facility. Conformity to OHS Act regulations required investigation into the safe operation of the designed equipment with particular reference to driven and rotating machinery sub-regulations of the Act. A hazard analYSis and operability study was also undertaken. Lastly, the research calculates a financial valuation of the project to ascertain whether a plant baker should be interested in implementing wet-mill technology. The research concludes with a discussion of the various successes of the three research areas, and states any further investigation that may be required before full implementation.
Low velocity impact energy absorption of fibrous metal-matrix composites using smart materials.
(2003) Gopal, Ajith Karamshiel.; Adali, Sarp.
In general, the basic concept of an intelligent material is defined as the multifunctional material that has a sensor, a processor and an actuator function in the material that allows it to maintain optimum conditions in response to environmental changes. Despite the fact that these materials have demonstrated varying degrees of success in shape and position control, active and passive control of vibration and acoustic transmission of materials subjected to dynamic loads, impact damage and creep resistance in structures and have been applied in industries from aerospace to biomechanics to civil engineering structures, very little literature is available on the subject. Thus, the objective of this dissertation is to add to the fundamental understanding of the behaviour of these special materials by investigating the possibility of a magnetostrictive SMA hybrid metalmatrix composite beam with piezoelectric actuator, to enhance the materials load attenuation and energy absorption characteristics under low velocity impact loading. The methodology employed in this investigation is driven by two primary factors. The first is the unique approach that the author puts forward to attempt to simplify the characterisation of damage in not just metal matrix composites, but in materials in general. The second factor is the lack of available literature on smart material energy absorption as well as a lack of precise theory for short fibre composites. The methodology includes an extensive literature review, the development of an analytical model, based on the new damage modulus approach, verification of the model using experimental results presented by Agag et. aI., adjustment of the model to include smart material effects and finally numerical simulation using the MATLAB® software to predict the effect of smart materials on the energy absorption capacity of the material under impact. The results show that the damage modulus (ED) is a material characteristic and can be derived from the stress strain diagram. Further, it takes into account degradation of the material through the plastic region, up to the point just before ultimate failure. Thus, ED lends itself to the simplification of many damage models in terms of a reducing sustainable load and energy absorption capacity. Only the energy consumed through material rupture remains to be characterised. The results also show that smart fibres diminish the capacity of the beam to sustain a load, but increase the displacement to failure. Thus, for a compatible substrate material, this increased displacement translates to a significant enhancement of energy absorption characteristics. The effect of prestrain on energy absorption is also considered and there appears to be a definite turning point where the dissertation thus achieves its objective in investigating the ability of smart materials to enhance the energy absorption characteristics of regular fibre reinforced metal-matrix composite materials subject to low velocity impact loading. Of equal importance to the achievement of this objective is the introduction in the dissertation of the unique damage modulus that goes to the foundation of material characterisation for mechanical engineering design and has profound implications in damage theory and future design methodologies. Significant learning has taken place in the execution of this PhD endeavour and this dissertation will no doubt contribute to other investigations in the field of smart materials.

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