Orientador: Joni Augusto Cirelli / Resumo: A qualidade do tecido ósseo representa condição “sine qua non” para a estabilidade e longevidade de implantes biomédicos. Diante de fatores sistêmicos relacionados à insuficiência e/ou má qualidade do tecido ósseo peri-implantar, o desenvolvimento de superfícies de titânio com atividade osteogênica é amplamente incentivado na área da implantodontia. Sendo assim, este Estudo avaliou diferentes formas de tratamentos da superfície das amostras de titânio comercialmente puro (Ticp) e titânio liga 6Alumínio-4Vanádio, que visam o favorecimento dos mecanismos celulares de osteogênese. Este estudo foi divido em 2 capítulos. Na publicação 1 as amostras foram divididas em 3 grupos de acordo com os tratamentos (Grupo 1: Titânio comercialmente puro – MS; Grupo 2: Tratamento com NaOH - AES; Grupo 3: Tratamento com NaOH associado à deposição de Estrôncio (Sr) – Sr-AES. Os resultados demonstraram que as superfícies dos Grupos 2 e 3 apresentaram-se mais rugosas, quando avaliadas em perfilômetro, e mais hidrofílicas em teste de molhabilidade, em comparação às do Grupo 1 (p < 0.05, One Way Anova). As células em contato com a superfície do Grupo 3 apresentaram espraiamento celular mais evidente, em comparação aos Grupos 1 e 2, indicando que a adição do estrôncio às amostras foi favorável ao desenvolvimento das células precursoras ósseas. Na publicação, as amostras foram divididas em 3 grupos de acordo com os diferentes tratamentos. Grupo A: titânio comercialmente puro – Ticp; Grupo B: Ti-6Al-4V... (Resumo completo, clicar acesso eletrônico abaixo) / Doutor

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, in fulfilment of the requirements for the degree of Master of Science in Engineering. Johannesburg, 21 July 2016 / The use of supercapacitors for energy storage is an attractive approach considering their ability to deliver high levels of electrical power, unlimited charge/discharge cycles, green environmental protection and long operating lifetimes. Despite the satisfactory power density, supercapacitors are yet to match the energy densities of batteries and fuel cells, reducing the competitiveness as a revolutionary energy storage device. Therefore, the biggest challenge for supercapacitors is the trade-off between energy density and power density. This presents an opportunity to enhance the electrochemical capacitance and mechanical stability of an electrode. Previous attempts to get around the problem include developing porous nanostructured electrodes with extremely large effective areas. One of the emerging high-power supercapacitor electrode materials is molybdenum disulfide (MoS2), a member of the transition-metal dichalcogenides (TMDs). Its higher intrinsic fast ionic conductivity and higher theoretical capacity have attracted a lot of attention, particularly in supercapacitors. In addition to double-layer capacitance, diffusion of the ions into the MoS2 at slow scan rates gives rise to Faradaic capacitance. Analogous to Ru in RuO2, the Mo center atom displays a range of oxidation states from +2 to +6. This plays an important role in enhancing charge storage capabilities. However, the electronic conductivity of MoS2 is still lower compared to graphite, and the specific capacitance of MoS2 is still very limited when used alone for energy storage applications. As evident in several literature reports, there is a need to improve the capacitance of MoS2 with conductive materials such as carbon nanotubes (CNT), polyaniline (PANI), polypyrrole (PPy), and reduced graphene (r-GO). Carbon nanospheres (CNS) have, in the past, improved the conductivity of cathode material in Li-ion batteries, owing to their appealing electrical properties, chemical stability and high surface area. The main objective of this dissertation research is to develop nanocomposite materials based on molybdenum sulphide with carbon nanospheres for pseudocapacitors with simultaneously high power density and energy density at low production cost. The research was carried out in two phases, namely, (i) Symmetric pseudocapacitors based on molybdenum disulfide (MoS2)-modified carbon nanospheres: Correlating physico-chemistry and synergistic interaction on energy storage and (ii) The effects of morphology re-arrangements on the pseudocapacitive properties of mesoporous molybdenum disulfide (MoS2) nanoflakes. The physico-chemical properties of the MoS2 layered materials have been interrogated using the surface area analysis (BET), scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray diffraction (XRD), Raman, fourier-transform infrared (FTIR) spectroscopy, and advanced electrochemistry including cyclic voltammetry (CV), galvanostatic cycling with potential limitation (GCPL), repetitive electrochemical cycling tests, and electrochemical impedance spectroscopy (EIS). In the first phase, Molybdenum disulfide-modified carbon nanospheres (MoS2/CNS) with two different morphologies (spherical and flower-like) have been synthesized using hydrothermal techniques and investigated as symmetric pseudocapacitors in aqueous electrolyte. The two different MoS2/CNS layered materials exhibit unique differences in morphology, surface areas, and structural parameters, which have been correlated with their electrochemical capacitive properties. The flower-like morphology (f-MoS2/CNS) shows lattice expansion (XRD), large surface area (BET analysis), and small-sized nanostructures (corroborated by the larger FWHM of the Raman and XRD data). As a contrast to the f-MoS2/CNS, the spherical morphology (s-MoS2/CNS) shows lattice contraction, small surface area with relatively large-sized nanostructures. The presence of CNS on the MoS2 structure leads to slight softening of the characteristic Raman bands (E12g and A1g modes) with larger FWHM. The MoS2 and its CNS-based composites have been tested in symmetric electrochemical capacitors in aqueous 1 M Na2SO4 solution. CNS improves the conductivity of the MoS2 and synergistically enhanced the electrochemical capacitive properties of the materials, especially the f-MoS2/CNS-based symmetric cells (most notably, in terms of capacitance retention). The maximum specific capacitance for f-MoS2/CNS-based pseudocapacitor show a maximum capacitance of 231 F g-1 with high energy density 26 Wh kg-1 and power density 6443 W kg-1. For the s-MoS2/CNS-based pseudocapcitor, the equivalent values are 108 F g-1, 7.4 Wh kg-1 and 3700 W kg-1. The high-performance of the f-MoS2/CNS is consistent with its physico-chemical properties as determined by the spectroscopic and microscopic data. In the second phase, Mesoporous molybdenum disulfide (MoS2) with different morphologies has been prepared via a hydrothermal method using different solvents, water or water/acetone mixtures. The MoS2 obtained with water alone gave graphene-like nanoflakes (g-MoS2) while the other with water/acetone (1:1 ratio) gave a hollow-like morphology (h-MoS2). Both materials are modified with carbon nanospheres as conductive materials and investigated as symmetric pseudocapacitors in aqueous electrolyte (1 M Na2SO4 solution). Interestingly, a simple change of synthesis solvents confers on the MoS2 materials different morphologies, surface areas, and structural parameters, correlated by electrochemical capacitive properties. The g-MoS2 exhibits higher surface area, higher capacitance parameters (specific capacitance of 183 F g-1, maximum energy density of 9.2 Wh kg-1 and power density of 2.9 kW kg-1) but less stable electrochemical cycling compared to the h-MoS2. These findings have opened doors for further exploration of the synergistic effects between MoS2 graphene-like sheets and CNS for energy storage. / MT2017

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfiment of the requirements for the degree of Master or Science in Engineering. Johannesburg, 1993. / The stress concentration factors around rectangular holes in carbon-fibre reinforced epoxy plates, subject uniaxial loads, were investigated experimentally and theoretically. To obtain theoretical solutions, two approaches were adopted; the finite element method and the theory of elasticity using the method of complex variable functions. Reflective photoelasticity was used as the experimental method. The determination of the stress concentration factor around a rectangular hole in a glass-fibrereinforced plate was attempted using transmissive photoelasticity, but no meaningful results were obtained. [Abbreviated Abstract. Open document to view full version} / MT2017

The problem examined is an infinite anisotropic layer with a through crack at arbitrary orientation, subjected to uniform in-plane remote loading. The purpose of this study is to gain a better understanding of several theoretical models for predicting the direction of crack propagation and the level of load causing crack extension, and to present a new model for predicting the critical load. The discussed models are particularly examined in detail with regard to the physical parameters affecting the results. Comparison is made with available experimental results. It is shown that the normal stress ratio theory provides good agreement with experimental crack growth direction, independent of physical parameters, and that the newly proposed traction ratio theory predicts well the critical load causing crack extension. / M.S.

The present work presents the results of an investigation of properties of polyphenylene sulfide (PPS) reinforced with random, continuous glass fibers, approximately 30% by weight. The investigation included both characterization of the mechanical properties and nondestructive inspection of the material. The objectives of the nondestructive inspection program were twofold: i) to determine nondestructive testing techniques were most responsive to developing damage and ii) to identify the damage modes using the nondestructive testing methods. The mechanical testing program involved the study of three types of specimens: straight sided tensile coupon, dogbone, and streamline. The streamline specimen typically fails in the narrow region and therefore appears to be relatively unaffected by stress concentrations induced by the specimen geometry. Results are given for all three specimen types and comparisons made for the measured mechanical properties. Several nondestructive testing methods, including C-scan, ultrasonic attenuation, acoustic emission, X-ray radiography, and edge replication, were applied to study the damage developed under quasi-static tension loading of this material. The C-scan, edge replication, and X-ray radiography tests were performed both initially and after intermediate stages of loading. These three tests appear to be unresponsive to the developing damage. That is, these techniques were unable to detect any distinctive patterns around the regions of final failure. The most responsive NDT techniques are ultrasonic attenuation and acoustic emission. Both of these methods yield quite distinct changes with increasing load. The acoustic emission tests, for example, show an extremely rapid rise in count rate at loads of about two-thirds of ultimate. The ultrasonic attenuation measurements display maxima and minima when taken in real-time as the specimen is loaded. In an effort to determine the damage mechanisms in the material and to understand the results of the NDE tests, virgin and damaged specimens were destructively examined with the aid of a scanning electron microscope (SEM). The SEM appears to show that the acoustic emission production is corning from cracking of the transverse glass fibers. The results of all tests to date are presented together with recommendations and conclusions for the application of nondestructive test methods to PPS. / Master of Science

Results of an experimental study of the failure and crippling of thin-walled open section prismatic compression members are presented. Twenty-four specimens were tested, 13 of which were channel sections and the other 11 were zee sections. Three specimens were made of 2024-T3 aluminum. The remaining 21 specimens were made of AS4-3502 graphite-epoxy. All specimens were tested to failure. Seventeen specimens exhibited local buckling of flanges and webs prior to failure, four exhibited global column buckling prior to failure, two exhibited material short column failure, and one exhibited unstable postbuckling behavior prior to failure. The buckling loads for each specimen were also calculated by a computer code and compared to experimental buckling loads. Good correlation was achieved for specimens that did not buckle as columns. The graphite-epoxy specimens which buckled locally had significant postbuckling response prior to failure at a maximum load (crippling). Differences in the crippling failure and compressive strength failure are discussed for the graphite-epoxy specimens. / Master of Science

This study addresses the issue of adjusting the proportion of load transmitted by each hole in a multiplehole joint so that the joint capacity is a maximum. Specifically two-hole-in-series joints are examined. The results indicate that when each hole reacts 50% of the total load, the joint capacity is not a maximum. One hole generally is understressed at joint failure. The algorithm developed to determine the load proportion at each hole which results in maximum capacity is discussed. The algorithm includes two-dimensional finite-element stress analysis and a failure criteria. The algorithm is used to study the effects of joint width, hole spacing, and hole to joint-end distance on load proportioning and capacity. To study hole size effects, two hole diameters are considered. Three laminates are considered: a quasi-isotropic laminate; a cross-ply laminate; and a 45 degree angle-ply laminate. By proportioning the load, capacity can be increased generally from 5 to 10%. In some cases a greater increase is possible. / M.S.

The Illinois Institute of Technology Research Institute (IITRI) composite compression test method is probably the most widely accepted as producing accurate results. Difficulties associated with the application of this method, however, have fueled continued research into alternate methods. In this study, the Wyoming End-Loaded Side-Supported (ELSS) test scheme was investigated in a combined shear/end loaded mode. This system was examined experimentally and analytically to establish the method as a reasonable alternative to IITRI testing. Combined shear/end loading was accomplished by applying a controlled amount of clamping force to the stabilizing blocks, allowing them to transmit shear force to the coupon faces through friction. The fabrication of test specimens from a BASF graphite IBMI material system is described in detail, including the application of a novel "press-clave" processing system developed at Virginia Tech. This system allows for cost-effective manufacture of flat panels under conditions similar to autoclave processing. For the material system employed in this study, this process proved superior to conventional hot press processing. Experimental results include strengths and failure modes for both tabbed and untabbed coupons tested by the combined loading ELSS method, and these data are compared to the results by the IITRI method. Strength was found to increase with increasing clamping, but reached a maximum with both untabbed and tabbed specimens. The maximum strength achieved with untabbed specimens was still significantly below the IITRI value, but the tabbed specimens reached strengths comparable to the IITRI data. The failure mode also changed with increased clamping, from end crushing to brooming with untabbed specimens, and from end crushing to shear failure with tabbed specimens. As the strength and failure mode achieved with the combined loading ELSS method using tabbed specimens are both similar to those seen in the IITRI tests, this modified technique can be considered equivalent to the IITRI method. Preliminary data from tests using novel nonbonded tabs were also similar to those given by the IITRI method. The finite element method was used to analyze the effect of increasing the clamping force. Competing effects of locally complex and severe stresses at the coupon end and a stress concentration which develops at the end of the gage section were shown to limit the maximum strength. Tabs appear to reduce the stress concentration while further decreasing the stresses at the end, allowing results comparable to those given by the IITRI method to be achieved. / Master of Science

The feasibility study of subscale notched specimens to determine the shear response of composites is presented. The investigation consists of finite element analyses, conventional strain-gaged testing, and photomechanics experiments. Several notch geometries of the subscale specimens are studied, the standard 900 V -notch, U-notch, and circular notch. The investigation is performed on two different material systems, a standard high performance graphite/epoxy (AS4/3501-6) material and an SMC R-28 material reinforced with 28% volume fraction strand glass fiber. The moduli obtained from the subscale specimens are compared with those obtained from the standard specimens. Different degrees of twisting observed in testing the sub scale specimens are discussed. Numerical and experimental results of the SMC R-28 materials are presented. The dependence of the measured shear modulus on the relative orientation of the specimen in the panel is identified. The application of the subscale, circular notched specimens to obtain the shear modulus of the SMC material is discussed. / Master of Science

The focus of this work is the buckling response of symmetrically laminated composite plates having a planform area in the shape of an isosceles trapezoid. The loading is assumed to be inplane and applied perpendicular to the parallel ends of the plate. The tapered edges of the plate are assumed to have simply supported boundary conditions, while the parallel ends are assumed to have either simply supported or clamped boundary conditions. Plates with one end being up to 3 times narrower than the other end, and the plate being up to 3 time longer than the width of the wide end are considered. A semi-analytic closed-form solution based on energy principles and the Trefftz stability criterion is derived and solutions are obtained using the Rayleigh-Ritz method. Intrinsic in this solution is a simplified prebuckling analysis which approximates the inplane force resultant distributions by the forms N_x=P/W(x) and N_y=N_xy=0, where P is the applied load and W(x) is the plate width which, for the trapezoidal planform, varies linearly with the lengthwise coordinate x. The out-of plane displacement is approximated by a double trigonometric series. This analysis is posed in terms of four nondimensional parameters representing orthotropic and anisotropic material properties, and two nondimensional parameters representing geometric properties. With nondimensionalization, the analysis is well suited for parametric studies. The analysis uses standard eigenvalue extraction routines and converges using 5 terms in the out-of-plane displacement series. It appears that this analysis captures the buckling response of plates having tapered planform and should be a useful design tool. For comparison purposes, a number of specific plate geometry, ply orientation, and stacking sequence combinations are investigated using the general purpose finite element code ABAQUS. Comparison of buckling coefficients calculated using the semi-analytical model and the finite element model show agreement within 5%, in general, and within 15% for the worst cases. In addition to the good agreement between the semi-analytical analysis and the finite element results, the finite element model also suggests that the simplified inplane force resultant distribution assumed in the analysis is valid. In order to verify both the finite element and semi-analytical analyses, buckling loads are measured for graphite/epoxy plates having a wide range of plate geometries and stacking sequences. Test fixtures, instrumentation system, and experimental technique are described. Experimental results for the buckling load, the buckled mode shape, and the prebuckling plate stiffness are presented and show good agreement with the analytical results regarding the buckling load and the prebuckling plate stiffness. However, the experimental results show that for some cases the analysis underpredicts the number of halfwaves in the buckled mode shape. In the context of the definitions of taper ratio and aspect ratio used in this study, it is concluded that the buckling load always increases as taper ratio increases for a given aspect ratio for plates having simply supported boundary conditions on the parallel ends. There are combinations of plate geometry and ply stacking sequences, however, that reverse this trend for plates having clamped boundary conditions on the parallel ends such that an increase in the taper ratio causes a decrease in the buckling load. The clamped boundary conditions on the parallel ends of the plate are shown to increase the buckling load compared to simply supported boundary conditions. Also, anisotropy (the D₁₆ and D₂₆ terms) is shown to decrease the buckling load and skew the buckled mode shape for both the simply supported and clamped boundary conditions. / Master of Science