The thesis is divided in three parts based largely on published articles or on manuscripts submitted for publication. First we propose a new method which is called the shooting-bead method. This method is a fast and easy experimental technique for evaluating cantilever stiffness and flexural rigidity of semi-flexible to semi-rigid rod-like biological and nano-filaments based on the measurement of just two distances. The method is based on applying a force normal to the filament with a microsphere bead trapped in the laser tweezer followed by its sudden release. Through a simple measurement of the distances that the bead moves, the flexural rigidity of the filament can be found from the formula derived in this paper. Then we take into account the effects of the viscous drag force exerted on the filament itself. To this end, we have defined a key variable, called the filament energy-loss factor (or filament drag factor) that accounts for all the energy-loss effects. It has been shown that the effect due to the consideration of filament energy-loss factor on calculation of the flexural rigidity increases with increasing the flexibility of the filament. Finally, in the third part we discuss the effect of ultrasound on the microtubules. Here we have analytically solved equations of motion for the vibrational dynamics of an MT that is attached at its two ends. This is especially relevant for MTs during mitosis when they attach to chromosomes and centrosomes. Our analysis applies to MTs present inside a viscous solution and when driven by an ultrasound plane wave. We have shown that with using ultrasound plane waves the resonance condition for the MT treated as a rigid rod cannot be provided, and in order to achieve resonance we should excite a single mode of the MT with a harmonic number larger than a threshold value introduced in this thesis. Single mode excitation not only helps to transfer the minimum amount of energy to the surrounding medium compared with multi-mode excitation but it also allows for a simultaneous high-amplitude and high-quality factor which is impossible when using plane waves.

Recently, the use of Mechanically Fastened Fiber-Reinforced Polymer (MF-FRP) systems has emerged as a viable means for flexural strengthening of reinforced concrete members. The technique is suitable for emergency repairs where constructability and speed of installation are critical requirements. The MF-FRP system consists of pre-cured FRP laminates with enhanced longitudinal bearing strength that are attached to the concrete substrate by means of mechanical steel anchors. This research project presents an experimental investigation comprising a series of flexural tests on scaled one-way RC slabs. The test matrix includes MF-FRP strengthened specimens, a counterpart with the externally bonded (EB) FRP reinforcement, and a control specimen. The effects of fastener layout and laminate length on strength increase and failure mode were studied. It is shown that with proper selection of fastener layout the MF-FRP system results in a significant deformability and strength increase, where the latter is comparable to that attained using EB-FRP sheets. Specific gaps on the existing analytical procedures for flexural strengthening with MF-FRP systems are finally discussed.

Glass is a common material in each person’s life, e.g. drinking vessels, windows, displays, insulation and optical fibres. By modifying the glass surface it is possible to change the performance of the entire glass object, generally known as Surface Engineering. Ion exchange is a convenient technique to modify the glass surface composition and its properties, e.g. optical, mechanical, electrical and chemical properties, without ruining the surface finish of the glass.   This thesis reports the findings of two different research tasks; characterisation of the single-side ion exchange process and the novel properties induced. The characterisation of the ion exchange process was mainly performed by utilising a novel analytical equipment: the Surface Ablation Cell (SAC), allowing continuous removal of the flat glass surface by controlled isotropic dissolution. SAC-AAS has provided concentration vs. depth profiles of float glass ion exchanged with K+, Cu+, Rb+ and Cs+. In addition, SEM-EDX has provided concentration vs. depth profiles of Ag+ ion exchanged samples and validation of a copper concentration vs. depth profile. From the concentration vs. depth profiles, the effective diffusion coefficients and activation energies of the ion exchange processes have been calculated. Depending on the treatment time and treatment temperature, penetration depths in the range of 5-10 μm (Rb+, Cs+), 20-30 μm (K+, Cu+) and 80-100 μm (Ag+) can be readily obtained. The effective diffusion coefficients followed the order Ag+>K+>Cu+>Rb+>Cs+. This is in accordance with the ionic radii for the alkali ions (K+<Rb+<Cs+) but reverse for the noble metal ions (Cu+<Ag+).   The glass properties modified by single-side ion exchange have mainly been characterised by UV-VIS spectroscopy and flexural strength measurements. Cu+ and Ag+ ion exchange give rise to surface colouration, Cu+ copper-ruby and Ag+ yellow/amber. The surface-ruby colouration was found to depend on the residual tin ions in the tin-side of the float glass. The flexural strength was studied using the coaxial double ring-test method which also was suitable for holed specimens. The flexural strength of K+ ion exchanged float glass samples was found to substantially increase compared to untreated.

Fibre-reinforced-polymer (FRP) composites have been widely used for the flexural strengthening of reinforced concrete (RC) structures. Flexural strengthening methods with FRP include external bonding of FRP composites (EB system) and insertion of FRP strips or bars into grooves cut into the concrete (near-surface-mounted or NSM system). Recently, a prestressed FRP strengthening system has been developed and investigated, whereby the FRP reinforcement is pretensioned prior to attachment to the concrete to maximize the use of the high tensile strength of the FRP reinforcement. Existing studies have shown that the ultimate load carrying capacity and serviceability were greatly improved in FRP flexural strengthened beams. However, the only disadvantage of the FRP strengthening system is the reduction of deformability compared to that of unstrengthened structures due to the limited strain capacity of the FRP reinforcement and premature debonding failure. Structures with low deformability may fail suddenly without warning to evacuate, resulting in catastrophic failure. Therefore, a study on the improvement of deformability is critical for the effective use of FRP strengthening systems. In this study, a partially bonded concept is introduced and applied to various FRP strengthening methods, with the specific objective of increasing deformability in FRP strengthened beams. The FRP reinforcement is usually completely bonded to the concrete tensile surface, while a portion of the FRP length is intentionally unbonded in the partially bonded system in order to improve deformability while sustaining high load carrying capacity. To investigate the general behaviour of the partially bonded system, a new analytical model has been developed because conventional section analysis used for analysis of the fully bonded system is not applicable due to strain incompatibility at the FRP reinforcement level within the unbonded length. The analysis shows that a partially bonded system has a high potential to improve deformability without the loss of strength capacity. An extensive experimental program was conducted to verify the analytical model and to investigate the actual behaviour of the partially bonded beams. A total of seventeen, 3.5m long, RC T-beams were constructed and tested. One of them is an unstrengthened control beam, while the other 16 beams consist of four test groups that were strengthened by different strengthening methods: non-prestressed EB, non-prestressed NSM, 40% prestressed NSM, and 60% prestressed NSM. To allow investigation of the effect of partially unbonding, each group has different unbonded lengths and includes a fully bonded beam. For the non-prestressed EB strengthened beams, the failure mode of all beams was premature FRP debonding failure without regard to the bond condition. The ultimate strength and the ultimate deformability of the partially bonded beams were improved compared to the fully bonded beam. This was because the typical intermediate debonding failure that occurred in the fully bonded beam was avoided due to intentional unbonding in the partially bonded beams. The analytical model predicted the general behaviour of the EB strengthened beams well except at the ultimate response due to the premature debonding failure. A three-dimensional nonlinear finite element (FE) analysis was performed utilizing interfacial elements and contact modeling to investigate the debonding failure of this system. The FE analysis represented the behaviour of the debonding failure and bond stress distributions at FRP-concrete interface of both the fully bonded and partially bonded beams well. For the non-prestressed NSM strengthened beams, the premature debonding failure that occurred in the EB strengthened beams was not observed, and almost the full capacity of FRP was exhibited. Prominent stiffness reduction was observed in terms of load-deflection diagrams at the post-yielding stage with the increase of the unbonded length. This stiffness reduction increased the deformability of the partially bonded beams for a given applied load after steel yielding in comparison to the fully bonded beam. The FRP started to slip at high load levels and the concrete crushed gradually with a gradual loss of the beam’s cross-section, inducing nonlinear behaviour near the ultimate state of the beams. To address this behaviour, an advanced analytical model utilizing idealized section model and slip model is proposed to consider the FRP slip and concrete gradual failure. Prestressed NSM strengthened beams were very effective to improve the cracking load, to decrease the deflection at service load, and to increase the ultimate load compared to non-prestressed NSM strengthened beams. This improvement was greater as the prestressing level increased. The partially bonded prestressed beams showed an improvement in deformability compared to the fully bonded prestressed beams while minimizing the reduction of the ultimate load carrying capacity and serviceability. The partially bonded system was more effective to improve the deformability at higher levels of prestressing force. Based on the model developed, a parametric study was performed varying the main parameters. This showed that the FRP strengthened beam that has an FRP area (Af) less than the balanced FRP area (Af,b) of the beam has a high potential to improve the deformability as the unbonded length increases. The balanced FRP area is increased as the concrete strength and the FRP prestressing force are increased, or as the area of the steel reinforcement decreases. Finally, design recommendations and procedures are proposed for the effective use of the partially bonded system to improve the deformability of FRP strengthened concrete beams.

Fibre-reinforced-polymer (FRP) composites have been widely used for the flexural strengthening of reinforced concrete (RC) structures. Flexural strengthening methods with FRP include external bonding of FRP composites (EB system) and insertion of FRP strips or bars into grooves cut into the concrete (near-surface-mounted or NSM system). Recently, a prestressed FRP strengthening system has been developed and investigated, whereby the FRP reinforcement is pretensioned prior to attachment to the concrete to maximize the use of the high tensile strength of the FRP reinforcement. Existing studies have shown that the ultimate load carrying capacity and serviceability were greatly improved in FRP flexural strengthened beams. However, the only disadvantage of the FRP strengthening system is the reduction of deformability compared to that of unstrengthened structures due to the limited strain capacity of the FRP reinforcement and premature debonding failure. Structures with low deformability may fail suddenly without warning to evacuate, resulting in catastrophic failure. Therefore, a study on the improvement of deformability is critical for the effective use of FRP strengthening systems. In this study, a partially bonded concept is introduced and applied to various FRP strengthening methods, with the specific objective of increasing deformability in FRP strengthened beams. The FRP reinforcement is usually completely bonded to the concrete tensile surface, while a portion of the FRP length is intentionally unbonded in the partially bonded system in order to improve deformability while sustaining high load carrying capacity. To investigate the general behaviour of the partially bonded system, a new analytical model has been developed because conventional section analysis used for analysis of the fully bonded system is not applicable due to strain incompatibility at the FRP reinforcement level within the unbonded length. The analysis shows that a partially bonded system has a high potential to improve deformability without the loss of strength capacity. An extensive experimental program was conducted to verify the analytical model and to investigate the actual behaviour of the partially bonded beams. A total of seventeen, 3.5m long, RC T-beams were constructed and tested. One of them is an unstrengthened control beam, while the other 16 beams consist of four test groups that were strengthened by different strengthening methods: non-prestressed EB, non-prestressed NSM, 40% prestressed NSM, and 60% prestressed NSM. To allow investigation of the effect of partially unbonding, each group has different unbonded lengths and includes a fully bonded beam. For the non-prestressed EB strengthened beams, the failure mode of all beams was premature FRP debonding failure without regard to the bond condition. The ultimate strength and the ultimate deformability of the partially bonded beams were improved compared to the fully bonded beam. This was because the typical intermediate debonding failure that occurred in the fully bonded beam was avoided due to intentional unbonding in the partially bonded beams. The analytical model predicted the general behaviour of the EB strengthened beams well except at the ultimate response due to the premature debonding failure. A three-dimensional nonlinear finite element (FE) analysis was performed utilizing interfacial elements and contact modeling to investigate the debonding failure of this system. The FE analysis represented the behaviour of the debonding failure and bond stress distributions at FRP-concrete interface of both the fully bonded and partially bonded beams well. For the non-prestressed NSM strengthened beams, the premature debonding failure that occurred in the EB strengthened beams was not observed, and almost the full capacity of FRP was exhibited. Prominent stiffness reduction was observed in terms of load-deflection diagrams at the post-yielding stage with the increase of the unbonded length. This stiffness reduction increased the deformability of the partially bonded beams for a given applied load after steel yielding in comparison to the fully bonded beam. The FRP started to slip at high load levels and the concrete crushed gradually with a gradual loss of the beam’s cross-section, inducing nonlinear behaviour near the ultimate state of the beams. To address this behaviour, an advanced analytical model utilizing idealized section model and slip model is proposed to consider the FRP slip and concrete gradual failure. Prestressed NSM strengthened beams were very effective to improve the cracking load, to decrease the deflection at service load, and to increase the ultimate load compared to non-prestressed NSM strengthened beams. This improvement was greater as the prestressing level increased. The partially bonded prestressed beams showed an improvement in deformability compared to the fully bonded prestressed beams while minimizing the reduction of the ultimate load carrying capacity and serviceability. The partially bonded system was more effective to improve the deformability at higher levels of prestressing force. Based on the model developed, a parametric study was performed varying the main parameters. This showed that the FRP strengthened beam that has an FRP area (Af) less than the balanced FRP area (Af,b) of the beam has a high potential to improve the deformability as the unbonded length increases. The balanced FRP area is increased as the concrete strength and the FRP prestressing force are increased, or as the area of the steel reinforcement decreases. Finally, design recommendations and procedures are proposed for the effective use of the partially bonded system to improve the deformability of FRP strengthened concrete beams.

This work focuses mainly on the resistance of members to flexural buckling according to Eurocode 3. The work provides the mathematical backgrounds to the equations and buckling curves presented in Eurocode 3. The work also, attempts to reveal how different imperfections influence the flexural buckling resistance which is demonstrated through Finite Element (FE) simulations. The work presents modeling and analysis on a steel column in ABAQUS 6.14. Linear and non-linear buckling analyses of the steel column, with the influence of imperfections, are implemented in this work. Specifically, the imperfections considered in this study are material plasticity, initial bow and residual stress. The influence of initial bow imperfection of 0.1% of the length of the column considering flexural buckling was found to be 45.28% of the Euler buckling load. The influence of residual stresses, with a magnitude of maximum about 13% in the flange and 35% in the web, of the yielding strength, on flexural buckling is about 31.9% of the design Euler buckling load. The combined effect of residual stress and initial bow imperfection on flexural buckling is about 45.34% of the design Euler buckling load.

No description available.

Hollow glass microspheres have been used extensively in the automotive and marine industries as an additive for reducing weight and saving material costs. They are also added to paints and other materials for their reflective properties. They have shown promise for weight critical applications, but have thus far resulted in materials with low fracture toughness and impact resistance when combined with thermosetting resins in syntactic foam. The advent of commercially available microspheres with a wide range of crushing strengths, densities and adhesive properties has given new impetus to research into syntactic foam with better fracture behaviour. Current research suggests that the beneficial effects on fracture and impact resistance gained by the addition of solid reinforcements such as rubber and ceramic particles are not seen with the addition of hollow glass microspheres. The research presented in this paper has examined the mechanisms for fracture resistance in glass microsphere filled epoxy (GMFE) syntactic foams, as well as determined the effect microsphere crushing strength and adhesion strength has on the material???s fracture toughness. The flexural properties of various GMFE have also been determined. GMFE were manufactured with varying microsphere volume fraction up to 50%, and with variances in microsphere crushing strength and adhesion. The specimens were tested for Mode I fracture toughness in a three point single edge notched bending setup as described in ASTM D5045 as well as a three point flexural setup as described in ASTM D790-3. Fracture surfaces were inspected using scanning electron microscope imaging to identify the fracture mechanisms in the presence of microspheres. Results indicate a positive effect on fracture toughness resulting from new fracture areas created as tails in the wake of the microspheres in the fracture plane. Results also indicate a negative effect on fracture toughness resulting from weak microspheres or from interfacial disbonding at the fracture plane. These two effects combine to show an increase in GMFE fracture toughness as the volume fraction of microspheres is increased to between 10 ??? 20% volume fraction (where the positive effect dominates), with a reduction in fracture toughness as microspheres are added further (where the negative effect dominates).

Made available in DSpace on 2014-06-11T19:28:56Z (GMT). No. of bitstreams: 0 Previous issue date: 2003-02-25Bitstream added on 2014-06-13T19:58:18Z : No. of bitstreams: 1 seo_rs_me_arafo.pdf: 703350 bytes, checksum: 5c30291cb31b160b0c3ae925308ad49c (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O procedimento de reembasamento da prótese é normalmente utilizado para restabelecer a adaptação entre a prótese e o tecido bucal. As resinas autopolimerizáveis são um dos materiais indicados para o reembasamento. No entanto, tem sido demonstrado que, após a polimerização das resinas autopolimerizáveis, nem todo o monômero é convertido em polímero e esse monômero residual pode afetar as propriedades mecânicas desses materiais. Estudos têm sugerido que o conteúdo de monômero residual pode ser reduzido pela irradiação em microondas ou tratamento em banho de água. Esse estudo avaliou o efeito dos tratamentos térmicos sobre a resistência à flexão e dureza Vickers de quatro resinas autopolimerizáveis para reembasamento (Duraliner II - D, Kooliner-K, Tokuso Rebase Fast - TR e Ufi Gel Hard - UGH) e uma resina termopolimerizável (Lucitone 550 - L). Para cada material, trinta corpos-de-prova foram confeccionados e igualmente divididos em três grupos. No grupo controle, os corpos-de-prova foram submetidos ao teste de resistência à flexão imediatamente após sua polimerização. Previamente ao teste, os grupos 2 e 3 foram submetidos ao tratamentos complementares em banho de água e irradiação por microondas, respectivamente. Os corpos-de-prova do material para base de prótese foram armazenados em água por 48 horas a 37o l 1oC previamente ao teste. As medidas de força foram realizadas em máquina de ensaio universal MTS 810 com uma velocidade de 5 mm/min, utilizando o teste em três pontos a uma distância de 50 mm entre os apoios. Em seguida, um dos fragmentos do corpo-de-prova foi submetido ao teste de dureza Vickers. Os valores de dureza foram determinados utilizando-se uma carga de 25 gf (resinas K, TR, L e UGH) e 10 gf para a resina D, após 30 segundos de contato. Doze mensurações de dureza foram realizadas em cada corpo-de-prova e... / To maintain the prosthesis-tissue relationship, denture base reline procedure is commonly required. Autopolymerizing resins are one of the materials indicated for relining. It has been shown that, after polymerization, not all the monomer is converted to polymer in autopolymerizing resins and this residual monomer could detrimentally affect the mechanical properties of the materials. It has been suggested that the residual monomer could be decreased by microwave irradiation or water bath heat-treatments. This study investigated the effect of heat treatments on the flexural strength and Vickers hardness of four autopolymerizing reline resins (Duraliner II - D, Kooliner-K, Tokuso Rebase Fast-TR and Ufi Gel Hard-UGH) and one heat-polymerized resin (Lucitone 550-L). For each material, 30 specimens were made and equally divided into three groups. In control group, the specimens were submitted to the flexural strength test immediately after polymerization. Before testing, groups 2 and 3 were submitted to water bath and microwave post-cure treatments, respectively. The denture base material specimens were stored in water for 48 h at 37o l 1oC before they were bend-tested. Force measurements were made with a testing machine MTS 810 at a crosshead speed of 5 mm/min using a three-point bending fixture with a span of 50 mm. Thereafter, one fragment of specimen was submitted to Vickers microhardness test. The values were determined by using a 25 gf load (resins K, TR, UGH and L) and 10 gf for resin D, after 30 s contact. Twelve hardness measurements were taken on each specimen and the average was then calculated. Kruskal-Wallis non-parametric test was used for determination of statistical significance (p<0.01). The results demonstrated that: compared to the control groups, the flexural strength of TR and...(Complete abstract, click electronic access below)

Made available in DSpace on 2014-10-09T12:44:27Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:23Z (GMT). No. of bitstreams: 1 06908.pdf: 2703320 bytes, checksum: 38c6007057a454b93e257e7f851f366a (MD5) / Dissertacao [Mestrado] / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP