This thesis investigates the application of ultra-high modulus carbon fiber reinforced polymer (CFRP) plates to strengthen damaged reinforced concrete beams and slender columns. In the first phase, two different pre-repair loading histories were simulated in seven 3000x300x150 mm reinforced concrete beams, namely cracking within the elastic range, and overloading in the plastic range. After unloading, the beams were repaired with either high- or ultra-high modulus (210 or 400 GPa) CFRP plates, or a hybrid system, and then reloaded to failure. It was shown that the level of pre-existing damage has an insignificant effect on the strengthening effectiveness and the failure mode at ultimate. The 210 and 400 GPa CFRP of reinforcement ratio ρf = 0.17% increased the ultimate strength by up to 29 and 51%, respectively, despite the 40% lower tensile strength of the 400 GPa CFRP, due to the change in failure mode from debonding to rupture. Doubling ρf of the 400 GPa CFRP to 0.34% resulted in a 63% overall gain in flexural strength, only 8% increase in ultimate strength over ρf = 0.17%, due to change in failure mode from rupture to concrete cover delamination. The beam retrofitted by hybrid CFRP showed remarkable pseudo ductility and warning signs before failure. However, a parametric study revealed a critical balance in proportioning the areas of hybrid CFRP to achieve reliable pseudo ductility. In the beam with ρf =0.34%, this was achieved using a maximum of 30% ρf of the 400 GPa CFRP. The second phase of this thesis presents an analytical model developed by modifying the provisions of the ACI 318-08 code and employing the computer software Response 2000, to predict the performance of CFRP strengthened slender reinforced concrete columns. Response 2000 is used to establish the interaction curve while the modified ACI 318-08 code is used to acquire the slender column loading path to failure including the second order effects. The model predicts that the effectiveness of the FRP strengthening system increases as the slenderness ratio and FRP reinforcement ratio increase. / Thesis (Master, Civil Engineering) -- Queen's University, 2013-09-24 12:36:48.352

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<div>The rate effect of fiber-matrix interfacial debonding behavior of SC-15 epoxy and various fiber reinforcements was studied via in-situ visualization of the debonding event. Special focus has been placed on the dynamic transverse debonding of single fiber reinforced polymer composites. In this study, the debonding force history, debonding initiation, debonding crack velocity, and crack geometry were characterized using a quasi-static load frame and a modified tension Kolsky bar at loading velocities of 0.25 mm/s and 2.5 m/s. Cruciform-shaped specimens were used for interfacial transverse debonding between SC-15 epoxy matrix and various fiber reinforcements including S-2 glass, Kevlar® KM2, and tungsten fiber materials. The load history and high-speed images of the debonding event were simultaneously recorded. A major increase was observed for the average peak debonding force and a minor increase was observed for the average crack velocity with increasing loading velocity. The crack geometry of the cruciform specimens under both loading velocities was also tracked. Scanning electron microscopy of the recovered specimens revealed the debonding direction along the fiber-matrix interface through angled patterns on the failure surface.</div><div><br></div><div>The dynamic shear debonding of single fiber reinforced plastic composites were also studied via the real-time visualization with the fiber pull-out method. The interfacial shear debonding was studied between SC-15 epoxy and fiber reinforcements including S-2 glass, tungsten, steel, and carbon composite Z-pin fiber materials at 2.5 m/s and 5.0 m/s. Both S-2 glass fiber and Z-pin experienced catastrophic interfacial debonding whereas tungsten and steel wire experienced both catastrophic debonding and stick-slip behavior. Scanning electron microscope imaging of recovered epoxy beads revealed a snap-back behavior around the meniscus region of the bead for S-2 glass, tungsten, and steel fiber materials at 5.0 m/s whereas those at 2.5 m/s exhibited no snap-back behavior.</div>

Tissue, among the highest value added paper products, finds extensive application in modern society. Continued efforts are being made to further improve tissue properties, such as strength, softness and water absorbency. Besides the efforts on characterizing facial tissue softness, this study focuses on tissue quality improvement through chemical means. The application of a wet strength resin, Kymene1500 and a debonding agent, Softrite7516 onto cellulose fibers is considered. First, the adsorption kinetics of the two chemical additives onto cellulose fibers was studied. The adsorption mechanisms were proposed and validated by kinetic data. A novel apparatus was designed in this study, and represented the first in the field to collect real-time data, which has the potential to be applied to the adsorption kinetic study of other types of paper additives. Second, the effects of Kymene1500 and Softrite7516 on various sheet properties were studied. The results provide quantitative information on tissue additives effects on sheet properties. It is shown that the combined application of the additives can overcome the disadvantages of individual species and produce sheets with both wet strength and softness. Finally, environmental-benign debonding agents with polyoxyethylene chains were applied to the sheets, and the effects of two design parameters, i.e., fatty acid and degree of ethoxylation, on tissue properties were investigated.

Thermally induced interfacial stress states between fiber and matrix at cryogenic temperature were studied using three-dimensional finite element based micromechanics. Mismatch of the coefficient of thermal expansion between fiber and matrix, and mismatch of coefficient of thermal expansion between plies with different fiber orientation were considered. In order to approximate irregular fiber distributions and to model irregular fiber arrangements, various types of unit cells, which can represent nonuniformity, were constructed and from the results the worst case of fiber distributions that can have serious stress states were suggested. Since it is difficult to measure the fiber transverse coefficient of thermal expansion at the micro scale, there is an uncertainty problem for stress analysis. In order to investigate the effect of error in assumed fiber transverse coefficient of thermal expansion on thermally induced interfacial stresses, systematic studies were carried out. In this paper, the effect of measurement errors on the local stress states will be studied. Also, in order to determine fiber transverse CTE values from lamina properties, a back calculation method is used for various composite systems.

Thesis(M.S.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographic references.

Orientador: Simonides Consani / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba / Made available in DSpace on 2018-08-07T04:24:28Z (GMT). No. of bitstreams: 1 Tavares_StenyoWanderley_D.pdf: 4135316 bytes, checksum: 2a1db19579aa0bcb7036ac454b9d537d (MD5) Previous issue date: 2006 / Resumo: O objetivo desta pesquisa foi comparar in vitro diferentes métodos de remoção da resina residual do esmalte dentário, após o descolamento de bráquetes. Cinquenta terceiros molares foram separados em 5 grupos (n=10). Foram fixados bráquetes metálicos com o compósito ortodôntico Transbond XT, após condicionamento do esmalte com ácido fosfórico a 37%. Os corpos-de-prova foram armazenados água à temperatura ambiente, por 24 horas. Após a remoção dos bráquetes com pistola removedora (Orthosource), a resina remanescente foi removida por diferentes tipos de tratamento: grupo I ¿ Jato de óxido de alumínio, grupo II ¿ ponta de carboneto de tungstênio (30 lâminas) em alta rotação; grupo III ¿ ponta de óxido de alumínio (Shofu) em alta rotação, grupo IV ¿ sistema Profin, grupo V ¿ alicate removedor de resina. Depois da remoção da resina foi realizado polimento com pasta de pedra pomes e água em todas as amostras. A avaliação foi realizada antes da colagem, depois da remoção e após o polimento, por meio da análise rugosimétrica de superfície e observação em microscopia eletrônica de varredurra. Os valores de rugosidade foram submetidos à análise de variância a ao teste de Tukey (5%). Os resultados demonstraram que em todas as fases, o alicate removedor de resina foi método que mostrou os melhores resultados. Depois da remoção da resina residual, os métodos com broca de carboneto de tungstênio (30 lâminas) e com ponta de óxido de alumínio mostraram os maiores valores de rugosidade com diferença estatística significante em relação aos demais. O polimento foi importante para o restabelecimento da lisura superficial do esmalte, em todos os métodos de remoção da resina residual / Abstract: The purpose of this study was to compare different in vivo methods of dental enamel residual resin removal after brackets debonding. Fifty third molars were separated in 5 groups of 10 teeth. Metal brackets were fixed with Transbond XT orthodontic composite, after enamel conditioning with 37% phosphoric acid. Specimens were stored in water at room temperature for 24 hours. After brackets debonding with a removal plier (Orthosource), residual resin was removed through different treatment methods: Group I- aluminium oxide blaster, group II ¿ high speed tungsten carbide bur (30 laminae), group V ¿ resin removal plier. After resin elimination it was accomplished pumice and water polishing in all specimens. Evaluation was consummated before bonding, after removal, and also after polishing, trrought roughness surface analysis and scanning electron microscopy observation. Roughness values were submitted to variance analysis and Tukey test (5%). Results showed that the removal method which did not present significant statistical difference in roughness surface enamel values in all treatment methods was resin removal plier. Polishing was important for enamel superficial smoothness recovery in all methods for removal residual resin / Doutorado / Ortodontia / Doutor em Radiologia Odontológica

Introduction: One factor that contributes greatly to the lower face appearance and orthodontists have the ability to affect is lip profile. Clinical assessment of the lip profile is an important element in the decision of orthodontic treatment planning and in the evaluation of treatment progress and outcome. Three known factors influence the lip profile; the lip thickness, the underlying bone, and the tooth position. The positions and inclinations of the anterior teeth can affect the lip position, but it is unclear whether orthodontic brackets bonded to the labial surface of anterior teeth move the lip position and thereafter change the lip profile. Therefore, it is necessary to determine if orthodontic brackets bonded to the labial surface of the anterior dentition have any impact on lip profile. Objective: The objective of this project was to determine the effect that bonded brackets have on lip profile utilizing a standardized lateral photographic cephalogram analysis during the bonding and debonding stages. Methods: To determine the effect of bonded brackets on lip profile, digital photographic cephalometry was used. The patient was seated against a white backdrop in the standardized natural head position. Photographs were taken 5 feet from the patient, centered and level with the middle of the tragus of the right ear and were digitally analyzed using Dolphin Imaging software. Photos were acquired from 4 time points: before bonding (BT0) and after bonding (BT1) for the bonding group, and before debonding (DT0) and after debonding (DT1) for the debonding group. Upper and lower lip to E-plane, subnasale and lower lip to H-Line, superior sulcus depth, nasolabial angle, Z angle, upper and lower lip protrusion, and upper and lower lip to S-line were measured and analyzed statistically. The correlation of tooth angulation, lip thickness (determined using existing cephalometric radiographs), and bracket thickness on effect of lip position was also determined. Results: There are significant differences in all measurements of the lip profile, except superior sulcus depth and nasolabial angle, between BT0 and BT1 at the bonding stage. In the bonding stage, change in Z angle was correlated to initial lower lip thickness and change in upper lip protrusion was correlated to the initial upper lip thickness at the vermilion boarder and upper incisor bracket thickness. There was no significant difference noted between DT0 and DT1 at the debonding stage. Conclusion: Brackets have a significant effect on lip profile when bonding labial orthodontic brackets. Brackets have no significant effect on lip profile when debonding brackets. Therefore, a direct clinical assessment of lip profile before debonding is valid with no interference imposed by bonded orthodontic brackets.

Objective: This study was conducted to compare the shear bond strengths, patterns of bond failure and enamel surfaces after debonding two ceramic brackets (ClearVu and Radiance Plus) and one standard metal bracket (Mini Uni-Twin). Background: Ceramic brackets are an esthetic alternative to metal brackets. The mean shear bond strength of ceramic brackets is significantly greater than for metal brackets. Excessive bond strength can result in pain upon debonding, damage to the bracket or permanent damage to the enamel including flaking, cracks or tooth fracture. Numerous studies have evaluated techniques to reduce the risk of enamel damage when debonding ceramic brackets, including the use of debonding pliers. Debonding pliers produce a concentrated stress within the adhesive, resulting in cohesive failures within the resin or adhesive failures outside the resin. Methods: A total of 75 caries-free extracted human premolar teeth were randomly divided into 3 groups: ClearVu ceramic bracket (TP Orthodontics, LaPorte, IN), Radiance Plus ceramic bracket (American Orthodontics, Sheboygan, WI) and Mini Uni-Twin metal bracket (3M Unitek, Monrovia, CA). The Instron Universal Testing Machine Model 8841 with a customized jig with a bracket removing plier was used to debond the brackets. The teeth were microscopically evaluated to determine the location of bond failure. Selected teeth were evaluated with the scanning electron microscope to evaluate for enamel cracks and tear-outs. Results: A one-way ANOVA was created and no significant differences in shear bond strength were discovered between the three groups. Using a chi-square test of independence it was determined that the brackets all possessed a different ARI score. After examining the standardized residuals, we found that Radiance Plus Ceramic bracket and ClearVu Ceramic bracket were both likely to have favorable bond failure patterns, compared to the Mini Uni-Twin Metal bracket. Radiance Plus was most likely to debond at the bracket-adhesive surface, with a majority or all of the adhesive on the tooth after debond. Teeth with unfavorable bond failure patterns (ARI score of 0 or 1) were evaluated with the scanning electron microscope. 11% of the total teeth in the study had enamel damage, including cracks and tear-outs. 62.5% of these teeth were from the ClearVu ceramic bracket group. Conclusions: Our results show that both Radiance Plus ceramic bracket and ClearVu ceramic brackets are comparable to the gold standard metal bracket used in this study, the Mini Uni-Twin, in terms of shear bond strength. Radiance Plus ceramic bracket had the most favorable bond failure pattern, but shattered more during debonding. ClearVu ceramic bracket had the most enamel damage when evaluated with the scanning electron microscope. American Orthodontics’ Radiance Plus Ceramic bracket is the recommended bracket of those studied.

Yes / Nowadays Fiber Reinforced Polymers (FRPs) represent a well-established technique for rehabilitation of Reinforced Concrete (RC) and masonry structures. However, the severe degradation of mechanical properties of FRP under high temperature and fire as well as poor sustainability represents major weak points of organic-based systems. The use of eco-friendly inorganic geopolymeric matrices, alternative to the polymeric resins, would be highly desirable to overcome these issues. The present work aims to investigate the bond characteristic of a novel Steel Reinforced Geopolymeric Matrix (SRGM) strengthening system externally bonded to a concrete substrate having low mechanical properties. SRGM composite material consists of stainless steel cords embedded into a fireproof geopolymeric matrix. Single-lap shear tests by varying the bonded length were carried out. The main failure mode observed of SRGM-concrete joints was debonding at the fiber-matrix interface. Test results also suggest the effective bond length. On the basis of the experimental results, a cohesive bond-slip law was proposed. / Part of the analyses were developed within the activities of Rete dei Laboratori Universitari di Ingegneria Sismica (ReLUIS) for the research program funded by the Dipartimento di Protezione Civile (DPC), Progetto DPC/ReLUIS 2016–AQ DPC/ReLUIS 2014–2016.