A dificuldade de realizar a patência apical, tendo em vista que os canais radiculares apresentam algum grau de curvatura, exigiu o desenvolvimento de instrumentos rotatórios para agilizar o tempo operatório e facilitar sua execução. O objetivo deste estudo foi avaliar a influência de diferentes instrumentos de patência, utilizados 1 mm além do forame apical, no tempo de ação, transporte e centralização do canal radicular de canais radiculares curvos. Trinta e três raízes mesiais de molares superiores com curvatura entre 20 e 40 graus e raio menor que 10 mm foram selecionadas e divididas em 3 grupos (n = 11): R-Pilot #12.5 taper 0.04 (VDW, Munich, Alemanha), ProDesign Logic #25 taper 0.01 (Easy Equipamentos Odontologicos, Belo Horizonte, Brasil) e ProGlider #16 e taper variável de 0.02 a 0.08 (Dentsply Maillefer, Ballaigues, Suiça). Através de imagens pré e pós-operatórias de microtomografia computadorizada foram feitas as análises de transporte e centralização do canal radicular. Ainda, o tempo de ação de cada um dos instrumentos foi cronometrado. Para avaliar o transporte, foi utilizado o teste ANOVA. Para avaliar a centralização foi utilizado o teste Kruskal-Wallis. O tempo de ação foi avaliado pelo teste de Kruskal-Wallis e Post hoc de Dunn. O nível de significância foi de 5% para todos os testes aplicados. Não houve diferença estatística entre os grupos nas análises de transporte e centralização. Já na análise de tempo, o instrumento ProGlider se mostrou significativamente mais rápido se comparado com o ProDesign Logic 25.01 (P<0,05), o instrumento R-Pilot não foi diferente do ProGlider e Logic (p>0,05). Os instrumentos de patência utilizados neste estudo, e trabalhados 1 mm além do forame apical, permaneceram relativamente centralizadas dentro do canal radicular e promoveram transporte apical mínimo, sendo clinicamente irrelevante. / The difficulty of performing the apical patency, considering that the root canals present some degree of curvature, required the development of rotary instruments to speed up the operative time and facilitate its execution. The aim of this study was to evaluate the influence of different glide path files, used 1 mm beyond the apical foramen, on the preparation time, apical transportation and centering of the root canal of curved roots. Thirty three mesiobuccal roots from maxillary molars, with 20 to 40 degrees of curvature and presenting radio curvature lower than 10 mm were selected and divided in 3 groups (n = 11): R-Pilot #12.5 taper 0.04 (VDW, Munich, Germany), ProDesign Logic #25 taper 0.01 (Easy Equipamentos Odontologicos, Belo Horizonte, Brazil) ProGlider #16 e taper variable of 0.02 to 0.08 (Dentsply Maillefer, Ballaigues, Switzerland). Analysis of transportation and centration of root canal was performed using pre and postoperative computerized microtomography images and the work time of each file was measured. To evaluate the apical transportation, ANOVA test was used, while a Kruskal-Wallis test was used to assess centering ability. As for action time, Kruskal-Wallis and Dunn tests were performed. The level of significance was 5 % in all tests. No statistical difference was found amongst the groups for the variables apical transportation and centralization. When evaluated the action time, the ProGlider file has been significantly faster when compared to ProDesign Logic 25.1 (P<0.05).while R-pilot has not differed from ProGlider and Logic (P>0.05). The glide path files used – 1 mm beyond the apical foramen – remained relatively centralized inside the root canal and promoted minimal apical transportation, expressing no clinical relevance.

Alloy NiTi with nearequiatomic composition of nickel and titan belongs to a group of metal materials with a shape memory effect (Shape memory alloys). NiTi alloys are a guite attractive materials not only as practical shape memory alloys with hight strenght and ductility but also as those exhibiting unique physical properties. The production of these matrerials is complying with chemical composition. Final charakteristics of alloy are influenced by these bounderies and also by mechanical-heat treatment. This work deal with DSC evaluation of homogenity of ingot structure of NiTi alloy containing 50,8 at.% Ni. The alloy was melted in Y2O3 cricible. In the end the results of DSC method are compared to the microstructure of alloy obtained by SEM and TEM methods.

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The unique ability of shape memory alloys (SMAs) to remember and recover their original shape after large deformation offers vast potential for their integration in advanced engineering applications. SMAs can generate recoverable shape changes of several percent strain even when opposed by large stresses owing to reversible deformation mechanisms such as twinning and stress-induced martensite. For the most part, these alloys have been largely used in the biomedical industry but with limited application in other fields. This limitation arises from the complexities of prevailing microstructural mechanisms that lead to dimensional instabilities during repeated thermomechanical cycling. Most of these mechanisms are still not fully understood, and for the most part unexplored. The objective of this work was to investigate these deformation and transformation mechanisms that operate within the low temperature martensite and high temperature austenite phases, and changes between these two states during thermomechanical cycling. This was accomplished by combined experimental and modeling efforts aided by an in situ neutron diffraction technique at stress and temperature. The primary focus was to investigate the thermomechanical response of a polycrystalline Ni49.9Ti50.1 (in at.%) shape memory alloy under uniaxial deformation conditions. Starting with the deformation of the cubic austenitic phase, the microstructural mechanisms responsible for the macroscopic inelastic strains during isothermal loading were investigated over a broad range of conditions. Stress-induced martensite, retained martensite, deformation twinning and slip processes were observed which helped in constructing a deformation map that contained the iv limits over which each of the identified mechanisms was dominant. Deformation of the monoclinic martensitic phase was also investigated where the microstructural changes (texture, lattice strains, and phase fractions) during room-temperature deformation and subsequent thermal cycling were captured and compared to the bulk macroscopic response of the alloy. This isothermal deformation was found to be a quick and efficient method for creating a strong and stable two-way shape memory effect. The evolution of inelastic strains with thermomechanical cycling of the same NiTi alloy, as it relates to the alloy stability, was also studied. The role of pre-loading the material in the austenite phase versus the martensite phase as a function of the active deformation modes (deformation processes as revealed in this work) were investigated from a macroscopic and microstructural perspective. The unique contribution from this work was the optimization of the transformation properties (e.g., actuation strain) as a function of deformation levels and pre-loading temperatures. Finally, the process used to set actuators, referred to as shape setting, was investigated while examining the bulk polycrystalline NiTi and the microstructure simultaneously through in situ neutron diffraction at stress and temperature. Knowledge gained from the binary NiTi study was extended to the investigation of a ternary Ni-rich Ni50.3Ti29.7Hf20 (in at.%) for use in high-temperature, high-force actuator applications. This alloy exhibited excellent dimensional stability and high work output that were attributed to a coherent, nanometer size precipitate phase that resulted from an aging treatment. Finally, work was initiated as part of this dissertation to develop sample environment equipment with multiaxial capabilities at elevated temperatures for the in situ neutron diffraction measurements of shape memory alloys on the VULCAN Diffractometer at Oak Ridge National Laboratory. The developed capability will immediately aid in making rapid multiaxial v measurements on shape memory alloys wherein the texture, strain and phase fraction evolution are followed with changes in temperature and stress. This work was supported by funding from the NASA Fundamental Aeronautics Program, Supersonics Project including (Grant No. NNX08AB51A). This work has also benefited from the use of the Lujan Neutron Scattering Center at LANSCE, which is funded by the Office of Basic Energy Sciences DOE. LANL is operated by Los Alamos National Security LLC under DOE Contract No. DE-AC52-06NA25396.

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In the last decade, metal-graphene composites have seen significant progress and have received increasing attention because of graphene's ability to improve the mechanical properties. The main mechanism of improvement in metal graphene composite is based on the impeding of dislocations by graphene sheets. The work includes studying the mechanisms behind the improvement caused by graphene sheets and particles using Molecular Dynamics and Density Functional Theory. Interatomic potentials that play an important role in determining the accuracy of Molecular dynamics simulations are developed for Cu-C, Ni-C, Ti-C, and Ni-Ti-C systems. Nanolayered metal-graphene composites are fabricated and the effect of graphene particles on crack's path are investigated by electron microscopy. The mechanisms behind crack's behavior is investigated by atomistic simulations and by comparing energy release rates. Metallic systems that do not deform by dislocations like metallic glasses, NiTi etc. are reinforced with graphene and are also examined by atomistic simulations. In addition, a novel metal-graphene composite in which the metal matrix undergoes a uniform large recoverable phase transformation when subjected to mechanical loading is proposed and investigated using atomistic simulations. The material has the potential to overcome the long-standing challenge of transferring the extraordinary mechanical performance of nanoscale materials to the bulk level. / Doctor of Philosophy / In the last decade, metal-graphene composites have seen significant progress and have received increasing attention because of graphene's ability to improve the mechanical properties. The main mechanism of improvement in metal graphene composite is based on the impeding of dislocations by graphene sheets. The work includes studying the mechanisms behind the improvement caused by graphene sheets and particles by studying the interaction of metal and Carbon atoms in graphene. Functions that simulate these interactions play important role in determining the accuracy simulations. These functions are developed for Cu-C, Ni-C, Ti-C, and Ni-Ti-C systems. Nanolayered metal-graphene composites are fabricated and the effect of graphene particles on crack's path are investigated by electron microscopy. The mechanisms behind crack's behavior is investigated by atomistic simulations and by comparing energy release rates. Metallic systems that do not deform by dislocations like metallic glasses, NiTi etc. are reinforced with graphene and are also examined by atomistic simulations. In addition, a novel Graphene-Metal composite in which the metal matrix undergoes a uniform large recoverable phase transformation when subjected to mechanical loading is proposed and investigated using atomistic simulations. The material has the potential to overcome the long-standing challenge of transferring the extraordinary mechanical performance of nanoscale materials to the bulk level.