A técnica All-on-Four foi idealizada visando diminuir a extensão do cantilever nas reabilitações de pacientes edêntulos com próteses implantossuportadas. Contudo, ainda persistem questionamentos relacionados ao comportamento biomecânico dos implantes e da própria técnica All-on-Four, posto que, questões como a perda óssea peri-implantar e falência de componentes da prótese ainda não estão claramente elucidadas. O objetivo da pesquisa foi avaliar a dissipação de tensões em próteses implantossuportadas dos tipos Branemark e All-on-Four, sob carga oclusal estática, e o papel do lado de balanceio e do comportamento do complexo implantes/próteses. Foram confeccionadas seis réplicas de mandíbula humana em resina fotoelástica, divididas em dois grupos:um com quatro implantes dispostos axialmente e paralelas entre si no espaço interforaminal (mandíbulas Branemark), e outro com quatro implantes inseridos de acordo com a técnica All-on-Four. Confeccionou-se uma prótese total implantossuportada, de maneira que se adaptasse em todas as seis mandíbulas. O experimento foi conduzido com o auxílio de um dispositivo giratório de carga, que permitiu a visualização das mandíbulas por todos os ângulos, sem alteração da carga aplicada. Após a fixação padronizada do corpo de prova no dispositivo, a prótese foi parafusada sobre os implantes da mandíbula. Os carregamentos de carga foram feitos em três pontos: no cantilever da prótese, no primeiro pré-molar e na incisal dos incisivos centrais inferiores. Para cada ponto de aplicação das cargas, fotografaram-se as mandíbulas nos lados de trabalho, de balanceio e na linha mediana, vestibular e na linha mediana também por lingual. Pelos resultados observados, quando as cargas foram aplicadas em regiões mais anteriores da prótese, as tensões nos implantes distais inclinados atenuaramse e as outras regiões da mandíbula apresentaram tensões menores e melhor distribuídas. As franjas também mostraram que a angulação dos implantes distais promoveu mudanças no eixo de rotação do conjunto implantes/prótese. Assim como verificou-se que o implante mais distal do lado de balanceio mostrou atuação conjunta com o implante distal do lado de trabalho nas mandíbulas com implantes axiais e, o mais distal do lado de balanceio nas mandíbulas com implantes inseridos segundo a técnica All-on-Four, mostrou tensão nos ápices, denotando função de estaca. Pela metodologia empregada foi possível concluir que, uma prótese total implantossuportada, segundo a técnica All-on-Four, apresentou melhor melhor dissipação das cargas oclusais e o lado de balanceio teve papel fundamental no auxílio à dissipação de cargas oclusais. / The All-on-Four technique was conceived in order to decrease the length of the cantilever in the rehabilitation of edentulous patients with implant-supported prosthesis. However, still persist questions related to the biomechanical behavior of implants and the proper technique All-on-Four, since issues such as peri-implant bone loss and failure of the prosthetic components are not yet clearly elucidated. The purpose of the study was to evaluate the dissipation of tensions in the Branemark implant-supported prosthesis and All-on-Four, under static occlusal load, and the role of the balancing side and the complex behavior of implants / prostheses. Six replicas of the human mandible were made in photoelastic resin, divided into two groups: one with four implants placed axially and parallel to each other in interforaminal space (Branemark jaws), and another four implants inserted according to the All-on-Four technique. It was made an implant-supported denture, so that would fit in all six jaws. The experiment was conducted with the aid of a rotating load device, which permitted visualization of the jaws from all angles, without changing the applied load. After the standardized setting of specimen in the device, the prosthesis was screwed onto the implants in the jaw. The cargo shipments were made on three points: the cantilever prosthesis, in the first premolar and the lower central incisor incisal. For each point of application of loads, photograph was taken from the work sides of the jaws, balancing and the midline, bucal view and the midline lingual also. By the observed results, when loads were applied to more anterior regions of the prosthesis, the stresses in the distal inclined implants attenuated and other regions of the mandible showed lower stresses and better distributed. The fringes also showed that the angulation of the distal implants promoted changes in the axis of rotation of the implant / prosthesis. As it was found that the most distal implantat on the balancing side showed joint action with the distal implant of the working side in the jaw with axial implants, and the most distal implant on the balancing side of jaw with implants inserted according to All-on Four technique, the tension showed apices, denoting stake function. For the methodology it was concluded that an implant-supported denture, according to the All-on-Four technique, had a better dissipation of occlusal loads and balancing side was fundamental hole in helping to dissipate occlusal loads.

A técnica All-on-Four foi idealizada visando diminuir a extensão do cantilever nas reabilitações de pacientes edêntulos com próteses implantossuportadas. Contudo, ainda persistem questionamentos relacionados ao comportamento biomecânico dos implantes e da própria técnica All-on-Four, posto que, questões como a perda óssea peri-implantar e falência de componentes da prótese ainda não estão claramente elucidadas. O objetivo da pesquisa foi avaliar a dissipação de tensões em próteses implantossuportadas dos tipos Branemark e All-on-Four, sob carga oclusal estática, e o papel do lado de balanceio e do comportamento do complexo implantes/próteses. Foram confeccionadas seis réplicas de mandíbula humana em resina fotoelástica, divididas em dois grupos:um com quatro implantes dispostos axialmente e paralelas entre si no espaço interforaminal (mandíbulas Branemark), e outro com quatro implantes inseridos de acordo com a técnica All-on-Four. Confeccionou-se uma prótese total implantossuportada, de maneira que se adaptasse em todas as seis mandíbulas. O experimento foi conduzido com o auxílio de um dispositivo giratório de carga, que permitiu a visualização das mandíbulas por todos os ângulos, sem alteração da carga aplicada. Após a fixação padronizada do corpo de prova no dispositivo, a prótese foi parafusada sobre os implantes da mandíbula. Os carregamentos de carga foram feitos em três pontos: no cantilever da prótese, no primeiro pré-molar e na incisal dos incisivos centrais inferiores. Para cada ponto de aplicação das cargas, fotografaram-se as mandíbulas nos lados de trabalho, de balanceio e na linha mediana, vestibular e na linha mediana também por lingual. Pelos resultados observados, quando as cargas foram aplicadas em regiões mais anteriores da prótese, as tensões nos implantes distais inclinados atenuaramse e as outras regiões da mandíbula apresentaram tensões menores e melhor distribuídas. As franjas também mostraram que a angulação dos implantes distais promoveu mudanças no eixo de rotação do conjunto implantes/prótese. Assim como verificou-se que o implante mais distal do lado de balanceio mostrou atuação conjunta com o implante distal do lado de trabalho nas mandíbulas com implantes axiais e, o mais distal do lado de balanceio nas mandíbulas com implantes inseridos segundo a técnica All-on-Four, mostrou tensão nos ápices, denotando função de estaca. Pela metodologia empregada foi possível concluir que, uma prótese total implantossuportada, segundo a técnica All-on-Four, apresentou melhor melhor dissipação das cargas oclusais e o lado de balanceio teve papel fundamental no auxílio à dissipação de cargas oclusais. / The All-on-Four technique was conceived in order to decrease the length of the cantilever in the rehabilitation of edentulous patients with implant-supported prosthesis. However, still persist questions related to the biomechanical behavior of implants and the proper technique All-on-Four, since issues such as peri-implant bone loss and failure of the prosthetic components are not yet clearly elucidated. The purpose of the study was to evaluate the dissipation of tensions in the Branemark implant-supported prosthesis and All-on-Four, under static occlusal load, and the role of the balancing side and the complex behavior of implants / prostheses. Six replicas of the human mandible were made in photoelastic resin, divided into two groups: one with four implants placed axially and parallel to each other in interforaminal space (Branemark jaws), and another four implants inserted according to the All-on-Four technique. It was made an implant-supported denture, so that would fit in all six jaws. The experiment was conducted with the aid of a rotating load device, which permitted visualization of the jaws from all angles, without changing the applied load. After the standardized setting of specimen in the device, the prosthesis was screwed onto the implants in the jaw. The cargo shipments were made on three points: the cantilever prosthesis, in the first premolar and the lower central incisor incisal. For each point of application of loads, photograph was taken from the work sides of the jaws, balancing and the midline, bucal view and the midline lingual also. By the observed results, when loads were applied to more anterior regions of the prosthesis, the stresses in the distal inclined implants attenuated and other regions of the mandible showed lower stresses and better distributed. The fringes also showed that the angulation of the distal implants promoted changes in the axis of rotation of the implant / prosthesis. As it was found that the most distal implantat on the balancing side showed joint action with the distal implant of the working side in the jaw with axial implants, and the most distal implant on the balancing side of jaw with implants inserted according to All-on Four technique, the tension showed apices, denoting stake function. For the methodology it was concluded that an implant-supported denture, according to the All-on-Four technique, had a better dissipation of occlusal loads and balancing side was fundamental hole in helping to dissipate occlusal loads.

Orientadores: Marcelo Marotta Araújo, Roger William Fernandes Moreira / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba / Made available in DSpace on 2018-08-23T00:56:38Z (GMT). No. of bitstreams: 1 Moura_AndrezzaLauriade_M.pdf: 4155630 bytes, checksum: 44572134d9e31084a7892cb0866a1d79 (MD5) Previous issue date: 2013 / Resumo: O propósito no estudo foi avaliar comparativamente, através de teste de carregamento linear e análise fractográfica, duas marcas de material de fixação interna estável com dois métodos de fixação em fraturas simuladas em corpo de hemimandíbulas de alumínio. O trabalho foi dividido em dois grupos: Grupo I com duas estruturas de alumínio semelhantes à hemimandíbulas e fixação com duas placas de titânio de quatro furos do sistema 2,0mm, sendo uma placa na zona de compressão e outra zona de tensão, totalizando 20 placas de titânio; e grupo II, com duas estruturas de alumínio semelhantes à hemimandíbulas e fixação de uma placa de titânio de quatro furos do sistema 2,0mm na zona neutra de corpo de mandíbula, totalizando 10 placas de titânio. Testes de carregamento linear foram realizados por meio da máquina para ensaio universal mecânica Instron®, até a fratura do material. Após os testes, foram realizadas as análises fractográficas das superfícies de fratura dos materiais de fixação (grupos I e II) através de microscópio eletrônico de varredura FEI®, com o objetivo de analisar orientações, texturas e falhas dos materiais. Médias e desvio padrão das cargas e deslocamentos foram avaliados aplicando-se a Análise de Variância (ANOVA) two-way e teste de Tukey em nível de significância de 5%. Os resultados mostraram que o método de fixação com duas placas retas de quatro furos apresentou maior resistência à carga (p<0,01), quando comparado ao grupo de apenas uma placa de titânio na zona neutra mandibular. Ainda, a marca Traumec® apresentou maior resistência mecânica (p<0,01) quando utilizada no método com duas placas de fixação e a marca Tóride® (p<0,01) apresentou maior resistência as carga quando utilizada no método com apenas uma placa de fixação. A fractografia informou que todas as fraturas ocorreram por sobrecarga dúctil e micromecanismo alveolar / Abstract: The purpose of the study was to comparatively evaluate, through linear load test and fractographic analysis, two brands of stabel internal fixation in two methods of fixation in simulated body fractures in aluminium hemimandibules. The study was divided into two groups: Group I with two aluminum structures similar to hemimandibles for fixation of one 2,0mm miniplate in the compression zone and another one in tension zone, totaling 20 miniplates; and group II, with two aluminum structures similar to hemimandibles for fixation of one 2,0mm miniplate in the neutral zone of the mandible, totaling 10 miniplates. Mechanical tests were performed via mechanical universal testing machine Instron¿ until complete failure of the material. After the tests, fractography analysis of fractured surfaces were done in all materials (groups I and II) by a FEI¿ scanning electron microscopy, with the objective of analyzing orientation and textures of materials failures. Means and standard deviations of load and displacement were evaluated by applying the analysis of variance (ANOVA) two-way and the Tukey test at a significance level of 5%. The results showed that the method of fixation with two titanium plates with four holes showed higher resistance loads (p<0,01), when compared to only one titanium plate in the neutral zone of the mandible. Furthermore, the brand Traumec¿ showed higher mechanical strength (p<0,01) when used in the method with two fixing plates and the brand Toride¿ (p<0,01) showed a higher resistance to loads when used in the method with only one miniplate. The fractography reported that all fractures occurred in ductile overload and alveolar micromechanisms / Mestrado / Cirurgia e Traumatologia Buco-Maxilo-Faciais / Mestra em Clínica Odontológica

Orientador: Kleber Gomes Franchini / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Ciências Médicas / Made available in DSpace on 2018-08-20T23:08:02Z (GMT). No. of bitstreams: 1 Cardoso_Leandro_M.pdf: 3831901 bytes, checksum: 40e5df211d7e6fd923f654bd8d3a1ec1 (MD5) Previous issue date: 2012 / Resumo: Nas doenças do coração ocorre hipertrofia e remodelamento do ventrículo esquerdo com impacto negativo na evolução clínica. Esses fatores influenciam independentemente o risco cardiovascular por elevarem a predisposição a infartos do miocárdio, ao desenvolvimento de insuficiência cardíaca e ao aparecimento de arritmias ventriculares graves. Estruturalmente ocorrem crescimento e degeneração dos miócitos cardíacos, fibrose e alterações da microcirculação. Estas alterações comprometem irreversivelmente a histoarquitetura do miocárdio, limitando a eficácia dos tratamentos convencionais, principalmente no estágio mais avançado caracterizado pela insuficiência cardíaca. A rede de sinalização celular envolvida na resposta das células miocárdicas (miócito e não miócitos) a forças mecânicas tem papel crítico na compreensão da patogênese da hipertrofia. A quinase de adesão focal (FAK), uma enzima associada à sinalização por integrinas, é ativada precocemente e exerce influência no desenvolvimento e sustentação da resposta hipertrófica do miocárdio à sobrecarga pressórica. Nesse estudo foi avaliado o efeito de um composto inédito derivado de quinazolina (BZLO) com potencial ação inibitória da FAK no coração de camundongos submetidos à sobrecarga pressórica por coarctação da aorta. In vitro, esse composto inibiu a atividade catalítica da FAK purificada com IC50 de 1nM. In vivo, o tratamento dos camundongos submetidos à coarctação da aorta com o composto (BZLO) provocou inibição do resíduo Tyr397 da FAK. Demonstrando que o composto não só preveniu, mas também promoveu regressão da hipertrofia do ventrículo esquerdo típica do modelo, acompanhada de atenuação da hipertrofia dos cardiomiócitos e da fibrose intersticial, e preservação da função ventricular. Esses resultados indicam que o tratamento com o composto (BZLO), presumivelmente por inibir a FAK, atenua as alterações estruturais e funcionais provenientes da sobrecarga pressórica crônica no ventrículo esquerdo de camundongos, sugerindo seu potencial como alternativa na prevenção e tratamento da insuficiência cardíaca / Abstract: Cardiac remodeling and hypertrophy have negative impact in the evolution of heart disease. They raise predisposition to myocardium infarction, heart failure and fatal ventricular arrhythmias, being independent markers of cardiovascular prognosis. Cardiomyocyte growth followed by degeneration, interstitial fibrosis and alterations in the microcirculation can be detected structurally in hypertrophic hearts. These alterations jeopardize myocardium tissue architecture irreversibly limiting therapeutic efficacy especially in advanced stages of disease with heart failure. The understanding of signaling network in response to mechanical stimuli is crucial in the study of cardiac hypertrophy. Focal adhesion kinase (FAK) an enzyme linked to signaling by integrins is activated in response to pressure overload and influences the development of myocardial hypertrophic response. In the present study, a compound based on quinazoline scaffold which is a FAK inhibitor, named BZLO, is examined for its effects on cardiac hypertrophy of mice model of aortic constriction. BZLO strongly inhibits catalytic activity of purified FAK in vitro (IC50 = 1nM). Satisfactory bioavailability of BZLO was observed after oral administration. BZLO treatment decreased FAK phosphorylation at Tyr397 and attenuated cardiomyocyte growth and interstitial fibrosis preserving cardiac function in the mice model of chronic pressure overload induced by aortic constriction. These findings suggest that BZLO is effective in attenuating the deleterious structural and functional consequences of chronic pressure overload in mice heart, suggesting that it has the potential to be considered as an option for the prevention and treatment of heart failure / Mestrado / Fisiopatologia Médica / Mestre em Ciências

Indiana University-Purdue University Indianapolis (IUPUI) / Background: Interim restoration for a lost anterior tooth is often needed for temporary esthetic and functional purposes. Materials for interim restorations usually have less strength than ceramic or gold and can suffer from fracture. Several approaches have been proposed to reinforce interim restorations, among which fiber reinforcement has been regarded as one of the most effective methods. However, some studies have found that the limitation of this method is the poor polymerization between the fibers and the composite resin, which can cause debonding and failure. 64 Purpose: The purpose of this study was to investigate the effects of different polymerization methods as well as fiber types on the mechanical behavior of fiberreinforced composite resin. Material and Methods: A 0.2-mm thick fiber layer from strip fibers or mesh fibers embedded in uncured monomers w as fabricated with polymerization (two-step method) or without polymerization (one-step method), on top of which a 1.8-mm composite layer was added to make a bar-shape sample, followed by a final polymerization. Seventy-five specimens were fabricated and divided into one control group and four experimental groups (n=15), according to the type of glass fiber (strip or mesh) and polymerization methods (one-step or two-step). Specimens were tested for flexural strength, flexural modulus, and microhardness. The failure modes of specimens were observed by scanning electron microscopy (SEM). Results: The fiber types showed significant effect on the flexural strength of test specimens (F = 469.48; p < 0.05), but the polymerization methods had no significant effect (F = 0.05; p = 0.82). The interaction between these two variables was not significant (F = 1.73; p = 0.19). In addition, both fiber types and polymerization steps affected the flexural modulus of test specimens (F = 9.71; p < 0.05 for fiber type, and F = 12.17; p < 0.05 for polymerization method). However, the interaction between these two variables was not significant (F = 0.40; p = 0.53). Both fiber types and polymerization steps affected the Knoop hardness number of test specimens (F = 5.73; p < 0.05 for polymerization method. and F = 349.99; p < 0.05 for fiber type) and the interaction between these two variables was also significant (F = 5.73; p < 0.05). SEM images revealed the failure mode tended to become repairable while fiber reinforcement was 65 existed. However, different polymerization methods did not change the failure mode. Conclusion: The strip fibers showed better mechanical behavior than mesh fibers and were suggested for use in composite resin reinforcement. However, different polymerization methods did not have significant effect on the strength and the failure mode of fiber-reinforced composite

Indiana University-Purdue University Indianapolis (IUPUI) / Traditional resin luting agents generally have mechanical properties that are superior to the newer so-called “universal” self-etching/self-adhesive resin luting agents. However, recent reports indicate that some properties of these new luting agents have been improved, approaching those of the traditional etch and rinse resin luting agents. The objective of this study was to test some mechanical properties of four of these self-etching/self-adhesive resin luting agents [Maxcem Elite (ME), Multilink Automix (MA), RelyX Unicem (RU), SmartCem 2 (SC)] and compare them to a traditional etch and rinse resin luting agent [RelyX ARC (RA)] and a resin-modified glass ionomer luting cement [Fuji Plus (FP)], both of which have much longer histories of clinical success. By comparing the properties of the newer cements to the standards, it may be possible to determine how clinically successful the newer cements may be. The mechanical properties tested were flexural strength (FS) and shear bond strength (SBS). The FS test included making beams of each material, storing them in water for periods of time (24 hours and 90 days) and then performing a three-point bending test on a universal testing machine. The 90 day groups were thermocycled. The SBS test involved preparing human molar specimens, making flat dentin surfaces. Composite cylinders were fabricated, luted to the dentin surfaces with each of the materials tested, stored in water for periods of time (24 hours or 90 days), and then a knife edge shear test was performed on a universal testing machine. The 90 day groups were thermocycled. A Weibull-distribution survival analysis was performed. The results revealed significant differences in the FS of all materials tested at 24 hours. After 90 days and thermocycling, only SC and RA were not significantly different. At both time periods, FP had the lowest and MA the highest FS. The SBS results showed MA, RA, and RU to have the highest bond strengths; SC and ME the lowest at 24 hours. After 90 days and thermocycling, RA had significantly higher bond strength than all other groups; ME, FP and SC had the lowest. The self-etching/self-adhesive resin luting agents all performed at least as well as FP, with the exception of SC (SBS 24 hour). They did not all perform as well as RA, with the exception of SC (FS 90 day), MA (SBS 24 hour, FS 24 hour and 90 day), and RU (SBS 24 hour). The newer luting agents should expect to have clinical success, regarding flexural strength and shear bond strength, at least as good as resin-modified glass ionomer luting cements and approach the level of traditional etch and rinse resin luting agents.

Keratinocyte traction forces play a crucial role in wound healing. The aim of this study was to develop a novel cell traction force (CTF) transducer system based on cholesteryl ester liquid crystals (LC). Keratinocytes cultured on LC induced linear and isolated deformation lines in the LC surface. As suggested by the fluorescence staining, the deformation lines appeared to correlate with the forces generated by the contraction of circumferential actin filaments which were transmitted to the LC surface via the focal adhesions. Due to the linear viscoelastic behavior of the LC, Hooke's equation was used to quantify the CTFs by associating Young's modulus of LC to the cell induced stresses and biaxial strain in forming the LC deformation. Young's modulus of the LC was profiled by using spherical indentation and determined at approximately 87.1+/-17.2kPa. A new technique involving cytochalasin-B treatment was used to disrupt the intracellular force generating actin fibers, and consequently the biaxial strain in the LC induced by the cells was determined. Due to the improved sensitivity and spatial resolution ( approximately 1mum) of the LC based CTF transducer, a wide range of CTFs was determined (10-120nN). These were found to be linearly proportional to the length of the deformations. The linear relationship of CTF-deformations was then applied in a bespoke CTF mapping software to estimate CTFs and to map CTF fields. The generated CTF map highlighted distinct distributions and different magnitude of CTFs were revealed for polarized and non-polarized keratinocytes.

El texto completo de este trabajo no está disponible en el Repositorio Académico UPC por restricciones de la casa editorial donde ha sido publicado. / PURPOSE: To evaluate the effect of aqueous solutions of chlorhexidine digluconate (CHX) in different concentrations on bond strength to eroded dentin up to 6 months, using normal dentin as a control. METHODS: Exposed flat dentin of extracted third molars was only ground with 600-grit SiC paper/1 minute (normal dentin - N), or subsequently eroded by a regular-cola soft-drink (eroded dentin - E). N and E were acid-etched, washed, dried and rehydrated with 1.5 μL, respectively, of distillated water (control - NC / EC); of 0.004% CHX (N0.004% / E0.004%); or of 2% CHX (N2% / E2%). Adper Single Bond 2 was applied in all specimens and resin composite buildups were constructed with Filtek Z350. Specimens were sectioned in beams, which were tested (μTBS) immediately or after 6 months of aging. RESULTS: Microtensile bond strength to eroded dentin was always significantly lower than that to normal dentin. Application of tested CHX solutions did not exert a significant effect immediately; however, after aging, the 2% CHX prevented abrupt bond strength loss both to eroded and normal dentin. / Revisión por pares

El texto completo de este trabajo no está disponible en el Repositorio Académico UPC por restricciones de la casa editorial donde ha sido publicado. / PURPOSE: To assess the influence of simulated oral erosive/abrasive challenges on the bond strength of an etch-and-rinse two-step bonding system to enamel using an in situ/ex vivo protocol. METHODS: Bovine enamel blocks were prepared and randomly assigned to four groups: CONT - control (no challenge), ABR - 3x/day-1 minute toothbrushing; ERO - 3x/day - 5 minutes extraoral immersion into regular Coca Cola; and ERO+ABR - erosive protocol followed by a 1-minute toothbrushing. Eight blocks were placed into an acrylic palatal appliance for each volunteer (n = 13), who wore the appliance for 5 days. Two blocks were subjected to each of the four challenges. Subsequently, all the blocks were washed with tap water and Adper Single Bond 2/Filtek Z350 were placed. After 24 hours, 1 mm2 beams were obtained from each block to be tested with the microtensile bond strength test (50 N load at 0.5 mm/minute). The data were statistically analyzed by one-way RM-ANOVA and Tukey's tests (alpha = 0.05). RESULTS: No difference was detected among the ABR, ERO, and CONT groups (P > 0.05). ERO+ABR group yielded lower bond strengths than either the ABR and ERO groups (P < 0.0113). / Revisión por pares

Schraubenverbindungen sind eine technische Lösung um Stromschienen aus Aluminium mechanisch und elektrisch zu verbinden. Als stationäre Verbindungen sollen sie für eine Zeit von 30 Jahren und mehr den Betriebsstrom übertragen ohne dabei die genormten, zulässigen Grenztemperaturen zu überschreiten. Die Grundvoraussetzung für eine langzeitstabile, stromführende Verbindung ist ein geringer Anfangswert des Verbindungswiderstands nach der Montage. Dieser ist abhängig von der Kontaktkraft und kann für jede Kombination aus Fügeelementen, Werkstoffen und Topografie der Leiteroberflächen an der konstruierten Verbindung experimentell bestimmt werden. Allgemeingültige Modellrechnungen zum elektrischen Kontaktverhalten einer Schraubenverbindung mit Stromschienen waren bisher nicht möglich. In dieser Arbeit wurde durch numerische Berechnungen und experimentelle Untersuchungen eine Korrelation zwischen dem mechanischen und dem elektrischen Kontaktverhalten einer Schraubenverbindung mit Stromschienen hergestellt. Es wurde die inhomogene mechanische Spannungsverteilung auf der Kontaktfläche zwischen den Stromschienen bestimmt und damit ein Modell zum Berechnen des elektrischen Kontakt- und Verbindungswiderstands mit der Berücksichtigung des tatsächlich stromdurchflossenen Leitermaterials aufgestellt. Der Verbindungswiderstand kann sich, abhängig von der Temperatur und Zeit, durch verschiedene Alterungsmechanismen erhöhen. Das Altern durch den Abbau der Kontaktkraft wurde an Schraubenverbindungen mit unbeschichteten Stromschienen aus verschiedenen Aluminiumwerkstoffen untersucht. Es wurde die Kontaktkraft und der Verbindungswiderstand über einen Zeitraum von bis zu vier Jahren bei Temperaturen zwischen (80 … 160) °C bestimmt. Diese Untersuchungen wurden für ein System mit und ein System ohne federnde Fügeelemente durchgeführt, sowie die Kontaktkraft für eine Betriebszeit von 30 Jahren berechnet. Im Vergleich mit der experimentell bestimmten Mindestkontaktkraft und dem Werkstoffverhalten wurde eine Prognose zur Langzeitstabilität der stromführenden Verbindungen für eine konstante Belastung im Betrieb gegeben. Weiterhin wurden mit dem zeit und temperaturabhängigen Verhalten der Aluminiumwerkstoffe zulässige Grenz-temperaturen ermittelt, bei denen keine Entfestigung während der Betriebszeit auftritt. Für Schraubenverbindungen mit vernickelten und versilberten Stromschienen wird eine identische, dauerhaft zulässige Grenztemperatur von 115 °C in der Norm angegeben [N1]. Die elektrischen und mechanischen Eigenschaften der metallischen Überzüge, sowie die Reaktivität mit der Umgebung sind aber sehr unterschiedlich. An stromführenden und stromlos im Wärmeschrank bei 115 °C und 140 °C gelagerten Verbindungen wurde der Verbindungs-widerstand bis zu einer Zeit nach t = 25.000 h bestimmt. Es wurde das elektrische Kontakt- und Langzeitverhalten von Schraubenverbindungen mit zwei beschichteten Stromschienen, sowie einer beschichteten und einer unbeschichteten Stromschiene aus Aluminium untersucht und bewertet. Abhängig vom Schichtaufbau des metallischen Überzugs mit verschiedenen Zwischenschichten und Schichtdicken wurde der Einfluss der Interdiffusion mit der Bildung intermetallischer Phasen (IMP) auf das Langzeitverhalten der Verbindungen untersucht.:1 Einleitung 2 Werkstoffe für elektrische Leiter und metallische Überzüge 2.1 Aluminiumwerkstoffe für die Elektrotechnik 2.1.1 Einfluss der Mikrostruktur 2.1.2 Herstellen, Umformen und Nachbehandeln 2.1.3 Ausscheidungshärten von Al-Mg-Si-Legierungen 2.2 Metallische Überzüge aus Silber und Nickel 2.2.1 Elektrolytisches Beschichten 2.2.2 Autokatalytisches Beschichten 3 Grundlagen zu stromdurchflossenen Flächenkontakten 3.1 Kontaktverhalten in einer Schraubenverbindung mit Stromschienen 3.2 Gütefaktor zum Beurteilen der Qualität der stromführenden Verbindung 4 Alterung stromführender Verbindungen 4.1 Chemische Reaktionen 4.2 Kraftabbau in einer Schraubenverbindung 4.2.1 Elastische und plastische Verformung 4.2.2 Zeit- und temperaturabhängige Werkstoffentfestigung 4.2.3 Viskoplastische Verformung abhängig von der Temperatur 4.2.4 Berechnen der Kontaktkraft 4.3 Interdiffusion zwischen unterschiedlichen metallischen Werkstoffen 4.3.1 Metallische Überzüge aus Silber 4.3.2 Metallische Überzüge aus Nickel als Zwischen- und Deckschicht 5 Aufgabenstellung 6 Untersuchungen zu beschichteten und unbeschichteten elektrischen Flächenkontakten 6.1 Experimentell ermittelte Eigenschaften der Aluminiumwerkstoffe 6.2 Geometrie der untersuchten Stromschienen und Fügeelemente der Schraubenverbindungen 6.2.1 Schraubenverbindung ohne federnde Fügeelemente (OFF) 6.2.2 Schraubenverbindung mit federnden Fügeelementen (MFF) [79] 6.3 Vorbehandlung, Montage und Inbetriebnahme der Langzeitversuche 6.4 Erzeugen und Messen der Kontaktkraft im Langzeitversuch 7 Elektrisches Kontakt- und Langzeitverhalten von Schraubenverbindungen mit unbeschichteten Stromschienen 7.1 Untersuchungen zum Kontaktverhalten 7.1.1 Mechanisches Berechnungsmodell 7.1.2 Elektrisches Berechnungsmodell 7.2 Untersuchungen zum Langzeitverhalten 7.2.1 Zeit- und temperaturabhängige Härte des Aluminiums 7.2.2 Zeit- und temperaturabhängige elektrische Leitfähigkeit des Aluminiums 7.2.3 Versuchsergebnisse zum Langzeitverhalten 7.2.4 Abschätzen der Restkontaktkraft 7.2.5 Zusammenhang zwischen der Kraft und dem Widerstand der Verbindung 7.3 Zusammenfassung 8 Elektrisches Kontakt- und Langzeitverhalten von Schraubenverbindungen mit vernickelten und versilberten Stromschienen 8.1 Untersuchungen zum Kontaktverhalten 8.2 Langzeitverhalten von Schraubenverbindungen mit zwei identisch beschichteten Stromschienen 8.2.1 Zeit- und temperaturabhängige Härte der metallischen Überzugwerkstoffe 8.2.2 Zeit- und temperaturabhängige elektrische Leitfähigkeit des Ni P (Typ 5) 8.3 Kraftabbau an Schraubenverbindungen mit zwei identisch beschichteten Stromschienen 8.4 Langzeitverhalten von Schraubenverbindungen mit einer beschichteten und einer unbeschichteten Stromschiene 8.5 Mikroskopische Untersuchungen 8.6 Weitere Untersuchungen zur Alterung von Schraubenverbindungen mit zwei vernickelten Stromschienen 8.6.1 Einfluss des Phosphorgehaltes in metallischen Überzügen aus Ni P 8.6.2 Einfluss der Art der thermischen Alterungsprüfung – Dauerlast / Wechsellast 8.7 Zusammenfassung 9 Ausblick Literaturverzeichnis Abbildungsverzeichnis Tabellenverzeichnis Anhang / A bolted joint is one technical possibility for mechanically and electrically connecting two busbars made of aluminium. This stationary connection shall carry the operating current for more than 30 years without exceeding the permissible limiting temperature given by international standards. For long-term stable, current-carrying connections a good electrical contact behaviour with a low initial value of the joint resistance is required after bolting. The joint resistance depends on contact force and can be measured at the constructed electrical joint for each combination of joining elements, conductor materials and pretreatment of conductor surfaces. General calculations for the electrical contact behaviour of current-carrying joints with flat contact surfaces, such as bolted joints with busbars, were not possible until now. In this thesis numerical calculations and experimental investigations were used to establish the relationship between mechanical and electrical contact behaviour of a bolted joint with busbars. In the first step, the inhomogeneous distribution of the mechanical stress was calculated on the contact area between two busbars. In the second step, a calculation model for the joint resistance and the contact resistance was created and verified by experiments. The joint resistance can increase by different ageing mechanisms depending on operating temperature and time. Ageing by the reduction of contact force was investigated on bolted joints with uncoated busbars made of various aluminium alloys. In long-term tests, these joints were loaded with temperatures between 80 °C and 160 °C. The contact forces and joint resistances were determined for up to four years of operation. Bolted joints with spring elements and without spring elements were investigated. Based on the results of these long-term tests, the contact force was calculated for up to 30 years of operation and compared with the experimentally determined minimum contact force of the joint. Together with the temperature and time dependent behaviour of the conductor materials, the long-term stability of the joints was evaluated for the case of constant thermal load during operation. Furthermore, permissible limiting temperatures at which no softening occurs during operation could be determined for various aluminium alloys. An identical limiting temperature of 115 °C is permanently permitted for bolted joints with nickel-coated and silver-coated busbars [N1] but the mechanical and electrical properties of the materials for these metallic coatings are very different. The chemical reactivity of both coatings also differs according to the environment. In long-term tests at current-carrying joints and joints which were aged in ovens at temperatures of (115 and 140) °C, the joint resistances were determined up to an operating time of t = 25.000 hours. Bolted joints with two identical coated busbars and also bolted joints with one coated and one bare busbar made of aluminium were investigated and evaluated. The influence of metallic coatings with different intermediate layers and layer thicknesses on the contact and long-term behaviour of the joints were examined. Due to interdiffusion between different materials, intermetallic compounds (IMC) can be formed. The ageing of bolted joints with coated busbars caused by the formation of IMC with poor electrical and mechanical properties compared to pure metals was investigated.:1 Einleitung 2 Werkstoffe für elektrische Leiter und metallische Überzüge 2.1 Aluminiumwerkstoffe für die Elektrotechnik 2.1.1 Einfluss der Mikrostruktur 2.1.2 Herstellen, Umformen und Nachbehandeln 2.1.3 Ausscheidungshärten von Al-Mg-Si-Legierungen 2.2 Metallische Überzüge aus Silber und Nickel 2.2.1 Elektrolytisches Beschichten 2.2.2 Autokatalytisches Beschichten 3 Grundlagen zu stromdurchflossenen Flächenkontakten 3.1 Kontaktverhalten in einer Schraubenverbindung mit Stromschienen 3.2 Gütefaktor zum Beurteilen der Qualität der stromführenden Verbindung 4 Alterung stromführender Verbindungen 4.1 Chemische Reaktionen 4.2 Kraftabbau in einer Schraubenverbindung 4.2.1 Elastische und plastische Verformung 4.2.2 Zeit- und temperaturabhängige Werkstoffentfestigung 4.2.3 Viskoplastische Verformung abhängig von der Temperatur 4.2.4 Berechnen der Kontaktkraft 4.3 Interdiffusion zwischen unterschiedlichen metallischen Werkstoffen 4.3.1 Metallische Überzüge aus Silber 4.3.2 Metallische Überzüge aus Nickel als Zwischen- und Deckschicht 5 Aufgabenstellung 6 Untersuchungen zu beschichteten und unbeschichteten elektrischen Flächenkontakten 6.1 Experimentell ermittelte Eigenschaften der Aluminiumwerkstoffe 6.2 Geometrie der untersuchten Stromschienen und Fügeelemente der Schraubenverbindungen 6.2.1 Schraubenverbindung ohne federnde Fügeelemente (OFF) 6.2.2 Schraubenverbindung mit federnden Fügeelementen (MFF) [79] 6.3 Vorbehandlung, Montage und Inbetriebnahme der Langzeitversuche 6.4 Erzeugen und Messen der Kontaktkraft im Langzeitversuch 7 Elektrisches Kontakt- und Langzeitverhalten von Schraubenverbindungen mit unbeschichteten Stromschienen 7.1 Untersuchungen zum Kontaktverhalten 7.1.1 Mechanisches Berechnungsmodell 7.1.2 Elektrisches Berechnungsmodell 7.2 Untersuchungen zum Langzeitverhalten 7.2.1 Zeit- und temperaturabhängige Härte des Aluminiums 7.2.2 Zeit- und temperaturabhängige elektrische Leitfähigkeit des Aluminiums 7.2.3 Versuchsergebnisse zum Langzeitverhalten 7.2.4 Abschätzen der Restkontaktkraft 7.2.5 Zusammenhang zwischen der Kraft und dem Widerstand der Verbindung 7.3 Zusammenfassung 8 Elektrisches Kontakt- und Langzeitverhalten von Schraubenverbindungen mit vernickelten und versilberten Stromschienen 8.1 Untersuchungen zum Kontaktverhalten 8.2 Langzeitverhalten von Schraubenverbindungen mit zwei identisch beschichteten Stromschienen 8.2.1 Zeit- und temperaturabhängige Härte der metallischen Überzugwerkstoffe 8.2.2 Zeit- und temperaturabhängige elektrische Leitfähigkeit des Ni P (Typ 5) 8.3 Kraftabbau an Schraubenverbindungen mit zwei identisch beschichteten Stromschienen 8.4 Langzeitverhalten von Schraubenverbindungen mit einer beschichteten und einer unbeschichteten Stromschiene 8.5 Mikroskopische Untersuchungen 8.6 Weitere Untersuchungen zur Alterung von Schraubenverbindungen mit zwei vernickelten Stromschienen 8.6.1 Einfluss des Phosphorgehaltes in metallischen Überzügen aus Ni P 8.6.2 Einfluss der Art der thermischen Alterungsprüfung – Dauerlast / Wechsellast 8.7 Zusammenfassung 9 Ausblick Literaturverzeichnis Abbildungsverzeichnis Tabellenverzeichnis Anhang