The interfacial fracture performance of dicyandiamide cured epoxy/steel adhesive systems was thoroughly investigated. Fracture mechanics based testing was utilized to study several variables which were believed to influence the epoxy/steel interphase region, specifically the elasomeric toughener concentration, the dicyandiamide concentration, and the cure temperature. Bulk mechanical measurements were conducted to provide background information for comparison with the fracture data, and surface analyses were carried out on the neat adhesives and failed fracture specimens to provide insight into the locus and causes of failure. The addition of toughener drastically impacted the morphological, bulk mechanical, and adhesive properties in these latent cure systems. Modulus values decreased and bulk fracture toughness values increased with increasing toughener content. Static double cantilever beam (DCB), fatigue DCB, and notched coating adhesion (NCA) interfacial fracture performances all increased. X-ray photoelectron spectroscopy (XPS) and tunneling electron microscopy (TEM) analyses of the failed specimens revealed that chemical changes were more prominent at the epoxy/steel interphase than in the bulk of the materials. Morphological variations were also apparent with toughener level variations, but for a single formulation no differences between the bulk and intephase morphologies were seen. Evaluations were conducted on a series of elastomer modified model epoxy formulations cured with varying amounts of dicyandiamide. The modulus and bulk fracture toughness values were shown to be independent of dicyandiamide concentration, whereas the adhesive performance was greatly influenced. For increases in the concentration of dicyandiamide, single lap shear (SLS) failure strength values increased while quasi-static DCB and NCA test performances decreased. Fatigue DCB results showed improved adhesive performance at both high and low levels of dicyandiamide content. The results of the failure surface evaluations suggest that dicyandiamide variations produce significant chemical changes only in the epoxy/steel interphase region, and not in the bulk. Analyses were conducted on all of the above systems using two additional cure temperatures. The purpose of this work was to alter the dicyandiamide solubility, and possibly the dicy/epoxy reaction mechanisms, and to determine what influence these changes had on the interfacial fracture performance. In general it was found that performance increased as the cure temperature was increased. / Ph. D.

O objetivo deste estudo foi avaliar os resultados radiográficos obtidos pelas analises de subtração radiográfica digital e linear de implantes dentários com superfície SLA e SLActive submetidos a carga funcional e sobrecarga oclusal precoce restaurados com reconstruções em cantilever (pôntico suspenso). Cinco cães beagle tiveram seus pré-molares mandibulares extraídos bilateralmente. Após três meses, retalhos foram elevados e seis implantes (três SLA e três SLActive) foram instalados em um desenho de boca dividida e aleatorização por blocos. Após quatro semanas, os implantes foram restaurados em cada lado da mandíbula da seguinte forma: uma coroa unitária com contatos oclusais estáveis (OE), uma coroa e uma unidade de cantilever com contatos oclusais excessivos (SO), e um implante protegido pela unidade em cantilever que não recebeu carga funcional (NR). Os cães foram mantidos em um programa de controle de placa periódico, durante o período do experimento. Radiografias padronizadas foram tomadas utilizando-se guias radiográficas individualizadas e padronizadas em dois momentos: na instalação das próteses e 24 semanas após o carregamento. Análises de subtração radiográfica digital e medições lineares (entre um plano projetado entre os ombros do implante e o primeiro contato implante-osso) foram realizadas. As análises estatísticas, ANOVA para medidas repetidas, ANOVA para dados equilibrados e teste t de Bonferroni foram utilizados para identificar diferenças entre as médias, entre os seis grupos avaliados: SLA OE, SLA SO, SLA NR, SLActive OE, SLActive SO e SLActive NR. Achados gerais similares foram observados para os grupos SLA e SLActive (todos os grupos OE, NR e SO) em relação ao nível ósseo peri-implantar e as dimensões das áreas indicando alterações de densidade óssea ao redor dos implantes. As mensurações lineares variaram de 1,61 mm (grupo SLActive SO) a 1,94 mm (grupo SLA SO) no tempo 0 (antes da aplicação das cargas funcionais) e 2,00 mm (grupo SLA SO) a 2,99 mm (grupo SLActive NR) na avaliação após 24 semanas, sem diferenças estatisticamente significativas dentro ou entre-grupos (p = 0,672). Com relação à área de mudança de densidade óssea, esta variou de 0,91 mm2 (grupo SLA OE) para 1,40 mm2 (grupo SLA SO), mas sem diferenças significativas entre os grupos (p = 0,568). Por outro lado, um ganho de densidade óssea estatisticamente significativa foi encontrado para o grupo SLA com sobrecarga oclusal (p = 0,012). Nenhuma diferença significativa na alteração de densidade óssea foi detectada entre os outros cinco grupos (p> 0,05). Em conclusão, a sobrecarga oclusal precoce aplicada sobre implantes restaurados com reconstruções em cantilever, não levou a mudanças significativas na altura óssea peri-implantar após 24 semanas. No entanto, a densidade óssea ao redor de implantes SLA com sobrecarga oclusal, foi significativamente maior que nos outros grupos. / The objective of this study was to evaluate the radiographic outcomes of SLA and SLActive dental implants submitted to functional load and early occlusal overload restored with cantilever reconstructions. Five beagle dogs had their mandibular premolars extracted bilaterally. After three months, flaps were raised and six implants (three SLA and three SLActive) were installed in a block-randomized split-mouth design. After four weeks, implants were restored on each side of the mandible as follows: one single crown with stable occlusal contacts (OE), one crown and a cantilever unit with overt occlusal contacts (SO), and an implant protected by the cantilever unit not submitted to functional load (NR). The dogs were maintained in a strict and periodic plaque control program during the period of the experiment. Standardized radiographies were taken using standardized and individualized radiographic stents in two distinct moments: at prostheses installation and 24-weeks after loading. Digital subtraction radiography analyses and linear measurements were performed. Statistical analyses used repeated measures ANOVA and ANOVA for balanced data and the Bonferroni Student t test to identify differences between the means of the six evaluated groups: SLA OE, SLA SO, SLA NR, SLActive OE, SLActive SO and SLActive NR. Similar findings were found for SLA and SLActive groups regarding the peri-implant bone level and the area of bone density change around implants. Baseline linear measurements ranged from 1.61 mm (SLActive SO group) to 1.94 mm (SLA SO group) at baseline, and from 2.00 mm (SLA SO group) to 2.99 mm (SLActive NR group) at the 24-week evaluation, with no statistically significant differences within- or between-groups (p=0.672). With respect to the areas of bone density change, they ranged from 0.91 mm2 (SLA OE group) to 1.40 mm2 (SLA SO group), but without significant differences between groups (p=0.568). On the other hand, a statistically significant bone density gain was found for the overloaded SLA group (p=0.012). No significant differences in bone density change were detected between the other five groups (p>0.05). In conclusion, the early occlusal overload applied to implants restored with cantilever reconstructions did not lead to significant changes in the peri-implant bone height. However, bone density around overloaded SLA implants was significantly higher than in the other groups.

O objetivo deste estudo foi avaliar os resultados radiográficos obtidos pelas analises de subtração radiográfica digital e linear de implantes dentários com superfície SLA e SLActive submetidos a carga funcional e sobrecarga oclusal precoce restaurados com reconstruções em cantilever (pôntico suspenso). Cinco cães beagle tiveram seus pré-molares mandibulares extraídos bilateralmente. Após três meses, retalhos foram elevados e seis implantes (três SLA e três SLActive) foram instalados em um desenho de boca dividida e aleatorização por blocos. Após quatro semanas, os implantes foram restaurados em cada lado da mandíbula da seguinte forma: uma coroa unitária com contatos oclusais estáveis (OE), uma coroa e uma unidade de cantilever com contatos oclusais excessivos (SO), e um implante protegido pela unidade em cantilever que não recebeu carga funcional (NR). Os cães foram mantidos em um programa de controle de placa periódico, durante o período do experimento. Radiografias padronizadas foram tomadas utilizando-se guias radiográficas individualizadas e padronizadas em dois momentos: na instalação das próteses e 24 semanas após o carregamento. Análises de subtração radiográfica digital e medições lineares (entre um plano projetado entre os ombros do implante e o primeiro contato implante-osso) foram realizadas. As análises estatísticas, ANOVA para medidas repetidas, ANOVA para dados equilibrados e teste t de Bonferroni foram utilizados para identificar diferenças entre as médias, entre os seis grupos avaliados: SLA OE, SLA SO, SLA NR, SLActive OE, SLActive SO e SLActive NR. Achados gerais similares foram observados para os grupos SLA e SLActive (todos os grupos OE, NR e SO) em relação ao nível ósseo peri-implantar e as dimensões das áreas indicando alterações de densidade óssea ao redor dos implantes. As mensurações lineares variaram de 1,61 mm (grupo SLActive SO) a 1,94 mm (grupo SLA SO) no tempo 0 (antes da aplicação das cargas funcionais) e 2,00 mm (grupo SLA SO) a 2,99 mm (grupo SLActive NR) na avaliação após 24 semanas, sem diferenças estatisticamente significativas dentro ou entre-grupos (p = 0,672). Com relação à área de mudança de densidade óssea, esta variou de 0,91 mm2 (grupo SLA OE) para 1,40 mm2 (grupo SLA SO), mas sem diferenças significativas entre os grupos (p = 0,568). Por outro lado, um ganho de densidade óssea estatisticamente significativa foi encontrado para o grupo SLA com sobrecarga oclusal (p = 0,012). Nenhuma diferença significativa na alteração de densidade óssea foi detectada entre os outros cinco grupos (p> 0,05). Em conclusão, a sobrecarga oclusal precoce aplicada sobre implantes restaurados com reconstruções em cantilever, não levou a mudanças significativas na altura óssea peri-implantar após 24 semanas. No entanto, a densidade óssea ao redor de implantes SLA com sobrecarga oclusal, foi significativamente maior que nos outros grupos. / The objective of this study was to evaluate the radiographic outcomes of SLA and SLActive dental implants submitted to functional load and early occlusal overload restored with cantilever reconstructions. Five beagle dogs had their mandibular premolars extracted bilaterally. After three months, flaps were raised and six implants (three SLA and three SLActive) were installed in a block-randomized split-mouth design. After four weeks, implants were restored on each side of the mandible as follows: one single crown with stable occlusal contacts (OE), one crown and a cantilever unit with overt occlusal contacts (SO), and an implant protected by the cantilever unit not submitted to functional load (NR). The dogs were maintained in a strict and periodic plaque control program during the period of the experiment. Standardized radiographies were taken using standardized and individualized radiographic stents in two distinct moments: at prostheses installation and 24-weeks after loading. Digital subtraction radiography analyses and linear measurements were performed. Statistical analyses used repeated measures ANOVA and ANOVA for balanced data and the Bonferroni Student t test to identify differences between the means of the six evaluated groups: SLA OE, SLA SO, SLA NR, SLActive OE, SLActive SO and SLActive NR. Similar findings were found for SLA and SLActive groups regarding the peri-implant bone level and the area of bone density change around implants. Baseline linear measurements ranged from 1.61 mm (SLActive SO group) to 1.94 mm (SLA SO group) at baseline, and from 2.00 mm (SLA SO group) to 2.99 mm (SLActive NR group) at the 24-week evaluation, with no statistically significant differences within- or between-groups (p=0.672). With respect to the areas of bone density change, they ranged from 0.91 mm2 (SLA OE group) to 1.40 mm2 (SLA SO group), but without significant differences between groups (p=0.568). On the other hand, a statistically significant bone density gain was found for the overloaded SLA group (p=0.012). No significant differences in bone density change were detected between the other five groups (p>0.05). In conclusion, the early occlusal overload applied to implants restored with cantilever reconstructions did not lead to significant changes in the peri-implant bone height. However, bone density around overloaded SLA implants was significantly higher than in the other groups.

The diploma thesis deals with the design of the supporting structure of a road bridge over a reservoir. Two variants of bridging were processed. The selected variant is a three span continuous beam. It is made of box girder cross section with a variable height. The structure has a total length of 156,8 m and is built using balanced cantilever method. The bridge is designed and assessed according to the limit states for temporary and permanent design situations. Structural analysis, drawing documentation and visualization of the bridge is part of the work.

Low-temperature magnetic force microscopy was used to study the phase diagram of a La1/3Pr1/3Ca1/3MnO3 thin film grown on a (110) NdGaO3 (NGO) substrate by pulsed laser deposition. Traditionally, one can observe the phase change at the nanoscale level as the sample is cooled from room temperature through the transition temperature to liquid nitrogen temperatures, but in this case a fixed voltage ranging from 0 V to 31 V was applied before each cooling cycle. From in and ex situ transport measurements, it is observed that the temperature of the peak of the transition increases with applied field; however, the MFM images show that the magnetic transition begins at a lower temperature with the same increase in field. Thus, this dissertation shows that a new voltage control exists for the phase transition in certain manganites. / text

The objective of this study is to develop a robust portable nano-calorimeter sensor for detection of energetic materials, primarily explosives, combustible materials and propellants. A micro-cantilever sensor array is actuated thermally using bi-morph structure consisting of gold (Au: 400 nm) and silicon nitride (Si3N4: 600 nm) thin film layers of sub-micron thickness. An array of micro-heaters is integrated with the microcantilevers at their base. On electrically activating the micro-heaters at different actuation currents the microcantilevers undergo thermo-mechanical deformation, due to differential coefficient of thermal expansion. This deformation is tracked by monitoring the reflected ray from a laser illuminating the individual microcantilevers (i.e., using the optical lever principle). In the presence of explosive vapors, the change in bending response of microcantilever is affected by the induced thermal stresses arising from temperature changes due to adsorption and combustion reactions (catalyzed by the gold surface). A parametric study was performed for investigating the optimum values by varying the thickness and length in parallel with the heater power since the sensor sensitivity is enhanced by the optimum geometry as well as operating conditions for the sensor (e.g., temperature distribution within the microcantilever, power supply, concentration of the analyte, etc.). Also, for the geometry present in this study the nano-coatings of high thermal conductivity materials (e.g., Carbon Nanotubes: CNTs) over the microcantilever surface enables maximizing the thermally induced stress, which results in the enhancement of sensor sensitivity. For this purpose, CNTs are synthesized by post-growth method over the metal (e.g., Palladium Chloride: PdCl2) catalyst arrays pre-deposited by Dip-Pen Nanolithography (DPN) technique. The threshold current for differential actuation of the microcantilevers is correlated with the catalytic activity of a particular explosive (combustible vapor) over the metal (Au) catalysts and the corresponding vapor pressure. Numerical modeling is also explored to study the variation of temperature, species concentration and deflection of individual microcantilevers as a function of actuation current. Joule-heating in the resistive heating elements was coupled with the gaseous combustion at the heated surface to obtain the temperature profile and therefore the deflection of a microcantilever by calculating the thermally induced stress and strain relationship. The sensitivity of the threshold current of the sensor that is used for the specific detection and identification of individual explosives samples - is predicted to depend on the chemical kinetics and the vapor pressure. The simulation results showed similar trends with the experimental results for monitoring the bending response of the microcantilever sensors to explosive vapors (e.g., Acetone and 2-Propanol) as a function of the actuation current.

Aeroelastic behavior prediction is often confined to analytical or highly computational methods, so I developed a low degree of freedom computational method using structural finite elements and unsteady loading to cover a gap in the literature. Finite elements are readily suitable for determination of the free vibration characteristics of eccentric, elastic structures, and the free vibration characteristics fundamentally determine the aeroelastic behavior. I used Theodorsen’s unsteady strip loading formulation to model the aerodynamic loading on linear elastic structures assuming harmonic motion. I applied Hassig’s ‘p-k’ method to predict the flutter boundary of nonsymmetric, aeroelastic systems. I investigated the application of a quintic interpolation assumed displacement shape to accurately predict higher order characteristic effects compared to linear analytical results. I show that quintic interpolation is especially accurate over cubic interpolation when multi-modal interactions are considered in low degree of freedom flutter behavior for high aspect ratio HALE aircraft wings.

A research group at University of Skövde has developed an interphase element for implementation in the commercial FE-software Abaqus. The element is using the Tvergaard & Hutchinson cohesive law and is implemented in Abaqus Explicit version 6.7 using the VUEL subroutine. This bachelor degree project is referring to evaluate the interphase element and also highlight problems with the element. The behavior of the interphase element is evaluated in mode I using Double Cantilever Beam (DCB)-specimens and in mode II using End Notch Flexure (ENF)-specimens. The results from the simulations are compared and validated to an analytical solution. FE-simulations performed with the interphase element show very good agreement with theory when using DCB- or ENF-specimens. The only exception is when an ENF-specimen has distorted elements. When using explicit finite element software the critical time step is of great importance for the results of the analyses. If a too long time step is used, the simulation will fail to complete or complete with errors. A feasible equation for predicting the critical time step for the interphase element has been developed by the research group and the reliability of this equation is evaluated. The result from simulations shows an excellent agreement with the equation when the interphase element governs the critical time step. However when the adherends governs the critical time step the equation gives a time step that is too large. A modification of this equation is suggested.

This dissertation aims to advance the current state of use of silicon atomic force microscope (AFM) cantilevers with integrated heaters. To this end, the research consists of two primary thrusts - demonstrating new applications for the cantilevers, and advancing the current state of understanding of their thermal and mechanical behavior to enable further applications. Among new applications, two are described. In the first application, the cantilevers are used for nanoscale material deposition, using heat to modulate the delivery of material from the nanoscale tip. In the second application, the cantilever performs thermal analysis with nanoscale spatial resolution, enabling thermal characterization of near surface and composite interphase regions that cannot be measured with bulk analysis techniques. The second thrust of the research seeks to address fundamental questions concerning the precision use of heated cantilevers. Efforts to this end include characterizing the mechanical, electrical, and thermal behavior of the cantilevers, and optimizing calibration methodology. A technique is developed for calibrating the cantilever spring constant while operating at elevated temperature. Finally, an analytical model is developed for the heat flow in the cantilever tip and relevant dimensionless numbers that govern the relative importance of the various components of the thermal environment are identified. The dimensionless numbers permit exploration of the sensitivity of the tip-substrate interface temperature to the environmental conditions.

This work describes two closed-loop atomic force microscopy methods that utilize the heated silicon probe to interrogate surfaces. The first method identifies the softening temperatures of a selected polymer and organic substrate as a function of contact force and surface hardness. Motivation partly stems from nanosampling, which requires knowledge of phase-specific transitions to identify and extract mass from multicomponent systems for chemical analysis. In the second method, the cantilever is implemented as a Kelvin probe to study the effect of temperature on the measured contact potential. The objective is to ascertain whether the probe functions as a capable electrode for scanning Kelvin probe microscopy (SKPM) applications. This was achieved by performing heated force-distance experiments on a biased gold film with the tip operating at various potentials. Both experiments examine the interaction between the tip and substrate and analyze sample effects both induced and sensed by the cantilever.