Nesta pesquisa foi realizada a avaliação da influência das ciclagens térmica, mecânica e de pH na resistência de união de sistemas adesivos à dentina de dentes decíduos. Para tal, cavidades oclusais foram preparadas em 80 molares decíduos e restauradas com os sistemas adesivos Single Bond e Clearfil SE Bond e resina composta Z100. Os dentes restaurados com cada um dos sistemas adesivos foram divididos em oito grupos (n= 5), de acordo com as condições de tratamento: ciclagem térmica (2000 ciclos, 5°C e 55°C), ciclagem de pH (10 ciclos, 8 horas de imersão em solução desmineralizadora e 16 em solução remineralizadora), ciclagem mecânica (100.000 ciclos, 8 kg), térmica/pH, térmica/mecânica, pH/mecânica e térmica/pH/mecânica, além do grupo controle. Os dentes foram seccionados perpendicularmente à interface de união e foram obtidos espécimes com área de superfície aderida com cerca de 0,8 mm 2 . Os espécimes foram submetidos ao teste de microtração e à análise do padrão de fratura em microscopia eletrônica de varredura. Os valores obtidos, expressos em MPa, foram submetidos à Análise de Variância (p < 0,05). Não foram encontradas diferenças estatísticas significantes na comparação entre os sistemas adesivos avaliados nem para os grupos submetidos à aplicação dos estresses térmico, mecânico e térmico/pH. Os demais grupos apresentaram valores de resistência de união inferiores àqueles obtidos pelo grupo controle (p < 0,05) Fraturas do tipo adesiva/mista foram as mais prevalentes (95,9%). A resistência de união dos sistemas adesivos avaliados é negativamente influenciada pela aplicação combinada das tensões com naturezas distintas. / The influence of thermal, mechanical load and pH cycling on adhesive systems bond strength to primary dentin was evaluated. Occlusal cavities in 80 primary molars were prepared with diamond bur and restored with Single Bond and Clearfil SE Bond adhesive systems and Z100 composite. Teeth restored with each adhesive system were shared into eight groups according treatment condition: thermal cycling (2000 cycle, 5°C and 55°C), pH cycling (10 cycles, demineralization solution immersion to 8 hours and 16 hours in remineralization solution), mechanical load cycling (100.000 cycles, 8kg), thermal/pH, thermal/mechanical load, pH/mechanical load and thermal/pH/mechanical load, besides control groups. The teeth were transversally sectioned in two axis rendering 0,8mm 2 stick shaped specimen. Sticks were then submitted to microtensile bond testing with a crosshead speed of 1mm/min. Fracture analysis was performed by scanning electron microscopy. Bond strength means expressed in MPa were submitted to two-wav ANOVA (p<0.05). No statistically significant differences were found between the adhesive systems nor to thermal, mechanical load and thermal/pH stresses groups. Lower bond strength values were found to other groups compared to control (p<0.05). Adhesive/mixed failures were prevalent (95.9%). Bond strengths of evaluated adhesive systems were negatively influenced by distinct tension application.

Los volantes de inercia superan a las baterías eléctricas por su capacidad de absorber y ceder energía en poco tiempo y, si se fabrican con materiales compuestos, también por su reducido peso. La tesis presenta un estudio sobre los rotores de materiales compuestos aplicados a los acumuladores cinéticos para hacerlos más asequibles a usos industriales baratos. Para ello se proponen dos objetivos: obtener un sistema analítico de cálculo, y mejorar el diseño de rotores de bajo coste.Se desarrolla un sistema analítico de cálculo muy completo, tanto en las cargas como en las tensiones. Se consideran todas las cargas necesarias para el diseño mecánico del rotor: la fuerza centrífuga, la fuerza de aceleración y las tensiones residuales, térmica y de hidratación; y se determinan todas las componentes, normales y cortantes, de la tensión para cada punto del rotor.El cálculo en condiciones de tensión plana, utilizado por la mayoría de autores, se amplía con el cálculo en deformación axial constante, que es una variante mejorada de la deformación plana. Se comprueba que sus resultados son mejores que los de tensión plana cuando se comparan con los obtenidos en modelos de elementos finitos. Paralelamente, como aportación nueva de la tesis, se deducen las funciones de la variación de la tensión axial y de la tensión cortante radial-axial a lo largo del eje longitudinal del rotor. A partir de estos resultados se desarrolla un sistema general de cálculo que, además de unificar los sistemas de tensión plana y deformación axial constante, permite determinar todas las tensiones en cualquier posición radial-axial del rotor.Este sistema unificado de cálculo se amplia con tres particularidades: una aplicación de cálculo para resolver rotores multicapa, las ecuaciones especiales para los materiales singulares no resolubles con las ecuaciones generales, y el cálculo de capas con fibras orientadas axialmente aplicadas para refuerzo en configuraciones especiales.Con el objeto de mejorar las prestaciones del rotor se estudian dos procedimientos para crear tensiones de pretensado: generando tensiones durante el bobinado y utilizando las tensiones residuales térmicas. En el primero se elabora un sistema analítico de cálculo para determinar las tensiones residuales de bobinado y se complementa con una simulación mediante elementos finitos basada en submodelos incrementales. Ambos cálculos son capaces de simular el material no curado aplicando las propiedades viscoelásticas de los ensayos experimentales de otros autores. En el segundo se presenta un sistema nuevo, denominado pretensado térmico, basado en el curado por etapas, que genera tensiones residuales parecidas a las de bobinado pero con menos problemas de fabricación.El diseño de volantes se aplica a tres configuraciones básicas: rotores híbridos multicapa con materiales de rigidez progresiva, rotores de un solo material con anillos de elastómero y rotores con pretensado térmico.Sus prestaciones se valoran con tres variables: la masa, el volumen y el coste del material; de las cuales el coste es la principal y se utiliza para la optimización de la geometría.En cada configuración se determina la energía máxima para distintas relaciones de radios del rotor y se compara con el rotor de un sólo material. Se utilizan los materiales básicos usados en la fabricación de rotores: la fibra de carbono con matriz epoxi, la fibra de vidrio con matriz epoxi, el aluminio y el acero. Los dos materiales compuestos ofrecen mejores resultados que los metales, pero disminuyen sensiblemente en rotores con espesor de pared grande. En estos casos, la energía por unidad de coste mejora aplicando los anillos elásticos y el pretensado térmico. / Flywheels are better than electric batteries in that they absorb and yield energy in shorter time and, if made out of composite materials, also in that they weight less. This thesis presents a study of composite material rotors applied to kinetic accumulators in order to make them usable for low cost general industrial uses. Two objectives are proposed: a) to develop an analytical system for computation and b) to design alternatives in order to improve the performance on low-cost rotors.The analytical system is intended to be very complete, considering all relevant types of external loads and stress components. For the former, centrifugal, acceleration forces and residual, thermal and moisture stresses are included. For the latter, five normal and shear components are computed at each point of the rotor.The usual plane stress condition is expanded with the consideration of constant axial strain, along the lines of the plane strain hypothesis but with greater accuracy. It is shown that the current theory results fit the ones from finite elements much better than those from plain stress. As a new contribution, the functions for the axial stress and the radial-axial stress along the axis of the rotor are developed. From these results, a general system that unifies the plane stress and constant axial strain can compute the stress state at any position.In addition, the unified system includes three novel aspects: an extension of computation for multi-layer rotors, special equations for some materials in which behaviour present singularities and the computation of layers with fibers along the axial direction, which can be useful as a reinforcement for some configurations.Two procedures that can create beneficial residual stresses are studied: generating stresses during the filament winding and using the thermal stresses. For the first, analytical expressions are developed and validated and complemented with especially developed finite elements based on incremental submodels. In both cases the material is characterized by viscoelastic properties taken from the literature. For the second, a new procedure called thermal prestress is based on the accumulation of partial curing processes (by stages), which is able to create residual stresses similar to those of winding but involving simpler manufacturing.Three basic configurations are studied for the design: hybrid rotors with progressive stiffness along the radius, single material rotors with elastomer thin rings and rotors manufactured with thermal prestress, evaluating the performance as a function of the mass, volume and cost of the material. The latter is defined as the most important, and it is used as a reference for the geometry optimization.The maximum energy stored on each of the configurations is compared with that of a single material rotor, using the most common ones: glass and carbon fiber both with epoxy matrix, aluminium and steel. Results show that glass/epoxy has the highest storing capability per unit cost, although the number is greatly reduced when the thickness increases. If this rotor has a thin layer of carbon/epoxy, the capability does not increase, although it does with distributed elastomeric layers. There is also an increase with fabrication based on the thermal prestress technique.

This study expands on the work of ElHajjar and HajAli (2003) on a quantitative thermoelastic strain analysis method for composite materials. Computational models for various prepreg and thicksection composites are validated with experiments using this quantitative strain analysis method. This study provides this thermomechanical calibrations for prepreg S2glass/epoxy, Carbon/epoxy, and pultruded Eglass/polyester. A research collaboration with the Institute of Paper Science and Technology (IPST) focused on infrared thermography for defect detection in wood and fibrous materials and structural systems. This study provides some detailed information on various testing setups for fiber and corrugated board systems to analyze anomalies and manufacturing defects. Quantitative infrared thermography is suggested as a preferred method for assessing the bond quality in corrugated paper systems. Methods for tracking fullfield thermal data during fatigue have been developed for FRP composites. The temperature changes on the surface of an FRP composite caused by damage during fatigue are tracked and thermoelastic stress analysis (TSA) technique is developed to relate the surface deformation to the IR emission. Infrared thermography is developed for fatigue damage detection in FRP composites with stochastic methods for analyzing this fullfield data. Future damage detection techniques in aging aircraft will require quantitative and noncontact nondestructive evaluation (NDE) methods especially for composite components. Infrared (IR) thermograpy techniques are qualitatively used to assess and indirectly infer the durability of structural systems. A research collaboration with Lockheed Martin for nondestructive evaluation of composite lap shear joints led to a development of thermoelastic stress analysis techniques for evaluation aerospace structures. Infrared thermography is used to investigate failure initiation and progression in composite lap shear joints.

Forging temperature is one of the basic considerations in forging processes. In warm forging, the metals are forged at temperatures about the recrystallization temperature and below the traditional hot forging temperature. Warm forging has many advantages when compared to hot and cold forging. Accuracy and surface finish of the parts is improved compared to hot forging while ductility is increased and forming loads are reduced when compared to cold forging. In this study, forging process of a part which is currently produced at the hot forging temperature range and which needs some improvements in accuracy, material usage and energy concepts, is analyzed. The forging process sequence design with a new preform design for the particular part is proposed in warm forging temperature range and the proposed process is simulated using Finite Element Method. In the simulations, coupled thermal mechanical analyses are performed and the dies are modeled as deformable bodies to execute die stress analysis. Experimental study is also carried out in METU-BILTIR Center Forging Research and Application Laboratory and it has been observed that numerical and experimental results are in good agreement. In the study, material wastage is reduced by proposing using of a square cross section billet instead of a circular one, energy saving and better accuracy in part dimensions is achieved by reducing the forging temperature from the hot forging to the warm forging temperature range.

Semi-hot or warm forging is an economical alternative to the conventional forging processes by combining advantages of hot and cold forging processes. In this study, a new forging process sequence and design of the preform die for a part which has been produced by hot forging are proposed to be produced by semi-hot forging. Thermo-mechanical finite element analyses are performed over the stages of forging process. The billet and the dies are modeled as elastic-plastic bodies. Effects of preform die geometry on the die stresses and the forging load are investigated using finite element method. Comparison of the results obtained by using two different commercial finite element analysis programs is done for semi-hot and hot forging temperature ranges. The forging temperatures are determined for the particular part and the experiments are conducted by using the 1000 ton forging press. The parts are produced without any defects and material wastage in the form of flash is reduced. The numerical results are also compared with the experimental results and a good agreement is achieved.

Failure of metallic structures operating under shock loading is a common occurrence in engineering applications. It is difficult to estimate the response of complicated systems analytically, due to structure&rsquo / s dynamic characteristics and varying loadings. Therefore, experimental, numerical or a combination of both methods are used for evaluations. The experimental analysis of the shocks due to firing is done for 12.7mm Gatling gun and 25mm cannon. During the tests, the Gatling gun and the cannon are located on military Stabilized Machine Gun Platform and Stabilized Cannon Platform respectively. For the firing tests, ICP (integrated circuit piezoelectric) accelerometers are attached to obtain the loading history for corresponding points. Shock Response Spectrum (SRS) analysis (nCode Glypworks) is done to define the equivalent shock profiles created on test pieces and the mount of 25mm cannon by means of the gun and the cannon firing. Transient shock analysis of the test pieces and the mount are done by applying the obtained shock profiles on the parts in a finite element model (ANSYS). Furthermore, experimental stress analysis due to shock loading is performed for two different types of material and different thicknesses of the test pieces. The input data for the analysis is obtained through measurements from strain rosette precisely located at the critical location of the test pieces. As a result of the thesis, a proposal is tried to be introduced where strain energy density theory is applied to predict the shock failure at military structures.

Recycling of plastics always plays an important role in keeping our environment better and safe. With the rise in usage of plastics and industrialization, the need for recycling the plastics has become a big business and is getting bigger. This thesis work was done for a company called Rapid Granulator AB, which works with the recycling of plastics as a big trade in Sweden. Like all the industries across the globe are trying to be economical in every way, Rapid Granulator AB wanted to develop an economical design of their high quality granulating knife. For achieving the economical design, they wanted to study the behaviour of the rotating knife during the process of producing plastic granules. The granulator cutting process was simulated and numerical analysis was done on the rotating knife of a plastic granulator machine by using the finite element code ABAQUS with 3D stress elements to find out the critical stresses and forces acting on the rotating knife. The bolt preload was applied by Abaqus/Standard, and the results of implicit analysis were imported to Abaqus/Explicit for the impact analysis where the flow of stresses on the rotating knife during the impact with materials were simulated and studied. The study was done on knife models of different thickness to see if the thickness of the current knife model can be reduced. Analysis were done also on a knife model assembly with a double sided cutting edge knife to see if the knife model can be used to its full extent. The simulation models and analysis results were given to the company to develop a more economical knife model.

Šiame darbe pateikti kuro kaloringumo priklausomybės nuo drėgmės skaičiavimai. Atlikus bandymus, nustatyta katilo nominali ir minimali galia. Skaičiuojant tiesioginiu ir netiesioginiu metodu nustatytas katilo naudingumo keficientas. Atlikta katilo korpuso įtempimo būvio analizė. Buvo skaičiuojama katilo šiluminė varža, pateikti pasiūlymai katilo techninių parametrų gerinimui. / This paper presents the dependence on fuel moisture calorie calculations, tests the boiler nominal and minimum power. Calculation of direct and indirect method keficientas the boiler. Boiler body made of life stress analysis. The calculated resistance of the boiler įiluminė, proposals to improve technical parameters of the boiler.

No description available.

No description available.