Effect of Ageing on the Mechanical Performance of Thermoset Polymers: A Statistical Approach

The present work investigates the effect of three different ageing processes (natural, 100% relative humidity and salt spray) on the mechanical performance of two thermoset polymers, epoxy and polyester, commonly used as matrix phase in composite materials. A full factorial design is conducted to evaluate the effect of significant factors and interactions on moisture absorption, tensile and compressive strength and modulus of elasticity of the thermosets. Both polymers reveal a decrease in moisture absorption in the saline environment compared to the completely saturated condition (100% RH). Polyester polymers in harsh environments exhibit higher compressive properties compared to those subjected to natural conditioning. In general, polyester polymers, which are most affected by the positive effect of additional cross-linking, have less moisture absorption and superior mechanical properties compared to epoxy, which is more affected by the negative effect of plasticization

The Effect of Aluminium Surface Treatments on the Bonding Properties of Silica-Modified Epoxy Adhesive Joints: A Statistical Approach

A full factorial design is carried out to investigate the effects of different surface treatments, the inclusion of silica microparticles and the use of wash primer on the apparent shear strength and adherent strength of single-lap aluminium joints. Scanning electron microscopy, surface energy and roughness measurements are performed to characterise the aluminium surface. The results show that the use of wash primer decreases the apparent shear strength of the joints significantly. The cohesive failure of the primer is the main cause of the reduction in strength. On the other hand, the inclusion of 10 wt.% of silica microparticles in the adhesive layers increases the shear strength by 26%. Surfaces treated with NaOH for one minute, without using a wash primer, result in the most resistant joint. In contrast to the apparent shear strength, adherent strength is most effective when only degreasing is considered

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements

Untitled in english

Baseado no Fêmur e na prótese Coxo-Femural, realiza-se uma avaliação do comportamento mecânico dos ossos e suas próteses, analisando a influência do material e a forma da prótese na transmissão dos carregamentos ao osso de sorte a evitar a perda da união implante-osso e a aumentar a vida útil da prótese. Em primeiro lugar, realiza-se um estudo, baseado em levantamento bibliográfico, das características e composição do material ósseo humano. Em seguida, estuda-se a interação prótese-osso, em especifico a prótese coxo-femural por ser uma das mais empregadas na atualidade, alem do estudo dos métodos para a análise da transmissão de carregamentos e dos métodos de ensaios não destrutivos para a verificação dos resultados teóricos. A análise da transmissão dos carregamentos ao osso foi feita através de modelos de implantes de próteses coxo-femural de diferentes dimensões e módulos de elasticidade, empregando dois programas de cálculo pelo método dos elementos finitos, denominados por sap90 (para análise em duas dimensões) e algor (para análise em três dimensões). Os resultados obtidos pelo método dos elementos finitos foram verificados com holografia interferométrica em modelos físicos, feitos em resina epoxy, moldados em gesso com a configuração do fêmur e próteses enxertadas, com dimensões e características similares as utilizadas nos modelos teóricos de elementos finitos.The mechanic behavior of the humen boné Femur and the total hip prosthesis are evaluated by analysis of influence of the material and the shape of the prosthesis in the transmission of the loads to the boné, in order to avoid to lost of the union implant-bone and increase the useful life of the prosthesis. In the first place, it was carried out a bibliografic revision based on study of the characteristics and composition of the human bonés material. Immediately, it was studied prosthesis-bone interaction of the total hip prosthesis, the methods for the analysis of loads transmission and not destructive tests for the verification of the theoretical outputs. The analysis of loads transmission to the boné was carried out in total hip prosthesis models of several dimension and elasticity modules, employing two programs of calculation for the Finite Elements Method, SAP90 (for analysis in two dimension) and ALGOR (for analysis in three dimension). The putputs gotten by the Finite Elements Method were verified by interferometric holography in physical models, manufactured in EPOXY resin, with the configuration of the fêmur and metals prosthesis were implanted. The dimension and characteristics of the physical models were similars to them utilized in the theoretical models of Finite Element Finaly, it is possible to conclude that both methods are good tools in order to evaluate the mechanical structural behavior of bonés and their prosthesis

TUNED MASS DAMPER DESIGN FOR BRIDGE

<p>The deterioration and collapse of structures that are subjected to periodic loads, such as railway bridges, cause economic damage to the country. A solution to the above is the placement of Tuned Mass Dampers. Objective: To design the main components and parameters of Tuned Mass Dampers. Materials and Methods: The mass, damping and stiffness of the Tuned Mass Dampers are determined from the dynamic characteristics of the bridge. Results and Discussion: The graphs are obtained with the mass, damping and stiffness values of the Tuned Mass Damper, which ensure the reduction of the amplitude of the oscillations in the bridge. The displacements of the bridge before and after placing the Tuned Mass Damper are also obtained. The stability of three variants of springs is sized and checked, a Germanmade damper is selected and a Tuned Mass Damper model is proposed with the final arrangement of its elements. Conclusions: A significant reduction in the amplitude of the oscillations of the "Case Study" bridge is achieved by incorporating a Tuned Mass Damper with the calculated parameters. The stiffness obtained is very high for the design of the springs, so it was decided to distribute this parameter in three variants of Tuned Mass Damper. A model is exposed where the arrangement of its components is displayed</p&gt

DISEÑO DE AMORTIGUADOR DE MASA SINTONIZADO PARA PUENTE

Introducción: El deterioro y colapso de estructuras que son sometidas a cargas periódicas, como los puentes de ferrocarril, ocasionan daños económicos al país. Una solución a lo antes expuesto es la colocación de Amortiguadores de Masa Sintonizados. Objetivos: Diseñar los principales componentes y parámetros de un Amortiguador de Masa Sintonizado. Materiales y Métodos: Se determina la masa, el amortiguamiento y la rigidez del Amortiguador de Masa Sintonizado a partir de las características dinámicas del puente. Resultados y discusión: Se obtienen las gráficas con los valores de masa, amortiguamiento y rigidez del Amortiguador de Masa Sintonizado, que aseguran la reducción de la amplitud de las oscilaciones en el puente. También se obtienen los desplazamientos del puente antes y después de colocar el Amortiguador de Masa Sintonizado. Se dimensiona y se chequea la estabilidad de tres variantes de resortes, se selecciona un amortiguador de fabricación alemana y se propone un modelo de Amortiguador de Masa Sintonizado con la disposición final de sus elementos. Conclusiones: Se alcanza una significativa reducción en la amplitud de las oscilaciones del puente “Caso de Estudio” al incorporarle un Amortiguador de Masa Sintonizado con los parámetros calculados. La rigidez obtenida es muy elevada para el diseño de los resortes por lo que se decide distribuir este parámetro en tres variantes de Amortiguador de Masa Sintonizado. Se expone un modelo donde se visualiza la disposición de sus componentes

INFLUENCIA DE LA MASA, LA RIGIDEZ Y EL AMORTIGUAMIENTO EN LA DINÁMICA DE AMORTIGUADORES DE MASA SINTONIZADOS

Introducción: La reducción de las vibraciones en estructuras longevas y carentes de mantenimiento como los puentes de ferrocarril en Cuba, es un tema que actualmente va cobrando importancia. Una vía para lograrlo es la colocación de Amortiguadores de Masa Sintonizados. Objetivo: Determinar la influencia de la masa, la rigidez y el amortiguamiento en la amplificación dinámica de la estructura. Materiales y Métodos: Se realiza un estudio dinámico del puente ferroviario ubicado en el km 560 del Ferrocarril Central y del Amortiguador de Masa Sintonizado para el control de las vibraciones. Se ajusta el problema real al modelo matemático de sistemas de uno y dos grados de libertad. Resultados y Discusión: Se determina la influencia de los parámetros básicos (masa, rigidez y amortiguamiento) en la amplificación dinámica de la estructura, los desplazamientos de cada grado de libertad y la amplitud de las oscilaciones del puente y del Amortiguador de Masa Sintonizado como respuesta a la fuerza de excitación. Conclusiones: Se obtiene la influencia de la masa, la rigidez y el amortiguamiento en la respuesta dinámica del sistema. Se resuelve el modelo de dos grados de libertad, variando solamente el coeficiente de amortiguamiento del Amortiguador de Masa Sintonizado y se obtienen las gráficas de posición-tiempo. En las funciones de respuesta en frecuencia, se comprueba que el sistema alcanza su mayor amplificación dinámica cuando la frecuencia de la vibración producida por una carga externa coincide con la frecuencia natural de la estructura

Mechanical Characterization of a Polymer/Natural Fibers/Bentonite Composite Material with Implementation of a Continuous Damage Model

A characterization of composite materials of a polyester matrix reinforced with natural fibers of Cuban henequen and organophilized Cuban bentonite was carried out, the experimental results of which are used to formulate, implement, and validate a scalar damage model. The fibers were added on a weight basis of 15, 20, and 25% as a reinforcing material, and organophilized Cuban bentonite, in amounts of 3, 5, and 7% by weight, was added. Samples containing only polymer and fibers showed the best mechanical performance for 25% of fiber, with increases of 51% in the tensile strength and 169% on the impact resistance. Samples containing polymer and clay showed the best results for 5% of bentonite, with increases of 89% in the tensile strength and 83% on the impact resistance, and samples containing 25% fiber and 5% clay were also prepared and achieved a 98% increase in the tensile strength and 219% in the impact strength. The scalar damage model deals with an internal variable, which corresponds to the damage variable, together with a failure surface that allows identifying the mechanical state of the material dependent on the mechanical stress, obtaining an adequate correlation with the results of the experimental tests