Machining of hybrid composites

Tese de doutoramento. Engenharia Mecânica. Faculdade de Engenharia. Universidade do Porto. 200

Analysis and quantification of damage in polymer composite materials

The specific characteristics of composite materials, like carbon fibre reinforced plastics, have been leading to their rising importance and widespread use. As these parts are normally produced in a nearnet shape, secondary operations, like drilling, are necessary prior to their assembly in complex structures. It is still difficult to define a machining process that enables free damage holes, due to the peculiar laminar nature of these materials. So, the definition of a drilling process that minimizes delamination and increases reliability in produced parts combined with satisfactory cost and productivity is still of major importance in the composites manufacturing industry. In this paper two sets of unidirectional coupons from plates with carbon fibre as reinforcement and epoxy resin as matrix, are drilled using five different drilling tool strategies and two feed rates for uneven damage extension. One of the strategies is the use of a pre-drilling option. Then the delamination is assessed using enhanced radiography and, finally, two diverse mechanical tests are performed on the resulting coupons: three point bending and pin bearing. The results allowed establishing and modelling, with the help of statistical tools, the relations between the damaged area caused by drilling and the material’s mechanical resistance. The bending resistance does not vary greatly with the damage area. On the other hand, the bearing resistance decreases with the increase of the damaged area.info:eu-repo/semantics/publishedVersio

Analyzing objects in images for estimating the delamination influence on load carrying capacity of composite laminates

The use of fiber reinforced plastics has increased in the last decades due to their unique properties. Advantages of their use are related with low weight, high strength and stiffness. Drilling of composite plates can be carried out in conventional machinery with some adaptations. However, the presence of typical defects like delamination can affect mechanical properties of produced parts. In this paper delamination influence in bearing stress of drilled hybrid carbon+glass/epoxy quasi-isotropic plates is studied by using image processing and analysis techniques. Results from bearing test show that damage minimization is an important mean to improve mechanical properties of the joint area of the plate. The appropriateness of the image processing and analysis techniques used in the measurement of the damaged area is demonstrated

Caracterización morfométrica de poblaciones de abejas (Apis mellifera iberiensis) de la region centro de Portugal

La morfometría se utiliza para la discriminación de varias (sub) especies de insectos, en particular en el campo de la Apis mellifera L. En Portugal continental, la A. m. iberiensis es considerada la principal raza autóctona, a pesar de la insuficiencia de estudios morfométricos que 'autentiquen' esta subespecie.info:eu-repo/semantics/publishedVersio

Delaminação na furação de laminados carbono/epóxido

A produção de peças estruturais em materiais compósitos, nomeadamente os de matriz epóxida reforçada com fibras de carbono, tem-se tornado cada vez mais importante face à combinação das suas características específicas, como elevada rigidez e o baixo peso. Embora por um lado o custo destes materiais tenha vindo a tornar-se numa barreira cada vez menor para a sua utilização, a necessidade de operações de acabamento, incluindo a furação, aumenta o custo final das peças dificultando a sua utilização. De facto, as dificuldades e os danos associados à operação de furação, e consequentes rejeições por falta de qualidade, podem acarretar um custo final considerável. Tais dificuldades resultam da natureza não-homogénea dos compósitos, podendo resultar na ocorrência de diversos tipos de dano, sendo os mais frequentes a delaminação, o arrancamento das fibras e os danos devidos ao sobreaquecimento da matriz.Neste trabalho são apresentados os resultados de um estudo comparativo de furação de placas carbono/epóxido, variando o diâmetro e a geometria da ferramenta e utilizando uma velocidade de corte constante e dois avanços distintos. Durante a furação foi efectuada uma medição das forças axiais para posterior comparação com a avaliação da extensão do dano. A análise de dano baseou-se na realização de ensaios não-destrutivos às placas furadas, por radiografia digital com recurso a líquidos contrastantes. Para medição da extensão do dano recorreu-se a técnicas de processamento e análise de imagem. Adicionalmente, os valores resultantes da aplicação de critérios de quantificação da extensão do dano foram comparados com os resultados do ensaio mecânico de esmagamento, "Bearing test" ASTM D5961 - 08.Os resultados experimentais obtidos permitem confirmar e quantificar a importância de uma selecção adequada das ferramentas e parâmetros de corte na minimização do dano causado pela execução de furos em laminados carbono/epóxido

Experimental assessment of delamination extension on carbon / epoxy drilled plates

In the last decades, composite materials have been getting predominance, due to their peculiar characteristics, making their application attractive in the most diverse areas. One of the most used machining processes is drilling. This process allows for the use of mechanical connections to join parts in non-permanent connections, unlike the adhesive joints which are permanent connections.Thus, there is a need for a broad assessment of the damage caused by the drilling to the material. This work presents a study on how the machining parameters affect the delamination extension by drilling a set of carbon fiber reinforced polymer plates. Enhanced radiography and image analysis techniques are utilized and, in the end, a correlation between these results and the mechanical characteristics of the machined plates is obtained. Different drilling parameters are used, namely two feed rates while keeping the spindle speed constant, and three different drill geometries (Step, Brad and Helical). The thrust force is monitored during drilling and after drilling, parts are non-destructively and destructively (bearing, pin-bearing) tested. The results show that, although the thrust force varies and the delamination extension is affected by machining parameters, the mechanical resistance obtained in the tests did not evidence significant variations. The results show that, although the thrust force, varying around 50% in average, and the delamination extension, with a variation of 8%, are affected by machining parameters, the mechanical resistance obtained in the tests did not evidence significant variations, with an average difference of 2%. The main outcome of this work is to demonstrate that existing bearing tests may not the most suitable ones to assess mechanical consequences of drilling damage extension

Acqusition and data analysis of the eco-efficiency for the establishment of indicators parameters for industrial environmental sustainability

The industrial activity is inevitably associated with a certain degradation of the environmental quality, because is not possible to guarantee that a manufacturing process can be totally innocuous. The eco-efficiency concept is globally accepted as a philosophy of entreprise management, that encourages the companies to become more competitive, innovative and environmentally responsible by promoting the link between its companies objectives for excellence and its objectives of environmental excellence issues. This link imposes the creation of an organizational methodology where the performance of the company is concordant with the sustainable development. The main propose of this project is to apply the concept of eco-efficiency to the particular case of the metallurgical and metal workshop industries through the development of the particular indicators needed and to produce a manual of procedures for implementation of the accurate solution