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- Avaliação de ferramentas para a furação de laminadosPublication . Durão, Luís M.; Gonçalves, Daniel J. S.; Albuquerque, Victor Hugo C. de; Tavares, João Manuel R. S.A utilização crescente de materiais compósitos nos mais variados domínios coloca novos desafios no projecto de ferramentas de corte dedicadas a este tipo de materiais, ao invés da tradicional adaptação das ferramentas desenvolvidas para materiais metálicos. Neste artigo apresenta-se um estudo comparativo de geometrias de broca com o objectivo de reduzir o dano associado. Para tal, são analisadas as forças desenvolvidas durante o processo de furação, a extensão da zona delaminada em redor do furo produzido e efectuados ensaios mecânicos com o objectivo de estabelecer uma correlação entre os diversos resultados e as características mecânicas das placas maquinadas. Assim, a referida comparação permite avaliar a importância da escolha adequada da geometria de ferramenta na diminuição do dano provocado e na melhoria das características mecânicas das peças envolvidas.
- Avaliação de ferramentas na furação de laminados compósitosPublication . Gonçalves, Daniel J. S.; Durão, Luís M.; Albuquerque, Victor Hugo C. de; Tavares, João Manuel R. S.; Baptista, A. P. M.The development of cutting tools becomes a challenge to the industry of composite materials to obtain high quality holes, minimizing damage. This work aims to examine the influence of various parameters such as feed rate and tool geometry on thrust forces developed during drilling operations and on the extent of damage. In this work, a comparative study of tool geometry with the aim of reducing the associated damage during drilling process is presented. In the end a good combination of tool geometry and drilling parameters based on experimental work will be presented.
- Damage evaluation of drilled carbon/epoxy laminates based on area assessment methodsPublication . Durão, Luís M.; Tavares, João Manuel R. S.; Albuquerque, Victor Hugo C. de; Gonçalves, Daniel J. S.The characteristics of carbon fibre reinforced laminates had widened their use, from aerospace to domestic appliances. A common characteristic is the need of drilling for assembly purposes. It is known that a drilling process that reduces the drill thrust force can decrease the risk of delamination. In this work, delamination assessment methods based on radiographic data are compared and correlated with mechanical test results (bearing test).
- Evaluation of tools and cutting conditions on carbon fibre reinforced laminatesPublication . Gonçalves, Daniel J. S.; Durão, Luís M.; Tavares, João Manuel R. S.; Albuquerque, Victor Hugo C. de; Marques, A. T.The distinctive characteristics of carbon fibre reinforced plastics, like low weight or high specific strength, had broadened their use to new fields. Due to the need of assembly to structures, machining operations like drilling are frequent. In result of composites inhomogeneity, this operation can lead to different damages that reduce mechanical strength of the parts in the connection area. From these damages, delamination is the most severe. A proper choice of tool and cutting parameters can reduce delamination substantially. In this work the results obtained with five different tool geometries are compared. Conclusions show that the choice of an adequate drill can reduce thrust forces, thus delamination damage.
- Drilling delamination outcomes on glass and sisal reinforced plasticsPublication . Durão, Luís M.; Gonçalves, Daniel J. S.; Tavares, João Manuel R. S.; Albuquerque, Victor Hugo C. de; Panzera, Túlio Hallak; Silva, Leandro J.; Vieira, A. Aguiar; Baptista, A. P. M.Nowadays, fibre reinforced plastics are used in a wide variety of applications. Apart from the most known reinforcement fibres, like glass or carbon, natural fibres can be seen as an economical alternative. However, some mistrust is yet limiting the use of such materials, being one of the main reasons the inconsistency normally found in their mechanical properties. It should be noticed that these materials are more used for their low density than for their high stiffness. In this work, two different types of reinforced plates were compared: glass reinforced epoxy plate and sisal reinforced epoxy plate. For material characterization purposes, tensile and flexural tests were carried out. Main properties of both materials, like elastic modulus, tensile strength or flexural modulus, are presented and compared with reference values. Afterwards, plates were drilled under two different feed rates: low and high, with two diverse tools: twist and brad type drill, while cutting speed was kept constant. Thrust forces during drilling were monitored. Then, delamination area around the hole was assessed by using digital images that were processed using a computational platform previously developed. Finally, drilled plates were mechanically tested for bearing and open-hole resistance. Results were compared and correlated with the measured delamination. Conclusions contribute to the understanding of natural fibres reinforced plastics as a substitute to glass fibres reinforced plastics, helping on cost reductions without compromising reliability, as well as the consequence of delamination on mechanical resistance of this type of composites.
- Drilling process of composite laminates – a tool based analysisPublication . Durão, Luís M.; Gonçalves, Daniel J. S.; Tavares, João Manuel R. S.; Albuquerque, Victor Hugo C. deThe distinctive characteristics of carbon fibre reinforced plastics, like low weight or high specific strength, had broadened their use to new fields. In order to join different components by using bolts, rivets or screws, one of the machining operations needed in composite structures is drilling. Usually, it is accepted that drilling can be carried out using conventional tools and machinery with adaptations. However, this operation can lead to different kind of damages being delamination the most severe as it can reduce the mechanical strength. The main mechanism responsible for delamination occurrence is the indentation caused by the drill chisel edge. It is accepted that a drilling process that reduces the thrust force exerted by the drill chisel edge during machining can decrease the risk of delamination. In this work, two combinations of the drilling process are compared: tool material – HSS, WC and PCD – and geometry – twist, Brad and step. The parameters considered for analysis include: thrust force, delamination extension open-hole strength and bearing strength. Statistical techniques are used in the evaluation. The work performed shows that a proper combination of the factors involved, like tool material, drill geometry or cutting parameters, can help to reduce the occurrence of delamination.
- Drilling tool geometry evaluation for reinforced composite laminatesPublication . Durão, Luís M.; Gonçalves, Daniel J. S.; Tavares, João Manuel R. S.; Albuquerque, Victor Hugo C. de; Vieira, A. Aguiar; Marques, A. T.In this work, a comparative study on different drill point geometries and feed rate for composite laminates drilling is presented. For this goal, thrust force monitoring during drilling, hole wall roughness measurement and delamination extension assessment after drilling is accomplished. Delamination is evaluated using enhanced radiography combined with a dedicated computational platform that integrates algorithms of image processing and analysis. An experimental procedure was planned and consequences were evaluated. Results show that a cautious combination of the factors involved, like drill tip geometry or feed rate, can promote the reduction of delamination damage.
- Comparative analysis of drills for composite laminatesPublication . Durão, Luís M.; Gonçalves, Daniel J. S.; Tavares, João Manuel R. S.; Albuquerque, Victor Hugo C. de; Marques, A. T.The characteristics of carbon fiber-reinforced plastics allow a very broad range of uses. Drilling is often necessary to assemble different components, but this can lead to various forms of damage, such as delamination which is the most severe. However, a reduced thrust force can decrease the risk of delamination. In this work, two variables of the drilling process were compared: tool material and geometry, as well as the effect of feed rate and cutting speed. The parameters that were analyzed include: thrust force, delamination extension and mechanical strength through open-hole tensile test, bearing test, and flexural test on drilled plates. The present work shows that a proper combination of all the factors involved in drilling operations, like tool material, tool geometry and cutting parameters, such as feed rate or cutting speed, can lead to the reduction of delamination damage and, consequently, to the enhancement of the mechanical properties of laminated parts in complex structures, evaluated by open-hole, bearing, or flexural tests.
- Avaliação da delaminação após furação em compósitos laminadosPublication . Durão, Luís M.; Gonçalves, Daniel J. S.; Albuquerque, Victor Hugo C. de; Tavares, João Manuel R. S.As características excepcionais dos materiais compósitos de matriz polimérica têm conduzido à sua crescente utilização em todos os domínios. A necessidade de ligar estas peças entre si obriga à realização frequente de operações de furação que, embora devidamente adaptada, pode provocar diferentes tipos de dano nas peças a ligar. Desses, o dano mais grave é a delaminação pelas suas consequências na perda das propriedades mecânicas. Neste trabalho é apresentado um estudo comparativo da extensão do dano em função da geometria de ferramenta utilizada. Para tal as placas foram radiografadas após furação e a imagem resultante segmentada para medição das áreas associadas. Os resultados mostram a importância de uma adequada geometria de ferramenta na redução do dano causado pela furação em compósitos laminados.
- Tool geometry evaluation for carbon reinforced composite laminatesPublication . Durão, Luís M.; Gonçalves, Daniel J. S.; Tavares, João Manuel R. S.; Albuquerque, Victor Hugo C. de; Marques, A. T.The use of composite laminates in complex structures has increased significantly. However, there are still some issues when considering their use, mainly related with machining, leading to some difficulties and lack of acceptance. In this work, a methodology to evaluate drill geometry and feed rate based on thrust force and delamination extension is presented.