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- Drilling damage in composite materialPublication . Durão, Luís M.; Tavares, João Manuel R. S.; Albuquerque, Victor Hugo C. de; Marques, Jorge Filipe Simões; Andrade, Óscar Nicolau GomesThe characteristics of carbon fibre reinforced laminates have widened their use from aerospace to domestic appliances, and new possibilities for their usage emerge almost daily. In many of the possible applications, the laminates need to be drilled 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, damage assessment methods based on data extracted from radiographic images are compared and correlated with mechanical test results—bearing test and delamination onset test—and analytical models. The results demonstrate the importance of an adequate selection of drilling tools and machining parameters to extend the life cycle of these laminates as a consequence of enhanced reliability.
- 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.
- Maquinagem não convencional sobre placas compósitasPublication . Albuquerque, Victor Hugo C. de; Durão, Luís M.; Tavares, João Manuel R. S.A utilização de materiais compósitos tem crescido nas últimas décadas em virtude do seu baixo peso, elevada resistência e rigidez. A furação de placas compósitas é um desafio que se coloca às indústrias que trabalham com este tipo de materiais, sendo frequente o recurso a ferramentas convencionais, normalmente utilizadas na construção mecânica, com adaptações. Neste trabalho, apresenta-se uma técnica não convencional baseada na furação por jacto de areia sendo avaliadas as descontinuidades causadas em placas compósitas. Durante este processo de furação, as camadas da placa não resistem o tempo necessário para concluir a perfuração, aquecendo e fragmentando- se, e a areia, com o impacto, perde rapidamente o poder abrasivo. Além disso, o tempo necessário para completar com sucesso a operação seria superior a 5 horas, uma vez que a primeira etapa de jateamento durou aproximadamente uma hora, sendo necessário no fim da mesma repor um novo isolamento devido desgaste sofrido. Nesse momento da operação o progresso obtido era imperceptível. O trabalho experimental realizado permite concluir que a furação por jacto de areia, utilizando um compressor com um caudal de 1700 l/min e jateadora de sucção, não se mostra uma ferramenta promissora para executar operações de furação em placas compósitas.
- Tool effects on hybrid laminates drillingPublication . Durão, Luís M.; Tavares, João Manuel R. S.; Albuquerque, Victor Hugo C. de; Marques, A. T.; Magalhães, A. G.; Vieira, A. AguiarFiber reinforced plastics are increasing their importance as one of the most interesting groups of material on account of their low weight, high strength, and stiffness. To obtain good quality holes, it is important to identify the type of material, ply stacking sequence, and fiber orientation. In this article, the drilling of quasi-isotropic hybrid carbon +glass/epoxy plates is analyzed. Two commercial drills and a special step drill are compared considering the thrust force and delamination extension. Results suggest that the proposed step drill can be a suitable option in laminate drilling.