This study has as its main objective to evaluate the effectiveness of the welding process by electrical resistance in a composite poly (ether-imide) matrix reinforced with continuous fibres of carbon, from the study of the thermal and mechanical properties of the welded joint. To evaluate the thermal properties of the welded material, samples were subjected to analysis by thermogravimetry and by thermomechanical analysis. With the intention to study the resulting weld interface, studies were made from the shear tests ILSS and Iosipescu, as well as end-notched flexure (ENF). The results of the thermal analysis in laminated non-welded PEI/ carbon fibre show that the beginning of degradation for these composites is 460 °C, and it is also evident that the glass transition temperature of welded samples is about 15% higher than the results from samples not welded. The mechanical tests show that there was an increase of 32 and 20%, respectively, in interlaminar shear results for the ILSS-and Iosipescu-welded samples when they are compared to samples not welded. The ENF test results show satisfactory values of interlaminar fracture toughness in the composite welded from the values found in the literature.
RESUMOAtualmente, muitos componentes destinados à indústria aeronáutica, que anteriormente utilizavam compósitos com matriz termorrígida, vêm sendo substituídos por aqueles que apresentam matriz termoplástica, devido principalmente às melhores propriedades mecânicas obtidas, possibilidade de reaproveitamento do mesmo e a facilidade na fabricação de peças grandes e complexas, que serão integradas para formar o componente final desejado, assim como a sua temperatura de serviço mais elevada. Entretanto, um dos principais problemas da utilização de compósitos poliméricos em aplicações estruturais consiste em sua união efetiva para a integração de componentes. Nos últimos anos, a soldagem por resistência elétrica vem sendo considerada como uma das mais promissoras técnicas para a união de compósitos, pois se trata de um processo com pouca preparação de superfície e com qualidade aceitável no setor industrial. O principal objetivo deste trabalho consiste no estudo de parâmetros de soldagem por resistência elétrica para o compósito polimérico PEI poli (éter-imida) reforçado com fibras de carbono e de vidro (sistema híbrido) para aplicações aeronáuticas. As amostras do compósito foram soldadas e submetidas ao ensaio de lap shear para obtenção de tensão de ruptura ao cisalhamento de juntas simples. A partir deste ensaio foram estabelecidas as variáveis mais adequadas para utilização neste processo. O método utilizado foi um planejamento experimental fatorial completo que permitiu, com um número menor de experimentos, explorar todo o espaço experimental de interesse, estabelecendo os valores mais adequados de corrente elétrica, pressão e tempo para o processo de soldagem estudado. Palavras-chave:Compósitos, Soldagem por Resistência Elétrica, PEI, Planejamento Experimental. ABSTRACTNowadays, many components applied in the aerospace industry, which had been previously used with thermoset matrix composites, are being replaced by those with thermoplastic matrix, which is mainly due to having better mechanical properties, the possibility of reuse and ease in manufacturing large and complex parts which will be integrated to form the desired component with higher service temperature. However, a major problem concerning the use of polymer composites for structural applications consists in its effective integration of components. Electrical resistance welding has been considered as one of the most promising techniques for bonding thermoplastic composites because it is a quick process with little surface preparation. The main objective of this work is to study the resistance welding parameters for PEI (polyether imide), and carbon and glass (hybrid) fibers laminates for aeronautical applications. The composite specimens were welded and subjected to the lap shear test in order to establish the most suitable variable in this process. It was used a full factorial design that allowed, with fewer experiments, exploring the whole experimental area of interest, establishing values of electric current, pressure and time for the studied wel...
Este é um artigo publicado em acesso aberto (Open Access) sob a licença Creative Commons Attribution Non-Commercial, que permite uso, distribuição e reprodução em qualquer meio, sem restrições desde que sem fins comerciais e que o trabalho original seja corretamente citado. Evaluation of the Interlaminar Resistance of Composite PEI/Carbon Fibers Welded by Electrical Resistance MethodAbstract: This study has as main objective to evaluate the effectiveness of the welding process by electrical resistance in composite poly (éterimida) matrix reinforced with continuous fibers of carbon, from the study of the thermal and mechanical properties of the welded joint.To evaluate the thermal properties of the welded material samples were subjected to analysis by thermogravimetry and by thermomechanical analysis. With the intention to study the resulting weld interface, studies were made from the shear tests ILSS and Iosipescu, as well as end-Notched Flexure (ENF). The results of the thermal analysis in laminated PEI / carbon fiber non-welded show that the beginning of degradation for these composites is 460 °C, and it is also evident that the glass transition temperature of welded samples is about 15% higher than the results from samples not welded. In the mechanical tests show that there was an increase of 32% and 20% respectively in interlaminar shear results for the ILSS and Iosipescu welded samples, when they are compared to samples not welded. The ENF test results show satisfactory values of interlaminar fracture toughness in the composite welded from the values found in literature.
This work aims to characterize the influence of hygrothermal conditioning on the mechanical and thermal behavior as well as the fractographic aspects of the interface of poly(ether imide) and glass fiber composite joints welded by electrical resistance using 400 mesh of AISI 304 stainless steel. The composites were mechanically characterized by Lap Shear Strength (LSS) and End Notched Flexure (ENF) testing to investigate maximum shear stress and energy from mode II interlaminar fracture toughness. Fractography was performed by SEM, while the influence on glass transition temperature and working temperature were evaluated by Dynamic-Mechanical Analysis and thermogravimetry. In the conditioned samples, the mechanical properties reduced 23% in the LSS test and 28% in the ENF test, while the fractography studies revealed elements of interlaminar and intralaminar fracture in both conditions. Thermal properties did not change significantly to disqualify this composite when applied to welding.
The technology for joining thermoplastics through welding offers numerous advantages over mechanical joining. Currently, the joining of composite parts with weight reduction and cost savings is being developed to improve aircraft performance. This paper proposes the use of oxygen-acetylene as a process for bonding composite materials. Oxyacetylene welding is a simple and economical method that can be suitable for polymeric materials. The advantage of applying this technique is a more accessible process that is composed of a portable system with low cost. In evaluating the welding efficiency for composite materials, the lap shear strength (LSS) mechanical test stands out among the most referenced essays in the literature. This work aimed to study the development of oxyacetylene flame welding as well as the optimization of welding parameters for polyetherimide/glass fiber composite. The optimization was performed using complete factorial planning 22 as a tool, and the variables studied were time and distance of the flame. With the optimized condition set as the response variable with the highest lap shear value, the joints obtained were measured for their quality by means of end-notched flexure mechanical testing, thermal analysis, and fracture analysis after LSS testing using optical and electronic microscopy.
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