This study aimed to develop a model to analyze the residual strength of composites after low-velocity impact, using three-point bending and compression after impact tests. Two types of composite laminates with an orthophthalic polymer matrix were used: one reinforced with bidirectional E-glass fabric and the other reinforced with bidirectional Kevlar-49 fabric. To that end, an equation was developed to assess loss of strength and stiffness after impact at different distances from the impact point, and this equation was not found in any previously searched article. The results demonstrate that the laminate based in glass fiber is more appropriate for the repair process.

No abstract

The purpose of this work was to study the effects of low-pressure oxygen plasma treatment on the surface characteristics of kevlar fabric. For comparison purposes, samples treated with oxygenated plasma were prepared and characterised under different experimental conditions, i.e. a treatment time variation of 10, 30 and 60 minutes under a constant pressure of 4 mBar, using a pulsed current source. We analysed the effects of chemical and physical changes to the surface of the material aiming at improved hydrophilicity attributed to the formation of roughness on the surface of fibres, thus obtaining optimal parameters for future works. Changes in the chemical composition of the surface as well as in the superficial roughness of fibres before and after treatment were determined by FTIR, TGA, XRD and wettability testing. SEM was used as a complementary technique to monitor the changes triggered by the procedures using oxygen plasma.

The aim of this study was to analyze the effect of hybridization on impact and residual strength in composites as well as the types of damage caused by the impacts, quantifying the delaminated area of the test specimens. Two 11-layer composite laminates were developed, one with bidirectional glass fiber woven and the other a hybrid with three layers of bidirectional aramid fiber substituting the outer layers and the middle layer of the glass fiber. The materials revealed that the hybrid laminate obtained greater impact strength withstanding one impact of 76 J, albeit with an increase in the damaged area of between 64 and 85 cm2, resulting in a decline in mechanical properties along nearly the entire test specimen. This contrasts with what occurred in the glass fiber laminates, which recovered over 80% of their mechanical properties for a distance of 35 mm from the edge of the impactor. Moreover, it demonstrated that the variation in residual strength can be represented by an equation and that there is a relation between the damage area and the residual properties of the glass fiber material.

RESUMOEste trabalho tem por objetivo fazer uma análise A utilização dos materiais compósitos estar sendo amplamente investigada para a aplicação em formas estruturais, tendo em visto esta utilização o objetivo desse trabalho consiste em fazer uma análise comparativa das propriedades mecânicas de tração uniaxial em compósitos reforçado por fibra de vidro quando os mesmos passaram por uma imersão em petróleo no período de 365 dias e por um envelhecimento acelerado, sob ação simultânea de temperatura e umidade. Após os ensaios mecânicos pode ser feito uma avaliação comparativa do comportamento das propriedades mecânicas como módulo de elasticidade, tensão de ruptura, deformação de ruptura e tensão máxima. Para efeitos de comparação, usou-se o material sem nenhum tipo de ação externa (petróleo ou envelhecimento), ou seja, estado original e o material submetido ao efeito da imersão em petróleo e do envelhecimento acelerado. Ao final, os laminados em estudo, foram submetidos à caracterização final da fratura. Podemos concluir que para o ensaio de tração houve uma queda em torno de 25% para o material envelhecido e 16% para o imerso em petróleo, para a tensão máxima, já para o módulo elástico, os percentuais de retenção foram em torno de 28% e 16%, para o imerso em petróleo e o envelhecido, respectivamente. Na caracterização da fratura, os principais tipos de danos em materiais compósitos foram observados, como por exemplo, fraturas adesivas, coesivas na fibra e na matriz PALAVRAS-CHAVE: Propriedades Mecânicas, Materiais Compósitos, Envelhecimento Acelerado, Petróleo. INFLUENCE OF ACCELERATED AGING IN MECHANICAL PROPERTIES OF GFR IMMERSED IN OIL ABSTRACTThis study aims to analyze the use of composite materials being widely investigated for application in structural forms, having seen this use our aim is to make a comparative analysis of the mechanical properties of uniaxial tensile composite carbon fiber reinforced glass when they passed through an immersion oil in the period of 365 days and an accelerated aging under simultaneous action of temperature and humidity. After the mechanical tests can be made a comparative evaluation of the behavior of mechanical properties such as elastic modulus, rupture stress, break strain, and maximum stress. For comparison purposes, we used the material without any external action (petroleum or aging), that is, original state, and the material subjected to the effect of the immersion oil and accelerated aging. Finally, the laminated study were submitted to the final characterization of the fracture. We can conclude that for the tensile test there was a drop of around 25% for the aged material and 16% for the immersed in oil to the maximum voltage, as for elastic modulus, retention rates were around 28% and 16% for the immersed in oil and aged, respectively. In characterizing the fracture, the main types of damage in composite materials have been observed, such as fractures adhesive, cohesive in fiber and the matrix.