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Autor(a/res): Priscilla Rocha Vieira, Eliane Maria Lopes Carvalho, Janine Domingos Vieira, Romildo Dias Toledo Filho
Resumo: The aim of this research is to investigate the behavior of pultruded Glass-fiber Reinforced Polymer (GFRP) composite materials subjected to fatigue loads. Static tests were performed to estimate the material strength and modulus of elasticity. Constant-amplitude axial tension-tension fatigue tests were conducted with a cyclic stress ratio of R = 0.1 and a frequency of 4Hz in order to establish fatigue life characteristics (S-N curve) and identify damage evolution and failure modes for the composite material. Generally, the damages developed in fatigue tests were characterized primarily by cracks in the matrix, followed by possible delamination of the material layers and finally the fiber failure and the specimen rupture. Tomography images were used to better understand the architecture of the composite material. It was observed that the layers of the fibers are not perfectly aligned and uniform and there is a substantial quantity of voids resulting in a very heterogeneous material which can explain the scatter of the experimental results.
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Autor(a/res); Andrielli Morais de Oliveira, Flávio de Andrade Silva, Eduardo de Moraes Rego Fairbairn e Romildo Dias Toledo Filho.
Resumo: This paper reports the experimental findings on the tensile behavior of strain-hardening cement-based composites (SHCC). The composites were subjected to the combined effects of elevated temperatures and internal moisture condition. Uniaxial tensile tests on dumbbell-shaped SHCC specimens with in situ temperature control were performed at 22, 60 and 100 °C. In addition, the effect of the internal humidity of SHCC (95, 50, 20 and 0%) coupled to the elevated temperatures was investigated. It was shown that the tensile strength decreases and the strain capacity increases with an increase in temperature. The influence of the internal moisture conditions was more significant in high temperatures. The strain capacity reduced significantly with a decrease in the humidity level. The crack pattern of the SHCC specimens was determined. Furthermore, single fiber pullout tests were performed under the considered high temperatures condition. Finally, the results are discussed based on the thermogravimetry analysis of the PVA fiber, alterations on its microstructure and surface coating.
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Autor(a/res): Bartosz Zukowski, Flávio de Andrade Silva e Romildo Dias Toledo Filho.
Resumo: The work in hand presents the design process of Strain Hardening Cement-based Composite reinforced with natural curauá fiber. The matrix fracture energy and matrix-fiber bond were studied and implemented into the theoretical model for critical fiber volume prediction, which was verified by mechanical tests for tensile, bending and compression strength. The influence of matrix-fiber bond on critical fiber volume is presented. The fiber properties are improved by two-stage treatment. Firstly, hot water (80 °C) washing in water changed every 3 h. Secondly, immersion in 1% solution of calcium hydroxide Ca(OH)2 with water for 60 min for calcium deposition on fiber surface to increase bond properties. The critical fiber volume predicted by the model was 4% for 20 mm treated curauá fiber and was verified on the composites, which presented strain-hardening behavior under tensile test and deflection-hardening under bending.
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