Estudo do acúmulo de dano pela técnica de excitação por impulso no laminado fibra de carbono 5HS/matriz epóxi
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Data
2019-02-11
Autores
Maciel, Maísa Milanez Ávila Dias [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Compósitos reforçados com fibra de carbono são muito utilizados como componentes estruturais na indústria aeronáutica e, em geral, estão sujeitas à esforços dinâmicos, o que pode levar a um processo de perda de propriedade mecânica. Dessa forma conhecer o mecanismo de acúmulo de danos em fadiga de nesse material é fundamental. Neste trabalho, a perda de integridade em compósitos tramados foi monitorada por meio do decaimento do módulo elástico dinâmico em consequência do acúmulo de danos. Para isso, compósitos de tecido de carbono tramado tipo 5HS com matriz epóxi, processado via moldagem por transferência de resina (RTM), foram caracterizados quanto à sua fração volumétrica, resistência à tração e resistência ao cisalhamento. Foi, então, obtida uma média de 54,45%∓1,7 de fibra entre os laminados e uma média de 3,48%∓0,9 de vazios. Pelo cisalhamento Iosipescu, foi observada a média de 97,96 MPa de tensão máxima e 3,35 GPa de módulo cisalhante no plano xy. A resistência a tração dos corpos de prova com entalhe (OHT) foi de 494,00 MPa sendo 59,87 GPa de módulo elástico e 0,021 como coeficiente de poisson. O material foi também ensaiado por fadiga em R = 0,1, quando o decaimento do módulo de elasticidade foi monitorado pela técnica de excitação por impulso, para a degradação das propriedades mecânicas de cada corpo de prova do início até a fratura do mesmo. Foram observados 3 estágios principais, o estágio inicial até 9,0 x 104 ciclos, o qual apresentou um rápido decaimento. O segundo estágio, até 8,0 x 105 ciclos, que apresentou um decaimento quase-linear. O último estágio, até 1,0 x 106 ciclos, relacionado à presença de delaminações extensas fora da área entalhada. Em geral, o primeiro estágio foi associado a um decaimento de 1,7%, seguido por um decaimento de 4,2% no segundo, e para os corpos de prova que apresentaram o último estágio o decaimento foi em torno de 3,4%
Carbon fiber composites are widely used as structural components aircraft industry, and are commonly subjected to dynamic loads, which can lead to damage accumulation and mechanical property decay. Therefore, knowing the mechanisms of damage accumulation of fatigue loads is critical, because it avoids loss of structural integrity to a critical limit. In this work, the integrity loss was monitored by the dynamic elastic modulus decay as a consequence of the accumulation of damage. For this a 5HS woven carbon fiber composite laminate processed by resin transfer molding (RTM) were characterized in relation to their fiber volume fraction, void content, ultimate tensile strength and ultimate shear strength. The fiber volume fractions an average of 54.45% ∓1.7 of fiber fraction and an average of 3.48% ∓0.9 of voids was obtained for the laminates. The shear strength analysis used was the Iosipescu test, in which an average of 97.96 MPa of maximum stress and 3.35 GPa of shear modulus in the xy plane were obtained. For the with the open hole tensile tests (OHT) it was obtained an average of 494.00 MPa for maximum stress, 59.87 GPa for elastic modulus and 0.021 for the Poisson ratio. The specimens were monitored during the cyclic tests at constant stress ratio (R) equal to 0.1. The stiffness reduction was measured by impulse excitation technique, which allowed to follow the degradation of the mechanical properties of each specimen from the beginning of the test until fracture. Three main stages of degradation were observed, the initial stage up to 9.0 x 104 cycles, which presented a rapid decay. The second stage, up to 8.0 x 105 cycles, presented a quasi-linear decay. The last stage, up to 1.0 x 106 cycles, of decay was related to the presence of extensive delamination occurring outside the notched area. In general, the first stage was associated with a decay of 1.7%, followed by a decay of 4.2% in the second, and for the test bodies that presented the last stage the decay was around 3.4%
Carbon fiber composites are widely used as structural components aircraft industry, and are commonly subjected to dynamic loads, which can lead to damage accumulation and mechanical property decay. Therefore, knowing the mechanisms of damage accumulation of fatigue loads is critical, because it avoids loss of structural integrity to a critical limit. In this work, the integrity loss was monitored by the dynamic elastic modulus decay as a consequence of the accumulation of damage. For this a 5HS woven carbon fiber composite laminate processed by resin transfer molding (RTM) were characterized in relation to their fiber volume fraction, void content, ultimate tensile strength and ultimate shear strength. The fiber volume fractions an average of 54.45% ∓1.7 of fiber fraction and an average of 3.48% ∓0.9 of voids was obtained for the laminates. The shear strength analysis used was the Iosipescu test, in which an average of 97.96 MPa of maximum stress and 3.35 GPa of shear modulus in the xy plane were obtained. For the with the open hole tensile tests (OHT) it was obtained an average of 494.00 MPa for maximum stress, 59.87 GPa for elastic modulus and 0.021 for the Poisson ratio. The specimens were monitored during the cyclic tests at constant stress ratio (R) equal to 0.1. The stiffness reduction was measured by impulse excitation technique, which allowed to follow the degradation of the mechanical properties of each specimen from the beginning of the test until fracture. Three main stages of degradation were observed, the initial stage up to 9.0 x 104 cycles, which presented a rapid decay. The second stage, up to 8.0 x 105 cycles, presented a quasi-linear decay. The last stage, up to 1.0 x 106 cycles, of decay was related to the presence of extensive delamination occurring outside the notched area. In general, the first stage was associated with a decay of 1.7%, followed by a decay of 4.2% in the second, and for the test bodies that presented the last stage the decay was around 3.4%
Descrição
Palavras-chave
Carbono/Epóxi, módulo residual, 5HS, Fadiga, Falha, Fibras de carbono, Resinas epóxi, Carbon/Epoxy, Residual modulus, Fatigue, Failure, Fibras de carbono