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Desenvolvimento e validação de estratégias de reparação de materiais compósitos avançados
| Name: | Description: | Size: | Format: | |
|---|---|---|---|---|
| 7.84 MB | Adobe PDF |
Advisor(s)
Abstract(s)
A procura pela utilização de materiais compósitos na indústria aeroespacial tem aumentado
significativamente ao longo dos últimos anos devido ao bom compromisso entre propriedades
mecânicas e massa, que estes materiais permitem obter. No entanto, devido às condições de
utilização cada vez mais exigentes, as estruturas em materiais compósitas são sujeitas a danos
que comprometem a sua capacidade estrutural. A reparação eficaz destas estruturas torna-se
assim uma técnica necessária para o reaproveitamento dos materiais, de forma a evitar custos
elevados de produção e a procurar a sustentabilidade do meio ambiente.
Este estudo tem como objetivo investigar a capacidade de restituição de métodos de reparação
para materiais compósitos de alto desempenho, como é o caso dos pré-impregnados de fibra
de carbono com matriz epóxida, após o aparecimento e respetiva identificação de fissuras
superficiais. Foram escolhidas duas técnicas distintas de reparação por ligação adesiva,
nomeadamente preenchimento da fissura com resina e substituição das peles danificadas em
formato de escalonado. Foram realizados ensaios de tração e flexão a 3 pontos para ambas,
com o intuito de avaliar o seu comportamento através de curvas força-deslocamento, tensões
presentes na ligação adesiva dos provetes, carga máxima, energia de rotura e modos de rotura.
Relativamente à análise numérica, as mesmas geometrias ensaiadas experimentalmente foram
replicadas com recurso ao Método de Elementos Finitos, e mais especificamente a modelos de
dano coesivo e ao critério de cedência de Tsai-Wu, e analisadas nas mesmas condições, de
forma a verificar a capacidade de simulação da rotura de materiais compósitos e adesivos
presentes na reparação.
Os resultados numéricos apresentaram boa concordância com os resultados experimentais e
foi possível prever o comportamento linear e não-linear das estruturas com boa precisão, assim
como validar a técnica utilizada para a previsão adequada do comportamento dos adesivos
utilizados aquando da sua propagação de dano. No geral, esta análise permitiu verificar que o
método de reparação por substituição das peles danificadas em formato de escalonado permite
restituir cerca de 90 % da integridade estrutural do componente reparado, à tração e à flexão,
enquanto o método de reparação por preenchimento da fissura com uma mistura de resina
indicou uma discrepância elevada com as propriedades mecânicas da estrutura original.
The demand for the use of advanced composite materials in the aerospace industry has increased significantly in recent years due to good compromise between mechanical properties and mass that these materials can achieve. However, due to the increasingly tough conditions of use, composite structures are subjected to damage that jeopardizes their structural integrity. The effective repair of these structures has, therefore, become a necessary technique for the reuse of materials, to avoid high production costs and seek environmental sustainability. This study aims to investigate the restitution capacity of repair methods for high-performance composite materials, such as carbon fiber prepregs with an epoxy matrix, after the appearance and identification of surface cracks. Two different adhesive repair techniques were chosen, namely filling the crack with resin and substitution of the damaged material in a stepped-taper format. Tensile and 3-point bending tests were performed for both methods to assess their behavior through load-displacement curves, stress concentration in the specimen’s adhesive, maximum load, failure energy and failure modes. Regarding the numerical analysis, the same geometries tested experimentally were replicated using the Finite Element Method, specifically cohesive zone models and the Tsai-Wu criterion, and analyzed under the same conditions, to verify their ability to simulate failure of the composite materials and adhesives present in the repair. The numerical results were in accordance with the experimental results, and it was possible to predict the linear and non-linear behavior of the structures with good accuracy, as well as validating the technique used to adequately predict the used adhesives behavior while the damage propagates. Overall, this analysis showed that the repair method of damaged composite skins substitution in a stepped-taper format restores around 90 % of the structural integrity of the repaired component, under tensile and flexural loads, while the repair method of filling the crack with a resin mixture showed a high discrepancy with the mechanical properties of the original structure.
The demand for the use of advanced composite materials in the aerospace industry has increased significantly in recent years due to good compromise between mechanical properties and mass that these materials can achieve. However, due to the increasingly tough conditions of use, composite structures are subjected to damage that jeopardizes their structural integrity. The effective repair of these structures has, therefore, become a necessary technique for the reuse of materials, to avoid high production costs and seek environmental sustainability. This study aims to investigate the restitution capacity of repair methods for high-performance composite materials, such as carbon fiber prepregs with an epoxy matrix, after the appearance and identification of surface cracks. Two different adhesive repair techniques were chosen, namely filling the crack with resin and substitution of the damaged material in a stepped-taper format. Tensile and 3-point bending tests were performed for both methods to assess their behavior through load-displacement curves, stress concentration in the specimen’s adhesive, maximum load, failure energy and failure modes. Regarding the numerical analysis, the same geometries tested experimentally were replicated using the Finite Element Method, specifically cohesive zone models and the Tsai-Wu criterion, and analyzed under the same conditions, to verify their ability to simulate failure of the composite materials and adhesives present in the repair. The numerical results were in accordance with the experimental results, and it was possible to predict the linear and non-linear behavior of the structures with good accuracy, as well as validating the technique used to adequately predict the used adhesives behavior while the damage propagates. Overall, this analysis showed that the repair method of damaged composite skins substitution in a stepped-taper format restores around 90 % of the structural integrity of the repaired component, under tensile and flexural loads, while the repair method of filling the crack with a resin mixture showed a high discrepancy with the mechanical properties of the original structure.
Description
Keywords
Materiais compósitos Fissuras superficiais Reparação adesiva Método de elementos finitos Modelos de dano coesivo critério de Tsai-Wu