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Advisor(s)
Abstract(s)
Os materiais compósitos estão cada vez mais presentes nas aeronaves, tanto comerciais
como militares. Assim, durante todo o percurso de voo da aeronave, mas essencialmente
na descolagem, aterragem ou nos serviços de manutenção, estas estão sujeitas a impactos.
De entre os vários impactos, os classificados de baixa velocidade são os mais frequentes
e os mais perigosos para estruturas compósitas devido ao dano induzido não ser visível
através de uma simples inspeção visual. Segundo a literatura, estes eventos induzem,
para além das fissuras da matriz, delaminações e rotura das fibras que são responsáveis
por elevadas perdas de resistência residual. Assim, com vista a repor a integridade estrutural é sugerido remover apenas a área danificada e repará-la com recurso a remendos
devidamente colados à estrutura sã. Esta reparação pode envolver remendos simples ou
duplos e, no caso dos últimos, a cavidade resultante da remoção do dano pode, ou não,
ser preenchida com resina.
Este trabalho pretende, assim, avaliar a resistência ao impacto de baixa velocidade de
cascas devidamente reparadas, uma vez que a literatura não reporta muitos trabalhos
com vista a consolidar este conhecimento. Para tal, estudou-se o efeito do tamanho da
reparação, considerando remendos compósitos com diferentes comprimentos e utilizados na forma de reparações simples e de dupla sobreposição com preenchimento da cavidade por resina semelhante à da matriz do laminado. Foi possível concluir que no caso
das reparações simples a vida de fadiga por impacto é insensível ao tamanho do remendo,
mas o estudo sugere que seja dependente da sua espessura. Na verdade, independentemente do tamanho do remendo colado, a ruína ocorreu sempre no remendo laminado.
No que concerne às reparações duplas, a resistência ao impacto revelou-se dependente
do tamanho do remendo devido à rigidez induzida na estrutura curva. A maior vida à
fadiga foi obtida com o remendo de maiores dimensões, chegando mesmo a ser superior
à obtida nos laminados de controlo (sem defeito).
Composite materials are increasingly present in aircrafts, both commercial and military. Thus, throughout the flight path of the aircraft, but essentially on take-off, landing or maintenance services, they are subject to impact. Among the various impacts, those classified as low-speed are the most frequent and the most dangerous for composite structures due to induced damage not being visible through a simple visual inspection. According to the literature, these events induce, in addition to matrix fissures, delaminations and fiber breaks that are responsible for high losses of residual resistance. Thus, in order to restore structural integrity, it is suggested to remove only the damaged area and repair it using patches pro-perly glued to the healthy structure. This repair may involve single or double patches and, in the case of the latter, the cavity resulting from the removal of the damage may or may not be filled with resin. Therefore, this work intends to evaluate the resistance to the low speed impact of properly repaired shells, since the literature does not report many works in order to consolidate this knowledge. For this purpose, the effect of the repair size was studied, considering composite patches with different lengths and used in the form of simple and double overlapping repairs with filling of the cavity with resin similar to that of the laminate matrix. It was possible to conclude that in the case of simple repairs the life of impact fatigue is insensitive to the size of the patch, but the study suggests that it is dependent on its thickness. In fact, regardless of the size of the glued patch, the ruin always occurred in the laminated patch. With regard to double repairs, the impact resistance proved to be dependent on the size of the patch due to the rigidity induced in the curved structure. The longest fatigue life was obtained with the largest patch, even exceeding that obtained in the control laminates (without defect).
Composite materials are increasingly present in aircrafts, both commercial and military. Thus, throughout the flight path of the aircraft, but essentially on take-off, landing or maintenance services, they are subject to impact. Among the various impacts, those classified as low-speed are the most frequent and the most dangerous for composite structures due to induced damage not being visible through a simple visual inspection. According to the literature, these events induce, in addition to matrix fissures, delaminations and fiber breaks that are responsible for high losses of residual resistance. Thus, in order to restore structural integrity, it is suggested to remove only the damaged area and repair it using patches pro-perly glued to the healthy structure. This repair may involve single or double patches and, in the case of the latter, the cavity resulting from the removal of the damage may or may not be filled with resin. Therefore, this work intends to evaluate the resistance to the low speed impact of properly repaired shells, since the literature does not report many works in order to consolidate this knowledge. For this purpose, the effect of the repair size was studied, considering composite patches with different lengths and used in the form of simple and double overlapping repairs with filling of the cavity with resin similar to that of the laminate matrix. It was possible to conclude that in the case of simple repairs the life of impact fatigue is insensitive to the size of the patch, but the study suggests that it is dependent on its thickness. In fact, regardless of the size of the glued patch, the ruin always occurred in the laminated patch. With regard to double repairs, the impact resistance proved to be dependent on the size of the patch due to the rigidity induced in the curved structure. The longest fatigue life was obtained with the largest patch, even exceeding that obtained in the control laminates (without defect).
Description
Keywords
Compósitos Fadiga Por Impacto Reparação de Placas Curvas Resistência Ao Impacto