Microscale evaluation of epoxy matrix composites containing thermoplastic healing agent
Epoxy matrix composites are often subjected to adverse service conditions leading to the formation of microcracks. Microcracks are of great concern because they can act as nucleation sites for more prejudicial types of damage, such as delamination. Among the solutions to mitigate the deleterious...
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| Formato: | doctoralThesis |
| Idioma: | pt_BR |
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Universidade Federal do Rio Grande do Norte
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| Endereço do item: | https://repositorio.ufrn.br/handle/123456789/50952 |
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| Resumo: | Epoxy matrix composites are often subjected to adverse service conditions leading to the
formation of microcracks. Microcracks are of great concern because they can act as nucleation sites
for more prejudicial types of damage, such as delamination. Among the solutions to mitigate the
deleterious effect of matrix microcracking is the use of thermoplastic healing agents. Poly(ethyleneco-methacrylic acid) (EMAA) has been particularly used as a thermoplastic healing agent because of
its suitable chemical and physical properties. When the material is heated, the thermoplastic phase
dispersed in the epoxy matrix is allowed to flow into microcracks and restore mechanical properties.
The addition of EMAA particles, however, may alter chemical and thermomechanical properties of
epoxy composites. These changes may also affect other fundamental features of epoxy composites,
such as their fiber-matrix interfacial properties. Therefore, the objectives of this work are: (1) study
the effects of EMAA addition on epoxy formation, (2) investigate the effect of EMAA addition on
fiber-matrix interfacial properties, and (3) study the potential for self-healing through
micromechanical testing. The effect of a 10 wt.% EMAA modified epoxy was investigated through
infrared spectroscopy and differential scanning calorimetry (DSC) experiments. The results
suggested that EMAA addition may cause changes during the epoxy network formation. Then, single
fiber pull-out tests were used to characterize the fiber interfacial shear strength (IFSS) of pure and
modified epoxy systems, as well as between fiber and pure EMAA. IFSS results of pure and modified
epoxy were quite similar, revealing that epoxy modification did not significantly alter fiber-matrix
interfacial properties. On the other hand, IFSS measurements of fiber-EMAA presented considerably
lower values than fiber-epoxy, suggesting that healing is most likely held by fiber-epoxy or EMAAepoxy interactions. A novel method to assess the healing efficiency (η) using optically monitored
single fiber pull-out testing was proposed. According to the data obtained, healing efficiency of
EMAA modified epoxy was lower than that of pure epoxy systems. The attenuated matrix shrinkage
effect due to the addition of rubbery EMAA particles, along with the lower IFSS results of EMAAfiber are proposed to explain the observed low η values. Complementary tests investigated
thermomechanical properties and the curing of the EMAA modified epoxy, along with the effect of
healing on the chemical structure and its IFSS properties. |
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