Shape memory property of carbon fiber / epoxy resin composite materials

We investigated an effect of carbon fiber on shape memory property of carbon fiber / shape memory polymer (epoxy resin) composites by using dynamic mechanical analysis (DMA), shape memory test, and mechanical constitutive model. As a result of DMA, the storage modulus (E') of the composite material (CF/EP) was improved by CF component, as compared with that of the pure epoxy resin (pure EP). Especially, E' at rubbery region was remarkably increased with two decades. From the results of shape memory test, CF/EP showed good shape recovery behavior as well as pure EP. Contrary, the shape fixity ratio of CF/EP was lower than that of pure EP. This is because that the difference in E' below/above the glass transition temperature (Tg ) of CF/EP became smaller (less than one decade) than pure EP (two decades). In addition, the shape recovery of CF/EP started at lower temperature than Tg, although the recovery of pure EP showed around Tg. In order to examine the shape recovery behavior of CF/EP, we compared the viscoelastic properties of three samples, pure EP, CF layer and the composite. As a result, the CF layer had higher E' than CF/EP, and no significant change in E' occurred around Tg. From the results, we speculated that the CF layer acted as a shape recovery component for the composite material. Furthermore, we proposed a mechanical constitutive model, in which the CF layer was assumed as the recover component, to qualitatively explain the shape recovery behavior of CF/EP composite. The simulated result by the constitutive model reproduced the trend of anomalous shape recovery behavior below Tg of CF/EP. © 2021 The Society of Materials Science, Japan.