Effect of nanofiller length and orientation distributions on Mode I fracture toughness of unidirectional fiber composites

Abstract

Although several experiments demonstrate a statistical variability of length and orientation of nanofillers in composites, a limited number of analytical studies include these effects in the prediction of fracture energy, particularly in composites containing micro-sized continuous fibers together with nano-sized fillers such as carbon nanotubes. In this investigation, we model the Mode I interlaminar fracture toughness of unidirectional fiber composites containing carbon nanotubes with known length and orientation distributions. A micromechanical model, based on an analytical framework developed for ''classical'' short fiber composites, is presented to quantify the enhancement of fracture toughness due to either carbon nanotube pullout from the matrix or carbon nanotube fracture. The results show remarkable differences compared to the models that utilize a unique (average) carbon nanotube length value, especially with regard to maximum achievable energy enhancement, depending on mean length and on interfacial shear strength between carbon nanotubes and matrix. Some key characteristics of the carbon nanotube statistical length distribution are also analyzed along with the limit of mean carbon nanotube length between the two competing mechanisms of toughening. The analytical framework is also supported by Mode I fracture toughness experiments conducted on nanofilled S2-glass fiber/epoxy laminated composites. The inclusion of experimentally determined distributions of carbon nanotube lengths in the presented model led to good estimations of the effect of carbon nanotubes on the Mode I interlaminar fracture toughness. Comparable results were obtained for carbon nanofibers, as well.

Investigation on the flexural response of multiscale anisogrid composite panels reinforced with carbon fibers and multi-walled carbon nanotubes

“…The second is toughening mechanism associated to the crack bridging of MWCNTs. 42–46

Figure 7.Alterations of Energy absorption at different weight fractions of MWCNTs.

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“…The second is toughening mechanism associated to the crack bridging of MWCNTs. [42][43][44][45][46] The most important failure mechanisms in fiber reinforced polymer composites are matrix cracking and fiber-matrix debonding. 47 Because of the remarkable stiffness of MWCNTs compared to the epoxy matrix, high stress gradient in the vicinage of the fillers is created which leads to the formation of stress concentration in these zones and creation of micro-cracks in to the polymer matrix.…”

Ruthenium oxide–carbon-based nanofiller-reinforced conducting polymer nanocomposites and their supercapacitor applications

“…The composites including micro-sized continuous fibers together with nano-sized fillers such as carbon nanotubes have limited studies which include these materials effects in the prediction of fracture energy [68]. Carbon fibers (CFs) have been employed for biosensor applications such as synthesis of poly(epsilon-caprolactone) (PCL)-based nanocomposite films [69].…”

Micromechanics-based phase field fracture modelling of CNT composites

“…Below this critical length, only CNT pull-out contributes to the fracture energy of the composite, while the bridging effect is given by the sum of CNT pull-out and rupture contributions for average lengths above the critical length. The previous formulation was extended by Menna et al [31] to take into account statistical distributions of the length and orientation of CNTs. However, no agglomeration effects have been considered in these works.…”