An Assessment of the SFFT in Hierarchical Composite Materials

Abstract

The science of materials has witnessed a notorious development of composite materials using nano-scale reinforcements such as nano-tubes, nano-flakes, or nano-fibers, all with promising exceptional mechanical properties. However, when these composites have been used to replace advanced fiber reinforced composites materials in certain applications, the results have been poor or definitively insufficient. An approach proposed to take advantages of the nano-scale material outstanding properties is their use in hierarchical composite materials, that is, in multi-scale composites materials. The use of the single-fiber fragmentation test to measure the IFFS is analyzed in this paper considering the presence of the nano-reinforcement material in the hierarchical composite material. A parametric study of the stress distribution for a monofilament carbon fiber whose surface is modified with carbon nanotubes (CNT) and embedded in an epoxy resin is first discussed. The analysis at two different scales, nano- and micro-scales and the stress interactions between them was necessary. For this purpose, concepts of the mechanics of a heterogeneous media, specifically the Mori-Tanaka Methods was used for the nano-scale interactions. The finite element method was used for the micro-scale. The linear elastic results reveal that, when the CNT are present in the carbon fiber-surface, contribute to a better stress distribution along the fiber-matrix interface once the fiberfragmentation process is started. However, the presence of the CNT may contribute to the appearance of large stress concentrations in the surrounding matrix, especially when the CNTs are randomly oriented. An attempt to establish relationships between the stress-transfer behavior and the physico-chemical interactions is made.