Micro-scale strain mapping in nano-engineered fiber-reinforced composites

Full-field strain measurement in materials that exhibit mechanical heterogeneity at the micro-scale are of great interest. This is particularly important in the emerging field of nano-engineered fiber-reinforced composites, where the effects of nano-modifications are as-yet uncharacterized. Formerly, the authors proposed a methodology to analyze deformations in conventional laminated composites at the micro-scale via digital image correlation (DIC). In the present study, this technique is applied to capture strain heterogeneity in microfiber-reinforced laminated composites that are additionally modified with aligned carbon nanotubes (CNTs), grown radially on microfibers as aligned forests. The composite is loaded in transverse three-point bending inside an environmental scanning electron microscope. The paper describes acquisition of 2D displacement and strain maps, and investigates the effect of CNTs on the deformation of these hierarchical architectures. As a prerequisite for micro-DIC, a high-quality nanoscale random speckle pattern of alumina particles is deposited on the surface. A finite element model of the micro- and nano-structure geometry, with boundary conditions obtained from microscopy and DIC analysis. A good correlation between experimental and modeling results was obtained, indicating that the micro-scale DIC is a promising technique to study deformation in nano-engineered composites.