Quasi-static and dynamic fracture behavior of particulate polymer composites: A study of nano- vs. micro-size filler and loading-rate effects

Abstract

The role of nano- vs. micro-filler particle size-scale on static and dynamic fracture behaviors of silica-filled epoxy is examined. Particulate composites of epoxy matrix are studied under quasi-static and stress-wave loading conditions. Mode-I crack initiation and crack growth behaviors are examined using 2D digital image correlation method and high-speed photography in symmetrically impacted specimens. The measured displacement fields are analyzed using 2D crack-tip fields for dynamically propagating cracks in brittle solids to extract stress intensity factor (KId) histories, and crack velocity histories (V). KId–V plots for each type of composite are also presented. The quasi-static fracture tests show fracture toughness enhancement in case of nanocomposites relative to micro-particle filled ones. On the other hand, the dynamic crack-initiation toughness is consistently higher for micro-particle filled composites relative to the nano-filler counterparts. These counterintuitive results are supported by crack velocity histories in nanocomposites being significantly higher than that observed in micro-filler cases. The characteristic KId–V profiles suggest higher terminal velocities and lower dynamic fracture toughness for nanocomposites. Also, the post-mortem analyses of fracture surfaces reveal greater surface ruggedness for nanocomposites under quasi-static conditions. However, the opposite is evident under dynamic loading conditions. The qualitative and quantitative fractographic measurements correlate well with the measured fracture parameters for both quasi-static and dynamic fracture tests.