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

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.