Is Nano Always Better? Static and Dynamic Fracture Study of Particulate Polymer Composites
In this work, the role of nano- versus 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.
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Is Nano Always Better? Static and Dynamic Fracture Study of Particulate Polymer Composites K.C. Jajam and H.V. Tippur
Abstract In this work, the role of nano- versus 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 histories (KId) and crack velocity histories (V). The quasi-static fracture tests show enhanced fracture toughness for 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. The crack velocities in nanocomposites are significantly higher than that observed in micro-filler cases. 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. Keywords Particulate composites • Size effects • Loading-rate effects • Nanocomposites • Fracture • Fractography • Optical measurements • High-speed photography
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Introduction
Particulate polymer composites are used in a variety of engineering applications. These are generally multiphase materials with polymer matrix phase reinforced with fillers of different sizes and shapes. The addition of rigid fillers play vital role in optimizing overall stiffness, impact energy absorption and thermo-mechanical characteristics of the resulting composite system. However, the effect of particle size-scale (nano- vs. micro-) could vary the fracture response of these materials depending upon the nature of loading, quasi-static or dynamic. A review [1–4] on fracture behavior of micron-size rigid filler composites shows improved fracture toughness relative to unfilled matrix. Also, a modest improvement in quasi-static fracture toughness KIc and stiffness have been reported by several researchers [5–10] using nano-fillers in the last few years. It should be noted that most studies to date on fracture behavior of particle-filled composites have been performed quasi-statically and very limited data exists from a dynamic failure perspective. Among the few dynamic fracture investigations reported on particulate composites include the study of filler particle size on the mode-I fracture behavior of glass-filled epoxy conducted by Kitey and Tippur [11]. Their work shows that micron-size spherical glass beads of different mean diameter (11–200
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