Effect of Filler Particle Shape on Dynamic Fracture Behavior of Glass-Filled Epoxy
The effect of filler shape and filler volume fraction (micron sized rods, flakes and spheres) on dynamic fracture behavior of particulate polymer composites (PPC) is studied. The mode-I dynamic fracture experiments are carried out on pre-notched glass-fil
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Effect of Filler Particle Shape on Dynamic Fracture Behavior of Glass-Filled Epoxy Vinod Kushvaha and Hareesh Tippur
Abstract The effect of filler shape and filler volume fraction (micron sized rods, flakes and spheres) on dynamic fracture behavior of particulate polymer composites (PPC) is studied. The mode-I dynamic fracture experiments are carried out on pre-notched glass-filled epoxy specimens. An experimental set-up comprised of a long-bar apparatus to deliver one-point impact loading to an unconstrained specimen, is used in conjunction with a gas-gun. A controlled stress pulse is delivered to the specimen by impacting the long-bar by a striker launched using a gas-gun. A crack propagates into the specimen dynamically and is captured using high-speed photography (~300,000 frames per second). Using the Digital Image Correlation (DIC) method, in-plane displacement fields around the crack tip are determined from the speckle images recorded during the fracture event. With these, dynamic fracture toughness histories are evaluated to examine the filler shape effects. The results show pronounced improvement fracture toughness for all filler types with rod-shaped fillers producing ~145% increase in crack initiation toughness over unfilled epoxy at 15% Vf with flakes and spheres showing ~97% and ~67% improvement, respectively. Keywords Dynamic fracture • Particulate composites • Filler shape effects • DIC • High-speed photography
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Introduction
The particle-filled polymer composites have been widely used in various engineering fields due to their excellent mechanical characteristics, chemical resistance, electric insulation, and adhesion properties. They are also relatively easy to process at a relatively low cost. Their structural simplicity in terms of macroscopic isotropy, unlike fiber reinforced composite, is another aspect which often makes it quite desirable for mechanical design. In particulate composites, the fillers modify their mechanical performance by reinforcing the polymer matrix. Therefore, the filler concentration, filler size and shape, and filler interfacial strength with the polymer matrix have a significant impact on the mechanical properties of PPC. Among the various modifications of mechanical properties, the stiffening, strengthening and toughening of the polymer matrix are the most useful for engineering applications. Polymers are normally modified by the addition of inorganic-particulate fillers, such as alumina, mica or silica etc. Song et al. studied the particle shape effects on the fracture and ductility of a spherical and an irregular particulate-reinforced 6061-Al composite containing Al2O3 20% by volume under quasi-static tensile loading [1]. The spherical particles produced a slightly lower yield strength and work hardening rate but a considerably higher ductility than the irregular particle counterpart. The finite element analysis results indicate that the distinction between the failure modes for these two composites can be attributed to the differences in the development of in
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