Dynamic compression behavior of glass filled epoxy composites: Influence of filler shape and exposure to high temperature

The effect of filler shape, volume fraction and high temperature cycle on the dynamic compression behavior of rigid particle filled polymer composite is demonstrated by performing experiments using split-Hopkinson pressure bar (SHPB) setup. Two glass filler variants, spherical particles and milled fibers, are reinforced into epoxy matrix upto 10% volume fraction. Two sets of test specimens are prepared; room temperature cured (RTC) and high temperature exposed (HTE) - the ones prepared by subjecting RTC composites to a temperature cycle beyond their glass transition temperature (Tg). The yield stress of milled fiber composites which are consistently higher in HTE cases increases with increasing filler volume fraction whereas it remains nearly constant in all spherical particle composites. While RTC materials exhibit strain softening characteristics, the post-yield strain hardening behavior of HTE composites is attributed to the increased cross-link density of epoxy matrix. Debonded fillers and their foot-prints on the crushed surfaces of HTE composites indicate the relaxation of residual stresses, developed at the filler/matrix interface during curing process. Computational analyses suggest that the average matrix stress in composites remains unaffected by the shape of the inclusions whereas comparatively higher inclusion stresses indicate that slender fillers provide better resistance to deformation when compared to the circular ones. Near constant stresses in circular inclusions at low volume fractions is attributed to the large inter-particle separation. Computational results complement experimental observations where the milled fiber composites consistently exhibited higher yield stress when compared the spherical particle counterparts.