Strain rate sensitivity of toughened epoxy

The high strain rate behaviour of toughened epoxy is explored under compressive loadings. A cycloaliphatic epoxy was toughened using different types of preformed fillers: epoxy-coated elastomeric poly(dimethylsiloxane) (CSR) and thermoplastic polystyrene microspheres. The toughening ability of the fillers was quantified in terms of improvement in izod impact strength. Our studies revealed that the disadvantages associated with liquid rubber toughening, especially lowering of the glass transition temperature (T g) and storage modulus, could be overcome by using poly(dimethylsiloxane) (PDMS) microspheres. The izod impact strength increased by 33 % upon addition of 3 % w/w amino-polystyrene microspheres, and ~125 % upon introduction of CSR (5 % w/w). High strain rate studies performed using split Hopkinson pressure bar revealed that the compressive strength of epoxy and the toughened compositions were significantly enhanced at high strain rates (~103 s−1) compared with that at quasi-static loading conditions (~10−1 s−1). The effect of filler type on the strain rate sensitivity of the base polymer was established by comparing the property enhancement factor (PEF). Although introduction of elastomeric microspheres led to a lower compressive strength of epoxy, the PEF associated with the rubber-toughened composites was substantially higher than that with the thermoplastic-toughened analogous compositions, which was attributed to the viscous energy absorption in PDMS resulting from the dynamic rubber to glass transition at high strain rates.