An epoxy was modified using polysiloxane core-shell rubber (S-CSR) particles with a T_g of -100°C. The particles did not alter the epoxy T_g, but the modulus and the yield stress were reduced. The fracture energies were measured from 20°C to -109°C. The S-CSR linearly increased the fracture energy, and a maximum of 947 J/m~2 was measured at 20°C. The particles significantly toughened the epoxy even at cryogenic temperatures. The toughening mechanisms were identified as shear band yielding and cavitation enabling plastic void growth. A theoretical model was used to predict the toughness over the entire temperature range. The predicted fracture energies were compared well with the experimental data.
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