Mode I and II fracture behaviour of rubber modified brittle epoxies

The effect of rubber modification on a brittle epoxy system cured using DDS has been studied in terms of fracture behaviour. Fracture mechanism, deformation and fracture surface characteristics under mode II loading have been investigated in comparison with those under mode I loading. For mode II fracture, two different types of tests were employed ie four-point shear tests for bulky epoxies and compact shear specimen tests for adhesive layers sandwiched between 6060-T5 aluminium. The fracture toughness in the former has been found to decrease with rubber modification. Fracture surfaces were examined in association with this result and was discussed in terms of cavitation and shear deformation. The fracture toughness in the latter for rubber modified epoxies has been found to also decrease as compared to the control. This result was discussed in relation to the density of tunnelling of microcracks. Also it was found that the fracture toughness of the control under mode II loading for either type is higher than that under mode I loading.