Toughening Mechanism of Nano-rubber Particles in Epoxy Resin under Different Strain Rates

In order to understand the toughening mechanism of nano-rubber partieles toughened epoxy resin, the mode I fracture toughness of 6 wt% nano-rubber particles in epoxy resin was investigated under low strain rates (5 x 10(-4) s(-1), 1 x 10(-1) s(-1), 2.5 x 10(-1) s(-1)) and high strain rate (90 s(-1)) respectively. The results showed the nano-rubber particles can significantly toughen epoxy by 158%, 283% and 309% under low strain rates, respectively. However, compared with toughness obtained under low strain rates of 5 x 10(-4) s(-1), 1 x 10(-1) s(-1) and 2.5 x 10(-1) s(-1), at high strain rate of 90 s(-1), the fracture toughness of the unmodified epoxy was significantly increased due to the dynamic effect, however, the toughening effect of nano-rubber particles on epoxy resin was reduced obviously. Optical microscopy images showed whitening zone displayed on fractured nano-rubber particle modified epoxy specimen was obviously reduced as the strain rate increased from 5 x 10(-4) s(-1) to 2.5 x 10(-1) s(-1) and even disappeared under high strain rate of 90 s(-1). Polarized microscopy images displayed that the area of the crack tip deformation zones in both nano-rubber particle modified epoxy and unmodified epoxy was reduced when the strain rate was increased. The SEM observations indicated the strain rate variation alters the extent of plastic void growth and rubber cavitations, and finally leads to different toughening effects.