Damage detection of rubber toughened nanocomposites in the fracture process zone using carbon nanotubes

A detailed experimental study is conducted using multi-walled carbon nanotubes (MWCNTs) as a sensory network to understand damage initiation and growth within the process zone of epoxy particulate composites under opening mode fracture loading. Thermoset epoxy resin composites are toughened with three weight fractions of carboxyl-terminated butadiene acrylonitrile copolymer (CTBN) rubber (10 phr, 20 phr and 30 phr). Single-edge notch tension (SENT) geometry and far-field tensile loading conditions are used for this study. A modified four-point probe methodology coupled with a high-resolution data acquisition system is employed to capture the electrical response within the process zone of fracture test specimens. For each composite, the damage initiation and growth associated with linear and non-linear deformation is analyzed and discussed with respect to the change in crack tip opening displacement (CTOD). Although the electrical response did not differ qualitatively with the addition of both 10 phr and 20 phr rubber to epoxy, addition of 30 phr of rubber showed a significantly different response both qualitatively and quantitatively. This is the result of several mechanisms such as disentanglement and stretching of epoxy matrix molecules, micro-crack blunting, debonding of rubber particles, void growth and propagation.