Investigating mixed-mode (I/II) fracture in epoxies using digital image correlation: Composite GIIc performance from resin measurements

The digital image correlation technique is applied to investigate mixed-mode (I/II) fracture in five aerospace epoxy formulations, four of which are experimentally toughened. Stress intensity factors are extracted from displacement fields using the Williams method for a range of mode mixities. From these measurements, values of an effective resin KIIc are deduced and these are shown to have a statistically significant relationship with measured composite GIIc mode II toughness values. The differences in constraint between composite and bulk resin specimens are discussed.