Toughening response of a crack-tip surrounded by a local elastic gradient

The healing process exhibited by biological structures has inspired the creation of engineered materials capable of impeding crack propagation. Furthermore, recent observation of local elastic modification at the crack-tip has shown drastic improvement in the fracture behavior of materials. By taking advantage of the highly temperature dependent elastic properties of a thermo-responsive shape memory polyurethane, an annular elastic gradient around the crack-tip is created by applying thermal energy. A large reduction (similar to 95% decreases) in the stress intensity factor is obtained. To fully understand the toughening mechanism, finite element and micromechanics models are created to simulate fracture behavior of a compact tension specimen with local property modification of thermo-responsive polymers at the crack-tip. The modeling results are validated through the use of a digital image correlation technique which can be utilized to provide the stress intensity factor at the crack-tip, confirming the toughening mechanism and the accuracy of the models.