Abstract
Evaluation of the fracture toughness of nanostructured metals is largely limited by the incapability of current techniques to process samples sufficiently large for standard fracture tests. Here, a custom designed contactless crack opening displacement gauging system is presented for accurately measuring load-line displacement and instantaneous crack length during fracture tests with miniaturized specimens, which is in particular suitable for determining the fracture resistance of nanostructured metals. For illustrating the application of this gauge, the J-integral fracture resistance curves were determined for an ultrafine grained Cu processed by equal channel angular pressing and a nanotwinned Cu synthesized by electro-deposition. The ultrafine grained Cu exhibits a fracture toughness of 66 MPa m1/2; while the fracture toughness is 39 and 55 MPa m1/2 for the nanotwinned Cu with an average grain size of 6 and 16 µm, respectively. The underlying damage mechanisms responsible for the measured fracture toughness are discussed.
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