Evaluation of static and dynamic fracture toughness in ceramics

Abstract

In the present study, static fracture toughness of ceramics is evaluated by a three point bending test using a precracked specimen. The obtained results are compared with the ones obtained by conventional static fracture toughness testing methods. Moreover, dynamic fracture toughness of ceramics is evaluated by the impact response curve method using a strain gage attached onto the specimen in an instrumented Charpy impact test. Furthermore, an influence of notch root radius on the fracture toughness is examined experimentally and theoretically. As a result, it has been shown that a static fracture toughness test using the precracked specimen evaluates a lower bound of static fracture toughness in comparison with one obtained from the traditional test method. Dynamic fracture toughness K d in partially stabilized zirconia has been observed to increase with loading rate . K. On the other hand, K d in Si 3N 4 has decreased once and then increased with increase of . K. This phenomenon suggests an existence of minimum K d value in Si 3N 4 at a certain . K level. It has also been shown that fracture toughness depends on notch root radius, and the variation of fracture toughness with notch root radius follows the theoretical formula presented by Williams.