Object Grating Method Application in Strain Determination on CTOD Tests

摘要

Standard fracture toughness tests require standard specimens with the presumption that mechanical properties are uniform in the crack growth direction. Standards for crack tip opening displacement (CTOD) fracture tests prescribe remote crack mouth opening displacement, which can lead to inadequate results in the case of heterogeneous materials properties. This paper describes the application of an object grating method (OGM) on the fracture behaviour of a heterogeneous specimen. Fracture behaviour is described by measuring deformation on the surface of a specimen, in terms of CTOD and, consequently, by strain determination. An OGM is advantageously used when measuring modified CTOD tests on two specimens with an initial crack in a macroscopic heterogeneous welded joint. Results significantly show that fracture behaviour depends on the material in the vicinity of the crack tip concerning the direction of crack propagation.