J-integral evaluation of small specimens

Abstract

Three-dimensional elastic-plastic analyses were carried out for two small specimens using finite deformation theory. For a 1 4 in. ( c. 0·64cm) compact tension (CT) specimen of 1 mm thickness, the J-integral along the crack front is higher at the midsection of the specimen than at the surface of the specimen. The J-integral at the midsection of the specimen coincides with the J value estimated by the conventional Merkle-Corten equation using 0·8 B 0 ( B 0 = specimen thickness) as an effective thickness. For a 2 mm × 2 mm × 11 mm three-point bend specimen, the J-integral distribution along the crack front is similar to that of the 1 4 in. CT specimen. The J-integral at the midsection of the specimen can be estimated from the load versus displacement curve within a 10% error by Rice's conventional equation using 0·85 B 0 as the effective thickness. The three-point bend specimen is more appropriate for the fracture toughness test of a small specimen than the 1 4 in. CT specimen.