MECHANICS OF DEFORMATION AND DUCTILE TEARING IN CRACKED ROUND BAR SPECIMENS

This paper presents observations and analyses of the deformation and e arly stage of ductile tearing in cracked round bar (CRB) fracture spec imens. Fracture surface topography analysis (FRASTA), stability analys is and simple kinematic analysis are applied to CRB specimens of HY-13 0 steel and pressure vessel steel welds. The J-resistance curve for HY -130 steel is constructed; over the first 250 mu m or so of Crack exte nsion and bounds on the amount of crack extension preceding the point of maximum load are established. Further, the influence of crack growt h on J(Ic) defined at maximum load is assessed and it is argued that, for small CRB specimens, this definition is consistent with that of st andard testing methods. It is shown that crack mouth and crack tip ope ning displacement values can be readily estimated from global displace ment measurements with extensometers. It is also shown that bending of the CRB specimen due to an eccentric ligament has a relatively small effect (< 5%) on the toughness value of tough alloys. These results po int the way for future research and should prove useful in establishin g more reliable, simple, testing practices and in developing validated data analysis methods for CRB fracture tests. (C) 1998 Elsevier Scien ce Ltd.