FRACTURE TOUGHNESS BEHAVIOUR OF THICK-WALLED NODULAR CAST IRON AT ELEVATED LOADING RATES

摘要

In consideration of the specific demands required for heavy-section ductile cast iron (DCI) for transport and storage casks the fracture mechanics research programme of BAM is focused on a systematic material characterization under static and dynamic loading conditions with respect to such parameters as microstructure, test temperature, sample size and loading rate. In the present study, ductile cast iron from an original DCI container with a wide variety of microstructure was investigated in order to determine the materials fracture toughness under dynamic loading conditions in the temperature range from -50°C to +22°C using three-point bending specimens with thicknesses of 140 mm and 15 mm, respectively. In contrast to static fracture behaviour, the fracture toughness values of thick-walled DCI at higher loading rates show a remarkable reduction with decreasing temperature between +22°C and -50°C and a significant shift of the transition range from -40°C up to +22°C. On the other hand, the lower bound fracture toughness value used in the design code for transport and storage casks of DCI in Germany was confirmed for dynamic loading conditions by these first investigations using large specimens. Furthermore, at present, BAM works on a research program which comprises systematic investigations of the mechanical and fracture mechanical behaviour of heavy section DCI at elevated loading rates.