DUCTILE TO BRITTLE TRANSITION FRACTURE-BEHAVIOR OF DUCTILE STEEL AT HIGH-STRAIN RATES

320x75x18mm 3 point bend specimen have been subjected to impact testin g. The material was a micro alloyed structural steel of three differen t heat treatment qualities. The micro structure consisted of layers of perlite in a ferrite matrix. The experiments were performed at 30 and 45m/s. Depending on load rate the fracture was ductile, brittle or in a mixed mode. Simulations of the experiments showed strain rates of 1 0(3) to 10(4). At low impact velocity some specimen could withstand th e initial load without failing. A maximum likelihood model are used to fit the specimen behaviour to the experimental data.