Ductile to brittle transition fracture behaviour of ductile steel at high strain rates

320x75x18mm 3 point bend specimen have been subjected to impact testing. The material was a micro alloyed structural steel of three different 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 10(3) to 10(4). At low impact velocity some specimen could withstand the initial load without failing. A maximum likelihood model are used to fit the specimen behaviour to the experimental data.