FRACTURE-BEHAVIOR OF STEEL 20-MNMONI-5-5 UNDER STRESS WAVE LOADING

Crack initiation in fine grained 20 MnMoNi 5 5 steel has been investig ated under stress wave loading conditions in the temperature range fro m -50 degrees C to 20 degrees C by a loading setup similar the ''Split Hopkinson Pressure Bar'' technique. For temperatures up to 20 degrees C, fracture occurs by cleavage and K-Id approaches and falls below th e reference fracture toughness, while at room temperature stable crack growth occurs with a J(i) close to the static initiation value of the J-integral. The analysis of the crack tip configuration suggests that stable crack growth is the result of the following simultaneously ind uced stochastical processes: generation of constrained local microcrac ks, blunting of the individual crack tips and the deformation of mater ial bridges at different regions along the crack tip front.