On the Behavior of Dynamic Crack Initiation in 3 Point Bend Steel Specimens

Experiments and numerical simulations on dynamically loaded 3-point bend ductile steel specimens are made with the objective to find ductile crack growth criteria applicable for dynamic loading. The recordings during the experiments include high speed photography, mid support force measurements and detections of impact, The end points of the specimen are impacted by a U-shaped hammer. To investigate the effect of friction forces parallel with the specimen surface introduced during impact due to the bending of the specimen, two different boundary conditions at the impact points are considered in the simulations : roller and locking. The experiments give results between these two extremes, which indicate that the boundary condition at the impact points has an important influence on the behavior of the specimen. Upper and lower bounds for the critical J-integral values at onset of crack growth are estimated.