On the void growth in C-Mn structural steel during plastic deformation

A procedure has been established to measure the relationship between void growth, plastic strain and stress triaxiality during the fracture of a C--Mn structural steel (BS4360Gr50D). A calibration factor for void growth was determined using smooth tensile specimen tests and precracked side-grooved three-point bend bar tests. The factor was expected to be applicable over a rather wide range of the constraint generating geometries. The experimental void growth relation shows a real void growth rate in the structural steel which is smaller than that determined by the Rice--Tracey's void growth theory for stress triaxialities, sigma sub m / sigma > approx 1.2. However, when the sigma sub m / sigma value is < approx 1.2, the void growth predicted by the Rice--Tracey's theory tends to slightly underestimate the void growth in the steel. The variations of the plastic strain and relative void volume have been measured and evaluated ahead of the blunting crack tip in the precracked side-grooved three-point bend specimens at the point where the ductile tearing initiated. These results are related to theories for the level of triaxial stresses. 16 ref.--AA