Fragmentation of as-drawn pearlitic steel wires during torsion tests

During free end torsion tests of cold drawn eutectoid steel wire, primary fracture frequently causes further fragmentation of the wire. The size and orientation distribution of the pre-existing microcracks at the moment of the primary fracture, and the unloading stress waves determine the secondary fracturing behaviour. A model has been developed to predict the distribution of the position of the first secondary fracture. A very good agreement is obtained between measured and calculated results. Moreover, as a by-product of the calculation, the delamination toughness of the drawn wires has been estimated to have a value between 6.8 and 16.4 MPa√m, which, on the scarce evidence available for this important material parameter, seems very plausible.