In the previous paper, the authors' method for breaking high carbon steel rod into billets was introduced, in which a cross-sectional crack was developed from a slight sharp peripheral notch of the rod by rapid local heating and cooling. Furthermore, the hardness and residual stress distributions of unnotched specimens of high carbon chromium steel (SUJ 2) were measured after they were subjected to local treatment under various heating and cooling conditions including optimum ones for breaking notched rods.
In the present study, the residual stress distribution in the notched section of SUJ 2 specimens caused by local rapid heating and cooling was evaluated by FEM calculations based on the assumption that the heat-treated state is substantially the same between the unnotched and notched specimens. First, the measured residual stress distribution in the unnotched specimen was reproduced in the unnotched FEM model in which local initial strain distribution was properly given. Secondly, the same local initial strain distribution was applied to the FEM model having a notch or crack extending from the notch root.
The crack lengths developed in the actual rod breaking tests were discussed in relation to the residual stress distribution calculated using the notched FEM model as well as the mechanical properties of rods.
The results obtained are as follows.
(1) The distribution of axial residual stress measured in the unnotched specimen was satisfactorily reproduced by giving a reasonable local initial strain distribution to FEM model.
(2) The calculated residual tensile stress in the axial direction near the notch root was relatively higher and more deeply distributed under conditions causing cracks than under those not causing cracks.
(3) The breaking tests of SUJ 2 rods showed that cracks propagated to the depth where the calculated axial stress at 0.1mm depth from crack tip (σeff) comes down to a value nearly equal to the net breaking strength of the rods (σt).
