In this paper a method of applying the theory of pop-in subcritical crack growth is described and important reasons for the roll's fracture in such a case have been revealed. It is stressed that the roll's fracture is due to the unstable extension of the surface cracks. For this reason the calculation of the stress intensity factor K of the roll is of considerable interest.
However, the roll being a circular cylinder, its fracture calculation is much more difficult than that of plate in bending or shearing. Hence, rather than attempt to make an exact analysis of this complicated problem, let us obtain instead an approximate expression for the stress intensity factor K. Various definitions of SIF K and their applications in the hot roll are given in this paper.
An approximation for calculation of maximum stress intensity factor of the roll is derived by means of a mechanical model of semi-infinite plate with an edge crack, thus the calculation of the maximum stress intensity factor of the crack tip in the roll is simplified. As a numerical example, the approximate expression is applied to the hot mill flat roll loaded by rectangular distribution. The calculation results are also examined with the experiments in the present paper and are found to be in good agreement with those of experiments.
K,-K,,, fracture condition of the roll has also been discussed, a topic so far not yet verified by previous workers.