Strength of tubular billets in cyclical expansion

We present the results of an investigation into the stress—strain state of the outside surface of treated billets, at the point at which fallure of the billets begins. The strains have been determined by a scaling grid method. Stresses have been calculated in accordance with flow theory. In order to estimate the degree of utilized ductility, we employed a tensor description of damage accumulation. We have derived the relationship of such ductility as a function of the technical process parameters. A method is proposed for the determination of limit technological parameters, as well as a method to estimate the probability of billet failure.