MODERN CONCEPTS OF THE THEORY OF FRACTURE IN Metal Forming AND ITS APPLICATION FOR COLD ROLLING OF PIPESReport 2. PREDICTION OF FRACTURE DURING COLD ROLLING OF PIPES

Abstract

The article develops an approach to assessing the possibility of pipe destruction during cold rolling based on the criterion of accumulated damage by A. A. Bogatov. In continuation of the well-known works, this study proposes a more complete and improved method for calculating damage based on dividing the rolling cone into sections of monotonous and quasi-monotonous deformation. In order to transfer the research results to the entire rolling passage, regression relationships between the geometric characteristics of momentary deformation foci and the components of the strain tensor were established based on known experimental data. The main stages of calculating the final damage are considered: calculation of the trajectory of the particle through the working cone; calculation of the stress-strain state in each section; calculation of accumulated damage and its assessment. When analyzing multi-pass rolling schemes with intermediate heat treatments, formulas are proposed for calculating the healing of damage during heat treatment. To assess the final damage, two threshold values were identified, corresponding to the formation of energy-stable micropores and chains of microcracks, which leads to a decrease in the operational characteristics of pipes. Generalization of the methodology made it possible to develop rational rolling routes based on the analysis of damage accumulation under various rolling modes and tool calibrations of cold rolling mills for pipes.