Construction of a generalized hardening curve for isotropic plastic metal materials

Abstract

One of the main ways to increase reliability and at the same time reduce the materials consumption of pipes under pressure, used in the oil and gas transportation system, is to improve theoretical and computational meth-ods to predict critical loads in their walls. These studies are based on the problem of accuracy and reliability of calculations at the stage of determination of mechanical characteristics of structural materials. Prediction of ul-timate stresses and strains in the material is performed by approximation of experimental data using deformation curves or yield strenghth. The purpose of the work is to propose a universal way to obtain a generalized curve for better consistence with the experimental data for each specific material. The paper describes a method used to develop a one-parameter model of a generalized deformation curve for plastic metal materials. To obtain the parameter p value as a constant of the material, it is necessary to have the results of several simple biaxial tension experiments with various combinations of the principal stress ratios. For the most accurate calculation of constant material p, it is required to minimize the effect of errors at preparation, testing and result processing stages. The model verifi-cation for other materials and selection of additional quality indicators will allow satisfactory accuracy to describe the generalized deformation curve and predict the stress-strain state of the material. In combination with the methods for structural geometry, the obtained generalized curve can be used to predict the real stress values in pipe walls under pressure.