Numerical simulation of the creep process of titanium alloy VT6 under a multi-axis stress state taking into account the influence of an aggressive environment

Abstract

The problem of assessing the strength and resource of critical engineering objects is considered. The operating conditions of objects are characterized by high-temperature non-stationary thermomechanical effects, which lead to degradation of the initial strength properties of structural materials by the mechanism of long-term strength. From the standpoint of the mechanics of a damaged medium, a mathematical model has been developed that describes the kinetics of the stress-strain state and the accumulation of damage during material degradation by the mechanism of long-term strength under conditions of a complex multiaxial stress state. An experimental-theoretical method for finding the material parameters and scalar functions of the constitutive relations of the mechanics of a damaged medium based on the results of specially set experiments on laboratory samples is proposed. The results of experimental studies and numerical modeling of the short-term high-temperature creep of VT6 titanium alloy under uniaxial and multiaxial stress states are presented. The numerical results are compared with the data of field experiments. Particular attention is paid to the issues of modeling the process of unsteady creep for complex deformation modes, accompanied by the rotation of the main areas of stress tensors, deformations and creep deformations, taking into account the effect of an aggressive environment, which is simulated by preliminary hydrogenation of laboratory samples to various hydrogen concentrations by mass. It is shown that the developed version of the constitutive relations of the mechanics of a damaged medium allows, with sufficient accuracy for engineering calculations, to describe unsteady creep and long-term strength of structural alloys under multiaxial stress states, taking into account the effect of an aggressive medium (hydrogen corrosion).

Keywords

• unsteady creep
• long-term strength
• damage
• resource
• mathematical modeling
• basic experiment
• material parameters
• numerical and full-scale experiment
• aggressive environment
• hydrogen saturation