Abstract
In various engineering industries, including railroad transport, metal structural elements are sometimes operated under external thermomechanical loads while being also exposed to aggressive environments. The impact of an aggressive environment on the mechanical properties of metals is one of the dominant factors, which determines structure strength and service life, as it usually deteriorates the mechanical properties of materials. The thermodiffusion problem of determining the stress state of a steel shell structure is considered. The subject of the study is a compound steel shell of revolution loaded with internal pressure and operating in a hydrogen-containing environment at high temperatures. The purpose of this study is to determine the stress state of the shell taking into account the changes in the mechanical properties due to simultaneous exposure to temperature and hydrogen. In the suggested approach, the thermodiffusion and mechanical problems are coupled by taking into account the changes in stress-strain diagrams of steel samples as temperature and hydrogen concentration increase. The boundary problem of heat conduction and diffusion is solved using the finite elements method. The system of differential equations for the boundary problem of shell stress state is integrated using S. K. Godunov’s method of discrete orthogonalization. The method is based on stepwise orthogonalization of the solution vectors of the Cauchy problem. The obtained solution allowed determining the site of maximal stresses and drawing conclusions on the strength of the studied structure when increasing hydrogen concentration and internal pressure.
Highlights
The shell steel structural elements are widely used as structural elements in various industrial sectors, including railroad transport
The first one deals with a further study of the fundamentals and the processes of hydrogen embrittlement and ageing of metals, while the second focuses on the development of models and methods for predicting changes in the stress state to evaluate the remaining service life of the structure
The inner shell surface comes into contact with an aggressive hydrogen-containing environment with excess pressure р and temperature T, from which hydrogen diffuses into the shell to change the mechanical properties of material in the course of operation. The solving of this coupled thermodiffusion problem can be provided as follows: 1) solving the heat conduction problem to determine the temperature distribution in the shell over time T(t); 2) solving the problem of hydrogen diffusion into metal to determine hydrogen distribution taking heating into account c(t,T); 3) obtaining experimental dependences between stress σ, deformation ε, hydrogen concentration c and temperature Т for samples σ = f(ε, c, T) with uniaxial stress state; 4) determination of the stress state of the studied structure taking into account the changed physical and chemical properties of the material σ = f(p, c, T) at a given time t
Summary
The shell steel structural elements are widely used as structural elements in various industrial sectors, including railroad transport. The inner shell surface comes into contact with an aggressive hydrogen-containing environment with excess pressure р and temperature T, from which hydrogen diffuses into the shell to change the mechanical properties of material in the course of operation The solving of this coupled thermodiffusion problem can be provided as follows: 1) solving the heat conduction problem to determine the temperature distribution in the shell over time T(t); 2) solving the problem of hydrogen diffusion into metal to determine hydrogen distribution taking heating into account c(t,T); 3) obtaining experimental dependences between stress σ, deformation ε, hydrogen concentration c and temperature Т for samples σ = f(ε, c, T) with uniaxial stress state; 4) determination of the stress state of the studied structure taking into account the changed physical and chemical properties of the material σ = f(p, c, T) at a given time t. The problem of determination of the stress state of a shell structure shall be described by a set of equations from three systems of differential equations (1), (3), and (6) with certain initial and boundary conditions
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