The Influence Of The Hydrogen Concentration And FSW Weld Residual Stress On The Safety Service Of Structures

The energy crisis and environmental issues have become increasingly prominent.Hydrogen is highly concerned with the energy industry because of its high efficiency and cleanliness.The high-pressure gaseous hydrogen storage tank is used as a carrier for storing and transporting hydrogen,and its structural safety and service life need to be studied urgently in the development of hydrogen energy technology.Friction stir welding is a solid-phase joining process with low residual stress,small residual deformation and no welding wire,and is widely used in various industries including aerospace,automotive and manufacturing.In this paper,finite element analysis method is used to study the effect of residual stress and hydrogen concentration in the environment on the safety service of structures.According to the formula of fatigue crack propagation rate,the fatigue life of specimen is evaluated effectively.Firstly,taking into account the heat input characteristics of friction stir welding and using ABAQUS finite element software,a thermal input numerical model was established to simulate temperature field and stress field changes in the welding process.The results show that the temperature field is in the form of a "comet" and its maximum temperature is 1083 °C.The residual stress value in the central area of the weld is lower than the edge of the weld and is expressed as tensile stress.The residual stress far from the central area of the weld is expressed as compressive stress.It is also found that the peak value of the longitudinal residual stress decreases with the increase of the speed of the stirring head.Secondly,the residual stress field of the friction stir welding obtained is input to the finite element flat plate model with the central crack through the ABAQUS subroutine SIGINI to obtain the residual stress intensity factor.The fatigue crack growth rate and fatigue life can be predicted by the superposition method and the Forman formula.Based on the theory of hydrogen diffusion and the theory of hydrogen adsorption reducing surface energy,the influence of environmental hydrogen concentration on fatigue crack growth rate and fatigue life of components is studied.The results show that the residual stress will increase the stress ratio of fatigue load and shorten the fatigue life of welded components.Considering the effect of hydrogen,the stress corrosion effect greatly reduces the fatigue life of the component,especially when combined with residual stress,the corrosion effect is more obvious.