Coupled Hydrogen Concentration-Stress Field Simulation Based On Heat Transfer Analogy

In ocean engineering,chemical industry,nuclear engineering and other industry sector,metal materials often serve in hydrogen environment.As the smallest and lightest atom in nature,hydrogen diffuses and enriches in metal structure easily.With the help of hydrogen diffusion,long-range transportation of hydrogen will take place by dislocation movement,at the same time,hydrogen can also be trapped by various kinds of defects in materials(vacancy,dislocation,interface,micropore,microcrack,etc.)or segregate near defects.The hydrogen in materials will affect the movement and evolution of dislocations,which may influence the plastic deformation of materials.On the other hand,hydrogen trapped or segregated near defects will also affect the emission of dislocation and interfacial cohesive strength,which leads to hydrogen embrittlement.To understand hydrogen embrittlement and revealing its physical mechanism is an important topic in solid mechanics and material science,it has important theoretical significance and potential application prospects.To understand the hydrogen embrittlement,we need to study hydrogen diffusion in metal material.Hydrogen diffusion in the material is closely related to its concentration gradient,hydrostatic stress gradient and trap density.Although the hydrogen diffusion and heat conduction are different physical phenomenon,their governing equations are formally comparable,so that heat transfer analogy is one of the effective methods of hydrogen diffusion simulation.The main work of this paper includes:1.The method of solving the hydrogen diffusion equation based on heat transfer analogy and its implementation in ABAQUS.Coded in ABAQUS/UMAT,we calculated element hydrostatic stress gradient field as well as trap density,and then the coupling of temperature field(concentration field)and stress field was realized.Finally,coded in the secondary development interface provided by UMATHT,we solved hydrogen diffusion equation.2.Coupling calculation of elastoplastic stress field and hydrogen concentration field near the blunting crack tip.Based on the classical isotropic elasto-plastic constitutive model: power hardening constitutive,stress field and deformation field near the crack tip were solved,then,by heat transfer analogy,we got the hydrogen concentration field in the two-dimensional and three-dimensional crack samples,which provides a reference for further study in fracture of hydrogen embrittlement.3.Coupling calculation of hydrogen concentration field in crystals based on crystal plasticity constitutive.With the help of class library: ABAQUS/Python commands,we've built highly modular and parameterized crystal model in Python scripts,coupled with the hydrogen diffusion equation,by use of heat transfer analogy,we obtained the hydrogen concentration field of the crystal structure and studied the influence of crystal orientation,polycrystalline grain boundaries,grain size,along with loading rate in crystal hydrogen diffusion.