Residual stresses have been numerically determined in welded joints. In this study, the numerical model is based on the coupling of different physical phenomena considering the thermal, mechanical and metallurgical nature of a welding process. The ABAQUS software program was used to perform the numerical simulations, based on the finite element method (FEM). The aspects related to the mathematical modeling of complex welding procedures were pondered with the FEM: variations in the physical and mechanical properties of the materials as a function of the temperature; the transience and the speed of the welding process, the material phase transformations; the different mechanisms of heat exchange with the environment (convection and radiation); all them associated with a high level of nonlinearity. The heat source used in this analytical model for heat supply was the double ellipsoid model proposed by Goldak, in which a 60 mm × 50 mm and 3 mm rectangular ASTM AH36 steel plate was used for the TIG process simulations. Throughout this work, the optimization of the welding procedures currently practiced in petrochemical and ship building industries can be applied to reduce the levels of residual stresses.
en régimen elástico, bajo el efecto de una acción mecánica definida por una carga estática aplicada en el modo de fractura I y de una acción ambiental caracterizada por la difusión de hidrógeno a través de la estructura cristalina del material. Las ecuaciones que describen la evolución de las variables en la punta de la fisura forman un sistema no lineal de ecuaciones diferenciales ordinarias que es resuelto con el método de Runge-Kutta de 4 o orden. Los resultados obtenidos muestran la influencia del hidrógeno en la disminución del tiempo de inicio y propagación de fisuras, lo que es consistente con las observaciones macroscópicas del fenómeno de fragilización por hidrógeno Palabras clave: mecánica de la fractura, simulación numérica, propagación de fisuras, fragilización por hidrógeno
This paper presents a numerical simulation of the effect of hydrogen atomic diffusion on fatigue crack propagation on structural steels. The simulation was performed with a specimen type CT of API 5CT P110 steel, loaded in the tensile opening mode, in plane strain state and under the effects of a cyclic mechanical load and the hydrogen concentration at the crack tip. As hydrogen source, a cathodic protection system was considered, commonly used in subsea pipelines. The equations of evolution of variables at the crack tip form a non-linear system of ordinary differential equations that was solved by means of the 4th order Runge-Kutta method. The solid-solid diffusion through the lattice ahead of the crack tip was simulated using the finite difference method. The simulations results show that under these conditions, the fatigue crack evolution process is enhanced by the hydrogen presence in the material, and that the start time of the crack propagation decreases as its concentration increases. These results show good correlation and consistency with macroscopic observations, providing a better understanding of hydrogen embrittlement in fatigue crack propagation processes in structural steels.
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