A MODEL FOR THE BEHAVIOR OF MATERIALS WITH CRACKS UNDER HYDROGEN EMBRITTLEMENT CONDITIONS

We consider the slow growth of normal tension cracks as quasi-brittle behaviour under hydrogen embrittlement conditions. Experiments show th at the cracking resistance of a material in such cases is not a consta nt of the material, but is characterized by some function that relates the rate of crack growth to the stress intensity factor. We propose a numerical method for the calculation of opening mode crack growth whe n the kinetics are controlled by the gas diffusion into the material. The problems under consideration model the fracture phenomena inherent to structures (e.g. pressure vessels, pipelines) that operate in an a ggressive medium and in particular a hydrogen environment. In such pro blems it is necessary to calculate the pressure variation inside a cra ck as a result of gas diffusion and crack growth under the action of t his pressure. Hence it is necessary to solve problems of diffusion the ory and elasticity theory for a cracked medium together wit;? some add itional conditions that provide the link between these two fundamental problems. We study the case of an infinite medium containing a crack which occupies a plane domain of arbitrary shape. To avoid difficultie s related to the three-dimensionality of the problems, we reduce them to two-dimensional integro-differential equations for the crack domain . The integro-differential equation of the elasticity problem of the c rack is solved on the basis of the Boundary Element Method (BEM). The crack kinetics are calculated using a scheme previously introduced by one of the authors and then the BEM is used to solve the integral equa tion for the diffusion-into-the crack problem similar to the analogous problem of filtration of the fluid into a crack.