Calculation of hydrogen concentrations near crack tips using the boundary element method

Stress (strain)-induced hydrogen diffusion can be described theoretically by a partial differential equation with variable coefficients. In this paper, a special transformation is used to establish a boundary element method (BEM) to numerically simulate hydrogen diffusion in a specimen containing a crack . Calculations show that the hydrogen concentration in the plastic zone near a crack tip rises gradually with time. In metals, hydrogen diffuses continuously to the plastic zone, aggregates there, and, in the vicinity of the crack tip, may reach concentrations two orders of magnitude higher than the bulk concentration. Moreover, the hydrogen distribution in front of the crack tip varies with time. The peak hydrogen concentration moves gradually from the junction between the elastic and plastic zones to the crack tip. For a given time interval, multiple concentration peaks may occur, making it possible to form micro hydrogen embrittlement crevices in front of the crack tip. These results agree well with experimental observations of crack paths in the scanning electron microscope.