Mechanics of tungsten blistering: A finite element study

Tungsten exhibits a pronounced blistering behavior under severe hydrogen implantation to approximately 50 μm. The growth of a blister is controlled by the interplay between the gas pressure in the blister and the deformation of the blister cap. The stress concentration on the cap apex and at the boundary causes burst of a blister. Thus, blistering is affected by mechanics as well as by physics. In this paper, the mechanics of blistering is discussed focusing on the effect of plastic yield. A comprehensive parametric study was conducted by means of finite element analysis in order to investigate the impact of plastic yield on the bulging deformation for a wide range of gas pressure, yield stress and dilatation strain. The effect of cap thickness was also estimated. A general trend was found as follows: when yield stress is below 700 MPa, plastic yield plays a dominant role already at lower gas pressures (∼100 MPa) leading to a rapid increase of bulge height. In the case of large yield stress (>800 MPa), the bulging is governed by elastic strains, and its development is insignificant. The cap thickness proves to be a critical factor for bulge deformation. Concomitant cap dilatation shows a considerable impact on bulging only when the gas pressure is low (∼100 MPa).