Evaluation of helium embrittlement by two dimensional elastic—plastic finite element method

Abstract

Dependency of grain boundary helium ebrittlement on bubble morphology and workhardening is quantitatively evaluated by two dimensional FEM which is based on continuum body, von Mises' yield criterion, J2 flow theory, and nth power workhardening law. The plain stress condition is assumed. The following are conclusions: (1) The local necking near grain boundary (helium embrittlement) is a bifurcation phenomenon. It only occurs within limited parameters range of bubble size, bubble density and workhardening exponent. (2) No embrittlement under critical bubble size, weak dependency of total elongation on bubble size in intermediate bubble size, and rapid decrease of elongation for large bubble are found. (3) The high density bubble morphology leads to no local necking around bubbles because of reduction of strain concentration. (4) The decrease of workhardening exponent from 0.3 to 0.1 results in rapid reduction of total elongation, but further reduction of workhardening to 0.05 restores ductility.