A Discrete Dislocation Analysis of Hydrogen-Assisted Mode I Fracture
Nilgoon Irani (Eindhoven University of Tech.), Joris J. C. Remmers (Eindhoven University of Technology), Vikram Deshpande (Cambridge University)
Discrete Dislocation Plasticity
Tue 10:45 - 12:15
RI Hall 108
We have analyzed mode I crack growth using discrete dislocation analysis in a system which fails due to ”hydrogen-enhanced decohesion” mechanism. The case under study is a two-way coupled diffusion-mechanics problem which is based upon: (i) a quasi-static discrete dislocation analysis of mode I crack growth; (ii) a quasi-static stress assisted hydrogen concentration formulation; (iii) a cohesive law depending on hydrogen concentration. Furthermore, we consider two types of hydrogen diffusion with one assuming fast distribution of hydrogen solutes with respect to the crack growth and the other assuming slow hydrogen diffusion which leads to a constant hydrogen concentration throughout our simulation. Comparing the results of these two methods reveals the impact of hydrostatic stresses on hydrogen embrittlement. In this research we have shown that hydrogen solutes reduce material toughness and the dislocation activity which results in a smaller plastic region at the crack tip. Further increase in hydrogen concentration will lead to an extreme case with few dislocation activity and hence fracture becomes brittle. Moreover, we conclude that in order to be able to model hydrogen-enhanced decohesion mechanism one must consider cohesive strengths as large as 20 times the yield stress, which is not possible while employing continuum plasticity.