Mechanisms of Ductile Fracture: Void Growth by Dislocation -Loop Emission and Hydrogen-Assisted Crack Propagation

271 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006.The effect of hydrogen interstitials on void growth and coalescence has been investigated during crack propagation in materials which fail by ductile processes in the presence of hydrogen. First the hydrogen effect on dislocation mobility and lattice dilatation was considered to establish the material constitutive law. Simulations in a unit cell containing a void were carried out to devise traction-separation laws reflecting the hydrogen effect on void growth and coalescence over a range of stress triaxialities representative of the material constraint ahead of a crack tip. A triaxiality/hydrogen-informed cohesive element was devised to simulate the effect of the microscopic void response in the fracture process zone on the macroscopic crack propagation under plane strain small scale yielding conditions. Numerical results from crack growth simulations in the A533B pressure vessel steel indicate that hydrogen reduces both the initiation toughness and eliminates the tearing resistance of the material.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD