  The quasicontinuum method is used to simulate three-dimensional
Lomer-Cottrell junctions both in the absence and in the presence of an applied
stress. The simulations show that this type of junction is destroyed by an
unzipping mechanism in which the dislocations that form the junction are
gradually pulled apart along the junction segment. The calculated critical
stress needed for breaking the junction is comparable to that predicted by line
tension models. The simulations also demonstrate a strong influence of the
initial dislocation line directions on the breaking mechanism, an effect that
is neglected in the macroscopic treatment of the hardening effect of junctions.
