  Through tridimensonal numerical simulations of crack propagating in material
with an elastic moduli heterogeneity it is shown that the presence of a simple
inclusion can affect dramatically the propagation of the crack. Both the
presence of soft and hard inclusions can lead to the arrest of a crack front.
Here the mechanism leading to the arrest of the crack are described and shown
to depend on the nature of the inclusion. This is also the case in regimes
where the presence of the inclusion leads to a slow down of the crack.
