We use discrete element method (DEM) simulations to study the evolution of defects during sintering. In DEM, the particulate nature of the sintering powder is taken explicitly into account because each particle is modeled as a discrete entity interacting with its neighbors. This allows to treat naturally the gain or the loss of contacts between particles, and to explicitly take particle rearrangement into account. These effects are particularly important when looking for the nucleation, growth or healing of local heterogeneities such as defects. We first study the evolution of a crack (generated, e.g., during ejection or drying processes) when no geometrical constraint is imposed. We then investigate how constrained sintering between two parallel planes may lead to crack initiation and growth. We show that the extent of interparticle rearrangement plays a major role in the evolution of the crack under such conditions. The main conclusion of these simulations is that some geometrical constraint is necessary for a defect to grow into a crack and that the presence of an initial defect is not a necessary condition to initiate cracks.