Is it possible to simulate a ductile fracture initiated a crack using a XFEM crack and a traction separation law for the material damage initiation criteria ?
I'm not sure what you mean with XFEM.
But it is possible to model crack initiatiation and propagation. However I only a method for this when you use layers in your model, in such a way that the damage can only grow through the boundaries of the layers.
For instance by using layers modelled as seperate parts with cohesive elements inbetween. Alternatively you can use cohesive surface interaction.
I think you can apply the traction separation law both with cohesive elements and the cohesive surface interaction.