I am using XFEM in Abaqus. In one of my model, I used maximum principal strain based damage initiation criteria and evolution of fracture based on fracture energy. In this study I took whole element of model as enriched region and a micro crack is super imposed on model.
Damage initiation and evolution is applicable on enriched region and also in cohesive element.
So what is difference between cohesive and enriched element?
Enriched elements use p-enrichment (polinomial enrichment), where the element shape function is improved multiplying by polinomial functions.
Cohesive elements are used to simulate crack propagation. In few words, these elements try to relate stress and displacement with the vanishment of the cohesive forces (atomic level) during crack opening.
I hope to help you
Best regards.
XFEM is based on 2 groups of added DOFs: tip enrichments and heaviside. Heavisde is used along the crack to model the strong discontinuty in the domain. However, tip enrichment is used to reproduce the singularity of stress at the crack tip.
Without going into the technicalities I think the best way to describe it from a user's point of view is the following:
1) Cohesive elements will fail, to allow a crack to propagate through themselves. So you need to know the expected crack and propagation direction before the analysis, and place your cohesive elements there.
2) The XFEM will generate and propagate the crack through the element, where and when the conditions are right for it. It will effectively split your elements. Also, you don't need to know where the crack starts, and which way it propagates before the analysis, it is part of the solution.
Hope this helps,
Best regards,
David
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