Periodic nodal constraint and crack probelms

[KhaledNabilSharafeldin]

Hello,

I am considering using MFEM for implementing a plasticity model package and have a couple of questions regarding MFEM capabilities, or how easy would it be to implement:

• How complex is it to implement a periodic condition of the form $u^{+}=u^{-}+u^{1}$, where $u^{1}$ represents a boundary corner node which may not always be known (part of the solution, not a known boundary condition)? Alternatively, instead of directly modifying the stiffness matrix, is it feasible to enforce this condition using a Lagrange multiplier constraint?
• I am aware of the creation and importation of arbitrarily shaped meshes, how straightforward is it to modify such meshes to simulate crack propagation, either by extending the surface or incorporating Extended Finite Element Method (XFEM)?

Thanks in advance.