**crack_release

Description

This BC is used to propagate a crack (release DOFs) according to node-extrapolated material values (note there can be some significant error due to the extrapolation error, especially with the high variable gradients found around crack tips).

Syntax

**crack_release \(~\,~\,\) nset  dof  var-value-list

where nset is the node set defining the ligament through which the crack propagates, and dof is the fixed DOF name (e.g. U2). Following these entries, a list of variable-value combinations are to be entered to specify the crack growth criterion.

Example

For a plasticity problem a maximum allowable plastic strain equivalent of \(20\%\) could be used (remember the name of \(p\) - here epcum depends on the material law used).

**crack_release
  middle U2 epcum 0.20

Or one could use a secondary material variable such as the von Mises stress as a ultimate tensile strength.

**crack_release
  ligament U2 sig::mises 520.0
  ligament U1 sig::mises 520.0