Crack Settings

This section needs writing. Below are some items that will be used or moved else where.

Commands (temp)

Scripted commands

AltPropagate ContactPosition Friction JContour ImperfectInterface MovePlane Propagate PropagateLength

In XML files

   <Cracks>
       <Propagate criterion='1' direction='0' traction='0'/>
       <AltPropagate criterion='7' direction='4' traction='0'/>
       <PropagateLength>2.5</PropagateLength>
       <JContour type='1' size="2" terms="1"/>
       <Friction>0.3</Friction>
       <MovePlane type='avg' prevent='no'/>
       <ContactPosition>0.8</ContactPosition>
   </Cracks>

Crack Propagation Commands

In max energy release rate (or max hoop stress), the crack direction is at angle θ (which is ccw from self similar growth) and obeys

      [math]\displaystyle{ \cos\theta = {3R^2 + \sqrt{1+8R^2} \over 1+9R^2} \quad {\rm and} \quad \sin\theta = \mp\sqrt{1-\cos^2\theta} = \mp\left | R(3\cos\theta - 1)\right| }[/math]

where R = K_II/K_I. The second term is negative or positive depending on K_II being positive or negative. In the limit of K_I to zero, cos θ = 1/3 for crack direction of -70.5 (or +70.5) degrees. This method requires K_I and K_II which can only be done for isotropic (and subclasses), mooney, heisotropic (and subclass), and viscoelastic. All use initial, low strain modulus to calculate stress intensity factors.

Above is same as

      [math]\displaystyle{ \tan {\theta\over 2} = {1\over 4}\left({1\over R} \mp \sqrt{{1\over R^2} + 8}\right) }[/math]

where negative of positive is determined by sign of K_II.

in cod hoop direction, the code uses the max energy release rate method, but assumes R = δ_t/δ_n or ratio of the sliding and opening crack opening displacements. This method can be used for any material.