Crack Settings

These command control modeling of explicit cracks and whether or not those cracks propagate

Crack Settings Commands

In scripted files, crack properties are controlled by various commands described below. In XML input file, all global crack setting commands are within a <Cracks> element that must be within the <MPMHeader>:

<Cracks>
   (crack setting commands)
</Cracks>

The commands are

• Friction and ImperfectInterface
• Crack Propagation Commands
• JContour
• ContactPosition
• MovePlane

In XML files

   <Cracks>
        <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.