### 22.6.4. Material Cutoffs

This option in the Material New/Modify panel lets you change cutoff values that are used by Autodyn. The following fields are available:

Maximum Expansion

  This is used to limit the maximum expansion of a cell. If the expansion of a cell exceeds this maximum value, it is reduced to this value.

Minimum Density Factor (Euler)

  This cutoff prevents floating point errors due to small quantities of mass in an Euler cell. It is used to ensure that the minimum amount of a particular materials mass in a cell is never less than

  {density cutoff} * {reference density} * {cell volume}

  if {density cutoff} > 0.0

  or

  - {density cutoff} * {cell volume}

  if the {density cutoff} < 0.0

  The default value of 1.0E-4 should be adequate for most problems. You might need to change this value if you have a material which expands to well below its reference density (e.g. high explosive expanding into a vacuum or air).

Minimum Density Factor (SPH) and Maximum Density Factor (SPH)

  These options let you define minimum and maximum density values for the SPH regions of your problem.

Minimum Soundspeed

  This is used to help avoid division by zero in the time step calculation and avoid the possibility of taking the square root of a negative value of C2. If the computed soundspeed is less than this cutoff, it is set equal to the cutoff value.

Maximum Soundspeed (SPH)

  This is used to limit the maximum soundspeed for SPH. If the soundspeed exceeds this maximum value, it is reduced to this value.

Maximum Temperature

  This is used to limit the maximum temperature within a cell. If the temperature within a cell exceeds this maximum value, it is reduced to this value.

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