Pressure Traction Law

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The Traction Law

This traction law applies a constant stress that is normal to the crack surface. It can be used to model a pressure-loaded crack. The stress can be entered in one of two ways:

You can either apply a constant stress or provide a user-defined function to let the stress vary in time. Even if you want a constant stress, experience shows that applying that full stress from the start of calculation may cause local vibrations and less stable results. If it often better to ramp the stress up to the constant stress by applying an appropriate ramping function.

Failure

This traction does not fail; it just continues to apply normal stress. By using a function, the stress can be time dependent.

Traction Law Properties

The following properties are used to create a pressure traction law:

Property Description Units Default
stress Enter constant normal stress. Use negative stress for a pressure loaded crack. pressure units none
function Alternatively, the stress can be entered as a user-defined function of time. pressure units none
minCOD Specify a minimum, normal, crack opening displacement below which no pressure is applied. This parameter can model pressure induced by a substance that needs room to enter the crack; it is ignored if it is negative length units -1

If a function is used, any entered stress property is ignored.