Pressure Traction Law

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 can cause large, local vibrations and lead to unstable results. If it usually 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.	MPa	none
function	Alternatively, the stress can be entered as a user-defined function of time.	MPM	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	mm	-1

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