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doc:user:elements:boundaries:pressure_shear

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# Pressure and shear

## Materials

Since pressure/shear interactions are boundary conditions interactions (LoadingInteraction), no materials must be associated to the element.

## Element

Therefore, the first step consist in defining an ElementProperties, as

prp = ElementProperties(typeEl)
prp.put(param1, value1)
prp.depend(param1, fct1, Lock1)) #optional
...

where

 typeEl desired element (for example Traction[2|3]DElement) param1 name of the property associated to the element (for example PRESSURE) value1 value of the corresponding property fct1 function which characterizes the dependency of the property (optional: no fct if no dependency) Lock1 Lock which defines the dependency variable of the property (compulsory if there is a dependency)

### Traction2DElement, Traction3DElement

Traction/shear element for a mesh made of quadrangles in 2D or hexaedra in 3D.

#### Parameters

Name Description Dependency
STIFFMETHOD Method used to compute the stiffness matrix
= STIFF_ANALYTIC : analytic matrix (default)
= STIFF_NUMERIC : numerical matrix
-
PRESSURE Pressure on the entity on which the propriety is applied time
SHEAR_KSI / SHEAR_ETA Shear along $\xi$ or $\eta$ on the entity on which the propriety is applied time
NPG Number of integration points (default : 2) -

### TriangleTraction3DElement

Traction/shear element for a mesh made of tetrahedra

#### Parameters

Name Description Dependency
STIFFMETHOD Method used to compute the stiffness matrix\\= STIFF_ANALYTIC : analytic matrix (default)
= STIFF_NUMERIC : numerical matrix
Not applicable, only the numerical one exists !
-
PRESSURE Pressure on the entity on which the propriety is applied time
SHEAR_KSI / SHEAR_ETA Shear along $\xi$ or $\eta$ on the entity on which the propriety is applied time
NPG Number of integration points (default : 1) -

### ContactTraction2DElement, ContactTraction3DElement

Derivations of Traction2DElement and Traction3DElement with the possibility to set the traction/shear force of a node to zero, when this node is in contact within a specified contact interaction. To determine the contact status, the contact flag of the previous time step is used.

#### Parameters

Name Description Dependency
STIFFMETHOD Method used to compute the stiffness matrix
= STIFF_ANALYTIC : analytic matrix (default)
= STIFF_NUMERIC : numerical matrix
-
PRESSURE Pressure on the entity on which the propriety is applied time
SHEAR_KSI / SHEAR_ETA Shear along $\xi$ or $\eta$ on the entity on which the propriety is applied time
NPG Number of integration points (default : 2) -
NBR_CONTACT_INTERACTION Number of the contact interaction, which is tested for the contact status -

## Interaction

The interaction is defined as:

load = LoadingInteraction(no)
...
interactionset.add(load)

where

 no number of the Interaction gObject1, gObject2 meshed geometric entity where the boundary conditions are applied prp Properties of boundary condition elements to generate

### Remark

Traction, pressure and shear is generated by “traction elements”. Their definition requires a specific Interaction called LoadingInteraction, to which is associated an ElementProperties. These should not be mixed with dead loads. In most cases, traction elements should be chosen over dead loads:

• traction (or pressure/shear) is always defined in local axes, so the direction of the force depends on the orientation of the edge/face on which it is applied.
• traction is divided properly over all edges/faces on which the Interaction is applied. Consequently, the resultant force does not depend on the mesh.

Traction element is used backwards in 3D, so a positive value must be applied to generate a pressure. !!