hexa (adhesive)

Restriction: Available in Abaqus, Nastran, OptiStruct, and PAM-CRASH 2G.

This realization creates a continuous or discontinuous hexa weld with a predefined pattern.

For Abaqus, this realization uses the prop_abaqus_acm.tcl property script. For Nastran and OptiStruct, prop_nastran_acm.tcl is used.

All defined information is stored on the connector, and can be exported into the connector .xml file.

Seam Hexas are created from the Seam panel.

The HEXA elements will be centered about the seam connector if the seam connector is not close to a free edge. If the distance between the seam connector and free edge of a component is less than half the width of the HEXA, then the realization of HEXA elements will start from the seam connector and will be extruded in the direction away from the edge.

For OptiStruct and Nastran solvers, the HEXA elements are tied to a shell using RBE3s at locations where the HEXA nodes and shell nodes are non-coincident. If the HEXA nodes and shell nodes are coincident then RBE2s will be used to tie them.

This realization type is intended to work on meshes, both shells and solids.

The hexa dimension depends on the following settings:

The length of a hexa is predefined by the distribution of the test points along the seam connector. This is defined by spacing or density during the connector creation.
The width of the single hexa depends on the number of strips and the defined total width of the seam, which is measured perpendicular to the seam direction.
The thickness of a single hexa depends on the number of defined coats and the selected thickness option.

The available thickness options interact with the consider shell thickness option and offset for hexa positioning option. In the figures below, the green seams on the left take into account the thickness as well as the shell offset. This information is used for dimensioning and positioning the hexas. For the pink seams on the right side, the hexas are always positioned around the exact middle between the current shell positions. The shell thicknesses are taken into account only for the hexa height, but not for the positioning. The orange lines and arrows in the figures below illustrate the dependencies for the positioning.

shell gap: The seam completely and exactly fills the gap between the two shells. Shell thicknesses and offsets are not considered.

Figure 3.
maintain gap: The seam is positioned in the exact middle between the shells. The seam thickness is adjusted, that on both sides the gap between shell and seam fits the defined gap size. Shell thicknesses and offsets are not considered.

Figure 4.
(t1+t2)/2: The seam thickness is calculated by averaging both shell thicknesses. On the left side the offsets and thicknesses are taken into account, so that the seam is positioned around the middle of the air gap. On the right side the seam is just positioned around the middle of the shell positions.

Figure 5.
midthickness: On the left side the exact air gap is determined and filled with the seam. On the right side the seam thickness is calculated by subtracting half the thickness of both shells from the total distance of the shells.

Figure 6.
const. thickness: The thickness of the seam is predefined for both; on the left side the seam is positioned around the middle of the air gap, on the right side around the middle of the two shells.

Figure 7.

The following options are available for Hexa Position:

Anything with "edge": Snapping to edge activated when using any of the hexa position options that refer to an “edge”. This is to ensure that the connector can identify an “edge” to realize to.
Midpoint to connector: The connector realization will follow the connector line until the connector line is in space (Figure 8). At which point it will try to realize at the closest projections within tolerance (Figure 9). Once the connector is outside of the tolerance it will fail (Figure 10).; Figure 8.; Figure 9.; Figure 10.

The following options are available for Adjust Width:

This parameter will try to limit the self-intersection of the connector and creation of poor quality hexa elements around sharp corners.

None: Allows the hexa to self-intersect.; Figure 11.
Reduce Width: Reduces the inner width to find a position where the mesh is not intersecting.; Figure 12.
Move Hexa: Performs the same operation as the previous option by reducing the inner width to find a position where the mesh is not intersecting. This will then add the removed width back to the outer diameter to maintain the specified width.; Figure 13.