Meshing procedure >
Crack block library
The crack-block methodology and meshing procedure
The elements forming the crack front in each crack-block are modelled using collapsed 8 or 20 noded brick elements depending upon the user's uncracked mesh. For 20 noded elements, the user has an option to control the midside node positions extending radially from the crack front - the default option provides quarter point nodes. The crack front itself is seen as a line of nodes on the crack-block surface. The internal mesh of the crack-block coarsens away from the crack front such that some of the crack-block faces can be matched with standard brick elements to allow them to be merged with a user-supplied mesh. These crack-blocks are referred to as standard crack-blocks. The other highly populated faces can be left as free surfaces, symmetry surfaces, or connected to other compatible crack-blocks. In some crack-blocks all of the external surfaces are highly populated surfaces. These special crack-blocks, referred to as large crack-blocks, must be tied to the rest of the user-supplied mesh.
In the simplest case of all, a cracked mesh may contain only a single crack-block (and therefore a single crack front). If there is a single crack-block then only one side of the crack (i.e. one crack face) is modelled and symmetry constraints should be applied. These can be applied in the uncracked mesh and automatically updated by Zencrack.
If both sides of the crack (i.e. both crack faces) are to be modelled, then pairs of crack-blocks are used with a face-to-face match of the crack-blocks. An example with crack-blocks used in a face-to-face match is shown below. This is a displaced plot with the visible part of one crack face shaded for clarity.
Crack-blocks are grouped into "families" for ease of use. All crack-blocks within a family can be placed alongside one another to form a crack front. The different crack-blocks within a family may have different numbers of elements along their individual crack fronts giving flexibility in their application. A typical crack-block family is shown below.