Zencrack 9.3-1

What's New in Zencrack?

Zencrack 9.3-1

The base code for Zencrack version 9.3-1 was finalised on 6 September 2023 and released in September 2023

The highlights for this release are:

first implementation of remeshing with multiple cracks
improved remeshing algorithms for growth at chamfers and corners
ability to plot contours of cycle count and load spectrum passes (or the equivalent time values in a time dependent analysis)

Remeshing with multiple cracks

Remeshing now supports inclusion of multiple cracks into a model. This initial multi-crack implementation requires that the remesh regions of separate cracks do not touch or overlap. In some cases it may be necessary to use the ELEMENT SET parameter on the *CRACK FRONT keyword of one or more crack definitions to define elements sets for the remeshing regions to ensure there is no overlap. If, during a growth analysis, two or more remesh regions expand and touch or overlap, the analysis will stop.

Animations of growth in multi-crack remeshing models are included at the end of this page.

Example of growth profiles: 2-crack remeshing analysis in a disk model

Example of growth profiles: 3-crack remeshing analysis with cracks located at a chamfer

Remeshing improvements and changes

Cutting the crack plane into the mesh

Improvements have been made in the calculations related to cutting the crack plane into the mesh as the crack grows. Specifically, there was previously a chance that as a crack grows past a corner the internal representation of the crack plane may not have extended fully through the mesh. This resulted in an inability to cut the crack plane fully into the model and the failure of the growth run. This process is now improved and there is significantly less chance of the crack plane failing to cut fully through the model as a crack reaches a corner and grows past it.

Improvements in creation of ring elements

The generation of ring elements is improved to reduce distortion where:

the free surface is curved,
the crack front meets the surface at a small angle,
there is a local change in curvature along the crack front close to the free surface.

In some cases this means that an analysis is able to continue where previously it may have failed.

Extra checks for inside-out crack front elements (#1)

Parabolic elements with quarter-point nodes are numerically more sensitive to becoming inside-out due to distortion in their overall shape than elements with midside nodes. Such distortions may arise as a crack passes a chamfer or corner in a model. In order to reduce the possibility of the analysis stopping, the remeshing process detects inside-out parabolic crack front elements and, if there are any, converts all collapsed elements for that crack front to have radial nodes at the midside position for that analysis step. The elements are then more robust though it is possible that there may still be inside-out issues. The possibility to change crack front element topology is the default behaviour and can be turned off via an option in the GUI ini file.

Extra checks for inside-out crack front elements (#2)

In the final stage of ring creation for a surface breaking crack front some nodes on the end planes of the rings are adjusted to also be on the exterior surface of the model. As a crack passes a corner the positioning of such nodes may introduce inside-out elements in the rings. If there are no inside-out elements in the rings before this final adjustment, the program reinstates those valid ring elements. The possibility to reinstate the valid elements is the default behaviour and can be turned off via an option in the GUI ini file.

Trimming the ends of the crack front

In crack growth analysis there may sometimes be undesirable effects introduced in the crack profile shape from growth calculations related to the nodes on the ends of the crack (i.e. crack front nodes on the surface of the model). In particular this can occur when there has been a sudden change in geometry at the free surface e.g. at a sharp corner. A new option for remeshing, RemeshTrimEnds, is added to the [REMESHING] section of the zencrack_gui.ini file. This option allows the crack growth increment calculated for the end nodes from the integration scheme to be rejected. A new representation of the profile is generated by linear or parabolic extension of the next two or three corner nodes on the crack front. This can have beneficial effects in terms of retaining a meaningful crack profile. The default behaviour is that this option is off - it must be activated by changing the setting in the GUI .ini file.

Zencrack GUI changes

A capability is added to allow contour fills or ISO contours lines on crack surfaces for: cycles, time, load spectrum passes, time history passes. Such plots provide a visual aid to understanding the cycle or time history development from a growth run in addition to the crack shape development. Contours may be displayed simultaneously on results from multiple runs to aid comparisons. Contouring is available on the Display Crack Profiles screen via a new drop-down that enables changing the crack surface representation from a plain surface to a contoured or ISO line representation.

Support is added for display of pyramid element types (i.e. explicit square based pyramid elements rather than collapsed hex elements in a pyramidal topological shape). In practice this means:

Abaqus: C3D5
Ansys: no such element types
Simcenter Nastran: CPYRAM (5 noded linear and 13 noded parabolic)

The default colours for these element types are added to the existing parameter SURFACEBYTYPE in the [COLOURS] section of the zencrack_gui.ini file.

The 'Display crack profiles' screen has a new button when a model has more than one crack front. In addition to the standard 'Apply' button there is now an option to 'Apply to all crack profiles'. When comparing results from multiple models, this button makes it simpler to ensure all crack profile display attributes from a single analysis are the same.

Other Changes

Abaqus interface

Support is added to the GUI for display of Abaqus 5 noded pyramid elements.

The status value of the Abaqus GAP keyword in keyabq.dat is changed to enable gap definitions to be passed to the cracked mesh.

A possible error reading copnnectivity data if a connectivity line has a trailing comma has been addressed. This was assigned bug reference ZENCR547.

A possible array bounds issue when processing an Abaqus mesh with the Abaqus converter program has been fixed. This issue related to set definitions with no data lines. This was assigned bug reference ZENCR546.

Ansys interface

The keyans.dat file is updated for Ansys 2023R2.

Simcenter Nastran interface

Support is added to the GUI for display of 5 and 13 noded pyramid elements, CPYRAM.

Documentation

The interface manuals for Abaqus and Ansys have their temperature sections re-written to improve the description of temperature handling in a remeshing analysis.

An extra example is added to the Examples Manual for multi-crack remeshing and is included in the demos folder of the Zencrack installation.