Interface to Abaqus - support issues

This page gives information on the interface to Abaqus that may help in running jobs and improving the performance you obtain with this interface. Some key items that you may have missed in the user manual are also included.

Which versions of Abaqus is Zencrack interfaced to?

Zencrack is interfaced to Abaqus/Standard. Testing has been conducted up to and including Abaqus/Standard 6.9-1 and 6.9-EF1.

Level of precision for contour integrals and stress intensity factors

The default option for extracting contour integral results and nodal displacements from an Abaqus analysis is that the values are taken from the .dat file. This is the default because it does not require the use of an Abaqus user subroutine. However, these values have limited precision. In particular, in a model with both sides of the crack included, it may be that the global displacements near the crack are several orders of magnitude greater than the local crack opening displacements. In such cases the displacement values extracted from the .dat file may be of insufficient precision to allow the local crack opening displacements to be calculated accurately. This results in poor values for the stress intensity factors calculated from the displacements.

An alternative method is available to extract results from the .fil file. This requires the use of a supplied Abaqus user subroutine, URDFIL. To use results from the .fil file:

• Specify RESULTS=fil-user on the ENERGY RELEASE RATE keyword.
• Specify an Abaqus user subroutine by using the USER keyword
• Ensure that the subroutine contains the URDFIL coding supplied with Zencrack. This is located in the installed file "fe_abaqus\zcr-jint.for" (or zcr-ctint.for for Ct-integrals rather than j-integrals). If no other user subroutine coding is used for the analysis, you can simply copy the zcr-jint.for file to the local job directory. The USER keyword would then be *USER, FILE=zcr-jint.for.
• Note that the .for extension is .f for Unix installations.

Using Zencrack with Abaqus 6.5-6.8

The issue described below has no workaround in Zencrack 7.3e and all earlier versions. A solution to address this issue is included in Zencrack 7.3f and later versions as described below.

In Abaqus 6.5 a new capability was added with respect to contour integral evaluation. For all nodes on the crack face a surface normal is automatically defined by Abaqus. Testing with Abaqus 6.5pr8 (pre-release v8) showed that if these normals are defined by Abaqus AND the virtual crack extensions do not lie in the crack plane at the crack front, the resulting contour integral values may be incorrect. This type of out-of-plane virtual crack extension is used by Zencrack for cases where both sides of the crack are modelled. Hence the results from Zencrack with Abaqus 6.5 may be incorrect for such cases although the Zencrack analysis will appear to have run successfully. Any errors introduced appear to be small and likely to go un-noticed.

This issue exists in all Abaqus 6.5 versions. An initial bug fix was put in place in Abaqus 6.6 but this did not cover all possible scenarios. A further fix was introduced into Abaqus 6.8. Both fixes were under the Abaqus bug reference v65_1487. Some inconsistencies still appear to exist in Abaqus 6.8 relating to this issue and these are under investigation.

In the meantime for Zencrack versions 7.3f to all 7.5 releases it is suggested that the variable ZCRABAQUSVER should be set to 6.5 to invoke the workaround that was originally introduced into Zencrack to address the issue in Abaqus 6.5. This workaround can be successfully used in Abaqus 6.5, 6.6, 6.7 and 6.8.

The Zencrack runzcr script file located in the tools folder includes a compatibility setting (variable ZCRABAQUSVER) to describe the Abaqus version that is being used. If this is set to 6.5 the automatic calculation of surface normals by Abaqus is de-activated. The analysis then behaves consistently with Abaqus 6.4. Up to and including all Zencrack v7.5 releases the calculation of surface normals when using Abaqus 6.6, 6.7 or 6.8 can be de-activated by setting ZCRABAQUSVER=6.5.

Using Zencrack with Abaqus Extended Functionality releases

The issue described in this section affects Zencrack 7.4a and all earlier versions on Windows platforms only. This issue is fixed in version 7.5.

The Zencrack installation program for Windows platforms does not allow automatic configuration of Zencrack with Abaqus Extended Functionality releases. The following procedure should be used:

• Run the setup program as described in the Installation Manual.
• At the prompt asking for the name of the top level Abaqus folder enter the valid top level folder for your Abaqus EF installation.
• When asked to enter the Abaqus version enter the appropriate details e.g. 661 for 6.6-EF1. Ignore the subsequent warning that the executable does not exist.
• Continue the remaining options and use the 's' option to save (continue with a 'y' when warned again that the Abaqus location is invalid).

Using Zencrack with Abaqus 6.5-4 (or later)

The issue described in this section affects Zencrack 7.4 and all earlier versions. This issue is fixed in Zencrack 7.4a.

Zencrack v7.4 (or earlier) may not run correctly with Abaqus 6.5-4 or later versions. They may either:

• Fail with error 5020 - end of file reading temperatures, or ..
• Give a warning that displacements were not read correctly and end with zero crack growth at all nodes (because the opening status is "closed" for all nodes).

This issue has arisen as a result of changes to the ordering of output tables in the .dat file of the Abaqus 6.5-4 release. The change was as a result of a bug identified in an earlier release of Abaqus v6.5.

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