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 6.10-1 (including EF releases).

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 Linux installations.

Using the Zencrack 7.6 plug-ins with Abaqus 6.10

The original plugins supplied with Zencrack 7.6 for use with Abaqus/CAE work with Abaqus versions 6.8 and 6.9. They will cause an error if used with Abaqus 6.10 due to a change in the version of Python that is used with Abaqus 6.10. New plugin files are available in these zip files:

For 32bit Windows	zcr76_plugins_2010_07_26_windows_x86-32.zip
For 64bit Windows	zcr76_plugins_2010_07_26_windows_x86-64.zip
For 64bit Linux	zcr76_plugins_2010_07_26_linux_x86-64.tar.gz

The files should be unzipped to the "fe_abaqus" folder of your Zencrack installation. Then follow the normal instructions in section 4.3 of the Installation And Execution Manual for configuring the plugins with Abaqus 6.10.

Please note that the above stand-alone updates for the plugins are also included in the main Zencrack download file. If you downloaded Zencrack after 27 July 2010 you do not need to separately download these plugin updates.

Using Zencrack with Abaqus 6.5-6.10

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 could 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.

An initial bug fix was put in place in Abaqus 6.6. This did not cover all possible scenarios and a further fix was introduced into Abaqus 6.8, both fixes being under Abaqus bug reference v65_1487. Some inconsistencies still existed in Abaqus 6.8 and the fixes were removed for Abaqus 6.9, with the result that the default behaviour was similar to Abaqus 6.5.

For consistent behaviour in Zencrack analyses when using Abaqus 6.5 to 6.10, it is recommended to use an Abaqus workaround that turns off the calculation of crack face normals. The analyses then behave like Abaqus 6.4. This is done by setting an appropriate value of variable ZCRABAQUSVER in the Zencrack runzcr script file. This file is located in the tools folder of the Zencrack installation.

• For Zencrack v7.6: the calculation of surface normals can be de-activated by setting ZCRABAQUSVER=6.5, 6.6, 6.7, 6.8, or 6.9. This can be done for any Abaqus version 6.5 through 6.10, including EF releases.
• For Zencrack v7.3f to v7.5: the calculation of surface normals can be de-activated by setting ZCRABAQUSVER=6.5. This can be done for any Abaqus version 6.5 through 6.10, including EF releases.
• For Zencrack v7.3e and earlier versions: there is no workaround.

Where possible you should set ZCRABAQUSVER to the actual version of Abaqus that is being used. However, if this is not possible, for example when using Abaqus 6.10, you should set ZCRABAQUSVER to an earlier version number. If the setting for ZCRABAQUSVER and the actual Abaqus version being used are different, a warning will be produced in the .rep file that the analysis has used a different Abaqus version than indicated by the setting. This warning can be ignored.

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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