Zencrack is interfaced to Simcenter Nastran and NX Nastran from the Zencrack v7.9-3 release. Testing has been conducted up to and including Simcenter Nastran 2406. Note that at least Version 10.0 of NX Nastran is required - earlier releases are not supported.

The interface supports solution types SOL101 and SOL401. Note that the J-integral option requires SOL401.

Simcenter Nastran Desktop licenses include a checksum in input files created by their associated pre-processor which only allows execution of the file as generated by the pre-processor. This prevents uses of this type of input file with Zencrack since a fundamental part of the process is that Zencrack modifies the input file.

Enterprise licensing enables Simcenter Nastran to solve any valid Nastran input file from any pre-processor, including after modifications by Zencrack.

Simcenter Nastran can exist as a basic package with additional modules. Zencrack requires SOL101 as a minimum and Simcenter Nastran Multistep Nonlinear SOL401 for calculation of J-integrals.

If the "modified input file" requirement is satisfied and appropriate SOL types are available, Zencrack can use Simcenter Nastran as part of a stand-alone installation or when Simcenter Nastran is packaged within Simcenter3D or Femap.

Solution types 101 and 401 are supported for a Zencrack analysis. Fracture mechanics parameters at nodes along the crack front are available as follows:

• SOL401: J-integrals via the Simcenter Nastran CRAKTP and VCEV options.
• SOL401 and SOL101: The stress intensity factors K_I, K_II and K_III calculated from nodal displacements (linear elastic isotropic materials).

If an analysis uses SOL101 then fracture mechanics parameters are calculated using the displacements from the f.e. solution. If SOL401 is used, the analysis calculates two sets of fracture mechanics parameters: one using displacements and one using J-integral results from the f.e. solution. The default behaviour in that case is that the J-integral results are used to drive crack growth calculations. These options are controlled on the *ENERGY RELEASE RATE keyword in the Zencrack input file.

Zencrack calculates J-integrals via the Simcenter Nastran CRAKTP and VCEV options in a SOL401 analysis. As of Simcenter Nastran 2406 the following issues may affect calculation of J-integrals:

• If a model contains more than 10 rings of hex elements around a crack front, a J-integral request for 11 or more contour rings can cause the Simcenter Nastran analysis to fail, hang or produce invalid J-integral results. A workaround is to limit the request for contour integrals to 10 rings via an option in the Zencrack input file:
  *ENERGY RELEASE RATE, CONTOURS=10
• If an embedded crack is modelled (i.e. a continuous crack front that does not cut the free surface of the mesh), the J-integral values at the notional "end 2" of the crack front definition are incorrect. A workaround for an embedded crack is to drive the analysis using displacement-based stress intensity factors:
  *ENERGY RELEASE RATE, MAGNITUDE DADN=SIF-displacement, DIRECTION DADN=SIF-displacement
• If a CELAS2 spring element is included in a mesh, the J-integral calculations return values of zero. There is no direct workaround other than to avoid using a spring element.
  

These issues are under investigation with Siemens.

There are two ways that the number of processors for Simcenter Nastran / NX Nastran jobs executed by Zencrack can be specified:

• Variable ZCR_OPTIONS_NXNASTRAN in the zencrack.ini file can be used to define parameters passed to the Nastran command line for all Zencrack jobs. The parallel option can be added to this parameter. Refer to the file itself (located in the Zencrack tools folder) or the Installation And Execution Manual for more information about this variable.
• The command line option "-fe" can be used when executing a Zencrack job. This defines parameters to be passed to the Nastran command line for that particular Zencrack job. The parameters should be surrounded by quotes. For example, to use 4 processors:

  runzcrXX -j jobname -fe "parallel=4"
  

  From version 7.9, this command line option can be used when a job is started from the "Run Zencrack" screen of the Zencrack GUI.

If the parallel parameter is defined using both methods, the command line value takes precedence.

Note that the Zencrack setup program requests information about the number of processors and configures the zencrack.ini file accordingly during the installation process.

Consideration should be given to using the Nastran command line option "scratch=yes" to prevent creation of potentially large .DBALL and .MASTER files. This can be done in a similar way to addition of the "parallel" option described above:

• By adding "scratch=yes" to the variable ZCR_OPTIONS_NXNASTRAN in the zencrack.ini file.
• By using the command line option "-fe" when executing a Zencrack job

runzcrXX -j jobname -fe "scratch=yes"

Care should be taken when using SOL101 or SOL401 to ensure that an appropriate element formulation is used. For example, if a model containing 20 noded CHEXA elements and a SOL401 statement is converted to SOL101 by simply changing the SOL specification, the element formulation defaults to a different setting for SOL101 than would be used for the SOL401 analysis.

In order to replicate the SOL401 element formulation in a SOL101 analysis the following options should be set on the PSOLID option(s) in the uncracked mesh:

For 20 noded elements:

SOL401 allows only a full 3x3x3 integration. Use IN=3 and ISOP=1 to invoke this in a SOL101 analysis. For example:

$* SOL401    PID     MID   CORDM      IN  STRESS    ISOP    FCTN
PSOLID         1       1       1                           SMECH

$* SOL101    PID     MID   CORDM      IN  STRESS    ISOP    FCTN
PSOLID         1       1       1       3               1   SMECH

For 8 noded elements:

SOL401 allows two integration options. The default is 2x2x2 with bubble function. This cannot be exactly replicated in SOL101. The alternative is 2x2x2 full integration set by IN=2. This can be replicated in a SOL101 analysis by IN=2 and ISOP=1. For example:

$* SOL401    PID     MID   CORDM      IN  STRESS    ISOP    FCTN
PSOLID         1       1       1       2                   SMECH

$* SOL101    PID     MID   CORDM      IN  STRESS    ISOP    FCTN
PSOLID         1       1       1       2               1   SMECH

In moving from NX 12 to a Continuous Release cycle the internal numbering and folder locations of NX and Simcenter Nastran installations can no longer be extracted by the Zencrack setup program for Zencrack 8.3-1 (and earlier). It is recommended to "not configure" Nastran during the setup phase and then edit the zencrack.ini file afterwards to correctly configure the version. For example, the entries for Nastran installed as part of an NX installation would be:

For the 1899 branch:
ZCR_NXNASTRAN = C:\Program Files\Siemens\NX1899\NXNASTRAN\bin\nastran.exe
ZCR_NXNASTRAN_VER = 2020.1

For the 1872 branch:
ZCR_NXNASTRAN = C:\Program Files\Siemens\NX1872\NXNASTRAN\bin\nastran.exe
ZCR_NXNASTRAN_VER = 2019.2

For the 1847 branch:
ZCR_NXNASTRAN = C:\Program Files\Siemens\NX\NXNASTRAN\bin\nastran.exe
ZCR_NXNASTRAN_VER = 2019.1