Finite element interface to Abaqus

Zencrack has an interface to Abaqus/Standard. A brief overview of the interface is given below. In addition to the interface to the Abaqus analysis code, a plug-in capability is provided for use within the Abaqus/CAE interactive environment. This capability allows generation and review of a complete Zencrack input file from within the Abaqus/CAE environment.

• An uncracked mesh must be supplied as an Abaqus .inp file. This may be generated in any suitable pre-processor.
• Zencrack then combines the uncracked mesh with data in the Zencrack input file to create a .inp file for the cracked component.
• The cracked mesh is submitted for analysis by Abaqus.
• When the Abaqus analysis is completed, Zencrack extracts results directly from the .dat file - these results are generated via output requests that were created in the cracked mesh .inp file.
• In some cases there may be inadequate precision in the data in the .dat file. An option is available to use results from the .fil file instead. This requires the use of a supplied Abaqus user subroutine (urdfil).

If crack growth is required, Zencrack carries out crack advancement using the results of the Abaqus analysis and generates a new .inp file for an advanced crack position. The new cracked mesh is then submitted for analysis. This process is shown schematically in the Zencrack flowchart.

This interface is able to provide the following fracture mechinics parameters after processing the results from an Abaqus analysis:

• The magnitude and direction of the maximum energy release rate, G, at each node along the crack front.
• Calculated via data from the Abaqus *CONTOUR INTEGRAL, TYPE=J option.
• For non-linear analysis this term is J, though it is processed in the same way by Zencrack.
• The stress intensity factors K_I, K_II and K_III at each node along the crack front.
• Calculated from nodal displacements.
• Direction for crack growth is calculated from Ks.
• The stress intensity factors are also converted into an equivalent energy term.
• Equations used are only valid for linear elastic isotropic materials.
• The stress intensity factors from the option *CONTOUR INTEGRAL, TYPE=K FACTORS can also be requested though they are not currently processed by Zencrack.
• The T-stresses from the option *CONTOUR INTEGRAL, TYPE=T-STRESS can also be requested and processed by Zencrack.

The analysis results may be post-processed using the utility programs provided with Zencrack. These allow generation of a .csv file for use in a spreadsheet and the creation of crack growth profile representations for crack growth analyses. In addition, all of the standard Abaqus output files are available for post-processing e.g. the .odb file. During a crack growth analysis, the standard Abaqus files can be saved after successive Abaqus analyses to allow subsequent post-processing of multiple crack positions.

A plug-in capability is provided for use within Abaqus/CAE and /Viewer. The plug-in appears as a "Zencrack tree" alongside the Model and Results trees and allows generation and review of a complete Zencrack input file from within /CAE or Viewer.

Some data for the Zencrack input file is related directly to nodes and/or elements in the uncracked mesh file. By opening an odb file for the uncracked model, this data for the Zencrack input file can be picked directly from the model on the screen.

The plug-in also contains a "crack front viewer" option. This is primarily intended to allow definition of splines for the Zencrack user-defined initial crack front option. However, this capability is useful in other ways. For example:

• for allowing the initial crack position to be visualised while partitioning and meshing the uncracked model
• for displaying one or more crack positions from a growth analysis
• for displaying (x,y,z) positions at which data is reported in a csv file when using the "process" post-processing utility program.

A short video is available giving an example of the use of the plug-in to define a complete Zencrack input file. It includes picking of crack-block, split set, relaxation and edge data.

"Analysis options"

"Split set picker"

"Crack front viewer"

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