Details for version 7.2 and 7.1

There were many enhancements in Zencrack versions 7.2 and 7.1. The major items are listed below.

• Implementation of Ansys interface, including crack growth prediction. The crack tip opening displacement method is used to determine the stress intensity factors and energy release rate since Ansys does not incorporate a j-integral type energy release rate capability. This interface has been tested with Ansys 6 and Ansys 7, but not yet with Ansys 8.
• Abaqus and Marc interfaces can base growth calculations on displacement based results as an option to the default energy based results. Keyword *ENERGY RELEASE RATE, PREDICTION=ENERGY or DISPLACEMENT.
• Time dependent or combined time and fatigue crack growth prediction can be carried out. New options are available to enter da/dt data and time dependent load and temperature data for time based analysis.
• Material, crack growth data and threshold data can now be temperature dependent. Keywords *MATERIAL, *CRACK GROWTH DATA and *THRESHOLD.
• A new scheme is introduced to control the integration step size between f.e. analyses based on the maximum allowable error in G between the last 2 f.e. runs. This is defined on keyword TOLERANCE. This scheme allows a more reliably and accurate result to be obtained in terms of elapsed cycles.
• A fully automated control of the analysis step size can now be achieved by omitting keyword TOLERANCE.
• Load system superposition method 1 is complimented by a method 2 option that can be used when non-linearities are present (e.g. crack face contact).
• Retardation models are available (basic Willenborg and generalised Willenborg).
• A user defined crack front can be specified using the POINTS method on keyword CRACK FRONT. Zencrack positions a cubic spline through the points and the crack front nodes are positioned along the cubic spline. This allows for a better representation of unusual crack front shapes and can be used as a manual restart capability.
• The user defined crack front can allow solution of break-through problems at geometric discontinuities (e.g. corner to through crack) by allowing a 2 phase analysis.
• The starting point in a spectrum file can be specified using the START or COMPLETED options on keyword SPECTRUM.
• Boundary shifting and transfer routines have been made more robust and general e.g. they now cater for curved element edges, rotation of crack-blocks during non-planar growth to minimise element distortion and have checks to prevent crack-blocks becoming too small compared to adjacent elements.
• Transfer of crack-blocks to new element locations is extended to work for multiple cracks in a model.
• The transfer of crack-blocks to new locations is extended to work for non-planar crack growth cases.
• A relaxation algorithm is implemented to reduce element distortion around the crack-blocks when boundary shifting is activated. In many cases this allows more growth to be undertaken than would otherwise be possible. It can also improve non-planar growth results. Keywords *RELAX and *RELAX DATA.
• Rotation and resizing of the crack blocks takes place during mesh updates. This provides better element quality inside the crack blocks and enables improved non-planar performance.
• Any node that has been moved from a surface or edge is mapped back onto the surfaces as defined by the original nodes and elements of the uncracked mesh. Previously only nodes in the crack-blocks were repositioned back onto curved outer surfaces. This improves the way the program operates on meshes with curved outer surfaces.
• A "transition element" capability is introduced to improve surface based tying between large crack-blocks and the surrounding mesh (Abaqus interface only). This option introduces a layer of elements between the crack-block and surrounding mesh to ensure that there are no master / slave incompatibility issues.
• Crack face loading is updated on all crack face elements after transfer of crack-blocks to a new location.
• Crack face contact applied via *CONTACT is updated on all crack face elements after transfer of crack-blocks to a new location (Abaqus interface only).
• Selection of crack fronts onto which crack face contact is automatically generated. Keyword *CONTACT, CRACK FRONT=SELECTED or ALL
• All Abaqus *DLOAD options are processed and updated if necessary in all Abaqus analysis steps. Previously only the first *DLOAD in step 1 was updated.
• Displacements are now extracted from the Abaqus .fil file as well as j-integrals if the *ENERGY RELEASE RATE, RESULTS=FIL-USER option is used.
• Threshold data input as TYPE=POINTS is interpolated using log-linear or harter-t to be consistent with interpolation methods for tabular growth data.
• The first step at which files are saved and the interval after that at which files are saved can be defined on keyword *SAVE.
• Maximum number of f.e. runs is increased from 99 to 999.
• All calculations are now in double precision. In version 7.0 only the integration scheme used double precision.
• Crack-blocks can be inserted into 8 noded bricks as well as 20 noded bricks.
• The number of available user subroutines has been increased.