Pre and Post Processing
Two pre-processing utility programs (relating to fatigue crack growth analysis) are provided with Zencrack:
Two utility programs are provided to further post-process the Zencrack results. These are largely considered legacy utilities as the Zencrack GUI provides the fastest means of producing this type of output. However, there may be cases where manual execution of these utilities is useful.
- "process" - generation of data for plotting results at crack front nodes
- "3dmesh" - generation of crack growth profile plots.
The tanh utility allows use of crack growth data which is in the standard tanh equation form by generating tabular format data from the tanh equation. The tabular data is generated as a function of stress ratio. Interpolation between the tabular curves will not be identical to direct use of the tanh equation, but if enough curves are generated the differences will be negligible.
The input to this utility is a set of coefficients for the tanh equation and control values to specify the output curve creation. The output is a set of tabular growth curves in a format ready for use on the Zencrack option *CRACK GROWTH DATA, TYPE=TABULAR.
The alternative to the use of this pre-processing utility is that a user subroutine is written to directly use the tanh equation data.
Crack growth data in tabular form derived from tanh equation
The rainflow utility has been developed to perform cycle counting of uncounted load spectra using the "rainflow" algorithm. The generated spectrum files are in a format that can be used by Zencrack directly on the option *LOAD SYSTEM, TYPE=SPECTRUM. The program includes a capability for inclusion of time dependent information in the spectrum data for compatibility with the combined fatigue and time dependent growth capability in Zencrack.
The input to the program is an uncounted spectrum file. This consists of one data point per record (i.e. load level) for time independent spectra and two data points per record for time dependent spectra (i.e. load level, time).
The program can handle load spectra with a large number of data points. Random uncounted spectrum with 8 million data points have been analysed for testing purposes. The upper limit on the number of data points is determined by available memory.
The rainflow utility program is also used during an analysis when load history definitions that support "on-the-fly" cycle counting are used.
Raw data : Load vs time
Counted cycles : Load range vs cycle number
The "process" utility program allows generation of a csv (comma separated variable) file containing detailed information for one or more positions on a crack front. This allows easy importing of data into a spreadsheet where the results can be plotted and analysed. This type of processing is essential in order to understand the large amount of data that can be generated in an analysis. Information can be extracted at:
- specified node positions
- a parametric distance along each crack profile
- at intersection of each crack profile with a plane
Note that the plane intersection method is not currently supported with the Zencrack GUI.
An example of the difference in where the data is extracted for these three methods is shown here:
- Process at a node position along each crack front, the "mid" node position in this example (red line).
- Process at a parametric position along each crack front, s=0.5 in this example (yellow line).
- Process at a user defined plane intersection along each crack front (blue line).
Example of three different path definitions
A Microsoft Excel template is supplied to allow plots to be quickly generated from the csv file. The template is intended for use with a crack growth analysis but can readily be modified for other applications (e.g. single f.e. steps with multiple sets of results through a time history).
When using the template with results from a crack growth analysis, graphs are automatically available for:
- Sum of da vs Cycles (for fatigue and combined fatigue/time dependent growth analysis)
- Sum of da vs Time (for time dependent and combined fatigue/time dependent growth analysis)
- Stress intensity factors vs Sum of da
- Energy release rate vs Sum of da
- %Error in sqrt(G) terms vs Sum of da (this graph indicates solution accuracy).
The "3dmesh" utility program is an alternative to import of results into the Zencrack GUI and allows the crack growth history to be represented by a f.e. mesh that can then be viewed in a pre-processor. For example:
The output from 3dmesh may also be superimposed on the uncracked mesh to allow visualisation of the profiles against the specimen geometry. For example:
Crack growth profiles from utility program "3dmesh" superimposed on the model geometry
Pre and Post Processing
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