This example demonstrates integrating CARES with the ANSYS Probabilistic Design System (ANSYS/PDS). This methodology accounts for stochastic variables such as loading, component geometry, material properties, and lifing parameters on component probability of survival over time.
1. This example works from the following folder:
..\Cares 9.5\examples\ansys\PDS\
2. Open bendbar.mac in a text editor such as Notepad.
3. Find the system calls near the bottom of the file that specify the path to CARES. Verify the accuracy of the folder path to the CARES bin folder. Note that the quotes are required.
/sys, “C:\CRT Inc\Cares 9.5\bin\x64\ac19\AnsCares19295” bendbar /sys, “C:\CRT Inc\Cares 9.5\bin\x64\Life95” bendbar
4. Close bendbar.mac (saving if changes were made).
ANSYS
5. Open ANSYS setting the current path to
..\Cares 9.5\examples\ansys\PDS\
and the jobname to bendbar
6. At the ANSYS command line Enter:
/input,bendbar,mac
7. It is expected that you may get an error on the VREAD command.
If the error occurs:
a. Choose ANSYS 19.2 as the program and set the results file to ‘bendbar.rst’
b. Set the Symmetry Segments to 4.0
a. Set the Fracture Criteria to PIA
b. Set the Parameter Options to Override 12. [ File | Save ]
13. Close CARES ANSYS
14. Return to ANSYS and Enter:
/quit /clear Yes
/input,bendbar,mac
15. This time you should get a successful solution and the final line in the ANSYS Command Output Window should be
Pfail = 0.1166434202E-01 16. To run the PDS function on this model, Enter:
/input,bendbar_PDS,mac
17. In the “bendbar_report” folder open the file “bendbar_report.html” to view the results.
We find that given the distributions assigned to the varying parameters in this example (Height, Width, Weibull Slope, and Weibull Scale) the Probability of Failure is significantly dependent on the Weibull parameters while the effect on Probability of Failure of the changes in Height and Width were insignificant.
The handoff of the Weibull Parameters from ANSYS/PDS to CARES occurs through the use of the override.cmp file. The user’s input file must create and write this file. CARES deletes the override file during processing to ensure the file is reset for each subsequent PDS run.
The top part of the CARES section in bendbar.mac provides an example of how the override.cmp file is created and how the material information and parameters are written:
Temp1=25.
Weib_Slope1=10.
Weib_Scale1=200.
*CFOPEN,override,cmp ! OPEN - CARES Material Parameter File
*vwrite, TEMP1, Weib_Slope1, Weib_Scale1 ('Vol 1 ', 3(E13.5))
*CFCLOS ! CLOSE - CMP File
Here the first part of the format line of the VWRITE command indicates a Volume material, Vol, followed by a space and the Material ID. The temperature and Weibull parameters are passed as parameters.
Override Multiple Temperatures
If multiple temperature Weibull parameters exist for this model they may be included as follows:
Temp1=25.
*CFOPEN,override,cmp ! OPEN - CARES Material Parameter File
*vwrite, TEMP1, Weib_Slope1, Weib_Scale1
Override Multiple Materials
If the Weibull parameters are to be assigned to multiple materials they may be included as follows:
Temp1=25.
Weib_Slope1=10.
Weib_Scale1=200.
Weib_Slope2=15.
Weib_Scale2=140.
*CFOPEN,override,cmp ! OPEN - CARES Material Parameter File
*vwrite, TEMP1, Weib_Slope1, Weib_Scale1 ('Vol 1 ', 3(E13.5))
*vwrite, TEMP1, Weib_Slope2, Weib_Scale2 ('Sur 101 ', 3(E13.5))
*vwrite, TEMP1, Weib_Slope2, Weib_Scale2 ('Sur 102 ', 3(E13.5))
*vwrite, TEMP1, Weib_Slope2, Weib_Scale2 ('Sur 103 ', 3(E13.5))
*CFCLOS ! CLOSE - CMP File
Here one set of Weibull parameters applies to the Volume material while another set applies to the Surface materials 101, 102, and 103.
Glossary
CARES – Ceramics Analysis and Reliability Evaluation of Structures FEA – Finite Element Analysis
FEM – Finite Element Model File Extensions:
ICL – Input to CARES/Life OCL – Output from CARES/Life
RST – ANSYS results file translated by ANSCARES to the CN9 or CP9.
CN9 – CARES 9 Neutral file (service load) CP9 – CARES 9 Neutral file (proof test load)
SUR – CARES Surface file generated by the ANSCARES surf macro. The SUR and the RST file are translated by ANSCARES to create the CN9 (CP9).
RR9 – CARES 9 Risk of Rupture file. Output by CARES for application within ANSYS to the FEM.
Jobname – The root word of each Project filename. The Jobname used within the finite element program need not match the Jobname used within CARES.
Load Step – In finite element analysis a component may be subjected to varying loads for varying durations. Each increment in load is a single load step.
Neutral file – The CN9 (CP9) file contains the subelement stress results at each load step for a component. This file is generated by a CARES interface code that translates a finite element results file into the CARES formatted Neutral file. The CARES program then directly reads the Neutral file during reliability analysis.
Project – A collection of interrelated files that share a common Jobname.
Subelements – The integration points of the elements. The finite element stress results are listed within the results file (and subsequently in the CN9 file) at the subelement or integration point level. Consequently, CARES performs reliability analysis on the load steps of each subelement.
Transient analysis – A reliability analysis preformed on a component subjected to multiple load steps. Although fast fracture reliability boils down to the load step of maximum stress, this is not true for time dependent reliability across multiple load steps. For time dependent reliability all load steps must be considered through recursive iteration.
Weibull Distribution – Parameter estimation of the fast fracture of brittle components follows the Weibull distribution. In turn fast fracture component reliability is based on these Weibull parameters.