XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX''"> Concluding Remarks
The branch of engineering science concerned with linear elastic fracture mechanics (LEFM) is by no means a new one. The earliest work in the UK dates back to Inglis (1913) but the major developments took place following the research of Griffith and Rae in 1920, and Irwin in the USA in 1956; and LEFM has since flourished.
There are three modes of crack growth. Mode I - opening, Mode II - sliding, Mode III - tearing. Of the three modes, mode 1 is by far the most common. It is quite difficult to make cracks grow in modes 2 or 3. For these reasons MSC Fatigue only supports Mode I.
Analysis without an FE Model
It is not actually necessary to use a FE model to run a Crack Growth analysis. You may find this more convenient.
Invoking PCRACK from a system prompt by typing the symbol, pcrack, will place you in its main menu mode where you can preprocess (rainflow and cycle reorder), run a full fracture analysis, output or display a time history or enter its utility menus. Within the Utilities, there is an option where you can create a simple input file (.fes file). You will be prompted for all the pertinent information including the far field stress.
Hint: | A stress tensor is expected but you can simply put in one value for the X-component and zero for the rest and specify the X-component only to be used in the analysis. |
MSC Fatigue Files
MSC Fatigue Crack Growth analysis creates the same files as the other methods with the following two exceptions:
Table 7‑2 File | Description |
jobname.tcy (simple_cg.tcy) | This binary file is the equivalent of the jobname.fpp preprocessing file created after rainflow cycle counting for the other two methods. The jobname.tcy file is also the result of the rainflow cycle count but after time cycle reordering created by PCRACK’s preprocessing phase. It serves as the input to the actual Crack Growth analysis. The Action, Partial Analysis on the Job Control... form will create all files up to this point and then stop. |
jobname.crg (simple_cg.crg) | This is the results file of a fracture analysis created by PCRACK when a Full Analysis is requested. It is a binary file and can be processed by the result listing facility, PCPOST, only. It cannot be read back into Pre & Post or MSC Patran to create life contour plots as with the jobname.fef file created by the other methods. |
Hint: | If you experience difficulty with a Crack Growth job, check the following files for clues: batlog.lst, jobname.sta, jobname.msg, pfatigue.prt. It is also helpful to interactively run the programs from the system prompt by issuing the proper commands: pksol, pcrack, pcpost. |
Exit from Pre & Post or MSC Patran when finished with this exercise.
