The following table explains each of the options for the general setup parameters:
Parameter Description
Analysis Three basic fatigue analysis types are possible: Crack Initiation, Crack Growth, and Total Life (S-N). Other types of analysis are available also and explained in their respective chapters. SeeVibration Fatigue (Ch. 8),Multiaxial Fatigue(Ch. 6),Rotating Structures Analysis (Ch. 10),Software Strain Gauges(Ch. 11), andWeld Analysis (Ch. 9).
Results Location This parameter tells MSC.Fatigue whether to expect Nodal stress/strain results or Elemental centroid stress/strain results. This dictates whether the user is setting up a global multi-node or global multi-element fatigue analysis. Subsequent parameters, results file types, and results displays are dependent on whether nodal or elemental data is being considered. If nodal data is being considered, the resulting fatigue lives are reported at the nodes. Conversely, if elemental data is being considered, the fatigue lives are reported at the element centroids.
Fatigue cracks invariably occur at free surfaces, and hence when a crack initiation method is used, node points results are usually
required. The exception is when a shell model is used, element centroid results may be extrapolated to the top or bottom surface. This is useful when there may be some doubt as to the accuracy of the node point results due to extrapolation and/or nodal averaging practices. The spot weld analyzer uses forces and moments from both nodes and elements.
The SEAM-weld analyzer takes stresses from both the top and bottom surface and needs both nodes and elements for this.
Nodal Averaging Depending on how the finite element results are defined, nodal averaging of the stresses or strains may take place. If grid point stresses exist and are selected, no averaging will occur. However if the stresses or strains selected for the fatigue analysis are elemental based, such as results at integration points or elemental nodal values such that each element has a different value at the shared grid points, then nodal averaging will occur. This averaging is done on a global basis such that every contributing element surrounding a particular node will be used in the averaging. The exception to this is if Group is selected in which case only elements in the Current Group will be used in the averaging.
For the SEAM-weld analyzer only the current group can be used and no choice will be given.
F.E. Results For crack initiation, the fatigue analyzer may use either Stress, Strain, or E-P Input results from the finite element analysis. For crack growth and total life, only stress results can be used and no choice will be given. If Stress is selected, the intermediatejobname.fesfile will contain nodal or element stresses for each load case or time step as opposed to strains. This selection should make no difference to the final results of a crack initiation calculation, as MSC.Fatigue will always calculate the strains. The exception is when shell results are used. In this case, Stress should be selected because only 2D results are available and the absence of the out-of-plane strains will cause incorrect calculation of combined parameters. Another exception: when Strain results are selected, the analyzer requires finite element results in the form of six (6) components of strain, three (3) direct strains and three (3)
engineering shear strains (i.e. two times the tensor shear strains). If FE strains are not available in this form, Stress results should be selected.
Selecting E-P Input allows for elastic-plastic input when doing a crack imitation or a multiaxial CI analysis. The spotweld analyzer uses only forces and no choice will be given.
Results Units This option menu is active for all analysis types utilizing stress results.
The stress unit type must be identified for proper conversions within the fatigue analyzer. Available units are MPa, Pascals, PSI, KSI,
KG/M**2. This parameter is set to None if the Tensor parameter is set to strain. The spot weld analyzer requires both cross sectional forces and moments from the CBAR elements representing the spot welds. For this reason, both the force and dimension units are required.
Allowable options for forces & dimensions are: N and m, N and mm, lbf and in, and kip and in.
Jobname In this databox, the user supplies a unique name by which to distinguish the fatigue job. All subsequent forms will key off of this jobname when performing certain tasks. If the jobname already exists when submitting the job, permission for overwrite will be requested.
This jobname is limited to thirty-two (32) characters. Also, if a jobname is typed into this databox and the user presses the
<RETURN>
key the program will check for its existence and ask the user if he wishes to read in the old job parameters.Title A descriptive textual title can be supplied in this databox. The length is limited to eighty (80) characters.
Parameter Description
Main Index
The MSC.Fatigue Jobname. The MSC.Fatigue jobname is used in all unique file names created during a MSC.Fatigue run, and is used for retrieving previously executed MSC.Fatigue jobs for editing, re-running and results display. The jobname is a character string containing a maximum of 32 characters with no spaces. On some systems, characters such as [, *, /, or : , are not allowed, and in fact only alphanumeric characters are recommended. The jobname related files generated during a MSC.Fatigue run are shown in the table below.
Important: The same answers should result whether stress or strain FE results are used in a crack initiation analysis. However, if the Young’s modulus is different between the finite element analysis and the MSC.Fatigue material being used, significant differences in fatigue results can occur when comparing between stresses and strains. For strain results, no conversion is necessary. Total life and crack growth jobs use stress tensors, so no conversion is required or allowed. Also there could be a problem using strains with 2-D elements if any combined strain component is used which includes the Z-component strain. This is because the Z-component strain appears as zero from 2D elements in the .fesfile which is not generally true. Absolute maximum principal, x and y component strain should be unaffected.
Filename Description
jobname.fin Job parameter file (ASCII).
jobname.fes MSC.Fatigue Input file (Binary).
jobname.asc ASCII version of thejobname.fesfile.
jobname.fpp MSC.Fatigue intermediate results file (Binary).
jobname.msg/log MSC.Fatigue message and log files (ASCII).
jobname.sta Job status file (ASCII).
jobname.fef Global multi-node/element results file (ASCII).
jobname.fos Factor of Safety results file(ASCII).
jobname.abo Job abort file (ASCII).
jobname.tcy Time ordered stress cycles file (Binary).
jobname.crg Crack growth results file (Binary).
jobname.vec Surface normals file (ASCII).
jobname.fpr Job currently active alert file (ASCII).
jobnamenn.kfl/.kfm Stress concentration-Life XY data for specific node/element, nn (ASCII/Binary).
jobnamenn.dcl/.dcm Design criterion-Life XY data (ASCII/Binary).
jobnamenn.fal/.fam Scale factor-Life XY data (ASCII/Binary).
jobnamenn.rfl/.rfm Residual stress-Life XY data (ASCII/Binary).