XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX''"> Introduction
This chapter on vibration fatigue analysis using a total life approach consists of descriptions of various MSC Fatigue modules and the job setup required to perform the analysis. These modules can be accessed from subordinate forms of the MSC Fatigue main form within the MSC Fatigue Pre & Post or MSC Patran programs.
It is possible to carry out a MSC Fatigue analysis outside the pre- and post-processing environments such as the MSC Patran environment by executing the analysis programs from the system prompt. The main reason for doing this is to provide an alternative and sometimes faster route for carrying out multiple computations with only one or two small changes to the analysis parameters. This can be achieved because the MSC Fatigue job parameters and the nodal or elemental fatigue data are stored in ASCII files. For completeness, a general schematic showing the analysis route is shown in
Figure 8‑1. The aspects of this figure are described throughout this chapter.
There are two modules for vibration fatigue analysis delivered with this system. Each has its own special purpose. In summary, the module FEVIB is the vibration fatigue analyzer that accepts multi-location input files from finite element results. These results can be either a combination of transfer functions from a frequency response analysis with corresponding loading input PSDs or the output response PSDs from a random vibration analysis.
The other module is MFLF which is a more specialized single location analyzer which works directly from a response PSD which can come from anywhere such as a test measurement or the response output from a single location of a FEVIB analysis.
The job setup is described specifically for vibration fatigue analyses in
Job Setup, 609, however it is recommended that you be familiar with, at the least,
Using MSC Fatigue (Ch. 2). Although it does not deal directly with vibration fatigue analysis, many of the basic principles are applicable and only discussed there.
Terminal Definition
MSC Fatigue runs on a wide range of computers and graphics devices. The parameters used by each graphics device must be defined by using the MENM module, prior to the first use of MSC Fatigue. For details, please see
Module Operations (Ch. 17). This is automatically accomplished when running MSC Fatigue from a pre- and postprocessing environment such as MSC Patran and is transparent to the user and defaults to the Motif driver.
.
Figure 8‑1 Aa MSC Fatigue Vibration Submittal Schematic
Basic Information
All programs in the MSC Fatigue system may be executed by typing the name of the program or its symbol. These programs may ask questions which are not normally presented to you since they are executed as batch jobs when called from the pre/postprocessing environment. The programs normally used in a typical or basic fatigue analysis are listed below.
1. Data Preparation
PFMAT | Materials Database Manager |
PTIME | Loading Input Power Spectrum and Time History Database Manager, including ASCII Time History File Convertor |
MMFD | A Multi-file Display Program |
2. Global Multi-Node/Element Analysis
| Model database (MSC Patran) to Fatigue Input Translator |
| New model database (MSC Patran) to Fatigue Input Translator |
| FE-Fatigue Analyzer (damage summation) |
| Global Fatigue Results Postprocessor |
3. Design Optimization Analyzer
| Single Node/Element Total Life (S-N) |
| Cycle/Damage 3-Dimensional Histogram Display |
| Display of output (and input) PSDs |
| Single location vibration fatigue analyzer |
4. General Utilities
| FES File ASCII/Binary Convertor |
PFTRM | Terminal Driver |
MCONFIL | Binary to Binary File Convertor |
Analysis Route
The actual programs necessary to complete a global multi-node or element vibration fatigue analysis are:
| Shell script (necessary for submittal from MSC Fatigue Pre & Post or MSC Patran) |
| Translator (creates the fatigue input file filename.fes) |
| New Translator (creates the fatigue input filename.fes) |
| Fatigue analyzer (accepts response PSD or FRF/input load PSD combinations) |
| Design optimization and sensitivity studies as well as access to other graphical tools are all accessible from FEVIB. |
The programs and options must be used in this sequence, unless you know the critical location ahead of time, then you may skip directly to the design optimization stage. The results may be reviewed using
PFPOST or by inspecting the ASCII nodal or element results file (
jobname.fef) using a text editor or by inspecting fringe plots directly within the pre/postprocessor.
Necessary Files
When a global multi-node fatigue analysis is set up using the MSC Fatigue pre-/post-processing menus, these are the files necessary to run the analysis and the files that are created.
jobname.fin | This file contains all the analysis parameters that were defined in the main and subordinate MSC Fatigue forms such as the analysis type and job titles. A full description of this file is contained in The Job Information File (jobname.fin), 336. |
Database | Other pertinent information such as the nodes or elements and the FE results from which to calculate fatigue life is contained in the database in the form of a group or groups. The component stresses or strains from these locations will be used, scaled, superimposed and resolved (dependent on various parameter requests) and used in the fatigue calculations. |
Additional Files | Other files that are necessary to complete a successful fatigue analysis are the loading power spectrum files (ptime.adb, ptime.tdb and *.psd), and the materials database (nmats.mbd) which is generally held in a central location and not necessary to be located in the user’s local directory. |
The first of these files is ASCII and may be edited using a standard text file editor. Although this method of defining the MSC Fatigue job parameters is not as automated as using the MSC Fatigue Pre & Post menus, it does offer a simple and rapid method of changing a few job parameters without the encumbrance of a menu structure.
After the translator has been run (described in
The Translator (PAT3FAT or FATTRANS) and Submit Script, 608) and the fatigue input file (
jobname.fes) has been created, the fatigue analyzer,
FEVIB, is run which is controlled through a submission script called FatigueSubmit. The fatigue analysis is actually performed by the program
FEVIB. When run in interactive mode, this program asks for a number of input parameters which are passed in through the
jobname.fin, and
jobname.fes files when run from the MSC Fatigue Pre & Post menus. A full description of file content is provided in
Description of Files, 336.
The Translator (PAT3FAT or FATTRANS) and Submit Script
MSC Fatigue uses a translator to combine the information in the database and the job information file (jobname.fin) to create the fatigue input file (jobname.fes). For this reason, the translator must be run each time any information is changed in the database and/or the results and information files such as if the FEA analysis has been rerun.
To run the translator, the following command should be used:
pat3fat jobname
or
fattrans jobname
PAT3FAT or FATTRANS both produce a
jobname.fes file which is a binary file. An ASCII to binary and binary to ASCII file convertor is provided for the
jobname.fes file. The convertor program is part of the FEVIB module and is described in
Utilities, 653. A description of the ASCII and binary versions of the fatigue input file (
jobname.asc/fes) is provided in
The Fatigue Input File (jobname.fes), 368. Remember that the fatigue executables can only read the binary version and the ASCII version must always be converted back to binary via FEVIB’s utility options.
Once a job is translated and an input file has been created, the actual control of this job from MSC Patran is done through a script file or program called FatigueSubmit. An example of this file is provided in
CFG File Specific Parameters, 350.