The main module delivered with any basic MSC.Fatigue system is PTIME. This basic module has been used extensively throughout these example problems and allows for the following:

From PTIME it is possible to access certain display and manipulation modules that have already been described in the various exercise problems in this manual such as:

In addition to PTIME, the following utility modules exist to help in the definition of loading information:

MART allows you to take any time signal or even a histogram and apply arithmetic operations such as adding, subtracting, multiplying, or dividing by a constant. You can normalize a signal to a new mean, raise it to a power, apply trigonometric or logarithmic functions, take the absolute value or use the linear equation Y=mX+c. You can apply these arithmetic operations to the entire signal or only a portion thereof.

For example, use PTIME to Copy to central the signal SAETRN. Use MART to raise the signal from 1000 seconds to the end of the signal by the power 1.1.

Above are the results, before and after as displayed by MMFD.

MCOE allows you to tabularly view, edit, or create multiple time signals (files/channels) simultaneously. As an example:

There are a number commands at the top of the spreadsheet that are useful for editing and viewing data. These are:

File: This has only two options, Back or OK. Both will end the editing session and quit from MCOE. Only OK will actually save any changes.

View: These commands under this pull-down are simple. They allow you to scroll up or down, right or left, or to the beginning or end of the spreadsheet.

Goto: This allows you to specify which row to go to based on the X value (time).

finD: This will find the next row in the current column with the value specified based on the criteria of greater than, less than, between, or closest to.

Opts: This is perhaps the most useful of the commands for editing the tabular data. These options are discussed below.

Pref: This sets preferences. For example, how you would like to select cells, or view number formats in the columns. You can even scale the X-axis (time) and define the format of exported files.

Next: This finds the next number based on the previously set finD command.

The following options are available for editing the spreadsheet (see the MSC.Fatigue User’s Guide for options not mentioned here). Experiment with any of these as you see fit.

Gap: This command appends the specified duration of time onto the end of a signal. You type a number into the automatically selected cell and a linear interpolation occurs filling the cells in-between. The next time duration gap is determined from you entering another data value in the selected cell with interpolation occurring again. This cycle continues until you select another cell or invoke some other command.

Delete: This deletes all cells within the specified time duration. Cells below the deleted cells move up and close the gap.

Copy: Copies the data values in the specified time duration.

paSte: Pastes values that have been copied into the specified time duration overwriting any existing values.

cYcle: Appends a saw tooth type signal to the end of a column by specifying the maximum/minimum, range, number of cycles and mean.

Insert: Inserts the number of points or the time duration specified at the current row for the specified columns. A start and end data value are requested and intermediate values are linearly interpolated.

Append: Appends to the end of the signal the length of time or the number of points specified. It also requests a beginning and ending value and all other values in-between are linearly interpolated.

Join: This command asks for a start time and an end time and changes all values in-between based on a linear interpolation for the specified data columns.

Export: Creates a file with default extension .txt of the columns of data in the spreadsheet.

Plot: Plots the specified columns using the MMFD multi-file display program.

Rescale and offset: Specifies a start time and an end time, the column(s) to apply the scaling and offset, and the scale factor and the offset values.

Format columns: This allows you to hide or unhide columns from the spreadsheet, fix (or unfix) them to protect columns from data entry if desired, and to group columns for multiple column operations in other options.

eXit: This is the same as OK from the File pull-down to save and exit.

Quit: This is the same as Back from the File pull-down exit without saving.

The rainflow cycle counter, mCYC, processes a time series signal, by extracting fatigue cycles according to the rainflow cycle counting algorithm. The utility is useful as it allows the user to count cycles using the same parameters (gate, range, bin width) for comparing and assessing various time signals. The results are presented in the form of a range-mean or a max-min matrix which can be displayed or used as input to mCLF or MSLF. In addition, a file containing a description of each cycle can be generated. If the time of each cycle can be stored, this file may also be used in crack growth analysis.

For example, use PTIME to Copy from central the time history, SAETRN.

The following form is displayed if both or Histogram is selected above.

The fields that are activated depend upon whether the environment keyword HISTFORM is set to MINMAX (use the full range from minimum to maximum values) or BINSIZ (specify on the minimum and the bin width).

The output histogram using the range-mean option is shown below.

MFRM is a formula processor for time series data or histogram files. It is a very powerful tool that includes its own programming language. Virtually any formula can be applied to any number of time history or histogram files. The formulas are defined via an ASCII template file that is created manually using a text editor. MFRM then reads the template file and executes the commands. After execution the resultant files can be graphically displayed.

As a quick example, define a file called example.frm using any text editor with the following content:

; --- Define all the files ---
%QYFIL /FILE=F1 /PROMPT="Enter filename" /TYPE=INPUT
%DFFIL /FILE=F2 /NAME=positive /TYPE=OUTPUT /OV=y
%DFFIL /FILE=F3 /NAME=negative /TYPE=OUTPUT /OV=y
%DFFIL /FILE=F4 /NAME=positive2 /TYPE=OUTPUT /OV=y
%DFFIL /FILE=F5 /NAME=negative2 /TYPE=OUTPUT /OV=y
;
; --- Carry out the calculations ---
;
%BEGIN
;
%IF(F1 > 0)
	F2=F1
%ELSE
	F2=0
%ENDIF
%IF(F1 < 0)
	F3=F1
%ELSE
	F3=0
%ENDIF
F4=MAX(F1,0)
F5=MIN(F1,0)
;
%END

Next, invoke MFRM from the system prompt or by selecting the Formula Processor option from the Advanced Loading Utilities pull-down menu under Tools | MSC.Fatigue (for Patran) or under Tools | Fatigue Utilities (for Pre & Post).

The processing will begin once this input file has been selected. If you look carefully at the template file you can see what operations are being executed. The first line prompts for the input file to process. Internally the input file will be known as a variable called F1. The next four lines define output files that will be internally knows as variables F2, F3, F4, and F5 respectively. They are given the names positive, negative, positive2, and negative2. The default file extension is .dac.

The next section of the template file contains the operations to be performed. These operations take F1 and break it up into its positive component and its negative component. This can be accomplished in two ways. The first way is done in the first IF-ELSE-ENDIF command by setting any points greater than zero in file F1 to file F2 and anything less than zero to zero. The second IF-ELSE-ENDIF command then does the negative side. The final two lines accomplish the exact same task by using the intrinsic math function MAX and MIN by taking the maximum or minimum of each point in the signal by comparing to zero.

MFRM has the ability to perform very complex operations using IF statements, LOOPs, arithmetic, logarithmic and trigonometric functions as well as addition, subtraction, multiplication, division, and raising to a power. See the MSC.Fatigue User’s Guide for a full description of the MFRM commands and language syntax.

 

MLEN allows you to adjust the length of time signals by extracting or deleting sections, and concatenating files. Signals can be reversed and the starting and ending points of each signal can be smoothed. These operations can be on a single file or multiple files simultaneously.

For example, use PTIME to Copy from central the three SAE histories, SAETRN, SAESUS, and SAEBRAKT. Then use MLEN to extract a section from each simultaneously such that each signal is the same length.

The first 1898 seconds of each signal is extracted and new files called saetrn.mod, saesus.mod, and saebrakt.mod are created. The before and after displays using MMFD are shown below.

MMFM is a module that allows for addition, subtraction, multiplication, division and vector addition of multiple time signals.

Addition of individual files is as such: file1 + file2 + ... + fileN.

Subtraction of individual files is as such: file1 - (file2 + file3 + ... + fineN).

Multiplication is as such: file1 * file2 * ... * fileN.

Division is as such: file1 / (file2 * file3 * ... * fileN).

Vector addition is performed as follows: (file12 + file22)1/2 or
(file12 + file22 + file32)1/2.

Experiment by taking the three signals from the previous exercise and performing the various arithmetic operations. For example, here is a plot where the three signals were added together. Note that the original signals were of varying length.

 

MPVXMUL extracts turning points (maxima and minima or “peaks” and “valleys”) from single parameter files such as .dac and RPC multiple data - channel files. The peak valley extraction process maintains synchronous phase by writing corresponding data values to all the output files whenever a turning point is found in any channel. Facilities for gating out small peak valley pairs by absolute value or by percentage of range, on each channel, are available.

MSIMMAX performs simultaneous values analysis on either multi-channels in a single RPC file or multiple DAC files from the same test. Two analysis methods are available. The first uses a “control” channel, from which turning points are extracted and scanned for the highest peaks, the lowest valleys or the highest absolute maxima. Up to 50 of these events may be saved, with their positions in the data. The simultaneous values of all the other channels at these positions are saved into the output files. The second method scans each of the input channels for the single largest maximum, minimum or absolute maximum. For each channel, the simultaneous values of all other channels at the position of the largest event is saved into the output files.

The output file created is a tab separated ASCII file suitable for input to a spreadsheet or word processing package.

MADA, amplitude distribution analysis, calculates the probability density distribution (which defines the probability of finding a value of a particular magnitude within the population of measured values) and other function of a time signal.

For example if you use saetrn.dac as input to MADA and set the Analysis Type to Prob. Distribution, it will output a file saetrn.ada shown here which is the probability density function of Y-values.

MASD performs a frequency analysis of a time signal to determine frequency content. Various output types are available which are beyond the scope of this text. Perhaps the best use of this module comes in vibration fatigue problems for converting time signals into power spectral density functions (PSDFs).

As an example, let us convert the time signal SAETRN, used in many of the previous sections in this chapter into a PSDF, which will quickly show us the frequency content of the signal.

A display of the resulting PSDF is shown above. Note that only one predominate frequency is present in the signal at around 1/2 Hz plus a DC component at zero Hz. This PSDF could be used as input to a vibration fatigue analysis.

MFFF uses filtering techniques to remove frequency content from a signal. As an example, invoke PTIME and create a white noise signal:

MBFL also uses filtering techniques to remove frequency content from a signal. If you perform the same steps as the previous section on the MFFF module and perform a Band pass filter between 20 and 30 Hz on the NOISE.DAC file with the new Output Filename set to NOISE3 you will get the top plot to the right. Notice the difference in the filtering between MBFL and MFFF. MBFL allows for some leakage and gives a smoother transition instead of completely eliminating frequency content.

MFRA performs frequency response analysis and calculates the transfer function of a single input, single response system. Perhaps the most useful application of this module is to compute the cross correlation function between the two supplied response signals. These correlation terms can then be used as input to a vibration fatigue analysis. As an example:

When the analysis is done, you can then use these PSDF and their cross correlation terms as loading input to a vibration fatigue analysis. By using PTIME you can set up the PSD matrix information for these three input loadings from Add an entry... | Psd matrix, the size of the matrix being 3x3. All the files from the transfer function analysis (*.sxx, *.syy, *.sxy) must be loaded into PTIME first. The matrix of PSDF and cross correlation files would look like this:

MRSTATS analyzes a time signal and produces a number of running statistics about the signal, each of which can be plotted by the standard plotting routines such as MQLD (quick look display), MTPD (two parameter display), or MMFD (multi-file display).

 

 

The statistics that are determined are running: RMS (.rms), Standard Deviation (.rsd), Mean (.mea), Maximum Value (.max), Minimum Value (.min), Absolute Maximum Value (.abs), Area Under Data (.are). Each new signal is defined by its extension. The statistics are determined by breaking the signal into segments and calculating the statistics on each segment. The length of a segment and the overlap of each adjacent segment is user definable. Try running saetrn.dac through MRSTATS. Shown here are the statistical signals produced from running MRSTATS against the SAE signal saetrn.dac.

MMFILMNP allows you to view and manipulate/change header and extra detail information in any signal. It also can be used to validate the integrity of a file. Use this module if you wish to quickly and easily change axis labels or units and title information or you wish to validate the signal which will try and correct or flag any problems with the file.