Aside from the FE based fatigue analyzers described in detail in these exercises, the following fatigue analysis utilities are also available, some of which have been described in earlier exercises. Most accept stress or strain response data as input. These response signals can be measured or simulated from FE analysis. For instance, FEFAT has the ability to output the stress or strain response time signal at any desired location on the FE model. FEVIB also has the same ability to output a response PSDF at any location. These can be used as input to the single location fatigue analyzers described below.

MSLF is a Total Life or S-N analyzer. It accepts a stress response time signal as input in the form of a .dac file. It also can accept rainflow histograms or simple constant amplitude or maximum/minimum input. Operation is simple and very similar to that of the FE equivalent fatigue analyzer FEFAT.

When invoked the first time, you are led through a series of setup screens to define the job. Once the job is defined, you are then taken to a Postprocessing Options menu where you can modify any aspect of the job setup and recalculate the results.

As an example, use PTIME to copy from central the three SAE time histories SAETRN, SAESUS, SAEBRAKT, if they have not already been copied over from an earlier exercise. We will assume they are stress responses this time.

Exit from MSLF when you are finished.

MCLF is a single location Crack Initiation fatigue analyzer. It accepts a strain response time signal as input in the form of a .dac file. It also can accept rainflow histograms or simple constant amplitude or maximum/minimum strain input. Operation is simple and very similar to that of the FE equivalent fatigue analyzer FEFAT.

When invoked the first time, you are lead through a series of setup screens to define the job. Once the job is defined you are then placed in a Post Processing Options menu where you can modify any aspect of the job setup and recalculate the results.

As an exercise, use PTIME to Copy from central the three SAE time histories SAETRN, SAESUS, SAEBRAKT, if they have not been copied already from an earlier exercise.

Exit from MCLF when you are finished.

MCDA is a 2D cycle and damage histogram display program. It allows you to look at cycles vs. range or cycles vs. mean of cycle or damage data or both simultaneously. You may specify up to two different cycle histograms with default extensions of .cyo for comparison purposes. It automatically looks for a corresponding .dhh, damage histograms, if they exist.

As an example, in the last exercise using MCLF you analyzed three different time signals, saetrn.dac, saesus.dac, and saebrakt.dac. Corresponding .cyo and .dhh files should exist in your directory.

MCYL is a convenient utility to list a cycles file to the screen or a file. Cycle files are produced by various MSC.Fatigue programs and have the extensions .cyc, .clf, .slf, or .tcy. For example in the previous exercise a cycles file called saetrn.slf was produced.

Chose list a Cycles file and select saetrn.slf as the Input Filename to list the cycles file.

A cycles and/or damage matrix can also be created from a cycles file or listed to the screen or a file. A cycles or damage matrix can also be written to a file that is formatted for import to a spreadsheet program.

MTCD is a time correlated damage analyzer. It is similar in nature to MCLF in that it is strain based and calculates damage based on Crack Initiation, the difference being that damage is summed over time and in the sequence that the cycles are seen. To see this do the following:

Use the SAE time histories SAETRN as in the previous MCLF example. Again we are assuming this signal is a strain response.

Exit from MTCD when you are finished.

MFLF is a single location, stress-based fatigue analysis module that accepts stress response PSDFs as input. This module has also been mentioned in an earlier chapter. As an example of usage copy over the original SAE history saetrn.dac to your working directory. This signal is assumed to contain a stress time response.

Use MASD to convert the time signal into the frequency domain by converting it to a PSDF. See the section on MASD in this chapter for instruction on how to do this. Use all the default settings. The output file name should be saetrn.psd.

Exit from MFLF when you are finished.

Stress-Strain Analysis processes rosetta data and finite element data from MSC.Fatigue, including software strain gauges. It creates outputs suitable for use by either the stress or strain-life fatigue analyzers. It also provides an indication of the state of multiaxiality present, suggests possible processing routines through the fatigue analyzers and has a multiaxial fatigue analyzer that works by using a MSC.Fatigue .fes file. In addition to this, the module can be used to convert elastic-plastic strain records, measured on one material, to that of another material. It can also convert elastic-plastic strain records to equivalent fully elastic ones and visa-versa.

MMLF is a single location multiaxial fatigue analyzer based on Crack Initiation and has been briefly referred to in a previous chapter. It requires three strain input signals which typically come from strain gauge rosettes. For rectangular rosettes the signals are separated by 45 degrees. For delta rosettes the signals are separated by 60 degrees.

As an example, take the three SAE histories that we have been using thus far (saetrn.dac, saesus.dac, saebrakt.dac), except run them through MLEN and chop them all to 1800 seconds. (See the previous section on MLEN to learn how to do this.) We will assume that these new signals are from a rectangular rosette.

Exit from MMLF when you are finished.

MFCG calculates the Paris Law coefficient, C, and exponent, m, in the expression da/dN = C(ΔK)m from actual raw test data obtained under constant amplitude loading conditions.

MKTAN is the database library for calculating the stress concentration factors, Kt, of various geometries. In a sense it is very similar to the PKSOL utility function for calculating compliance functions for Crack Growth analysis. The value of Kt calculated can be used as the Kt or Kf input to the single location analyzers, MSLF and MCLF. Both a secured database of standard geometries and a user database for user defined geometries is available.

The elastic stress concentration factor, Kt, is the ratio of the maximum stress at a stress raiser to the nominal stress computed by the ordinary strength- of-material formulae, using the dimensions of the net section. It can be used to account for the presence of a notch within a component or structure.

The magnitude of the Kt required depends on the nature of the notch and its geometry. It is well known that small notches have less effect in fatigue than is indicated by Kt. This has led to the idea of a fatigue concentration factor, Kf, which is normally less than Kt, being introduced and being used to replace Kt within Neuber's rule.

Kf is related to Kt according to: Kf = 1 + (Kt - 1) / {1 + }

where:

p' is a material constant dependent on grain size and strength and r is the notch root radius.

As an example of calculating a Kt value: