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FAQs

Which options are available for FEMFAT batch Jobs?
The Batch Job feature is intended to allow FEMFAT to run in the background automatically with no interactive input on the user interface. It is especially helpful to use batch jobs when a number of FEMFAT analyses must be carried out (e.g. engine run-up). Typically, a FEMFAT job in the batch mode is invoked
using the following call:


…/bin/femfat –job=jobfilename (Linux)
…/bin/femfat.bat –job=jobfilename (Windows)


This standard call can be expanded using additional Parameters which offer the user a wide range of possibilities. For example, it is possible to specify a separate scratch Directory for the individual jobs,


…/bin/femfat –job=jobfilename -scr=Scratch_Directory
(Linux)


…/bin/femfat.bat –job=jobfilename -scr=Scratch_Directory
(Windows)


or disable individual modules (here: PLAST):


…/bin/femfat –job=jobfilename -noplast (Linux)
…/bin/femfat.bat –job=jobfilename –noplast (Windows)


A detailed overview of all available parameters can be found in the “FEMFAT_Introduction.pdf” manual. This manual is contained in the installation directory in both German and English along with all the other module manuals.

 

The file userdefparam.dbs cannot be found – What should be done?
The background for this message is that during the Definition of the new working directory in the ini file, a path was selected for the material import which does not contain the userdefparam. dbs file.

This database makes it possible to adapt fundamental properties which are material-class specific (slope exponent of S/N curve, material-dependent exponent, exponents for gradient
influence, etc.).

If you have not made any modifications in the database, then you can ignore this message and click “OK”. In this case, FEMFAT uses the database with the respective default values
from the installation directory.

If you have modified the userdefparam.dbs file and wish to use it, then you must either copy the database to the specific working directory or change the default import path for materials
in the FEMFAT settings to reflect the corresponding save location.

 

What inferences concerning the fatigue life can be made based on the endurance safety factors?
Often, after an endurance safety analysis has been made, the additional question arises of how many cycles the component can sustain under the load which is to be applied. In the case of single-level load spectra, this question can be answered by means of a simple conversion between safety factor and fatigue life:

If the safety factor is less than 1, in order to calculate the sustainable number of cycles N, the degree of utilization (= reciprocal of the safety factor 1/SFA) is raised to the power of the negative slope k of the (local) S/N curve and multiplied by the (local) endurance cycle limit ND:


N =ND* (1/SFA ) -k


If the safety factor is greater than 1, the conversion depends on the Miner rule used:  

By the way, this conversion can be carried out very conveniently using the FEMFAT Results Manager in which the above-mentioned case differentiation for the safety factor can be made automatically with the help of the formula Editor.