Introducing FEMFAT inside Ansys v4.11

We are excited to announce the release of FEMFAT inside Ansys v4.11, now compatible with ANSYS 2024 R2 and ANSYS 2025 R1. This latest version brings a host of new features and improvements designed to streamline your workflow and enhance your simulation capabilities. 

Key Updates in FEMFAT inside Ansys v4.11: 

1. Support for Weld Definition Files (*.wdf): 

You can now import Weld Definition files directly into your analysis, making it easier to integrate welding data into your simulations. 

2. Enhanced Message File Functionality: 

The Message File, which contains all warnings and errors from FEMFAT runs, has been upgraded. You can now highlight elements related to specific warnings and errors directly in the Geometry window. This feature allows you to quickly localize and address issues within your model, potentially filtering them by damage or endurance safety factor values. The search functionality in the Worksheet window (accessible via CTRL+F) has also been implemented for the Message File object. 

3. One-Click Insertion of Analysis Result Objects:

Simplify your workflow with the new one-click option to insert all available result objects of an analysis at once. This feature is accessible via the FEMFAT toolbar.

4. Direct Renaming of Analyses:

You can now rename analyses directly within the Mechanical Tree, providing greater flexibility and organization in your projects.

5. Copy/Paste Material Data and Node Characteristics:

The ability to copy and paste Material Data and Node Characteristics across different analyses has been added. This functionality allows you to efficiently transfer data between analyses using the Copy and Paste buttons in the FEMFAT Toolbar.

A look Back at the 7th Indian FEMFAT User Meeting in Pune

On March 6, 2025, the 7th Indian FEMFAT User Meeting took place at the magnificent Hotel Sheraton Grand in Pune, India. This prestigious event drew around 170 participants from various sectors of the engineering community, providing a vibrant platform for professionals to exchange expertise and experiences in the field of durability analysis. With 15 external presentations and the latest FEMFAT features showcased by ECS, the meeting was a resounding success. 

Event Highlights: 

The event featured a diverse range of topics, including weld and spot analyses, components under thermal load, elastomers, material data, benchmark studies, and drivetrain components. Notable presentations included success stories from TATA and VECV on weld and spot analyses, thermomechanical analysis of a cylinder head by TATA, and shape optimization of a piston by Wabtec. Mahindra Swaraj captivated us with their simulation of a shaker test for a tractor fender, Knorr Bremse impressed with a FEMFAT analysis of the compressor crankcase and air dryer housing using SPECTRAL, and Mercedes wowed us with their analysis of an oil pan on the differential housing. The discussions covered a wide array of applications, from sports cars and heavy commercial vehicles to locomotives and motorcycles.

As part dimensions continue to decrease, it has become more and more common to perform fatigue tests using thin specimens, with thicknesses ranging from 1 to 3mm. However, the fatigue test for fully reversed conditions (stress ratio R=-1) then poses significant difficulties due to buckling problems. As a result, fatigue tests are often conducted under pulsating conditions (stress ratio R=0).

On the other hand, FEMFAT requires information on the S-N curve under R=-1 conditions, including the alternating tensile strength σalt (endurance limit), slope kalt, and cycle limit NC,alt. In other words, the test results from pulsating tests cannot be imported directly in FEMFAT but need prior processing. And that is exactly what this article is about: guiding you through this process.

What you need to know to solve this challenge is that in FEMFAT all S-N curve parameters are adjusted based on the mean stress influence (see Figure 1). ​​​​​​​

Consequently, the endurance limit for R=-1 conditions can rather easily be inferred through mean stress sensitivity. However, both the slope and cycle limit of the S-N curve under R=-1 conditions require somewhat more complex calculations.

But let’s start with the requirements first: what are the minimum input data from testing in this scenario under consideration?

• Ultimate Tensile Strength (UTS)
• S/N curve data from pulsating test:
  • Pulsating endurance strength σpuls
  • Slope of pulsating S-N curve kpuls
  • Cycle limit for pulsating S-N curve NC,puls

First step: Computation of the alternating strength σalt 

Here the mean stress sensitivity M is needed. This value indicates how strongly the mean stress influences the fatigue strength. In the Haigh diagram the mean stress sensitivity is visualized as connecting line between alternating strength σalt and pulsating strength σpuls. For the computation we will use the following relation between mean stress sensitivity M, σpuls and σalt:

To compute σalt from this relation we need M in addition to σpuls. Since in FEMFAT M is a material class specific parameter, we can generate an arbitrary material to identify it. To do so, open the FEMFAT Material Generator, select the appropriate material class and enter the UTS value. If known, adjust the yield strength to the value from test. Calculate the mean stress sensitivity M from the generated values for σpuls and σalt.

Now we can use equation 1, insert the known values M and σpuls to compute σalt.

Second step: Computation of slope kalt and cycle limit Nc,alt

To compute the slope kalt we will make use of the relations depicted in figure 1: the local slope varies along the curve defined by the points B1 and B2. Deflection point B1 represents the range of the pure alternating period test where the stress amplitudes are in the range of the ultimate stress limit. The decrease in the load cycle number as moving to point B2, with a load cycle number 1, can be interpreted as a decrease in the crack-closing bias under high static tensile prestressing.

Analogously we get for

To compute kalt that way we need to know the terms from the nominator Nc,alt and NUTS.

As we already know, the cycle limits under pulsating Nc,puls and alternating conditions Nc,alt are connected by the mean stress influence. FEMFAT uses the following empirical formula to describe this relation (see FEMFAT theory manual):

With these relations, the slope kalt under alternating loading conditions can be calculated from equation 2.

In the final step, enter the values in the Material Generator under the S-N data menu and save the material.

Example

Given Data

As an example, we consider an iron material (fine-grained steel), for which the following test data are available:

First step: Computation of the alternating strength σalt 

With the material class characteristic mean stress sensitivity M=0.1448  we use equation 1 to compute

Second step: Computation of slope kalt and cycle limit Nc,alt

The cycle limit can be calculated directly from equation 3:

We enter the values in the Material Generator under the S-N data menu and save the material.

As a verification we use this material to analyze the fatigue behavior under pulsating loading condition.​​​​​​​