Inventor FEA - Force Load vs. Bearing Load?

So you are running an FEA analysis in Inventor, and you need to apply a load to a cylindrical face. Do you use a regular "Force Load" or a "Bearing Load"? The answer really depends on how the force should be distributed on the face in question. A bearing load will apply the load in a parabolic distribution, while the force load will be an even distribution.

Huh?

OK, lets take a look at a couple of loading scenarios and the results that each provides. I have used the shock tube from one of the Inventor sample files as an example.

In the first analysis I used a Force Load. Notice that the stress is not centered on the cylindrical face, but rather along its edges as if the cylinder was being stretched.

In the second analysis I used a bearing load. Note that the highest stress is focused on the center of the cylinder. This is much more realistic in a case where a bearing or shaft is acting radially on the cylindrical face.

Contributed by Ben of the CAD Geeks

FEA Convergence - Ensuring accurate simulation results in Inventor

One of the foreign concepts to many people new to FEA is the idea of "Convergence". Convergence is an analytical method that many analysts use to determine the quality of their FEA results. Since FEA uses small elements to solve complex problems, a larger number of smaller elements can sometimes yield more accurate results. But how small is small enough when it comes to element sizes? This is where convergence comes into play. Convergence in Inventor Simulation is actually a series of settings that can be used to automatically make mesh elements smaller, and help determine if results are accurate.

The basic concept is that the mesh will automatically be made of smaller elements and solved until the results of the refined mesh fall within a percentage of the previous mesh. In other words: The smaller mesh is no longer significantly changing the results, and it making it smaller would yield diminishing returns.

In the image below, convergence settings were used to determine the validity of the FEA results. Before using convergence, the stress in the model was calculated to be 5.85 ksi. After turning on convergence (which refines the mesh and makes it smaller), the stress was calculated to be 6.205ksi with only .448% defiation from the previous iteration. This shows us that we can trust our FEA setup and gives us more confidence in our solution.

Contributed by Ben of the Tata Technologies CAD Geeks

It's not just stress that produces instability

In the Inventor Simulation Suite and Inventor Professional, the FEA solver can determine if a design will fail due to a high stress in the model, but this might only be half the story. If the model is in compression and is a thin or elongated structure, the model could fail due to its structural instability (Buckling) rather than deformation due to high stress. The Autodesk Algor solution includes critical buckling analysis to ensure this won't be the primary mode of failure.

Thin walled plastic parts or sheet metal could be susceptible to buckling as well as traditional problems like truss or structural frame design.


While the structure below might have a high safety factor of 30 or more for the stress analysis, the buckling analysis shows only a multiplier of 27. This indicates that the structure could fail due to buckling rather than only exceeding the yield point of the material.














Contributed by Ben of the Tata Technologies CAD Geeks

Simulating Heat Transfer

As some of you may have heard, Autodesk has recently acquired Algor FEA technology which further strengthens the simulation capabilities for its customers. One element of the Algor technology is the ability to simulate heat transfer scenarios for both steady state and transient(time based) problems.


Here is an example of a temperature applied to electrical contacts being dissipated over time to arrive at a steady state temperature. This can help us to determine questions like: Will my chip overheat? Do I need to include additional cooling fins?




.


Check out this video of the temperature arriving at steady state: Watch video Here


Contributed by Ben of the CAD Geeks

2D FEA - Get results from your designs

On this episode of the AutoCAD Mechanical CAD GEEKS....

We find Jim in a STRESSful situation. He has a design that has been in the field for a while and works pretty well, but now he needs to create a new version and test it out.

In the old days that meant designing one up and having it built for the sole purpose of breaking it and recording forces.

Since his company has gotten with the times and updated his regular AutoCAD to AutoCAD Mechanical he has power at his finger tips. This comes in the form of mechanical calculators.

Check out this great video on how he did his new design FEA.

Watch it here:

Enjoy,

Jim.......Another INCAT CAD Geek!

Advanced Simulation on Autodesk Labs

I just found the time to check out the new Advanced Simulation technology preview on Autodesk Labs, and I am mightily impressed with the direction Autodesk is taking this technology. You can define all kinds of design variants and design criteria to use in a functional study.

Take a look at this video for an example of this new technology in use:

Watch Video

Contributed by Ben of the INCAT CAD Geeks

FEA - Reverse Engineered

One of the easliy overlooked features of the FEA module in Inventor Pro's FEA is the ability to reverse engineer the loading scenarios by specifying a known deflection instead of a load. This allows you to determine if a part will be structurally sound at a known deflection, and also allows us to determine the reaction forces at a known deflection.

Take a look at this video for an example of this hidden gem:

Watch Video

Contributed by Ben of the INCAT CAD Geeks