FEA: A Beautiful Lie (Until Proven Otherwise)

I couldn’t say it better myself.  It is wonderful to see finite element analysis (FEA) become more accessible.  I even hope to one day see designers use FEA to perform preliminary analysis and reduce the workload for engineers.  This reduces the total cost to clients.  It allows the engineers to better utilize their high value skills, rather than spend hours on low value meshing and geometry cleanup.  And hopefully all this cost savings encourages clients to wider use of FEA and more optimized structures.  Save money, save steel resources, help the environment.  Everything sounds great . . . unless we get it wrong.  I’m happy to see that sentiment reflected in this article.

Is Easy FEA Simulation-Fo-All Finally Here? Well, Kinda

When we see the output from FEA, everyone gets excited by the menagerie of colorful pictures.  We forget how little meaning those pictures have.  In FEA, the computer faithfully solves a series of mathematical equations, with absolutely no guarantee that the equations match reality.  For all you know, the computer just solved a network of connections between social media posts.  FEA still requires engineering knowledge to ensure those equations actually model reality, with accurate results.   For every simulation, we must remember that it is wrong, until proven correct.  As a client, you should expect the same standard when reading FEA reports.  Any FEA report should include enough information to prove that the simulation is correct and delivered accurate results.  Otherwise, it is simply a colorful lie.

The mesh size makes the largest difference to how well any FEA simulation predicts stresses.  And don’t believe anyone that claims they can determine the mesh resolution just from examining results.  Compare the two pictures below.  They show a very simple case of a plate bending with a hole in the center.  The picture on the left shows a medium resolution mesh size.  Many FEA engineers would look at this plot and conclude that the results are reasonable and the simulation is probably correct.  WRONG!  That medium resolution mesh predicted a peak stress of 485 MPa.  Compare that to the picture on the right, showing a high resolution mesh.  Same simulation, but the high resolution mesh showed a peak stress of 809 MPa.  The FEA had an error of 40%!  That much error is the difference between perfectly fine, and you need to buy a new steel plate.  This demonstrates the critical need for engineers to carefully examine all FEA results and prevent devastating errors.  And clients must demand that due diligence.

The widespread use of FEA is great.  And everyone benefits by reduced costs for FEA.  But never forget that FEA is more than just software.  At some point, every simulation requires careful application of engineering knowledge to ensure the software matches reality.  Otherwise, it is just a colorful lie.