SolidWorks Simulation: What is Von Mises Stress? – Part 2 of 2

For engineers, determining stress can be stressful. A design must be strong enough to endure everyday forces or it won’t make it to production. So how do you determine if your design can handle the stress it is intended to bear? With SOLIDWORKS Simulation the answer is easy – a von Mises stress value. Welcome back to Part 2 of our explanation of what exactly von Mises stress is, and why it is such a crucial measurement in a SOLIDWORKS Simulation study.

When we left off in Part 1, we uncovered some of the complications that occur when working with stress induced by complex (multi-directional) loading. We need to find a way to combine three individual principal and three shear stresses into a single resolved stress value, to which we can compare. This is where Richard Elder von Mises comes into play.

Von Mises is credited with coming up with what is arguably the most accepted yield criterion (way of resolving these stresses). He designed an equation that takes in each shear and principal stress value, and in turn spits out a single “von Mises stress value”, which can be compared to a yield strength of the material. If the value is greater than the yield strength, the part is failing according to his criteria. If it is less, then the part is said to be within the yield criteria and is not failing (for yield failure only). The equation for von Mises stress is shown below.

Vonmises _2

Note the sigma’s (σ) correspond to normal stress values, and the taus (τ) are the shear stress values.

…OK, you lost me…

I know that formula is scary, but hopefully you’re still with me. All that this formula does is convert each of the six numbers that you input (the right side of the equals sign) into a single value (left side). The von Mises stress is the default stress plot because it’s a way to show one value we’re concerned about – resolved stress.

That is a lot of math. My brain hurts…

Don’t worry! Thanks to SOLIDWORKS, you don’t need to calculate all those complicated numbers by yourself. The SOLIDWORKS Simulation Study does the work for you. It calculates the principal and shear at each location, plugs them into the von Mises formula to give one resolved value, and then plots it for you. DONE!

Vonmises _3

If you’ve ever dug around the SOLIDWORKS Simulation options for stress plots, you will find that you can verify this. You may have noticed that you can plot the principal or shear stresses individually. There might be scenarios where you’d want to look at these individual results, especially considering failure from certain directions. When results are calculated for the simulation you can plot any number of these stresses and display them in your results as needed. Other failure mechanisms would require a full analysis of the principal stresses to assure the model is safe. In most cases though, you’re simply asking “is my part failing?” In that scenario, von Mises stress plot is the way to go.

Fantastic! I’ll remember that when I’m looking at my stress plots!

Now that you know all the steps that SOLIDWORKS goes through in solving your simulation study, don’t you feel more confident in the results that it gives you? Of course, it is always important to verify that your simulation is set up correctly and meshed properly to produce accurate results. Still, SOLIDWORKS Simulation is an incredible tool that utilizes valid strength of materials equations to solve for its results. There’s no guessing involved; it knows what’s going on and has done the math to back it up.  SOLIDWORKS Simulation – a stress-free way to calculate stress!

Want to know more about how SOLIDWORKS can reduce your engineering stress? Give us a call today!