Hey, Where Did That Crack Come From?


Written by: Brad Rach, Application Engineer

Brad Off-RoadingAs an off-road enthusiast, I understand one’s desire to customize and personalize your vehicle. I recently encountered a situation on my own vehicle that was surprising and left me curious enough to utilize my SOLIDWORKS simulation suite in order to better understand what the root cause of the issue is, and what I may be able to do to prevent future complications.

So, quick background story, I purchased a new slip-on muffler for my off-road vehicle a couple years ago. The sound was amazing and the performance improvement was notable. I utilized this muffler for two years before I noticed a surprising development. The entire wall near the inlet has developed a crack, see below:

Crack in Muffler

How could this have happened? I was floored that this muffler was essentially destroyed. So I put on my SOLIDWORKS simulation mantle, and ran some random vibration tests so at least I could understand what lead to this breakage.

Muffler Simulation

By using the SOLIDWORKS Simulation premium package, I was able to run a vibration analysis so I could review the stresses which my muffler experienced and see a matching region of stress to the crack in the physical part. For those not familiar with the simulation categories, I used our Dynamic simulation capabilities and utilized the Random Vibration aspect because of the nature of the environment in which the model is required to survive in. Essentially, the model has the opportunity to be variably excited from predefined locations based on the ground being driven over. For more information on Random Vibration, I recommend this Overview Paper.

Results like this are not only valuable, but invaluable, in detecting potential and future design failures. With tools like SOLIDWORKS Simulation, you can anticipate consistently stressed regions and edit the design based off virtual feedback.

This gave me some insight into the driving forces and resultant damage which has caused havoc on my exhaust over a two-season period, in dune metrics that’s roughly 2000 miles of brutal terrain. I took this a step further and ran a fatigue test on it, just to verify what I already knew would happen with this region eventually failing completely. From here I took it a step further and used SOLIDWORKS to design a solution to my dilemma.

How do I repair the exhaust so I can continue using it? I ran several simulations but settled on a solution which had me introduce a 1/4″ plate of steel on the interior surface of the rear exhaust wall.

After finalizing the simulation, I knew that a solution was possible without needing to replace the muffler. I was able to use a 1/4″ piece of sheet steel, and use a plasma cutter to cut a circle which fit inside the muffler housing, then cutting a 1.25″ hole in the center of that steel for the exhaust to flow through.

I then used screws to secure the back of the exhaust to the 1/4″ steel cutout. Then welded the exhaust back together. The result wasn’t nearly as beautiful as the original weldless design, but the muffler was functional again AND sounded just as good as before the disaster.



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2 Responses to Hey, Where Did That Crack Come From?

  1. I have the same question as Dan. Also with such a drastic change in shape and such a small corner radius, thermal stress due to expansion may have also contributed, along with any circular tool marks from drawing (i suppose) or welding stresses at the end of the tube. From the patina of the muffler after 2 years of use, I would guess that the tube is made of Stainless Steel (?)
    Could also there have been some stress corrosion cracking due to Chlorides in the products of combustion and the use of Austenitic SS.?

  2. Dan Bovinich says:

    I’m confused. The high stress area in red on the Similation is where the small diameter meets the face (end of the large diameter). The actual crack is on the outer rim. Not anywhere near the Simulation results. What am I missing?

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