Fatigue Failure in a Cylinder

We at Meadows Analysis & Design have seen some interesting problems. One of these was a customer who was experiencing a failure inside a large cylinder. This hydraulic cylinder was over a foot in diameter, and with the hydraulic pressure could produce almost a million pounds of force!

The piston was held in place by some socket head cap screws, and these were breaking during operation leaving the head inside the cylinder chamber for the piston to slam into each stroke. The operator would not be aware of anything until the piston was completely ripped off. This was an expensive repair, and the manufacturer hired our team at Meadows Analysis to investigate.

The picture above shows the configuration of the cylinder.

The picture below shows the cap screws holding the piston onto the rod with analysis data.

Piston_Bolt Close Up

Note that each one of these cap screws is over 1″ in diameter.

What we found was that during operation, the cylinder was being energized to maximum pressure then external forces were being applied to add enough force to break through the load. When the load was broken, the cylinder rushed into the backstop allowing the piston to collide and the bolts to see extreme forces. This over a short time caused fatigue failure of one or more bolts. Subsequent events caused all to fail until the piston was not attached to the rod.

VonMises Stress_Overall

Meadows Analysis Engineers then worked with the manufacturer to design a connection that would survive the abusive nature of operation. We predicted that the internal pressure was nearly doubled by the additional force applied resulting in well over 1.5 million pounds of force.

It’s often hard to conceptualize failure without quantification and analysis of the multiple forces at work. It takes both collaboration and analytical insights. Just another example of how we approach situations that demand an answer and resolution.

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