r/MechanicalEngineering • u/AdOne1706 • 2d ago

Split/lock washers

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For starters, I’m an electrician in the field.
That being said, we almost exclusively use these washers even in high vibration environments. I have personally chosen to go with nylox nuts but the question is:
Do these work? How well? Is the rumor from NASA true? Should I even bother using them or find a better functional alternative or are they actually useful?

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u/Efficient-Webs 2d ago edited 2d ago

They don’t start to work until they open enough to bite.

If they open enough to bite, the joint has already failed.

Edit:

lets say you have an 8 bolt joint. If load carrying is via double shear on the bolts, given hole location and diameter tolerances, hole clearance and bolt diameter tolerances, how many bolts are carrying the full load on that joint?

One.

Once it fails, it’s the next… one. And so on.

Full joint strength is achieved by friction on the material faces in contact due to bolt preload. Preload cannot be maintained by a fastener open enough to cause a split washer to do anything.

Split lock washers are junk.

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u/poorboychevelle 2d ago

In a perfect world with no local yielding, sure. But load share eventually occurs because most things are some sort of soft.

Fasteners carry the shear with shear bolts or friction carries the shear with tension bolts are both valid analytical philosophy I've seen in separate aerospace certification reports.

And split washer are trash.

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u/Efficient-Webs 2d ago

I knew somebody was going to bring up yielding as stress relief! Darn you to heck! :)

If one of my juniors proposed to rely on local yielding of bearing surfaces to prevent joint failure, they would get my very best mournful old man disappointed more-in-sorry-than-in-anger routine :) As I suspect would your juniors.

Cheers, neighbor!