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RE: slip joint/friction weld

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That reminds me of the tie rod ends in a car steering system.  The tie rod ends have a tapered stud that enters the tie rod link.  The tie rod stud is in bending because of the eccentric load applied at the ball part of the joint, but the bending is transferred into pure compression at the tapered stud so the tapered part doesn’t have to transfer bending.  It’s pretty confusing - I read about this in a SAE report years ago.  I can’t explain it but I recall there is something to this theory.

 

From: Gray Hodge [mailto:ghodge(--nospam--at)hodgedesign.com]
Sent: Tuesday, February 16, 2010 12:34 PM
To: seaint(--nospam--at)seaint.org
Subject: slip joint/friction weld

 

To all,

 

I have been asked to review a connection which the manufacturer refers to as a friction weld but which looks more like a slip joint to me.  The connection is for two sections of a light pole, and I’m sure you have all seen something just like it.  The pole consists of two sections of tapered pipe so that upper section of pipe slips over the top end of the lower section of pipe, and there are no mechanical connectors at the joint.  The overlap is roughly equivalent to twice the average diameter at the slip connection.  There is no tension at the connection – only compression in the pole and bending due to lateral loads.  The task seemed relatively simple, at first, but then I tried to analyze it.  I can reason out that the vertical load is transferred by the upper pipe section bearing on the lower section and that the moment will be transferred by a resisting couple across the joint.  I suppose that friction resistance will become important if the taper is severe enough, but these pipe sections have a fairly gentle taper.  Is anyone familiar with a methodology for checking a connection of this nature?

 

Thanks.