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Date:         Mon, 5 Oct 2009 17:03:30 -0700
Reply-To:     neil N <musomuso@GMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         neil N <musomuso@GMAIL.COM>
Subject:      Re: Stupid wire question...really... (temp 2 wire)
Comments: To: David Beierl <dbeierl@attglobal.net>
In-Reply-To:  <4aca7c2d.02c3f10a.6d05.105b@mx.google.com>
Content-Type: text/plain; charset=ISO-8859-1

Awesome. Thanks!

I see what you mean.

Thanks for explaining the "how" behind this.

Neil.

On Mon, Oct 5, 2009 at 4:07 PM, David Beierl <dbeierl@attglobal.net> wrote: > At 06:46 PM 10/5/2009, neil N wrote: >> >> So adding shrink wrap would keep the original wire near connector from >> bending as much, thus hastening the stock wire casings' demise? Not >> clear about the "how" behind this,  but of course trust you're right. > > There are two issues involved.  The one I mentioned is simply that the > shrink-wrap stiffens the wire so that bends near the connector prefer the > more flexible section right at the connector.  You can see this effect in > your own photo where the wires do a reverse bend right at the connector. >  The short radius of the curve overstresses the tired insulation and it > splits. > > The second is the problem that happens any time you have a sharp junction > between two different stiffnesses.  In electronics we call it an impedance > mismatch; mechanical types call it a stress raiser.  In either case energy > is concentrated at the junction between the two.  It's the reason why the > transmission 3-4 slider fails, the reason why the old Zenith terminal CRTs > used to break off their mountings from the rest of the case in shipping > every single time, the reason why you have to bevel the edge when you're > cutting a tire-tube patch to size.  The closer you get to perfectly sharp > transition, the closer the stress gets to infinite.  It's also the reason > why a windshield crack will keep on extending until you drill a little hole > in front of it.  And related to why you need a great big hammer to move > something, and a small one to deform it at the surface. > > In this case the change between terminal and wire is the critical one; > flexing there will lead to the wire itself fatiguing and falling off the > terminal.  The shrink-wrap contributes by forcing more bend to take place > near/at the terminal than otherwise would.  In itself it's not enough of a > difference to cause much of this type problem. > > David >

-- Neil Nicholson '81 VanaJetta 2.0 "Jaco"

http://tubaneil.googlepages.com/

http://groups.google.com/group/vanagons-with-vw-inline-4-cylinder-gas-engines


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