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Solder splices/connections

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rv8iator(at)gmail.com
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Posted: Wed Sep 28, 2016 1:34 pm Post subject: Solder splices/connections

The stress riser that occurs at the interface between wire strands and solder filled wire strands if not mechanically supported is a candidate for fatigue failure due to vibration induced flexing of the wire

This is true of field splices and soldiered pin/wire connection.

Good mechanical support/strain relief is imperative to prevent fatigue failure of the connection/soldier joint.

A good crimped connection does see a stress riser at the crimp/wire interface... BUT the transition is not as sharp as with soldier wicked into wire strands.  With crimped pins the wire is generally supported upstream from the crimp thus creating a mechanical support for the connection.  This can be true for soldered joints as well... AS LONG as no solder has wicked up the wire strands beyond the point of mechanical support.  The finer the wire strands (as in very flexible type conductors) the greater the likelihood that solder will wick further up the strands potentially going beyond the insulation.

Studies done here where I have been a test engineer on medical electronic equipment have demonstrated the fragility of soldered wire connections.  All pins are crimped and strain relieved by connection of the wire outer sheath to the connector body and by the cable outer sheath to the connector shell.

Chris Stone

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nuckolls.bob(at)aeroelect
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Posted: Thu Sep 29, 2016 8:57 am Post subject: Solder splices/connections

At 04:29 PM 9/28/2016, you wrote:

  	  Quote: 	
		  The stress riser that occurs at the interface between wire strands and solder filled wire strands if not mechanically supported is a candidate for fatigue failure due to vibration induced flexing of the wire



 This is true of field splices and soldiered pin/wire connection.



 Good mechanical support/strain relief is imperative to prevent fatigue failure of the connection/soldier joint. 	


   Yes, stresses due to flexing of any material is

   a function of thickness/diameter of object and

   the magnitude of the bending . . . which under

   vibration gives rise to cyclical tension/compression

   forces on the material.  A second  of 1" copper rod

   flexed through x-degrees will fail in a tiny fraction

   of the same cycles impressed on a 0.020" strand of

   copper. This is why welding cable is made from a bizillion

   strands of copper 'cat hair' as are braided copper

   bonding straps . . . 



  http://tinyurl.com/jxsf55j



   . . . are unlikely to fail under flexure stresses

   over lifetime of the installation. Whether or not

   a solder-solidification of strands presents a more/less

   severe stress riser point than a crimp-

   solidification is kinda splitting hairs.

   When used in a situation that imposes

   cyclical forces on the joint, there is

   significant risk of failure at the

   transition from solid to strands in BOTH

   technologies.



   This fact of physics gave rise to the double

   crimped, 'pre insulated' terminals of all stripe

   but most famously, PIDG style terminals

   offered by many suppliers for the last 

   70 or so years.



  http://tinyurl.com/zkmh7kj



   When the joining is effected with solder,

   folks in-the-know strive to achieve two

   goals. Join the wires and support the

   insulation just outside the junction.



  http://tinyurl.com/ju4gvvg



   Arguments favoring one process over the other

   have no solid foundation in risk reduction.

   It's not difficult to apply either process

   in a manner that will exceed the service

   life of the airplane.



   You can mess up a potentially good crimped

   installation too.



  http://tinyurl.com/hekmvyz



   This terminal was observed on an accident

   aircraft where, amongst many other shorfalls,

   some terminals were not properly installed.

   Understand the physics, acquire the tools

   and PRACTICE.

  



 

 

   Bob . . .

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