epoxy joint

[Mike Hester]

Now y'all don't be bogarting those joints.

-M

  ----- Original Message ----- 
  From: Cameron Smith 
  To: discussion at nsrca.org 
  Sent: Monday, January 17, 2005 1:42 PM
  Subject: RE: epoxy joint


  I want to hear about the Hawaiian Locals!!!

   

  -----Original Message-----
  From: discussion-request at nsrca.org [mailto:discussion-request at nsrca.org] On Behalf Of Rcmaster199 at aol.com
  Sent: Monday, January 17, 2005 1:25 PM
  To: discussion at nsrca.org
  Subject: Re: epoxy joint

   

  Interesting, Gray. Would you also discuss some details about chopped filler (say 1/16" to 1/2" chop length) and continuous strand filler? Also how material stiffness and impact resistance are affected?

   

  MattK

   

   

  In a message dated 1/17/2005 1:18:24 PM Eastern Standard Time, amirneshati at earthlink.net writes:

    ----- Original Message ----- 

    From: Gray E Fowler 

    To: discussion at nsrca.org 

    Sent: Monday, January 17, 2005 9:57 AM

    Subject: Re: epoxy joint

     


    John, 

    I do not understand what you mean composite horns/balsa.....but I do know a thing about joints ( I once lived in Hawaii hanging out with the locals). 
    Epoxy is the "toughest" unfilled. By this I means in a seam joint the primary stress will be flexing, and an unfilled epoxy can handle this the best. 
    Milled fibers are about 1/64" long. In a composite the fibers are far stronger than the resin. The job of the resin is to flex a little to enable stress to be transferred from one fiber to another. The problem with milled fibers is that as the transfer stress it is only for that 1/64 of a inch and then it terminates creating a stress riser. The epoxy then fractures at the end of that fiber at a stress level much lower than if the fiber was not there at all. These type of fibers work great on thermoplastics which are much softer and flexable, but not so great on thermosets. Milled fibers in an epoxy will reduce elongation, reduce tensile strength, increase the heat distortion temperature, increase hardness and increase compression strength. 

    Microballoons are not structural, they are used to reduce density. The volume is huge and the balloons are weak therefore the mixture is weaker in every aspect. The reality is though that a microballoon epoxy is still usually strong enough for our applications. Add this to the fact that we are always striving for weight reduction and you can determine the proper application. 

    Filets in general are useless other than for cosmetic reasons. On a properly assembled bond joint the filet will never see stress until the load capacity of the joint itself is exceed. At that point the joint breaks and considering that the joint itself is orders of magnitude stronger than the filet, the filet breaks instantly. Filets are dead weight, and usually more dead weight than you think it is-but man they sure look GOOD when someone inspects the inside of your plane-which in this hobby is second only to winning the NATs (sorry-cannot always stop the sarcasm).  



    Gray Fowler
    Principal Chemical Engineer
    Composites Engineering 

   
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.f3a.us/pipermail/nsrca-discussion/attachments/20050117/bb937106/attachment-0001.html