epoxy joint

[Jim Ivey]

Gray
What are the negatives to thinning with alcohol. Suppose you add fiber filler the epoxy gets thicker.Suppose you thin to a just a little to work well.Have you hurt the joints strength.I do it and it never has failed. This way I use much less.
Lotta talk here about epoxy and none about thinning.

Jim Ivey
> 
> From: Gray E Fowler <gfowler at raytheon.com>
> Date: 2005/01/17 Mon PM 05:34:36 EST
> 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
> 
> 
> Chopped fibers actually work well. A chopped fiberglass of about 1.0" can 
> approach most of the properties of continuos fiberglass(as long as the 
> fiber volume is sufficient). Shorter fiber such as 0.5" and 0.25" increase 
> most of the properties of neat epoxy resin also. In essence they are long 
> enough to transfer some load through the matrix.  An 8% by weight chopped 
> fiberglass in epoxy looks like wet cat hair. Pack enough fiber in (fiber 
> volumes greater than 30%) and even a FILLET can now transfer load and can become useful.  Of course all of this is 
> way too much for our applications.
> Chopped fibers suck in my industry because we need absolute predicability. 
> Not knowing exactly how the fiber is oriented or what the void volume is 
> is impossible to analyze (FEA).  Chopped fiber is never as good or as 
> light as continuous fiber. Chopped fiber does not give you "Maximum 
> efficiency of materials" which means  it is too heavy to rely on. On 
> Aeroslave planes, I mix 3-4% chopped carbon fiber to beef up the 
> microballoon-epoxy corner fill material.
> First thing I had to learn to do when transitioning from building missiles 
> to building pattern planes is not to build it too strong. Remember.....If 
> you cannot break it then you made it too heavy!
> 
> 
> 
> Gray Fowler
> Principal Chemical Engineer
> Composites Engineering
> 


=================================================
To access the email archives for this list, go to
http://lists.f3a.us/pipermail/nsrca-discussion/
To be removed from this list, go to http://www.nsrca.org/discussionA.htm
and follow the instructions.