epoxy joint

[Wayne Galligan]

Jim,

My experience with thinning epoxy is that it weakens it and it also causes
shrinkage. Something you DO NOT want in a joint area.   I am sure Gray will
concur.

Wayne G


----- Original Message ----- 
From: "Jim Ivey" <jivey61 at bellsouth.net>
To: <discussion at nsrca.org>
Sent: Monday, January 17, 2005 9:13 PM
Subject: Re: Re: epoxy joint


> 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
> >
>
>
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