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<DIV><FONT face=Arial size=2>thanx...croz</FONT></DIV>
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<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=gfowler@raytheon.com href="mailto:gfowler@raytheon.com">Gray E
Fowler</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=discussion@nsrca.org
href="mailto:discussion@nsrca.org">discussion@nsrca.org</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Monday, January 17, 2005 4:08
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: epoxy joint</DIV>
<DIV><BR></DIV><BR><FONT face=sans-serif size=2>John,</FONT> <BR><BR><FONT
face=sans-serif size=2>On something like a lite ply former, I usually put a
filet like amount on the former to ensure complete wet out and complete gap
fill. The result is an absolute minimal filet-cuz the tip of my finger is
curved. This is just to make sure the entire joint is complete, because you
really cannot QC the joint-not to add a filet. </FONT><BR><FONT
face=sans-serif size=2>Also a gob of really strong epoxy WILL increase bond
strength IF the epoxy is stronger than the substrate such as lite ply. But
this is a bass-ackwards application and once again dead
weight.<BR><BR><BR><BR>Gray Fowler<BR>Principal Chemical
Engineer<BR>Composites Engineering</FONT> <BR><BR><BR>
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<TD><FONT face=sans-serif size=1><B>"John Ferrell"
<johnferrell@earthlink.net></B></FONT> <BR><FONT face=sans-serif
size=1>Sent by: discussion-request@nsrca.org</FONT>
<P><FONT face=sans-serif size=1>01/17/2005 02:01 PM</FONT> <BR><FONT
face=sans-serif size=1>Please respond to discussion</FONT> <BR></P>
<TD><FONT face=Arial size=1> </FONT><BR><FONT
face=sans-serif size=1> To:
<discussion@nsrca.org></FONT> <BR><FONT
face=sans-serif size=1> cc:
</FONT> <BR><FONT face=sans-serif size=1>
Subject: Re: epoxy
joint</FONT></TR></TBODY></TABLE><BR><BR><BR><FONT face=Arial size=2>"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, "</FONT> <BR><FONT
size=3> </FONT> <BR><FONT face=Arial size=2>Awesome! and
embarrassing!</FONT> <BR><FONT face=Arial size=2>I cannot even guess how many
formers & stringers I have carefully encumbered with beautiful, heavy
worthless fillets...Sometimes adding bits of string to the mix in imitation of
pylon racers...</FONT> <BR><FONT size=3> </FONT> <BR><FONT face=Arial
size=2>But you just made future building easier...</FONT> <BR><FONT
size=3> </FONT> <BR><FONT face=Arial size=2>John Ferrell
</FONT><FONT face=Arial color=blue size=2><U><BR></U></FONT><A
href="http://dixienc.us/"><FONT face=Arial color=blue
size=2><U>http://DixieNC.US</U></FONT></A> <BR><FONT size=3>----- Original
Message ----- </FONT><BR><FONT size=3><B>From:</B> </FONT><A
href="mailto:gfowler@raytheon.com"><FONT color=blue size=3><U>Gray E
Fowler</U></FONT></A><FONT size=3> </FONT><BR><FONT size=3><B>To:</B>
</FONT><A href="mailto:discussion@nsrca.org"><FONT color=blue
size=3><U>discussion@nsrca.org</U></FONT></A><FONT size=3> </FONT><BR><FONT
size=3><B>Sent:</B> Monday, January 17, 2005 9:57 AM</FONT> <BR><FONT
size=3><B>Subject:</B> Re: epoxy joint</FONT> <BR><BR><FONT face=sans-serif
size=2><BR>John,</FONT><FONT size=3> <BR></FONT><FONT face=sans-serif
size=2><BR>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).</FONT><FONT size=3> </FONT><FONT face=sans-serif size=2><BR>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.</FONT><FONT
size=3> </FONT><FONT face=sans-serif size=2><BR>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 <B>little</B> 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<B> reduce</B> elongation,
<B>reduce</B> tensile strength, <B>increase</B> the heat distortion
temperature, <B>increase</B> hardness and <B>increase</B> compression
strength.</FONT><FONT size=3> <BR></FONT><FONT face=sans-serif
size=2><BR>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. </FONT><FONT size=3><BR></FONT><FONT face=sans-serif
size=2><BR>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).
<BR><BR><BR><BR>Gray Fowler<BR>Principal Chemical Engineer<BR>Composites
Engineering</FONT><FONT size=3> <BR><BR></FONT>
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<TD width="44%"><FONT face=sans-serif size=1><B>"John Crozier"
<sjcrozier@comcast.net></B></FONT><FONT size=3> </FONT><FONT
face=sans-serif size=1><BR>Sent by:
discussion-request@nsrca.org</FONT><FONT size=3> </FONT>
<P><FONT face=sans-serif size=1>01/15/2005 09:35 AM</FONT><FONT size=3>
</FONT><FONT face=sans-serif size=1><BR>Please respond to
discussion</FONT><FONT size=3> </FONT></P>
<TD width="52%"><FONT face=Arial size=1>
</FONT><FONT face=sans-serif size=1><BR> To:
"discussion nsrca"
<discussion@nsrca.org></FONT><FONT size=3> </FONT><FONT
face=sans-serif size=1><BR> cc:
</FONT><FONT size=3> </FONT><FONT face=sans-serif
size=1><BR> Subject:
epoxy joint</FONT></TR></TBODY></TABLE><BR><FONT
size=3><BR><BR></FONT><FONT face=Arial size=2><BR>Sometime in my crafting
life, I have acquired the notion that adding milled glass, micro-balloons,
etc., to epoxy when making a good fitting joint, only weakens the joint.
(diminishes, or dilutes the bonding strength of the epoxy).</FONT><FONT
size=3> </FONT><FONT face=Arial size=2><BR>In this case it would be composite
horns to balsa. No fillet is needed.</FONT><FONT size=3> </FONT><FONT
face=Arial size=2><BR>Anybody wanna jump in?</FONT><FONT size=3>
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