epoxy joint

[Gray E Fowler]

I will answer the "local" question first, since it is more fun. 1978, 
Kailua Hawaii. Lived with my parents during first summer off from college.
Got a job a aTexaco station, where as I was the only Haole other than the 
owner. My co workers were a Japanese, a Chinese a Potugese, a Hawaian and 
a Samoan. Worked nights alone with the Chinese dude. Every night we 
ordered Chinese food, and then he would say......smoke a joint? in twisted 
Hawaian-Chineses English. He then proceeded to whip out a half smoked 
joint of approximately 0.125" in diameter, counter to the "american 
fatty". Two tokes (thats all it took) and back to work. I always declined 
of course. Never could figure out when he had smoked the first half.
Surfed the North Shore all day, pumped gas  at night.
My favorite pastime was giving directions to the tourists...like I knew 
where these places were.....but they got directions anyway.



Gray Fowler
Principal Chemical Engineer
Composites Engineering




"Cameron Smith" <dentdoc007 at bellsouth.net>
Sent by: discussion-request at nsrca.org
01/17/2005 12:42 PM
Please respond to discussion

 
        To:     <discussion at nsrca.org>
        cc: 
        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 
 

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