Composite Tube Joining

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bvahnee

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Nov 21, 2021
Messages
7
Hello everyone,

I run a small manufacturing company located north of Boston. Over the past year & a half I’ve been developing a mechanical fastening system specifically for carbon fiber tubes. If you or someone you know needs help designing, manufacturing, and testing a composite tube frame (or another component with tube construction) I would love to help. The amount of destructive testing done on the fastener is pretty extensive so I can help with providing tube diameter and wall thickness specs for the load expected on the joint. Thanks for the consideration.

Advanced Engineering Corp.
Danvers, MA

shockabsorber.jpg
 

bvahnee

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Nov 21, 2021
Messages
7
I am curious about your fasteners in the corners. Are they structural?
If I’m interpreting your question correctly, yes the fasteners on the corners are structural. The airframe nose in the photo uses 18 fastener bodies with 4 locking detents per, on 1/16 sidewall in its weakest configuration it’ll begin failing at around 3500 lb per joint. As a tech demo, I just need it to stay together under its own weight, on a real build I’d probably be using an HD version with 12 detents per fastener body.
 

wanttobuild

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Jun 13, 2015
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kuttawa, ky
Let me see if I can be more specific, the fasteners you are developing can be used to join composite tubing for airframe construction?
Is this correct?
 

proppastie

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Pictures individual fasteners? Hard to see exactly what you are doing.
 

bvahnee

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Nov 21, 2021
Messages
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Let me see if I can be more specific, the fasteners you are developing can be used to join composite tubing for airframe construction?
Is this correct?
I’m not an aerospace engineer, so to say yes I’d be lying. If someone else is making a frame with a connection system that requires drilling & using screws/bolts to secure it to the tube, then theoretically my fastener will work even better. I’ve tested tubes from .25” to 4” OD with varying wall thicknesses, so I could give you ballpark figures on tube requirements for a particular load.
 

David L. Downey

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Aug 7, 2019
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Harleysville, PA
How are you managing the galvanic attack to the aluminum? McD did an atrocious job on the original Harrier. when we disassembled many of the carbon/aluminum fitting assemblies there was a "shell" made of paint where the aluminum had been. As far as I know the V-22 was managed better...I hope! Granted these are both salt water risk aircraft.
 

bvahnee

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Nov 21, 2021
Messages
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How are you managing the galvanic attack to the aluminum? McD did an atrocious job on the original Harrier. when we disassembled many of the carbon/aluminum fitting assemblies there was a "shell" made of paint where the aluminum had been. As far as I know the V-22 was managed better...I hope! Granted these are both salt water risk aircraft.
Type 2 or 3 anodizing on each individual component of the fastener if we’re talking aluminum. I can just as easily machine everything from something more exotic if the application required it; for prototyping purposes aluminum is my go-to to keep it cheap, these prototypes are funded out of my own pocket. I’m hoping to team up with someone in the industry so I can do more in-depth analysis on exactly this subject. Cheers.
 

PiperCruisin

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Jan 17, 2017
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Idaho
Type 2 or 3 anodizing on each individual component of the fastener if we’re talking aluminum. I can just as easily machine everything from something more exotic if the application required it; for prototyping purposes aluminum is my go-to to keep it cheap, these prototypes are funded out of my own pocket. I’m hoping to team up with someone in the industry so I can do more in-depth analysis on exactly this subject. Cheers.
You might test it after you have thermally cycled it a few times. The CTE of carbon fiber components is significantly lower than aluminum. Steel would be a better match, but heavier and a bit harder to machine. However, in that size may not be a problem.
 

bvahnee

Member
Joined
Nov 21, 2021
Messages
7
You might test it after you have thermally cycled it a few times. The CTE of carbon fiber components is significantly lower than aluminum. Steel would be a better match, but heavier and a bit harder to machine. However, in that size may not be a problem.
Absolutely, trust me I’d love to send the models out to someone like Desktop Metal & have them run it thru some of that fancy AI software so they could optimize both the material and design, I’m not there yet. Out of aluminum, the fastener will work just fine for most applications; the carbon matrix fails way before the aluminum does. Thermal cycling would have to be pretty extreme to affect the fastener. Aluminum gets hot it expands and hugs the interior of the carbon more, it gets cold it becomes a little loose. Tolerances on everything in those photos is +/- .002” or better, including the cutouts on the carbon. Bring it +200 or -200, yeah you got me, I have no idea.
 

PiperCruisin

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Thermal cycling would have to be pretty extreme to affect the fastener. Aluminum gets hot it expands and hugs the interior of the carbon more, it gets cold it becomes a little loose.
Aircraft (GA) can be in the hot desert where the structure is 140F? and then climb to altitude and get close to freezing (10 to 14k foot for general GA). Airliners have a much bigger swing, but not the market you're going for. The deltaT is moderate, but inconsequential.
 
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