Best way to joint fabricated carbon strut structure.


Best way to joint fabricated carbon strut structure.
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Tobias
Tobias
Tobias
posted 12 Years Ago HOT
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Hi there,
I am pretty new to working with carbon, but have a good background in other materials.

I am working on designing a strutted framework, fabricated out of 5mm pultruded carbon tube, and I thought it best to seek some advice about how best to make the joints. My plan is to build a jig which holds everything flat, and use a braided sleeve to form a reinforced skin. However since I also plan on painting the structure, I don't necessarily need the braid for aesthetics, however I also don't want 'spider knees' at each join. 

To simplify things, lets assume i am building a small chair, with some structural triangulation, which needs to hold about 10kg ( so in real world terms I guess it has to be over-engineered to not fail under 50kg, or something of the kind ).

In my crude drawing I have 3 potential jointing processes, but I wonder if there is another I have not considered, or if I would be better off making a mould and a core, and using a cast component joined by tubes, rather than attempting to join struts together. 

Thanks,
T
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Tobias
Tobias
Tobias
posted 11 Years Ago HOT
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Posts: 6, Visits: 16
For future reference, I've just had confirmation from customer service at Permabond that the correct adhesive for structural bonds between, for example, metal and composites is their ES550 and ES558. They are described as:                
         
            
               
                  "single-part epoxy pastewhich flows like solder when heated during curing.The adhesive is toughened for maximum impactresistance, along with excellent peel and shearstrength. ES558 is ideal for bonding a wide range ofmaterials including metals, ferrites, ceramics andcomposites."

ES550 is a non-flowing adhesive, whereas the 558 will flow through a capillary joint.

ET515 is described as:

"ET515 is a semi-flexible toughenedadhesive with good adhesion to a variety ofsubstrates such as wood, metal, ceramics and someplastics and composites. It’s a relatively fast curingepoxy; reaching handling strength in 15 minutes. It isideal for bonding different materials wheredifferential thermal expansion is anticipated."

This confirms my conclusion that the ET515 is best suited to situations where a bond between large surfaces which have differing tensile qualities, for example adhering a wood veneer to a piece of spring steel (if you can find an application for such a purpose). Comparing the shear strengths between the adhesives also confirms my findings: ET515 Mild steel 8 - 12 N/mm2, ES558/550 Steel 27 - 41 N/mm2.

Thankfully I don't think I had any failures due to leftover release agents. Most of the structure was built from pultruded tube, and all of the failure points were between the composite and metal components of the structure. My revised version of the structures will use different components and adhesives for sure.

                  
         
            
               
                   


                                                            
         
            
               
                  


                                                                                    
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Best way to joint fabricated carbon strut structure.
Tobias - 12 Years Ago
     The strongest of the 3 is the tube joiner in aluminium. Such inserts are commonly used to join...
Warren (Staff) - 12 Years Ago
     Hi Warren, So if you were to build such a structure, you would work with alloy inserts and a braided...
Tobias - 12 Years Ago
     They should be bonded in using a structural adhesive like our Normal 0...
Warren (Staff) - 12 Years Ago
             It would appear that the ET515 has no structural value at all, as it seems to neither bond to...
Tobias - 12 Years Ago
                 Hello Tobias I have used the above adhesive on the top fairing mount on my classic racing...
carbonfibreworks - 12 Years Ago
                     Hmm, this was a 20mm carbon tube, and the join was to a strut coming in below, by means of an...
Tobias - 12 Years Ago
                         I will post an image of the part on Friday. Regards Chris carbonfibreworks.co.uk
carbonfibreworks - 12 Years Ago
     When bonding any metal I still use the wet sanding technique using 240 wet and dry sometimes 120 and...
Shaneer22 - 12 Years Ago
     how big is the gap?? I have used ET515 personally for bonding inserts and its been a good bond. You...
Warren (Staff) - 12 Years Ago
     As above, I've used that to bond halves of wings together and not had a failure yet
ajb100 - 12 Years Ago
     I generally consider an adhesive to be something which adheres with a chemical bond, in this kind of...
Tobias - 12 Years Ago
     If you are adhereing it to smooth (albeit degreased) aluminium then I would have expected the...
Warren (Staff) - 12 Years Ago
     For future reference, I've just had confirmation from customer service at Permabond that the correct...
Tobias - 11 Years Ago

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