Joining CF panels with rivets and adhesive. Questions about sheer loading, torsion, etc.

[Mongo]

Are there examples on the internet of super strong structures with panels being riveted together?

What about joining two panels with an angle clip that is riveted and bonded?

[Anthony Fairhurst]

Hi Mongo,

There is just about anything on the internet! I found a pretty cool webpage, "History of Rivets & 20 Facts You Might Not Know" where they note some megastructures assembled with rivets. Unfortunately there is nothing about composites on this webpage but interesting nonetheless.

However, seeing as rivets are typically permanent fasteners, this is not a good joining method to be used with carbon fiber panels in super strong structures expected to last a long time. The reasoning is the effects and presence of galvanic corrosion. You can read more about galvanic corrosion here. Basically carbon is electrically conductive and upon contact with actively corroding metals, the difference in electrical properties will cause ions to be pulled from the metal to the composite and corrode quicker over time (3-5 years instead of 10+)*. *Please note I am not a chemist or metallurgist so my "dummy's statement to galvanic corrosion" is coming from a dummy!

Best way to join composites is bonding. Second best is bolts as they can be easily replaced if you were to notice any corrosion. One way to reduce the risk of corrosion is by placing a barrier in-between the metal and carbon, such as fiberglass, plastics, or other non-conductive materials.

Hope this helps!

Anthony

[Mongo]

I am hoping to find some load test data on CF panels joined with brackets.  I want to learn about CF panels being secured with angled brackets using adhesive, rivets, bolts, or a combination and see how they compare to single piece structures that came out of a mold.  My goal is to utilize an effective fabrication process to create a strong, but lightweight structure that uses minimal tooling.  No plugs, no molds, no need for vacuum bags, etc.  Just order flat panels that are cut on a CNC table and delivered to my door ready to be assembled.

 

[John Kimball]

The quick answer to your question is that load test data exists for specific projects, but they may differ greatly from your project.

The long answer is a lot more complicated, but is possible given what you want to accomplish. Bonding panels together, especially at right angles, requires much more than just bonding them together. unlike welding, composites rely on surface area to achieve strength when connecting. So you would need some angles bonded to both plates or panels in order to achieve a proper support and bond. This is fairly easy if you only need right angles, but if you need anything else, you have to fabricate the angles first with the correct angles, then you can bond them in place. bolting or riveting them together will never give you the same integrity as an adhesive bond. You can use rivets or bolts to aid in fixturing the parts as the adhesive cures, but in the end, the fasteners will not give you any more strength to the bond area. It’s all about surface area. A bolt will never provide the same surface area fixing as an adhesive bond line will. I’ve often heard fasteners used in adhesive applications as “chicken fasteners”, because the the engineer is too chicken the rely on the adhesive 😅.

Another method often used is the bond the plates or panels together the way you want them and then wet lay carbon fiber strips in the corners to mimic a bonded angle. Generally, this works really well with polyester resin parts, but with epoxy laminates, it takes a lot of surface prep to ensure proper bonding of wet layup against cured laminates.

This article may help you understand better: https://journals.sagepub.com/doi/pdf/10.1243/14644207JMDA219

It talks about bonding cored panels, but is applicable to non-cored plates as well.

[Mongo]

@John Kimball  I have been reading the scientific journal that you had posted in your previous comment.  Where can I access all the supporting cited sources from the paper?  There are 129 sources attached that I want to investigate and I don't want to pay for each publication.

[lo_0l]

5 hours ago, Mongo said:

@John Kimball  I have been reading the scientific journal that you had posted in your previous comment.  Where can I access all the supporting cited sources from the paper?  There are 129 sources attached that I want to investigate and I don't want to pay for each publication.

Hey @Mongo,

Within any paper you can usually copy the citation and right click and 'search for...' depending on your browser or copy and paste it into Google or your favorite search engine like below:

 

 

 Usually, the source will pop right up 👍