Toughened Epoxy Structural Adhesives

[hanabi]

Has anyone ever used something such as these, they form "flexible, resilient bonds":
https://www.mcmaster.com/epoxies/toughened-epoxy-structural-adhesives/

The application that I am thinking about is the exterior fin root fillet.

Joe O

 

[g.pitts]

I've used some of these 3M products as a potting compound for a motor controller design I was involved with a few years ago. We had zero issues with the material for that particular use, and it worked great, but it's more than a little spendy per unit volume as compared to RocketPoxy that I use on my external and internal body tube fillets (I use a stronger adhesive for the fin to motor tube bonding and fillets). The particular 3M product I used - and I don't recall which it was - would require the rocket to set for several hours (like overnight) before I'd be comfortable rotating the rocket to apply the next set of fillets. Our cure time for the 24 hour products was more like 36 hours, possibly because of the amount of material we were using to fill the controller heatsink.

As I mentioned, I use RocketPoxy, which (going from memory) has a tensile strength of about 7600 psi, and sets a bit more quickly than what I'm seeing with the 3M product specs (although they do tout a few that are "non-sagging"). RocketPoxy is also considerably less expensive at less than $15 for 8 ounces or two quarts for less than $75. RocketPoxy also cures to a "rubbery" type of feel. Unless the 3M products are something that you just really want to try, and there's nothing wrong with that, I might look to alternative solutions for your external fillets.

 

[Pepe Le Pew]

Joe O, you can use a good quality epoxy and mix cotton flock into it and form your fillets. Cotton flock is used in the homebuilt aircraft industry and is considered a structural bonding adhesive. I have tons of the stuff and use it regularly. Depending on your application (model, low, mid or high power) epoxy can be the hobby shop variety or the more exotic West Systems or Loctite Hysol stuff. At any rate any high quality epoxy will work great!