Battle of the Epoxies: A Road to BALLS Experiment

[A5tr0 An0n]

I would simplify your test. Instead of actual fin shape I would do something more repeatable. a 1"x1" tab makes the math easy. What are you hoping to learn that cant be found on data sheets?

I have actually consider that. I also was going to bond to a airframe! I have since then decided to order a plate of G10 for this project.

Data sheets do not tell you the ideal surface preparation method, how well they adhere to various materials, how they perform at various temperatures, how they might behave in aerospace fields, etc. Granted some do actually tell you some of that information, some do not. This test is not to say oh yeah they were right 10kpsi is in fact this epoxy's tensile strength, it is for me to determine the best preparation method, strongest adhesive bond of various epoxies, how strong they are at various temperatures, and how different additives effect them.

This testing is not for any old flight. It is for my L3 flight, where the adhesive bonds need to be superb. I thought that show casing my results might help others who are planning a M3+ flight.

 

[JohnCoker]

This test is is for me to determine the best preparation method, strongest adhesive bond of various epoxies, how strong they are at various temperatures, and how different additives effect them.

If you start with 3 samples per test, test 2 epoxies and 2 "prep methods" (1 temperature, no additives), you're talking 12 samples. If you're really going to go to that trouble, I suggest you figure out a way to accurately test the strength (sadly, rocketmaterials.com is gone now).

I agree it's interesting to test with our techniques and materials, which was also the motivation for my tests. I actually expected that variations on technique and materials would swamp the differences between epoxies. However, even with my home-made samples, I got pretty consistent results and measured a significant strength difference.

Testing the fin/airframe bond seems very relevant since it's unlike any laboratory-prepared ASTM blank used in a lap-shear test.

 

[MarkH]

I was perusing the URRG site and found this.

https://forum.urrg.org/index.php?topic=17.0

Proline 4500 is on par ( a little weaker) with JB Weld strength wise, based on this data point.

 

[dixontj93060]

I was perusing the URRG site and found this.

https://forum.urrg.org/index.php?topic=17.0

Proline 4500 is on par ( a little weaker) with JB Weld strength wise, based on this data point.

That Rocketpoxy is some great stuff--I just wish they'd hurry and come out with the high temp version!

 

[flynfrog]

I have actually consider that. I also was going to bond to a airframe! I have since then decided to order a plate of G10 for this project.

Data sheets do not tell you the ideal surface preparation method, how well they adhere to various materials, how they perform at various temperatures, how they might behave in aerospace fields, etc. Granted some do actually tell you some of that information, some do not. This test is not to say oh yeah they were right 10kpsi is in fact this epoxy's tensile strength, it is for me to determine the best preparation method, strongest adhesive bond of various epoxies, how strong they are at various temperatures, and how different additives effect them.

This testing is not for any old flight. It is for my L3 flight, where the adhesive bonds need to be superb. I thought that show casing my results might help others who are planning a M3+ flight.

https://www.henkelna.com/us/content_data/14258_LT4536_TT_Aerospace_Surface_Preparation_Guide.pdf

Degreasing Non-Metals

Solvents or detergent solutions can be used to remove mold-release agents or waxes from plastics. Such
commercial detergents as represented by “Sprex” (DuBois Chemical Co., 1120 West Front, Cincinnati, Ohio)
are suitable. Acetone or methyl alcohol are effective solvents, depending on the type of plastic to be cleaned.
The adverse effect of solvents on some polymeric materials should be checked before their use.

Surface Abrasion

Smooth surfaces can be improved for bonding by roughening with abrasives such as medium-grit emery
paper. Abrasion should always be followed by degreasing to remove contaminants and loose particles.

Blasting with a fine grit is the best method for removing surface deposits – oxide films, tarnish, rust, mill scale
and other contaminants – from metals. This method should be used only on structures thick enough to resist
distortion. With thinner materials, contaminants should be removed by vapor honing. This method is similar
to grit blasting but uses high-velocity water or steam instead of air. If neither method is appropriate, abrasive
discs, belts, cloth, medium-grit emery paper, or wire brushes can be used. Plastics should be roughened with
abrasive discs, belts, cloth or emery paper to remove mold release agents. Medium-grit emery paper will give
the best results.

Surface abrasion can also remove other surface contaminants as well as weak, low molecular weight
components which can be concentrated at the surface due to their exclusion during solidification or
crystallization of some polymers.2 Also during solidification of both thermoplastic and thermoset materials,
there is often an orientation of the more polar groups towards the interior, leaving a concentration of lower
polarity, lower energy groups on the surface.3 Abrasion can open up access to the more energetic polymer
interior.

Chemical Treatment

Chemical or electrolytic pretreatments of a bonding surface can greatly increase the strength of the bond.
Pretreating can etch the surface of a metal, and form a highly adherent oxide. Environmental resistance can
often be greatly increased by such treatment. Etching solutions should be prepared in glass, porcelain,
polyethylene, polypropylene or tetrafluoroethylene fluorocarbon laboratory ware and stirred with rods of the
same material. Metals other than those to be etched should not touch the solutions. For solutions containing
hydrofluoric acid or fluorides, TFE fluorocarbon should be used. Solutions in plastic trays can be heated by
immersion in hot water baths; hot plates or infrared heaters can be used for glass and porcelain trays. See
Caution section below for safe procedures.

Don't get me wrong I think your test is a good idea and we will all benefit from it. But most of the testing you are about to do has been done over and over. Read pretty much any composite aircraft spec and it will start to get repetitive. Most of the aerospace epoxies do list strengths on different materials and prep methods and temp tolerance. If they don't list what you are trying to do they usually are not good at it. If you are dead set on doing a MD mach 3 L3 Cert Bird I would not cheap out trying to use hobby level epoxies or laminating resins for structural bonds.

 

[flynfrog]

one more thing you are not testing that my actually be more useful is joint design. If you read some of the papers I linked in the sticky they give some analysis of how important the joint design is including the fillet.

Maybe a bending test using the same epoxy with different size fillets to get an idea of how big you need them. The pieces i glued together for the sticky tore apart the laminate before the adhesive failed. Something to keep in mind. Your glue may not be the weak link

 

[A5tr0 An0n]

If you start with 3 samples per test, test 2 epoxies and 2 "prep methods" (1 temperature, no additives), you're talking 12 samples. If you're really going to go to that trouble, I suggest you figure out a way to accurately test the strength (sadly, rocketmaterials.com is gone now).

I agree it's interesting to test with our techniques and materials, which was also the motivation for my tests. I actually expected that variations on technique and materials would swamp the differences between epoxies. However, even with my home-made samples, I got pretty consistent results and measured a significant strength difference.

Testing the fin/airframe bond seems very relevant since it's unlike any laboratory-prepared ASTM blank used in a lap-shear test.

As of now I am estimating ~20 samples. I would love to get better testing done but I imagine that the testing equipment would cost more than all of my internal organs. I am not opposed to sending them off to be analyzed. I am not sure how much something of that nature would cost. You might know the best since you have been through it before?


BTW it is www.rocketmaterials.org not .com.

I have the same expectations on surface preparation. A lot of aerospace organizations list it as being of utmost importance. I understand why but I am interested to see how much this plays a role in the average persons build capabilities.

 

[daveyfire]

I imagine that the testing equipment would cost more than all of my internal organs. I am not opposed to sending them off to be analyzed.

Your internal organs or the samples?

 

[A5tr0 An0n]

I was perusing the URRG site and found this.

https://forum.urrg.org/index.php?topic=17.0

Proline 4500 is on par ( a little weaker) with JB Weld strength wise, based on this data point.

Yes, but the rocketpoxy surprised me.

That Rocketpoxy is some great stuff--I just wish they'd hurry and come out with the high temp version!

Any news on this? As far as I know they are wanting it to be a 1:1 mixture and are having trouble getting it down to that. I think that is a ridiculous excuse to make me wait. Howvere with the higher service temp. it will almost certainly have a lower shear strength.

 

[A5tr0 An0n]

Your internal organs or the samples?

Haha…. both to get this accomplished!

 

[A5tr0 An0n]

https://www.henkelna.com/us/content_data/14258_LT4536_TT_Aerospace_Surface_Preparation_Guide.pdf




Don't get me wrong I think your test is a good idea and we will all benefit from it. But most of the testing you are about to do has been done over and over. Read pretty much any composite aircraft spec and it will start to get repetitive. Most of the aerospace epoxies do list strengths on different materials and prep methods and temp tolerance. If they don't list what you are trying to do they usually are not good at it. If you are dead set on doing a MD mach 3 L3 Cert Bird I would not cheap out trying to use hobby level epoxies or laminating resins for structural bonds.

No worries. I know where you are coming from. Yes you are right, some of it has been done over and over again. But I am not convinced that some of it is useful for us per se. I have looked at quite a lot of different industrial epoxies and they do not tell you what they adhere best to and not. For example Cotronics 4525 and Henkel 9394C-2 do not specify. So if they have listed the same materials then I would love to see that. As far as the repeated testing, I am not convinced that the previous testing surfaces for what I am trying. Granted my tests are much much cruder, I just think that this is aimed for us and not a aerospace company with the ability for precision like construction.

I am interested in which epoxy offers the best of everything relevant while bonding to G10 FWFG and FWCF. My FWCF has been grinned down to a the correct OD and I have heard of concern with adhesion when that is done. So I want to find out if I need to switch to FG or if this AF with be able to adhere well. That is something I think the data sheets cannot help me with (but I could be wrong). I have not said I would ever use an epoxy other than an industrial type. In fact I have 4 different industrial types of epoxies at home now. However the laminating epoxy idea came from a engineer at Aeropoxy. He stated that its adhesion is stronger than anything they sell (including their adhesives), but it will have to be filled for obvious reasons.

one more thing you are not testing that my actually be more useful is joint design. If you read some of the papers I linked in the sticky they give some analysis of how important the joint design is including the fillet.

Maybe a bending test using the same epoxy with different size fillets to get an idea of how big you need them.

Now that is something to consider! I was just going to use a "monstrous fillet," instead of finding the "right," size. That would make more sense trying to find it, if you ask me. That is a great point, thank you.

The pieces i glued together for the sticky tore apart the laminate before the adhesive failed. Something to keep in mind. Your glue may not be the weak link

Yes… that is something I am hoping does not happen lol. On the bright side it lets me know that the structure failed before the fillet and I have nothing to worry about in regards to which epoxy to use, but on the other side I miss out on some rather good information. I think either way there is something to be learned.

Mat

 

[bobkrech]

You really have to be careful on how you conduct the tests and how you interpret data sheet information.

There are really 2 main applications for epoxy resins: 1.) laminating fibers into composites and 2.) structurally bonding composite structures together. The applications are very different and require epoxies with somewhat different properties.

The neat tensile strength of a laminating epoxy is less relevant than the strength of the manufacture composite as the primary parameter of importance is the property of the composite. In a composite, the strength of the fiber is what provides the tensile strength as the purpose of the resin is to hold the fibers in the proper alignment to withstand the stress of the application. The strength versus temperature important because if the service temperature is above the Tg, the stiffness of the composite will rapidly approach the stiffness of a wet noodle.

The neat tensile and shear strength of a structural epoxy matters as it is usually used to attach two structural components together without significant fiber interaction. Using a fiber filled resin helps, but unless there is significant layups over the 2 bonded components, the two pieces are held together as an assembly by the epoxy resin and depending on the applied stress, the bond will fail in either tension, compression or shear.

When you test the strength of a laminated composite or structural epoxy bond, you need to make dog bone shaped samples for the tensile tester or your results will be effected by the clamping. ANSI and other specifications should be consulted for the proper testing configurations.

Bob

 

[flynfrog]

No worries. I know where you are coming from. Yes you are right, some of it has been done over and over again. But I am not convinced that some of it is useful for us per se. I have looked at quite a lot of different industrial epoxies and they do not tell you what they adhere best to and not. For example Cotronics 4525 and Henkel 9394C-2 do not specify. So if they have listed the same materials then I would love to see that. As far as the repeated testing, I am not convinced that the previous testing surfaces for what I am trying. Granted my tests are much much cruder, I just think that this is aimed for us and not a aerospace company with the ability for precision like construction.

I am interested in which epoxy offers the best of everything relevant while bonding to G10 FWFG and FWCF. My FWCF has been grinned down to a the correct OD and I have heard of concern with adhesion when that is done. So I want to find out if I need to switch to FG or if this AF with be able to adhere well. That is something I think the data sheets cannot help me with (but I could be wrong). I have not said I would ever use an epoxy other than an industrial type. In fact I have 4 different industrial types of epoxies at home now. However the laminating epoxy idea came from a engineer at Aeropoxy. He stated that its adhesion is stronger than anything they sell (including their adhesives), but it will have to be filled for obvious reasons.




Now that is something to consider! I was just going to use a "monstrous fillet," instead of finding the "right," size. That would make more sense trying to find it, if you ask me. That is a great point, thank you.



Yes… that is something I am hoping does not happen lol. On the bright side it lets me know that the structure failed before the fillet and I have nothing to worry about in regards to which epoxy to use, but on the other side I miss out on some rather good information. I think either way there is something to be learned.

Mat

I used to have about a million dollars of 9394NA bonding research at previous company I worked for. Things I shouldn't have left in my desk when the company went under.... As for your ground tubes just check the last picture in my bonding sticky. You still need to scuff them to activate the surface. Try to do it right before you bond. You shouldn't have any issues.

 

[flynfrog]

on your real rocket do you plan to do a T2T over the adhesive? If that is so keep in mind the load paths. Your adhesive might not matter as much

 

[A5tr0 An0n]

I used to have about a million dollars of 9394NA bonding research at previous company I worked for. Things I shouldn't have left in my desk when the company went under.... As for your ground tubes just check the last picture in my bonding sticky. You still need to scuff them to activate the surface. Try to do it right before you bond. You shouldn't have any issues.

What I was getting at with the tubes OD being turned down was that some mentioned concerns that even with the right surface preparation the resultant bond is not as strong as a tube that has not been brought down to the desired OD. I am not so certain that on this level it will play a major role. I think with the right adhesive and surface preparation that the bond will arguably be stronger than the materials it is bonding.

EDIT: I must say I love that last photo you've got there!

on your real rocket do you plan to do a T2T over the adhesive? If that is so keep in mind the load paths. Your adhesive might not matter as much

I think I am leaning in that direction for added survivability points. I honestly do not want to. I was originally hoping to just have great surface preparation, a strong adhesive/bond, carbon laminated fins, very large reinforced fillets with brackets underneath, metal leading edges, and high temperature paint over it all. Now it is looking like I will have 2 layers of t2t… but I am still slightly undecided.

I am however under the thought that the adhesive does matter even with t2t, although yes not as much once t2t is laid on. But you are right I would not have to go to as much trouble as I currently am. In a strange way… I want to.

 

[Aksrockets]

.125' G10 plate.....

Now it is looking like I will have 2 layers of t2t… but I am still slightly undecided.

*cringe*
Have you done considerable research into other N5800 flights? A while back James D shredded a mongoose 98 on an N5800. It had solid .25in carbon fins and 4 layers of T2T. Mach 3.7 (or there abouts) had no problem pulling them off. I strongly urge you to reconsider your fin plans. Go with solid carbon fiber (as I recommended earlier), with a high TG laminating epoxy (look at Cotronics 4451), 4+ layers of T2T (possibly triaxial) and a high heat coating. Dont cut corners on poor fin materials.

[video=youtube;3LiQBPutUok]https://www.youtube.com/watch?v=3LiQBPutUok[/video]

Alex

 

[A5tr0 An0n]

*cringe*
Have you done considerable research into other N5800 flights? A while back James D shredded a mongoose 98 on an N5800. It had solid .25in carbon fins and 4 layers of T2T. Mach 3.7 (or there abouts) had no problem pulling them off. I strongly urge you to reconsider your fin plans. Go with solid carbon fiber (as I recommended earlier), with a high TG laminating epoxy (look at Cotronics 4451), 4+ layers of T2T (possibly triaxial) and a high heat coating. Dont cut corners on poor fin materials.

[video=youtube;3LiQBPutUok]https://www.youtube.com/watch?v=3LiQBPutUok[/video]

Alex

Read my other thread Enjoy. There are no corners being cut. Do you mean Cotronics 4461? Thats their low viscosity high temp epoxy (which I have and have used before).I have looked at more N5800 flights in detail than most. Do you know what can/cannot survive? Mad Max survived with no t2t. He had 0.125" thick Al fins with 3 layers of carbon on the fin. I am obviously aware that it is a different core material but a 0.125" G10 fin with 5 layers of carbon and 2 layers of t2t would most likely not fail due to flutter (assuming a decent angle of attack). I am not saying that FG>CF; we all know that CF has a higher flutter velocity. As I have also said previously before I am not dead certain on G10 fins but that is where I am leaning. Pegasus III IMO failed (initially at least) from delamination and it was a mongoose, which means it was not stable for that kind of flight to begin with. Nothing good was going to come out of his flight or Gerald's (booth flew a mongoose). Also unless he had custom fins (I do not think he did), then they were not .25" thick. I think you might be confusing the 1/4" bevel on the fins with the thickness but I could be wrong on that. I am more concerned about protecting the fins from getting ripped off due to a unforseen high angle of incidence and not flutter. Also i should not see more than M3.5 at most. Different materials will absorb the harmonics better than just carbon by itself, plus the thickness and choice of materials leads me to be able to not worry about flutter. Also I will have very good "ablative paint," that will eat up harmful energy before it can compromise my fins, not to mention metal brackets and metal leading edges for attachment and delamination prevention. If you read my other thread in detail I think a lot of this would have not had to been said.

 

[CarVac]

Also I will have very good "ablative paint," that will eat up harmful energy before it can compromise my fins, not to mention metal brackets and metal leading edges for attachment and delamination prevention. If you read my other thread in detail I think a lot of this would have not had to been said.

You seem to be waffling around: are you gluing the fins down or using metal brackets? You have this thread where you're testing epoxies, but now you decide to do metal brackets?


Secondly, tip-to-tip has two purposes: one is stiffening of the fin, and the other is the strengthening of the attachment. If you're using aluminum brackets for the fin roots, then you don't need T2T for attachment, and you should just use a stiffer fin instead of attaching the fins and then using inferior layup techniques for stiffening. If you're not using aluminum brackets, then you need to do tip-to-tip and somehow apply aluminum protection on top of that. Paint will help, but only a little.

 

[JimJarvis50]

If you're using aluminum brackets for the fin roots, then you don't need T2T for attachment, and you should just use a stiffer fin instead of attaching the fins and then using inferior layup techniques for stiffening. If you're not using aluminum brackets, then you need to do tip-to-tip and somehow apply aluminum protection on top of that. Paint will help, but only a little.

Just out of curiosity, how would these brackets be attached to the airframe? I can understand a bracket attached to the airframe and to the fin with bolts or by welding. What's the process with a composite tube?

Jim

Jim

 

[A5tr0 An0n]

You seem to be waffling around: are you gluing the fins down or using metal brackets? You have this thread where you're testing epoxies, but now you decide to do metal brackets?

Secondly, tip-to-tip has two purposes: one is stiffening of the fin, and the other is the strengthening of the attachment. If you're using aluminum brackets for the fin roots, then you don't need T2T for attachment, and you should just use a stiffer fin instead of attaching the fins and then using inferior layup techniques for stiffening. If you're not using aluminum brackets, then you need to do tip-to-tip and somehow apply aluminum protection on top of that. Paint will help, but only a little.

The only "waffling," WAS between using brackets under the fillets or not. YOU even commented on the post that I stated that. It is post #61 of Here.

Thats been my whole dilemma Carlo… I have been wanting to get away from doing t2t by supplementing the brackets in place of t2t. I spoke with someone who raised concern about it not being able to survive a angle of attack without t2t. I personally had a worse case scenario of 5 degrees. I decided to plan for a worse (possible worser case?) scenario I might as well just lay it up with a couple layers. I honestly want to do it without the t2t. I am internally stuck at this point. But if I do go without t2t I will probably go with CF for the core.

 

[A5tr0 An0n]

Just out of curiosity, how would these brackets be attached to the airframe? I can understand a bracket attached to the airframe and to the fin with bolts or by welding. What's the process with a composite tube?

Jim

Jim

Drilled and tapped into the fins and AF. Everything is ~3mm+ where the bolts will go.

 

[CarVac]

Just out of curiosity, how would these brackets be attached to the airframe? I can understand a bracket attached to the airframe and to the fin with bolts or by welding. What's the process with a composite tube?

Jim

Jim

Mad Max had countersunk holes drilled on the inside of the airframe, letting the fin be bolted down, and anchored to the inner layers of the tube, preventing delamination. That way, the loads would be compression in one fillet, tension in the bolt, and not much in the other fillet.

 

[A5tr0 An0n]

Mad Max had countersunk holes drilled on the inside of the airframe, letting the fin be bolted down, and anchored to the inner layers of the tube, preventing delamination. That way, the loads would be compression in one fillet, tension in the bolt, and not much in the other fillet.

Yes, I was thinking of something along these lines.

 

[BLKKROW]

Yes, I was thinking of something along these lines.

Can I ask when you plan on building/flying this rocket?

 

[A5tr0 An0n]

Can I ask when you plan on building/flying this rocket?

Yes you may.

https://www.rocketryforum.com/showthread.php?65113-98mm-Min-Dia-L3-Build

 

[BLKKROW]

I have read your other thread and did not see the date you wanted to fly. It just seems you are jumping into a build with out doing a lot of research.

I know you don't want to hear that and I know I am no expert. I can only speak from what I have read and what I have studied. If I recall correctly you are a engineering study like myself and as an engineering student I like how you are approaching the problem. I just feel like you can research a little more and study into previous rockets that have flown.

 

[butalane]

*cringe*
Have you done considerable research into other N5800 flights? A while back James D shredded a mongoose 98 on an N5800. It had solid .25in carbon fins and 4 layers of T2T. Mach 3.7 (or there abouts) had no problem pulling them off. I strongly urge you to reconsider your fin plans. Go with solid carbon fiber (as I recommended earlier), with a high TG laminating epoxy (look at Cotronics 4451), 4+ layers of T2T (possibly triaxial) and a high heat coating. Dont cut corners on poor fin materials.


Alex

 

[A5tr0 An0n]

I have read your other thread and did not see the date you wanted to fly. It just seems you are jumping into a build with out doing a lot of research.

I know you don't want to hear that and I know I am no expert. I can only speak from what I have read and what I have studied. If I recall correctly you are a engineering study like myself and as an engineering student I like how you are approaching the problem. I just feel like you can research a little more and study into previous rockets that have flown.

I find it hard to believe that you read my thread (in detail) and have stated this. I specified the launch in the FIRST sentence. I have looked into a lot of past flights and I have thought about this for more than a year (although not in such detail the entire year). I was planning on this flight launching last year, I am glad I did not. Furthermore the only aspect that is still TBD is the fin attachment, per se. This is the point of this thread for me to play around with various "subjects," while under static load to determine which is the best mixture to use for this flight.

So what do you think needs further research? It would help me out to hear your opinions.

 

[JimJarvis50]

Yes, I was thinking of something along these lines.

So, you would tap the airframe and screw in the bolts from the outside, not going past the ID of the airframe? Whereas Mad Max came from the other direction? Sorry for my ignorance on this concept.

Jim

 

[A5tr0 An0n]

So, you would tap the airframe and screw in the bolts from the outside, not going past the ID of the airframe? Whereas Mad Max came from the other direction? Sorry for my ignorance on this concept.

Jim

No, ideally from the inside. I think that makes a little more sense to me.

Also Jim, on a more personal note I have not yet had time to go to the post office. I should be able to tomorrow.