OF Course NOT! A one inch thick cored deck will be stronger than a solid fiberglass deck of equal weight per square foot.
Which epoxy resin?
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I completely agree with that. I thought you might have gotten into the merlot a little early today.
Pound for Pound not Thick for Thick
I think Ross is saying, not to put words in his mouth that a 1 pound solid layup will be weaker than a 1 pound cored layup. So let's say a 1 pound layup of solid FRP is a quarter inch thick, and a 1 pound cored layup is an inch thick with 3/32 on each side of FRP and the rest some kind of coring. Putting a beam of each into bending that the cored beam will support more weight (bending puts the top in compression and the bottom in tension and the neutral axis in pure shear).
I am just reading about a new potential coring material called Nida-Core that is a fibre reinforced foam material. Sounds very promising for light weight and high strength, plus the foam to resin strength is well understood by industry and the added resin as part of the foam should increase strength at the interface greatly. Might be worth considering if you have a deck delamination project to deal with.
I think Ross is saying, not to put words in his mouth that a 1 pound solid layup will be weaker than a 1 pound cored layup. So let's say a 1 pound layup of solid FRP is a quarter inch thick, and a 1 pound cored layup is an inch thick with 3/32 on each side of FRP and the rest some kind of coring. Putting a beam of each into bending that the cored beam will support more weight (bending puts the top in compression and the bottom in tension and the neutral axis in pure shear).
I am just reading about a new potential coring material called Nida-Core that is a fibre reinforced foam material. Sounds very promising for light weight and high strength, plus the foam to resin strength is well understood by industry and the added resin as part of the foam should increase strength at the interface greatly. Might be worth considering if you have a deck delamination project to deal with.
You got it right! sandwich constructions are continous "I" beams. A 3 ton solid square bar 30 feet long would be a far better bridge beam if it were rolled into an "I" beam.
Boat builders have been trying different core materials from the beginning. many of the early open fishing boats had corrogated cardboard used as stiffeners soaked with resin and covered with glass cloth.
Right after my last post yesterday I went to the shop and cut some plywood and some fiberglass tape, mixed some polyester resin and put them together.Today when I got home from work I peeled the glass tape off the plywood with this result.
Attachments
Which is why most of the books recommend using EPOXY resin for structural repairs... since the secondary bonding (adhesive) characteristics of epoxies far surpass that of the polyester or vinylester resins.
Mythbusters
Great television show. I saw one a few weeks ago where they made a boat out of old newspapers that they molded wet and then froze. They then mounted about a 40 HP motor on the thing and took it for a ride. It actually worked. They drove it around for a while then it started to melt and sink so they got it back to the dock. Why not just coat the newspaper with epoxy and you'd have a real boat?
Great television show. I saw one a few weeks ago where they made a boat out of old newspapers that they molded wet and then froze. They then mounted about a 40 HP motor on the thing and took it for a ride. It actually worked. They drove it around for a while then it started to melt and sink so they got it back to the dock. Why not just coat the newspaper with epoxy and you'd have a real boat?
Dog, the other result observed is that the polyester bond and the strength of the glass is approximately equal. The resin pulled off the plywood in some places and off the glass fabric in other places. This was a peel loading so the most severe that can be imposed. I am sure that with epoxy the glass or the plywood would have failed. If the load had been in tensile or shear the bond would have stayed intact and the glass would have failed for the simple reason that the cross sectional area of the glass and the bond area favor the bond. Duck tape does wonderful things but it does peel off also.
Just tested the epoxy, fiberglass on plywood. The epoxy adhered very well to the plywood but the fiberglass peeled off the epoxy with a little more force than from the polyester. The peeling force was 90 degrees to the plywood. I would use either resin for a repair depending upon what I had on hand.
Testing and ASTM
Just curious if these test methods meet ASTM standards. Also can you run some fatigue tests on your samples so we can see how each will perform when subjected to millions of reversing stress application to duplicate the effects of waves hitting the boat over thousands of miles of sailing? You may also want to run tests on the notch sensitivity of each sample to see the effects of installing through hull fittings in the area of repairs.
Isn't there well documented industry information on the strengths of these kinds of joints?
Just curious if these test methods meet ASTM standards. Also can you run some fatigue tests on your samples so we can see how each will perform when subjected to millions of reversing stress application to duplicate the effects of waves hitting the boat over thousands of miles of sailing? You may also want to run tests on the notch sensitivity of each sample to see the effects of installing through hull fittings in the area of repairs.
Isn't there well documented industry information on the strengths of these kinds of joints?
Re: Testing and ASTM
Dave, These are sample made just as you or I will will make repairs.
I am completely familar with ASTM having been a member for many years and no they won't meet any standards of repeatable test methods. I can't even quantify them. I have read hundreds of pages concerning fiberglass/resin constructions. Vinylester resins are used for aircraft skins. Thousand of boats have been built with polyester resins and thousands have been repaired with polyester resins.
My question was: Is epoxy of such superior bonding strength that polyester resin should be forgotten? My conclusion is simply that epoxy is better but that there are enough variables in field repair work that the superior qualities of epoxy will not be the pass/fail reason for a repair. Poorly done work with epoxy will not be compensated by the superior qualities of the resin. Properly done repairs using polyester resin will last as long as the rest of the vessel.
My conclusion is that if you are more comfortable using epoxy then do so. But there is a limit to just how strong the repair has to be. That limit is defined by the strength of the surrounding material.
Dave, These are sample made just as you or I will will make repairs.
I am completely familar with ASTM having been a member for many years and no they won't meet any standards of repeatable test methods. I can't even quantify them. I have read hundreds of pages concerning fiberglass/resin constructions. Vinylester resins are used for aircraft skins. Thousand of boats have been built with polyester resins and thousands have been repaired with polyester resins.
My question was: Is epoxy of such superior bonding strength that polyester resin should be forgotten? My conclusion is simply that epoxy is better but that there are enough variables in field repair work that the superior qualities of epoxy will not be the pass/fail reason for a repair. Poorly done work with epoxy will not be compensated by the superior qualities of the resin. Properly done repairs using polyester resin will last as long as the rest of the vessel.
My conclusion is that if you are more comfortable using epoxy then do so. But there is a limit to just how strong the repair has to be. That limit is defined by the strength of the surrounding material.
FRP Applications
Unfortunately FRP is less a science then we might think. The announcement this week that Boeing was delaying, again, their first flight of the dreamliner is cause for concern to all FRP boat owners. The reason for the delay? Unexpected stresses in the root of the wing connection in the carbon fiber fuselage of the structure. In simple terms they discovered stresses on strain gages during testing that their zillion dollar solid models and FEA programs did not predict. Now as any boat owner knows, you can not just reinforce those areas as it may create a stress concentration at another point, so my gut feel is a major effort will be required to redesign and remodel that area of the aircraft. Very bad news for Boeing, 3 Billion dollars of orders cancelled in the last few days. So if big old Boeing with godzillions of engineers and money for testing can't figure it out, then we don't have a chance. Ross in his little old garage and his hunk of plywood is doing real live emperical studies that maybe Boeing should consider instead of putting all their faith in computer programs. The best designer I ever knew would never make anything with a radius smaller than his thumb, after he left all the high flying BYE's (bright young engineers) had recurring failures as they trusted to their computers versus real life experience. Nice test Ross, keep up the good work! In fact it reminds me of glassing the bottom of my sailing dinghy. The bottom was a flat sheet of plywood. I used West system and woven cloth, looked exactly like your test.
Dave
Unfortunately FRP is less a science then we might think. The announcement this week that Boeing was delaying, again, their first flight of the dreamliner is cause for concern to all FRP boat owners. The reason for the delay? Unexpected stresses in the root of the wing connection in the carbon fiber fuselage of the structure. In simple terms they discovered stresses on strain gages during testing that their zillion dollar solid models and FEA programs did not predict. Now as any boat owner knows, you can not just reinforce those areas as it may create a stress concentration at another point, so my gut feel is a major effort will be required to redesign and remodel that area of the aircraft. Very bad news for Boeing, 3 Billion dollars of orders cancelled in the last few days. So if big old Boeing with godzillions of engineers and money for testing can't figure it out, then we don't have a chance. Ross in his little old garage and his hunk of plywood is doing real live emperical studies that maybe Boeing should consider instead of putting all their faith in computer programs. The best designer I ever knew would never make anything with a radius smaller than his thumb, after he left all the high flying BYE's (bright young engineers) had recurring failures as they trusted to their computers versus real life experience. Nice test Ross, keep up the good work! In fact it reminds me of glassing the bottom of my sailing dinghy. The bottom was a flat sheet of plywood. I used West system and woven cloth, looked exactly like your test.
Dave
I enjoyed the discussion my little question invoked. That is what I love about this forum. Anyway, the clear epoxy and hardner came a couple of days ago. Hopefully this week I will get to try it out while repairing the rot in the deck at my chainplates. The pumps look a little cheap. That my be the weak link. I will post the experience
thanks
keith
thanks
keith
http://cgi.ebay.com/EPOXY-RESIN-BOA...66:2|39:1|72:1205|240:1308|301:1|293:1|294:50
I liked this epoxy. I thought the video sales pitch was very convincing. I emailed the guy that mixes this stuff a few times. We had an interesting discussion about the existence of God, then I bought his epoxy.
No pumps came with it. But I was mixing 8oz. at a time. If you are laying it on fast you can get that much down before it starts to gel. That's when it was 90 degrees outside. Now I would have to mix less. I paid $40 a gal. This particular link is 2 gal. for $80.
I liked this epoxy. I thought the video sales pitch was very convincing. I emailed the guy that mixes this stuff a few times. We had an interesting discussion about the existence of God, then I bought his epoxy.
No pumps came with it. But I was mixing 8oz. at a time. If you are laying it on fast you can get that much down before it starts to gel. That's when it was 90 degrees outside. Now I would have to mix less. I paid $40 a gal. This particular link is 2 gal. for $80.
Hi, Hermit. What type of jobs were you doing with this particular epoxy? I need to cover a rudder, take care of a keel, and patch a hole. Do you think that it could do it all? In addition I would need some fillers, micro balloons, etc. that I saw on the site.
I stripped all the fairing compound off the keel and I added 1/2" to 3/4" thickness around the keel. There is no fairing compound on my keel now, just solid glass and epoxy. The reason I did that is because I don't want anther catalina smile. The adhesion of this epoxy is very good compared to polyester resin. I don't have experience with other epoxies so I don't know how it compares to them.
It is difficult to by polyester resin at the price of this guys epoxy.
I think it would do well for all of the things you are doing with it. From my reading and limited experience with these types of plastics, I think that the surface prep is more important than what type of resin or epoxy you are using.
I see you are in Waco. where do you sail there? Or do you trailer it to a lot of places?
It is difficult to by polyester resin at the price of this guys epoxy.
I think it would do well for all of the things you are doing with it. From my reading and limited experience with these types of plastics, I think that the surface prep is more important than what type of resin or epoxy you are using.
I see you are in Waco. where do you sail there? Or do you trailer it to a lot of places?
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