Vinylester question

Maybe if you were going to compare two different types of foam you would use similar specs. Divinycell H100 is a 6.3 pound foam. CoreCell A550 is a 5 pound foam. Why did you not compare H80 to A550?

H80 is a 5 pound foam

H80's shear is 138 and H100's is 193.

Just curious?

Originally Posted by tgundberg

Okay, looks like mr. War Whoop needs a little course in sandwich construction.

First, lets look at strength. If something is strong enough to take a certain load, it doesn't break...right? In sandwich construction, the preferred mode of failure for core materials is shear when in flexure. A crosslinked PVC foam (Divinycell H100) has a shear strength at yield of 193 psi. A similar density SAN foam (Corecell A550) has a shear strength of 164 psi. This means that the PVC foam can take more load (stress, psi) than the SAN before it fails, also known as being stronger in shear. The only difference is failure mode. X-linked PVC fails in a brittle manner, SAN in a ductile (or plastic) manner.

Next is stiffness. In sandwich construction stiffness is measured by the flexural rigidity of the cross section, not just the moment of inertia. Flexural rigidity, D = EI with I = Moment of inertia and E = Elastic (or Young's) moduli of the materials. The moment of interia is created by the geometry of the cross section, or basically how thick the section is. In sandwich construction, this I component is produced from the distance between the skin layers' neutral axis. If this is comprimised, the stiffness of the geometry is also.

The E component is based on the elastic moduli or basic stiffness of the materials in the sandwich. For the core materials, this component is shear modulus. A PVC foam (H100) has a shear modulus of 5800 psi. A comparable SAN foam (A550) has a 5130 psi shear modulus.

When the sandwich as a whole bends, two types of deflections occur, bending and shear. The bending component is due to the skins actually bending with their neutral axis distance being kept constant. The shear deflection is due to the core material shear stiffness. Basically, the lower the shear stiffness of the core, the more it will deflect in shear. When it deflects this way, the distance between the skins neutral axis shortens and the stiffness again decreases.

Again, the PVC foam is able to take more load and deflect less than the SAN foam before failure. Please refer to "The Handbook of Sandwich Construction" by Dan Zenkert if you don't believe me.

As for slamming loads (the main reason for impact tests), these can be designed for with suitable dynamic data (such as Heller and Jasper's work on boat hull wave slamming). Hitting 3" wide sample laminates with a hammer does not replicate waves pounding on a boat hull. In hulls you have large panels which take up the energy of the impact so if one does run into something pointy, the result is a local puncture and not a total delamination. I seem to recall a Divinycell cored boat have another boat run into it in open sea, and it was the competitors boat which suffered the most damage (by the way, that boat, the Illbruck won last years Volvo sailing race AND was completely made with prepreg).

After all this, SAN or PVC, an offshore powerboat hull can be and has been built with either core and perform well, personal preferences aside. Just because someone's been drinking Johannsen's kool aid for so many years doesn't mean PVC foam is crap.

Also H80's shear modulus 4495.

He did not go that route because he is a Tech for Diab:
divinycell

[Anthony DeLima]

Hi

I've tried to gather info about Vinylester. I know of projects using it w. handlayup and no hightemp curing. On the net I've read that to get the most of vinylester it needs heat during curing.

Since I'm trying to gather information for my first larger project I've decided that the difference in cost between the available resins Vinylester seem to be the choice for me. But does it have the extra qualities I'm seeking (water restance and strength) if I don't use heat for curing.

How des the temp affect the material?

Anyone with good information?

Thanx

2 Years ago I presented a paper on the cure kenetics of VE resins. First off the Dow Derakane manuel is a very good place to start. At first you will notice that the curing of a VE resin is no laughing matter. The degree of cure is directly related to strength development and durability. In every case with a room temperature cure regardless of the promotion package and catalyst we did not acheive the published Tg 2's (in fact we were not even close). Truth be told the published figures were probably based on elevated temperature cured coupons. So the long and short of it is that you are welcome to a copy of the paper I would be glad to send it out as an e-mail attachment.
Thanks Tony@forterts.com

The reason he did not compare H80 with A550 is because the density of H80 is 5 pcf (min 4.5 pcf). A550 has a min density of 5.7 pcf according to ATC's literature. H100 is a 6.25 pcf foam with a min density of 5.6 pcf.

Yes and it should be noted that both companies tested on their own using slightly different test methods. These were NOT results by independent study comparing both cores at the same time using identical method of testing.

So you cannot fairly compare using one companies figures against the other.

[Theo]

Cores are preferences of the manufacturers. But as the best under impact and compreson balsa seems to be the best. Just make sure water doesnt get into it. Under infusion all the airvoids should be sealed with resin. Different strokes for different folks.

All this talk about cores.. My current boat is 1982 fiberglass. Its not cored in the hull, its solid glass and gives me zero trouble. The decks are glass and have no core foam material. By viewing, it appears to MAYBE have wood on the decks in between the outer layer and inner layer of mat within the boat itself. No place on the deck is squishy, cracked, leaky or other. The reason I suspect some wood in the decks is the house and flybridge have a layer of wood. Several holes have been drilled and I can see wood in there, in between layers of glass. So yes htere is some amount of water infusion into strutures that has not manifiested any type of issue in 22 years... I guess if I drilled holes every 2 inches many years ago I might maybe have to fix the rot, maybe?

My quesiton then is why would you want or need to use core material. Seems to me that there is much debate over something that is not needed and can apparently cause issues. What is it I am missing here.. What are advantages of any core over good old glass layers and a small amount of wood for structure? Or for that matter, just plain layers of glass.

James

[Vanbokklen]

Did anyone save that pdf by sp systems that Jeff posted in this thread? The number two post in this thread?

[zerogara]

This has been one of the most informative threads I've seen on this forum. All this talk about testing made me think of why and why not lab testing is appropriate. Laboratory work by definition is aimed into simulating an isolated system from real life and measuring variables and analyzing to deduce some facts, support a theory compare ....etc.
Impact testing: Slaming on waves on a boat's bottom is not the same as taking a hammer and slaming it on a piece of composite. Yes and no, I think.
What if the hull was of a model and it had a total surface of 1 sq.foot and the testing hammer has also 1 sq.foot? So size is of the essence.
What does it mean when one takes a 1/2 sq.inch hammer/rod and exerts pressure on a laminate? Depending on the method of lamination, thickness etc. there is a minimum area that is affected by this pressure on that 1/2sq.in point and from that point on the effect of that specific pressure and/or impact is negligible. Or the moments reacting to the force become neglidgible from some distance away. Is the material on the edge of your transom really affected by a rod carrying a 50lb force on near the bow? Not really, but 10" away there are measurable reactions. And I'm not talking about a 10" model again but let's say a 30' boat. Impact is also different than force/pressure on a surface. It has to do with energy absorption.
The hammering test might be usefull to figuring out how the hull would react to impact with a floating or submerged object, not of wave slamming. Helmet testing is all about energy absorption and not total surface pressure.

Just some loose thoughts from reading through this great thread.

There is MORE than one thinks that can NOT transfer from physics and laboratory environments into creation and real situation testing. Computer modeling has speed up the circle of design. producing. testing.failing.redesigning.....etc...etc..
Design, build, break, go back and do it better...
Imagine the fool that designed a boat, had it built to every detail, packed it all with a year's worth of supplies and took off to go around the globe and break a record.

That's the fun of it all.

[War Whoop]

We use drop hammer testing ,a by product ot that will tell you good news or bad! like the If's you can reach the dock in event of mishap!

[OldYachtie]

http://www.reichhold.com/docs/bullet...(33375-30).pdf

Reichhold makes a vinylester resin designed for room temperature cure. It is Hydrex HF100, and its elongation to failure is 3%, compared to maybe 2% for polyester resins. In general, its properties seem typical for vinylester resins. It is quite low in viscosity, and is meant for vacuum infusion.

Re vinylester curing temp: Does this difference reduce over time? 176 degrees farenheit (or so) is a pretty high temperature for a boatshop. Talk about a sweatshop. But hey, it isn't the heat, its' the resin fumes, right?[/quote]

[mcollins07]

Originally Posted by Guest

All this talk about cores..
My quesiton then is why would you want or need to use core material. Seems to me that there is much debate over something that is not needed and can apparently cause issues. What is it I am missing here.. What are advantages of any core over good old glass layers and a small amount of wood for structure? Or for that matter, just plain layers of glass.

A composit gives you much more strength for the weight of the material. If you have a 1" layer of core glued between two 1/4" layers of fiberglass it will be almost as stiff as 1.5" of fiberglass. The compresability is closer to the compresability of the fiberglass than to the compresability of the core material. Overall it is a much stronger material with much less weight. The ratio of the thickness of the core to the thickness of the shell (fiberglass) is critical to optimizing for the properties you want. For something like a boat, you might choose to have a thicker shell layer on the outside than on the inside. This would increase you impact resistance from the outside, but only provide a stiffness close to a liminate with two shell layers of the smaller thickness. So, you can tailor a composit to get the optimum properties for the amount least amount of matrials, cost, and weight.

In regard to using plywood and keeping it simple, using plywood as a core matrial is a very reasonable choice for a home built boat. The plywood is easy to work with, the builder is usually already familar with its properties, etc. Laminating the wood with expoxy gives drastically improved properties over just the wood. If you are trying to create a racer, this is probably not the best choice, because your core matrial is probably heavier than your competitors.

Hopefully this gives you an idea of how to use the concepts and you can review literature on the Modulus of Elasticity to work out numbers.

Michael