toughen epoxy

[idkfa]

Been researching epoxies and came across:

Toughened two-phase epoxy, and less tough single-phase epoxy.

A toughen epoxy is a hard epoxy that's not brittle?
And it is always more desired than single-phase for hull laminates? ie. higher elongation?

So a high elongation epoxy can be either hard or soft, and further the hard one will be tough and not brittle, cause it is high elongation?

tks,

[PAR]

Epoxy can be formulated to have just about any set of physical attributes. Without knowing what brand and formulation you are talking about, answering anything about this epoxy you've come across is futile. What is the brand and product number/description?

[idkfa]

Thanks Par, if infer correctly, you are saying a single phase un-toughened resin could have a higher elongation and hardness than a toughened two-phase resin?

Sorry I don't have the specs of either resin, yet. This was in response to my asking a resin formulator (who advertised marine laminating resin) for a higher (80C) temp cure resin. Guess it was expected I would know what was meant.

I'm trying breakdown "toughened" in terms of modulus, shore hardness and elongation? values normally presented, toughness (or brittleness) is not presented as a value and so are general terms? or does it refer more to the "two-phase". ie. Two-phase resins are "toughened" resins?

[PAR]

I'll assume your use of single or two phase resin system terminology, is a room cure or post cure requirement. This is just a hardener formulation difference, though as a rule you can expect better preformance from a post cure product, checking the physical attributes of the cured goo is the only way to tell. Post curing products have been developed to handle specific production and laminating techniques. For example, in a factory, making big parts in a mold, you can lay in a pre-peg product, to the desired laminate thickness and then stuff the mold in an autoclave. This can be done in a dry, fairly neat and clean environment, as you don't have liquid resin being splashed around the shop. On the other hand, how many shops have an autoclave handy when they need one.

[tunnels]

Toughtened !! also mean semi rubberized ??
Have used a special epoxy adhesive designed for hull and deck joins plus the internal keel grid systems that dosent let go and it is a semi flexable epoxy , could be interprated as tough !!!. The peelability is whats important !
is better to move and hang on rather than be hard and break or tear the surface away .

[PAR]

Tunnels, you could be right on some formulations, but it's not necessarily the case that it's rubbery. Again, epoxy can be formulated to just about any set of physical attributes you might desire. You just have to be careful in what qualities you desire.

[tunnels]

Rubbery was the only word i could think of at the time !
The adhesive we used was sort of rubbery because if you tried to chisel it ,it bounced a little and did not cut .Stuck like nothing ive ever used before or since .
For hull and deck joins we had no fastnings what so ever on 36 foot racing yachts , completely round the entire hull including across the transom .
Even a boat that had been tee boned during a race the join never came apart at all , just completely shattered the glass gunwhale and part of the deck and the top edge of the hull , made new bits ,scarf the joins ,and was back racing the very next day like nothing had ever happened . Last time i saw the boat after 4 years it is still going strong as before .

[waikikin]

Originally Posted by tunnels

Rubbery was the only word i could think of at the time !
The adhesive we used was sort of rubbery because if you tried to chisel it ,it bounced a little and did not cut .Stuck like nothing ive ever used before or since .
For hull and deck joins we had no fastnings what so ever on 36 foot racing yachts , completely round the entire hull including across the transom .
Even a boat that had been tee boned during a race the join never came apart at all , just completely shattered the glass gunwhale and part of the deck and the top edge of the hull , made new bits ,scarf the joins ,and was back racing the very next day like nothing had ever happened . Last time i saw the boat after 4 years it is still going strong as before .

Could it be rubber toughened epoxy, I've never used it but was told of it by Rob Denny when he was at Adhesive Technologies in the 80s, apparently used then to glue alu spars together at ZapSpar from distant memory.

http://www.sciencedirect.com/science...32386183900708 ...?

[tunnels]

Originally Posted by waikikin

Could it be rubber toughened epoxy, I've never used it but was told of it by Rob Denny when he was at Adhesive Technologies in the 80s, apparently used then to glue alu spars together at ZapSpar from distant memory.

http://www.sciencedirect.com/science...32386183900708 ...?

Sounds like the same stuff . Its magic and would trust my life with anything held together with it !! It just wont let go

[Steve W]

I used to own a snowboard manufacturing company back in the early thru late 90s and during early prototyping we put boards together with epoxies i had around the shop, it was quite an education really, we used to build multiple board the same but with different resins and then take them to the half pipe, West didnt work at all,we had one board break in half on the first run, Systems Three worked we didnt break those boards which i put down to better elongation, we also tested a Hexel resins which was recomended by a supplier which also broke, we built a lot of boards with a Jeffco epoxy which was specially formulated for press molding snowboards which worked ok but we(and everyone else) were still plagued by poor adhesion to the many different materials at the sidewalls. We eventually settled on a Toughened press mold epoxy from Hardman which was awesome and solve all delam problems. I should point out that snowboards much more difficult to make stay together than anything i have encounted in boatbuilding, they are thin, flexible and are abused like nothing else in sub zero temperatures and come back for more, the epoxy has to bond together wood or foam core with glass laminates plastic tip and tail and sidewalls and rubber foil and hardened steel edges and aluminum tip and tail protectors, uhmwpe bases and various plastic top sheets, all cooked in a press at 30 tons of pressure and 100 degrees c for 8 minutes. Boatbuilding epoxies have an easy life by comparison.
Steve.

[tunnels]

Like i have tried to pointout that all epoxies are not born equal and theres a list as long as you arm of possibles . take a very skilled epoxy person to know what works for what or can point and advise on what you might try for your work .

[idkfa]

The US Navy selected Derakane 8084 resin for hull and deck laminates of the Leadership 44 yachts; high-elongation, high-strength and rubber-toughened - Proboat Oct/Nov 2011 pg 116.

DERAKANE 8084 Resin is an elastomer-modified epoxy vinyl ester designed to offer increased adhesive strength, superior resistance to abrasion and severe mechanical stress, while giving greater toughness and elongation.

Tensile Elongation 8 to 10 %
Barcol Hardness 30

http://www.derakane.com/derakaneCont...uctCode=536004

I would have thought toughened(rubberised) resins, would only be good for hull/deck joints?

True the enemy is ultimately fatigue, but there must be some strength trade-off?

[tunnels]

I would have thought toughened(rubberised) resins, would only be good for hull/deck joints?

Boats need to twist and flex , twist and flex are not the same thing . with flex panels hulls will hold together in exstreme situations , also if a boat twists it will deflect . couple the two together and you have a almost indistructable boat !!so you need a flexable resins but Tough is best !!. Dont want the laminates letting go and coming apart . To go with this what glass would you use ?? anyone want a to take a guess ?

[idkfa]

Uni or stitched triax S-glass?

Toughness has more to do with Flexural strength or Elongation (tensile% as per Derakane doc)?

What i'm getting at is, tensile modulus X elongation = tensile strength. Then if toughness has little effect on tensile modulus then ultimate strength should be little affected?

?Resins (themselves) are isotropic (like aluminium), so elongation should be both tensile and flexural? How is flexural modulus measured? By bending a very thin (one molecule thick) rod of resin?

[idkfa]

From supplier:-

We use so called "second-phase toughening". We add to a composition some component, which is compatible with the rest of resin while uncured, but upon curing it becomes incompatible and gradually separates into second phase. That second phase usually consists of microballs of softer material with diameter 1-20 microns inside of more rigid matrix. The concentration of this second phase is usually 1-5%.

When microcrack starts growing under stress or as result of impact, it hits that second phase and cannot go through it becase of its softer nature. So the microcrack has to go around of that microball losing its energy and stopping its growth.

Such second-phase toughened material has toughness usually 2-5 times higher than untoughened, at the same time almost not losing anything in modulus, hardness and thermal properties (like glass transition temperature, thermal stability, etc.) because those properties are mostly influenced by the matrix, which practically didn't change in this type of toughening.