Structural panel bulkhead joining question.

The duflex panels seem to work, from memory strength is about 80-85% but the aspect of stiffness through the join area is very similar. Duflex as a product has never really impressed me, the use of 8x4 units enhances transport & great for the marketing of "kits" but is pretty subby to doing full length panels, the dryish laminates although apparently "acceptable" to the market are flawed to the standards imposed by my training, Groper- your infused panels appear to be of a much higher standard than what I've seen in duflex, your proposal of a bonding flange including your inner skin continuity seems pretty convenient especially if the bulkhead is already fitted(which I'm sure it is), Michaels point about avoiding the bulkhead is valid & standard practice- I remember from some metal builds a plating join usually falls outside of 150mm from transverse framing/bulkheads, which ever you do, some "ribbands" or battens will help with holding each panel fair till things set up. Seeing as your the designer & builder it's up to you in the end to make the judgement. All the best from Jeff.

 

Thanks Jeff, i held the same opinion - which is why i didnt use duflex for my build, it would have been convenient otherwise...

im a little facinated by the jointing methods and why they work or fail... if anyone has any examples of failure modes on these type of joins, please post them!

 

There might be something here...
http://www.google.com/search?num=10...0.116.964.12j1.13.0...0.0...1ac.1.qLLCRZtmbq4

In your original post, as a pure guess, I can imagine that without an inner blue tape to make a continuous green skin, that forces might cause shear and buckling of the inner green skin(s) which could result in the bulkhead splitting down the center. An inner blue tape would make for a continuous inner skin and would also tie the two tabbing flanges of the bulkhead together.

If there was a big load like a collision put on the hull between bulkheads, that would put the inner skin in tension. If that tension can't be transferred across the butt joint by an inner tape, it seems it couldn't do anything else but pull on the tabbing flange and split the bulkhead.

The weak point would seem to be the edges of the panels as I wonder if there is actually any fiberglass there. Especially at the corners where the edge and faces meet. If there is glass on the edges, I can't imagine it's tied into the face skins with much continuity of strength.

 

The weak point ---My God you could pick the boat up with a crane with this bulk head and shake it like a dog with a rabbit and it would not fail.

 

Imagine this joint without a continuous inner skin...





http://www.sciencedirect.com/science/article/pii/S0143749610000199


.

 

Tunnos, there's really no comparison between your spanish gel/coremat/450 chop boat & one built from duflex. The manufacturers of duflex have done heaps of testing & there's Schionning, Oram & others catamarans with plenty of miles on them over a decade to prove the material. http://www.atlcomposites.com.au/atl_composites2/products/composite_panels/duflex Here's a link for you. Jeff.

 

Interesting paper sam.

This is ostensibly a WTB to hull connection issue. The problem occurs with the overlap, linking the 2 out of plane surfaces together. There are those that “overlay” this in thinking it is beneficial and providing better structural support. It is not without merit. However, the flexibility of the joint is just as important as the strength. Remember, Composite structure has a low modulus, thus these structures are deflection driven, not stress driven. Since if the overlaminate is too thick (as most seem to do) the joint is too stiff creating high through thickness stresses at the corners and it delaminates and upon further loading the layers delaminate from the unsupported fillet.

Trouble is to successfully design this characteristic into the structure/joint a structural “hard spot” is to be avoided. So with WTB type connections what is best, flexibility or strength? The strength being the thick overlaminate or the flexibility which yields a much thinner overlaminate. To effectively transfer this out of plane load the overlaminate and the radius are important. The goal being to have the through thickness and in-plane stress being equal.

The problem with having an overlaminate that is too thick is that it is stiff, too stiff. High through thickness stress are created at the corner and delaminates, from the fillet. But all the time the in-plane stress is lower in the overlaminate. So the objective is to increase the in-plane stress and the stress at the fillet.

So just adding too much overlaminate makes the whole joint too stiff, thus reducing the deflections and through thickness stress. But all this does is reduce the in—pane stress and the fillet stress. It also transfers the “hard spot” from the fillet to the structure.

To prevent this it is desirable to have a thin overlaminate so that it bends (flexible) and can transfer the load into its in-plane direction. Because it is now flexing the through thickness stresses are lower than if stiffer. Thus, having an increase in the fillet radius assists in providing more leverage, or stiffness, on the joint, even though it is thinner.

So it is all about the compromises with the 2 principal variables for WTB-hull joints, that being the overlaminate and the fillet radius.

This has been highlighted with experimentations and analysis in the paper “Experiments of Top-Hat-Stiffened panels of Fibre-Reinforced-Plastic Boat Structures” by Prof Shenoi et al, in Marine Technology, January 2007. It provides excellent guidance to address this dichotomy of strength versus flexibility.

 

Thank you for the post with the info !!

Ok now i understand how it all works .
If the person that started this thread had read and absorbed the instuction sheets and fully understood the technology this thread really should not exsist and should never be asking such questions !!! the information is all there !! just reread the process and do whats written down .

I missed that 2000 issue of Professional boat builder magazine !!
Its west system so it must be good stuff , and if you look closely at the joining theres more to it than first meets the eye when you look at the cut join and see how its actually done . very clever !!and deffinitly no room for any sort of error and she'll be right mate attatude !!
Like i said you should never have had to ask any such question . its all there in black and white on paper or on the screen !!

 

Given your statement here in red is exactly why the questions should be asked & it's how a forum should be working......... then we can all learn. Jeff.

 

AdHoc,

Thanks for a well written and explained approach, we can all add our own "thoughts", and of course they are relevant from experience, but your answer is an explanation that we can all understand and most importantly, comprehend.

Thank you.

 

Ad Hoc, I see your fillet made of 'crestomer'. Can we assume that the boat is(was) made of Polyester laminates?
In this thread I found little attention towards the building material. Are we only talking about Balsa-"Duflex" (ATL) and only about bulkheads, or are other cores i.e. foam or even Honeycomb and locations under consideration as well ?
I see the fillet on the drawing with 12 mm radius, which is in conflict of what I hear from other sources.
In epoxy building we usually use a blend with fibres (high density) or with microspheres (lower density). >I took the words from WEST system terminology - no copyright offense meant <
but the radius usually is asked to be at panel thickness. Cover laminate then is about 150% of the panel face laminate with a widened overlap.
Would you have links or own views to share here, please?

 

Well: We have some boats around here that are made like this (so-called Z-joint). And they do not break - so it cannot be wrong.

From the engineering side I can agree to the method. We presently make one boat like this, only with PVC core.
If the joints fail, then rather from production mistakes: - A milled joint can be broken while moving the panels in the work shop. The joint method may fail because of misalignment or insufficient contact. Also the 'Z-press' mentioned needs to be well aligned and maintained.
Personally I am not too happy with interrupted fibres along a joint line and for panels with higher loads in the plane I would rather add a continuous additional layer after joining or at least a tape to bridge. And lastly I agree to all comments before: Never ever to join panels on a b'head without continuous laminates.

 

The hull structure, for this catamaran was made from:

Woven SP RE295 and S14EB490 using Reichold Dion 9102 resin.

 

Resin info

DION® 9102 SERIES Bisphenol-Epoxy Vinyl Ester Resins

http://www.reichhold.com/documents/904_DION9102SERIES.pdf

 

Yaaaay - Tunnels mastered Google !!!

Well done you technocrat