Honeycomb fatigue

I will appreciate if only PROFESSIONALS reply to this topic
From a knowledgeable friend I received a confusing information that honeycomb laminated hulls are not long lasting in hot climates like i.e. Saudi Arabia.
I have never before heard of such problems and so I wonder what may be the reason.
Anyone out there to comment, contribute or to discuss?

 

honeycomb panels fail in slightly different ways to "normal" cores. Since normal cores are just basically isotropic (foam) or orthotropic (woods). Honeycomb can fail under:
1 strength
2 stiffness
3 panel buckling
4 shear crimping
5 skin wrinkling
6 intra-cell buckling
7 local compression.

Normal cores are basically the same as 1,2 and 7 in terms of failure/strength modes.

However what this, and 'normal' cores come down to, is always the bond between the core and the skins, no.s 3,4,5 and 6, and with 'normal' composites this depends on what skins are being used too. This is where most failures occur, this layer of bonding. However once this occurs in a honeycomb panel, it may not spell the end of the member as it would do in other cores. Since there is a degree of redundancy which generally does not exist in other types.

So long as the honeycomb is good quality (fit for the job) and the method of manufacture is well documented with proper QA procedures used, then the fatigue should be as good, if not better in some cases, than standard composites. Such as good old hexel 3003

But, as with everything fatigue related, it is not a one liner reply. Many aspects need to be considered, such as: adequate shear paths, load transfers reducing stress concentrations etc etc. For 'all' composites the production methods and QA or lack of QA has more of an influence than any other 'issues' related to whether the material being used is adequate.

So, if in a hot climate, the main point of discussion will be the bonding adhesive between the core and skins, is this suitable for high temperature environments. If so, case closed!

 

Hakim, good to see You here

Good test before using a HexaCor-type honeycomb is to try peel-off surface fabric. Some cheap honeycombs are very easy to peel-off and this will lead to delamination in future.

Another issue is heat resistance, I expect most of polypropylene cores are limited to 60C. Don’t paint Your boat in black, OK?

For shear strength HexaCor is compatible to foam cores of 60-80 kg/m3 density, but cheaper cores are not.

 

So it is not so much a question of material, but of procedure. I was wondering the same.
In my present case it is about a 55kts power boat, monohull. The appointed material is Epoxy-Sandwich (vacuum, but no infusion) with Hexacor or Nida-core. In the hull bottom it probably makes sense to use crosslinked foam instead of Honeycomb - it should have more bonding surface to the laminate.

 

I knew that I saw your face before

 

You can't use HexaCor or NidaCore on bottom of planning boat desigend for 55kts. It does not comply for shear strength, even high-strength grade.

Only foam of 130-150 kg/m3 density minimum, Airex R63 being the best solution.

 

Like everything in structural design, too many variables gives too many answers.
Airex 63.5 has a density of 60 kg/m^3, whereas R63.140 has a density of 140 kg/m^3.

So to say it does not comply for shear strengths only has meaning when the applied loads have been determined and hence what load paths are required to shed said loads. This is also subject to the way the structure is arranged. Just as in any boat. So i wouldn't say cart blanche not to use it, just "design" the structure first, then see which material is best suited.

 

2Ad Hoc,
There is no sence to use Airex of 60kg/m3 (cost!), I am talking about R63.140 that is 140 kg/m3, it is flexible and is developed for high-loaded areas.

For honeycombs - from the experience we have every day designing different types and size of boats I can guarantee that it will not comply for shear strength on the bottom of 55kts boat (unless we are talking about small tender).

 

Alik

I'm not disagreeing with you. But without more detailed information on the boat its size, how the structure is arranged what duty the boat shall be, or expected life, detailed structural design etc etc...i cannot say 100% for sure "..that it will not comply for shear strength on the bottom of 55kts boat..".
Just need more data, or rather, as i said...need to design it first then say yah or nah.

I just don't like the presumptive method of "design". I prefer to do it all from first principals and see what does or does not work afterwards, not before, that's all.

 

2Ad Hoc
You are right. Actually we do not need to worry in this particular case, all boats they claim to build for 60kts finally deliver only 12kts

 

Doh!

 

Ha Ha Haaaah!
I am happy to say that I was NOT involved in the hull design of that case!
(If so, I would rather have consulted Albatross design - anyone knows that company?)

My present investigation is about a remake of a 1972 speed boat with a designer then who knew what he was doing...

 

The boat in question HERE is 13.70 m with Lcwl 10.6 m and Bmax 2.9 m. In 1972 there were two Cummings 350 HP in it with a weight of 7.6 t. The idea for 2010 is to have it lighter and faster. Previous company hobby-designers are excluded from the project!

 

Hakim, I know that was not You, that was another guy

 

I know that you know. Actually all Thailand knows and this is HIS problem