The effects of a foam core?

[General Specific]

In a composite board with a foam core what property does the foam give the board, and how? Airex foam has little strength and does not accept resin but is fairly rigid with tight bubbles, the only way i could see it helping is the walls of the carbom/glass/whatever around the core acting as load bearers. I made a carbon/glass deck with a Merbau vertical lam core, the wood carbon combo makes the deck stronger than a drunken irishman while being only a few mm thick. How does foam add strength?

[shapeshifter]

it doesn't. the purpose of the foam core within certain structures is to maintain the shape of the outer shell and doing so with the least amount of additional weight. the core simply acts as a space filler. in such structures all of the properties desired from a deck resides totaly in this outer shell.

[Mikejnr]

it doesn't. the purpose of the foam core within certain structures is to maintain the shape of the outer shell and doing
so with the least amount of additional weight. the core simply acts as a space filler. in such structures all of the properties desired from a deck resides totaly in this outer shell.

If all the cores does is hold shape why not use the composites to do this, and totally remove the core. the foam wouldnt
have either torsion or tensile strength so it servers no purpose in structural applications. i can see it helping in compression
a little bit but the foam is still much weaker than the shell.

the carbon/glass can hold shape it has both tensile and torsion strength, so why not make just straight composite boards without cores?.

[akary]

the thicker the core is, the stiffer the deck is for the exact same composites.

that extra thickness puts more leverage on your glass, bamboo, CF, maple, hickory, or whatever, progressively more toward the top and bottom layers. the core material itself has almost no bearing on stiffness, but foam cores that are not scrimmed can crush if they take a lot of abuse.

the length between trucks also affects spring. long length puts leverage on the deck and flexes it more.

the thin deck with more fiberglass than the thick deck that is as stiff as the thick deck will be much more springy (sorry about the awkward sentence). the thick core also dampens the ride, and this is more noticeable with inelastic core materials. this the thin slalom decks and beefy bombers.

there's a math formula for this, not that anyone wants to learn math in their free time.

[coopaloop]

The foam core in many other applications is actually removed, such as bike frames. If you were really hell bent on shedding the weight of your board, you could use a chemical to dissolve the inner core and leave you with a skateboard just as strong, but a few ounces lighter.

[shapeshifter]

it doesn't. the purpose of the foam core within certain structures is to maintain the shape of the outer shell and doing
so with the least amount of additional weight. the core simply acts as a space filler. in such structures all of the properties desired from a deck resides totaly in this outer shell.

If all the cores does is hold shape why not use the composites to do this, and totally remove the core. the foam wouldnt
have either torsion or tensile strength so it servers no purpose in structural applications. i can see it helping in compression
a little bit but the foam is still much weaker than the shell.

the carbon/glass can hold shape it has both tensile and torsion strength, so why not make just straight composite boards without cores?.

yeah, that's kind of the reason why i have moved away from the foam core designs. some rigidity is good but at the same time a bit of flexibility is desired when designing a core... there's definitely a balance to achieve otherwise you wind up with something too stiff, akin to a lifeless log. don't get me wrong, foam has it's virtues, closed cell means it won't accept (much) water which is advantageous in water (snow) sports, granted in skateboarding this isn't a huge issue. if i were to make now it would be hollow with arched beams running down the length of the deck like a synetic structure. the process of assembling this precludes vacuum pressing or high pressure which leads one to reassess current manufacturing methodologies.

wish i could get back to building boards but right now i'm busy setting up production for something totally different yet skating related.

[THOR-ONE]

if the strenght of the core doesn't matter at all then why should a regular pink/blue insulation foam not be used?

as well, what about that core-cell foam that has perferations in it? wouldn't those holes help create an internal resin matrix adding strength?

[Iron Chef]

I could see it being advantageous right around the bolt holes, but other than that, I cant see it doing a whole lot for the structural integrity.

But then, really not a whole lot of reason to remove it.

[brainfartalerts]

if the strength of the core doesn't matter at all then why should a regular pink/blue insulation foam not be used?

It is about distributed loading.
Dedicated core materials are stronger and compress less than insulating materials. Weaken or remove the core material and your skin has to be far stronger in order to maintain shape under point loads (feet, truck base plates, screws, etc...) between supports (edges, ribs, plate mounts) which takes you back to producing a solid structure. You have to balance the strength-to-weight of the surface material against the strength-to-weight of your core.

Iron Chef makes the point about reinforcing the bolt holes in the post following yours and is on the money. Unfortunately, the compression strength of most foam cores does not begin to approach a wood, resin, metal or composite materials so most gear builders will create non-foam hard-points in the mounting areas to keep screws from pulling through.

as well, what about that core-cell foam that has perforations in it??
wouldn't those holes help create an internal resin matrix adding strength?

yes but the stated purpose by the manufacturer is to help provide resin migration through the layup

[THOR-ONE]

i think some of you might be interested in this.

http://boatdesign.net/articles/foam-core/

it explains alot of this stuff pretty well.

[Mikejnr]

so what im getting is the core does:
1) helps distrubute load/loads
2) holds shape
3) helps with impact (compression)
4) requires less labour ( less composite plies )
5) add's minimal strength

but if you have a foam core you need to reinforce the bolt holes with something stronger ( wood, metal, resin )