Ollie, you might want to look at the failure mode of the skin. Obviously stress is going to be M.y/I, but you might want to see if that stress is getting anywhere close to local buckling - this can cause failure well below theoretical compressive strength. Bond strength to core could well be the decider.
devil’s advocate here, but those photos look like the most useless application of carbon fiber imaginable.
Haha Sorry stonburner, and no problem!
Hey Ollie, even though they are giant corpo I think it's safe to assume they generally know what they are doing since they have the dough and quality riders to give feedback on this stuff. From what they told you, it would suggest the pop is NOT coming from the carbon but from the tail area instead correct? I'm wondering how that function would be effected by anything that would stiffen that area, like would carbon on the deck dampen or improve the "POP"?
In response to the info from Benjamin Thompson, the deck strength should be equal to the bottom strength; therefore carbon would be best applied to the deck as well?
Also if you do get a chance to test our stuff I would suggest looking into the "vector net" also which has become a semi-popular alternative to the more rigid carbon shown in the pictures.
Meagain, while I would be lying if I said I fully understood your intelligent reply " Given the same boundary conditions and same geometry stiffer materials with higher Youngs Modulus (E) generally have a higher vibration frequency" I'm glad to know I am grasping the concept lol! Regarding the "ramp" you suggested about the carbon would that be achieved by simply trimming it into a tapered end rather than a rounded one as shown in the pic?
Hey afoaf,
what would be your recommendation for a more useful application of the carbon?
All respect give to Benjamin, and you didn’t post his quote so I don’t really know his thought on it, but I disagree that the deck and bottom need equal strength. As a matter of fact, nobody builds decks and bottoms with equal strength.
You stand on the deck. The rocker curve in convex on the bottom as opposed to concave on the deck.
If done right it is way more complicated than just throw some carbon and call it a day. Tension, compression, impact, elasticity, flex and rebound, weight, foil, volume, stringer and thickness are a start of the considerations. Then add in core properties. Sorry to those in the “Keep It Simple Stupid” team, but you can do so much more.
Look at Coil glassing. Not glass at all according to Mike, and clearly they do more than two layers on top, one layer on bottom.
Did I mention Cordura? = - )
Deadshaper is incorrect twice?
Please quote where Deadshaper specifically states “boards break from the bottom skin stretching first.”
Only two? You know for a “fact” he discontinued this practice.
After all, we do not want to disseminate disinformation …
Hey Everysurfer,
It was posted by Marsh, second comment, first page. I see what you mean that thickness and contours and core strength play a much larger factor than just a strip of carbon or skin of glass/resin or other materials. Thanks for blowing my mind lol! It always amazes me how much of what is out there is done just because that’s the way everyone else does it and impresses me when analytical minds start testing materials scientifically to try and achieve a better end result backed by real information.
I stand corrected. Back in 2007, deadshaper did two boards with equal glassing, top and bottom. And at the time he thought boards break from the bottom skin stretching first.
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I stand corrected. Back in 2007, deadshaper did two boards with equal glassing, top and bottom. And at the time he thought boards break from the bottom skin stretching first.
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Deadshaper is incorrect twice? Please quote where Deadshaper specifically states boards break from bottom stretching first.
Only two? You know “for a fact” he has discontinued this practice.
After all, we do not want to disseminate disinformation …
That’s from the thread **YOU **posted earlier
I said he did two boards this way. I didn’t say he did ONLY two boards this way.
A fiberglass skin will fail in compression before it fails in tension. Because of the curve of the rocker boards **USUALLY **break when the deck side compresses BEFORE the bottom skin rips in tension.
Look at a snapped board. USUALLY the foam break is not at the same place where the bottom skin tears. This is because the deck failed, and the blank broke in two pieces, then wave action sheared the bottom cloth. Sometimes the bottom doesn’t tear at all. This is called a buckle.
Since the bottom is already stronger in its failure mode than the deck, more glass is **USUALLY **put on the deck than the bottom.
Really Dr. stoned bumer Phd., for a smart guy, you seem to struggle with the basics.
Is it possible that you misconstrued the meaning of Deadshaper’s simple statement?
Perhaps Deadshaper provided a brief single-sentence summary of a 4-part sequence:
1. The bottom stretches.
2. The deck skin and upper core buckle (compressive failure).
3. The bottom then experiences tensile failure.
4. The surfboard snaps in two.
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No.
Stony, I know how boards break. After 20 years out of the water, you need to go surfing. Find a board that has broken. Not just pictures. Look at it closely. See how it broke. It will all become clear.
Are you both contractor and mechanical engineer? I am neither.
I stated my interpretation of Deadshaper’s explanation.
Apparently you are always correct. At least, you think so …
EDIT:
I do not believe I stated that surfboards always snap in two. I did say breaks begin with compressive failure of the deck skin and upper core surface. However, the bottom must stretch before that can happen.
BTW I believe my summary succinctly states what you tried to express …
Hi Stoneburner,
Deadshaper give many good info on tech to build in thread you mention but is theory of break is wrong.
Take a piece of eps, laminate both side with 4oz epoxy and make a 4 point flex test:
while sample flex, skin in tensil stretch while skin in compression buckle because skin are thin. Foam “try to keep” buckling skin with it but it’s create too much shear forces for foam so it’s torn and the free skin buckling to break.
This is what happen whatever the material of skin, if skin are enough thin and core is enough weak. I am mechanical teacher, every year my studdent made flex test and every year it’s what happen, then i explain it theoricaly with formulas, it’s right every time such as 2+2=4.
Buckling is a killer for slender parts that experiment compression even for material strong in compression like concrete.
Sorry for my franglish
“while sample flex, skin in tensil stretch while skin in compression buckle because skin are thin.”
Hi lemat -
This has always been the case for me with my own experiences.
Re: deck vs bottom buckling… I have seen boards buckled on the bottom. I believe the more common deck buckles may be attributed to deck dents and soft spot/delams creating hinge points.
An issue that crossed my mind regarding the equality of laminates on each side is the difference in shape of the deck and bottom. On most boards, channel bottoms being an exception, the bottom is a relatively flat panel while the deck is more contoured. The dome of the deck and the curvature of the rail crown creates a more ‘3-D’ shape.
Does the overall build become unbalanced in stiffness when this difference between deck and bottom countours is considered? Maybe more so when the additional reinforcement of the deck (for dent prevention) is taken in to consideration?
Hi John,
Compress side can be bottom so bottom can buckle. Crown deck shape make an high point at centre where constraints are max, best reinforcement against buckling must be at this place.
No. Structurally a surfboard is a beam and it’s properties are defined by the Young’s modulus (E) of the materials it is made of and the second moment of area of each element of the shape in cross section (I). When a beam is bent one skin experiences compressive stress and the other tensile stress, at some point between there is a zero stress, this is called the neutral axis. In a non symmetrical shape the neutral axis will be closer to one skin than the other but it will still be balanced about the neutral axis as far as the maths is concerned - the stiffness is just the sum of the E.I’s for each element. The stress in the skins will be different but not significantly.
In engineering it is usual to specify the stiffness of a structure and then optimise the beam materials and shape according to other considerations - cost, weight, size, etc., but two beams with the same E.I will behave the same way in terms of deflection.
Precisely.
For the deck to buckle, the bottom skin must stretch – and the deck skin must compress – simultaneously. Obviously, the opposite would be true if one were riding the surfboard upside down.
If the endpoints of a line are even loosely fixed/anchored, the line must increase in length when deflected from its static state – simple geometry.
This is a commonly understood concept among skate deck builders.
I would think a certain number of foam compressions, pressure dings, would create potential failure points on the deck.
Nope. If the bottom streched, there would be no compressive load in the deck, so why would the deck fail in compression?
Apparently you did not read Meagain’s post. Or you do not grasp the concept of the simultaneous nature of beam tension/compression …
A surfboard is a thin beam just like a skateboard deck is.