Quasi Static Impact Tests: Part 3a of Garage R&D Protocol

General Discussion
1

Here’s an easy, cheap and reliable way to test the impact resistance of most surfboard composites:

http://www.youtube.com/watch?v=Z_SlOVejSTU

NOTES ON TEST:

  1. Specimens should have at least 1in of foam depth, however they don't need to be laminated on the bottom side.  There needs to be at least 1.5in of lamination around the edge of the load applicator (c-clamp pad).  So if your load applicator has 1in diameter, the specimen should be at least 4 in wide (1.5+1.5+1).
  2. Specimens should be layed-up exactly how they would be on a surfboard (hot coat and gloss if applicable)
  3. The metal pad of the c-clamp that I used has a 1in diameter, this is ideal.  Make sure the pad is smooth and does not have sharp edges that will cut into the laminate.  If the edges are sharp, you can put a piece of plastic (lid of a recyclable plastic container, ie. a thermoplastic sheet 1/32in thick) between the clamp and the composite.
  4. The load applicator should be round.  This is because the load must be unbiased in direction.
  5. Whatever dimensions you go with for your specimens, you must always stick with those dimensions, otherwise it will be difficult to compare results!  Same thing for load applicator...must always be the same.  Whatever loading rate you use (1 crank per 10 secs or 1 crank per 20 secs), you must always use that rate for all specimens.
  6. When you crank the c-clamp, record the highest load before it settles.
  7. After typing data into spreadsheet-->do scatter plot-->ignore last two data points-->Add trendline-->use linear curve fit-->show equation on chart.  Equation will be in the form of y=mx+b...remember middle school algebra?   b doesn't matter but a  larger m means less pressure dings.  The max load (last data point) is the strength or resistance to cracking.   So you want a high m value and high load value.  They often come together, but sometimes they don't.
 

If anyone wants to get more advanced/technical, I have attached a powerpoint that I gave at UCSD, a year ago. (The second half of the slides are easier to digest)

Garage R&D Protocol for working with a new composite:

I)Test Specimens
  1)Flex test
  2)Buckling/Breaking test
  3a)Quasi Static Impact test and/or
  3b)Drop Weight Test
II)Full Scale
  1)Load-Displacement Test
  2)Natural Frequency Test
  3)Go surf!

(still debating whether or not to put in a torsional test)

2

Powerpoint didn’t get attached for some reason.  If you want it, PM me with your email and I’ll send it.

Benjamin

3

Torsional will come into it eventually. Someone else here mentioned the reason a lot of people still like pu boards is the centre line axis.

This is something composite boards without a stringer do not have built in and a legitimate area that hasn't been explored enough yet.

4

My theory on torsion reckons that torsion is bad for effective double pumping. A stringered board which has its stiffness concentrated down the centre will twist more easily than a stringerless board of equivalent longitudinal stiffness. Therefore the stringered board will be less responsive to the double pump. I say double pump because in a big top to bottom turn there is more time to bank the bottom extra to compensate for the twist, but the double pump is something that needs to respond quickly to small twitching movements.

5

Let all say thin parabolic stringers!

6

Benjamin,

As a long-time lurker, seldom poster, I just want to say thanks for what you've contributed to the forum.  I think you've breathed some fresh intelligence and thought provocation into the mix of unquantified, subjective observations and opinions that have been all but beaten to death here over the years.

Please keep it coming.

7

newschoolblue, thanks.

I’m loving how quite this thread is…one number is worth a thousand words.

 

One other thing, I’m partly regretting saying the “m” relates to how easily the layup will get pressure dings (not cracks).  It is kinda true and kinda not, but I don’t really want to go into advanced mechanics.  So for now, just pay attention to the “m” value…develop a feeling for how it relates to pressure dings.

8

Bump for this.

The reason you're not getting more views/replies is that your title is too boring :-)

Ya gotta put in some more exciting words, like "China", or ''parabolic'', or ''CNC''.