Home Made Materials Testing Machine

General Discussion
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I converted my drill press to test bending strength of composite sandwiches. I made a big pully wheel that attaches to the handles of the drill press. A steel cable wraps around the pully and connects around another pully, then to a bucket which is filled with a known amount of weight. The force of the press is about 5 times larger than the weight in the bucket. A test section is placed on two small platforms, one on each end of the table. I made a special plywood/kevlar foot which attatches to the chuck on the press. Deflection is mesured with a gage on the press. I plan on measuring the stiffness and ultimate strength of different combinations of materials. I can then compare the weight vs. strength. I think the strongest section will be layered from the center out as:

1: eps with vertical balsa shear web

2: spackle of epoxy/microballoons

3: divinymat imbeded with carbon tow longitudinaly in each groove.

4: spackle of epoxy/microballoons

5: kevlar cloth

The best test section will be used to make a combat airplane. The

plane will be subjected to crazy G forces, midair collisions, and

strikes from propellers moving at 15,000 rpm. It’s gotta be

strong!!

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more pics

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eps/divinymat/carbon/balsa/kevlar test section. I loaded it with a force of almost 60 lbs. Only 1/8" deflectioin.

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I calibrated the machine with a 2 1/4 lb weight in the bucket. The scale reads 11 1/2 lbs. The mechanical advantage is about 5x.

Here are the first three test sections.

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I really like some of the stuff you’re doing! One suggestion would be to have the load place on quickly to better simulate what the board is going through.

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Hey!

great stuff indeed. Would it be possible for you to do a control? like test a piece out of a regularly sandwiched eps so we can see the difference of the test piece to the control piece. it would be interesting to see! Thanks.

Rio

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for denting and impact strength remember impulse=force/time

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I tested a test section. Failure in shear at 80 lbs while bending. Resisted pressures up to 3262 psi

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I made some improvements. I replaced the weights with turnbuckles and a fish scale. Here is the next test section. Eps with 1/16" vertical grain stringer, 3 strips of carbon tow and 5 oz kevlar. I plan on making a spreadsheeet that will take into account: weight, volume, cross section area, stiffness, hardness, and ultimate strength. I will then create three ratios. A density/stiffness ratio, a densty/hardness ratio, and a weight/ultimate strength ratio. These three ratios will be the judge of the usability and application of the structure.

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My next test may get some attention… Im going to make two eps / 6oz test sections. One with a 1/16" stringer with vertical grain and one with horizontal grain. I think the vertical grain may be stiffer.

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I added a digital caliper to measure the deflection. Much more precise!! I finished making the eps / balsa stringer / 6 oz test sections. I hope to prove that a verticly oriented grain on a stringer will result in a stronger surfboard. I made an excell document and I have a full analysis of each test section that I have tested. So far I have tested 6 different sections. I plan on posting my complete data on each test section. Hopefully I can inspire some different composite lay-ups for surfboards.

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Here is the data for the vertical grain stringer vs. the horizontal grain stringer. I could Imagine making a board with a hybrid stringer of varying vertical and horizontal grain to control the stiffness of the board through its whole length. Check out the graphs. Vertical grain is so much stronger!!!

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nice to see a more scientific approach

also if you counted grain per inch you could come up with a more predictable flex pattern.

also if the skins were quartersawn/split

they would transfer soundwaves more efficiently.

improving the harmonic resonance .

btw stiffer is not neccesarily stronger

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Ohh, maan…

with data, calculations, graphs, constant improvements…

this is truly beautiful. And well thought out, reproducible - ohh, man, truly beautiful. Elegant even.

You made my week… and it has already been a very good week. This is the neatest thing I have seen here in many a moon.

Thank you.

doc…

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NOTE!!! The excell document indicates that the test section is one layer of 6 oz top and 2 on the bottom. This is wrong. It is 2 on top and one on bottom.

and the weight is wrong on one of them. They are both 18 grams. This will throw all the density ratios off

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Ooooo Ahhhhh…

This takes me back to the days when I used to break stuff for a living.

Good Times

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increasing stiffness doesnt equal strength.

stiff boards crease and break.

flexible boards just bend and bounce back.

although your testing procedure is exellent,

foil and core thickness has so much more effect on panel stiffness.

you need to be careful how you analyse this data and how it relates to the

durability/performance of a surfboard as a whole.

while using quartersawn timber in places is valid

i would say it is a minor variable in the strength and performance of a composite board.

increasing skin density increases point impact resistence and increases panel stiffness

but too much and the board will be a dog

increasing the durability of the core/skin materials is more relevant then what glass go’s where.

you would need to do point loading experiments on built boards to be truly valid.

also i believe its important to relise that boards can break

with the deck skin under tension forces as well as compression.

so you would need to turn the foiled panel upside down and do other types of load tests.

and thats just the beggining.

which is why i think ill stick to the esoteric/artistic approach to board making

it feels nice

it looks purty

lets see if that works

a classic example in material durabiltiy analyisis

is in metallurgy

the term hardness

and the term toughness

hard doesnt scratch but can be brittle

tough is not brittle and difficult to scratch as well

in surfboard building these descriptions need to be understood

strength is a fairly vague description of durability

if we place all performance aspects aside, and just focuss on durability.

we need an acurate and agreed apon deffinition of terms,

before scientific testing process become relevant.

when we use the combination of the terms flexibility ,toughness and stiffness.

that would/could equal strength

so x amount of stiffness times y amount of toughness over stiffness might equal s or strength

but rocker is still king in surfboard design

18

At work I do similar tests to determine flexural strength of concrete (you too ryan??). I’ve considered bringing surfboard materials to work and breaking them, but haven’t gotten around to it yet.

If surfboard components are anything like concrete, rate of loading will have a significant effect on the results. Too fast = poor strength. But as mentioned earlier, maybe a faster load rate would apply more to surfing.

Here’s the formula used to calculate flexural strength:

R= PL/bd^2

where:

R= flexural strength (mPa)

P= maximum applied load (newtons)

L= span length

b= average breadth of specimen

d= average depth of specimen

I like the drill press rig!

796×599 55.7 KB

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Quote:

If surfboard components are anything like concrete, rate of loading will have a significant effect on the results. Too fast = poor strength. But as mentioned earlier, maybe a faster load rate would apply more to surfing.

Any Ideas of how to load a material quickly and still produce accurate measurments?? Video camera maybe?? then analyzing the video

I uploaded a copy of the spread sheet. NOTE: there are 11 work sheats in the spread sheet, One for each material I tested.

http://www.geocities.com/lpcdefg/compositematerials.xls

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Not sure exactly how your drill press is set up, but if you are using the depth gauge to measure deflection, consider using a magnet stuck to the gauge as a marker.

As the depth changes the magnet slides down the guage, and when the loading is finished and the drill press returns to zero depth, the magnet remains marking the maximum depth/deflection.

Of course this would only work if loading is ceased immediately after failure of the test specimen. Maybe impractical for your setup, but an idea nonetheless.