Flax Part2

I made 3 sample layups using flax. The samples measured 3 inches wide by 33 inches long. After pressing the samples over night I took some basic measurements and conducted torsion and deflection tests which a detailed below. Before getting to the test details here’s a materials list used in the samples and testing:

Material list:
Flax Weight – 350gsm or 10.3 ounces
Flax Thickness – .7mm
Carbon Fiber (CF) weight 9.4oz
Carbon Fiber thickness .36mm
Poplar veneer 1/16in or 1.6mm
Epoxy – Resin Research
Brick – 5lbs 2.6 oz (2340g)
Wixey digital angle gauge
Torque wrench – Apply 10 foot lbs
Pressure 40psi

All materials were cut to 3 x 33 inches.

Sample1 – 1 flax, 2 layers poplar veneer, 1 flax
Sample2 – 2 flax, 2 layers poplar veneer, 2 flax
Sample3 – 1 flax, 1 CF, 2 layers poplar veneer, 1 flax, 1 CF

Lacking any electronic measuring devices, aside from the Wixey Digital Angle Gauge, I relied on using scientific measuring methods. Here’s how I conducted my tests.

Deflection Test
To test the amount of deflection I setup the samples on a work bench and let the samples hang over by 12 inches. I fastened the Wixey gauge to the end of the sample and set it to zero. I then placed the a weight (brick) on the sample and let the Wixey gauge measure the deflection angle.

See pics below:

Sample fastened to work bench with gauge attached.

Deflection test

Deflection test

Weight (brick) is placed on the sample and the deflection is measured. In this test the deflection was 1.3 degrees.

Deflection test

Deflection test

The same test was performed on all 3 samples.

Torsion Test
The torsion test measures how much the sample would twist when 10 foots pounds of force was applied using the torque wrench. Each sample was clamped to the work bench and with an over hang of 6 inches. I fastened a clamp to the end of the sample and placed the angle guage to the clamp. The clamp has a large nut in the center that I place the torque wrench and applied 10 foot ponds of force. The angle gauge measures the angle.

Torsion test set up

Torsion test set up

Torsion test set up

Torsion test set up

Torsion test set up with torque wrench

Torsion test set up with torque wrench

The test was performed an each sample.

Here are the test results:

Control Sample Layup Dry Weight  Weight after Pressing Thickness after pressing Torsion Test Deflection Test
Sample 1 flax, 2- poplar veneer, flax 5.4oz (153g) 9.1oz (255g) 4.15mm 15.5 degrees 10 degrees
Sample 2 2-flax, 2-poplar veneer, 2 flax 6.5oz (184g) 11.7oz (330g) 5.23mm 8.3 degrees 5.7 degrees
Sample 3 CF, flax, 2- poplar veneer, flax, CF 7.0oz (198g) 10.2oz (288g) 4.82mm 8.4 degrees 1.3 degrees

Sample 1 is relatively soft both torsionally (twisting) and longitudinally (deflection).  Since the flax is biaxial and only 10.3 oz it’s what I expected.

Sample 2 (double layer of flax) is about twice as rigid as sample 1 as you would expect both torsionally and longitudinally.

Sample 3 (single flax and carbon fiber) is very rigid  longitudinally as it deflected just over 1 degree. The carbon fiber really make it rigid. However it was a little surprising to see that torsionally it’s about the same as using 2 layers of flax.

To make a rough comparison I performed a deflection test on an old fiber glass (FG) sample I had made using 20 oz triaxial fiber glass. The big difference in the FG sample from the above samples is the FG sample has a ptex base, otherwise the layup process was the same. The FG sample deflect 4.3 degrees, not a huge difference from sample 2. In the torsion test on the FG sample it was about 12 degrees. So it seemed a bit softer which is a little surprising since triaxial weave provides more torsion rigidity than a biaxial weave.

Conclusion- (IMHO)

1. Using a single layer of flax above and below the core alone will not make for a very rigid ski. Too soft for an adult male skier.

2. Using 2 layers of flax above and below the core seems a good choice if a fairly rigid ski, similar to using 20 oz triaxial FG. I’m assuming the ski will be fairly damp since the flax does seem to consume more epoxy than FG.

3. Using a single layer of flax and CF will make for a lighter weight and rigid ski. This may make for a good combination of a lively ski with some damp qualities.

I think I see 2 skis in my future using sample 2 and 3 layups. 🙂

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