Fablab based composite testing

This page goes through fabric and layup techniques to determine the best combination to use in the Fablab network. Following round 3 of testing it was decided to continue with Duck canvas material given its low cost and wide availability.

Round 4 - Investigating performance for different weights of canvas

The canvas is available in a range of weights, therefore the first round of experiementation is to see how differently the different weights perform and also determine how many layers are needed.

Weight 7.3 oz 9.3 oz 10 oz 12 oz
Vendor Product & Vendor Product & Vendor Product & Vendor Product & Vendor
Mass 4 layer coupons 9.4g 9.4g 12.0g 11.9g 12.4g 12.7g 12.8g 12.7g
Mass 3 layer coupon 6.6g 6.6g 8.2g 8.4g 8.8g 8.8g 9.0g 9.1g
Thickness 3 layer coupon 1.7mm 1.7mm = average 1.7mm 2.0mm 1.9mm = average 1.95mm 2.2mm 2.1mm = average 2.15mm 2.2mm 2.1mm = average 2.15mm
Thickness 4 layer coupon 2.0mm 2.1mm = average 2.05mm 2.6mm 2.5mm = average 2.65mm 2.7mm 2.7mm = average 2.7mm 2.7mm 2.8mm = average 2.75mm

I laid up 2 samples of each material. 1 sample contains 3 layers and the other samples contains 4 layers. I then applied breater and a 2 thin layers of bleeder and pulled out excess epoxy using a vacuum bag. The 3 layer samples weren't fully saturated with epoxy due to some issues with the holes in the bag, despite this we continued to mill samples.

Harith and I milled coupons on the Shopbot using a 1/8", 2 flute, down cut, square end mill.

The same fixturing from round 3 was used for testing in this round. As mentioned previously, the central contact point in the 3 point bending test is 3D printed and therefore introduces a certain amount of compliance into the system however given that we're focused on comparative stiffness testing, this setup is suitable.

This graph was created in the Jupyer notebook titled coupon_test_round_4.ipynb. It shows that the canvas sample is the stiffest and therefore we'll continue with thicker canvas material.