Hello all, today was a highly productive day for Olin Sailbot. The mechanical, coding and electrical teams were in full swing. On the mechanical side, a great deal of progress was made with the deck, including tests on the honeycomb material that the deck will be fabricated from.
Test : A piece of the mast material was inserted into a sample piece of the honeycomb material as we anticipate attaching it when the sails arrive. The piece of the mast was pulled with 10-12 lbs at 9 inches, with a resultant force of 90-108 in. lbs.
Observations : At approximately 7 lbs at 9 inches ( 63 in* lbs.), the epoxy around the mast began to fail. However, the honeycomb was flexible enough to withstand approximately 30 degrees of bending without failing. As we have shrouds which prevent this excessive motion, our mast should never be moving this much and therefore the honeycomb will withstand the forces on it.
Test : We anticipate that the shrouds will be attached to the outer edges of the deck using eyebolts. In place of eyebolts, we used normal bolts and pulled on them at an angle of approximately 10 degrees with as much force as possible. There were three different situations tested: a bolt with no nut, a bolt with a nut, and a bolt with a washer and a nut.
Observations : Even when pulled at the greatest possible force (to the point at which I could not measure the force and I could not physically pull any harder), the honeycomb showed no signs of failure. In fact, the bolt itself began to bend before the honeycomb did. This was on the bolt with no nut or washer, and so was the ‘weakest’ of all the situations. This result reinforces what we had hoped before, namely that our shrouds will be strong enough to hold the mast stable and therefore we do not have to worry about the honeycomb around the mast step failing.
Carbon Fiber test
Test: To test the strength of the epoxy bond between the carbon fiber (which the hull is made from) and the honeycomb (which the deck is made from) we attached a clamp to the excess carbon fiber on a test piece and pulled from there. There were two different attachments of the carbon fiber to the honeycomb. One strip of carbon fiber was epoxied to honeycomb
which had been scratched, while the fiber strip was epoxied to the honeycomb with its surface left as it was. We then ran two tests, one pulling normal to the honeycomb and one parallel to the honeycomb.
Observations pulling normal to honeycomb: When the carbon strip without scratches was pulled, it immediately broke. While this did not show the strength of the connection, it did show us that the carbon fiber has a failure mode when bent at a sharp angle along the grain of the fibers. When we tested the fiber attached on scratches, I pulled until the scale maxed out at 40 lbs and I couldn’t pull anymore.
Observations pulling parallel to honeycomb : When the carbon strip connected with scratches was tested, I again went beyond the range of the scale and finally broke the string. I concluded from this that we do not have to worry about the carbon fiber detaching from the honeycomb as long as we scratch the honeycomb first.
The result of all this was that we know our material’s failure points, and we have decided we are working far within these. Good things were found out! We are well on our way to a finished boat, and with the end in sight the process is getting even more exciting.