From the "dont try this at home kids" department of our F16 build.


For several reasons we opted to go for homebuilt carbon chainplates instead of 316 stainless steel plates in our project.

We were a bit uncertain of the strength of our chainplates so we deviced a way to test them.

We figured the max static load to be about 250kg on the chainplates. Add a 4x safety factor for dynamic loads and we are targeting a static safe load of 1000kg.

The design we choose is a stainless steel tube with two layers of glass wrapped around for insulation. Then fold layers of uni and bi-directional carbon over the tube. Add pressure and cook in the oven.

We dont want to put a critical component like this into our boats without testing. Besides, testing is fun (but dangerous)

We deviced a stress test based on a winch and several lines of increasing strength. Max capacity of the winch was 4000kg.

A sample of our carbon cooking was glued to a 24mm ply plate with additional layers of glass to spread the load. The layup was the same as we planned to use in our boats.

When applying tension to our test rig until the line with know strenght broke, we got a rough measurement on the loads acceptable.

We started with 4mm dynema and nearly maxed out our winch capacity when we got to 8mm dynema lines of 3900kg breaking strength. This indicates that we are safe to put these chainplates into our boats.

The 4mm bolt we used to connect the line and the chainplate bent badly even if the shackle was a tight fit. We also had some small deformation of the steel tube inside the chainplate due to the bolt bending. No visible signs of delamination or damages to the glass or carbon layup.

If somebody decides to replicate our test rig. Do take care to secure the plate with the chainplate so it does not go flying as the line snaps.
Dimension all strops in the system to be far above the breaking strength of the line you are testing.
Stand well back and use a remote control to operate the winch.
There is a lot of force involved! Think before doing anything!

Are you also going to test shock loads ?

Laminate tend to behave differently under slowly applied static loads and shock loads. Well, more so then metals

Wouter

I thought about testing for shock loads but the risks for having sharp objects flying through the air are significantly larger. I dont want to spend time building a complex testing environment.

I think the static load test indicates that relevant shock loads will be within the performance envelope of the chainplates. If we have e.g. a 1 ton or larger shock load going into the chainplate I think a broken chainplate is going to be a smaller problem then where the crew will land after their flight