The Payload Bulkhead interfaces between the Avionics Bay and the Nose Cone, and more specifically between the piston, the Avionics tower, and the Payload.
Rev. 1: Pathfinder
The Pathfinder revision was a basic flat plate with a centering ring welded on.
Rev. 2: Hermes
All load from main and drogue parachute opening will go through the Payload bulkhead (whereas we expect all reaction load from piston separation to go through the Avionics bulkhead). While we are currently working to qualify an upper bound on deployment forces, we ran some simulations at 3000lbs (an over-estimate) in order to determine an approximate thickness. In these simulations, we applied the load evenly between the four bolt holes and fixed the lower surface of the upper lip as a fixed geometry. Part material was Aluminum 6061. All runs were performed under the finest basic mesh but we did not refine the mesh for bolt holes.
For our first run, we tried a Bulkhead with a upper and lower step thickness of 0.5" each. The results showed that this bulkhead would not yield under 3000lbs:
Then, we reduced the thickness to be 0.25" on each step and found that the bulkhead would yield, particularly around the bolt holes and at the contact point with the Avionics Bay coupler, but that overall displacement would be small (~0.2mm):
Then, we increased the upper thickness to be 0.375" (this is logistically easier to increase since it does not impose an increase on AV Bay coupler length), kept the lower thickness to 0.25", but added a piston seating cut of 0.125" depth. As one can imagine, results were generally speaking similar, with actually a slightly lower displacement:
