You are reading a single comment by @Emyr and its replies.
Click here to read the full conversation.
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
Emyr
Not an engineer, but I think you should be looking at this:
https://www.engineersedge.com/calculators/flat-plate-deflection.htm
The dimensions should be 700 x 550mm
HDPE has a tensile modulus of about 1200 and a poisson ratio of 0.46.
You'll probably want it to survive a sizable child standing on one foot in the center of a gap. Let's say a child's foot has a contact patch with a radius of roughly 30mm and at 50kg that would give (500N/(pi*30mm^2) 0.2N/mm2.
A sheet of 15mm thick would then give you a displacement of ~4mm, which sounds acceptable. But that sheet would weigh about 30kg, which is a bit much. If you reduce that weight to 20kg by making the weight 10mm you'd get a displacement of 15mm, not sure if it'll survive that and don't know how to tell. Perhaps tell your children not to climb on the trailer, you'd get away with a far thinner sheet.
These are static loads though, riding over rough roads will introduce all sorts of vibrations but I had switched to the design faculty by then so I don't have a clue.