Talk Composites - The Forum for Advanced Composites

Has anyone made a laminated composite "Live hinge"?

http://www.talkcomposites.com/Topic12368.aspx

By cookeaa - 7/23/2014 4:03:52 PM

I'm considering a project making a lightweight single wheeled cycle touring trailer, these typically need a horizontal hinge point to accommodate cornering, most simply use a fairly standard bearing/bushing and shaft arrangement of some sort. 

But it occurred to me I could design some sort of live hinge insert using a laminate of some sort, the advantages being it would save weight and possibly be simpler/easier to manufacture, and if it was done as an insert rather than as part of the trailer's structure it would allow me to replace a worn or broken hinge element more easily... 

I know some RC aircraft and cars use laminated composite live hinges and I've definantely seen MTBs that use them as part of their suspension systems, so its not a completely novel concept... 

My real question is what sort of reinforcement, and resins should I use? 
It would need to allow movement in only one plane of maybe 90 - 120 degrees (45-60* either side), and it would be under pretty much constant tensile loads from towing so I guess most/all of the reinforcement would need to be aligned to that primary load path and tolerate lots of lateral flex. 

And just how flexible is a "flexible" epoxy? or should I be looking at other resins? 
By Fasta - 9/2/2014 10:12:25 AM

I have made lots of thin Kevlar/epoxy hinges for a small wing and element but this hinge only moves through about 45 degrees max.

You need to match up an appropriate laminate thickness and size of bridging  hinge to suit your load and use etc.

For my purpose they are just one layer of 170g Kevlar 45 deg and epoxy resin and it bridges a gap of 3mm.