Basically any overcenter/toggle mechanism will not release because of an applied load until it undergoes significant deformation, or excessive wear at the pivot points.
"Load binders" comprising an overcenter toggle, chain, and hooks will _not_ release as a response to any given load within their capability.
They can be released by manually manipulating the toggle, which is not what the OP asked for. ... it is also best done with a long prybar or similar tool, because the stored strain energy will be converted into kinetic energy of the various parts, which can do significant damage to persons or objects in the immediate vicinity.
Similarly, if you're going to separate two connected ropes at a significant level of tension, you need to be sure that no person is close enough to be injured by whatever parts will be flying after the separation starts.
Now, as for how to do it, what comes to mind is a fairly precisely made detent, either using die springs directly, or using weaker springs set up as a sort of pilot mechanism to an _under_center toggle. It's actually a fairly difficult sophomore kinematics problem, that becomes a dangerous kinetics problem at the moment of release.
I think I read once that aircraft carrier catapults are allowed to build steam pressure behind a piston until a standardized barbell shaped holdback bar fractures under axial tension, releasing the catapult and the aircraft to move forward. I.e., the bars are consumed, one per launch.
I'd tend to prefer that frangible bar type release for its simple geometry, but you may have buy name-brand steel and machine it with unobvious precision to get predictable and repeatable results, so the consumables cost per release may be higher than you anticipate.
Mike Halloran
Pembroke Pines, FL, USA
