Nonlinear rubberband type thing - "k" dropping fast as it is stretched

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Discussion Overview

The discussion revolves around finding materials and methods to create a specific displacement versus force curve, particularly one that resembles the behavior of a rubber band under tension. The focus includes material properties, design considerations, and potential applications in experimental setups.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant seeks materials that can produce a desired displacement versus force curve, specifically looking for durable, non-messy options that can withstand at least 100 stretch cycles.
  • Another participant suggests a piston-cylinder system connected to a balloon as a model that exhibits similar pressure behavior, where high pressure is required initially and then decreases as volume increases.
  • There is a question about the axes of the graph, with one participant confirming that displacement is on the x-axis and force on the y-axis, while speculating about potential hysteresis effects if the axes were reversed.
  • One participant raises a question about the units being used in the context of the discussion, asking for clarification on whether they are in mg, g, kg, tonne, or N.
  • A later reply mentions that rubber bands may not behave uniformly and suggests that a spring and cam mechanism could achieve the desired behavior reliably, emphasizing that the specific magnitudes of force and displacement will influence the design realization.

Areas of Agreement / Disagreement

Participants express differing views on the best materials and mechanisms to achieve the desired curve, indicating that multiple competing approaches are being considered without a clear consensus on the optimal solution.

Contextual Notes

There are unresolved questions regarding the specific properties of materials and the implications of different design choices on the resulting force-displacement behavior. The discussion also highlights the potential variability in rubber band performance.

Swamp Thing
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What materials can I try in order to get a curve of displacement versus force that looks somewhat like this..
(of course, there would be a small kink around the origin where the ends of the rubberband are closer together than its length, which is not shown here).

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I am looking for something that will last at least 100 stretch cycles and is not messy, so for example liquid based colloidal stuff won't be suitable. Is there something one can whip up using silicone and some additive, say? Or something that exists commonly or is available on Amazon?
 
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Swamp Thing said:
What materials can I try in order to get a curve of displacement versus force that looks somewhat like this..
A piston in a cylinder, like a bicycle pump, that is connected to a balloon. As the piston moves, high pressure is needed to begin inflating the balloon, then the pressure falls rapidly as the balloon volume rises.
 
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Swamp Thing said:
a curve of displacement versus force
the graph is not labelled.
Is stress ( force ) along the y-axis, and strain ( displacement ) along the x-axis ?
 
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Sorry... X is displacement and Y is force.

(If it was the other way round, there would be some interesting hystereses type things going on I guess)
 
That response is like a symmetrical over-centre latch.
Are the units mg, g, kg, tonne or N ?
 
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Baluncore said:
That response is like a symmetrical over-centre latch.
Are the units mg, g, kg, tonne or N ?
I just arrived here and was wanting to put your comment in. You'd done it already!

Rubber bands will not all behave the same. I would say that a spring and cam would do what you want - very reliably. As in the above, the magnitudes of force and displacement will determine how you actually realise the design.
 

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