Variable K elastic constant ?

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Discussion Overview

The discussion revolves around the concept of a variable elastic constant (K) in springs or other physical methods, specifically exploring whether a spring can exhibit different elastic constants when subjected to compression versus decompression. The inquiry touches on theoretical and practical aspects of elasticity in materials.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions if a spring can have different K values when compressed versus decompressed, suggesting a potential for a variable elastic constant.
  • Another participant proposes that rubber could serve as a spring with a variable K, noting that K would depend on the hardness of the rubber, but expresses uncertainty about its practical application.
  • A third participant introduces the idea of viscosity or plastic deformation affecting the elastic constant, but cautions against using this to violate the first law of thermodynamics.
  • Another participant notes that many polymers exhibit different K values in tension compared to compression, describing the phenomenon of 'tension stiffening' and providing examples such as reinforced concrete and various fabrics.

Areas of Agreement / Disagreement

Participants present multiple competing views regarding the existence and practicality of a variable K elastic constant, with no consensus reached on the feasibility of such a spring or the implications of different materials.

Contextual Notes

Some assumptions about material behavior and definitions of elasticity may be missing, and the discussion includes unresolved questions about practical implementations and the limits of elasticity in various materials.

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"Variable" K elastic constant ??

Difficult to put the topics on the right place...

Is there any spring (or any physical method) that could have different K elastic constant on one sense of movement than on the other?

For example K = 100 (or another value) when compressing and K = 75 (or another value) when decompressing?
 
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I think that the simpler spring with variable K elastic constant could be made from rubber.
When you stretch this rubber spring the elastic constant would take a value K (the value of K depends on who hard is the rubber).
On the other hand during the compression of the spring the value of the elastic constant is K=0.
I’m not sure if practically a rubber spring could work but theoretically it is possible.
 
Sorta - if you throw in viscosity or plastic deformation or something like that. If you're hoping to use that to overcome the first law of thermodynamics though, no.
 
Almost any polymer (and some other materials) will have a different (and variable) K in tension from that in compression (except for small strains). Under tension, the polymer chains straighten out and stiffen - under compression they tend to buckle and are less stiff. The effect is called 'tension stiffening'.

Reinforced concrete does something similar - as do most fabrics (wool, cotton, etc)
 

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