The difference of bulk and young modulus

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Discussion Overview

The discussion centers on the differences between bulk modulus and Young's modulus, exploring their definitions and applications in material science. Participants seek clarification on why these two moduli are sometimes compared in literature despite their distinct physical meanings.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants assert that Young's modulus pertains to stretching, while bulk modulus relates to compressing.
  • One participant emphasizes that Young's modulus is defined as tensile stress over tensile strain, whereas bulk modulus is defined as bulk stress over bulk strain.
  • Another participant elaborates on the mathematical relationship between the two moduli, noting that Young's modulus can be expressed in terms of bulk modulus and Poisson's ratio, particularly highlighting that they can be approximately equal under certain conditions.

Areas of Agreement / Disagreement

Participants generally agree that Young's modulus and bulk modulus are different concepts, but there is some contention regarding the implications of their relationship and the conditions under which they may be compared.

Contextual Notes

There are unresolved aspects regarding the specific conditions under which the two moduli may be considered approximately equal, as well as the implications of Poisson's ratio in this context.

saray1360
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Hi everyone,

I want to know what the difference between bulk modulus and young modulus is? In some papers, it seems that they have compared the value of these two as if they are the same.

Could anyone help me with this regard?

Regards,
Sara
 
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Youngs modulus refers to stretching and bulk modulus refers to compressing.
 
it is not the answer, sorry
 
Youngs modulus and bulk modulus are different..The former is tensile stress/tensile strain the latter is bulk stress/bulk strain.
 
Dadface said:
Youngs modulus and bulk modulus are different..The former is tensile stress/tensile strain the latter is bulk stress/bulk strain.

The bulk modulus K is the amount of pressure required to obtain a certain change in volume per unit volume. The Young's modulus is E=3(1-2\nu)K (*). For a rod (long, thin geometry), it is the amount of axial stress (compression or tension) required to obtain a certain change in axial length per unit length. They are approximately equal when \nu is near 0.33, which is common for metals (but not for ceramics or elastomers).

(*) \nu is Poisson's ratio, the ratio of the lateral contraction over the axial contraction for a rod under axial load.

EDIT: Removed unnecessary comment.
 
Last edited:

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