Is Section Modulus the same as a cross sections bending strength modulus ?

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Discussion Overview

The discussion revolves around the relationship between "Section Modulus" and "bending strength modulus" in the context of engineering specifications for a rear underun protection device on a lorry. Participants explore whether these terms refer to the same concept or represent different entities, particularly in relation to the requirements set by an ECE directive.

Discussion Character

  • Debate/contested
  • Technical explanation

Main Points Raised

  • Mech King questions if "bending strength modulus" refers to the "Section Modulus" as specified in the ECE directive for a steel beam.
  • One participant suggests that the bending strength modulus is indeed the section modulus, citing the unit of measurement as volume.
  • Another participant clarifies that the flexural modulus of elasticity has units of pascals and distinguishes it from flexural rigidity, which has units of N*m^2.
  • Mech King agrees with the clarification that "bending strength modulus" likely refers to the elastic section modulus.

Areas of Agreement / Disagreement

There is some agreement that "bending strength modulus" may refer to the elastic section modulus, but the terminology and definitions remain contested among participants.

Contextual Notes

Participants express uncertainty regarding the definitions and units associated with bending strength modulus and section modulus, indicating a need for clarity on these terms.

Mech King
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Is "Section Modulus" the same as a cross sections "bending strength modulus"?

Good afternoon everyone,

I am following an ECE directive that sets out the requirements for the properties of a "Rear underun protection device" for the rear of a lorry.

It states that the underun bar must consist of a "steel beam whos cross-section has a bending strength modulus of at least 20cm^3"

Are they referring to the "Section modulus"? or is what they are stating a completely different entity.

Trying to find the appropriate person to speak to for this directive is proving abit of a nightmare, oh the joys of bureaucracy eh!

What are your thoughts?

Mech King
 
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From the looks of the information given, I would say it is indeed the section modulus because the unit is volume.

I believe bending strength modulus is the same as flexural modulus defined as:

EI or N/m^2 * m ^4 = N*m^2

Please correct me if i am wrong, but this is my take on this.
 
Nick Bruno: No, flexural modulus of elasticity has units of Pa (pascals), as does tensile modulus of elasticity. And E*I, which has units of N*m^2, is called flexural rigidity, not the names you listed.

Mech King: I agree that "bending strength modulus" in your above post is elastic section modulus.
 


Thanks for your replies chaps,

much appreciated.

Cheers
 

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