What is torsional modulus, and where is it specified?

  • Thread starter jamesson
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In summary, the equation for minimum link length in lattice hinge design uses a quantity called Torsional Modulus, denoted as G. While this value cannot be found in literature, it can be calculated through testing and is typically around 1.7GPa for acrylic material. The author of the article seems to have used a slightly different value for G in their calculations, resulting in a slightly different value than the one found in literature. The shear modulus, also denoted as G, is commonly used in materials testing and is related to the Young's modulus through a torsion test.
  • #1
jamesson
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The attached site seems to use a quantity Torsional Modulus for which I cannot find neither the formal definition or a material spec
In the equation for minimum link length here

https://www.defproc.co.uk/analysis/lattice-hinge-design-choosing-torsional-stress/

he uses a quantity Torsional Modulus, denoted as G, which I cannot seem to find either a definition for or any kind of expected value. Shear modulus (also commonly denoted as G) is defined and published in multiple sources for the material he uses (acrylic). Google says it is 1.7GPa.

Now, from his description it seems fairly clear what he means by G and how he uses it. I tried to backsolve for G and this is what I got;

G_calculation.GIF

So, either my calculation is off or he's using some source I haven't found.

Thanks so much in advance for any assistance

Joe

PS - sorry if this belongs in materials, if so please let me know and I'll move it.
 
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  • #2
This must be the shear modulus. Your result is ##2.08 \ GPa## so not that far from value known from literature. Author of this article could have used slightly different shear modulus in his calculations than the value you’ve found in literature.
 
  • #3
Thanks so much. What's your source for shear modulus, please?
 
  • #4
It’s calculated through testing like young’s modules but instead of relating stress to strain the shear modules relates shear stress to shear strain through a torsion test. Most materials that are isotopic like steal had a young’s to shear modules relation, G=E/2(1+v) where v = poison ratio.
 

Related to What is torsional modulus, and where is it specified?

1. What is torsional modulus?

Torsional modulus, also known as shear modulus or modulus of rigidity, is a material property that measures the resistance of a material to shear stress. It is a measure of how much a material can deform when subjected to a twisting force.

2. How is torsional modulus different from other modulus values?

Torsional modulus is different from other modulus values, such as Young's modulus and bulk modulus, because it specifically measures a material's resistance to shear stress, rather than tensile or compressive stress.

3. Where is torsional modulus specified?

Torsional modulus is typically specified in material data sheets or engineering design manuals. It can also be calculated experimentally using specialized equipment.

4. How is torsional modulus used in engineering?

Torsional modulus is an important property in engineering, particularly in the design of structures that are subjected to twisting forces, such as shafts, springs, and beams. It is also used in the design of materials for applications that require high shear strength, such as in the aerospace and automotive industries.

5. How does temperature affect torsional modulus?

Temperature can have a significant impact on the torsional modulus of a material. In general, torsional modulus decreases with increasing temperature, as thermal energy causes the material's molecules to vibrate more and become less resistant to shear stress. This is an important consideration in material selection for applications that involve varying temperatures.

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