Material Properties - Shear Modulus discrepency

[samstreet101]

Whilst trying to replicate an example of a mild steel bar in torsion I came across a discrepency in the default value for the shear modulus/modulus of rigidity for Mild Steel in Inventor's material library.

It lists the shear modulus as 140250MPa or 140.25GPa, however, after looking at various sources including matweb and steel stockists, almost all of them settle on a shear modulus of around 77-80GPa for Mild Steel. I was looking at grade 1018 Cold Rolled which is I believe the most common grade.

I was wondering where exactly Autodesk gets its data for material properties and how it accounts for this discrepency (if indeed it is one)

[henderh · Accepted solution]

Hi Sam,

  Thank you for bringing this to our attention.  It is a known issue entered in our database as 1466253.

  You are correct that if we calcuate if via G = E / 2(1+Nu) we get 85.94 GPa, where E is Young's Modulus (220 GPa) and Nu = Poisson's ratio (0.28).

  If you are concerned about simulation results using the Shear Modulus value, we don't use it directly.  We use the E and Nu values.  Also, in the Stress Analysis report, we use the calculated G value.

  We apologize for the inconvenience this may be causing.

Best regards, -Hugh

[samstreet101]

Thanks very much for the timely reply Hugh,

That clears that up nicely and puts my mind as ease. I suspected it wasn't using the 140GPa value as the simulation results tended to agree (more or less) with what I calculated it to be anyway.

Thanks again,

Sam