Frame analysis Stress Formula

[johnster100]

Hi There,

I've been using the frame analysis formula in inventor to design some shipping frames. I often get a very High Smax value when I look at my results. From what i can see Inventor seems to sum Bending (in X and Y) and axial stress to give this value. Does anyone know the exact formula they use?

thanks,

warrellsy

[garytang · Accepted solution]

Hi warrellsy,

You are right, the formula is Smax = Smax(Mx) + Smax(My) + Saxial. This is common formula for generic shape which calculates worst possible stress.

Another situation is when Export to Autodesk Robot Stress Analysis (ARSA) is used. ARSA is able to map most of Inventor sections to ARSA sections and therefore use shape specific formulas. E.g. round sections should be calculated by formula Smax = sqrt(Smax(My)^2 + Smax(Mz)^2) + Saxial.

Similarly Smin = Smin(Mx) + Smin(My) - Saxial

Regards,

Jan Vonasek

Autodesk Inc.

[Vikas.Patel]

Hei

Can you please explain your theory for Smax i have got in my analysis.

check atteched picture

Thank you in advance.

Vikas

[HarryP108]

This is clearly incorrect, unless I need to go to grade school maths class again.

I recently analysed a frame and had a frame that showed Smax(Mx) = 326.9 MPa, Smax (My) = 370.2 MPa and Saxial = 0 MPa.

Smax = 370.2 MPa;  not 697.1 MPa.

[johnsonshiue]

Hi Paul,

Frame Analysis isn't FEA. It uses simple geometry and kinematic relationship to come up with the analysis in 3D. The formula Gary mentioned here is to cover worst case scenario. If you want accurate stress analysis, you need to use FEA (Inventor Stress Analysis or Inventor NASTRAN).

Many thanks!

[HarryP108]

I'm aware of that. I was referring to - and using - Frame Analysis.