Section Modulus for Beam/Bending Calculations

[RobJV]

I have read many questions and answers on section modulus in inventor and know about region properties and various FEA properties that don't quite give me the section modulus.  I can calculate the section modulus of unique (built up) parts only by performing a bunch of math or moving sketches.  Is there not a simple way for me to look at a profile oriented in the xy plane and get the Ixx/Iyy and the section modulus in the x and y direction directly from a dialog box?  Why can't inventor do that?

Rob

[johnsonshiue]

Hi Rob,

Indeed, it would be nice if Section Modulus is computed automatically. The tricky thing is that the property actually depends on the shape and also its neutral axis. It is probably not that easy to develop a general algorithm to compute it unfortunately.

Many thanks!

[RobJV]

Hi Johnson,

Thanks for your response!  I think you brainiacs at Autodesk could take care of this though. 🙂 

1. Unless I am mistaken in my understanding of the results I am getting from the region properties dialog box, why can't you give us the area moment of inertia with respect to the centroid BUT in the correct sketch orientation and then divide by the distance from the horizontal or vertical outer most fiber to get the section modulus in those direction?  As I see it now,  the principal axis is rotated (depending on the custom shape) which essentially gives you results for the beam lying in that orientation which is unhelpful in most calculations (unless my forces are all in those two planes).  (Please let me know if my understanding is incorrect as I could be out to lunch.)
2. Without enough verification calculations, I think I have to take the Inertia Tensor values (area moment of inertia in the sketch coordinate system) and then divide by (sketch origin + centroid offset) to get section modulus.   (overly simplified explanation and I will test more)

Rob

[imajar]

What you are doings sounds the same as what I do, playing with sketch coordinate system to get them to align with the axes I want and figure out distances between sketch origins, centroids and extreme fibers.

I agree it is a but cumbersome, but at least it is possible.  But to the point of your question, I do not know of any other way to get the section modulus out of Inventor for generic shapes and it would be convenient if Inventor could calculate it. . . 

[Cris-Ideas]

@johnsonshiue 

Just copy the code from Autocad.

It can calculate section properties for nay region in any orientation. And also gives centroid and principal moments right out of the box.

So coding is not that difficult after all.

Also it had already been done, and what is even more convenient for inventor team, it was done by Autodesk.

So you have the code available.

Cris.

[johnsonshiue]

Hi Cris,

Points are taken! I am not saying it is impossible to do. There are equations available. Also, AutoCAD can do it already. To certain degree, you can consider AutoCAD and Inventor are one solution. They complement each other from time to time. It would be great if everything could have been done in one product. But, it is just not the way things work. We do have significant number of users using AutoCAD and Inventor but quite a lot of them only use one. So, how to make everybody happy is an art.

Inventor is extending its workflows to better support structures and buildings. This request may sound far-fetched in the past. Now it sounds very relevant. I will work with the project team to understand it better.

Many thanks!

[RobJV]

It is now 3 years later - does the newest version of Inventor have the ability to do this yet?  As an engineer, it would be great to pull these values without having to do a bunch of manipulation as earlier stated.  Does anybody have a routine that has the ability to do this?