NX area moment of inertia calc - how do I specify the neutral axis?
NX area moment of inertia calc - how do I specify the neutral axis?
(OP)
In NX 7.5, how do I calculate the area moment of inertia about a specific axis?
I've tried 2 methods, and NX does not let me specity the axis the area is revolved around. For example a 2mm by 8mm rectangle has 2 neutral axes, which give 2 very different area moments of inertia.
Ix = (2 * 8^3)/12 = 85.33mm^4
Iy = (8 * 2^3)/12 = 5.33mm^4
Here's the 2 methods I've tried, but both give the same result. It chooses an axis based on how the part was modeled rather than letting me choose it for each calculation.
1. Analysis, Section Inertia..., Parellel Sections, Section Normal. (The Section Normal is perpendicular to the neutral axis or axis to revolve the area around.)
2. Analysis, Section Inertia..., Existing Section.
Thanks.
Joe Sawicki, P.E.
mechanical design engineer
I've tried 2 methods, and NX does not let me specity the axis the area is revolved around. For example a 2mm by 8mm rectangle has 2 neutral axes, which give 2 very different area moments of inertia.
Ix = (2 * 8^3)/12 = 85.33mm^4
Iy = (8 * 2^3)/12 = 5.33mm^4
Here's the 2 methods I've tried, but both give the same result. It chooses an axis based on how the part was modeled rather than letting me choose it for each calculation.
1. Analysis, Section Inertia..., Parellel Sections, Section Normal. (The Section Normal is perpendicular to the neutral axis or axis to revolve the area around.)
2. Analysis, Section Inertia..., Existing Section.
Thanks.
Joe Sawicki, P.E.
mechanical design engineer





RE: NX area moment of inertia calc - how do I specify the neutral axis?
Analysis -> Advanced Mass Properties -> Area Using Cureves...
John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
Siemens PLM:
UG/NX Museum:
To an Engineer, the glass is twice as big as it needs to be.
RE: NX area moment of inertia calc - how do I specify the neutral axis?
The WCS has 3 axes: x, y, and z. Do you mean line up the x-axis with the axis of rotation? Or will y and z also work?
For NX7.5, Analysis-> Advanced Mass Properties-> Area Using Curves, I there's dialog box called Analysis with these 4 choices:
-Boundary (Permanent)
-Boundary (Temporary)
-Face (Permanent)
-Face (Temporary)
Any recommendations between these 4. I've tried all 4 without success. I don't see a "moment of inertia" option. This should be easy to calculate moment of inertia for a 2D face. Imagine a solid block with one face being a 2mm by 8mm rectangle. All I need to do is calculate that face's area moment of inertia about its neutral axis. Piece of cake, right? Have you tried it before?
Thank you.
Joe Sawicki, P.E.
mechanical design engineer
RE: NX area moment of inertia calc - how do I specify the neutral axis?
I use the 'Boundary (Temporary)' option, since this will allow you to either select curves (but not edges) or a face. And while there is a 'Moments of Inertia' option, I usually just just press the 'List All' button and get everything in the listing window, which can be saved as a text file for later reference and to help document your work. However, you have to actually get to the proper dialog before you can continue. After
John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
Siemens PLM:
UG/NX Museum:
To an Engineer, the glass is twice as big as it needs to be.
RE: NX area moment of inertia calc - how do I specify the neutral axis?
I followed your advice, selected the face, and then the command prompt reads "Select Object 1." What is "Object 1," and what do I select? See attached prt and ppt files. Thanks for your help.
http://files.engineering.com/getfile.aspx?folder=e...
http://files.engineering.com/getfile.aspx?folder=e...
Joe Sawicki, P.E.
mechanical design engineer
RE: NX area moment of inertia calc - how do I specify the neutral axis?
And here is where I usually hit the 'List All' button.
John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
Siemens PLM:
UG/NX Museum:
To an Engineer, the glass is twice as big as it needs to be.
RE: NX area moment of inertia calc - how do I specify the neutral axis?
Joe Sawicki, P.E.
mechanical design engineer
RE: NX area moment of inertia calc - how do I specify the neutral axis?
Anyway, I was given the job of designing these profiles, determining their section moduli as well as cross sectional area, profile perimeter and minimum included circle size (these last three numbers were used by our aluminum vendor when they quoted tooling costs and production costs). So for about a year I was doing this manually by making full-size hand-drawn profiles and then using a 'planimeter', a really cool little watch-like mechanism, to compute the area of the 2D profiles (but only if you were really careful tracing the profile of course):
Of course, even with that data I still needed to calculate the section modulus using transform coordinates.
When we bought our first Unigraphics system, which we really justified so as to help get toolpaths generated to keep our machine shop busy, we didn't even know this functionality existed. Then about a month later I was messing around and discovered this capability, which was great. It took me maybe half-a-day per profile to do it manually, but now in a single afternoon I could knock-out a half-dozen fully drawn and documented designs. Later, while attending a Users Meeting, I met some people from Alcoa and Alcan, two of the earliest users of Unigraphics, and they explained that they had both demanded that this capability be part of Unigraphics since it was so key to enhancing the productivity of their extrusion business.
If you look at the options on the menu below, you'll see what I mean when I say it included all of the types of info that would be important for anyone designing extruded profiles, their tooling and then quoting the cost of the final extrusions:
John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
Siemens PLM:
UG/NX Museum:
To an Engineer, the glass is twice as big as it needs to be.
RE: NX area moment of inertia calc - how do I specify the neutral axis?