Finite Element Analysis (FEA) in AutoDesk Inventor
This is just one hub in a series of 15 hubs on using AutoDesk Inventor for 3D modeling. The index hub is here.
Figuring it out
Finite Element Analysis (FEA) is a very handy simulation technique that allows engineers to test their models before they even make them. Imagine taking a 3D model of a crane and adding a load to it without even having built the structure. FEA saves companies boatloads of money every year because they can test their systems to find weaknesses before they cause problems. AutoDesk Inventor allows you to do this as well, and makes it pretty easy, too.
In this tutorial you'll learn how to add forces to our shelf model and test it using FEA. Then you'll see how to look at the results and generate a report on the part. You'll be amazed at all the different things FEA can tell you.
FEA in Inventor
To get started, go to the "Environments" tab and click on "Stress Analysis," right next to "Dynamic Simulation." This should open up a whole new tab called "Stress Analysis." Once we're on that tab, we need to add a force, fix a point, define materials, and run the simulation.
Add a Force
First, let's add a force. Click on "Force" under the "Loads" panel. Add a location and a direction, and then enter the magnitude. I entered 500lb, since I've decided that the shelf is going to be used for some pretty heavy stuff, and I added it at the end of the big support, since I figure you could hang a heavy part from there to examine it. You can see the force I added in Picture 1, although later I reversed the direction with the button that shows two arrows coming out of a plane.
Define the Materials
Before Inventor can determine stresses, we need to tell it what materials to use. Click on the "Assign" button on the "Material" panel. A list of all the parts will come up, as shown in Picture 2. By default, each part has a material designation in its own file, but the option to override these defaults is given here.
Since we haven't assigned any materials before, go to the "Override Material" column and click the down arrow for each part to assign it the material you want. If you want them to be all the same, select them all by clicking on the first one, holding down shift, and clicking on the last one. Then click the down arrow on any part in the "Override Material" column and change it. That will change every part to the material you have just chosen.
Fixing a Surface
This is where we tell the program what points are completely immobile, like in Picture 4. Fixing a surface is as easy as clicking the "Fixed" button on the "Constraints" panel and then clicking on the surface, edge, or point that you want to fix. Done.
Running the Analysis
To start the analysis, go to the "Simulate" button on the "Solve" panel. Picture 5 shows the analysis running. It shouldn't take too long, but keep in mind that the computer needs to take your part and divide it into thousands, if not millions, of little sections and calculate forces for each one. Of course, that all depends on the size of the part and the settings for the mesh. After the analysis is complete, the image will change and a new tree will come up on the left side that allows you to select which results you want to see.
Using the Results
Expand various parts of the tree on the left side to see all the different results. Double click on a particular one to display it on the screen. Some that you might find interesting are the displacement, safety factor, and von Mises Stress.
The displacement shows you how far each part of the structure moved. Picture 7 shows the movement in the Z direction as an example. If you select the von Mises stress, you should see a colorful image depicting the size of the von Mises stress at various points, as in Picture 5. You can use these values to compare to the ultimate yield stress of your given material to determine if failure will occur. I won't go into detail on that, since this is about 3D modeling and not engineering. Safety factors are another factor of engineering interest that you can bring up. Basically, it tells you how many times you can multiply the load before failure, so a safety factor of one would mean the part would fail at the load you have given it. Safety factors vary widely per industry.
Picture 6 shows a spot on the base that is showing the highest stress. If this were a design for manufacture, I would definitely fix something as simple as the base, but this is just a 3D modeling example, so I'll forego the extra work.
Viewing the Mesh
For curiosity's sake, Picture 8 shows the mesh that Inventor made of the part before testing it. Notice how large the sections are at simple geometries and how small they are at complex corners. This keeps things accurate and efficient. You can check out your own mesh by going to the "Mesh View" button under the "Prepare" panel.
Generating a Report
Picture 9 shows the menu for generating a report. To get here, go to the "Report" button on the panel of the same name. In the menu, select what you want in the report, add extra information, and determine the format. The options are somewhat limited - you can choose .html, .mhtml, and .rtf. The first two are webpages and the the last is a rich text format word processing document. If you happen to word for AutoDesk, tell them that .pdf would be handy.
Picture 10 shows the report that Inventor generates. As expected, the report is heavy on numbers and pictures, and low on flowing prose. If you do the defaults, you'll get quite a few pictures, a number of tables, and some file specifics. You can maximize and minimize sections, but in the end it will always be a simple, computer generated report.
Before I wrote this tutorial, I had only had experience with AutoDesk Algor, now called AutoDesk Simulation, for FEA. I'm impressed with how easy it is to work directly out of Inventor, but if you want to work in a separate program just for FEA, go ahead. You'll have to install AutoDesk Simulation and export your model to it from the "Add-Ins" tab in Inventor. Be aware, though, that it's not nearly as user-friendly as Inventor.
Well, that is that, You just got introduced to some of the most interesting parts of engineering, and you thought you were just reading a modeling tutorial! We aren't done yet, though. One more tutorial, straight ahead.
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