Machine Design

Easy-to-use FEA tells more about your products

One long-developing engineering trend is for designers and less-skilled engineers to make a first-pass analyses of their designs. Then if a part isn't up to snuff, it can be changed right away by people most adept at doing so.

The bracket was designed in Alibre Design Professional and stress analyzed in DesignCheck from Algor Inc. The software works only on single parts. Calling up the meshing functions (a brick element mesher) lets users apply coarse or fine meshes simply by positioning the slider bar.
A library includes properties for a few dozen common materials. Users can add materials and adjust properties.
A right-click pulls up menus for meshing and adding loads and boundary conditions. To add the effects of bolts, a surface boundary condition fixes the inside of the bolt-holes.
Arrows around the large hole indicate an applied load.
An HTML report on the analysis could be emailed to anyone for review and comment. Its table of contents appears to the left. The results for a 500-lb load show low stresses for an aluminum bracket. It also shows that the top two holes are doing no work, so they can be eliminated. In addition, thinner and possibly less-expensive material could be used for the selected load.

The trend has been slow to develop because FEA can take many weeks to learn. Recent FEA packages, however, are easier to work with as developers trim features unlikely to be used and streamline tasks.

DesignCheck from Algor Inc., Pittsburgh, is one such analysis program. It was originally introduced to work with solid models from the Alibre Design and Alibre Design Professional CAD systems, from Alibre Inc., Richardson, Tex., and handles linear-static simulations. It took only 2 hr to load the software, build a solid model, view an analysis demo, and run a linear-static stress simulation. I'd say that qualifies as easy to use.

For an introduction to the software, I watched a self-running demo that described the stress analysis of a bracket. The demo shows a sequence of selections and introduces several features.

DesignCheck starts when users select it from the Add-On menu under Tools in the CAD software. From there on, it is quite intuitive -- mesh the part, apply boundary conditions, apply a load, run the analysis, and examine results. Each takes a few selections. The only challenge is learning the mechanics of doing just that, which are shown in the demo. For example, to apply a boundary condition, users select the surface and right click the mouse. That brings up a menu that allows fixing surfaces. After jumping from demo to model a couple times, the selections seemed second nature.

But the demo only introduces about 30% of the software's functions, such as applying surface loads and constraints, which are used most often. Learning to apply point forces or displacements, which are used less often, takes a little digging. Fortunately, the developer tells how in an HTML user's guide that comes with the software. Another tutorial is available from the Algor Web site and a free Webcast is available online at (Type DesignCheck in the search field to locate it.)

When an analysis finishes, users can capture images and send them to others for comments. Cutting planes are also available to show internal stresses.

Users will quickly see the value of having a solid modeler and simulation program closely connected. A check on the strength of the bracket after shaping it tells whether or not the design is working. For example, examining the results image shows that the top two holes through which bolts would connect are doing no work, and so could be omitted.

DesignCheck seems a good way to get comfortable with FEA. The software uses the same user interface as Algor's Professional product line so users can upgrade to additional analysis capability as their needs change. The product can be leased for $495 for three months, or $1,485 per year. The software also works on models from Autodesk's Mechanical Desktop and Inventor, Solid Edge, Cadkey, SolidWorks, Pro/E, and others.

DesignCheck for Alibre Design Professional comes from Algor Inc., 150 Beta Dr., Pittsburgh, PA 15238, (412) 967-2700,

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