Machine Design

Online expert runs your FEA

Small and midsized companies may not afford to keep a full-time FEA expert on staff.

Senior Editor

The bracket assembly has been stress analyzed for a load on the Allen-head hex screw. The table shows three of four results requested by the designer in columns to the lower right. The Original Design showed high stresses in a fillet that was enlarged for the Original Design+ analysis. Red background indicates stresses above an allowable value. Maximum value is in the Limit column. Original Design + Material (not entirely visible) shows lower stress when switching the body from aluminum to steel, but still high. Green shading indicates acceptable values.

The material list shows all assembly parts are of steel. But if minimum weight is a requirement, an analysis could be done with the holder bracket made of duralumin.

An analysis lets a user assign maximum allowable values for qualities such as Von Mises stresses. If this value is exceeded in a simulation, its background field turns red, thereby alerting the user to potential hazards.

The need to analyze designs is handled somewhat by the simple linear-static capability of FEA software that comes in a few CAD packages. So when jobs grow more complex, or demand more exhaustive studies, small companies might turn to the simulation capability of, from PlassoTech Inc., Calabasas, Calif.

The recent service gives design firms a way to get designs analyzed in reasonably short periods by experienced people and without bringing in expensive consulting engineers. The company's timing seems right because many clients expect simulation reports to accompany outsourced design work.

The system works like this: designers who register at Testmydesign.comcan download software that lets them work with TMD engineers. It takes a few minutes but the software installs itself. Designers read CAD models into the software running on their desktop and then check it in to the Web-site project portal with notes and documents telling the TMD engineer what to do. "TMD recognizes the feature-based structure of the CAD data," says PlassoTech CTO Yuri Kizimovich. "However, only some special geometry snapshots are sent outside the users desktop. Hence, original CAD IP doesn't leave local desktop." Even without talking to TMD engineers, designers can tag their models with notes that tell of design necessities such as weight limitations or material requirements. The point is that users need not learn FEA.

TMD software reads the dimensions and materials assigned to the model. These values can be changed for a particular analysis, or function study in the PlassoTech parlance. For example, the software recognizes parts in an assembly so selecting the part and its material icon lets the designer change the assigned material. The local material database holds about 17 materials from which to choose. "If a particular one is not available, a MatWeb icon lets users import data for many other materials from the online database. After analysis, users get results they requested along with the usual color contoured 3D models for further examination.

Users that get comfortable with the software can use a wizard to set up an analysis. Just work through the wizard's icons to assign materials, constraints, loads, and results. Checking them into the Project Portal tells a TMD expert to take over. According to Kizimovich, users sufficiently familiar with the software can opt to run their own analysis and bypass the TMD support.

But before that, designer and TMD engineer would probably start collaborating after an initial analysis. I took the role of designer and Kizimovich, the TMD engineer. As usual, the first run turned up a few model peculiarities. The bolt at the end of the test bracket, for example, acted like a rod in a hole rather than a bolt, and that's because the designer did not model the many small details required for screw threads, a frequent tactic to minimize model size. The TMD analyst pointed this out and I gave approval to fasten the bolt to the hole so that it behaves appropriately. "To straighten out problems like this, the designer and TMD engineer could get online together to see the problem in 3D and discuss an acceptable solution," says Kizimovich.

After an initial adjustment, the design may still reveal problems. For example, the assembly in the images showed high stresses in a sensitive location. At the designer's prompting, the TMD engineer might initiate a second study to see how changing a fillet affects results. If that does not reduce stresses enough, the designer might suggest a different material for the body, such as steel instead of aluminum. Additional analyses are added as needed. Results are summarized in a spreadsheet, a presentation method that differs from most FEA programs. Designers and engineers can try TestMyDesign.comfor 30 days at no charge.


Hide comments


  • Allowed HTML tags: <em> <strong> <blockquote> <br> <p>

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.