Machine Design

Focused FEA lets designers run fatigue analysis

MSC.Acumen provides the interface to MSC.Nastran and MSC.Fatigue for automotive supplier Hayes-Lemmerz. One function of the interface automates meshing.

Stress results are also automated. MSC.Patran shows principal stresses on one wheel design for the prescribed rotational loads.

Three plots of different locations on a wheel show stress behavior through one rotation. Wheels are subject to high-cycle fatigue, which is defined with low loads and life greater than 100,000 cycles. Hayes-Lemmerz uses the stress-life (S-N) or total life method in MSC.Fatigue for high-cycle fatigue applications. The applied stress is within the elastic range. Should a crack even begin, the design has failed and a redesign begins.

Engineers with Hayes-Lemmerz International run every automobile wheel they design through rigorous FEA and fatigue simulations, thanks to the integration provided by MSC.Acumen.

The software creates the mesh, and applies loads, boundary condition, and constraints. Special functions eliminate manual work previously required to identify peak stresses from multiple loads. Each design generated by the Northville, Mich., company is physically tested as a final check before manufacturing to correlate simulation results and provide customer specified test and validation data.

Part of the manufacturer's problem was that wheels had to be designed in one of three CAD systems, I-DEAS, Catia, or Unigraphics, one for each of their customers. Analysts had to manually prepare each model for simulation. "We spent too much time cleaning geometry and creating meshes," says Khosrow Namdarian, an analyst with the manufacturer. "Then it took at least a day to run a simulation on one design," he adds. MSC.Nastran provided rotary and radial wheel loading tests, and MSC.Fatigue simulated high-cycle fatigue. Physical tests that followed often resulted in revisions and additional testing. "Writing a report, making copies, and distributing it consumed still more time," he adds.

Integrating MSC.Nastran and MSC.Fatigue through MSC.Acumen automates simulation to the point where Hayes-Lemmerz's engineers can control designs from initial through final test. Simulation is now performed on every design without a dedicated analyst. "Designers run stress and fatigue predictions in less than an hour, and we optimize designs before physical testing, eliminating all but one set of physical tests per design," says Namdarian.

"Engineers can learn MSC.Acumen tools in an hour because it is almost completely automated," says Namdarian. "As a side benefit, we've been able to optimize wheel design for weight while maintaining strength. This has saved a quarter pound of aluminum per wheel on 4,000,000 wheels — 1 million pounds."

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