Palatine, IL —Electrical equipment giant Square D sponsors Andy Petree Racing's #55 Chevrolet race car, driven by Bobby Hamilton in NASCAR's Winston Cup series. Square D also supports finite element analysis (FEA) for the team's designers.
But lately, the race car has been gaining speed thanks to someone who doesn't even work for the team yet. Scott Littler, an engineering student at Ohio State University, currently works as an intern for Square D, and will join the company full time upon graduation this summer. He recently ran a series of analyses on the front suspension's lower control arm, where the team had seen repeated fractures and cracks.
I-DEAS software determined the reason for frequent cracking in the standard control arm. The Von Mises stress results showed the areas of greatest stress (in red).
The lower control arm has to take the weight of the car, resulting in a great deal of stress. The arm and its connections make up a complex assembly, in which the arm attaches to the chassis through mono-ball bearings. A spring located in the arm's "spring bucket" transmits the weight of the car to the control arm. A shock absorber and a swaybar link connect to either side of the spring bucket, respectively. A ball joint threaded into a ball joint ring is supported vertically at the tire.
Littler modeled the lower control arm in SDRC's I-DEAS, which Square D uses for FEA. Analysis results showed that a bend in the front leg of the part received the greatest stress, with additional high-stress areas at the bottom corners of the inside edge. In all, the stress level proved greater than steel can handle, resulting in the high incidence of cracking. Team technicians studied a physical lower control arm, and found that the cracks appeared just where analysis predicted.
Littler looked for ways to reduce the stress. "The rules of NASCAR keep a lid on technical innovation, so they couldn't change the material they used for the arm," he says. He came up with 10 possible design modifications, eventually finding that the greatest stress reduction could be obtained by adding an internal strap and c-sections cap at the tube bend.
The team has already implemented two of Littler's suggestions, and will make an internal modification to the way they build new arms for the cars. Littler is also working on an analysis of the car's rear axle.
For more information about Square D: Enter 542
For more information about I-DEAS from SDRC: Enter 543