Minimizing car tire prototypes with non-linear FEA

Every day, millions of car tires hit roads around the world. Analyzing this interaction between an automobile tire and the road is one of the most challenging problems in computational mechanics today. It is a very complex 3-D contact analysis, involving a complicated shape (tire cross section), composite materials (comprised of polyester or steel cords, steel wire beads, and rubber—leading to anisotropic behavior), uncertain loading conditions (mounting loads, inflation pressure, car weight, side impact, hitting a curb, temperature effects for a car cruising, etc.), and large deformations. Friction, dynamic, and fatigue effects are also important.

All leading tire manufacturers use nonlinear FEA to help design safer and better tires. While none has, as of yet, abandoned full-scale testing, FEA allows them to minimize the number of prototypes required by eliminating designs which are not structurally correct or optimal.

The tire is modeled using rubber continuum elements, a collection of 15 different isotropic and orthotropic materials. The metal wheel is modeled with continuum elements. The road is assumed to be rigid. The complete load history consists of: mounting the tire on the rim; internal pressurization up to 1.5 bar; applying the axial car load; and rolling down the road. The deformed tire shape is shown, and the contours are of the displacement magnitude as the tire begins rolling to the left. A good tire model is, by definition, very complex and typically consists of hundreds of thousands of 3-D elements.

In addition to the complexities of tire analysis, car and tire manufacturers also need to worry about occasional “buckling” of the bead region, tire wear for different tread designs, noise transmitted to the passenger cabin, ride comfort, tire puncture by a nail or glass, and traction effects due to rain, snow, and ice. Passenger safety, manufacturability at reasonable cost, and tire life are the most important design objectives, and each of these is significantly improved through finite element analysis.