New Computer Simulation Allows Tires To Be Road Tested "Virtually" Before Manufacture

The Penn State researchers include Dr. Moustafa El-Gindy, director of the Crash Safety and Vehicle Simulation Research Centers at Penn State's Pennsylvania Transportation Institute (PTI); Dr. Donald A. Streit, professor of mechanical engineering and director of the PTI Vehicle Systems and Safety Program; and doctoral student Yin Ping Chang. Dr. Argiris Kamoulakos, Gregg Svitchan and Dr. Etienne Gai of ESI provided technical support.

The international team developed the approach using Pam-Shock, software commercially available from ESI Group, which markets simulation packages for predictive virtual testing of industrial prototypes or processes. The approach will be described today (Oct. 9) at a joint ESI/Penn State seminar, "Simulating Rotating Tires on the Road," in Akron, Ohio.

El-Gindy says, "Tires are probably the most complex component of a vehicle and tire performance, especially at high speeds, is critical from the point of view of vehicle safety."

He explains that every tire has a maximum speed limit at which a "standing wave" occurs along the tire circumference causing deformation, a temperature rise and eventual failure. The speed at which the standing wave forms and failure occurs is usually found using a tire testing machine which rotates the tire in contact with a drum to measure durability and endurance.

Using the new Penn State/ESI software, engineers can now, for the first time, produce a computer simulation of any tire type at any tire inflation pressure rotating on a test drum and predict the formation of the standing wave. El-Gindy says the results obtained from the simulation show excellent agreement with experimental studies.

The Penn State researchers used the simulation, which can be run on a PC, to investigate the effects of different tire inflation pressures on the formation of the standing wave, the energy consumed by the tire, the forces acting on the tire spindle and the pressure at the patch where the tire meets the road. They found that, as the inflation pressure is reduced below the manufacturer's recommended value, the speed at which the standing wave forms is reduced and the energy consumed by the tire is increased significantly, resulting in a rapid increase in tire temperature, energy consumption, rolling resistance and fatigue.

In addition, the Penn State researchers used the simulation to study the road vibrations transmitted from the tire's contact patch to the chassis, an objective index of ride comfort. For the first time, they also included a virtual "bump" in the simulation to look at the effect of obstacles on the tire's performance and the comfort index. The simulation results were validated against previous experimental and simulation work and showed excellent agreement.

While there are other simulation packages available to analyze tire performance, the new Penn State/ESI approach is the only one that produces an actual visualization of the tire in contact with the test drum, the only one that simulates speeds up to 450 kilometers per hour (approximately 280 miles per hour) and the only one that can simulate a tire rolling over multiple "bumps."

The Penn State/ESI team used a mathematical technique, called non-linear finite element analysis, in which they "built" the visualization of the tire by dividing it up into numerous regions and connected subregions or elements for which numerical values are known or can be estimated. For example, their mathematical model of the tire includes 7880 shell elements, 4200 solid elements, 1680 membrane elements, 120 beam elements, and two rigid body elements for the rim and the road obstacle.

"Although the simulation will not replace actual road testing, it can help tire manufacturers predict and understand critical phenomenon earlier in the tire design process," El-Gindy says, "Designers will be able to input the specifications for their tire designs in the program and predict and even preview the design's road performance. We think this preview and prediction capability will help increase safety factors while saving time and money."