UNIVERSITY PARK, Pa. (Jan. 8, 2001)—Researchers at Penn State University have developed a computer simulation that will allow tire designers to perform virtual road tests while tires are still in the concept stage.
The simulation allows designers to establish the speed at which a "standing wave" is formed and a tire deforms, heats up and eventually blows out, said Moustafa El-Gindy, director of the Crash Safety and Vehicle Simulation Research Centers at Penn State´s Pennsylvania Transportation Institute.
"The ability to predict the standing wave did not exist before this work," he said. "It was always theory."
Current simulators only test tires under static conditions, whereas Penn State´s simulation tests them under dynamic stress, Mr. El-Gindy said.
"This is the way things are going to go in the future," he said. "There´s no way the tire companies are going to continue with only static testing for tires that will be used on the road."
Before, tire designers had to build a prototype tire and then test durability and endurance on a tire testing machine, Mr. El-Gindy said.
The simulation not only allows designers to "build" a tire virtually, but also a rim and test drum to run it on, he said. The program simulates a tire rolling on a test drum and enables engineers to adjust a myriad of factors, including compounds, tire pressure and others, Mr. El-Gindy said.
While the program cannot replace actual road testing, it will enable tire designers to test critical elements earlier in the design process, he said.
Being able to predict the standing wave also will allow more precise calculation of speed and temperature ratings for tires, Mr. El-Gindy noted.
Until now, speed ratings on tires have been based on theoretical models or some testing into what the critical speed of a tire is, he said. Penn State´s simulator will allow a true measure of the performance limits of tires, Mr. El-Gindy said.
"The tire must be characterized by the critical speed and the tire companies don´t know what the critical speed is," he said. "There is a need for more precise and accurate analysis of tires—and not statically."
Penn State´s simulator can test virtual tires at speeds up to 450 kilometers per hour (about 280 mph), Penn State said. It also allows designers to include "bumps" or other obstacles on the virtual drum to test tires under those stresses, Mr. El-Gindy said.
The program works through a mathematical technique called non-linear finite element analysis, in which a tire is "built" virtually by dividing it into numerous regions and connected subregions for which numerical values are known or can be estimated, Penn State said.
For example, the researchers´ mathematical model of a tire includes 7,880 shell elements, 4,200 solid elements, 1,680 membrane elements, 120 beam elements and two rigid body elements for the rim and road obstacle.
The program the researchers use to run the simulation is called Pam-Shock, finite element analysis software developed by France´s ESI Group, Mr. El-Gindy said.
The information that can be gleaned from dynamic analysis is much more detailed than what is available from static simulators, he said.
"It´s a step forward in terms of the finite element analysis that tire companies can do," Mr. El-Gindy said. "In terms of design before manufacturing, this will save them a lot of time."
Some analyses can be run on a simple PC, but detailed analyses require a work station and may take five to seven days to complete, he said. While static testing requires less computer time, it is less detailed and leaves a lot more work to be done when road testing actually occurs, El-Gindy said.
So far, Penn State researchers have used the simulation to find that when inflation pressure is reduced below a manufacturer´s recommended value, the speed at which the standing wave forms is reduced and the energy consumed by the tire increases significantly. This results in a rapid rise in tire temperature, energy consumption, rolling resistance and fatigue, Penn State said.
Results from the tests the researchers have performed show excellent agreement with experimental studies, according to Mr. El-Gindy. Penn State has a license from ESI Group that will allow it to run tests of companies´ tire designs, he said.
"We construct the tire as it is in reality, and then we can test it and give the results to a tire company," he said.
Penn State also can train tire company engineers in the use of the Pam-Shock software for dynamic testing of tires, Mr. El-Gindy said.
Penn State researchers demonstrated the simulation in October for companies including Goodyear, Pirelli North America Inc. and Caterpillar Co., he said. All showed interest in the project, Mr. El-Gindy said.