CenTiRe sees improvements with tire simulation, but says work remains

INDIANAPOLIS—The use of simulation has made great strides the past few decades to where it is an integral part of the tire development process, but it still has room to grow, according to the keynote speaker at the ACS Rubber Division Spring Technical Meeting in Indianapolis.

Ron Kennedy, managing director of the Center for Tire Research, said accuracy of the simulations currently limit their effectiveness in the process and is slowing their incorporation into the product approval process. Specifically, he said that simulations related to material response and properties are areas where improvements still need to be made.

CenTiRe is headquartered at Virginia Tech University and is a consortium between that school, the University of Akron and about 18 industry partners, including most of the leading tire makers. It conducts what Kennedy calls "pre-competitive research" in materials, tire physics, testing, manufacturing and sustainability that is directed by the industry members.

Kennedy said tire and tire/vehicle simulation date back to the 1930s. The beginning dealt mainly with analytical questions to predict tire shape change caused by prescribed loading. Computer-based simulations started around 1970, based on the finite element method, with tire/vehicle dynamics simulations following in the late 1980s to predict handling performance.

From there, he said the simulations have expanded to predict an increasing number of performance areas, and that usage for tire and manufacturing process development continues to grow.

"What we try to do with simulation is build less and test less," said Kennedy, who worked 37 years in the tire industry—much of it in simulation—for Firestone, Bridgestone/Firestone and Hankook, before retiring and moving to CenTiRe. "We want to reduce that cycle time so we get the product out the door quicker and better. The first time we build the tire, hopefully it will be a lot closer to what we want it to be."

He said the key is to get the tools in the hands of the people designing the product. They are the ones who know the trade-offs and the customers, and the goal is to develop simulation tools they can run themselves.

He told the Rubber Division audience that simulation fits in over all parts of tire development, including such areas as tire contact and stiffness prediction, state of cure prediction and forecasting cure temperature.

"It's a lot easier doing it on a computer than out in the factory with a thermocouple," Kennedy said. "After the tire is cured, it has to cool down. When it cools down, it changes shape. If it changes shape, that's going to change how the performance is. We want to be able to predict that."

Tire companies are doing a lot of work with tread wear simulation, and can predict hydroplaning behavior, showing how the tire loses contact and goes above the water. Similar models are used for icy road conditions, and can predict braking performance on ice.

The use of optimization tools can be set up to create models, run them and collect results, according to Kennedy. "It could be a couple hundred run, or just a simple optimization study," he said. "It can take many hours or days. And you go on and build the optimum design from there. It's a very powerful tool that's really starting to gain a lot of work in the tire companies."

But while scientists and engineers can predict some performance measurements, Kennedy said he is hearing that the tire companies and customers say the accuracy must improve.

"One thing I've heard more and more is they want it to have accuracy," he said. "They want to be able to look at a number. It's starting to get to where a trend watch is just not good enough."

Kennedy said as he left the industry and transitioned into his new role, he started to see some vehicle customers asking for simulation results in place of test results. "They were accepting some of our simulation results with some simple models that they could use in vehicle simulations," he said.

That led to more co-work between vehicle companies and their tire suppliers, as they worked to improve the models and get more capabilities.

"But we still have that accuracy questions," Kennedy said. "Tire development engineers and vehicle makers want to be able to rely on the results of the simulations. This is really to me limiting. I think getting that accuracy for those simulation models is probably more important than developing new capability."

Simulation of rubber materials is one area with much room for improvement.

"As I tried to improve the accuracies of the simulations I was working on, I kept butting my head up against the material representation and characterization," he said. "How do you get those better?"

Kennedy added that he wasn't looking to assess blame, just trying to emphasize the need to get better.

There are many ways to get models of materials, so it is important to determine which are best for use in tire development projects. For example, he found one model that worked well at room temperature, but another that was superior at elevated temperatures. That shows the need, he said, for a physical model that truly represents the materials in use.

Kennedy added that material modeling must run quickly, so the other parts of development can go forward.

"You have to represent the physics and you have to represent the chemistry," he said, "but we can't spend days waiting for an answer because our tire development engineers have to get that spec out and get that mold drawing out. If you don't deliver your results on time, they'll just leave without you."

The keynote speaker added that compound material characterization must deal with real tire operating conditions, and that information is needed beyond modulus and hysteresis, including such variables as more realistic and accurate friction representation.

Tire and material development currently are developed in separate parts within a tire company, and that must change.

The goal of simulations is to conduct product development in the virtual world before a physical sample is made; make an improved product quicker and with less cost; and give an insight into cause-effect relationships that can be leveraged to produce a better product.

Kennedy said that these principles hold true for both tires and materials, and the ability to bring the two areas together and eliminate silos in research and development would be a major step forward.

"Is there a way to take and build virtually to save on time and costs and tests?" Kennedy asked. If this can be accomplished, he said it's likely results will improve, and tire companies can "get the best tire out the door."