Tire industry continues transition toward virtual development

AKRON — The push toward sustainability is not abating, and time-to-market, like safety, remains critical for tire manufacturers.

As such, tire modeling is gaining traction at all levels of tire development — from manufacturing to fatigue and cold-weather testing.

"At this point, simulation is deeply embedded with every tire maker, not only in research and development departments but also in production engineering workflows," Will Mars, president and CEO of Findlay, Ohio-based Endurica L.L.C., told Tire Business sister publication Rubber News.

"Basic tire design targets — including dimensions and shape, load and deflection curves, footprint pressures and shapes — are routinely checked via simulation any time there is a new tire size or specification, or a change to an existing specification."

More advanced simulations can predict many key tire performance requirements, including rolling resistance, heat buildup, NVH, force and moment behavior, and durability.

"These tend to be used in developing engineering packages as due diligence for OEM contracts, or for design sensitivity studies focused on new product development," Mars said.

And major tire makers are out front with the move toward "virtuality."

"I'm guessing that it is routine these days for a large tire maker to have a team of 30-50 simulation engineers," he said.

But the transition to 100-percent virtual development, testing and production also is a ways away. Regulatory tests, which have to be passed to bring new tire designs to market, remain.

"Unless the government starts accepting simulation results in lieu of actual tests, I do not see a day when simulation will completely eliminate testing," Mars said. "But we are quickly evolving to a place where the expectation of passing all tests on the first try gets higher than it used to be.

"If you are not leveraging simulation effectively, you will not be able to compete in that context."

Michael Stackpole, president and founder of Stackpole Engineering Services Inc. of North Canton, Ohio, said simulations allow a driver to evaluate infinite combinations of models and designs, without having to build a physical tire or physical vehicle.

"You can imagine the advancements that had to happen for a driver to get realistic feedback at a computer—and we're just at the beginning of it," Stackpole told Rubber News. "The industry is moving quickly in the direction of relying less on physical prototypes and more on simulation models, especially during the initial design phase.

"I envision a day when every step of development can be done virtually."

Mars puts the nascence of virtual testing at about 1978, when HKS—or Hibbitt, Karlsson and Sorensen Inc.—was founded.

The group of engineers produced the abaqus finite element code, which distinguished itself "by focusing on solving nonlinear problems."

"There were many codes at the time, but ... this was ideal for tire analysis," Mars said. "The uptake by the tire industry was quite slow at first, with many competing alternatives. Most tire companies at the time were writing their own in-house codes."

But in the late 1980s and early 1990s, NASA funded the National Tire Modeling Program that sought to speed the adoption of simulation methods in tires.

The abaqus code became dominant in the tire industry "by perhaps the year 2000," Mars said.

"The adoption of simulation by the tire industry has been driven as much by software technology as by advances in computing capacity," Mars said.

Before virtual tire development technology, tire development "looked very different," Stackpole said.

"Tire OEMs would have to build a physical tire and run it on a flat trac machine to collect the data they needed to create a tire model," he said. "The process was costly, but there was no way to develop a virtual tire model without first building that physical tire."

And that can be expensive and wasteful.

"If the tire didn't test well and the driver didn't like it, it was back to the drawing board," Stackpole said. "This process required the creation of physical tires, which came with financial and time commitments. Simplified tire models were available, but their use was limited to basic tire performance characteristics."

As computers and tire modeling became more advanced, the industry began to leverage that technology.

"More importantly, they came to understand how the tire would interact with the vehicle," Stackpole said. "Simulation is now an integral part of the design and prototyping process for tire and vehicle OEMs.

"Everything about the technology is advancing quickly, from the complexity of the models to the industry's expectations of what these models should be able to do."

Soon, the industry also came to note the importance of simulating a tire's interaction with the road, as well.

The history of snow traction testing goes back to the 1970s, when CTI —now Smithers Rapra— created the first snow penetrometer. The 1980s and 1990s saw innovations in analysis, as well as the publication of several ASTM standards.

In 1999, the Mountain Snowflake—a regulatory threshold required in some cold weather regions—was introduced by the U.S. Tire Manufacturers Association and the Rubber Association of Canada.

After more than five decades of physical testing, much of it pioneered by Smithers, Principal Engineer Eric Pierce knows there is no easy path to simulating snow coefficients for cold-weather testing.

The process to achieve that goal, or at least toward much tighter testing parameters than currently are possible, will take time.

And it will take high-end mathematics to solve an overall algebraic challenge.

"The goal is to better predict what the tire and snow traction coefficient should be, given a particular range of metrics," Pierce told Rubber News. "This could lead to improved repeatability and consistency of results, potentially creating narrower test constraints or showing when results are beyond the expected result."

As the traction (or skid resistance) coefficient increases, the grip between the tire and surface increases (caused by braking).

On a compacted snow or ice surface, which is most frequently observed for testing and compliance companies like Akron-based Smithers, coefficients typically are between 0.1 to 0.4, depending on the type of tire tread and consistency of the specific snow or ice surface.

But unlike a relatively even surface like ice, the consistency of snow changes, and it changes quickly.

As the upper layers of snow are removed, freeze or melt, a relatively low coefficient of 0.2 to 0.3 (poor grip, high slippage) can increase to 0.4 or 0.5, as large ice granules form.

In Smithers' study, "Correlating tire traction performance on snow with measured parameters of ASTM F1805 using regression analysis," the designated wheel was an all-season tire.

"The first goal (of virtual modeling for traction testing) is to determine which characteristics—specifically measurable, tangible traits—of snow are the prime contributors to the tire/snow surface traction coefficient for one particular tire," Pierce said. "There is no quick repeatable, non-destructive way to measure and characterize a snow surface. Ice, on the other hand, is homogeneous in comparison to snow and currently allows for more predictability in tire/surface traction interactions."

Smithers hopes to build off this research, marrying both virtual tire modeling for manufacturing purposes with the virtual modeling of cold weather analytics.

Like Endurica's Mars, Pierce cautioned that a completely virtual-testing future is farther away than one might think.

Significant strides are being made at the Center for Tire Research (CenTiRe), a consortium of industry and academic partners based at Virginia Tech University and the University of Akron, Pierce said.

"This goal is far off from the current state of technology," he said. "The move toward a virtual environment-based future for tire development is being discussed in many circles right now.

"The existence of accurate snow material models or computational models is essential for better virtual development of winter tires. Such models could ensure better evaluation of the tire during the design and development stage before the manufacturing stage."

No one has a crystal ball for the moment when tires will break down, but Endurica certainly has a well-educated guess.

The Northwestern Ohio firm continues to draw attention for its simulated tire evaluation capabilities, this time from the Department of Energy for its work on tire tread pattern predictions.

"Where it was originally only possible to model a tire cross-section with a few hundred finite elements and days of computing time, today tire models are routinely solved having hundreds of thousands of elements, or even millions, in hours," Mars said.

"Simulation will never completely replace physical testing, but it will make it much easier to hit testing standards on the first prototype tire build."

Endurica was selected July 14 as a partner with Utah-based Coreform in the DOE project to explore simulated tire tread patterns, a crucial step in understanding tires emerging in the electrical vehicle space.

Coreform's computer simulation technology, known as isogeometric analysis, replaces the complex and time-consuming portions of computer simulation that are traditionally done through finite element analysis.

"Where there is alignment of broad society interests in energy and environmental issues with emerging capabilities like IGA, it makes sense for DOE to invest in high-risk, high-return technologies," Mars said. "Tire companies are often reluctant to be the first to take risks on unproven technology, so this funding really helps get over the initial hurdles."

Specifically, Endurica will apply Coreform's IGA in rolling resistance, heat buildup and wear behavior in tire treads. According to Mars, the software developed by Coreform "provides greater design clarity and detail" than finite element analysis.

The company will be able to provide key tire performance evaluations to the entire industry once testing is complete.

"Coreform's isogeometric analysis is going to make it much easier for tire companies to simulate tread pattern in full detail," Mars said. "In the past, much of the complex tread pattern has been neglected in analysis. The geometrical complexity was just too much for traditional methods, resulting in huge jobs."

Rubber part development has been a game of steady, iterative and incremental progress "for a very long time," Mars said.

But the rapid growth of EVs has been a major disruptor.

"Electric vehicle companies are really pushing the envelope and asking the most of tire and vehicle simulation technology," Stackpole said. "They've got a big job ahead of them in terms of getting new vehicles out there without any of the legacy data that the other players can rely on, so they've really embraced the virtual development model."

Mars said EVs bring "radically different design requirements."

"It is arguably the largest disruption that has come along since simulation has arrived," Mars said.

"Now that simulation is well-established, and now that there is heavy pressure on development agendas to get these designs right on the first try, it makes complete sense that they go together."

And if safety can be maintained, sustainability will follow.

"I couldn't begin to guess how many development tires we built and tested back in the early nineties," Stackpole said. "We had lots of experience with compounding and recipes, but no one really knew what to expect from a performance standpoint until the tire was built.

"Transitioning to this virtual development methodology results in not only cost savings, but a tremendous reduction in terms of the physical tires we would have to build, test and toss in those early days."