Endurica software gets better with aging

FINDLAY, Ohio—About four years ago, an OEM came to Endurica L.L.C., a pre-prototype solutions company that focuses on the predictive durability of elastomers, seeking a more accurate fatigue life estimate for a rubber component.

The customer had complained that its previous testing firm had missed the mark by a wide margin in its end-of-life predictions for the part, which was attached to a hot engine at one end and a cold frame at the other.

Such a drastic temperature range takes a toll on such parts, so Will Mars, Endurica founder and president, and his team set out to create algorithms that accounted for the influence of time and temperature on a rubber part—ultimately creating pioneering software that combines aging and crack growth predictions in the same simulation.

"This is one of our most significant developments to date because aging impacts so many applications," Mars said. "If there is a big temperature difference, or if there is significant self-heating, and if your part is expected to have long-term endurance, this feature is a real game-changer in terms of your ability to predict durability performance."

In essence, the software helps solve a root problem for OEMs: How does one perfect the chemistry of a tire, seal or gasket if one does not know how a part will react over time in a harsh environment?

"This is a feature that was developed and validated over the last few years in partnership with one of our Tier 1 automotive OEM users for an application where long-term exposure to high temperatures was leading to early part failures," Mars said. "The impetus for the software was that what they were doing was not working. It became obvious pretty quickly that aging was the missing part of the simulation."

When something goes wrong with a part, Mars said, it is usually due to poor decision-making in raw material selection.

Should an engine hose be made of silicone, which exhibits excellent aging but is susceptible to cracking? Should it be made of natural rubber, which is strong and crack-resistant, but ages poorly?

"Do they use natural rubber? Silicone? A TPE? I run into many poor decisions in the selection of materials," he said. "And testing is time consuming and expensive, offering no visibility into what happens if this is changed or that is changed. This could make a huge impact on material selection decisions, all of which depend completely on the conditions of the application—what the part is intended to do, and the loads and temperatures to which it will be subjected."

And numerical simulation provides a tried and true method for evaluating design features before making a larger investment in physical simulation, or before getting to the "build and break" stage, Mars said.

After the years-long project, Endurica was able to offer a customized version of the new simulation software to the OEM, and the official release of the predictive aging software came just last month, complete with a well-attended training webinar led by Endurica on its use.

"We've had a very good response to it so far," Mars said. "There has been a lot of interest. Aging is everywhere—look at Ford and Firestone and the aftermath there. Other studies have been on the shelf life of tires, and in oil and gas it's the same thing. When there is high pressure and high temperature, the rubber chemistry is crucial—and can save a company in downtime and its bottom line."

How it works

New data points offered in Endurica's software include age-equivalent time and age-influenced stiffness analytics, which, combined with crack growth simulation, make the new software unique, Mars said.

For years, Endurica has offered software that addresses crack growth simulation, another predictive measurement, but has never combined it with these two parameters.

"There is no other commercial software that does this," he said. "For a long time only academic papers were addressing the aging side. We have combined aging and crack growth in one simulation."

Endurica bases its software on the Finite Element Model, which develops mathematical equations for each "finite element" of a model—not chemical elements, but rather defined geometric domains on the specific rubber part that, when broken down and specified, can combine to define the overall predictive crack growth and aging of the entire part.

"Each little location has a finite element of the model," Mars said. "We write calculations for every one of these finite elements. In the context of the software, it's like a mini geometric domain that you are using to write a mathematical equation for the overall high stresses and strains of that finite element. High pressure and temperature will cause a part to fall apart faster than an element that has less of a load and is cold."

Certain material properties are measured for each finite element, Mars said, including the stiffness of rubber, a modulus that predicts how it will evolve with time and temperature; crack growth rate properties, or critical tearing energies based on the crack growth rate law; and strength and fatigue limit, or the intrinsic strength of rubber.

But new to the software is keeping track of age-equivalent time, to which the Arrhenius law is applied, Mars said. This foundational law for the software essentially is the ratio of the chemical reaction rate of the elastomer to temperature—that is, the hotter a part gets, the faster the chemical reaction will take place that fundamentally changes the elastomer.

The software uses the Arrhenius law to calculate the aging rate as a function of temperature, and then integrates this information "to find equivalent exposure time for each element in the finite element model," according to Endurica.

"We characterize the material," Mars said. "How does it change with time and temperature? We need to be able to imagine what is happening to a part in the field, down an oil and gas hole, or other harsh environment. The analysis is concerned with the part's history of loading. What temperatures and loads and stresses are around it?"

The software can be used to simulate aging conditions on all types of elastomers, even those that are proprietary or otherwise protected intellectual property, Mars said.

Integrated into the software is the ability to keep certain trade or material secrets under lock and key, in that only the parts of the simulations that an OEM or aftermarket customer wishes to share with another customer in the supply chain—or even a competitor—can be made public.

"Normally we provide a copy of the software to the customer's engineers and we support them and provide training," Mars said. "There is a license lease that we sell, and there is a paid-up version. There are different tiers for different customers."

The ability to keep trade secrets protected was a suggestion that came from another customer.

"They had spent $100,000 in testing materials and built this huge database and cache of information," Mars said. "Suddenly they felt very vulnerable that someone could would walk off with their data, and they suggested that we provide a way to encrypt that.

"So we introduced a feature that lets you measure loads at a track and then place any element you want under lock and key with a password on it. The OEM can share a part of their information without giving away everything to a third party company."

Mars said that with this practical aging software, rubber component manufacturers now have the opportunity to design better parts.

"I think we are going to be seeing a lot more well-designed things coming on the market," he said. "We are very excited to finally launch this capability."