Fatigue limit of particle-reinforced rubber improved by new method

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Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have increased the fatigue limit of particle-reinforced rubber, developing a new, multifaceted approach that allows the material to withstand higher loads and prevent crack growth during repeated use. This approach will not only increase the lifespan of rubber products such as tires, but also reduce the amount of pollution caused by rubber particles during use.

Published in Research Nature.

Naturally occurring rubber latex is soft and stretchy. For a variety of applications including tires, hoses and dampeners, rubbers are reinforced with hard particles such as carbon black and silica. Since their introduction, these particles have greatly improved the stiffness of rubbers, but not their resistance to crack growth when the material is cyclically stretched, known as the fatigue limit.

In fact, the fatigue limit of particle-reinforced rubbers has not improved much since it was first measured in the 1950s. This means that even with improvements in tires that increase wear resistance and reduce fuel consumption, small cracks can release large amounts of rubber particles into the environment, causing air pollution to humans and accumulating in streams and rivers.

In previous research, a team led by Zhigang Suo, the Alan E. and Marilyn M. Puckett Professor of Mechanics and Materials at SEAS, significantly increased the fatigue limit of rubbers by stretching the polymer chains and densifying the entanglement. But what about particle reinforced rubbers?

Assuming that the particles increase stiffness but do not affect the fatigue threshold, as commonly reported in the literature, the team added silica particles to their highly complex rubber. They were wrong.

„It was very surprising,” said Jason Steck, a former graduate student at SEAS and co-first author of the paper. „We didn’t expect that adding particles would increase the fatigue limit, but we found that it increased tenfold.”

Steck is now a research engineer at GE Aerospace.

In the Harvard group’s material, the polymer chains are long and highly tangled, while the particles are clustered and covalently bonded to the polymer chains.

Junsoo Kim, a former graduate student at SEAS and co-first author of the paper, said, „This material reduces stress around a crack at two length scales: the length of the polymer chains and the size of the particles. . . This combination stops crack growth in the material.

Kim is now an assistant professor of mechanical engineering at Northwestern University.

The team demonstrated their approach by cutting a crack in a piece of their material and then stretching it tens of thousands of times. In their tests, the crack never grew.

„Our approach to multidimensional stress reduction expands the space of material properties, opening the door to reducing polymer contamination and creating high-performance smooth machines,” said Suo, senior author of the study.

„Traditional approaches to designing new elastomeric materials have missed important insights into using multiscale stress deconcentration to achieve high-performance elastomeric materials for broad industrial applications,” said co-author Yakov Gutsovsky, a resident expert in Harvard’s Office of Technology Development. Paper. „The design principles developed and demonstrated in this work are applicable across a wide range of industries, including high-volume applications such as tires and industrial rubber products, as well as emerging applications such as wearable devices.”

Note: Steck J, Kim J, Gudzowski Y, Suo Z. Multiscale stress deconcentration increases the fatigue resistance of rubber. Nature. 2023;624(7991):303-308. doi: 10.1038/s41586-023-06782-2

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