Harvard Engineers Unveil Technique for Tenfold Increase in Rubber’s Resilience
Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have significantly enhanced the fatigue threshold of particle-reinforced rubber, introducing a novel multiscale approach that enables the material to withstand high loads and resist crack propagation through repeated usage. This breakthrough promises to extend the lifespan of rubber products like tires and aims to mitigate pollution caused by the shedding of rubber particles during their use.
Enhancing Particle-Reinforced Rubbers
Natural rubber latex exhibits softness and elasticity. To enhance its properties for various applications such as tires, hoses, and dampeners, rubbers are reinforced with rigid particles like carbon black and silica. While these particles significantly improve rubber stiffness, they do little to enhance resistance to crack growth under cyclic stretching, known as the fatigue threshold.
Since the 1950s, the fatigue threshold of particle-reinforced rubbers has seen minimal improvement. This limitation means that despite advancements in tire technology to improve wear resistance and reduce fuel consumption, small cracks can still release substantial amounts of rubber particles into the environment, contributing to air pollution and environmental degradation.
Novel Discoveries in Rubber Engineering
In previous research led by Zhigang Suo, Allen E., and Marilyn M. Puckett, Professor of Mechanics and Materials at SEAS, the team successfully increased the fatigue threshold of rubbers by elongating polymer chains and enhancing entanglements. However, the question remained: How would this approach fare with particle-reinforced rubbers?
Surprisingly, when silica particles were added to the highly entangled rubber, the fatigue threshold increased by a factor of ten, contrary to the expected outcome based on existing literature.
According to Jason Steck, a graduate student at SEAS and co-first author of the study, this unexpected result was a significant revelation. The material developed by the Harvard team features long and highly entangled polymer chains coupled with clustered silica particles covalently bonded to these chains. This unique combination effectively redistributes stress around cracks across two distinct length scales, preventing propagation within the material.
Implications and Future Prospects
The team substantiated their approach by subjecting a material sample with a deliberately introduced crack to tens of thousands of stretches, demonstrating that the crack remained stable without propagating.
Zhigang Suo emphasized the broader implications of their findings, stating that the multiscale stress deconcentration approach opens avenues for developing high-performance elastomeric materials with applications ranging from reducing polymer pollution to constructing advanced soft machines.
Yakov Kutsovsky, an Expert in Residence at the Harvard Office of Technology Development and co-author of the paper, highlighted the potential applicability of these design principles across various industries, including tire manufacturing, industrial rubber goods, and emerging fields such as wearable devices.
Read the original article on Nature.
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