A new study takes a step toward clarifying how soft materials, both natural and synthetic, deform under stress. The work by researchers at the University of Illinois at Urban-Champaign addresses a wide range of engineering challenges, including natural disasters such as landslides.
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CHAMPAIGN, Ill. – Understanding how soft materials deform under stress is critical to solving engineering challenges as diverse as pharmaceutical technology and landslide prevention. A new study linking a spectrum of soft material behaviors—previously thought to be independent—has led researchers to identify a new parameter they call the brittleness factor, which allows them to simplify the failure behavior of soft materials. This will ultimately help engineers design better materials to meet future challenges.
University of Illinois at Urbana-Champaign chemical and biomolecular engineering teacher Simon Rogers and graduate student Krutarth Kamani specialize in determining how soft materials yield to stress and have shown how solid and liquid physical states can exist together in the same material. This field is of great interest because of its importance for industrial, environmental and biomedical applications.
Along the way, the team identified a communication problem among scientists working in the field, causing a bottleneck between theoretical understanding of the behavior of soft materials and real-world applications.
When soft materials, whether natural or synthetic, deform under pressure, they reach a critical point where they either return to their original shape or undergo permanent deformation, like a piece of rubber band stretching or breaking. This process is known as yielding. A gradual transition to yielding is called ductile behavior, while an abrupt transition is called brittle behavior, the researchers said.
“At a recent conference, we realized that all of us who study soft materials from across Europe and North America could not agree on the relationship between brittle and ductile behavior, or how to define it.”
In the study published in the Proceedings of the National Academy of Sciences, instead of considering the behavior of soft materials as brittle or ductile, Rogers’ team considered a spectrum of elastic behaviors. This allowed the team to build a continuous model, which allowed them to discover the brittleness factor. This factor is critical for determining how and why soft materials deform.
Essentially, brittleness affects how permanently a material deforms under stress. The team’s model states that the higher the brittleness factor, the less permanently a soft material will deform before failing.
As in the team’s previous studies, the model was developed and tested using data from numerous experiments that subjected various soft materials to stress while measuring individual deformation responses using a device called a rheometer.
“We didn’t expect this study to explain so much,” said Rogers, who is also affiliated with the Beckman Institute for Advanced Science and Technology “We finally found a way to bring together under one physical umbrella a whole set of soft material behaviors. Previously, they had been studied independently or perhaps all applied simultaneously, but they had never been thought of as physically or mathematically connected.”
This discovery will allow researchers to explain precisely why some materials are more resistant to rapid failure than others, a question that has eluded researchers for decades.
“This single parameter surprisingly ties together so many puzzling observations that researchers have encountered over the years,” Kamani said.
“This work marks the point where we are approaching the top of the hill in understanding the behavior of soft materials,” Rogers said. “We have always felt like each step was taking us higher, but with no end in sight. Now we can see the top of the hill, we are closer to it, and we are free to move in any direction we want.”
The National Science Foundation supported this research.
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