Case Western Reserve University engineers unlock why materials jam under pressure
New model predicts industrial ‘shear jamming,’ giving manufacturers control—and opening doors to flexible body armor
Researchers at Case Western Reserve University have developed a model that predicts when industrial materials will jam under pressure—helping manufacturers prevent costly shutdowns and enabling the design of next-generation protective materials. That includes body armor.
The breakthrough discovery hinges on a deceptively simple factor: the roughness of microscopic particles or more simply their ability to rotate relative to one another.
Published in Newton, the research solves a decades-old mystery about “shear jamming”—why some dense particle suspensions flow smoothly under stress while others lock up unexpectedly, halting production lines.
Suspensions—mixtures of solid particles in liquids—are everywhere in modern manufacturing: from cement and ceramics to foods, pharmaceuticals and toothpaste. These materials must flow predictably during processing—not too runny, but also not so thick that they jam up when pumped through tubes.
Yet, despite their economic importance, industrial suspensions are still mainly formed by trial and error.
“Not knowing the physics behind shear jamming, often in industry you try to push as much material as you can through a system and then it will jam,” said Abhinendra Singh, assistant professor of macromolecular science and engineering at Case School of Engineering. “This leads to costly shutdowns. Often after it’s shut down, when you tap it, it flows smoothly again; but meanwhile, you’ve lost money and time.”
Using advanced computational modeling, Singh and his team found that internal particle network structure—not just thickness or viscosity—determines whether and how a suspension jams.
Smoother particles that can rotate relative to each other (like gears) form dense, highly connected, branching networks that distribute stress broadly. Rougher particles, where this rotation is restricted, form sparse, self-supporting chains that carry stress through relatively few contact points, causing the material to jam more quickly—even at lower concentrations.
Those structural differences provide what Singh calls “control knobs” for engineers.
“Our findings show that it is the internal network structure—not viscosity alone—that determines how a suspension behaves,” Singh said. “We can now predict how a material will behave under pressure and tune it to flow smoothly—or jam on command.”
By controlling whether a formulation builds dense, branching webs or sparse, chain-like structures, engineers can reduce unwanted jamming, lower energy costs, prevent clogging and improve uniformity during manufacturing.
But the implications extend beyond manufacturing efficiency, Singh said. Materials designed to jam rapidly under impact could be used in flexible, stab-resistant or bullet-resistant armor, sports equipment and other adaptive materials.
“A fluidic material that jams quickly under pressure can absorb and dissipate tremendous energy,” Singh said. “By engineering rough particles that form the right internal structure, we could create body armor that’s flexible and comfortable until the moment of impact.”
Shweta Sharma, a postdoctoral scholar in Singh’s group, was the study’s lead author. The work was supported by start-up funding from Case Western Reserve. Collaborators included Abhishek Sharma, assistant professor of chemical engineering at The Cooper Union for the Advancement of Science and Art.
