Shells and grapefruit inspire ‘non-cuttable’ material

The material was created by an international team of researchers led by Durham University and Fraunhofer IWU. The researchers got the idea for the new material from tough cellular grapefruit skin and fracture-resistant mollusc shells, specifically abalone.

Abalone shells are exceptionally strong due to their structure; they are made from tiny calcium carbonate tiles interlinked with a clingy protein. When the shell is struck, the tiles slide beside each other rather than shattering, with the protein deforming to take some of the force of the blow. This has attracted the interest of material scientists, who are taking inspiration from these structures to build super-strong body armour and other items.

The researchers replaced these organic materials with aluminium ceramics and a metallic foam matrix. Ceramics spheres are encased in this structure, creating a light, non-cuttable material.

The structure resists cutting by creating high-speed motion where it interacts with cutting tools. When a cutting tool like a blade or drill bit is applied, the spheres create vibrations, causing the force of the cutting tool to be effectively turned back on itself. This causes it to gradually erode until it is rendered entirely ineffective. As the ceramic spheres fragment, they reduce to a dust which fills the matrix and stiffens as the speed of the cutting tool is increased.

The material also resisted cutting by water jets, because the curved surfaces of the ceramic spheres widen the jet, reducing its cutting capacity.

“We were intrigued by how the cellular structure of the grapefruit and the tiled structure of mollusc shells can prevent damage to the fruit or the creatures inside, despite being made of relatively weak organic building blocks,” said Professor Stefan Szyniszewski, from Durham University. “These natural structures informed the working principle of our metallic-ceramic material, which is based on dynamic interaction with the applied load, in contrast to passive resistance.”

Szyniszewski described cutting through the new material as like “cutting through a jelly filled with nuggets”; if a tool cuts through the jelly, it hits the nuggets and the material vibrates in such a way as to damage the tool.

The researchers believe that this is the first manufactured non-cuttable material.

Co-author of the Scientific Reports study Dr Miranda Anderson, a University of Stirling philosopher, commented: “Because the successful resistance of our material system requires it to undergo internal transformations, we chose the name Proteus. In 1605, Francis Bacon compared natural materials to Proteus who “ever changed shapes” and he argued that through experimentation we can reveal the metamorphic qualities of materials.”

The researchers suggest that Proteus (patent pending) could be used to make bike locks, lightweight body armour, and protective equipment for people who work with power tools.