A metamaterial that can make use of origami to reduce shock

To be useful, materials need to maintain a constant Poisson ratio under pressure

A car that dashes against an obstacle suffers damages, first to its fenders. There is a keen interest to develop materials that can be sandwiched in the fender system which will absorb the shock and prevent the interiors from being damaged. Origami metamaterials that crumple rather than tear, and take the impact, can play an important role in such situations. Researchers from Indian Institute of Technology Madras have developed such a material, which could have many such uses.

When you crush or stretch a material along a particular direction, it undergoes a modification in the perpendicular, or lateral, direction. For example, take a clay cube and compress it along one face, it will then bulge out in the sides. The ratio between the deformation along the force and the deformation in a direction lateral to the force is called the Poisson ratio. The Poisson ratio can be positive or negative. While, as in the example of the clay cube, we can easily visualise a material with a positive Poisson ratio, it is somewhat counter-intuitive to consider a material with a negative Poisson ratio. In fact, there is a lot of interest in such materials – they are called auxetics. One uses of auxetic materials is in lining the soles of sports shoes, where it offers better support when running or jumping. “If we try to crush or impact an auxetic material, it offers resistance to the crushing load as the material below will try to contract inwards, making it ‘denser’ and therefore, preventing the crushing load from moving further into the material,” says Phanisri Pradeep Pratapa from the Structural Engineering Laboratory of the Department of Civil Engineering at the Indian Institute of Technology, Madras.