Researchers from l’ETH Zurich in Switzerland, from the California Institute of Technology in the USA and from Supméca in France have determined how certain liquids stiffen in response to powerful impacts such as the ones from firearms or micrometeorites. This work is published in the Proceedings of the National Academy of Sciences of the United States of America (*).
In France, the study has been carried out at Supméca by researchers of the Vibroacoustique and Structures team, in the Quartz Lab (EA 7393). It fits into the context of the ANR/FRAE Metaudible project. One of the strong expertises of the team relies on the propagation and the dissipation of vibrations and acoustical energy.
In particular, the Metaudible projet, co-funded by the Agence Nationale de la Recherche et the Fondation de Recherche pour l’Aéronautique et l’Espace in collaboration with the Université du Maine and the École Nationale des Travaux Publics de l’État, aims at studying and designing metamaterials for the absorption of sound by light, compact and innovative structures, especially for the needs of the aeronautic industry. In this context, new metamaterials, such as poro-granular materials, have been studied to tackle the issues of noise transmission and insulation.
At first glance, colloids resemble homogeneous liquids such as milk, blood plasma or sediments. But in fact they consist of particles in suspension. Some colloids have remarkable properties: they may stiffen following an impact and absorb surface shocks. This property is of interest for many applications, from bulletproof vests to protective shields for satellites. The team of Swiss, American and French researchers found that how these colloids work can change dramatically in response to very strong impacts. The scientists have also developed a model that makes these properties easier to understand. The team observed that when the colloidal particles are micrometer-sized, the force and speed of impact change how the shocks are absorbed. When the shock is particularly intense, the liquid no longer flows between the interstices and the suspended particles deform. This feature causes an extremely powerful dissipation of the mechanical energy.
This publication has been considered for a joint press release of the Fond National Suisse de la recherche scientifique (FNS), the Agence Nationale de la Recherche (ANR) et the Fondation de Recherche pour l’Aéronautique et l’Espace (FRAE) : FNS press release « Liquid shock absorbers »
(*) Buttinoni et al., Direct observation of impact propagation and absorption in dense colloidal monolayers. PNAS (2017). http://dx.doi.org/10.1073/pnas.1712266114