The capacity of materials to damp out vibrations is a function of the lag between stress and strain and is related to the anelastic strain: it is called damping capacity or internal friction.
The anelastic strain can result from the motion of structural defects such as point defects, dislocations, grain boundaries, the sliding of polymer chains.. and so on.
This technique was first exploited in the 1940’s:
– in Europe, by Snoek who studied the so-called Snoek relaxation in a iron containing small amounts of nitrogen or carbon.
– in the USA, by Zener who fast studied energy dissipation by thermal currents, internal friction due to macroeddy relaxations in ferromagnetic materials and then the internal friction in substitutional solid solutions, the so-called Zener relaxation.

Since the 50s and the 60s the literature concerning internal friction and ultrasonic attenuation in solids has been greatly enriched in many domains: point defects dislocations, grain boundaries, phase transformations, magneto-elastic relaxations, viscoelastic damping in polymers etc.

ICIFMS-20 is the 20th conference in a series that began in Providence (USA) in 1956 and continued in Ithaca (USA, 1961), Manchester (England, 1965), Providence (USA, 1969), Aachen (Germany, 1973), Tokyo (Japan, 1977), Lausanne (Switzerland 1981), Urbana (USA, 1985), Beijing (China, 1989), Rome (Italy, 1993), Poitiers (France, 1996), Buenos Aires (Argentina, 1999), Bilbao (Spain, 2002), Kyoto (Japan, 2005), Perugia (Italy, 2008), Lausanne (Switzerland, 2011), Hefei (China, 2014), Foz do Iguaçu (Brazil, 2017) Rome (Italy, 2022). In 2025, the conference returns to Lausanne for the 3rd time. The Conference started as International Conference on Internal Friction and Ultrasonic Attenuation in Solids (ICIFUAS) and for some decades included major contributions on solid state acoustics, regularly hosting scientific personalities such as C. Zener, P.G. Bordoni, T.S. Kê, A. Nowick, A.V. Granato, A. Seeger, to name a few.