Begun in 2002 as part of the 5th framework project, the network "Fractal structures and self-organization" was finally concluded during 2003 with the realisation of an experimental apparatus with which the properties of granular materials may be studied. This has been possible also through financing from MIUR within the FIRB project "Rheological propoerties of granular materials," in collaboration with the department of physics at "La Sapienza." The apparatus constitutes the first and only experimental investigation of granular media in Italy and permits the study of the reaction of granular materials to a shear force.
By means of the above device it has been possible to perform a time-resolved mesurements of the response of a granular material to an applied shear. We observe that at low driving shear rate the medium supports a mean constant stress with a non-Gaussian distribution and a yield threshold whereas at high driving rigidity vanishes, the mean stress
increases with velocity and is Gaussian distributed, confirming icollisional origin above the fluidization transition.
We show that the stress distribution is well reproduced by a
fibre bundle model with random load sharing.
There is an obvious practical interest in granular materials, which form an integral part of daily life and which play an important role in many industrial processes, such as in problems of transport and storing in agriculture, contructions and chemistry amongst many others. Highly industrialised European countries, such as France, Germany and Great Britian, as in America, have for at lease 10 years consistently dedicated considerable human and economic resources to the study of granular materials. Despite the obvious relevance these systems have for a large part of Italian industry (food, construction, chemistry, pharmaceutical etc), the study of their physical properties in our country is still little developed and confined to few research groups.
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