Experimental evidence of ageing and slow restoration of the weak-contact configuration in tilted 3D granular packings

Granular packings slowly driven towards their instability threshold are studied using a digital imaging technique as well as a nonlinear acoustic method. The former method allows us to study grain rearrangements on the surface during the tilting and the latter enables to selectively probe the modifications of the weak-contact fraction in the material bulk. Gradual ageing of both the surface activity and the weak-contact reconfigurations is observed as a result of repeated tilt cycles up to a given angle smaller than the angle of avalanche. For an aged configuration reached after several consecutive tilt cycles, abrupt resumption of the on-surface activity and of the weak-contact rearrangements occurs when the packing is subsequently inclined beyond the previous maximal tilting angle. This behavior is compared with literature results from numerical simulations of inclined 2D packings. It is also found that the aged weak-contact configurations exhibit spontaneous restoration towards the initial state if the packing remains at rest for tens of minutes. When the packing is titled forth and back between zero and near-critical angles, instead of ageing, the weak-contact configuration exhibits "internal weak-contact avalanches" in the vicinity of both the near-critical and zero angles. By contrast, the stronger-contact skeleton remains stable

Heterogeneous dynamics of a granular pack under vertical tapping

The dynamics of a tri-dimensional dense granular packing under gravity and vertical tapping is numerically investigated in a stationary state. A slowing-down of the dynamics is observed close to the bottom of the packing with a correlation length of 5–6d. In this perturbed zone, the self-intermediate scattering function, decaying slower than exponentially, suggests the existence of a heterogeneous dynamics. A characteristic time scale of the dynamics depending on the distance from the bottom of the packing is extracted. Our numerical results open the way to a systematic study of the influence of external driving force and of boundary conditions on the heterogeneity of the dynamics of granular packings under gravity

Das Element Produktwiederverwendung im Qualitaetskreislauf Ergebnisse des EUREKA Forschungsprojekts CLEANTECH (EU1104)

The objective of the European research initiative EUREKA is to motivate industry and research institutes in Europe for reinforced cross-border cooperation in the field of technological research and development. The aim is to concentrate the potential of specialists, knowledge, and financial resources for more effective use. In doing so, EUREKA contributes to Europe's competitiveness on the world market, to the development of a joint infrastructure and joint solutions. 24 European countries and the European Commission are members of EUREKA. CLEANTECH was demonstrating successfully - as it was done in other EUREKA projects - the European approach in a collaborative project in the area of industrial research and developments. Synergy and cooperative capabilities were used as the promoter to solve a common research task. It was possible to overcome the problem of different languages in a very early stage of the project so that the common goal could be reached by distribution of tasks according to specific capabilities of the partners. (orig.)SIGLEAvailable from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

Demontageaspekte im Qualitaetskreislauf Stand der Demontageaktivitaeten und Handlungsbedarf

In the field of complex technical consumer durables, the ability to recycle and disassemble has become an ever more important feature due to the awareness of our society. The possibility of cooperation with Austria, Sweden and Switzerland in the framework of an EUREKA research project has been examined in a BMFT commission. In addition, the Status Quo relating to the topic was determined and research and development focal points were also worked out. Furthermore, the first project suggestions with German responsibility have been worked out, which will now serve as a basis for further EUREKA project work with the interested parties. (orig.)Available from TIB Hannover: RN 8592(170) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman

Vibration-induced compaction of granular suspensions

International audienceWe investigate the compaction dynamics of vibrated granular suspensions using both digital imaging technique and MRI measurements. Starting from initialy loose packings, our experimental data suggest the existence of two stages in the compaction dynamics: a fast stage at short times where a rising compaction front propagates through the granular suspension and a slow stage at large times where the packing compacts slowly and homogeneously. The compaction dynamics in each stage can be well fitted to usual stretched exponential laws with stretching exponents equal to 2 and 0.45, respectively. The transition time between these two stages, tau(c), depends on the fluid viscosity, vibration intensity and grain diameter. We show that tau(-1)(c) and the velocity of the front decrease roughly linearly with the lubrication Peclet number, Pe(lub) related to the competition between the lubrication stress induced by vibrations and the granular pressure