Partners and International Organizations
(English)
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B, CH, DK, E, F, FIN, GR, H, IRL, IS, N, NL, P, S, SI, UK
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Abstract
(English)
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Work performed in LMC in the year 1999 and first trimester 2000 relate to the sections I (micromechanical computation method) and II (experimental identification of grain material properties) of a four sections programme. For section I, bibliographic investigations, including a comprehensive set of related papers for the last fifty years, have first been deepened. From this, a basic theoretical problem has been identified: the micro-macro transition problem for the kinematic variables, considered in the literature as not being completely solved yet. A theoretical study of this problem has been developed. Two original approaches have been defined. The first one (Discretised Geometrical Model, DGM, by Q.-C. He and C. Huet, 1999) makes use of a dicretisation procedure based on Voronoi-Delaunay tessellations into appropriate tetrahedrons, reducing the problem to the mutual displacements of the grain centers, considered as a simpler first approximation. The second one (Testing Volume Element approach, TVE, by C. Huet, 2000) is more general. It involves explicitly the testing boundary conditions and the full granular microstructure, making it possible to take into account the detailed geometry of the grains, of their contact regions and of the pores. Appropriate definitions of the macroscopic mechanical variables for finite and infinitesimal deformations have been defined in both approaches, and their relationships with corresponding micromechanical variables derived. Two draft scientific papers have been written on this basic subject and are about to be finalised for submission to specialised Journals. They are considered as key points for the following of the study. A new computer code able to process the contact problems between grains has been implemented, in co-operation with Prof. Alain Curnier, from EPFL/DGM. For section II, a methodological study has been conducted for experimental determination of the fracture mechanics properties of the rocky material constituting the grains. It is based on the (non-linear) fracture thermodynamics approach previously developed by Huet (1973, 1994, 1997). Experimental conditions allowing to perform fast stable Fracture Mechanics tests on the rocky materials constituting the grains have been elaborated. In addition, co-operation with LMS (Laboratory of Soil Mechanics in EPFL/DGC), our Swiss partner in the project has been continued on both the theoretical (constitutive equations) and experimental (help to LMS in experimental developments and access to LMC high power fatigue test facilities) viewpoints. In addition of frequent informal contacts, a two full days meeting was organised and took place on August 19 and 20, 1999 for discussion of the work done and organisation of the work still to be done. Contacts with the various international teams of the COST 337 have been maintained by participation to the works of the Management Committee and several Task Groups.
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