CRC 526 | Projectarea D

The mechanical behaviour of polyphase geological materials, with particular consideration of the involvement of fluids and melts, as well as phase transformations

D9 Fragmentation analysis of rocks under seismic loading conditions

Le

Summary
The microstructural analysis of rocks exposed at the surface provides information on the processes which took place when they were deeper in the Earth´s crust. During exhumation all metamorphic rocks have to pass upward through the brittle-ductile transition zone, with a relative maximum in strength and possible stress fluctuations related to seismic activity in the brittle upper crust. One of the microstructural features observed in rocks that were deformed near the brittle-ductile transition is the intense fragmentation of crystals of high-strength mineral phases like garnet embedded in a ductile quartz matrix. At which conditions and by which process such cracks are formed in brittle inclusions was the subject of extensive studies by geologists and material scientists in recent years. Although much progress in understanding the fragmentation process has been achieved, some important questions remain to be answered. Especially, the kinetics of crack nucleation and growth and the question of failure modes deserve further investigations. The aim of this project is to propose continuum mechanical models of fragmentation of brittle inclusions embedded in a ductile matrix and their finite element implementation. These models should enable one to calculate the total energy of the system inclusion+cracks+matrix. It should also be possible to predict the critical load at which cracks are nucleated as well as the crack density. Finally, the finite element implementation should lead to an efficient programming code which is general enough to solve problems with arbitrary geometric and loading conditions.

We start our fragmentation analysis with the estimation of the amount of energy release due to fragmentation under the static loading condition. The energy of the system inclusion+matrix before fragmentation is calculated using the Eshelby equivalent inclusion method. To estimate the energy release we regard the inclusion after fragmentation as a void.

This enables one to calculate the energy in the state of completed fragmentation. After knowing the stress field and the energy release the direction, the shape, and the crack density can be determined. We then investigate the kinetics of crack nucleation based on the energy concept and on the Fokker-Planck equation describing the change of crack length or crack volume as a random variable. Finally we take the inertial effects into account and analyse the dynamic fragmentation model based on the energy balance equation. Except some simple problems for which analytical solutions can be obtained, the fragmentation problems in the fully dynamic setting need to be handled by the numerical simulations using the finite element discretization. The results obtained by the theory and numerical simulations will be compared with the microfabrics of natural rocks.

D13 Diffusion processes at solid-solid-liquid interfaces

Doltsinis, Renner, Hackl

Summary
We propose to study diffusion processes at solid-solid-liquid interfaces at temperatures and pressures prevailing in the continental crust. The study aims to identify the dominating diffusion process (path and species) and constrain the corresponding diffusion coefficient for matter transport along interfaces between specific polycrystalline aggregates and fluids. In particular, we propose

  1. to investigate the effect of temperature, annealing period, fluid composition, and load on groove formation at polished surfaces of natural polycrystalline quartz and calcite rocks;
  2. to perform a continuum mechanics based theoretical study into groove formation for multi-component systems using analytical and numerical approaches; and
  3. to model the diffusion mechanisms leading to groove formation at an atomistic first principles level using ab initio molecular dynamics simulations.

Experiments will be conducted in externally heated hydrothermal pressure vessels, internally-heated piston cylinder apparatus, and a modified creep rig. Impurity contents will be specified by microprobing and infrared spectroscopy. Groove geometry will be determined using a scanning probe microscope. The investigation of groove characteristics will be combined with orientation information from scanning electron microscopy (EBSD). The continuum mechanics based analysis will provide constraints on groove shapes and their temporal development beyond the available theoretical framework for mono-elemental isotropic solids. A minimalistic molecular model of a quartz/liquid water interface shall serve as a starting point to investigate possible diffusion pathways of SiO2 molecules from the surface into the water and the nature of the resulting solvated species as well as changes in the diffusion properties of both, the solute species and the solvent H2O molecules in the presence of the quartz surface. In addition, theoretical infrared spectra will be calculated considering specific impurities and thus providing a better basis for the interpretation of observed spectra. Constraining diffusion kinetics in solid-liquid systems representative of continental crust will improve the understanding of strength recovery of faults by healing processes following an earthquake, and, more generally, the time scales of fluid conduit reorganization. Furthermore, the investigations will provide crucial input parameters for the modeling of fluid assisted creep processes.

nach oben

D1 (1999/2-2002/1)

Prof. H. Berns, Prof. B. Stöckhert


D2 (1999/2-2005/1)

Prof. W. Schmahl, Prof. B. Stöckhert


D3 (1999/2-2002/1)

Dr. K. Röller


D4 (1999/2-2005/1)

Dr. B. Skrotzki, Prof. G. Eggeler, Prof. B. Stöckhert


D6 (1999/2-2005/1)

Prof. W. Maresch, Dr. M. Burchard, Dr. Th. Fockenberg, Dr. O. Medenbach


D8 (2002/2-2008/1)

Prof. K. Hackl,


D10 (2002/2-2008/1)

Prof. J. Renner


D11 (2005/2-2008/1)

Prof. W. Maresch, Dr. N. Doltsinis, Dr. Th. Fockenberg


D12 (2005/2-2008/1)

Dr. C. Trepmann