402 research outputs found
Topological Complexity of Frictional Interfaces: Friction Networks
Through research conducted in this study, a network approach to the
correlation patterns of void spaces in rough fractures (crack type II) was
developed. We characterized friction networks with several networks
characteristics. The correlation among network properties with the fracture
permeability is the result of friction networks. The revealed hubs in the
complex aperture networks confirmed the importance of highly correlated groups
to conduct the highlighted features of the dynamical aperture field. We found
that there is a universal power law between the nodes' degree and motifs
frequency (for triangles it reads T(k)\proptok{\beta} ({\beta}
\approx2\pm0.3)). The investigation of localization effects on eigenvectors
shows a remarkable difference in parallel and perpendicular aperture patches.
Furthermore, we estimate the rate of stored energy in asperities so that we
found that the rate of radiated energy is higher in parallel friction networks
than it is in transverse directions. The final part of our research highlights
4 point sub-graph distribution and its correlation with fluid flow. For shear
rupture, we observed a similar trend in sub-graph distribution, resulting from
parallel and transversal aperture profiles (a superfamily phenomenon)
Network-Configurations of Dynamic Friction Patterns
The complex configurations of dynamic friction patterns-regarding real time
contact areas- are transformed into appropriate networks. With this
transformation of a system to network space, many properties can be inferred
about the structure and dynamics of the system. Here, we analyze the dynamics
of static friction, i.e. nucleation processes, with respect to "friction
networks". We show that networks can successfully capture the crack-like shear
ruptures and possible corresponding acoustic features. We found that the
fraction of triangles remarkably scales with the detachment fronts. There is a
universal power law between nodes' degree and motifs frequency (for triangles,
it reads T(k)\proptok{\beta} ({\beta} \approx2\pm0.4)). We confirmed the
obtained universality in aperture-based friction networks. Based on the
achieved results, we extracted a possible friction law in terms of network
parameters and compared it with the rate and state friction laws. In
particular, the evolutions of loops are scaled with power law, indicating the
aggregation of cycles around hub nodes. Also, the transition to slow rupture is
scaled with the fast variation of local heterogeneity. Furthermore, the motif
distributions and modularity space of networks -in terms of withinmodule degree
and participation coefficient-show non-uniform general trends, indicating a
universal aspect of energy flow in shear ruptures
Solitonic State in Microscopic Dynamic Failures
Onset of permanent deformation in crystalline materials under a sharp
indenter tip is accompanied by nucleation and propagation of defects. By
measuring the spatio-temporal strain field nearthe indenter tip during
indentation tests, we demonstrate that the dynamic strain history at the moment
of a displacement burst carries characteristics of formation and interaction of
local excitations, or solitons. We show that dynamic propagation of multiple
solitons is followed by a short time interval where the propagating fronts can
accelerate suddenly. As a result of such abrupt local accelerations, duration
of the fast-slip phase of a failure event is shortened. Our results show that
formation and annihilation of solitons mediate the microscopic fast weakening
phase, during which extreme acceleration and collision of solitons lead to
non-Newtonian behavior and Lorentz contraction, i.e., shortening of solitons
characteristic length. The results open new horizons for understanding dynamic
material response during failure and, more generally, complexity of earthquake
sources
Complex Networks on a Rock Joint
A complex network approach on a rough fracture is developed. In this manner,
some hidden metric spaces (similarity measurements) between apertures profiles
are set up and a general evolutionary network in two directions (in parallel
and perpendicular to the shear direction) is constructed. Also, an algorithm
(COmplex Networks on Apertures: CONA) is proposed in which evolving of a
network is accomplished using preferential detachments and attachments of edges
(based on a competition and game manner) while the number of nodes is fixed.
Also, evolving of clustering coefficients and number of edges display similar
patterns as well as are appeared in shear stress, hydraulic conductivity and
dilation changes, which can be engaged to estimate shear strength distribution
of asperities.Comment: ROCKENG09: Proceedings of the 3rd CANUS Rock Mechanics Symposium,
Toronto, May 2009 (Ed: M.Diederichs and G. Grasselli
- …