Fracture of three-dimensional fuse networks with quenched disorder

We study a fracture on a quasistatic time scale in a three-dimensional (3D) fuse network model with “strong” and “weak” disorder. These two cases differ noticeably in the development of the fracture. For strong disorder the damage scaling is very close to volumelike [number of broken bonds Nb∼L3/(lnL)0.3] unlike for weak disorder [Nb∼L2.4/(lnL)0.3]. With strong disorder global load sharing is only approximately valid. The size distribution of “avalanches” of broken fuses in the failure follows roughly a power-law scaling. The power-law exponent τ has a value close to 2, close to but differing from the exponent −5/2 expected of global load sharing. For weak disorder τ is about 1.5 which means that the decay of the size distribution is much slower than expected. These exponent values that characterize the development of damage prior to catastrophic failure are comparable to experimental ones. For the final fracture surfaces we observe a roughness exponent ζ≈0.4 for weak disorder. For strong disorder, severe finite size effects are seen, but the exponent seems to converge to the same value as for weak disorder, which is close to the one for the 3D random bond Ising domain wall universality class.Peer reviewe

Scaling of interfaces in brittle fracture and perfect plasticity

The roughness properties of two-dimensional fracture surfaces as created by the slow failure of random fuse networks are considered and compared to yield surfaces of perfect plasticity with similar disorder. By studying systems up to a linear size L=350 it is found that in the cases studied the fracture surfaces exhibit self-affine scaling with a roughness exponent close to 2/3, which is asymptotically exactly true for plasticity though finite-size effects are evident for both. The overlap of yield or minimum energy and fracture surfaces with exactly the same disorder configuration is shown to be a decreasing function of the system size and to be of a rather large magnitude for all cases studied. The typical ``overlap cluster'' length between pairs of such interfaces converges to a constant with $L$ increasing.Comment: Accepted for publication in Phys. Rev.

Statistical properties of fracture in a random spring model

Using large scale numerical simulations we analyze the statistical properties of fracture in the two dimensional random spring model and compare it with its scalar counterpart: the random fuse model. We first consider the process of crack localization measuring the evolution of damage as the external load is raised. We find that, as in the fuse model, damage is initially uniform and localizes at peak load. Scaling laws for the damage density, fracture strength and avalanche distributions follow with slight variations the behavior observed in the random fuse model. We thus conclude that scalar models provide a faithful representation of the fracture properties of disordered systems.Comment: 12 pages, 17 figures, 1 gif figur

Failure of planar fiber networks

We study the failure of planar random fiber networks with computer simulations. The networks are grown by adding flexible fibers one by one on a growing deposit [K. J. Niskanen and M. J. Alava, Phys. Rev. Lett. 73, 3475 (1994)], a process yielding realistic three dimensional network structures. The network thus obtained is mapped to an electrical analogue of the elastic problem, namely to a random fuse network with separate bond elements for the fiber-to-fiber contacts. The conductivity of the contacts (corresponding to the efficiency of stress transfer between fibers) is adjustable. We construct a simple effective medium theory for the current distribution and conductivity of the networks as a function of intra-fiber current transfer efficiency. This analysis compares favorably with the computed conductivity and with the fracture properties of fiber networks with varying fiber flexibility and network thickness. The failure characteristics are shown to obey scaling behavior, as expected of a disordered brittlematerial, which is explained by the high current end of the current distribution saturating in thick enough networks. For bond breaking, fracture load and strain can be estimated with the effective medium theory. For fiber breaking, we find the counter-intuitive result that failure is more likely to nucleate far from surfaces, as the stress is transmitted more effectively to the fibers in the interior.Peer reviewe

Diving in the Arctic : Cold Water Immersion’s Effects on Heart Rate Variability in Navy Divers

Introduction: Diving close to the Arctic circle means diving in cold water regardless of the time of year. The human body reacts to cold through autonomous nervous system (ANS)-mediated thermoregulatory mechanisms. Diving also induces ANS responses as a result of the diving reflex. Materials and Methods: In order to study ANS responses during diving in Arctic water temperatures, we retrospectively analyzed repeated 5-min heart rate variability (HRV) measures and the mean body temperature from dives at regular intervals using naval diving equipment measurement tests in 0◦C water. Three divers performed seven dives without physical activity (81–91 min), and two divers performed four dives with physical activity after 10 min of diving (0–10 min HRV recordings were included in the study). Results: Our study showed a significant increase in parasympathetic activity (PNS) at the beginning of the dives, after which PNS activity decreased significantly (measure 5–10 min). Subsequent measurements (15–20 min and onward) showed a significant increase in PNS activity over time. Conclusion: Our results suggest that the first PNS responses of the human diving reflex decrease quickly. Adverse effects of PNS activity should be considered on long and cold dives. To avoid concurrent sympathetic (SNS) and PNS activity at the beginning of dives, which in turn may increase the risk of arrhythmia in cold water, we suggest a short adaptation phase before physical activity. Moreover, we suggest it is prudent to give special attention to cardiovascular risk factors during pre-dive examinations for cold water divers. Keywords: diving reflex, diving response, sympathetic response, parasympathetic response, Arctic diving, cold water immersio

Diving in the Arctic: Cold Water Immersion’s Effects on Heart Rate Variability in Navy Divers

Introduction Diving close to the Arctic circle means diving in cold water regardless of the time of year. The human body reacts to cold through autonomous nervous system (ANS)-mediated thermoregulatory mechanisms. Diving also induces ANS responses as a result of the diving reflex. Materials and Methods In order to study ANS responses during diving in Arctic water temperatures, we retrospectively analyzed repeated 5-min heart rate variability (HRV) measures and the mean body temperature from dives at regular intervals using naval diving equipment measurement tests in 0 degrees C water. Three divers performed seven dives without physical activity (81-91 min), and two divers performed four dives with physical activity after 10 min of diving (0-10 min HRV recordings were included in the study). Results Our study showed a significant increase in parasympathetic activity (PNS) at the beginning of the dives, after which PNS activity decreased significantly (measure 5-10 min). Subsequent measurements (15-20 min and onward) showed a significant increase in PNS activity over time. Conclusion Our results suggest that the first PNS responses of the human diving reflex decrease quickly. Adverse effects of PNS activity should be considered on long and cold dives. To avoid concurrent sympathetic (SNS) and PNS activity at the beginning of dives, which in turn may increase the risk of arrhythmia in cold water, we suggest a short adaptation phase before physical activity. Moreover, we suggest it is prudent to give special attention to cardiovascular risk factors during pre-dive examinations for cold water divers.Peer reviewe

Quasi-static cracks and minimal energy surfaces

We compare the roughness of minimal energy(ME) surfaces and scalar ``quasi-static'' fracture surfaces(SQF). Two dimensional ME and SQF surfaces have the same roughness scaling, w sim L^zeta (L is system size) with zeta = 2/3. The 3-d ME and SQF results at strong disorder are consistent with the random-bond Ising exponent zeta (d >= 3) approx 0.21(5-d) (d is bulk dimension). However 3-d SQF surfaces are rougher than ME ones due to a larger prefactor. ME surfaces undergo a ``weakly rough'' to ``algebraically rough'' transition in 3-d, suggesting a similar behavior in fracture.Comment: 7 pages, aps.sty-latex, 7 figure

Roughness of Crack Interfaces in Two-Dimensional Beam Lattices

The roughness of crack interfaces is reported in quasistatic fracture, using an elastic network of beams with random breaking thresholds. For strong disorders we obtain 0.86(3) for the roughness exponent, a result which is very different from the minimum energy surface exponent, i.e., the value 2/3. A cross-over to lower values is observed as the disorder is reduced, the exponent in these cases being strongly dependent on the disorder.Comment: 9 pages, RevTeX, 3 figure

RD39 Status Report 2009

RD39 Status Report 2009. CERN RD39 Collaboration is developing super-radiation hard cryogenic silicon detectors for applications of LHC experiments and their future upgrades. The activities of RD39 Collaboration were focused in 2009 on concept of charge injected detector (CID)

Avalanches in Breakdown and Fracture Processes

We investigate the breakdown of disordered networks under the action of an increasing external---mechanical or electrical---force. We perform a mean-field analysis and estimate scaling exponents for the approach to the instability. By simulating two-dimensional models of electric breakdown and fracture we observe that the breakdown is preceded by avalanche events. The avalanches can be described by scaling laws, and the estimated values of the exponents are consistent with those found in mean-field theory. The breakdown point is characterized by a discontinuity in the macroscopic properties of the material, such as conductivity or elasticity, indicative of a first order transition. The scaling laws suggest an analogy with the behavior expected in spinodal nucleation.Comment: 15 pages, 12 figures, submitted to Phys. Rev. E, corrected typo in authors name, no changes to the pape