Fracture Mechanics

Groß, Dietmar; Seelig, Thomas

doi:10.1007/978-3-642-19240-1

Cited by 115 publications

(58 citation statements)

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“…For mode I cracks, a crack-tip stress is expressed as a function of π / K r 2 1 , where K 1 is a mode I stress-intensity factor, and r is radial distance from the crack-tip 41 . This form indicates that a tensile loading always gives a non-zero growth rate [42][43][44][45] . Therefore, we conclude that when centrifugal forces exceed gravitational forces in the neck, existing cracks will propagate across the neck, and the body will split into two components.…”

Section: Methodsmentioning

confidence: 96%

Fission and reconfiguration of bilobate comets as revealed by 67P/Churyumov–Gerasimenko

Hirabayashi

Scheeres

Chesley

et al. 2016

Nature

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The solid, central part of a comet--its nucleus--is subject to destructive processes, which cause nuclei to split at a rate of about 0.01 per year per comet. These destructive events are due to a range of possible thermophysical effects; however, the geophysical expressions of these effects are unknown. Separately, over two-thirds of comet nuclei that have been imaged at high resolution show bilobate shapes, including the nucleus of comet 67P/Churyumov-Gerasimenko (67P), visited by the Rosetta spacecraft. Analysis of the Rosetta observations suggests that 67P's components were brought together at low speed after their separate formation. Here, we study the structure and dynamics of 67P's nucleus. We find that sublimation torques have caused the nucleus to spin up in the past to form the large cracks observed on its neck. However, the chaotic evolution of its spin state has so far forestalled its splitting, although it should eventually reach a rapid enough spin rate to do so. Once this occurs, the separated components will be unable to escape each other; they will orbit each other for a time, ultimately undergoing a low-speed merger that will result in a new bilobate configuration. The components of four other imaged bilobate nuclei have volume ratios that are consistent with a similar reconfiguration cycle, pointing to such cycles as a fundamental process in the evolution of short-period comet nuclei. It has been shown that comets were not strong contributors to the so-called late heavy bombardment about 4 billion years ago. The reconfiguration process suggested here would preferentially decimate comet nuclei during migration to the inner solar system, perhaps explaining this lack of a substantial cometary flux.

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Section: Methodsmentioning

confidence: 96%

Fission and reconfiguration of bilobate comets as revealed by 67P/Churyumov–Gerasimenko

Hirabayashi

Scheeres

Chesley

et al. 2016

Nature

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“…A dynamic fracturing regime is defined by a continuously growing Mode I SIF, K Imax , which exceeds sediment fracture toughness, K Imax ≥ K Icrit (Gross & Seelig, 2011;Lawn, 1993). This leads to the fracturing of the muddy sediment by the ascending bubble and to unrestricted bubble ascent (Tarboush Sirhan et al, 2019).…”

Section: Methodsmentioning

confidence: 99%

“…According to the LEFM, the behavior of the crack is defined solely by its stress intensity factor (SIF) distribution, in our case Mode I SIF (K I ), over the evolving crack front (Gross & Seelig, 2011;Lawn, 1993). If K Imax (the maximal SIF which is always attained at the head of an ascending bubble; point B in Figure S1) exceeds sediment fracture toughness, K Icrit , indicating the strength of material at tensile failure, the bubble migrates upward; otherwise, it remains in place.…”

Section: Methodsmentioning

confidence: 99%

Methane Bubble Escape From Gas Horizon in Muddy Aquatic Sediment Under Periodic Wave Loading

Katsman

2019

Geophysical Research Letters

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Ebullition of greenhouse methane (CH4) from the aquatic sediments is often observed at various hydrostatic pressure drops: at low tides, waves, and even at atmospheric pressure drops. It is especially pronounced at the different vent structures, for example, pockmarks, mud volcanoes, and cold seeps. The modeling conducted in the current study suggests that long timescale (glacial to centennial frequency) sea level drops may induce “stable” bubble ascent and control the position of the gas horizon in muddy aquatic sediment. Bubbles escape in the “dynamic” regime from the shallow gas horizon and subsequently to the water column is more feasible under shorter‐period waves of higher amplitude travelling in shallow water. These findings are illustrated by examples of various vent structures (e.g., pockmarks), pronounced in shallow straits and bays, described in the literature.

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“…Even nominally brittle materials exhibit a very small plastic zone around crackfronts, which is not captured by the LEFM model [Gross and Seelig 2011]. Consequently, stress is not the proper measure for crack propagation, as it is singular at the crack-front.…”

Section: Fracture Criteriamentioning

confidence: 99%

“…where cR is the Rayleigh wave speed, which is approximately cR ≈ 0.9 µ/ρ, where ρ is the material's density [Gross and Seelig 2011]. …”

Section: Crack Propagationmentioning

confidence: 99%

High-resolution brittle fracture simulation with boundary elements

Hahn

Wojtan

2015

ACM Trans. Graph.

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We present a method for simulating brittle fracture under the assumptions of quasi-static linear elastic fracture mechanics (LEFM).Using the boundary element method (BEM) and Lagrangian crackfronts, we produce highly detailed fracture surfaces. The computational cost of the BEM is alleviated by using a low-resolution mesh and interpolating the resulting stress intensity factors when propagating the high-resolution crack-front.Our system produces physics-based fracture surfaces with high spatial and temporal resolution, taking spatial variation of material toughness and/or strength into account. It also allows for crack initiation to be handled separately from crack propagation, which is not only more reasonable from a physics perspective, but can also be used to control the simulation.Separating the resolution of the crack-front from the resolution of the computational mesh increases the efficiency and therefore the amount of visual detail on the resulting fracture surfaces. The BEM also allows us to re-use previously computed blocks of the system matrix.

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Fracture Mechanics

Cited by 115 publications

References 0 publications

Fission and reconfiguration of bilobate comets as revealed by 67P/Churyumov–Gerasimenko

Fission and reconfiguration of bilobate comets as revealed by 67P/Churyumov–Gerasimenko

Methane Bubble Escape From Gas Horizon in Muddy Aquatic Sediment Under Periodic Wave Loading

High-resolution brittle fracture simulation with boundary elements

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