# gst: monitoring of stable crack growth; crack tip behavior at the nanoscale (during ceramic fracture).

<< To understand fracture and make brittle materials more ductile, (AA) rely on modeling what happens at a crack tip. However, observing a crack tip in a brittle material is challenging: cracks propagate fast, and the events that (AA) are interested in observing occur at the nanoscale or below. Up to now, (They) were not able to observe what happens ahead of a moving crack tip. >>

<< In this work, (AA) show how by carefully performing fracture experiments inside a transmission electron microscope (They) can grow stable cracks while observing the nanoscale events happening at the crack tip. >>️

Oriol Gavalda-Diaz, Max Emmanuel, et al. Observing the crack tip behavior at the nanoscale during fracture of ceramics. PNAS. 121 (43) e2408292121. Oct 17, 2024.

https://www.pnas.org/doi/10.1073/pnas.2408292121 

Also: fracture, crack, behav in https://www.inkgmr.net/kwrds.html 

Keywords: gst, fracture, crack, behavior

# gst: critical crack length during fracture.

AA << established an inverse correlation between the strength of the material and the cracks which grow inside it—both the maximum crack and the one that sets in instability within the system, defined to be the critical crack. >>

AA << found that the maximum and the critical crack often differ from each other unless the disorder strength is extremely low. A phase diagram on the plane of disorder vs system size demarcates between the regions where the largest crack is the most vulnerable one and where they differ from each other but still show moderate correlation. >>️

Viswakannan R.K., Subhadeep Roy. Critical crack length during fracture. Phys. Rev. E 110, 024134. Aug 26, 2024.

https://journals.aps.org/pre/abstract/10.1103/PhysRevE.110.024134

Also: crack, instability, fluctuations, noise, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, crack, instability, fluctuations, noise, criticality

# gst: elastomers fail from the edge.

<< The performance of soft devices is limited by the fracture resistance of elastomers. (..) A key observation is that thicker elastomers can be significantly tougher than thinner ones. (AA) show that this surprising toughness enhancement in thick samples emerges from the 3D geometry of the fracture process. In contrast to the classical picture of a 2D crack, failure is driven by the growth of two separate “edge” cracks that nucleate early on at a sample’s sides. As loading is increased, these cracks propagate in towards the sample midplane. When they merge, samples reach their ultimate failure strength. In thicker samples, edge cracks need to propagate farther before meeting, resulting in increased sample toughness. (AA) demonstrate that edge-crack growth is controlled by the elastomer’s strain-stiffening properties. >>

️

Nan Xue, Rong Long, Eric R. Dufresne, Robert W. Style. Elastomers Fail from the Edge. Phys. Rev. X 14, 011054. March 22, 2024. 

https://journals.aps.org/prx/abstract/10.1103/PhysRevX.14.011054

Also: elastic, crack, in https://www.inkgmr.net/kwrds.html 

Keywords: gst, elastic, crack, elastomers, fracture

# gst: compression and fracture of ordered and disordered droplet rafts

AA << simulate a two-dimensional array of droplets being compressed between two walls. The droplets are adhesive due to an attractive depletion force. As one wall moves toward the other, the droplet array is compressed and eventually induced to rearrange. The rearrangement occurs via a fracture, where depletion bonds are quickly broken between a subset of droplets. >>

<< For monodisperse, hexagonally ordered droplet arrays, this fracture is preceded by a maximum force exerted on the walls, which drops rapidly after the fracture occurs. >>

<< In small droplet arrays a fracture is a single well-defined event, but for larger droplet arrays, competing fractures can be observed. These are fractures nucleated nearly simultaneously in different locations. >>

AA << also study the compression of bidisperse droplet arrays. The addition of a second droplet size further disrupts fracture events, showing differences between ideal crystalline arrays, crystalline arrays with a small number of defects, and fully amorphous arrays. >>

️

Pablo Eduardo Illing, Jean-Christophe Ono-dit-Biot, et al. Compression and fracture of ordered and disordered droplet rafts. Phys. Rev. E 109, 014610. Jan 17, 2024.

https://journals.aps.org/pre/abstract/10.1103/PhysRevE.109.014610

Also: drop, defect, fracture, crack, in https://www.inkgmr.net/kwrds.html

Also:  raft   https://flashontrack.blogspot.com/search?q=raft  

zattera (quasi-stochastic poetry) https://inkpi.blogspot.com/2005/04/1864-onda-di-liberazione.html  

randa (quasi-stochastic poetry) https://inkpi.blogspot.com/search?q=randa

Keywords: gst, drop, droplet, raft, defect, fracture, crack

# gst: when science meets poetry, an image of three-dimensional stepped cracks (bistability, and their transition to simple cracks)

<< Slow cracks may be simple, with no internal structure. The leading edge of a simple crack, the crack front, forms a single fracture plane in its wake. Slow cracks may also develop segmented crack fronts, each segment propagating along a separate fracture plane. These planes merge at locations that form steps along fracture surfaces. Steps are not stationary, but instead propagate within a crack front. Real-time measurements of crack front structure and energy flux reveal that step dynamics significantly increase energy dissipation and drastically alter crack dynamics. Simple and stepped cracks are each stable. By extending the use of energy balance to include 3D crack front structure, (AA) find that, while energy balance is obeyed, it is insufficient to select the energetically favorable crack growth mode. Transitions from stepped cracks to simple cracks occur only when their in-plane front lengths become equal and a perturbation momentarily changes step topology. Such 3D crack dynamics challenge our traditional understanding of fracture. >>

Meng Wang, Mokhtar Adda-Bedia, Jay Fineberg. Dynamics of three-dimensional stepped cracks, bistability, and their transition to simple cracks. Phys. Rev. Research 5, L012001. Jan 9, 2023. 

https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.5.L012001

Also

keyword 'crack' in FonT

https://flashontrack.blogspot.com/search?q=crack

keyword 'rottura' | 'crepa' | 'frattura' | 'rugosa' in Notes

(quasi-stochastic poetry)

https://inkpi.blogspot.com/search?q=rottura

https://inkpi.blogspot.com/search?q=crepa

https://inkpi.blogspot.com/search?q=frattura

https://inkpi.blogspot.com/search?q=rugosa

keywords 'meets poetry' in FonT

https://flashontrack.blogspot.com/search?q=meets+poetry

Keywords:  gst, transitions, dynamical phase transitions, crack, cracking,   fracture, roughness

# gst: apropos of instabilities, viscoelastic liquid bridges can be destabilized by torsion.

<< Liquid bridges are formed when liquids are constrained between two (or more) surfaces via the capillary force. They appear in a wide range of contexts including biology, medicine, and engineering. In the context of biology, liquid bridges enable animals like geckos to adhere to vertical walls (..) >>

<< By experiment and simulation, (AA) report that viscoelastic liquid bridges made of constant viscosity elastic liquids, a.k.a. Boger fluids, can be effectively destabilized by torsion. Under torsion, the deformation of the liquid bridge depends on the competition between elastocapillarity and torsion-induced normal stress effects. When the elastocapillary effect dominates, the liquid bridge undergoes elastocapillary instability and thins into a cylindrical thread, whose length increases and whose radius decays exponentially over time. When the torsion-induced normal stress effect dominates, the liquid bridge deforms in a way similar to edge fracture, a flow instability characterized by the sudden indentation of the fluid's free surface when a viscoelastic fluid is sheared at above a critical deformation rate. The vertical component of the normal stress causes the upper and lower portions of the liquid bridge to approach each other, and the radial component of the normal stress results in the liquid bridge thinning more quickly than under elastocapillarity. Whether such quick thinning continues until the bridge breaks depends on both the liquid bridge configuration and the level of torsion applied. >>️

San To Chan, Stylianos Varchanis, et al. Torsional instability of constant viscosity elastic liquid bridges. Soft Matter, 2022,18, 1965-1977. doi: 10.1039/ D1SM01804C. Feb 7, 2022. 

https://pubs.rsc.org/en/content/articlelanding/2022/SM/D1SM01804C

image: https://twitter.com/softmatter/status/1504473129074126851

Also

keyword 'instability' | 'instabilities' in FonT

https://flashontrack.blogspot.com/search?q=instability

https://flashontrack.blogspot.com/search?q=instabilities

keyword 'instabile' in Notes (quasi-stochastic poetry)

https://inkpi.blogspot.com/search?q=instabile

keyword 'torsione' in Notes (quasi-stochastic poetry)

https://inkpi.blogspot.com/search?q=torsione

keywords: instability, torsion, torsional instability, viscoelastic liquid, bridge

# gst: an atomic imaging of a (slow) crack

AA << successfully imaged the snapping of individual atomic bonds in a one-atom-thick sheet of rhenium disulfide ( ReS2) using scanning transmission electron microscopy. (STEM) >>

<< Because of its unusual chemistry, Re forms a 2D lattice with "lanes" that guide cracks, allowing the cracks to propagate with ease. The heavy element also efficiently deflects electrons, providing the signal needed to gain clear images. The study is a remarkable example of how a specific material can provide insight into the universal behavior of matter. >>

<< Because of its strong scattering, ReS2 provides an ideal target for STEM. (Interestingly, tungsten, the periodic-table neighbor of Re, has just one fewer proton and is routinely used in electron microscopy to stain viruses and bacterial flagella.)  >>

<< By measuring the deformation of the lattice around the crack, the team showed that the tearing stresses were concentrated around the crack tip. The stresses then decayed as the inverse square root of the distance from the tip, a finding that matches predictions for macroscopic materials. Using these measurements, the team defined a stress intensity threshold for cracks to propagate. >>

<< The images taken by Huang and colleagues used seconds-long exposure times, meaning they could only follow the propagation of the slowest crack (those that moved at a few angstroms per second). There is much interest in how faster cracks behave, as these cracks are subject to instabilities, meaning they can deviate from a straight line or form branches, for example. To observe faster cracks, future experiments could use reduced exposure times. >>

Itamar Kolvin. Atomic Imaging of Cracks. Physics 13, 193. Dec 9, 2020. 

https://physics.aps.org/articles/v13/193

Lingli Huang, Fangyuan Zheng, et al. In Situ Scanning Transmission Electron Microscopy Observations of Fracture at the Atomic Scale. Phys. Rev. Lett. 125, 246102. Dec 9, 2020.

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.125.246102

Also

(+)  the intriguing dynamics of a crack. Nov 7, 2017. 

https://flashontrack.blogspot.com/2017/11/gst-intriguing-dynamics-of-crack.html

(+) multiple cracks, simultaneously ... Oct 23, 2016.

https://flashontrack.blogspot.com/2016/10/s-gst-multiple-cracks-simultaneously.html

(+) onda criptica. May 22, 2005 (quasi-stochastic poetry)

https://inkpi.blogspot.com/2005/05/1641b-onda-criptica.html

(+) keyword "fracture" in FonT

https://flashontrack.blogspot.com/search?q=fracture

# gst: temblors with a 'boomerang' effect

<< The temblor shot eastward across a deep gash in the seafloor, and then zipped back to where it started at incredible speeds. It moved so fast it created the geologic version of a sonic boom. >>

Maya Wei-Haas. Weird ‘boomerang’ earthquake detected under the Atlantic Ocean. Aug 10, 2020.

https://www.nationalgeographic.com/science/2020/08/weird-boomerang-earthquake-detected-under-atlantic-ocean/   

AA << present an analysis of the 2016 Mw 7.1 earthquake on the Romanche fracture zone in the equatorial Atlantic, (..) (They) show that this rupture had two phases: (1) upward and eastward propagation towards a weaker region where the transform fault intersects the mid-ocean ridge, and then (2) an unusual back-propagation westwards at a supershear speed towards the centre of the fault. (..) deep rupture into weak fault segments facilitated greater seismic slip on shallow locked zones. This highlights that even earthquakes along a single distinct fault zone can be highly dynamic. Observations of back-propagating ruptures are sparse, and the possibility of reverse propagation is largely absent in rupture simulations and unaccounted for in hazard assessments. >>

Hicks, S.P., Okuwaki, R., et al. Back-propagating supershear rupture in the 2016 Mw 7.1 Romanche transform fault earthquake. Nat. Geosci. (2020). doi: 10.1038/ s41561-020-0619-9. Aug 10, 2020.

https://www.nature.com/articles/s41561-020-0619-9 

# chem: extreme superconductive in random atomic-scale mixture

<< High-entropy alloys (HEAs) are a new class of materials that are composed of multiple transition-metal elements in equimolar or near-equimolar ratios >>

<< many HEAs have been found in disordered solid-solution phases with body-centered-cubic, hexagonal closest-packed, and face-centered-cubic crystal structures >>

<< In many respects, HEAs display novel properties, including ultrahigh fracture toughness at cryogenic temperatures, excellent specific strength, and superior mechanical performance at high temperatures. In addition to their promising mechanical properties, some HEAs also exhibit interesting electronic properties: [TaNb]1−x(ZrHfTi)x HEAs were found to display superconductivity, for example >>

AA << report high-pressure studies on the superconducting HEA (TaNb)0.67(HfZrTi)0.33, [..] this alloy exhibits extraordinarily robust superconductivity - its zero-resistance superconducting state is still achieved even at a pressure of 190.6 GPa, or almost 2 megabars (1 Mbar = 1011 pascal), a pressure like that within the outer core of the earth. >>

Jing Guo, Honghong Wang, et al.  Robust zero resistance in a superconducting high-entropy alloy at pressures up to 190 GPa. PNAS 2017; 114 (50) 13144-7.  doi: 10.1073/pnas.1716981114.

http://www.pnas.org/content/114/50/13144

Laura Mgrdichian. A material that superconducts continuously up to extreme pressures.  Jan 17, 2018

https://m.phys.org/news/2018-01-material-superconducts-extreme-pressures.html

# gst: the intriguing dynamics of a crack

<< Cracks develop intricate patterns on the surfaces that they create >>

<< Although fracture mechanics predict that slow crack fronts should be straight and form mirror-like surfaces, facet-forming fronts propagate simultaneously within different planes separated by steps >>

Itamar Kolvin, Gil Cohen & Jay Fineberg. Topological defects govern crack front motion and facet formation on broken surfaces.  Nature Materials. doi: 10.1038/nmat5008 Oct 16, 2017

https://www.nature.com/nmat/journal/vaop/ncurrent/full/nmat5008.html

Novel technique reveals the intricate beauty of a cracked glass. Oct 31, 2017

http://new.huji.ac.il/en/article/35974

Intricate beauty of a cracked glass
Physics, math and special gels explain the formation of fracture patterns in brittle materials. Oct 31, 2017

https://www.sciencedaily.com/releases/2017/10/171031111457.htm

# gst: modeling around the edge of a crack

<< It is said that a weak link determines the strength of the entire chain. Likewise, defects or small cracks in a solid material may ultimately determine the strength of that material – how well it will withstand various forces >>

<< What, exactly, happens right around the edge of the crack, in the area in which those large stresses are concentrated? >>

The Breaking Point. What happens at the moving edge of crack? Aug 23, 2017

https://wis-wander.weizmann.ac.il/chemistry/breaking-point

https://www.sciencedaily.com/releases/2017/08/170823094054.htm

AA << show that cracks undergo an oscillatory instability controlled by small-scale, near crack-tip, elastic nonlinearity. This instability occurs above an ultrahigh critical velocity and features an intrinsic wavelength proportional to the ratio of the fracture energy to the elastic modulus (..) This ratio emerges as a fundamental scaling length assumed to play no role in the classical theory of cracks, but shown here to strongly influence crack dynamics >>

Chih-Hung Chen, Eran Bouchbinder & Alain Karma. Instability in dynamic fracture and the failure of the classical theory of cracks. Nature Physics doi: 10.1038/nphys4237 Publ. Aug 21, 2017

https://www.nature.com/nphys/journal/vaop/ncurrent/full/nphys4237.html

# s-gst: multiple cracks, simultaneously ...

<< While  the  initiation  of  fracture  in  brittle  solids  is  generally associated  with  the  preexistence  of  material  imperfections,  the mechanism  for  initiation  of  fracture  in  viscoelastic  fluids,  e.g.,  polymer melts  and  solutions,  remains  an  open  question. >>

<< The  images  reveal  the  simultaneous propagation  of  multiple  cracks >>

<< The  critical  stress  and  strain  for  the onset  of  crack  propagation  are  found  to  be  highly  reproducible  functions of  the  stretch  rate,  while  the  position  of  initiation  is  completely  random >>

Qian Huang, Nicolas J. Alvarez, et al. Multiple Cracks Propagate Simultaneously in Polymer Liquids in Tension. Phys. Rev. Lett. 117, 087801. Publ 15 Aug. 2016

http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.117.087801

Jay Fineberg. How to Fracture a Fluid. Aug.15, 2016

https://physics.aps.org/articles/v9/95