The Experts below are selected from a list of 91962 Experts worldwide ranked by ideXlab platform
Michael A Filler - One of the best experts on this subject based on the ideXlab platform.
-
interplay between defect propagation and surface hydrogen in silicon nanowire Kinking superstructures
ACS Nano, 2014Co-Authors: Naechul Shin, Miaofang Chi, Michael A FillerAbstract:Semiconductor nanowire Kinking superstructures, particularly those with long-range structural coherence, remain difficult to fabricate. Here, we combine high-resolution electron microscopy with operando infrared spectroscopy to show why this is the case for Si nanowires and, in doing so, reveal the interplay between defect propagation and surface chemistry during ⟨211⟩ → ⟨111⟩ and ⟨211⟩ → ⟨211⟩ Kinking. Our experiments show that adsorbed hydrogen atoms are responsible for selecting ⟨211⟩-oriented growth and indicate that a twin boundary imparts structural coherence. The twin boundary, only continuous at ⟨211⟩ → ⟨211⟩ kinks, reduces the symmetry of the trijunction and limits the number of degenerate directions available to the nanowire. These findings constitute a general approach for rationally engineering Kinking superstructures and also provide important insight into the role of surface chemical bonding during vapor–liquid–solid synthesis.
Bin Zhang - One of the best experts on this subject based on the ideXlab platform.
-
crack Kinking in h bn monolayer predicted by energy dissipation
Journal of Applied Physics, 2020Co-Authors: Hong Tian, Feng Pan, Bin ZhangAbstract:Rapid crack propagation in a strip of a hexagonal boron nitride monolayer is studied by molecular dynamics. Crack Kinking/branching takes place at high velocities under displacement loadings, accompanied by elastic waves dissipating the external supplied work besides the fresh surface energy. Cracks moving at a maximum velocity (∼74% of the Rayleigh wave velocity) do not branch immediately, which is governed by energy dissipation around the crack tip, instead, once the energy release rate (G) reaches a critical value of 19.75 J/m2 (∼5.9 times the surface energy density of 3.35 J/m2), Kinking occurs, which shows that G could predict the onset of Kinking/branching accurately. The dependences of G for crack initiation and branching on displacement-loading rate, strip size, and initial crack length are examined as well.
Sia Nemat-nasser - One of the best experts on this subject based on the ideXlab platform.
-
Energy release rate and crack Kinking
International Journal of Solids and Structures, 2003Co-Authors: K. Hayashi, Sia Nemat-nasserAbstract:Abstract A closed form solution is presented for the energy release rate at the onset of Kinking of a straight crack in an infinite elastic medium subjected to a predominantly Mode I loading. The solution is accurate to the second order of kink angle and is carried out by the method which models the kink as a continuous distribution of infinitesimal edge dislocations. On the basis of the maximum energy release rate criterion, simple expressions are obtained for the critical kink angle and the critical applied stress. The examination of the results shows that the second order solutions are in very good agreement, up to fairly large kink angles, with numerical results reported by others. It is also analytically established that the Irwin formula for the energy release rate remains valid under the predominantly Mode I loading, provided that the stress intensity factors in the formula are appropriately interpreted.
-
Crack Kinking under nonsymmetric loading
Engineering Fracture Mechanics, 2003Co-Authors: B. L. Karihaloo, Leon M. Keer, Sia Nemat-nasserAbstract:This paper considers an asymmetrically kinked, semi-infinite crack in a two-dimensional solid under mixed-mode loading and a stress acting parallel to the main crack, the latter providing the non-singular stress term, T, in the Irwin-Williams expansion of the crack tip field. The aim of the study is twofold: First, to obtain an almost closed-form solution for the stress intensity factors at the tip of the kink with a view to explaining a curious result observed by many authors that under predominantly Mode I loading the first order solution in small kink angle is accurate for considerably large kink angles and, second, to study the effect of the in-plane tensile stress on the stability of crack growth. Where possible, the results are compared with those available in the literature.
Corrado Maurini - One of the best experts on this subject based on the ideXlab platform.
-
Crack Kinking in a variational phase-field model of brittle fracture with strongly anisotropic surface energy
Journal of the Mechanics and Physics of Solids, 2019Co-Authors: Corrado MauriniAbstract:In strongly anisotropic materials the orientation-dependent fracture surface energy is a non-convex function of the crack angle. In this context, the classical Griffith model becomes ill-posed and requires a regularization. We revisit the crack Kinking problem in materials with strongly anisotropic surface energies by using a variational phase-field model. The model includes in the energy functional a quadratic term on the second gradient of the phase-field. This term has a regularizing effect, energetically penalizing the crack curvature. We provide analytical formulas for the dependence of the surface energy on the crack direction and develop an open-source finite-element solver for the higher-order phase-field problem. Quantitative numerical experiments for the crack Kinking problem show that the crack Kinking directions observed in our phase-field simulations are in close agreement with the generalized maximum energy release rate criterion. Finally, we revisit a thermal quenching experiment in the case of slabs with strongly anisotropic surface energies. We show that the anisotropy can strongly affect the observed crack patterns, either by stabilizing straight cracks or by inducing zigzag crack patterns. In the case of zigzag cracks, we observe that crack Kinking is always associated with an unstable propagation of a finite length add-crack in a single time-step.
A Zettl - One of the best experts on this subject based on the ideXlab platform.
-
buckling and Kinking force measurements on individual multiwalled carbon nanotubes
Physical Review B, 2007Co-Authors: K Jensen, William Mickelson, Andras Kis, A ZettlAbstract:Using an atomic force microscope operated inside a transmission electron microscope, we have studied the forces involved in buckling and Kinking an individual multiwalled carbon nanotube while observing its structure. In particular, we have measured an individual nanotube's asymptotic critical buckling load and critical Kinking load. The buckling results are well described by classical elastic theory, while the observed Kinking behavior requires a more involved analysis. Repeated buckling measurements on the same nanotube indicate an extremely high degree of elasticity and set a lower bound on the nanotube's yield strength of $1.7\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, higher than the yield strength of steel. Plastic deformation of the nanotube was eventually observed following Kinking.
