ALBERT — All Library Books, journals and Electronic Records Telegrafenberg

1

Electronic Resource

Lattice instability at a fast moving crack tip (1996)

Zhang, Y. W. ; Wang, T. C.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 80 (1996), S. 4332-4336

add to mindlist on the mindlist

Details

ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: A molecular dynamics method is used to analyze the dynamic propagation of an atomistic crack tip. The simulation shows that the crack propagates at a relatively constant global velocity which is well below the Rayleigh wave velocity. However the local propagation velocity oscillates violently, and it is limited by the longitudinal wave velocity. The crack velocity oscillation is caused by a repeated process of crack tip blunting and sharpening. When the crack tip opening displacement exceeds a certain critical value, a lattice instability takes place and results in dislocation emissions from the crack tip. Based on this concept, a criterion for dislocation emission from a moving crack tip is proposed. The simulation also identifies the emitted dislocation as a source for microcrack nucleation. A simple method is used to examine this nucleation process. © 1996 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.363383

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

Fulltext

2

Electronic Resource

Simulation of nucleation and emission of dislocations by molecular-dynamics method (1995)

Zhang, Y. W. ; Wang, T. C. ; Tang, Q. H.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 77 (1995), S. 2393-2399

add to mindlist on the mindlist

Details

ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: The nucleation and emission of dislocations from the crack tip under mode II loading are analyzed by the molecular-dynamics method in which the Finnis–Sinclair potential has been used. A suitable atom lattice configuration is employed to allow one to fully analyze the nucleation, emission, dissociation, and pileup of the dislocations. The calculated results show that although the pure mode II loading is applied, the crack tip generally exhibits a combined mode. The stress distributions before the dislocation emission are in agreement with the elasticity solution, but are not after the emission. The critical stress intensity factor corresponding to the dislocation nucleation KIIe is dependent on the loading rate K(overdot)II. The separations of a pair of partial dislocations and the full dislocations are also dependent on the loading rate. When the first partial dislocation is blocked, a pileup of dislocations can be set up. It is also found that the dislocation can move at subsonic wave speed (less than the shear wave speed) or at transonic speed (greater than the shear wave speed but less than the longitudinal wave speed) depending on the loading rate, but at the longitudinal wave speed which just corresponds to K(overdot)II=1.15 MPa (square root of)m/ps for copper, the atom lattice breaks down. © 1995 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.358764

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

Fulltext

3

Electronic Resource

Formation of epitaxially strained islands by controlled annealing (1999)

Zhang, Y. W.

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 75 (1999), S. 205-207

add to mindlist on the mindlist

Details

ISSN: 1077-3118

Source: AIP Digital Archive

Topics: Physics

Notes: A three-dimensional continuum method is developed to simulate the formation of epitaxially strained islands during controlled annealing. In the formulation, the strain energy density, surface energy and surface energy anisotropy are taken into account. Our simulations show that no surface energy anisotropy leads to spherical caps while high anisotropy leads to elongated islands. Under the present framework, a relatively uniform and regular island array can be obtained at a certain annealing time from a random surface. An almost perfectly uniform and regular island array can be obtained at a certain annealing time from a random surface with one dominant wavelength, which is in a specific range; for long-time annealing, these island arrays are undergoing ripening. © 1999 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.124320

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

Fulltext

4

Electronic Resource

Vertical self-alignment of quantum dots in superlattice (1999)

Zhang, Y. W. ; Xu, S. J. ; Chiu, C.-h.

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 74 (1999), S. 1809-1811

add to mindlist on the mindlist

Details

ISSN: 1077-3118

Source: AIP Digital Archive

Topics: Physics

Notes: Self-alignment of quantum dots separated by spacer layers is investigated by using a three-dimensional finite element method. We find that the morphology of the top islands is not just simply a reproduction of the buried islands. It is dependent on the arrangement of the buried islands, the interruption time, and the spacer layer thickness. If the buried islands are uniform and regular, with appropriate choice of their spacing and aspect ratio and with a thin spacer layer, there exists a regime in which the steady-state top islands are always uniform and regular, vertically aligned, and stable against small perturbations. For a thicker spacer layer, due to the change of the strain energy density distribution on top of the spacer layer, the top islands are misaligned with the buried islands. If the buried islands are not uniform and regular, our simulations demonstrate the top islands may self-assemble into more uniform and regular arrangements. © 1999 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.123093

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

Fulltext

5

Electronic Resource

Ammonium diaqua(ethylenediaminetetraacetato)scandium(III) trihydrate (1999)

Zhang, Y. W. ; Wang, Z. M. ; Jia, J. T. ; [et al.]

Oxford [u.a.] : International Union of Crystallography (IUCr)

Acta crystallographica 55 (1999), S. 1418-1420

add to mindlist on the mindlist

Details

ISSN: 1600-5759

Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001

Topics: Chemistry and Pharmacology , Geosciences , Physics

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1107/S0108270199008057

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

Fulltext

6

Electronic Resource

Optical design of the NSRL undulator beamline (1998)

Zhang, Y. W. ; Sheng, L. S. ; Zhang, G. B. ; [et al.]

Chester : International Union of Crystallography (IUCr)

Journal of synchrotron radiation 5 (1998), S. 559-561

add to mindlist on the mindlist

Details

ISSN: 1600-5775

Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001

Topics: Geosciences , Physics

Notes: The optical design of the NSRL undulator beamline is presented. The NSRL undulator has 29 periods of 9.2 cm that produce a photon energy of 7.7–124 eV with the fundamental and third harmonics at a ring energy of 800 MeV. The beamline consists of a typical Kirkpatrick–Baez prefocusing mirror system, a modified spherical-grating monochromator (SGM) and a refocusing toroidal mirror. The monochromator has two including angles of 148 and 157° with two plane mirrors inserted into the entrance arm in order to cover the wide energy range with high grating diffraction efficiency. Calculation shows that the resolving power of the monochromator can be greater than 5000 with the slits fully opened and 20000 with a 20 µm opening of the slits. The spot at the sample is about 1.5 (H) mm × 0.5 (V) mm.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1107/S0909049598000478

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

Fulltext

7

Electronic Resource

An analysis of the effects of symmetrical tilt grain boundaries on the plastic deformation (1995)

Zhang, Y. W. ; Wang, T. C.

Springer

Acta mechanica solida Sinica 8 (1995), S. 95-109

add to mindlist on the mindlist

Details

ISSN: 0894-9166

Keywords: simple polycrystal ; grain boundary

Source: Springer Online Journal Archives 1860-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics

Notes: Abstract A numerical investigation on the simple polycrystals containing three symmetrical tilt grain boundaries (GBs) is carried out within the framework of crystal plasticity which precisely considers the finite deformation and finite lattice rotation as well as elastic anisotropy. The calculated results show that the slip geometry and the redistribution of stresses arising from the anisotropy and boundary constraint play an important role in the plastic deformation in the simple polycrystals. The stress level along GB is sensitive to the load level and misorientation, and the stresses along GB are distributed nonuniformly. The GB may exhibit a softening or strengthening feature, which depends on the misorientation angle. The localized deformation bands usually develop accompanying the GB plastic deformation, the impingement of the localized band on the GB may result in another localized deformation band. The yield stresses with different misorientation angles are favorably compared with the experimental results.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02206795

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

Fulltext

8

Electronic Resource

A unified model for dislocation nucleation, dislocation emission and dislocation free zone (1996)

Wang, T. C. ; Wang, K. R. ; Zhang, Y. W.

Springer

International journal of fracture 78 (1996), S. 227-239

add to mindlist on the mindlist

Details

ISSN: 1573-2673

Source: Springer Online Journal Archives 1860-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Notes: Abstract In this paper, a unified model for dislocation nucleation, emission and dislocation free zone is proposed based on the Peierls framework. Three regions are identified ahead of the crack tip. The emitted dislocations, located away from the crack tip in the form of an inverse pileup, define the plastic zone. Between that zone and the cohesive zone immediately ahead of the crack tip, there is a dislocation free zone. With the stress field and the dislocation density field in the cohesive zone and plastic zone being, respectively, expressed in the first and second Chebyshev polynomial series, and the opening and slip displacements in trigonometric series, a set of nonlinear algebraic equations can be obtained and solved with the Newton-Raphson Method. The results of calculations for pure shearing and combined tension and shear loading after dislocation emission are given in detail. An approximate treatment of the dynamic effects of the dislocation emission is also developed in this paper, and the calculation results are in good agreement with those of molecular dynamics simulations.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00032475

Permalink