THE STRENGTH OF SUBMICRON-SIZED MATERIALS

2006 ◽  
Vol 20 (25n27) ◽  
pp. 3579-3586 ◽  
Author(s):  
A. H. W. NGAN ◽  
P. C. WO ◽  
L. ZUO ◽  
H. LI ◽  
N. AFRIN
Keyword(s):  
Yield Strength ◽  
Time Dependence ◽  
Experimental Evidence ◽  
Mechanical Behaviour ◽  
Survival Probability ◽  
Diffusion Length ◽  
Theoretical Explanation ◽  
Atomistic Simulations ◽  
Load Range ◽  
Scaling Model

Recent rapid advancements in nano- and micro-machinery technologies call for an urgent need to understand the mechanical behaviour of materials of dimensions in the sub-micron regime. The initial yield strength of submicron crystals exhibits remarkable statistical scatter as well as dependence upon size and time under load. Submicron-sized materials are also found to creep many orders of magnitude faster than bulk counterparts. In this paper, the recent experimental evidence for these phenomena is reviewed. Theoretical explanation of these phenomena is also discussed. The statistical scatter and time dependence of the yield strength are interpreted by a scaling model derived from atomistic simulations. The results indicate that, within a certain load range, the strength of a sub-micron sized material is not deterministic and can only be described by a survival probability. The much faster creep in the submicron regime is interpreted in terms of the much shorter diffusion length compared to bulk creep.

Instability in slotted wall tunnels

1958 ◽  
Vol 4 (3) ◽  
pp. 283-305 ◽  
Author(s):  
J. L. King ◽  
P. Boyle ◽  
J. B. Ogle
Keyword(s):  
Wind Tunnel ◽  
Experimental Evidence ◽  
Theoretical Explanation ◽  
Water Tunnel ◽  
Design Consideration ◽  
Working Section

A new water tunnel, incorporating a slotted wall working section, was found to suffer from severe vibration. A theoretical explanation is given for this, together with experimental evidence gleaned from this water tunnel and a small wind tunnel. It is shown that the oscillations are hydrodynamic in origin and are associated with the slotted wall design. Consideration is given to methods of elimination or reduction of the oscillations.

Atomistic Simulations of Dislocation-Interface Interactions in the Cu-Ni Multilayer System

1999 ◽  
Vol 578 ◽  
Author(s):  
Satish I. Rao ◽  
Peter M. Hazzledine
Keyword(s):  
Yield Strength ◽  
Elastic Moduli ◽  
Lattice Parameter ◽  
Stacking Fault ◽  
Chemical Effect ◽  
Atomistic Simulations ◽  
Embedded Atom Method ◽  
Embedded Atom ◽  
Coherency Strains ◽  
Stacking Fault Energies

AbstractMultilayered Cu-Ni has a peak yield strength four orders of magnitude higher than either Cu or Ni because the multitude of interfaces obstruct glissile dislocations. The barrier strengths of the interfaces may be traced to four mismatches across an interface: modulus, lattice parameter, chemical and slip geometry. This paper describes sample embedded atom method (EAM) simulations of dislocations crossing interfaces, designed to separate the effects of the four mismatches. The results confirm some classical calculations and emphasize the importance of three new effects (i) an interface-chemical effect in which dislocations are trapped by core spreading in the interface, (ii) a coherency-chemical effect caused by coherency strains changing effective stacking fault energies and (iii) a coherency-modulus effect in which coherency strains change elastic moduli (and hence the Koehler stress) significantly.

Time Dependence of the Segregation of Diffusing Solute in Nanocrystalline Materials

2002 ◽  
Vol 731 ◽  
Author(s):  
Irina V Belova ◽  
Graeme E Murch
Keyword(s):  
Monte Carlo ◽  
Grain Boundary ◽  
Monte Carlo Simulations ◽  
Time Dependence ◽  
Nanocrystalline Materials ◽  
Diffusion Length ◽  
Solute Diffusion ◽  
Reasonable Approximation ◽  
Solute Diffusivity ◽  
First Time

AbstractAt long times the effective solute diffusivity can be described by the (modified) Hart-Mortlock and Maxwell-Garnett equations for diffusion parallel and perpendicular to the grain boundary respectively. In this paper we analyze for the first time the time dependence of the effective solute diffusivity for these conditions. We assume that there are local regions (delineated by the diffusion length) in the grains adjacent to the grain boundary where the solute is equilibrated with the grain boundary. We write equations for the effective solute diffusivity with this assumption. Comparison with Monte Carlo simulations shows that this is quite a reasonable approximation for solute diffusion parallel to the grain boundary. For diffusion perpendicular to the grain boundary it is only a fair approximation unless the segregation is weak.

Atomistic simulations of effect of hydrogen atoms on mechanical behaviour of an α -Fe with symmetric tilt grain boundaries

2018 ◽  
Vol 382 (35) ◽  
pp. 2464-2469 ◽  
Author(s):  
H.Y. Song ◽  
C.F. Li ◽  
S.F. Geng ◽  
M.R. An ◽  
M.X. Xiao ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Mechanical Behaviour ◽  
Atomistic Simulations ◽  
Hydrogen Atoms ◽  
Symmetric Tilt

Effect of fabric on the behaviour of reservoir sandstones

2012 ◽  
Vol 49 (9) ◽  
pp. 1036-1051 ◽  
Author(s):  
Giovanny Alvarado ◽  
Neville Lui ◽  
Matthew R. Coop
Keyword(s):  
Shear Modulus ◽  
Experimental Evidence ◽  
Mechanical Behaviour ◽  
Confining Pressure ◽  
Large Strains ◽  
Hydrocarbon Reservoir ◽  
Small Strains ◽  
Reservoir Sandstones ◽  
Observed Behaviour ◽  
Stress Dependency

A laboratory investigation was undertaken on the mechanical behaviour of two sandstones that are commonly used as analogous hydrocarbon reservoir sandstones, using triaxial apparatuses with a capacity of up to 70 MPa confining pressure. Both materials are lightly cemented, but show a mechanical behaviour at large strains that is similar to that seen in rocks with much stronger cementation. At small strains, however, these materials behave more like uncemented sands in that they show a strong stress dependency of the shear modulus and yield takes places at relatively small strains. It is believed that fabric plays a fundamental role in the observed behaviour and this is supported by the experimental evidence, so that the concept of strong fabric in sandstones is introduced.

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