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Browsing by Author "Nabarro, FRN"

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Chemical driving force for rafting in superalloys

Author: Nabarro, FRN Date: 15 Aug 1997 The author provides a brief overview of the chemical driving forces for rafting in superalloys. Until recently, all theories of the driving force for rafting have considered the compositions of the two phases to be fixed, although accepting ... Read more
Coefficient of work-hardening in stage-IV

Author: Nabarro, FRN Date: 15 Apr 1994 The theory of work hardening in stage IV depends on the relation between the relative misorientation Psi of neighbouring subgrains and the plastic strain gamma (Psi = B gamma exp). The value of the constant B is suggested to be better related ... Read more
Creep at very low rates

Author: Nabarro, FRN Date: Feb 2002 The creep rate in a land-based power station must be less than 10(-11) s(-1). At these low rates of deformation the transport of matter occurs by the migration of vacancies rather than by the glide of dislocations. A quantitative understanding ... Read more
Do we have an acceptable model of power-law creep?

Author: Nabarro, FRN Date: 15 Dec 2004 Three models of power-law creep are frequently presented. Those of Weertman assume distributed sources of dislocations which spread until they meet dislocations from other sources. They then annihilate by bulk diffusion. If the density of ... Read more
Fifty-year study of the Peierls-Nabarro stress

Author: Nabarro, FRN Date: 30 Aug 1997 The origin of the Peierls model and its relation to that of Frenkel and Kontorova are described. Within this model there are three essentially different formulae for the stress required to move a dislocation rigidly through a perfect lattice, ... Read more
Grain size, stress and creep in polycrystalline solids

Author: Nabarro, FRN Date: Aug 2000 If a stress sigma is applied to a polycrystal of grain size L, the mode of creep deformation depends on the answers to the following questions: (i) Does sigma exceed the Peierls stress sigma (p); (ii) Does L exceed the dislocation spacing in ... Read more
Inclusions and inhomogeneities under stress

Author: Nabarro, FRN Date: Feb 1996 Some general theorems, new and old, concerning the behaviour of elastic inclusions and inhomogeneities in bodies without or with external stress, are assembled. The principal new result is that arbitrary external tractions cannot influence ... Read more
Nucleation of small angle boundaries

Author: Nabarro, FRN ; Wilsdorf, DK Date: Dec 1996 The internal stresses induced by the strain gradients in an array of lattice cells delineated by low-angle dislocation boundaries are partially relieved by the creation of new low-angle boundaries. This is shown to be a first-order transition, ... Read more
One-dimensional models of thermal activation under shear stress

Author: Nabarro, FRN Date: 2003 The analysis of thermal activation under shear stress in three- and even two-dimensional models presents unresolved problems. The analysis of one-dimensional models presented here may illuminate the study of more realistic models. For the ... Read more
Semi-empirical relationship between the hardness, grain size and mean free path of WC-Co

Author: Makhele-Lekala, L ; Luyckx, S ; Nabarro, FRN Date: 2001 The Vickers hardness of several well-characterized grades of WC-Co (23 in total) was measured. The mean grain size of these samples ranged from 0.6 to 5.0 mums and the cobalt content from 6 to 50 wt%. An empirical formula between hardness of ... Read more
Stress-driven grain growth

Author: Nabarro, FRN Date: 13 Nov 1998 This article shows the differences of two-dimensional polycrystal of a material with a rectangular unit cell with lattice spacing b and b (1 + epsilon), subjected to a uniform external stress sigma. Consider a grain in which the lattice vector ... Read more
Theoretical and experimental estimates of the Peierls stress

Author: Nabarro, FRN Date: Mar 1997 The Peierls stress is the stress required to move a dislocation through a perfect crystal lattice. Theoretical estimates show an exponential dependence on the ratio of the spacing between gliding planes and the unit slip distance. Nabarro ... Read more
Thermodynamic driving force for rafting in superalloys

Author: Nabarro, FRN ; Cress, CM ; Kotschy, P Date: Aug 1996 Eshelby’s energy-momentum tensor is used to provide an analytical expression for the driving force for rafting in the elastic regime in a super alloy with a high volume fraction of gamma'. The structure is modeled as a simple cubic array of ... Read more
Time constant of logarithmic creep and relaxation

Author: Nabarro, FRN Date: 15 Jul 2001 Under certain conditions, the plastic extension of a sample subjected to a constant stress is to a good approximation proportional to the logarithm of the time. Similarly, if a sample is plastically strained and unloaded, there are changes ... Read more
Two-phase materials for high-temperature service

Author: Nabarro, FRN Date: Sep 2000 The structure and properties of two families of lattice-coherent composites, those based on gamma' Ni3Al and those based on TiA/Ti3Al, are shown to have strong similarities. The coherent system of cubic/tetragonal Y2O3-stabilized ZrO2 is ... Read more

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Browsing by Author "Nabarro, FRN"

Browsing by Author "Nabarro, FRN"

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All of ResearchSpace

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