scholarly journals MESOSCALE DEFORMATION-INDUCED SURFACE PHENOMENA IN LOADED POLYCRYSTALS

2021 ◽  
Vol 19 (2) ◽  
pp. 187
Author(s):  
Varvara Romanova ◽  
Ruslan Balokhonov ◽  
Olga Zinovieva
Keyword(s):  
Free Surface ◽  
Plastic Strain ◽  
Grain Boundaries ◽  
Uniaxial Tension ◽  
Three Dimensional ◽  
Grain Structure ◽  
Surface Roughening ◽  
Surface Phenomena ◽  
Stress Concentrations

The paper reviews the results of numerical analyses for the micro-and mesoscale deformation-induced surface phenomena in three-dimensional polycrystals with the explicit account for the grain structure. The role of the free surface and grain boundaries in the appearance of the grain-scale stress concentrations and plastic strain nucleation is illustrated on the examples of aluminum polycrystals. Special attention is paid to the discussion of mesoscale deformation-induced surface roughening under uniaxial tension.

Simulation of Microstructural Evolution in Polycrystalline Films

1990 ◽  
Vol 202 ◽  
Author(s):  
H. J. Frost
Keyword(s):  
Free Surface ◽  
Surface Energy ◽  
Film Thickness ◽  
Grain Boundaries ◽  
Grain Growth ◽  
Driving Force ◽  
Three Dimensional ◽  
Grain Structure ◽  
Two Dimensional ◽  
Free Surfaces

ABSTRACTThis paper will review the topic of computer simulation of the evolution of grain structure in polycrystalline thin films, with particular attention to the modelling of the grain growth process. If the grain size is small compared to the film thickness, then the grain structure is three-dimensional. As the grains grow to become larger than the film thickness, so that most grains traverse the entire thickness of the film, the microstructure may approach the conditions for a two-dimensional grain structure. Both two- and three-dimensional grain growth have been simulated by various authors.When the grains become large enough for the microstructure to be two-dimensional, the surface energy associated with the two free surfaces of the film becomes comparable to the surface energy of the grain boundaries. In this condition, the free surface may profoundly effect the grain growth. One effect is that grooves may develop along the lines where the grain boundaries meet the free surfaces. This grooving may pin the boundaries against further migration and lead to grain-growth stagnation. Another possible effect is that differences in the free surface energy for grains with different crystallographic orientation may provide a driving force for the migration of the boundaries which is additional to that provided by grain boundary capillarity. Grains with favorable orientations will grow at the expense of grains with unfavorable orientations. The coupling of grain-growth stagnation with an additional driving force can produce abnormal or secondary grain growth in which a few grains grow very large by consuming the normal grains.

scholarly journals The Role of Slip Transmission on Plastic Strain accumulationacross Grain Boundaries

2012 ◽  
Vol 4 ◽  
pp. 169-178 ◽  
Author(s):  
Wael Abuzaid ◽  
Michael D. Sangid ◽  
Huseyin Sehitoglu ◽  
Jay Carroll ◽  
John Lambros
Keyword(s):  
Plastic Strain ◽  
Grain Boundaries ◽  
Slip Transmission

Yielding and Plastic Flow in Stainless Steel: A TEM Study of the Evolution of Microstructure Associated with the Stress-Strain Diagram

1980 ◽  
Vol 38 ◽  
pp. 386-387
Author(s):  
L.E. Murr ◽  
S-H. Wang
Keyword(s):  
Grain Boundaries ◽  
Elastic Stress ◽  
Metals And Alloys ◽  
Strain Diagram ◽  
Stress Concentrations ◽  
Polycrystalline Metals ◽  
Pile Up ◽  
Local Slip ◽  
Evolution Of Microstructure

In spite of the fascination with dislocation pile-ups and the description of flow in metals and alloys based upon pile-up models, evidence has existed for decades suggesting that slip often if not always starts at grain boundaries in polycrystalline metals and alloys. Hook and Hirth showed that elastic incompatibility could result in local slip at the boundary between bicrystals, and their contention that local elastic stress concentrations at grain boundaries would aid slip nucleation was confirmed by Carrington, etal. Ashby has also described polycrystalline metals and alloys as plastically non-homogeneous because gradients of plastic deformation are imposed by the grain boundaries, and Murr has discussed the role of grain boundary ledges as initial sources for dislocations when polycrystalline metals and alloys are deformed. Brentnall and Rostoker earlier concluded that grain boundaries are both sources of early dislocations and barriers limiting their movement at higher stresses, and that slip is confined to grains in which it was initiated until the yield point is reached.

The Consistent Second-Order Wave Theory and Its Application to a Submerged Spheroid

1970 ◽  
Vol 14 (01) ◽  
pp. 23-50
Author(s):  
Young H. Chey
Keyword(s):  
Free Surface ◽  
Solid Wall ◽  
Three Dimensional ◽  
Wave Theory ◽  
Order Theory ◽  
Wave Resistance ◽  
Second Order ◽  
Surface Phenomena ◽  
First Order ◽  
Theoretical Results

Because of the recognized inadequacy of first-order linearized surface-wave theory, the author has developed, for a three-dimensional body, a new second-order theory which provides a better description of free-surface phenomena. The new theory more accurately satisfies the kinematic boundary condition on the solid wall, and takes into account the nonlinearity of the condition at the free surface. The author applies the new theory to a submerged spheroid, to calculate wave resistance. Experiments were conducted to verify the theory, and their results are compared with the theoretical results. The comparison indicates that the use of the new theory leads to more accurate prediction of wave resistance.

On the Mechanism of Oxidation Resistance of W-Cr-Pd Alloys

2018 ◽  
Vol 383 ◽  
pp. 133-141
Author(s):  
Alon Kafri ◽  
Alexandra Makonovitsky ◽  
Roni Z. Shneck
Keyword(s):  
Free Surface ◽  
Grain Boundaries ◽  
Oxidation Resistance ◽  
Intermediate Layer ◽  
Elevated Temperatures ◽  
Fast Diffusion ◽  
External Layer ◽  
Present Contribution ◽  
Mechanism Of Oxidation

While studying activation sintering of tungsten, Evans [5] and Ito and Furusawa [6] revealed that W-Cr-Pd alloys exhibit unexpected oxidation resistance at elevated temperatures. The role of palladium in stimulating oxidation resistance in W-Cr alloys is the main aim of the present contribution. As previously observed, at 800 °C these alloys form a relatively dense protective scale that consists of an inner layer of Cr2O3, an intermediate layer of Cr2WO6 and an external layer of WO3. At 1200 °C only Cr2WO6 layer is found, since the Cr2O3 and WO3 evaporate. To determine the role of paladium, W and W-Pd alloys were coated with Cr layers and undergone diffusion experiments. An extraordinary affinity between the Cr and Pd was revealed, manifested by extremely fast inward diffusion of Cr along grain boundaries. In a second experiment the dissolution of Cr into W grains at 1300°C was followed and found to take place preferentially along grain boundaries. These observations assess that the Pd segregated at grain boundaries provides fast diffusion channels for Cr to the free surface and it imparts the significant improvement of the oxidation resistance of W alloys, as suggested by Lee and Simkovitz [10-12].

A New Empirical Relation for Free Surface Roughening

2011 ◽  
Vol 133 (1) ◽  
Author(s):  
Sergei Alexandrov ◽  
Ken-Ichi Manabe ◽  
Tsuyoshi Furushima
Keyword(s):  
Free Surface ◽  
Dimensional Space ◽  
Empirical Relation ◽  
Three Dimensional ◽  
Geometric Interpretation ◽  
Surface Roughening ◽  
Material Surface ◽  
Reasonable Assumption ◽  
Axis Of Symmetry ◽  
Geometric Surface

A new empirical relation for the conventional measures of free surface roughness is proposed. Its geometric interpretation is a surface in three-dimensional space. A set of tests feasible for practical realization is discussed. Some available experimental and numerical results are used to reveal various qualitative features of the geometric surface. In particular, a reasonable assumption is that it is a ruled surface for a class of materials. A typical cross section of the surface, which is a curve, has an axis of symmetry if the roughening rate is independent of the sense of the strain rate normal to the material surface, where the roughness parameters should be predicted. The curve has a minimum at the axis of symmetry. Finally, there are two points, where the curve has a maximum. A simple analytic expression to specify the relation proposed for a given material is provided to fit experimental data.

Elucidation of block boundaries as the dissolution channels in hydrated cement

1978 ◽  
Vol 36 (1) ◽  
pp. 484-485
Author(s):  
N.V. Belov ◽  
U.I. Papiashwili ◽  
B.E. Yudovich
Keyword(s):  
Liquid Phase ◽  
Grain Boundaries ◽  
Benzoyl Peroxide ◽  
Phase Contrast ◽  
Active Role ◽  
Point Of View ◽  
Hardened Cement ◽  
Hydrated Cement ◽  
Hardened Cement Paste

It has been almost universally adopted that dissolution of solids proceeds with development of uniform, continuous frontiers of reaction.However this point of view is doubtful / 1 /. E.g. we have proved the active role of the block (grain) boundaries in the main phases of cement, these boundaries being the areas of hydrate phases' nucleation / 2 /. It has brought to the supposition that the dissolution frontier of cement particles in water is discrete. It seems also probable that the dissolution proceeds through the channels, which serve both for the liquid phase movement and for the drainage of the incongruant solution products. These channels can be appeared along the block boundaries.In order to demonsrate it, we have offered the method of phase-contrast impregnation of the hardened cement paste with the solution of methyl metacrylahe and benzoyl peroxide. The viscosity of this solution is equal to that of water.

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