[1] Migration of grain boundaries in free-standing nanocrystalline thin films

Dynkin and Gutkin

Theoretical models are suggested which describe stress-coupled migration of grain boundaries in free-standing nanocrystalline films under external loading. The critical stresses for the start of migration and the transition from stable to unstable migration are calculated and analyzed in dependence on the grain size, grain boundary misorientation angle, film thickness, distance from the closest free surface, and migration direction. It is shown that the least stable are low-angle grain boundaries of larger length which emerge on surfaces of thinnest films.

[2] Insight into the phase transformations between Ice Ih and Ice II from electron backscatter diffraction data

D J Prior et al

Electron backscatter diffraction data from polycrystalline water ice, cycled three times through the 1h to II phase transformation, show that an area equivalent to the original grain-size (∼450μm) now comprises equant 10μm grains with a non-random crystallographic preferred orientation (CPO). Pole figures show small-circle ring and fence patterns characteristic of CPO development controlled by an orientation relationship during phase transformation. Misorientation analysis shows that one of two orientation relationships can explain the data: 1h/II, {10-10}1h/{0001}II or 1h/II, {10-10}1h/{0001}II .

[3] Comment on ”Simulation of damage evolution in composites: A phase-field model”

Emmerich and Pilipenko

Here we reassess the results of [S.B. Biner, S.Y. Hu Acta Matt. 57(2009) 2088-2097] on phase-field simulations of damage evolution in composite materials. In particular we discuss the validity of the results presented therein in the framework of linear elasticity theory.

Update: Reply to “comment on simulation of damage evolution In composites: a phase-field model by H. Emmerich and D. Pilipenko ”

Biner and Yu

Composites with superspherical inhomogeneities

R Hashemi et al

In contrast to the traditional study of composites containing ellipsoidal inclusions, we highlight some calculated results for the effective moduli when the inclusion shape can be described by the superspherical equation, TPHL_A_402075_O_XML_IMAGES\TPHL_A_402075_O_ILM0001.gif, such that when p = 2 it reduces to a sphere and when p → ∞ it becomes a perfect cube. We consider the cases of both aligned and randomly oriented superspherical inclusions with isotropic, cubic, and transversely isotropic properties, and show how the shape parameter, p, affects the overall moduli of the composites during the spherical to cuboidal transition.

Phil. Mag. lett., 89, 7, 439-451, 2009.

2D foam rheology

April 4, 2009

A simple analytical theory of localisation in 2D foam rheology

D Weaire, R J Clancy and S Hutzler

A very simple derivation is given for the dependence of localisation length on boundary velocity and various model parameters, in the continuum theory of 2D foam shear localisation. It is pointed out that the existence of distinct yield and limit stresses can complicate this theory for low boundary velocities, by introducing another mechanism for localisation, which does not depend on wall drag.

In a News and Views piece, Linda Schadler puts the recent work of Rittigstein et al on interfaces in model polymer nanocomposites in perspective:

Three important conclusions arise from this work. First, the size of the interfacial region (which is half the interparticle spacing or film thickness) can be as large as 250 nm, and depends on the degree of interaction between the polymer and the particle. Although this functionality remains to be quantified, this is one of the first times this behaviour has been proved and quantitatively measured in a controlled nanocomposite system. Second, they show a quantitative correlation between thin-film thickness and an ‘effective interparticle spacing’ at which changes in Tg begin to occur. Third, they find that the ageing rate — the rate at which the amorphous polymer approaches its equilibrium state — decreases dramatically in both the ‘real’ and ‘model’ nanocomposites, which implies that nanocomposite properties will be more stable than pure polymers over time.

Take a look!