https://research.birmingham.ac.uk/portal/files/45381603/Liu_et_al_Dislocation_network_in_additive_Materials_Today_2017.pdf

Dislocation network in additive manufactured steel breaks strength–ductility trade-off

In this paper an experimental and theoretical study of the deformation of a spherical liquid droplet colliding with a flat surface is presented. The theoretical model accounts for the presence of inertia, viscous, gravitation, surface tension, and wetting effects, including the phenomenon of contact‐angle hysteresis. Experiments with impingement surfaces of different wettability were performed. The study showed that the maximum splat radius decreased as the value of the advancing contact angle increased. The effect of impact velocity on droplet spreading was more pronounced when the wetting was limited. The experimental results were compared to the numerical predictions in terms of droplet deformation, splat radius, and splat height. The theoretical model predicted well the deformation of the impacting droplet, not only in the spreading phase, but also during recoiling and oscillation. The wettability of the substrate upon which the droplet impinges was found to affect significantly all phases of the spre...

Wetting effects on the spreading of a liquid droplet colliding with a flat surface: Experiment and modeling

Impact, recoil and splashing of molten metal droplets

The normal impact of a liquid drop on a dry solid surface is studied experimentally and theoretically. In this paper a strictly theoretical model is introduced, which predicts the evolution of the drop diameter. The spreading and receding phases of the impact are described by the motion of a rim appearing at the edge of the liquid film (lamella) due to the surface-tension forces. The mass and the momentum equations of the rim are considered, taking into account the effects of inertial, viscous and surface forces, and wettability. Also, simplified approximations for the maximum spreading diameter of the drop and for the velocity of the merging of the rim in the receding phase are obtained. The theoretical predictions agree well with available experimental data.

Normal impact of a liquid drop on a dry surface: model for spreading and receding

This study is devoted to a theoretical description of an unsteady laminar viscous flow in a spreading film of a Newtonian fluid. Such flow is generated by normal drop impact onto a dry substrate with high Weber and Reynolds numbers. An analytical self-similar solution for the viscous flow in the spreading drop is obtained which satisfies the full Navier–Stokes equations. The characteristic thickness of a boundary layer developed near the wall uniformly increases as a square root of time. An expression for the thickness of the boundary layer is used for the estimation of the residual film thickness formed by normal drop impact and the maximum spreading diameter. The theoretical predictions agree well with the existing experimental data. A possible explanation of the mechanism of formation of an uprising liquid sheet leading to splash is also proposed.

Inertia dominated drop collisions. II. An analytical solution of the Navier–Stokes equations for a spreading viscous film

Results are presented of a study of the splat-quench solidification of small, freely falling liquid drops of the alloy Nitronic 40W, which were allowed to impact on a solid, planar, horizontal substrate. The principal variable was the substrate material, with substrates of copper, alumina and fused quartz being used. The shapes of the solidified splats were correlated with a simplified model for the energetics of the splatting process and with the thermal conductivity of the substrate. The measured results are qualitatively in agreement with theoretical predictions, and suggestions are offered for a more comprehensive model of splat-quench solidification. A relationship between sessile droplet diameter and parent wire diameter is also presented and discussed.

Splat-quench solidification of freely falling liquid-metal drops by impact on a planar substrate

The free fall of a liquid-metal drop, heat transfer from the drop to its environment, and solidification of the drop are described for both gaseous and vacuum atmospheres. A simple model, in which the drop is assumed to fall rectilinearly, with behaviour like that of a rigid particle, is developed to describe cooling behaviour. Recalescence of supercooled drops is assumed to occur instantaneously when a specified temperature is passed. The effects of solidification and experimental parameters on drop cooling are calculated and discussed. Major results include temperature as a function of time, and of drag, time to complete solidification, and drag as a function of the fraction of the drop solidified.

Cooling and solidification of liquid-metal drops in a gaseous atmosphere

In samples in which at least one dimension, say 2R, is comparable to a penetration depth, λL, the flux-exclusion volume at fields below Hcl is less than the true sample volume. This “volume erosion” has two important consequences: (i) it causes the Meissner susceptibility to be less than the standard value -- for example, for a field-parallel plate, by a factor l-(l/x)tanh(x), where x = R/λL; (ii) it reduces the flux-exclusion energy density (based on the initial sample volume) by the square of that factor. In the latter case it calls for an enhanced applied field strength to terminate the Meissner state ~ that enhancement factor being accordingly \( 1/\sqrt {1 - (1/x)\tanh (x)} \). Both of these effects become more and more pronounced as T approaches Tc, since the field-penetration depth increases with temperature according to \( 1/\sqrt {1 - {t^4}} \), where t = T/Tc. The susceptibility-depletion and field-enhancement effects have been studied on a series of very fine filament composites (with NbTi filament diameters ranging from 0.5 to 11.6 μm), prepared from 23,000-filament NbTi/CuMn strands from which (to avoid unwanted proximity-effect coupling) the Cu has been removed by etching and replaced by epoxy. For example, at 4.2 K in the finest-filament material, susceptibility was found to be 1/15 of the Meissner value, and the sample exhibited a lower critical applied field of 607 gauss.

Critical Field Enhancement Due to Field Penetration in Fine-Filament Superconductors

Results are presented of magnetic-field calculations for multifilamentary (MF) superconductors, taking into account the penetration of magnetic flux into individual filaments. The filaments are assumed to be circular in cross section, infinitely long, and arranged parallel to one another on a hexagonal lattice. The externally applied magnetic field is taken to be directed perpendicular to the filament length. The problem is simplified by treating the medium as being effectively uniform in a plane perpendicular to the filament length, and a self-consistent formalism is used to calculate the interfilamentary magnetic field. Flux penetration into the filaments is described using the London theory. Magnetic fields outside and inside the filaments are calculated as functions of filament radius, the London penetration depth, the area fraction covered by filament cross sections, and the shape of the filament bundle.

J. K. McCoy

Papers

Splat-quench solidification of freely falling liquid-metal drops by impact on a planar substrate

Cooling and solidification of liquid-metal drops in a gaseous atmosphere

Critical Field Enhancement Due to Field Penetration in Fine-Filament Superconductors

Theory of Flux Penetration Effects Below H c 1 in Multifilamentary Superconductors