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.

J. H. Saunders

Papers

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