Influence of Sulphur Content on Structuring Dynamics during Nanosecond Pulsed Direct Laser Interference Patterning

The formation of melt and its spread in materials is the focus of many high temperature processes, for example, in laser welding and cutting. Surface active elements alter the surface tension gradient and therefore influence melt penetration depth and pool width. This study describes the application of direct laser interference patterning (DLIP) for structuring steel surfaces with diverse contents of the surface active element sulphur, which affects the melt convection pattern and the pool shape during the process. The laser fluence used is varied to analyse the different topographic features that can be produced depending on the absorbed laser intensity and the sulphur concentration. The results show that single peak geometries can be produced on substrates with sulphur contents lower than 300 ppm, while structures with split peaks form on higher sulphur content steels. The peak formation is explained using related conceptions of thermocapillary convection in weld pools. Numerical simulations based on a smoothed particle hydrodynamics (SPH) model are employed to further investigate the influence of the sulphur content in steel on the melt pool convection during nanosecond single-pulsed DLIP.

Sensitivity Analysis of Unsteady Corium Solidification in an Initially Emptied Horizontal Turbulent Pipe Flow

In a reactor core meltdown under postulated severe accidents, the molten material called corium could be ejected or relocated through existing vessel penetrations. There exists, however, a potential for plugging of melt flow due to its complete solidification providing the availability of an adequate heat sink. Simulations of the melt flow in a horizontal tube were carried out to conduct a sensitivity study on the effect of key parameters on the melt penetration distance and bulk temperature distribution of the corium. The Reynolds number was varied from 10,000 to 20,000, inlet temperature was varied from 2600 K to 3000 K, the corium thermal conductivity was varied from 10 W/m·K to 20 W/m·K, and the pipe diameter was varied from 0.0095 m to 0.019 m. In addition, a comparison was made with an analytical model based on a modified Epstein's model and a previous numerical model. The study provided insight into the lower bound, which was found to be 98 mm, and the upper bound was 258 mm when predicting the potential penetration length of corium in horizontal pipes.

Influence of HMW tail chains on the structural evolution of HDPE induced by second melt penetration

Hierarchical double skin–core structures were formed in the polyethylene injected samples and their orientation didn't increase monotonically with increasing high molecular weight (HMW) tail content under the special shear and temperature profiles.