Spatter Formation and Splashing Induced Defects in Laser-Based Powder Bed Fusion of AlSi10Mg Alloy: A Novel Hydrodynamics Modelling with Empirical Testing

Powder spattering and splashing in the melt pool are common phenomena during Laser-based Powder Bed Fusion (LPBF) of metallic materials having high fluidity. For this purpose, analytical and computational fluid dynamics (CFD) models have been deduced for the LPBF of AlSi10Mg alloy. The single printed layer’s dimensions were estimated using primary operating conditions for the analytical model. In CFD modelling, the volume of fluid and discrete element modelling techniques were applied to illustrate the splashing and spatter phenomena, providing a novel hydrodynamics CFD model for LPBF of AlSi10Mg alloy. The computational results were compared with the experimental analyses. A trial-and-error method was used to propose an optimized set of parameters for the LPBF of AlSi10Mg alloy. Laser scanning speed, laser spot diameter and laser power were changed. On the other hand, the powder layer thickness and hatch distance were kept constant. Following on, 20 samples were fabricated using the LPBF process. The printed samples’ microstructures were used to select optimized parameters for achieving defect-free parts. It was found that the recoil pressure, vaporization, high-speed vapor cloud, Marangoni flow, hydraulic pressure and buoyancy are all controlled by the laser-material interaction time. As the laser-AlSi10Mg material interaction period progresses, the forces presented above become dominant. Splashing occurs due to a combination of increased recoil pressure, laser-material interaction time, higher material’s fluidity, vaporization, dominancy of Marangoni flow, high-speed vapor cloud, hydraulic pressure, buoyancy, and transformation of keyhole from J-shape to reverse triangle-shape that is a tongue-like protrusion in the keyhole. In the LPBF of AlSi10Mg alloy, only the conduction mode melt flow has been determined. For multi-layers printing of AlSi10Mg alloy, the optimum operating conditions are laser power = 140 W, laser spot diameter = 180 µm, laser scanning speed = 0.6 m/s, powder layer thickness = 50 µm and hatch distance = 112 µm. These conditions have been identified using sample microstructures.

How to Determine the Dangerous Potential of Accidents to Domino Effect Detonation in a Hydrocarbon Processing Area?

The crude oil industry has been developed in recent decades due to the uses of this product, as well as its derivatives. One of the worst consequences phenomena that can occur in the process industry is the called domino effect. The domino effect or cascade effect occurs when an initiating event, such as a pool of fire or a vapor cloud explosion, causes a new number of accidents. Moreover, due to the importance of avoiding this phenomenon, the European Commission considers the domino effect analysis as mandatory for industrial facilities. There are methodologies in the specialized literature focused on quantifying the existing risks in the storage and processing of hydrocarbons. However, there is a tendency to develop new procedures that increase the risk perception of these accidents. In addition, it is necessary to develop a method that allows visualizing clearly and concisely the dangerous potential of fire and explosion accidents for the occurrence of the domino effect. Precisely, this research aims to predict the dangerous potential of fire and explosion accidents for the occurrence of the domino effect. For this purpose, a methodology consisting of three fundamental stages is developed. Finally, hydrocarbon storage and processing area is selected to apply the proposed methodology. Overall, the development of graphs that summarize information and show the dangerous potential regarding the escalation of fire and explosion accidents is vital in risk analysis. For the case study, the effectiveness of the same was demonstrated, since after its realization it was possible to increase the risk awareness of workers, technicians, and managers of the area taken as a case study.

Numerical Simulation of Leakage and Diffusion Process of LNG Storage Tanks

To investigate the evolution process of LNG (Liquefied Natural Gas) liquid pool and gas cloud diffusion, the Realizable k-ε model and Eluerian model were used to numerically simulate the liquid phase leakage and diffusion process of LNG storage tanks. The experimental results showed that some LNG flashed and vaporized rapidly to form a combustible cloud during the continuous leakage. The diffusion of the explosive cloud was divided into heavy gas accumulation, entrainment heat transfer, and light gas drift. The vapor cloud gradually separated into two parts from the whole “fan leaf shape”. One part was a heavy gas cloud; the other part was a light gas cloud that spread with the wind in the downwind direction. The change of leakage aperture had a greater impact on the whole spill and dispersion process of the storage tank. The increasing leakage aperture would lead to 10.3 times increase in liquid pool area, 78.5% increase in downwind dispersion of methane concentration at 0.5 LFL, 22.6% increase in crosswind dispersion of methane concentration at 0.5 LFL, and 249% increase in flammable vapor cloud volume. Within the variation range of the leakage aperture, the trend of the gas cloud diffusion remained consistent, but the time for the liquid pool to keep stable and the gas cloud to enter the next diffusion stage was delayed. The low-pressure cavity area within 200 m of the leeward surface of the storage tank would accumulate heavy gas for a long time, forming a local high concentration area, which should be an area of focus for alert prediction.

The first microseconds of a hypervelocity impact

ABSTRACT The earliest ejection process of impact cratering involves very high pressures and temperatures and causes near-surface material to be ejected faster than the initial impact velocity. On Earth, such material may be found hundreds to even thousands of kilometers away from the source crater as tektites. The mechanism yielding such great distances is not yet fully understood. Hypervelocity impact experiments give insights into this process, particularly as the technology necessary to record such rapid events in high temporal and spatial resolution has recently become available. To analyze the earliest stage of this hypervelocity process, two series of experiments were conducted with a two-stage light-gas gun, one using aluminum and the other using quartzite as target material. The vertical impacts of this study were recorded with a high-speed video camera at a temporal resolution of tens of nanoseconds for the first three microseconds after the projectile’s contact with the target. The images show a self-luminous, ellipsoidal vapor cloud expanding uprange. In order to obtain angle-resolved velocities of the expanding cloud, its entire front and the structure of the cloud were systematically investigated. The ejected material showed higher velocities at high angles to the target surface than at small angles, providing a possible explanation for the immense extent of the strewn fields.