0000000000871151
AUTHOR
Libin Lalu Koithara
Caractérisation et prédiction du rendement de projection lors du procédé de projection à froid – cas de la métallisation des polymères
This thesis work deals with the cold spray metallization of polymer substrates by aiming at an optimal deposition efficiency using experimental analysis combined with numerical simulation. Experimental observations of the powder jet using an ombroscopic analysis have revealed a generic behavior consisting of a uniform confined zone at the immediate exit of the nozzle followed by a dispersed zone. The supersonic flow at the nozzle exit being essentially axial, the powders are entrained to form a uniform jet. Beyond a certain distance, a dispersion appears. This distance is very important because it characterizes the behavior of the powders. It can alter the conditions for the elaboration of …
Turbulences of the supersonic gas flow during cold spraying and their negative effects: A DNS CFD analysis coupled with experimental observation and laser impulse high-speed shadowgraphs of the particles in-flight flow
Abstract This paper investigates the phenomenological flow during cold spraying through DNS CFD analysis and experimental observations. The transient DNS computation shows that the gas flow begins to be instable inside the nozzle and generates self-sustained intermittent swirls across the nozzle exit due the shearing behavior of the flow. There is alternate swirling within the separated sheared layers on top and then on bottom of the jet, at sporadic time intervals. The swirls are not strictly periodic in nature, but they recur with an irregular frequency. The temperature field exhibits analogous variation and the thermal turbulence produces a heating confinement within the end zone of the …
Flow phenomenon of micron-sized particles during cold spray additive manufacturing: High-speed optic observation and characterization
Abstract A high-speed laser shadowgraph observation of the particles flow during cold spraying enables a good phenomenological characterization. The particles in-flight behaviour develops a kinematics with two regimes regardless the powder nature. When leaving the nozzle, the particles form a regime of uniform jet over a certain distance along the flow direction, and then a regime of sparse jet while particles deviate in the radial direction. This dispersion increases away from the nozzle exit and exhibits thereby an event of oblique collision during an additive route process. Under such conditions, kinematic deficiency prevails since oblique collision has shown to alter the deposition effi…