Papers by Keyword: Jetting

Abstract: Porosity is a crucial property in cold sprayed coatings. If it can be beneficial for certain applications, e.g. lubricated contacts in tribology, it is generally detrimental for mechanical and anti-corrosion properties and for gas tightness of the coating. It is thus important to understand what are the process variables affecting coating porosity and quantify their effects. However, at present day, the experimental observation of cold spray coating build up and porosity creation mechanisms is far from achievable. In this study, a Coupled Eulerian Lagrangian (CEL) numerical 3D finite element analysis of single and multi-particle impacts was led to understand the mechanisms involved in the creation of porosity. All simulations were carried out on Abaqus/Explicit v6.14. Single particle impact simulations addressed the influence of mesh size, particle temperature, size and speed on particle temperature and equivalent plastic deformation after impact. Jetting phenomena appeared and their relationship to the mesh size was established. Nevertheless, the porosity creation mechanisms seemed to arise within the more complex context of multiple particle interactions at impact. For this reason, multiparticle impact simulations were carried out, based on experimental powder granulometry distributions and particle in-flight velocity measurements. Porosity in these simulations was quantified by computing the successive layered convex hulls of the particle cluster after impact. Individual particles were also tracked during the simulations, in order to understand the porosity creation mechanisms. Finally, those porosity rates were compared to those experimentally measured in 2D by SEM image analysis.

Abstract: Injection molding visualization is the experimental method of direct observation on the melt filling behavior in the mold cavity. By using developed visualization system, the influence of mold structure design on the injection molding product’s defects, such as jetting and weld were studied in this paper. The forming process of jetting was observed by the visual method, and results show that it is useful to avoid jetting by locating gate correctly. According to the generation of weld line in single gate cavity, an improved measure to adjust the weld locations by adding overflow traps was proposed. The result indicates that the overflow trap is good for adjusting weld location and makes the defects appear in the unimportant points of surface. Another experiment on the forming process of weld line in two-gate cavity with setting different distance parameters were carried out. The result shows that increasing of gates distance may significantly affect the performance of weld line.

Abstract: We present results from molecular dynamics simulations of shock-induced hydrodynamic void collapse in a model energetic crystal. During void collapse, hotspot formation is observed that leads to subsequent detonation. The hotspot formation mechanism is identified as shock energy focusing via jetting. There is another initiation mechanism that arises from the interaction of reflected shock waves with the rigid piston, which is considered to be an artifact. Such artifact can be eliminated by altering the location of the void. The detonation threshold as a function of the velocity of the driven piston is determined for various void geometries. It is found that a system containing a void has a lower detonation threshold than that of a perfect energetic crystal. The amount of reduction of the detonation threshold depends on the geometry of the void. For square voids, there exists a minimum size above which reduction of the detonation threshold occurs. Among voids that have an equal volume, the void that is elongated along the shock direction gives the lowest detonation threshold.