Abstract

This paper presents the application of a stabilized mixed pressure/velocity finite element formulation to the solution of viscoplastic non-Newtonian flows. Both Bingham and Herschel–Bulkley models are considered.

The detail of the discretization procedure is presented and the Orthogonal Subgrid Scale (OSS) stabilization technique is introduced to allow for the use of equal order interpolations in a consistent way. The matrix form of the problem is given.

A series of examples is presented to assess the accuracy of the method by comparison with the results obtained by other authors. The extrusion in a Bingham fluid and the movement of a moving and rotating cylinder are analyzed in detail. The evolution of the streamlines, the yielded and unyielded regions, the drag and lift forces are presented.

These benchmark examples show the capacity of the mixed OSS formulation to reproduce the behavior of a Bingham and Herschel–Bulkley flows with the required accuracy.

Abstract

EMAA copolymer neutralized with sodium salt is a type of ionomer with self-healing abilities. This polymer has been used as raw material for the manufacturing of nanocomposite material by the addition of multiwall carbon nanotubes (MWCNTs). The optimization of the extrusion process, as well as the mixing and dispersion of the nano-reinforcement in the polymeric matrix during extrusion, deals with the manufacturing of a homogeneous reinforced filament. The obtained filaments were used afterwards as feeding materials of a 3D polymer printing machine and tensile test samples were manufactured. Mechanical properties of both unreinforced and reinforced samples were tested. The MWCNTs-reinforced samples exhibited higher mechanical properties without affecting its self-healing ability.

Abstract

Lignin is one of the three major polymeric constituents of wood. It is a natural and renewable resource, and due to its structure it is the most abundant aromatic polymer on Earth. The present work reports the thermal and chemical characterization of a kraft lignin and the study of it’s mixing ability with two bioderived polyesters, namely PLA and PHB, to test their suitability for the production of green fibre.

Abstract

A hybrid multi-output approach which combined the Taguchi method and fuzzy logic was used in this research in order to optimise the mechanical and physical properties of PVC pipes. Eight techological parameters which mostly define the extrusion process were taken into consideration in order to obtain the best possible results for six measurable quality characteristics of PVC pipes. Eighteen experiments with the same number of different parameter value sets were conducted resulting in eighteen various PVC pipe samples. The sample from the second experiment showed the highest value of comprehensive output measure (COM = 0.615), while the lowest COM value (0.359) was noted with the sample no. 13. The results of ANOVA revealed that traction speed is the most significant parameter affecting multiple characteristics with contribution of 28.86%. The optimum combination of factors and their levels is A₁, B₃, C₃, D₂, E₂, F₃, G₃, H₂ – the sample produced at traction speed of 8.8 m/min, nozzle temperature of 211℃, expander doser speed of 23.2 rpm, extruder screw speed of 17.5 rpm, coextruder screw speed of 40.6 rpm, barrel temperature of 178 ℃, extruder mixture doser speed of 28.1 rpm and the coextruder mixture doser speed of 36.4 rpm.

Abstract

Abstract

An aluminium matrix nano-composite (AlMNC) was obtained by a powder metallurgy (P/M) process, consisting of an ex situ reinforcement of pre-alloyed AA6005A powders with 3% vol. of TiC nanoparticles (nTiC), high-energy mechanical milling (HEMM) and hot extrusion powder (HEP). AA6005A powder was chosen as matrix because it is a heat-treatable medium strength Al alloy with excellent corrosion resistance, extrusion performance and good weldability; and the nTiC particles due to their low density, good chemical stability and excellent combination of hardness and elastic modulus. HEMM allowed obtaining an ultra-fine grained (UFG) matrix, a uniform dispersion of the nano-reinforcement and its proper incorporation in the ductile matrix. Simultaneously, the repeated plastic deformation of matrix powder led to a high density of crystal defects, and the large number of dislocation barriers produced by nTiC particles are responsible of the obtained nanostructured composites. HEP allowed obtaining high quality extrudates with an a homogeneous distribution of nanoparticles. The hardness of the nanocomposite is almost 43 % higher than that of the unreinforced AA6005A, showing important increases in yield strength and ultimate tensile strength with a 5% elongation. The extruded profiles were Friction Stir Welded (FSW) obtaining sound welds. The grain size refinement on the stir zone (SZ), led to a slight increase in hardness in the welds.