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Abstract: Drawing is a well-established method to improve the mechanical properties of wet-spun fibers, as it orients the polymer chains, increases the chain density, and homogenizes the microstructure. This work aims to investigate how drawing variables, such as the draw ratio, drawing speed, and temperature affect the elastic modulus (E) and the strain at break (εB) of biobased wet-spun fibers constituted by neat polylactic acid (PLA) and a PLA/poly(dodecamethylene 2,5-furandicarboxylate) (PDoF) (80/20 wt/wt) blend. Drawing experiments were conducted with a design of experiment (DOE) approach following a 24 full factorial design. The results of the quasi-static tensile tests on the drawn fibers, analyzed by the analysis of variance (ANOVA) and modeled through the response surface methodology (RSM), highlight that the presence of PDoF significantly lowers E, which instead is maximized if the temperature and draw ratio are both low. On the other hand, εB is enhanced when the drawing is performed at a high temperature. Finally, a genetic algorithm was implemented to find the optimal combination of drawing parameters that maximize both E and εB. The resulting Pareto curve highlights that the temperature influences the mechanical results only for neat PLA fibers, as the stiffness increases by drawing at lower temperatures, while optimal Pareto points for PLA/PDoF fibers are mainly determined by the draw ratio and the draw rate.
Keywords: fibers, poly(lactic acid), furanoate polyesters, drawing, response surface methodology, genetic algorithms
Published in DKUM: 24.03.2025; Views: 0; Downloads: 2
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Abstract: With the development of spatial perceptions being one of the most important goals of visual art education, we analysed the influence of different didactic tools – dynamic or static in the development of pupils’ spatial perception. After an initial testing, we formed groups considering three different levels in their abilities to represent spatial organizations. In experimental groups pupils were introduced with the contents of the lesson using moving images while in control groups we used static images. Pupils had to make a drawing using the cues to represent space. While pupils from the advanced level did not show differences, in the second group they showed more detailed drawings in the case of the use of dynamic didactic means. Among the less talented pupils, the results showed a difference: improvement in the case of static images while dynamic images produced a kind of insecurity that did not allow the free development of pupils’ expression. We concluded that it is important to use the adequate didactic tools taking into account the goals we wish to achieve: dynamic images foster a unique experience of space but they can create insecurity and negative feelings in pupils that find it difficult to express themselves in terms of two dimensional representations of space.
Keywords: new technologies, didactic tool, dynamic and static images, drawing
Published in DKUM: 10.10.2017; Views: 1086; Downloads: 112
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Abstract: The crossing number of Sierpiński graphs ▫$S(n,k)$▫ and their regularizarions ▫$S^+(n,k)$▫ and ▫$S^{++}(n,k)$▫ are studied. Drawings of these graphs are presented and proved to be optimal for ▫$S^+(n,k)$▫ and ▫$S^{++}(n,k)$▫ for every ▫$n ge 1$▫ and ▫$k ge 1$▫. The crossing numbers of these graphs are expressed in terms of the crossing number of ▫$K_{k+1}$▫. These are the first nontrivial families of graphs of "fractal" type whose crossing number is known.
Keywords: matematika, teorija grafov, risanje grafov, prekrižno število, grafi Sierpińskega, avtomorfizmi grafov, mathematics, graf theory, graph drawing, crossing number, Sierpiński graphs, graph automorphism
Published in DKUM: 10.07.2015; Views: 1387; Downloads: 85
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Abstract: The paper presents an example of a link-drive mechanism for a deep drawing mechanical press. Because of its characteristics such a drive is much more appropriate than conventional crankshaft or eccentric drive. The existing design of the drive has proved unsatisfactory and does not meet all the demands and constraints, which are ideal for deep drawing process. Optimization of the drive is therefore necessary. The intention is to achieve the required velocity characteristics in a defined area of movement. Firstly, the drive is analyzed and a mathematical model is made and prepared for optimization procedure. The process is time-dependent, so it cannot be used directly in the optimization algorithm. Mathematical model is transformed intoa form suitable for the standard non-linear optimization procedure and then optimization is carried out. The method used is sequential quadratic programming. The final objective of the optimization process is to find such dimensions of link-drive members that the given requirements are satisfied in the best possible manner.
Keywords: mechanics, dynamics of mechanical systems, closed kinematic chains, mathematical modelling, non-linear optimization, drive optimization, drive dimensioning, kinematic analysis, link-drive mechanism, deep drawing press
Published in DKUM: 01.06.2012; Views: 2506; Downloads: 154
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Abstract: The demands for complicated products have increased dramatically over the last few years taking into consideration the utilisation of sheet metal, product quality and process conditions. For reliable product development and stable production process, the use of FEM is necessary. One of the most significant parameters in the sheet metal forming process is the blank holding force. In the research work, the optimisation of the blank holding force was performed with the help of FEM analysis. For the optimisation the geometry and the structure of the blank holder was optimised. The best results were obtained with flexible, segmented blank holders, which enables wider technological window for good parts.
Keywords: sheet metal forming, deep drawing, segmented holding system, finite elements method, optimization
Published in DKUM: 01.06.2012; Views: 2139; Downloads: 89
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