Strojniški vestnik – Journal of Mechanical Engineering, 2020
Needleless electrospinning is the process of forming thin material fibers from the open surface o... more Needleless electrospinning is the process of forming thin material fibers from the open surface of its solution or melt in a strong electrostatic field. Electrospun non-woven materials are used in various applications that require specific fiber diameters and pore size distributions. Fiber diameter depends on the properties of the polymer solution and manufacturing conditions. A needleless electrospinning process using the Nanospider setup was investigated using the commonly used polyamide 6 (PA6) solution in a mixture of acetic and formic acids. Polymer solutions with different polymer concentrations were characterized by viscosity, surface tension and electrical conductivity. An increase in polymer content in the solution resulted in the exponential increase of the solution viscosity, polynomial increase of electrical conductivity and had almost no effect on surface tension. The effect of the polymer concentration in the solution, as well as electrospinning voltage on fiber diamet...
Abstract This article has been retracted at the request of the Publisher and the Corresponding Au... more Abstract This article has been retracted at the request of the Publisher and the Corresponding Author due to similarity with the published article “Processability and mechanical properties of extensively recycled high density polyethylene, Polymer Degradation and Stability 114 (2015) 1-13” (http://doi:10.1016/j.polymdegradstab.2015.01.012) , by the same Corresponding Author. The article in Materials Today: Proceedings contains no new findings to those previously reported in Polymer Degradation and Stability .
V inženirskih aplikacijah imajo pomembno mesto slojevito ojacani poliestrski kompoziti, ki jih iz... more V inženirskih aplikacijah imajo pomembno mesto slojevito ojacani poliestrski kompoziti, ki jih izdelujejo "rocno". Pomembna lastnost teh kompozitov je, da lahko lokalno spreminjamo njihove mehanske lastnosti z volumskim deležem vlaken, s stevilom ojacitvenih plasti in njihovo orientiranostjo. Tako lahko dosežemo optimalne mehanske lastnosti nekega konstrukcijskega elementa ali konstrukcije. V clanku je predstavljena analiza vpliva navedenih parametrov na natezne lastnosti kompozitnega materiala. Podane bodo smernice, s katerimi lahko tehnolog na enostaven nacin predpise nacin laminiranja glede na lokalno napetostno oziroma deformacijsko stanje, doloceno z metodo koncnih ali robnih elementov.
Powder injection molding (PIM) is one of the most versatile methods for manufacturing small compl... more Powder injection molding (PIM) is one of the most versatile methods for manufacturing small complex shaped components from metal, ceramic powders for the use in many applications. Interesting applications of PIM include the automotive and aerospace industries. PIM can be used to combine multiple parts into a single part with complex geometry, and parts are lighter since porosity remains in the final part while the fatigue resistance increases. Therefore, it can be said that PIM can help reduce the weight of moving vehicles, which is a major concern from the environmental and economic point of view. One of the main limitations of current PIM technology is the long debinding time, which is one of the steps within the process. This has been partially solved by introducing binder systems that undergo catalytic sublimation. However, current catalytic binders have the main problem of high viscosity. In this study, two ways to decrease the viscosity of PIM feedstock materials with polyoxym...
Based on the realization that Newtonian fluids have the unique property to redirect the forces ap... more Based on the realization that Newtonian fluids have the unique property to redirect the forces applied to them in a perpendicular direction, a new apparatus, called the Granular Friction Analyzer (GFA), and the related GFA index, were proposed for characterizing the internal friction and related flow behavior of granular materials under uniaxial compression loading. The calculation of the GFA index is based on the integration of the internal pressure distribution along the cylinder wall, within which the granular material is being uniaxially compressed by a piston. In this paper an optical granular friction analyzer (O-GFA) is presented, where a digital image correlation (DIC) method is utilized to assess the cylinder strains used to calculate the internal pressure distribution. The main advantage of using the DIC method is that the starting point (piston–powder contact point) and the length of the integration considering the edge effects can be defined. By using the DIC full-field,...
Abstract Flow of granular materials is a complex process but it is important to measure, because ... more Abstract Flow of granular materials is a complex process but it is important to measure, because the flow of granular material during processing, handling and transportation strongly influences the quality of the final product and its cost. Flowability of granular materials depends on the characteristics of the material and on the conditions at which flow is occurring. Existing methods of measuring flowability of powders are described in this paper, and a new methodology is introduced to measure friction between granular materials under pressure induced with uniaxial compression. Apparatus also allows analysis of conditions at which granular material starts to flow when exposed to uniaxial compressive load, i.e., zero-rate flowability. We call the apparatus the Granular Friction Analyzer (GFA). The concept of the GFA was tested by measuring four different materials with different average particle sizes. It was observed that as the particle size decreases so does its zero-rate flowability. This is in agreement with powder literature. Therefore, it can be concluded that in general the GFA method can be a very useful tool to study friction between granular materials and conditions at which the granular material flow initiates, i.e. zero-rate flowability of powders under pressure. However, further improvements are required to increase its sensitivity and accuracy.
Strojniški vestnik – Journal of Mechanical Engineering, 2020
Needleless electrospinning is the process of forming thin material fibers from the open surface o... more Needleless electrospinning is the process of forming thin material fibers from the open surface of its solution or melt in a strong electrostatic field. Electrospun non-woven materials are used in various applications that require specific fiber diameters and pore size distributions. Fiber diameter depends on the properties of the polymer solution and manufacturing conditions. A needleless electrospinning process using the Nanospider setup was investigated using the commonly used polyamide 6 (PA6) solution in a mixture of acetic and formic acids. Polymer solutions with different polymer concentrations were characterized by viscosity, surface tension and electrical conductivity. An increase in polymer content in the solution resulted in the exponential increase of the solution viscosity, polynomial increase of electrical conductivity and had almost no effect on surface tension. The effect of the polymer concentration in the solution, as well as electrospinning voltage on fiber diamet...
Abstract This article has been retracted at the request of the Publisher and the Corresponding Au... more Abstract This article has been retracted at the request of the Publisher and the Corresponding Author due to similarity with the published article “Processability and mechanical properties of extensively recycled high density polyethylene, Polymer Degradation and Stability 114 (2015) 1-13” (http://doi:10.1016/j.polymdegradstab.2015.01.012) , by the same Corresponding Author. The article in Materials Today: Proceedings contains no new findings to those previously reported in Polymer Degradation and Stability .
V inženirskih aplikacijah imajo pomembno mesto slojevito ojacani poliestrski kompoziti, ki jih iz... more V inženirskih aplikacijah imajo pomembno mesto slojevito ojacani poliestrski kompoziti, ki jih izdelujejo "rocno". Pomembna lastnost teh kompozitov je, da lahko lokalno spreminjamo njihove mehanske lastnosti z volumskim deležem vlaken, s stevilom ojacitvenih plasti in njihovo orientiranostjo. Tako lahko dosežemo optimalne mehanske lastnosti nekega konstrukcijskega elementa ali konstrukcije. V clanku je predstavljena analiza vpliva navedenih parametrov na natezne lastnosti kompozitnega materiala. Podane bodo smernice, s katerimi lahko tehnolog na enostaven nacin predpise nacin laminiranja glede na lokalno napetostno oziroma deformacijsko stanje, doloceno z metodo koncnih ali robnih elementov.
Powder injection molding (PIM) is one of the most versatile methods for manufacturing small compl... more Powder injection molding (PIM) is one of the most versatile methods for manufacturing small complex shaped components from metal, ceramic powders for the use in many applications. Interesting applications of PIM include the automotive and aerospace industries. PIM can be used to combine multiple parts into a single part with complex geometry, and parts are lighter since porosity remains in the final part while the fatigue resistance increases. Therefore, it can be said that PIM can help reduce the weight of moving vehicles, which is a major concern from the environmental and economic point of view. One of the main limitations of current PIM technology is the long debinding time, which is one of the steps within the process. This has been partially solved by introducing binder systems that undergo catalytic sublimation. However, current catalytic binders have the main problem of high viscosity. In this study, two ways to decrease the viscosity of PIM feedstock materials with polyoxym...
Based on the realization that Newtonian fluids have the unique property to redirect the forces ap... more Based on the realization that Newtonian fluids have the unique property to redirect the forces applied to them in a perpendicular direction, a new apparatus, called the Granular Friction Analyzer (GFA), and the related GFA index, were proposed for characterizing the internal friction and related flow behavior of granular materials under uniaxial compression loading. The calculation of the GFA index is based on the integration of the internal pressure distribution along the cylinder wall, within which the granular material is being uniaxially compressed by a piston. In this paper an optical granular friction analyzer (O-GFA) is presented, where a digital image correlation (DIC) method is utilized to assess the cylinder strains used to calculate the internal pressure distribution. The main advantage of using the DIC method is that the starting point (piston–powder contact point) and the length of the integration considering the edge effects can be defined. By using the DIC full-field,...
Abstract Flow of granular materials is a complex process but it is important to measure, because ... more Abstract Flow of granular materials is a complex process but it is important to measure, because the flow of granular material during processing, handling and transportation strongly influences the quality of the final product and its cost. Flowability of granular materials depends on the characteristics of the material and on the conditions at which flow is occurring. Existing methods of measuring flowability of powders are described in this paper, and a new methodology is introduced to measure friction between granular materials under pressure induced with uniaxial compression. Apparatus also allows analysis of conditions at which granular material starts to flow when exposed to uniaxial compressive load, i.e., zero-rate flowability. We call the apparatus the Granular Friction Analyzer (GFA). The concept of the GFA was tested by measuring four different materials with different average particle sizes. It was observed that as the particle size decreases so does its zero-rate flowability. This is in agreement with powder literature. Therefore, it can be concluded that in general the GFA method can be a very useful tool to study friction between granular materials and conditions at which the granular material flow initiates, i.e. zero-rate flowability of powders under pressure. However, further improvements are required to increase its sensitivity and accuracy.
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