Petr Lepšík

Analysis and Measurement of the Charge Intensity of the Selected Electrospinning Electrodes

Polymer solutions due to their chemical and physical properties requires for efficient spinning with different intensity of the charge. This corresponds to the geometry of the design of the spinning electrode. The electrode may have geometry in the shape of a smooth cylinder to obtain a less intense charge. Contrary barbed roll or roll with strings produces locally extremely intensive charge. For selected geometry of electrodes FEM models describing the intensity and the potential of the electrostatic field have been established and the results were compared with the experimentally determined results. From a comparison of the results it is evident that on the basis of the FE model can be formed with a certain accuracy to design suitably shaped electrodes to obtain the most efficient process of production of nanofibers. Key words: Electrodes, electrospinning, charge, intensity, FEM

Numerical and Experimental Research of Design Optimization of Baths for the Production of Nanofibers by the Electrospinning

A study and analysis showed that the increase in production and the quantity of nanofibers obtained from electrospinning may be provided by not only increasing the potential gradient between the electrodes, but also by the suitable distribution of the intensity of the electrostatic field. Through a numerical simulation using the finite element method, it was found that the intensity distribution of the electrostatic field is influenced not only by the potential gradient, type and shape of the electrodes, polymer properties and its concentration, humidity, ambient temperature, but also by other parameters, such as relative permittivity of the material and shape of the construction geometry. Experiments have been done with the functional baths for polymer solution deposition with a different geometry and relative permittivity. By using the proposed changes in design and relative permittivity for the experiment with the polymer PVP with TiO2 at 23.2 ± 3 °C and humidity of 14.4 ± 3 % and a potential gradient of 60 kV, the production of nanofibers can be increased by about 50 ± 3%. Key words: Electrospinning, optimization, nanofibers, FEM, reservoir

Research of New Composites for Lightweight Construction with Low Impact on the Environment

New types of composite materials are currently very important for use in lightweight structures with very high strength and resistance to external influences. Therefore, it is increasingly used for their properties in all areas of industrial production. Their application offers a significant weight savings and reduction of a manufacturing energy consumption. But current composite properties are not at maximum level, thus development efforts are focused on their improvements. One of the problems of new composites is a study and description of an interface between the phases. The paper describes experimental and FEM analysis dealing with mechanical properties at the micro level. Analyses were focused on a cohesion and the strain at the interface of the system fiber-matrix-core. These composites are used for components of car parts such as doors, diffusers, spoilers and more detailed description can be applied for the improving of mechanical properties of composite structures.

Analysis of Changes in the Surface Quality of a UD Prepregs Composite due to Mechanical Loading

Optimizing the mechanical properties of composites is very important for light low energy constructions. Unidirectional prepreg (UD prepreg) is an intermediate product synthesizing a unidirectional layer of carbon fibres with a matrix. This can be used in the production of continuous fibres of reinforced composites. The individual layers can be stacked on top of each other to precisely orientate the layers and attain the maximum properties in a given direction. The resulting composite is ultra thin with the highest possible fraction of fibres. Prepreg composites are very high quality and have very good mechanical properties. They can be applied in sectors where the requirements for mechanical resistance are very high. This paper presents an experimental and numerical analysis of the surface of a composite and the changes that may occur to it under the influence of loading. The Ball Drop Test (ASTM D6024-07 / DIN 52306) was used as a stress test. Test samples scanned by image analysis showed that the surface properties of the UD prepreg were not disrupted, while scanning with AXIO IMAGER M2 showed apparent surface disruptions. From the numerical simulations it was determined that a directional orientation of the fibres of +45°/0°/-45° significantly affects their elastic properties.

FEM Modelling and Experimental Analysis of Mechanical Properties of Artificial Blood Vessel

This article deals with a study and optimization of technology for a production of low-diameter biodegradable vascular grafts using modified electrospinning device. This production method allows preparation of grafts with diameter under 6 mm, which serve as carriers of tissue cells. Also their production and establishing of a simulation model, which describes their behaviour under internal pressure. For this purpose spinning device was created with a rotary collector, which allows obtaining the desired fiber orientation that is perpendicular to the axis of rotation. This orientation is necessary for the efficient proliferation of cells and future mechanical properties of artificial blood vessels. Formations created in this way were subjected to mechanical testing. Based on obtained data a suitable material model and FEM model of artificial vessels was established. These vessels were loaded with internal pressure corresponding with standard blood pressure in human body (120/80 mmHg). The results allow assessing the behaviour of the blood vessels during cultivation and proliferation of the cells in bioreactor. This is very important, because in bioreactor a medium, which pulsed under some pressure, is applied. Based on the obtained results were recommended optimization of production process, which led to suitable vessel properties.

Experimental Analysis and Numerical Modelling of Interphase Interfaces of New Environmental Low-Energy Composites

Suitable mechanical properties of composites are very important for light low energy constructions. Their specific properties can offer high specific strength, but current composite properties are not at maximum level, and therefore the efforts of development on further improving are focused. Properties of composites depend not only on character of a matrix and reinforcement, but also on properties of an Interphase between these components. Experimental and numerical analysis dealing with the mechanical properties at the micro level for new types of energy-efficient fiber composites with reduced environmental impact has been compiled. For numerical analyses a finite element method (FEM) was used. Analyses were focused on the cohesion and stress at the interface of the system fiber-matrix-core. From the results can be seen that the specific orientation of the reinforcement relative to the direction of applied force significantly affects the resulting elastic modulus. When investigating the delamination of the layers, the influence of the fiber orientation of the reinforcement is evident. Also quality of the interface has a crucial influence.

Numerical Modelling and Experimental Measurement of Lifting Platform Construction for Car Relocation

Numerical modelling and experimental measurements led to the assessment of stress of structural nodes of scissor lifting platform, which is used for relocation of cars from a production line. It also led to optimization of producing process. Immediate load of scissor lifting platform by a car on stand causes additional bending moment that must be captured in a scissor mechanism. At the beginning the experimental measurements on the real lifting platform were made for obtaining of dependence of displacement, velocity and acceleration on time which was almost 1.5±0.1 g. Then dynamical analysis using a numerical method Runge Kutta 4th order of lifting platform were created. Model analysis showed that the initial immediate acceleration of lifting platform at start and immediate deceleration at stop lead to dynamic shocks. These dynamic shocks are due to long term operation dangerous because they permanently load not only pivots but also other parts – bearings and joining parts. A resonance may occur as well. In particular, dynamic shocks caused damage of structural nodes. Immediate load of scissor lifting platform by a car on stand causes additional bending moment. It is not appropriate in terms of long-term operation. Recommended load lifting platform should be symmetrical.

Innovation of Car Seat Construction Using TRIZ-Based Tool: Function-Oriented Search

The paper deals with the search and design of suitable security solution of an innovated construction of a car seat. The problem consists in the use of flexible reinforcements of the seats, which replaces an origin sheet metal. On this reinforcement the comfort seat cushion is placed on which a passenger sits. This reinforcement is pre-stressed with a certain force, but this force is inadequate during the crash. Consequently, the passenger can dip in the seat, which is very dangerous. Therefore it is necessary to use a suitable mechanism, for pre-stressing the reinforcement by a desired force in the case of crash. New TRIZ-based tool—Function-Oriented Search (FOS) method was utilized to find appropriate solutions. With its help several analogous solutions, which are applicable for this problem, were found. In the paper the advantages and disadvantages of these proposals are discussed, including the proposed optimal solution.

Dynamic Analysis of Lifting Platform Construction for Car Relocation

For a force assessment which acts in individual parts of a scissor lift platform for moving of cars from the production line a dynamic analysis and experimental studies were performed. The analysis of loads show that immediate loading of platforms by the car causes additional bending moment that must be captured in a scissor mechanism. Initially experimental measurements were carried out on the real platform for obtaining of trajectory, velocity and acceleration. Subsequently, model analysis of the lifting platform using four point Runge-Kutta method, were assembled. The model analyzes found that a step loading during acceleration and deceleration of the platforms leads to a dynamic impact that are unsafe due to long term use. The consequence of said is repeated overloading of pivots, bearings, fittings and other parts. Also the dynamic stress may be accompanied by the resonances.

Reduce of Head Injuries During Whiplash Using TRIZ Methodology

Currently, in the automotive industry great emphasis is put on reducing of the energy consumption of applied materials, weight reducing and performance optimizing. The reason is an environmental protection, sustainable development, reducing of fuel consumption and increasing of vehicle safety. One of the ways how to quickly find a suitable solution is the application of TRIZ method (theory of inventive problem solving). On existing solution is showed, how this method can help with an improvement of car headrest safety. With its help two solutions were designed and implemented. Their verification is done using FEM model. From the results of established models data for calculating the head injury criteria (HIC) factor have been obtained. From these data is clear that the proposed solutions improve the safety of headrest.