Michal Petrů

Testing of Tensile Properties of Carbon Prepreg Composite Rods with Adding of a Non-Composite Part

The global development of carbon composite materials has been devoting constantly in still more companies and research institutions. Pre-saturated fabrics known as prepregs have a significant position in this field. The common problem of many worldwide authors is how to determine their tensile strength. The problem with tensile load is mainly due to the extremely high strength of fibers filaments and structural fragility of the thin width of formed profiles. Therefore, indirect methods are usually used. They are based on a determination of the resonant frequencies or on a conversion of values obtained e.g. with bending test. In our case, some experiments have been based on the idea of added a non-composite material into the final structure. The aim of this work was also to find an appropriate modification of a surface of the additional element with regard to a mutual interaction, surface microstructure and mechanical properties of the resulting composite part.

Complex Approach to Conceptual Design of Machine Mechanically Extracting Oil from Jatropha curcas L. Seeds for Biomass-Based Fuel Production

One of important sources of biomass-based fuel is Jatropha curcas L. Great attention is paid to the biofuel produced from the oil extracted from the Jatropha curcas L. seeds. A mechanised extraction is the most efficient and feasible method for oil extraction for small-scale farmers but there is a need to extract oil in more efficient manner which would increase the labour productivity, decrease production costs, and increase benefits of small-scale farmers. On the other hand innovators should be aware that further machines development is possible only when applying the systematic approach and design methodology in all stages of engineering design. Systematic approach in this case means that designers and development engineers rigorously apply scientific knowledge, integrate different constraints and user priorities, carefully plan product and activities, and systematically solve technical problems. This paper therefore deals with the complex approach to design specification determining that can bring new innovative concepts to design of mechanical machines for oil extraction. The presented case study as the main part of the paper is focused on new concept of screw of machine mechanically extracting oil from Jatropha curcas L. seeds.

Experimental and Numerical Analysis of Stress and Stick-Slip Effect of the Test Stand

Experimental and numerical analysis describes the design of noise removal effect of the friction pair of trapezoidal screw in a special device call Stick-Slip effect. Solution of the problems builds on previous measurements and testing sliding pairs, which was testing in last analysis. The pair worked in the special bath oil, its characteristics is that it does not support the mechanical lubrication. Measurements and calculations showed that it is necessary to enlarge the diameter for 32 kN load trapezoidal screw. This will reduce the contact pressure, which leads to polish the contact surfaces. You then slip together better and are not as easily stick slip effect.

Analysis of the Tailgate Frame Composite Tube Mechanical Properties

Substitute of the traditional materials with new plastic-based and composite materials is a trend in todays automotive industry. Mechanical properties of the composite parts are highly influenced by the composite production (material of fibers and their distribution, type and density of a filler). Knowledge of the specific composite material mechanical properties is necessary for CAD modeling and FEM calculations during the assembly design. These mechanical properties can be obtained by creating a composite structure in FEM software. However, the real composite may be different from the ideal FEM model (due to inaccuracies in its manufacture). Therefore, it is highly advisable to verify the modeling results by measuring of the real composite material properties. Identification and verification of the composite tube mechanical properties used in the hybrid car tailgate are described in this paper.

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

Composite Production and Industrial Robot Trajectory Calculation

This paper discusses the problem of composite production. Composites often supplant traditional materials such as steel, iron, wood, etc. The most important advantages of composites are their high strength and flexibility, low weight, long lifespan and minimum maintenance. The technology used in this article is based on a winding of a carbon (or a glass) filament rovings on a polyurethane core which is a frame shape in 3D space with a circular cross section. The polyurethane frame is fastened to the robot-end-effector of the robot arm and during the winding process goes through a fiber-processing head on the basis of the suitably determined robot-end-effector trajectory. The fiber-processing head is fixed in robot working space and is composed of three guide lines with coils of carbon rovings. Quality production of described type of composite depends primarily on the correct winding of fibers on a polyurethane frame. It is especially needed to ensure the correct angles of the fibers winding on a polyurethane frame and the homogeneity of individual winding layers. The polyurethane frame is specified in the local Euclidean coordinate system E3, the origin of this system is in the robot-end-effector. We use the matrix calculus to enumerate the trajectory of the robot-end-effector to determine the desired passage of the frame through the fiber-processing head. A practical example of the passage of a polyurethane frame through fiber-processing head is dealt with in the article. Of course, the determining calculation of the robot trajectory can be used in other applications of industrial robot use.

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.

Numerical model describing optimization of fibres winding process on open and closed frame

This article discusses a numerical model describing optimization of fibres winding process on open and closed frame. The quality production of said type of composite frame depends primarily on the correct winding of fibers on a polyurethane core. It is especially needed to ensure the correct angles of the fibers winding on the polyurethane core and the homogeneity of individual winding layers. The article describes mathematical model for use an industrial robot in filament winding and how to calculate the trajectory of the robot. When winding fibers on the polyurethane core which is fastened to the robot-end-effector so that during the winding process goes through a fibre-processing head on the basis of the suitably determined robot-end-effector trajectory. We use the described numerical model and matrix calculus to enumerate the trajectory of the robot-end-effector to determine the desired passage of the frame through the fibre-processing head. The calculation of the trajectory was programmed in the Delphi development environment. Relations of the numerical model are important for use a real solving of the passage of a polyurethane core through fibre-processing head.

Experimental Analysis and Optimization of Vibrations of a Clamping Device by Using Hyperelastic Elements

Nowadays composite frames can be used, for its specific properties, in many fields of industry. Lightweight composite frames can be significant structural components in some transportations, flights and military applications. The main problem is how to use automatic applications for winding filaments of the carbon fibres on a closed spatial shaped core of product frames, that has been still doing by the hand manufacturing. For automatic production could be used unique prototype of robotic technology, which allows winding of the carbon fibres on closed shape into the core of a frame. The biggest problem of the clamping device, used for the closed frames, are their vibrations and resonance caused due to the rotary motions. The vibrations and resonance negatively affect the process of carbon fibres winding. Experimental measurements were carried out to determine the acceleration on individual arms of the clamping device, which reaches to 2.5±0.6 g. Minimizing of the vibration was performed by a hyperelastic elements which reduce vibrations to 0.4±0.15g.