This paper presents analytical and experimental procedures for estimating elastic properties of a plain weft-knitted fabric and of polymer composite materials reinforced by it. Cotton yarn and fabrics are being considered as an environmentally friendly alternative to synthetic reinforcement in polymer composites. In the present investigation, cotton yarn of different length and cotton knitted fabric specimens of different knitting directions were tested by tension in order to obtain the stress-strain response. Elastic moduli of the cotton yarn and knitted fabrics, having different load span and knitting directions, were obtained. Cotton knitted fabric composites with thermoset polymer matrices were manufactured and tested for stiffness and strength. Based on the Leaf and Glaskin model, a numerical (FEM) elastic properties averaging model was elaborated. Calculated elastic properties of composite materials have shown high compatibility with experimentally obtained values.
Fibers are usually used in High Performance Concrete with a purpose to increase bending strength and ductility. Important properties are the peak value of bearing stress (strength) and post-cracking behavior of bended element. In the framework of an experimental part, Ultra High Performance mix compositions were prepared using intensive mixer. Short steel fibers and carbon micro fibers in amount of 1% by volume, as well as its combination were used for cement matrix reinforcing. Results of compressive and bending tests proved an increase of strength value in the case of use both steel and carbon fibers. Carbon fibers were decreased the effect of explosive collapse of the UHPC cement matrix, at the same time still brittle bending behavior was take place. Steel fibers considerably improved bending ductility thanks to a pull-out mechanism of steel fibers. The best results were achieved in the case of combined application of both carbon and steel fibers.
The paper considers the possibility to derive energy from air or water in a non-traditional way (without using rotating equipment). For this purpose, the authors studied variations in the additional area of a vibrating object in a definite sequence found as the solution of an optimisation problem. In the work, stably moving mechatronic systems were synthesised and modelled, whose control is very simple (not requiring calibration), being a function of the changing sign of phase coordinates.
Fluid (water) flow translation motion conveyor (transporter) is being reviewed. In this device the actuator blades move in the plane axis parallel cycloidal motion, but the fluid flows away perpendicular to the rotation axis in translation direction. For this purpose the blade two component movement is synthesized by kinematics of the gear box: the first rotation takes place around the central axis of each blade, while the other rotation moves around this centre around the central axis of the transporter. The movement is designed in such a way that the central axis rotates twice as fast as the blades around its axles. The kinematics and dynamics of the transporter movement are analyzed, taking into account the characteristics of the drive motor and the blade interaction forces with fluid. The results of the analysis are shown in the graphs obtained by computer modelling. The possibility of creating a multi-element conveyor is being reviewed on the basis of one rotational element. In this case, it is possible to increase the efficiency of the system in such a way that the individual small conveyors in pairs operate in counter phase (rotates opposite). For transporter experimental investigations a special system is made inside the water tank. The system includes a rotating beam with a possibility to stick the devise in the end of this beam. Measurement sensors and the engine power system cable are connected to the control system via sliding contacts. A direct current electric motor is created in the conveyor drive. It allows to change the blade drive rotation number of a wide range. The design used in the work may also be used for other purposes, for example, for generation of energy from fluid flow. In this case, like before, all formulas can be used as calculation in relative interaction.
Collisions between solid objects in machine building, technology and everyday life are widespread. However, analysis of the movement of solid objects by analytical methods is difficult even in the case of plane motion. The main problem arises when the collision process occurs with several successive impulse points. Then the points of the collision contact move along the surface of the object. Therefore, the equation of the boundary conditions must be solved. In these cases, the only sensible option is to perform experimental investigations or simulations by computer programs. In the first part of this work, 3DOF's solid body movement is analysed in a vertical or horizontal plane with collisions against the walls of a fixed or moving endless mass container. Different body shapes with convex and concave sections are considered. Graphical analysis of displacements, velocities and accelerations is given. Opportunities for object orientation or transport on the bottom edge of the container are displayed. The second part deals with the movement of several solid bodies in a closed or open container. Opportunities and problems in the analysis of many DOF systems are shown. The third part of the thesis contains simple movement experiments that give good accuracy to theoretical modelling results. The difference can be explained by the properties of real objects, such as the change of the slip friction coefficient in the impact. The work results can be used in machine building and robot technology.
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