Karel Frydrýšek

Antibacterial activity of kaolinite/nanoTiO2 composites in relation to irradiation time.

The paper addresses laboratory preparation and antibacterial activity testing of kaolinite/nanoTiO2 composite in respect of the daylight irradiation time. Kaolinite/nanoTiO2 composites with 20 and 40 wt% of TiO2 were laboratory prepared, dried at 105 °C and calcined at 600 °C. The calcination caused transformation of kaolinite to metakaolinite and origination of the metakaolinite/nanoTiO2 composite. X-ray powder diffraction, Raman and FTIR spectroscopic methods revealed titanium dioxide only in the form of anatase in all evaluated samples (non-calcined and calcined) and also transformation of kaolinite to metakaolinite after the calcination treatment. Scanning electron microscopy was used as a method for characterization of morphology and elemental composition of the studied samples. A standard microdilution test was used to determine the antibacterial activity using four human pathogenic bacterial strains (Staphylococcus aureus, Escherichia coli, Enterococcus faecalis, Pseudomonas aeruginosa). A lamp with a wide spectrum bulb simulating daylight was used for induction of photocatalysis. The antibacterial assays found all the KATI samples to have antibacterial potency with different onset of the activity when calcined samples exhibited antibacterial activity earlier than the non-calcined. Significant difference in antibacterial activity of KATI samples for different bacterial strains was not observed.

The Study of Electrical Transport in Rubber Blends Filled by Single Wall Carbon Nanotubes

The paper deals with the electrical and mechanical properties of rubber blends filled by single wall carbon nanotubes (SWCNT-0,6 weight %). We have investigated the alternating current resistivity (ACR), real and imaginary part of dielectric constant,and loss factor .The addition of (SWCNT) to a rubber blend decreases ACR and increases constants ,and loss factor .

The Chosen Aspects of Materials and Construction Influence on the Tire Safety

Security of the road transport depends on the quality of basic and applied research concerning materials and internal construction of tires. The design shapes and material properties characterized by low hysteretic losses as well as a construction have an influence on the driving comfort, adhesion, wear resistance and fatigue resistance. Thick fibre reinforced composites are used extensively in rubber products such as tires and conveyer belts. Generally, the reinforced parts of rubber products on a sub macroscopic level are highly heterogeneous and anisotropic because they are composed of rubber compounds, and textile and steel cords. Rubber compounds consist of natural or synthetic rubber, carbon black, curing agents, cure accelerators, plasticizers, protective agents and other ingredients.

Stochastic Computer Approach Applied in the Reliability Assessment of Engineering Structures

The development of computer technology and reliability theory allows for a qualitative improvement of the safety and serviceability assessment of structural components and systems especially in engineering. The random characters of loads, materials, geometries etc. can be considered and evaluated. Using the Simulation-Based Reliability Assessment (SBRA) Method (i.e. Monte Carlo approach based on >106 of random simulations performed by computers) the application of a fully probabilistic approach to reliability assessment of selected structural components are indicated. Hence, two practical examples are solved (i.e. buckling of a complicated statically indeterminate frame structure and bending of screw implants in bones). Other applications are mentioned. Stochastic transformation models are used in order to express the response of the structural components including the 2nd order theory effects.

Measuring the Deflection of a Circular Plate on an Elastic Foundation and Comparison with Analytical and FE Approaches

The solution of the interaction between a structure and its foundation is an important problem in mechanics and technical applications. This paper presents a solution of a circular plate rested on an elastic (Winkler) foundation. A jig was created for the purpose of loading a circular plate with a specific bending moment and force on the plate circumference. Laboratory testing was performed to determine the deflection in the centre and at the edge of the plate. Measurement apparatus was assembled and measurements were carried out; the results of the measurement were compared with the analytical solutions and FEM results. On the basis of these comparisons, the foundation modulus was determined. The experiment, analytical solution and FEM give similar results, thus providing a solid basis for technical applications.

Monte Carlo Probabilistic Approach Applied for Solving Problems in Mining Engineering

The conference paper presents some computational probabilistic solutions (i.e. direct Monte Carlo simulations and SBRA—Simulation-Based Reliability Assessment Method) applied in the branch of mining engineering. At first, the strength analysis of a bucket wheel excavator used in opencast mines for the extraction of overlying soils is solved. The assessment focuses on the arm of this particular excavator. Quasi-dynamic analysis using Finite Element Method (FEM) and measurement records of the dynamic load during the operation of a large machine can be used to derive statistical inputs (cyclic loading histograms) for probabilistic reliability assessment. At second, the solution of a hard rock (ore) disintegration process is solved (i.e. the bit moves into the ore and subsequently disintegrates it). The probabilistic results are compared with experiments and new design of excavation tool is proposed.

Biomechanics – Elastic Foundation Applied in Modelling of Calcaneal Nails

Abstract This paper presents a strength analysis of a calcaneal nail (material Ti6Al4V and stainless steel) which is used to treat complex heel fractures. The application focuses on a unique calcaneal nail, the C-NAIL, produced by Medin a.s. (Nové Město na Moravě, Czech Republic). The paper first presents an analysis of fracture types, treatment methods and loading of the calcaneus. It then presents an analysis of limit conditions and loading. Calculations (displacement and stress) are performed for 6 and 7 fixing screws using FEM (Ansys Workbench 14 software). The calculation involves a new, original application of an elastic foundation, which effectively replaces the complex interaction of the calcaneal nail and the heel bone.

Straight Beams Rested on Nonlinear Elastic Foundations – Part 1 (Theory, Experiments, Numerical Approach)

This paper presents theory, experiments and numerical approaches suitable for the solution of straight plane beams rested on an elastic (Winklers) foundation, including nonlinearities. The nonlinear dependence of the reaction force on displacement in the foundation (i.e. the experimental data) can be described via bilateral linear or bilateral linear + cubic or bilateral linear + cubic + quintic approximations, or by unilateral approximation (i.e. by using the Least Squares Method). These applications lead to linear or nonlinear differential 4th-order equations. For solutions of nonlinear problems of mechanics, the Finite Difference Method (i.e. the Central Difference Method) and boundary conditions are applied. The solution and its evaluation is performed in second part of this article.

Straight Beams Rested on Nonlinear Elastic Foundations – Part 2 (Numerical Solutions, Results and Evaluation)

This paper presents numerical solutions of straight plane beam structures rested on an elastic (Winklers) foundation. It is a continuation of our previous work (see Part 1 of this article) focused on practical applications and solutions including nonlinearities in the foundation (i.e. bilateral linear, bilateral linear + cubic, bilateral linear + cubic + quintic approximations and unilateral approximation for dependencies of reaction forces on deflection in the foundation). For solutions of nonlinear problems of mechanics (i.e. differential 4th-order equations), the Finite Difference Method (i.e. the Central Difference Method) is applied in combination with the Newton (Newton–Raphson) Method. Finally, in one example, linear and nonlinear approaches are solved, evaluated and compared. In some cases, there are evident major differences between the linear and nonlinear solutions.

Stress-Strain Behaviour Simulation of Vanadium Microalloyed Steel with the Internal Defects During two Different Heating Strategies

This paper is focused on the explanation of a linkage between two different heating strategies and a grow of the internal casting defects, that are already present in continuously cast blooms made from vanadium micro-alloyed Cr-Mo steel. Internal defects initiation and propagation can be associated to unsuitable casting and heating conditions. Small casting voids surrounded by ferrite-bainite network enriched by carbides forming elements produce perfect conditions for crack grow during the bloom straightening, heating in the soaking pit and/or heat treatment. Moreover, we simulated the stress-strain behaviour of continuously cast round bloom during heating in soaking pit using the FEM software. It is shown that optimized heating strategy led to significantly lower rates of the plastic strain as a crucial value for the crack propagation.