Fulltext search in archive

The Zn-1.6Mg alloy was chosen because mechanical properties of this alloy are similar to human bones. It is necessary to describe corrosion behaviour of the Zn-1.6Mg alloy before using it for application as a biodegradable material. In this work, two types of corrosion rate measurements were used. One of them was an exposure test in model physiological solution marked as SBF (the simulated body fluid) and NaCl solution. The second method was measurement of potentiodynamic curves in the SBF and NaCl solutions. The aim of this work was to compare both methods and confirm similar trend of corrosion behaviour in model physiological solution (SBF and NaCl).

It is relatively complicated to effectively burn biomass. Combustion of biomass fuel itself as a renewable energy source does not automatically ensure the best use of its energy content with low emission production. Biomass combustion with bad settings of combustion conditions can be ineffective and with a high production of emissions. The article discusses the impact of humidity on the thermal technical parameters of the heat source. The influence of the relative humidity of combustion air and the fuel moisture on thermal power and emission production in automatic boiler for combustion of wood pellets were specifically determined. The results show that these properties of combustion air and biofuel have an effect on the thermal and emission parameters of biomass heat source. Biofuel moisture had higher impact on thermal power and emissions production in comparison with relative humidity of combustion air impact.

An article deals with a concept of increasing efficiency of a current production process of bearing ring machining. A goal is to substitute a generally expensive technology of cutting when at least the same integrity of a surface is kept. A theoretical part is focused on a characteristic and analysis of a given component including an applied material 100Cr6 from which bearing rings are made. A practical part analyses and suggests an innovation of increasing efficiency of the machining process. Series of samples would be tested experimentally at university conditions (Workroom C2 of Dept. of Machining Technology, Faculty of Mechanical Engineering, Brno University of Technology) using CNC Lathe Machine SP 280 SY.
The article describes individual production workplaces along with used tool equipment that includes for the process of increasing efficiency the innovation in the form of the change of the production process, changes of most cutting tools and cutting conditions needed for the turning of heat-treated bearing rings. The article also deals with a surface integrity after turning of bearing rings. The integrity is analysed using a touch measuring tools (a manual roughness tester TS100, a tool with an inductive sensor Form Talysurf Intra) and using a touchless measuring tool Alicona Infinite Forces G4, including the measurement of a residual tension in a surface layer (Barkhausen noise) by the tool Rollscan 300.
The article finishes with a wear test of replaceable cutting blades at applied cutting conditions with a follow-up discussion, which describes problematic steps that were done in particular phases of experimental testing, and with necessary concept of further testing of bearing rings.

Damping capacity of alloys is closely tied to the presence of defects including solute atoms, second phases and voids. The interaction between moving dislocations and point defects is one of the major internal damping mechanisms of magnesium alloys so the precipitates influence the damping capacity and contribute to damping properties. The article is focused on the analysis of the internal damping changes depending on the amplitude of the magnesium alloys AZ31 and AZ91 in as cast state and after homogenization annealing. In experimental measurements only resonance method was used. This method is based on continuous excitation of oscillations of the specimen and the entire apparatus vibrates at a frequency which is near to the resonance. Starting resonance frequency for all measurements was about f = 20500 Hz.

Additive layer manufacturing (ALM) methods such as selective laser melting (SLM) and laser metal deposition (LMD) enable production of parts with complicated shapes. Iron based aluminides are a new promising class of materials for high temperature applications. Near net shape production by ALM is specifically interesting in case of these wear resistant aluminides, where machining is difficult. In this article the microstructure of aluminides prepared by SLM and LMD will be compared with those prepared by spark plasma sintering of the same compositions.

An application of an adhesive bonding technology is limited by cyclic loading of an adhesive bond. The aim of the experiment is to clarify a fatigue behaviour (low-cyclic tests of the fatigue) of four structural two-component epoxy adhesives applied to an alloy AlCu4Mg. The aim of the research was to evaluate a service life of the adhesive bond in terms of its fatigue stressing at the quasi static shear test. From that reason values of a passing loading for low-cyclic fatigue test were chosen for tested adhesives, i.e. 25 %, 50 % and 75 % from a reference value of a maximum force gained at the static test according to CSN EN 1465. The critical value at the low-cyclic fatigue test was determined from the experiment results for the adhesive bond as 75 %. Most of the adhesive bonds did not reach 100 cycles at this value.
It is obvious from the results that the considerable change of the adhesive bond strength did not occur after 100 cycles at the passing loading corresponding to 25 % and 50 % of the average maximum strength of the adhesive bond. The average fall of the resultant adhesive bond strength was in the interval 3 % to 11 %.

The present study was directed to investigate the mechanical and tribological properties of 42CrMo4 (CSN 41 5142.3) steel, which was thermochemical treated by the technologies of tenifer, manganese phosphate and plasma nitriding combining with blackening. Plasma nitriding was carried out for the samples under different condition of gas mixture under temperature of 480ºC (plasma sputtering) and 500ºC (plasma nitriding process) for 10h. Besides determining the microhardness (HV 0.05), surface hardness, and microstructure, this paper also concentrates on the field of wear resistance evaluation and friction coefficient of these surface treatments. Based on "ball on flat" test, calotest, and profile observation, it was found that tenifer technology is suitable to increase the wear resistance, and manganese phosphate improves clearly not only wear resistance but also friction coefficient, which can be usable for weapon production.

This contribution describes the progress of wear and influences contributing to wear of a cutting tool during straightturning of the Nickel superalloy Inconel 718 according to W. Nr 2.4668. According to the ISO 513 standard this alloy belongs among heat resistant materials; it is a special Nickel alloy used primarily for machine parts in the aircraft industry. The experimental part was done for the purpose of testing suitability of proposed exchangeable cutting inserts intended for machining of Inconel 718. Mechanisms and magnitude of wear and durability of the tools were determined in accordance with the ISO 3685:1993 standard in order to evaluate suitability of the proposed tools.

The article deals with the problem of vertical vibration of vehicle model driving a horizontal curve of radius R = 100 m. A brief theoretical work on the topic is presented in the introduction part. Where a descriptions of the forces acting on the vehicle while passing through the curve are discussed. In the second part of this work, a detailed description of the vehicle model is given. The equations of motion of the vehicle model are then derived for vertical dynamic response of the mechanical system considered herein. Analysis of the effect of asymmetry is then performed when the vehicle is driving the curve at a constant speed v = 30 km/h, excitated by general kinematic excitations. Firstly, the asymmetrical model is considered and the results are then compared to a fully symmetrical model.

Nowadays, there is an effort to increase the economic effectiveness, including manual work, from the aspect of the modernization of production technologies. The brazing operation is one of the operations requiring skills and experience and therefore, the paper deals with modern brazing technology of aluminium alloy semi-products which are heated only in the electric furnaces. Application of heat can lead to the formation of the perfect join of semi-products based on such materials as A 3004 and AA 4045. A thin layer called Clad is deposited on one component of the AA 4045 material while the mentioned thin layer is molten to the prescribed temperature in the furnace but the most important fact is that there is not occurrence of melting in relation to the base material. After cooling, Clad creates a perfect metallurgical join between the joined surfaces. The resulting microstructure corresponds to silumin alloy. The transition between silumin alloy and aluminium matrixes of the component is continuous and without any defects in the form of discontinuities or pores and this fact was confirmed by the evaluation of the microstructure. This technology is used in the production of battery coolers in electric hybrid cars. Tightness of brazed join is controlled by pressure and helium tests. Analysed cooler was suitable from the aspect of the performed testing procedures.

Piping systems of boilers are mainly exposed by high temperatures, pressures and corrosive loads. This corresponds to the choice of materials boiler pipeline. These materials are in most cases special stainless steel for energetic equipment. Article deals with the evaluation of the resulting degradation of thermally stressed pipe boiler, which occurred after the increase boiler capacity. Degradation showed an increased amount of corrosion products on the inner surface of the pipeline, which resulted in clogging of pipes, formation of cracks and leakage of steam. Complex analysis was carried out of corrosion products and material microstructure pipelines. The result was that occurred to intergranular corrosion of pipelines in loaded state. On the basis of this was carried out analysis of the material in the unloaded state. Chemical composition and microstructure correspond to prescribed standards and requirements. Test of resistance to intergranular corrosion revealed that in the steel causing damage to the cohesion of the material along grain boundaries. It is for this type of material inadmissible. Therefore it is necessary in the case of increasing the performance of the boiler and thus the increase in temperature and pressure, to ensure a higher resistance to intergranular corrosion of the material.

The use of renewable energy sources in Slovakia is currently very debated issue. The main cause of this discussion is the increase of energy prices, which increasingly burden the population and companies. The use of renewable sources, including biomass, represents an important contribution to solve this problem. When new heat source is designed, several technical regulations and recommendations must be followed. The proposed device is intended to serve for combustion of biomass, in the form of wood, of pellets. The aim of this work is to describe the design process of the combustion device as the main source of thermal energy in our proposed micro-cogeneration unit.

The laser line scanners are coming to be frequently used in a field of dimensional inspection process. There are several phenomena that make the data acquisition more difficult. Particularly secondary reflection, direct reflection, scan overlapping, outlying points. The effect of these phenomena can be minimised by optimal setting of scanning parameters stated in this paper. The parameters were determined from an experimental measurements of 50 various parts. Additionally a thermal stability effect was measured at two types of Nikon scanners. The stabilisation time and the systematic error were determined for the scanner LC15Dx: 45 min, 20μm and 30 min and 37 μm for the LC60Dx scanner. It should help to prevent the systematic errors during the measurement.

Direct Metal Laser Sintering enables production of fully dense metal parts with comparable or higher tensile properties as compared to the conventionally produced parts. However, for a more widespread use of this additive manufacturing technique, material data should be obtained and evaluated with respect to the influencing manufacturing factors. In the case of Ti6Al4V alloy, the fatigue performance can be highly susceptible to the process related issues, such as build direction, porosity and surface condition. This study was undertaken to examine the fatigue life of Ti6Al4V specimens manufactured by Direct Metal Laser Sintering (DMLS) technique and to investigate the influence of the surface state on the fatigue life. A high degree of anisotropy in the fatigue performance associated with the specimen build orientation was determined.

The microstructure of an unmodified hypoeutectic Al-11%Si alloy comprises large primary α phase dendrites, eutectic β phase crystals and eutectic α phase. This composition is responsible for the alloy's low strength parameters, and it limits the extent of practical applications. The mechanical properties of hypoeutectic silumins can be improved through chemical modification as well as traditional or technological processing. Modification improves the mechanical properties of alloys through grain refinement. This study presents the results of modification of Al-11%Si alloy with chlorine base modifier (NaCl + CaCl + SrCl2). The influence of the analyzed modifiers on the mechanical properties (tensile strength, elongation and Brinell hardness) of the processed alloy was presented in graphs. The modification of a hypoeutectic Al-11%Si alloy improved the alloy's properties. The results of the tests indicate that the mechanical properties of the modified alloy are determined by differences compositions modifiers which are introduced to the alloy.

Failures of machines are caused by variety of external and internal effects and process that cause ultimately interruption of operation. These factors have resulted in changes of properties of machines parts and these changes are the first causes of technical failures. Wear is one of the major factors that contribute to the creation of failures and with this is connected generation of wear particles. Wear particles come into oil in lubrication system, where they cause contamination and degradation of lubricating properties and consequently it may result in major failure of machines. Among these contaminants are included mainly adhesive, abrasive and fatigue particles wear. The paper describes number and morphology of wear particles generated during modified Reichert test (friction pair - steel and aluminium alloy) analysed by LasetNet Fines device. Experiment also compared capability of lubrication of four different engine oils exposed to various weight load.

The paper presents the characteristics of a metal product called 'Back Cover' and its manufacturing process. The characteristic of quality inspection methods and control devices during manufacturing process of analysed product was conducted. An analysis of production and quality problems during manufacturing of the analysed product using qualitative and quantitative tools such as Ishikawa diagram and Pareto-Lorenz diagram were presented. Ishikawa diagram was used to identify areas that generate quality problems and Pareto-Lorenz diagram was used to quantify the quality problems and to distinguish the critical nonconformities. It was presented differences between visual control and visual inspection. BOST research was used to determine the validity of the use of visual control in the analysed company against the remaining factors of the manufacturing process. Created a series of validity of manufacturing process to capture the relationship between the place of the individual factors of the manufacturing process. The use of visual control turned out not to be the most important factor in the manufacturing process, according to the examined company the most important is the use of only reliable technology.

Weapons are special systems, which have high demand in terms of reliability, safety and durability especially in the case of automatic weapons. The most stressed parts of weapons are barrels, breech, locking elements etc. This paper si focused on the failure of locking element, which is used for set the breech baffle and for locking of the breech. From the structural point of view the locking element is highly dynamically stressed component. During the shooting cycles are the shocks transferred into these components, therefore specified material requirements of the locking element are needed. The material of locking element must be modified to hard surface with tough core with thickness corresponding to the size and frequency of shocks to prevent the fatigue failure. The manufacturing documentation wasn't available, therefore the chemical analysis was performed using the GDOES/Bulk method. The results were compared with material standards to determine the Czech steel equivalent. The damaged locking element was metallographically tested, the surface and microhardness testing was performed by Vickers method. The fracture surface morphology was using the light and electron microscopy (SEM) observed.

The paper dealt with tool-wear, tool-life and chip creation regarding the cutting speed for machining by conventional and coated tools. The cutting speed is influenced by several parameters. The determination of optimal cutting speed is challenging question. Situation is more complicated in case of coated tools. The important is criterion of optimization. Moreover, the presence of the coating changes chip creation process and stress state during cutting. The paper provides complete experimental T-vc dependencies obtained in turning regarding various parameters as depth of cut, feed for different machined and cutting tool materials. Paper describes also different tool-wear mechanisms of uncoated and coated tools. Finally, the paper analyzes stress state in tool as simplified model of contact of tool rake and chip for conventional and coated tools involving different mechanical properties of coating and substrate material, temperature and different thicknesses of coatings.

Based on the value of longitudinal distribution of the residual stresses in the strip with the cold rolled strip in different forms under stress loading, this paper establishes a finite element model. According to the simulation analysis on different stress curve functions and under some coefficient combining conditions of different stress curve functions, it is discovered that the stress acting lengths and the features are completely different under the actions of even-degree and odd-degree stress functions, and under the even-degree function, the residual stresses are distributed evenly at the far end of the strip, and the length location of the point where the residual stresses tends to be stable on the strip are linearly related to the strip width; under the odd-degree function, the residual stresses are distributed linearly in the horizontal direction of the strip while without any changes along the strip length. According to the analysis results of the strip's shear stress, a little strip shear stress is not enough to produce deformation. The result of this paper has profound guiding significance for cold-rolled strip flatness closed-loop control. Only with different control strategies for different flatness deviations after fitting, can the quality of the strip steel flatness be improved more effectively, thereby reducing the impact of the lag in flatness detection on the strip flatness control as far as possible.

ŠKODA VÝZKUM cooperated on the development of the NEOPLAN DMA low-floor articulated trolleybus intended for the Boston city (the United States). Multibody models and finite element models of the trolleybus were utilized in the stage of the vehicle design. The multibody models of the trolleybus were created in the alaska simulation tool and the simulations were especially aimed at determining forces acting in the trolleybus suspension elements and radius rods. At the end of the stage of computer modelling and testing the trolleybus prototype a decision to change the type of shock absorbers used in the axles' suspension was made. The impact of this change on forces acting in the trolleybus suspension elements (i.e. in air springs and shock absorbers) and radius rods on the trolleybus chassis when running on an uneven test track was investigated using multibody simulations. Time histories of the forces calculated utilising multibody models were used as input data of the trolleybus finite element models. Stress in the critical places of the trolleybus body structure was determined utilizing the finite element models.

The article describes experimental and numerical investigation of airflow inside the floor convector. Analysis was divided to two parts. First part was airflow visualization. This part was realized in two areas. At first the visualization was realized in the area between a fan outlet and a heat exchanger inlet using a continual laser and a video camera. Then the visualization was realized in the region above the heat exchanger outlet with a Particle image velocimetry. At last the flow behavior in domain between the fan outlet and the floor convector outlet was analyzed with a numerical simulation. Commercial software ANSYS Fluent in version 15.0 was used. Results from the numerical simulation and the experiments were compared and the flow behavior was examined.

The article analyses the measurement with increased absorption kinetics of hydrogen into the La0.85Ce0.15Ni5 alloy. Within a time interval of 180 s an amount of 0.142 kg (1.58 m3) of hydrogen was absorbed into 56 kg of alloy. The process of absorption was accompanied by an increased temperature of the bed. Therefore it was simultaneously cooled by a cooler using Peltier elements. The numerical calculation of non-stationary heat transfer within the bed was performed with a known amount of heat generated in the bed, known temperatures and flow rates. Simulation results allow us to determine temperature time paths at key points of the bed and give insight on the transient phenomena which occurs in the extreme load of the metal hydride (MH) bed. The temperature field is analyzed for different values of thermal conductivity, view of its change during the lifetime of metal hydride. This allows establishing safe limits for the absorption of hydrogen into a particular alloy.

The article presents numerical code which was developed for solution of inviscid compressible fluid flow in domains with deforming boundaries. This computational method for the numerical solution of the non-linear system of Euler equations in time-dependent domains was designed as the first step of solution of fluid-structure interaction problem. Arbitrary Lagrangian - Eulerian (ALE) description of continuum, combining Eulerian and Lagrangian approach, was used to describe the inviscid fluid flow in time-dependent domain. The spatial discretization was provided by finite volume method adapted for triangular computational grids. Inviscid fluxes were discretized by the Rusanov flux scheme and Van Leer flux splitting scheme. The computational code was validated using a case of inviscid fluid flow around vibrating airfoil NACA 0012 which was experimentally investigated by AGARD group in 1982. Boundary conditions and simulation parameters were set according to the conditions of experimental measurement and the rotation angle of the body was defined by a time-dependent function. The numerical results are compared with experimental data and results of other authors. The algorithm for the mesh deformation is presented.

The paper present the structural design of freight wagon chassis frame with adaptable loading platform with regard to the safe operation and assessment of the properties by the calculation methods of simulation analysis. 3D model of wagon was created in a computer program PTC/Creo. Wagon chassis frame was subjected to the static and dynamic analysis in programs ANSYS and ADAMS/Rail. On the basis of computer aided simulation analysis was optimized the frame of the wagon. This wagon chassis frame will be able to offer even more capacity and utilize less resources and energy than current wagons for intermodal transport.

Article deals with ultrasonic testing of the casting. It focuses on the problems that arise when testing of castings is made of non-ferrous metals. Theoretical introduction of article is dedicated to the most common types of casting defects and selecting technology for their reliable identification. The impact of the large anisotropic grain casting to propagate and attenuation of ultrasound it describes in theory. The examples of practical testing of Cu-alloy casting are presented in experimental part. Modern tools for simulation of ultrasound propagation in testing material were used for the correct setting techniques of UT testing as well as for the evaluation of the measurement results. Conventional direct contact ultrasound probe with frequencies of 5 MHz, 3.5 MHz and 2 MHz were used for all measurements. The results of experimental measurements referred in this article are recommendations for selecting equipment and accessories for casting testing made of non-ferrous metals.

NiTi alloy is characterized by many interesting properties assiciated with the shape memory behaviour. Since this material can be superelastic and recover the shape after deformation, it can be considered as potential matrix for composites. In this work, the possibility of preparation of NiTi matrix composites was tested. Two kinds of materials were studied - NiTi matrix composite reinforced by ceramic particles and in-situ composite containing NiTi and hard Ti2Ni phase obtained by reactive sintering of Ni+Ti mixture.

Aluminium is among the materials that found their application in composite systems. Aluminium matrix composites may form or may be present in the matrix in the form of fillers. Specific applications of aluminium may be present in the epoxy or other polymer matrices in the form of microparticles. Mutual interaction of resin and aluminium particles then creates the resulting properties of the material, which can be used both for surface treatment, and in the bonding and sealing. For this reason, adhesion and cohesion characteristics are among the leading characteristics of such systems. The paper describes cohesive characteristics of two-component epoxy resin filled with microparticles of 30.44 μm. The presence of particles changed tensile strength of resins from the value 49 MPa 30 MPa. The adhesion characteristics were evaluated on both aluminium and steel adherends. The presence of low concentrations of microparticles of aluminum, i.e. to 8% did not result to the statistically significant decrease of values of the shear strength of resin at both, aluminum and steel adherends.

The paper deals with the current topic of environmental taxes on the level of the Czech Republic. The urgency of the topic is highlighted by the dynamic international development of environmental taxation and continuous unification within the European Union. Environmental taxes affect the final consumers of solid fuels, electricity and natural gas and some other gases. The paper researches the impact of environmental taxes on a selected group of manufacturing business entities which are largely consumers of products taxed by environmental taxes. This type of taxes represents a part of corporate environmental costs and as such it is necessary to manage these costs. At first the paper examines the influence of environmental taxes on the enterprise performance after their introduction into the Czech tax system in 2008 and then there are proposed the indicators for monitoring and management of environmental taxes as a part of the enterprise costs. The influence of environmental taxes on business entities is researched by the profit and loss report item "consumption of material and energy", the economic result, rentability of assets indicator and also by the proposed material and energy costs rentability indicator. Further there are proposed two other ratio indicators for environmental taxes monitoring within the corporate costs which can also serve as one of the criteria for investment decision-making of an enterprise. For the correct quantification of the proposed indicators a reference accounting timetable is drafted which includes the environmental taxes analytical evidence and their integration into the corporate accounting.

The aim of the article is to present suitable changes at the conception of the angle of attack setting mechanism and the modification of the spring element at the load module SIMRAIL, part of roller rig RAILBCOT which faithfully simulates the behavior of the vehicle on a real track. RAILBCOT is the acronym for RAIL vehicles Brake COmponents Test stand. During the measurements were recorded imperfections, which could influence continuous testing, and would lead not to reliable and fully trusworthy results. The article describes three steps to improve the situation. The first step describes the stabilization of the members to prevent the occurrence of clearance. In the second step were started measurements at the roller rig at different operating speeds. In the third step is modified the angle of attack setting mechanism where was mechanical spring element changed by hydraulic spring element. Mentioned is also the need for increasing the stiffness of the spring element, which lack of stiffness caused loss of stability before the requesting speed. Modified was the gear lever, where was changed the transmission ratio and dimensioning of spring element.