Fulltext search in archive

Article deals with the detection of reduced stress in a braked railway wheel based on thermal transient analysis on virtual models, because they influence the characteristics of the railway wheels. Structural analysis was performed by means of the ANSYS Multiphysics program system package. Thermal transient analysis deals with the detection of temperature fields which are result of braking by brake block. The applied heat flux represents the heat generated by friction of brake block. It is applied to the quarter model because of the acceleration calculation. This analysis simulates two braking with subsequent by cooling. Distribution of the equivalent stress was detected in the cross section railway wheel, at selected points. The input parameters were used from the thermal transient analysis. These equivalent stresses result due to thermal load.

In most cases, construction materials are selected so as to attain the optimal technological properties at the lowest possible weight and cost. Studies on the improvement of the properties of casting alloys have been continuously conducted over the recent years. Both the microstructure and properties of alloys may be altered via modification with chemical components, optimization of the crystallization process, heat treatment or a combination of these methods. While searching for alternative methods of improving the engineering surface properties of hypo- and hypereutectic Al-Si alloy, an attempt was made to modify its microstructure with the use one of a heat sources. This paper presents the results of an experiment investigating the microstructure and the hardness of the Al-9%SiMg and Al-20%SiMg alloys processed by TIG welding method.

Cutting tool wear monitoring is one of key problems in automation of machining processes. Apart from the cutting tool wear monitoring for the cutting tool change and cutting tool failure, cutting tool wear monitoring may be one of the components for the adaptive control of a machining process. This paper is focused on the design of turning cutting tool wear sensors of the system flap - jet principal with increased extend. On the geometric principles in cutting with a turning cutting tool, the relations among the output of jet mouth, clearance angle and cutting tool wear were expressed. Two variants of turning cutting tool sensors were designed and experimentally verified. The results of experiments have proved the possibility to apply cutting tool wear sensor of the system flap - jet principal with increased extend in practical use.

In modern analysis of structures it is not only important to study structures subjected to static loading but also to study the effects of dynamic loading. One of the results of impact loading is the dynamic response of structures. This can cause far more damage than the effects of static loading. Composite materials are more and more used in engineering praxis. This allows the creation materials of high strength at low weight which are more durable then the same construction made of homogenous materials. This paper presents a study of dynamic response of carbon fiber reinforced polymer composite plates in the form of modal analysis and transient response (subjected to unit pulse point load in the center of the plate). The plate consists of layered uniaxial carbon fiber fabric and the layers are layered symmetrically at different angles for various variants. The response in the form of displacement magnitude is measured. At the end a comparison study is presented for each analysis.

The article presents the measurement results of the relaxation of long-term loaded compression springs manufactured out of non-alloy steel. The goal was to determine the differences between the interrupted and uninterrupted tests. During the relaxation test that lasted 5000 hr in a laboratory with a temperature of 22ºC, initial shear stress set at a value of 30% of the ultimate tensile strength of the material, decreased the strength of the springs with a wire diameter of 1 mm by 3.6%, springs with a wire diameter of 3.15 mm by 2.5%, and springs with a wire diameter of 5 mm by 1.3%. The difference in the results was found in tests 16 times and 4 times interrupted to measure the current relaxation. The results of intermittent tests cannot be considered as relaxation values for statically loaded springs. Conversely, when determining the maximum tension of quasi-statically loaded springs with respect to the relaxation, the uninterrupted relaxation tests cannot be used.

This article deals with the influence of the alloy temper during heat treatment on mechanical and corrosion properties of aluminium alloys 2024 (Al-Cu-Mg) and 6064 (Al-Mg-Si). For the experiment initial alloy tempers 2024-T351 and 6064-T8 were heat treated to three conditions - underaged, peak aged (T6) and overaged - to simulate the circumstances during the manufacturing process. Structure of all conditions and tempers was observed. The mechanical properties - hardness, yield strength, ultimate strength and elongation - and corrosion properties - maximum depth of corrosion attack peneration and corrosion rate in Audi immersion test for automotive industry (internal standard PV 11 13) - were measured. Structures of investigated alloy show evidence of intermediate phases arrangement in the direction of plastic deformation and they do not change during heat treatment. The lowest hardness, yield strength and ultimate strength have the underaged samples, the highest hardness, yield strength and ultimate strength have peak aged (2024) or initial samples (6064). Elongation decreases with ageing time or ageing temperature. In case of alloy 2024 corrosion rate and maximum depth of corrosion attack penetration increase with ageing time or temperature, in case of alloy 6064 corrosion rate increases with increasing ageing time or temperature while maximum depth of corrosion attack penetration decreases. Both alloys are attacked by intergranular corrosion with initiating surface pits.

This paper deals with evaluation of the controlling processes service reliability of degradation processes leading to embrittlement, fracture at elevated temperatures, fatigue and fatigue fracture with the possible effect of corrosion and with interaction of all the previously mentioned processes.

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.

The article deals with the design of a process recirculation air cooler for cooling natural gas when the latter is processed. The cooler is intended for extreme climatic conditions, and due to this reason, it is necessary when designing and fabricating the cooler to comply with the specific requirements for both the calculation and materials to be used on constructing it. In the winter period when the ambient temperature drops even below the solidification point of the medium the cooler works with reduced rpm of the fan, and when necessary, even in the recirculation mode, partial or full (depending on the ambient temperature). In this case, the inlet and outlet louvers are closed, and the recirculation louvers are opened. This system allows, using the control of the temperature of the inlet cooling air, to maintain the temperature of the cooled medium at the desired level.

The research into root causes of defects in cylinder head castings are described in the paper. Chemical composition of castings, evaluation of casting microstructure before and after the heat treatment and final inspection of casting quality from various points of view are parts of the research. The list of the most common defects in case of using five selected products is the result of the experiment. The objective of the research was to identify causes of defects in the process of cylinder head casting as well as to identify root causes of discrepancy using the quality management tool.

Biodegradation properties of magnesium and its alloys that can be used for implants are not satisfactory and cause serious problems. These problems can be solved by biodegradable surface coatings. Evaluation of biodegradation process of Mg-RE-Zr alloy surfaces after grinding and grinding followed by potential controlled electrodeposition of octacalcium phosphate (OCP) was investigated by electrochemical impedance spectroscopy measurements in this study. The potentiostatic electrodeposition treatment process was performed in water solution of 0.167 M CaCl2 and 0.1 M NH4H2PO4. The corrosion process on treated and nontreated samples after various exposure times was evaluated in 0.9% NaCl solution simulating body fluid environment at 37 °C. The significant increase of polarization resistance and time resistance against corrosion were found after electrochemical surface treatment.

The translation in this article analyses the technology of laser cutting, describes properties of laser cutting equipment the oxidation process of melting and sublimation laser cutting. In the article chemical composition of cutted material in the interaction with the quality of cutting edges from cut-outs is analysed. The measurement was performed on experimental samples made from steel grade S355 however the composition of chemical elements in each sample varied. On these experimental samples the cutting edges was examined for the purpose to find out the influence of chemical purity of material on the quality of components which were cut by using laser technology.

The fiber reinforced plastic (CFRP) are widely used in stacks with metallic materials. The parts are usually bolted together during assembling procedure. That is why drilling is one of the most widely used operations for machining of CFRP/metal and metal/CFRP stacks. That allows to obtain components, which combine high strength and low weight. This paper presents tool wear study based on the drilling experiment of CFRP/ steel stack. The most common problems of CFRP/metal stacks machining are CFRP delamination, fiber pull - out, thermal degradation and intensive tool wear. Last decade such parameters of CFRP/metal stacks drilling as axial force and torque are in the focus of researches. However, the cutting temperature in the drilling process of CFRP/metal stack and its influence on drill bit wear is still not fully gained at the present time. The purpose of current study is to investigate the effect of cutting temperature on the tool life of carbide drill. The temperature was measured with K type thermocouple which was embedded on the flank surface of the drill. Axial force was measured with dynamometer. Data of cutting temperature and axial force was digitalized with analog - digital converter (ACD) and visualized on personal computer (PC). The dominating tool wear mode when drilling CFRP/steel - was flank wear which was measured with optical microscope. The experimental study of cutting temperature effect on the tool wear of carbide drill was established. It was found that the most unfavourable combination of stack materials in the conditions of drill wear is CFRP/metal.

Authors define general dependability characteristics (reliability, maintainability, supportability and availability) and their measures. Further there is introduced method of data collection which shall be planned taking into account appropriate targets. Dependability data analysis needs clear understanding of an object, its operation, environment and physical attributes to be obtained required dependability measures which are described. These measures can be used as indicators for measuring maintenance impacts on reliability and maintainability. Data collection and its evaluation help to monitor the impact of maintenance on these indicators. Dependency between non-fulfillment of preventive maintenance and failure intensity including maintenance costs are also evaluated.

An adhesive bonding technology is a method of a connecting which is used at a construction of coach-works, agricultural machines etc. This method is suitable for workings with a serial production. Many research projects dealt with a preparation of adhesive bonds, degradation aspects etc. An area, which has not been properly investigated at present, is an influence of a loading speed on strength of the adhesive bond and a destruction time of the adhesive bond. Adhesive bonds are loaded by a different intensity and a speed at a practice.
The research focused on an evaluation of the influence of the loading speed at a temperature 22 ± 2 °C on the shear tensile strength, the time needed for the destruction and a failure area. Second part of the research was focused on the influence of a bending moment. This bending moment can be minimalized by using so-called underlaying sheet of metal. The underlaying sheet of metal was of a thickness corresponding to a thickness of the adhesive bonded material. Also a behaviour of the adhesive bonded material was observed within the research.

This article describes the effect of selected parameters of plasma nitriding on the change of dynamic parameters of steel DIN 1654/4. Plasma nitriding is currently used in a wide range of technical applications such as a final operation to improve the mechanical properties of components. This experimental investigation is devoted to the analysis of the influence of plasma nitriding on the notch toughness of structural steel DIN 1654/4 (CSN 41 2042.4). The test of the dynamic fracture behaviour of structural steel was carried out using by instrumental Charpy hammer on the plasma nitrided specimens with V and U notch, manufactured according to standard CSN ISO 148-1. The plasma nitriding was implemented at 500 (°C), process duration t = 10 and 20 (h) and variable gas mixture ratio of 24H2: 8N2 (l/h) and 8H2: 24N2 (l/h). The test results showed that nitrided steel has become more brittle. However, it was found that for different gas composition, the notch toughness has behaved quite diversely. The values of notch toughness of steel in case of gas ratio 8H2: 24N2 (l/h) were decreased but for gas ratio 24H2: 8N2 (l/h), with extension of time, the notch toughness was slightly increased.

Approximately equiatomic alloy Ni-Ti is commercially most successful member of shape memory material group. This paper concludes basic knowledge about properties, ways of preparation and possible applications of this unique material in medicine, industry, construction or everyday life.

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.

This paper is aimed at chemical-heat treatment of a selected material. The plasma nitriding layers were applied on the 41CrAlMo7-10 steel. The influence of plasma nitriding parameters on the thickness and microhardness of nitrided layers were investigated. Plasma nitriding was performed at 500°C with a mixture atmosphere of H2 and N2 in the plasma nitriding equipment. The pressure of plasma nitriding process was determined to be 280 Pa. The period of the plasma nitriding process was changeable from 5 to 30 hours. The microstructure and mechanical properties of the nitrided layers were studied by using GDOES spectrometry, optical microscopy, and hardness testing. The depths of the plasma nitriding layers were also estimated using cross-sectional microhardness profiles. Microhardness and surface hardness of mentioned samples were significantly increased. The measurements have shown that the period of plasma nitriding process has a significant influence on the depth of nitriding.

For the creation of the bond the treatment of the adhesive bonded surface is essential. The second important factor is the temperature of the environment to which the adhesive bond is exposed. It is a way of a degradation of adhesive bonds. The aim of the research was to evaluate the effect of adhesive bonded surface treatment of alloy AlCu4Mg and increased environmental temperature on a strength of adhesive bonds using two-component epoxies used in the transportation industry. As a bonding material AlCu4Mg was used, whose surface was in the first series mechanically and chemically treated. In the second series tested specimens were without the surface treatment. A destructive testing was conducted at a laboratory temperature 22 ± 2 °C and at increased temperatures, i.e. 40, 60 and 80 ± 2 °C. At a mutual comparison of the mechanical treatment and the chemical treatment of the adhesive bonded surface with un-treated surface, the tensile lap-shear strength increased by an average of 57.24 ± 18.52 %. The results show that there is a difference in the tensile lap-shear strength between the test temperatures in the interval 20-80 °C, the decrease was up to 88 %.

The aim of this research work was to determine the causes of the cracking unit rolled at initial hot rolling of the AlMg5 alloy. Failure occurs in the central area of rolled plate. In the alloy was carried out chemical composition of the material in the near the defect and its comparison with the chemical composition of the entire melt, which pointed to a significant reduction of the magnesium content of the area defect. Macroscopic, microscopic and fractography analysis were carried out both in the area of the fracture surface and in the immediate vicinity. The analysis indicated that the fracture surface, and also the structure in the area of the fracture surface show a character oxide inclusions and oxide films or spinel inclusions. The following EDS analysis were carried out on a scanning electron microscope to confirm the presence of oxide inclusions of spinel-type character Al2MgO4 on the fracture surface of the rolled material. It could be stated that when casting a gradual burning out of magnesium in casting furnace and thus to reducing it's some 0.5 - 1.0% and the formation of spinel inclusions. Spinel inclusions then initiated cracking during hot rolling.

Self-hardening aluminium alloy AlZn10Si8Mg represents an innovative class of light aluminium alloys and they present high mechanical properties, which make them suitable for many applications in different industrial fields, especially in transport industry. The most important and relevant feature of the self-hardening alloys is related to their good performance, without the need of any heat treatment: they are subjected to a natural ageing phenomenon at room temperature after a storage period of about 7-10 days. The possibility to avoid the heat treatment represents an important benefit, contributing to considerably reduce both the production cost of some components and the amount of energy. Furthermore, without heat treatment the risk of component's deformation during the production is eliminated.
The Charpy impact energy of experimental cast alloy was measured at -196°C, -20°C, 20°C, 50°C, 100°C, 150°C, 200°C, 250°C, 300°C, 350°C and 400°C in terms of the total absorbed energy. Effect of temperature to microstructural changes and fracture surface on the impact toughness was investigated. A combination different analytical techniques (light microscopy upon black-white etching, scanning electron microscopy (SEM) upon deep etching) were therefore been used for the identification of the various phases.

Dynamic characteristics of a machine-tool-workpiece system are not constant during machining, but they can be changed by a variable spindle position, a rising tool wear or a gradual change of a workpiece geometry. This paper deals with an influence of spindle unit extrusion on stability of a machining process. Two milling cutters with different rigidity, flexible and stiff, were used for experimental machining at three axis milling machines. Clamped milling cutters were extracted systematically and a frequency response function was measured simultaneously. Reached data (natural frequency and dynamic compliance) were used for finding a correlation between dynamic parameters and extrusion of the spindle. Critical extrusion of the spindle unit was predicted by an experimental measurement and an axial depth of cut thresholds was established for the stable machining.

The aim of this paper is to describe anodizing technology for deposition of Al2O3 coatings on Al substrates. Various methods of layer deposition were used for the experiments. Deposition was carried out in acidic environments, using sulphuric acid (H2SO4) and chromic acid (H2CrO4). Several samples were heat treated (annealed). Chemical composition of the substrate and the coating was tested by GDOS method using SA2000 and GDS 500A devices. Surface morphology and structure were evaluated by SEM, using VEGA5135 electron microscope. Selected mechanical properties as thickness, microhardness and adhesion were also determined.

This article deals with the influence of the alloy temper during heat treatment on mechanical and corrosion properties of aluminium alloys 2024 (Al-Cu-Mg) and 6064 (Al-Mg-Si). For the experiment initial alloy tempers 2024-T351 and 6064-T8 were heat treated to three conditions - underaged, peak aged (T6) and overaged - to simulate the circumstances during the manufacturing process. Structure of all conditions and tempers was observed. The mechanical properties - hardness, yield strength, ultimate strength and elongation - and corrosion properties - maximum depth of corrosion attack peneration and corrosion rate in Audi immersion test for automotive industry (internal standard PV 11 13) - were measured. Structures of investigated alloy show evidence of intermediate phases arrangement in the direction of plastic deformation and they do not change during heat treatment. The lowest hardness, yield strength and ultimate strength have the underaged samples, the highest hardness, yield strength and ultimate strength have peak aged (2024) or initial samples (6064). Elongation decreases with ageing time or ageing temperature. In case of alloy 2024 corrosion rate and maximum depth of corrosion attack penetration increase with ageing time or temperature, in case of alloy 6064 corrosion rate increases with increasing ageing time or temperature while maximum depth of corrosion attack penetration decreases. Both alloys are attacked by intergranular corrosion with initiating surface pits.

Fiber reinforced polymer Resin matrix composites have the good performance, and it is widely used in various fields to release the impact load. Therefore, the study of stress and strain characteristics is quite useful to in providing the reliable basis for the structural design. The tensile test is one of the important methods to detect the mechanic property of the material, which can be used to observe the deformation behavior of the material. Reinforced materials are often added to improve the mechanical properties of the composites, and characteristics and mechanical properties of composite materials will be obvious anisotropic. Damage behavior of resin matrix composite material with fiber reinforced is complex, and mechanical properties of it are quite difficult to obtain just through the experiments, so the finite element method becomes a useful tool to get the mechanical properties. In this paper, we developed the conventional finite element method to investigate the mechanical properties of composites material. The verification proves that the modified finite element method can get much accurate results.

The analysis of non-metallic initiating inclusions in fatigue live field is studied. The testing material for experiments is CSN 41 5340 steel (corresponds to 41CrAlMo7-10 or 1.8509). This steel is suitable for plasma nitriding process. The samples were heat treated and subsequently plasma nitrided, then subjected to the fatigue bending rotation tests. According to the principle of the tests are the conditions set to constant speed and decreasd load to 107 cycles if does not the fatigue fracture of the sample happens. The thickness of the diffusional nitride layer has been won using the microhardness measuring from the surface to the core of the samples. Using the fractographic analysis the nucleation point of fatigue crack has been evaluated. In the case of initiating inclusions the size and the chemical composition was measured. Comparing the won data to the plasma nitriding proces new results have been obtained.

Hydroxiapatite is ceramic material with properties and composition similar to the bone tissue. This makes it a suitable choice for biomaterials. However, hydroxyapatite alone has poor mechanical properties. Present paper shows two possible applications of hydroxyapatite in materials intended for medical applications. 1. Hydroxyapatite can be used as a layer which causes the material to be more bioactive. In this article the layer of HA is applied on WE43 by plasma spraying and structure, composition and adhesive properties are measured. 2. Hydroxyapatite can serve as reinforcement in metallic composite materials. Present work sum up properties of composite materials with 2, 5 and 10 wt.% of HA that were prepared by powder metallurgy route. The structure, hardness and compressive mechanical properties are characterized.

Paper deals with comparasion of methods for resolving stress state on the example of forged crane hook of selected load. For suitability of the comparasion is necessary to achieve comparable stress values by different methods. Problem of solving of different assignments by different methods is very extensive, and because of it, there is not clear answer, which of methods is universal and so always optimal. Any factors, that enter to the calculation and influence it, is the best way to choose an optimal method for solving of strength problems in mechanics.

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.