Fulltext search in archive

Ti-Al-Si alloys excel with their low density and good resistance against high-temperature oxidation in comparison with so far commonly used nickel alloys. Silicon in Ti-Al-Si alloys has significant positive effect on high-temperature oxidation due to increasing adhesion of oxide layer. The TiAl20Si20 alloy was evaluated as the best alloy from tested ones, because its oxide layer protected very well the basic material and TiAl20Si20 achieved good hardness after 400 hours of annealing.

The requirement for high strength and ductility is usually associated with martensitic microstructure with a certain amount of retained austenite. One of the innovative heat treatment processes that can lead to such microstructure is the Q&P process (Quenching and Partitioning). It can produce microstructures consisting of martensite and a certain amount of retained austenite, which exhibit strengths above 2000 MPa and elongation levels of more than 10%. The objective of this research was to explore the effects of the cooling rate in the Q&P process and evaluate the effects of various microstructure constituents on mechanical properties of high-strength steels. Three newly-created experimental steels, which contained 0.43% carbon and had reduced Ms temperatures thanks to manganese addition, were subjected to several heat treatment routes which involved various cooling rates. The cooling rates were chosen on the basis of calculations using the JMatPro software and earlier results. It was found that by varying the cooling rate one can obtain various mixed microstructures and a wide range of mechanical properties. The strengths were in the range of 1200-2300 MPa and A5mm elongation levels were up to 18%. Because the amount of retained austenite has a considerable impact on the resulting mechanical properties, it was measured by means of X-ray diffraction.

The paper deals with the design of a special machining tool for efficient production of detail on the T-groove of the clamping part. The introductory part of the paper is focused on introducing the Czech company. The practical part of the paper deals with the analysis of the existing state of machining of the clamping body and of the production of the T-groove detail and proposes an innovative solution in the form of more efficient machining process (partial production modification), which consists in the development and production of a special tool with replaceable inserts. The main reason for this partial modification is a significant reduction in unit machine time in the production of the T-groove detail on clamp body parts. Part of the contribution is in the process of streamlining the innovation made in the form of changes to the manufacturing process and the design of the cutting conditions required to produce the T-groove detail on the clamp body parts. The contribution is completed by a technical and economic evaluation, which is related to the analysis and comparison of both proposed production variants in terms of machine times, tool consumption / replaceable inserts and total production costs for the T-groove detail production on the clamp body parts.

This article presents the study of the influence of the bias voltage and CH4/N2 gas ratio on the structure and chemical composition of Cr(C,N) coatings. The coatings were deposited by cathodic arc evaporation of pure Cr (99.99 %) cathode under an atmosphere of a mixture of CH4 and N2 gasses at the low deposition temperature of 300 ˚C. The ratio of reactive gasses was changed from 0 to 100 %. Energy-dispersive spectroscopy showed a linear dependence of resulting C/N ratio on the process gas ratio. The roughness of layers prepared from a mixture of process gasses is higher compared to pure gasses.

Right after the ferrous alloys, aluminium alloys represent the most wide spread used constructional materials of these days. The main reason of such utilization rests mainly in their specific weight, availability, good mechanical properties and corrosion resistance. To enhance their mechanical properties is there, at majority of technically used aluminium alloys, applied thermal treatment. Wrought aluminium alloys are generally processed after the solution annealing and before their natural or artificial hardening. However, in light of the formability is the own ageing process quite undesirable due to strong decrease of the material formability properties. In this paper is evaluated the time change of the aluminium alloy AW-2024 mechanical properties after the solution annealing in dependence on different storage time before forming. Such change of the mechanical properties was evaluated by means of the static tensile test.

This article describes the formation of a composite coating in a polymer matrix on an aluminum alloy. It is a PMMA coating (polymethylmethacrylate) with the addition of TiO2 particles. Working with these particles requires not only safety but also a suitable preparation process to obtain particles of suitable size, their subsequent homogeneous distribution in the coating (particles of this size are influenced by electrostatically attractive forces and have a strong tendency to aggravate). The first part describes the material used, sample preparation and coating process, surface roughness measurement, SEM and EDS analysis of selected samples. The aim of the research is to find out whether it is possible to use dipping and brushing techniques when coating Al-Si alloys with polymeric materials. Consequently, what can be achieved is the roughness of the surface of the coated part compared to the uncoated surface (at different particle concentrations in the spin) and the distribution of TiO2 particles on the surface of the sample.

Direct Metal Laser Sintering (DMLS) is a method of Metal Additive Manufacturing which builds metal parts in a layer-by-layer procedure based on a CAD template. This method is diametrically different from machining methods such as turning or milling. Nowadays, DMLS is used for rapid manufacturing of complex metal parts. However, these products do not meet the requirements of high accuracy and surface quality. This paper deals with factors that are involved in the dimensional precision of DMLS production. The purpose of the Scale and Beam offset correction coefficients are described in the paper. Practical experiments and measurements were carried out and are presented here. Usual production accuracy was observed.

In this paper we observe dynamic mechanical properties of rubber mixtures - standard and CNT, where in the mixture CNT were dispersed nanoparticles - shape of carbon nanotubes (CNT). We used the testes apparatus by PerkinElmer "PYRIS Diamond Dynamic Mechanical Analyzer" for measuring mechanical properties. Dynamic mechanical analysis (DMA) is a technique used to study and characterize materials. It is the most useful for studying the viscoelastic behavior of polymers. A sinusoidal stress is applied and the strain in the material is measured, allowing one to determine the complex modulus. The temperature of the sample and the frequency of the stress are often varied, leading to variations in the complex modulus. Dynamic mechanical properties of tested mixtures are evaluated using frequency and thermal dependence. Dynamical tensile test we did during temperature program from 20 °C to 100 °C. We gradually applied frequencies 0.01 Hz, 0.5 Hz, 1 Hz, 10 Hz, 20 Hz and 50 Hz.

This paper describes selected aspects of design, optimization and manufacturing process of racing car's upright. Uprights described in this paper are formula student car's uprights. Formula Student is an international competition between university students, which must design and build a new prototype of the car each year, according to the FSAE rules. Uprights for most racing cars, formula student cars included, must meet wide specter of different requirements, like minimal weight, minimal stiffness etc. The first part of this contribution is concerned to design requirements and boundary conditions definition problematics like different uprights types. The following parts describe the material selection and possible optimization for the design and manufacture of the new uprights for the formula car. Manufacturing and final assembly of the part will be described.

The aim of this article is to calculate and compare the modal properties of the frame of the standard and modified freight wagon bogie design. Analysed frames represent the main support parts of the bogie, which are most often used in the Central Europe region. Determination of the modal properties belongs to the fundamental but very important step in the engineering design. In our case, modal analyses of bogie frames structures were carried out using the Finite Element Method. In order to perform numerical calculations based on FEM approach, Ansys package was used. Modal analyses of individual parts as well as substructures of rail vehicles is an inseparable part of the rail vehicles design process. In this article theoretical and practical consequences of obtained results from the modal analysis, i.e. eigenmodes and eigenfrequences of the analysed part of the bogie on its dynamic properties are presented.

Aiming at a kind of grinding head of high-speed precision roll grinder, its structure characteristics and heat source characteristics are analysed, and the characteristics of heat source is calculated. On these bases, the weakness of grinding thermal characteristics is found through the numerical analysis of thermal performance of roll grinding head, facing the thermal error of sensitive area, optimization method which unites multi objective and single objective are adopted to optimize the thrust oil film bearing of the roll grinding head, after that numerical analysis of thermal performance of roll grinding head is analysed. Analysis results show as follows: temperature of the optimized oil film thrust bearing is improved obviously. The oil film performance between the bearing and the main shaft is stability, and it has had effective prevent the phenomenon of metal dry friction happening. As a result, the grinding accuracy of the grinding roll is effectively improved.

Various industry sectors are using advanced high-strength steels nowadays. Application of these steels are often constrained by the capabilities of their manufacturing and processing technologies. To deliver the required properties, advanced high-strength steels must possess the prescribed microstructures which can be achieved by specific heat treatment routes, such as intercritical annealing or the Q&P process. Difficulties, however, arise in these materials' joining, and welding in particular. Welding profoundly affects the microstructure and mechanical properties of the product due to the amount of heat input and subsequent rapid cooling. For these reasons, laser welding and electron beam welding tests were carried out on experimental 42SiCr steel. Prior to welding, the material was treated using two different Q&P process sequences and one conventional quenching sequence. The weld metal, the heat affected zone and the base material were examined by metallographic methods and the impact of the introduced heat on the microstructure was studied.

The use of recycled or remelted alloys is one of the most common ways to reduce production costs. As the number of remelting increases, also chance of the chemical composition and the microstructure alteration is increasing, which has a major impact on the resulting mechanical properties. The microstructure of recycled alloys mostly affects the presence of iron and its negative effect on casting properties. The paper deals with the degree and the way of influence of the remelting on the microstructure of AlSI9Cu3 alloy with increased iron content to 1.4 wt. %. In the work are progressively evaluated changes of microstructures focused on the morphology and shape of the iron phases, dendritic structure change and pore formation due to remelting on AlSI9Cu3 alloy after natural aging and after the heat treatment (T5). The obtained results point to degradation of the microstructure due to multiple remelting with the possibility of partial improvement when applying heat treatment (T5).

Heat transfer evaluation in a plate heat exchanger (PHE) is one of the most common issue which is widely used in many engineering processes. The objective of this paper determine to formulate a global energy balance in a PHE and to study the heat losses, firstly focuses to study the heat transfer in countercurrent and parallel flow and to measure the temperature profile and to determine the number of transfer units (NTU) effectiveness of a plate heat exchanger. An addition to calculate the overall heat transfer coefficient using criteria equations, also focused to draw the temperature profile of the heat exchanger for both configurations countercurrent and parallel flow with temperature on the axial axis and thermocouple position on the horizontal axis. Furthermore discussed the behaior of temperature across the heat exchanger, compare the countercurrent and parallel flow arrangements, cpaing the experimental heat exchanger effectiveness with that estimated by the NTU method, the NTU effectiveness method application in the calculation of the output temperatures of a PHE. This concentric plate heat exchanger allows the study of heat transfer between hot water flowing through an internal sheets and cold water flowing in the ring area lying between the internal and external sheets, the plate heat exchanger allows measuring hot and cold water temperatures in different points of the heat exchanger.

High strength steel 22MnB5 according to DIN EN 10083-3 belongs to the group of HF steels frequently used in the production of coachwork. Using the thermo mechanical pressing can be achieved that these steels have strength of about 1500 MPa. The surface of this steel is provided with a protective coating to protect it from oxidation. Galvanic ally, a Zn-based layer is used to provide cathodic protection. The Zn-based layer is limited by the temperature which is insufficient for TMP. Hot-dip galvanizing is also applied to an Al-based layer that does not serve as a cathodic protection but is used as an effective oxidation barrier. The quality of the Al-Si layer is important with regard to the resulting quality of the formed blank. The properties of the surface Al-Si layer affect not only the conditions for their application to the steel blank but also the external conditions which are determined by the conditions of the thermo-mechanical processing into the shape of the finished product. To assess the properties of this layer, microscopy methods, namely light and electron microscopy, were used. On the basis of analyzes, conclusions were drawn that should lead to securing the Al-Si layer with the required properties.

This research is engaged in monitoring changes in the tribological behaviour of CrCN thin films at room and elevated (300°C) temperatures. The monitored thin films are deposited by cathodic arc deposition of a pure Cr (99.99 %) cathode under an atmosphere of a mixture of CH4 and N2 gasses. Tribological measurements were performed at a load of 10N, a rotational speed of 60 rpm, and a counterpart of ceramic material (Al2O3). The article also describes the evaluation of wear on the studied thin films due to tribological measurement and temperature.

This paper deals with surface integrity after hard milling of bearing steel 100Cr6. Surface integrity is expressed in terms of shape deviation as well as Barkhausen noise emission. Furthermore, components of cutting forces are also measured as a function of tool wear. Non homogeneity of cutting force distribution within the contact between the milling cutter and workpiece is discussed. The results of measurements indicate that shape as well as structure remarkable non homogeneity should be expected after hard milling due to missing full contact between milling cutter and workpiece. This non homogeneity can be monitored via Barkhausen noise technique. On the other hand, the competitive grinding cycles produced more homogenous surface and surface state is a function of infeed speed.

An adhesive bonding technology represents a prospective method of diverse materials connecting. Polyurethane (PUR) adhesives namely are used in an area of the adhesive bonding of wood and cellulose - based products. They gradually substitute formaldehyde-based adhesives. A higher reactivity of isocyanates with any compound having moving hydrogen namely, i.e. e.g. water, etc. is a significant disadvantage. An elimination of this negative factor is possible by adding a filler, e.g. PUR recyclate - based. The aim of the research is to determine an adhesive bond strength of the PUR adhesive modified with microparticles of crushed PUR foam (waste from a building - an insulation material). Improving of a tensile lap-shear strength and a material recyclation of the PUR foam are expected aims. Also a reduction of the adhesive price is a secondary output. Results of mechanical tests were supported by conclusions from a scanning electron microscopy (SEM) analysis with an aim to evaluate the interaction between the adhesive and the recycled filler. A diffusion of the adhesive into a wooden surface would occur at the wooden test samples and so mechanical properties of the modified adhesive would not be determined. This reason led to the research on the modification of the PUR adhesives LEAR D4, PP-6a17 and PP-7a within the adhesive bonded metal bond (a structural carbon steel S235J0). The research results proved a positive influence of the modification of the PUR adhesive with the microparticles of the PUR recyclate. The tensile lap-shear strength was increased. Results of SEM analysis proved a good wettability.

The works deals with a study of fillers influence on chosen mechanical properties of polyamide and the given influence was investigated by using of atomic force microscopy (AFM). Atomic force microscope NT-206 in a complex with control and image processing software is intended for measurement and analysis of surface microrelief and submicrorelief, objects of the micrometer and nanometer range with high resolution. Using AFM it is possible to scan spectroscopic curves that show dependence of composite action force of the probe and surface of the sample on distance between them - they are curves of approach /moving off. In presented measurements by using of spectroscopic curves, the homogeneity and ratio of Young's modulus for polyamide samples were evaluated. For each sample, the curve was created by using of five different places - points. We employed the general approximation and Snedonn's formula for analysis of data and calculation of Young's modulus off complete rake curve. The Sneddon's model gives the relationship between load gradient dP/dh and Young's modulus E.

Tramways in cities often ride in track curves of a small radius, which is followed by an increased effect of the vehicle on the track by the rail - wheel contact. Exactly with the aim to reduce these undesirable effects we designed a tram bogie with steered wheelsets. Moreower, for the vehicle passability trough strongly curved track inproovement, we proposed spcific, double treaded wheelset and coresponding track section. This invention is also registered under Patent Aplications Nr. a201701589 and Nr. a 201706685. A comparison of safety against derailment results for a tram vehicle running through a S-curve with considering of tread change is given in this paper. Three cases are compared: the first case is a T3 tram vehicle with original bogies, the other two cases represent a tram vehicle, which uses proposed inventions. Two ways of bogies placement under the vehicle body are investigated.

Nowadays, ever increasing demands are being made on equipment and machine structures. This fact negatively affects their lifespan, reliability and security. Internal damping is caused by material malfunctions in the microstructure, thermoelastic effects, movement of dislocations or the effects of swirling currents. This paper deals with microstructure, chemical composition and mechanical properties of ductile iron. These data are required as input parameters for computational modeling and numerical analysis. The numerical part is focused on the modal analysis of the homogeneous beam sample by finite element method in the ADINA software environment.

Mill-turn center is an advanced CNC machine tool. This paper presents a novel approach to the conceptual design of a mill-turn center. Firstly, the feature model of a mill-turn center is created based on a RW (representative workpiece) in a Top-down way. After that, two concurrent works are studied: the verification model of the machine tool is setup by transforming its finished feature model; the NC programming is done with the help of the technology of CAM (computer-aided manufacturing). Thirdly, the production verifying of the mill-turn center is fulfilled in the NVMS (NC verification manufacturing system). Lastly, the optimum structure dimension of two functional subassemblies and the correct layout of the machine tool can be confirmed with the modification and feedback. This is a universal method and can be used by the designer of CNC machine tool to promote their job target of quality, efficiency and cost.

The aim of the research was to compare a classical (turning) machining and an abrasive-free ultrasonic machining (bufo) at aluminium alloy. An ultrasonic set I - 4 consisted of the ultrasonic generator, power output 630 W and working frequency 22 kHz ± 10%, was used for the research. Three different cutting fluids containing nanoparticles were compared at the abrasive-free ultrasonic finishing. A rise of a hardness HV0.05 and HBW2.5/62.5 compared to the classical machining occurred at the application of the abrasive-free ultrasonic machining technology at the aluminium alloy by various cutting fluids containing nanoparticles. It is obvious from the results that a considerable fall of the surface roughness parameters Ra and Rz occurred at the application using the abrasive-free ultrasonic finishing.

Aluminium alloys with higher content of alloying elements are very susceptible to the emergence of crystal segregation that significantly affects the mechanical, physical and chemical properties of these alloys. Crystal segregation is called chemical heterogeneity in microscale and is formed during crystallization. Crystallization of alloys does not occur at a particular temperature, as is the case of pure metals, but in a certain temperature interval. During cooling of the melt occurs to formation of different regions within the dendritic cell that differs in chemical composition. Generally is crystal segregation defined as chemical heterogeneity formed during alloy crystallization that is enriched or deprived of alloying elements and impurities that segregate unevenly across the surface of the dendrites. In the central area of the dendritic cells is alloy deprived of alloying elements, while the outer parts of dendritic cells and in space between dendrites is the concentration of alloying elements richer. This concentration has a hyperbolic course, when the central region of dendritic cells has the lowest concentration of the alloying elements and the outer part of dendrite boughs and interdendritic space have the maximum. Distribution of individual elements has a recurring character and can be described by sine function. The distance between two main axes of dendritic cells is affected by the temperature interval between the liquidus and solidus for the given alloy, the cooling rate of the melt and temperature gradient during solidification. Formation of the crystal segregation in aluminium alloys rich in alloying element and additives cannot be prevented, it is possible only influence its scope and with the right choice of heat treatment parameters can be suppressed. To suppress the crystal segregation the castings are subjected to heat treatment which is called homogenization annealing. It is the diffusion process in which there occurs to a balancing of chemical composition of alloy and the uniformity of its structure.

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 correct determination of the shelf mass including content is very important for the proper function of a universal shelf stacker (USS) drives life and construction USS so that these elements were not overloaded. Weighing can be done by direct methods using various sensors tension and compression but also the indirect method, by the torque sensing of current frequency converter, which controls the speed of the three-phase asynchronous motor. This method does not require any additional construction or adaptation or additional sensors or electronic evaluation system power operation. Weighting method of shelf in USS is based on the fact that the torque converter current is proportional to the sum of the weight of the shelf and the extractor and its value provides almost every frequency converter. In contrast to the direct weighing method of the shelf it is obvious economic advantage of this method and the accuracy is sufficient for the operation of USS.

Stability lobe diagram predicted by the zeroth-order approximation (ZOA) method and the semi-discretization (SD) method were compared. The methods yielded similar predictions for high radial immersions under the specified cutting parameters and the cutting tool modal properties. As radial immersion was decreased, the disagreement between the predictions of the two methods grew. For very low radial immersions, the predicted lobe diagram differed considerably. The most prominent difference was an additional set of lobes corresponding to the new type of instability, the period doubling bifurcation which was predicted only by the SD method. Numerical simulation verification of the stability boundaries confirmed that the predictions of the SD were more accurate than those of the ZOA method.

Firefighter ladders are manufactured of aluminium alloy AA 6063. These ladders are a widely used technical tool for firefighting, for intervening firefighters and for rescued persons. The quality of the ladders is checked by so-called "user test" which is a non-destructive deflection test defined by CSN EN 1147. Unfortunately, this test is not sufficiently conclusive in terms of safety. Therefore, the project called "Safety improvement of extension ladders for firefighters" (VI20162020021) is focused on the complex assessment of the existing firefighter ladders through mathematical modelling, material analysis and real testing. In the present work structure and mechanical properties of samples (aluminium alloy AA 6063) taken from different areas of a firefighter ladder are presented. The obtained result confirm excellent mechanical properties of selected samples, such as tensile yield strength and ultimate tensile strength, at laboratory temperature but a huge decrease in these properties after exposure to temperatures above 200 °C for even short times. This results in the necessity to control temperatures in the proximity of the ladder, especially in the case when the ladder is located near a flame.

This paper describes the conception of vehicle interior which can help decrease the injury risk of unbelted passenger. This paper is primarily aimed to the field of rail vehicles, but the results are useful for more transportation industries. Some computer simulations for passive safety performance assessment were conducted in previous years. The FE models of the interiors based on data from actually operated vehicles were prepared for this purpose. The newly prepared simulations are close to the real interior models. Combinations of rigid walls were used for modelling. Each model contains a short python code which allows change of interior disposition. This approach is close to an optimisation process. The main goal is to compare all possible configurations of interior. In practise it is usually obvious which change can improve the passive safety, but with numerical approach is possible to find structures with unknown influences. The simulations were performed in software environment PAM-CRASH. It is used a dummy Multibody model of the human body ARB Hybrid III 50th percentile.

The article describes the course of a pressure test that was made to determine the maximum force in the case of breaking the integrity of the casting. Observation of the forks arm deformation can be done with using sensors on the universal tensile testing machine. Using a high-speed camera to monitor this test will provide results in digital form that can serve to further research. Subsequently, analysis of the material properties of the AlSi7Mn0.3 casting is described, using the methods of evaluation of mechanical and structural properties. Periodic tests check the castings status to ensure recurrent quality in order to achieve the required safety in accordance with the standards for road vehicles.