Fulltext search in archive

The Friction stir welding (FSW) is a complex process, depending on many factors: machine, clamping device, material and tools. Parameters that have a direct impact on the quality of the joint include the rotational speed, welding speed, clamping force, geometry and tool plunging depth. The paper presents the results of experimental studies concerning the effect of tool pin length on the microstructure and mechanical strength of joints of thin sheets made of Al 7075 alloy. A tool with an adjustable pin with concave shoulder was used to weld the joints. Different pin lengths were used, which were selected with respect to the thickness of the welded joint. The specimens were subjected to visual evaluation, metallographic tests and mechanical strength testing. The results indicate that the pin length has a decisive effect on the microstructural changes in the joint and thus influencing the strength of the FSW joints.

The paper topic is concerned with the issue of braking dynamics and adhesion coefficients of firefighting vehicles at fire rescue units. The real breaking distances at firefighting vehicles of the water tenders type are presented in the paper. The metering was made on the wet and/or dry asphalt, with different age of tires and the carload. Measured results should be used for drivers' education at fire rescue units to increase the safety during the emergency drives.

The Cargo Mix Problem (CMP) chooses and distributes types of containers to load into bay subsections of a container vessel. In this paper, we extend existing Mixed Integer Programming models for the CMP by considering containers with dangerous goods. We show that our model can be optimally solved in reasonable time using standard software.

The first aid is an important tool to save people's lives after traffic accidents. Drivers are the most-likely bystanders, who might help injured people at the traffic accident site. The current research aims to explore Czech learner drivers' knowledge and attitudes towards the first aid and to evaluate whether the first aid education increases the likelihood that a driver will provide the first aid for injuries resulting from traffic accidents. A questionnaire survey was conducted in 2015 among a sample of 370 Czech learner drivers at driving schools. The two groups of student drivers were compared - those who had attended the first aid classes (FAC) and those who had not. The learner drivers who had attended an FAC are more likely to know how to treat burns and serious injuries, contain external bleeding, and unblock the respiratory track. Those who had not attended an FAC would more often hesitate to provide the first aid because they resisted taking a leadership role to organize the scene, or they did not have suitable equipment. This supports the idea that increasing the quality of the first aid training for Czech student drivers would improve the traffic safety in the Czech Republic.

This paper reports the results of the experimentally determined effects of decontaminating agents on metal surfaces resulting from passive and active decontamination after sulphur mustard (Yperite) contamination. The paper includes an analysis of the experimentally obtained results for each metal (Zinc, Nickel, Aluminium, Brass, Steel, Copper).

The article presents the possibility of using the Between Satellite Single Difference method (BSSD) in the precise determination of the aircraft position in the Global Navigation Satellite System GLONASS navigation system. The paper presents the mathematical model of the BSSD method, describes the research test and presents the results of conducted examinations. The research test was conducted within the implementation of the GLONASS satellite technique in air navigation. The test research uses the actual GLONASS navigation data registered by the Topcon HiperPro receiver, mounted onboard a Cessna 172 aircraft. Obtained findings of the research work are interesting from the perspective of implementation of the GLONASS satellite technique in aviation. It should be emphasized that standard deviations of the determined position of the Cessna 172, using the BSSD method, do not exceed 2m. The article also determines the accuracy of a position of the Cessna 172 in the GLONASS solution with reference to a solution in the GPS navigation system.

The goal of the paper is to assess the territorial development in terms of the public rail transport in conditions of the Czech Republic or, more precisely, in the south of Bohemia. The capacity utilisation of the railway line No. 190 in the direction from Ceske Budejovice to the target station of Strakonice is analysed and the suitable deployment of the set of wagons, intended to be used in providing the basic transport services in the low-populated areas, is evaluated. The paper is concerned with the current situation in utilising the capacities on the railway line No. 190 with respect to the future utilisation of the railway links that will be affected by economic factors in the form of the reduced fare for students and pensioners. To this end, the mathematical and statistical methods, which will pre-define the suitability of the choice of capacities of the set of wagons in providing the basic transport services, will be applied.

The paper proposes a correction method of the oblique-angle vibration for laser doppler vibrometry. It briefly discusses the key mathematical approach considering the surface of the analysed object to be a reference plane and gives a practical example of the method proper application. The proposed correction method is practically verified by laboratory measurement of natural frequencies and mode shapes for vibrations of high voltage transformer housing. The results are further compared to equivalent accelerometer measurement.

Pollution of the air by gases and particulate matter is a problem of everyday life. Particulate matter (PM) is one of the hazardous pollutants causing deterioration of the environment and thus quality of life of the population. Long-term exposure to effects of increased concentrations of gaseous pollutants can also cause deterioration of the environment and human health. Particulate matter and gases production by the road transport is a burning issue, particularly for larger urban areas. Many factors influence the air quality what determines its development and changes. Air pollution monitoring was focused on a possible change in the concentrations of pollutants after the change of the crossroad - three-arm crossroad to the roundabout. The subject of this paper is monitoring particulate matter (PM1, PM2.5, PM10) and gases (nitrogen oxides NO, NO2, NOx) in the vicinity of crossroads in the urban area and an evaluation of fraction ratios PM10, PM2.5 and PM1 with regard to construction of crossroad, meteorological conditions and traffic volume. The roundabout has specific construction and routing traffic, what can influence on production and dispersion of traffic related emissions. The obtained results indicate a decrease in particulate matter concentrations at the roundabout over a three-arm crossroad and an increase in nitrogen oxides concentrations at the roundabout compared to the three-arm crossroad. According to the data obtained and analyzed, the PM10 particulate matter concentrations at the roundabout could be reduced by up to 50% over the three-arm crossroad.

Porous silicon (pSi) samples were prepared by electrochemical etching of p-type silicon (p-type Si) substrate. Three pSi samples with different parameters of electrochemical etching (electrical potential, etching time, etching current) were prepared and analyzed. We studied the influence of electrochemical etching parameters on spectral reflectance of pSi structure. A modification of interference pattern was observed due to changes of microstructure. We determined the thickness of pSi layers from spectral reflectance. Solar cells with a porous structure achieve high efficiency and long life. These solar cells are predestined for use in transport.

Errata: Communications - Scientific Letters of the University of Zilina, 21(1), 2019, Passsenger Ride Comfort and International Roughness Index Specifications in the Slovak Republic, p. 15-22.

The article presents the results of research into the strength of the hatch covers of general-purpose open wagons. It was detected that strength of the standard hatch covers is not provided in operational loading diagrams. Therefore, new designs of the hatch covers for open wagons were proposed. The results of the strength calculation, implemented with the finite element method, make it possible to conclude that at basic and additional operational loading diagrams the strength values for proposed designs of hatch covers do not exceed the admissible values. The research conducted can contribute to a higher strength of the carrying structures of the bodies of general-purpose open wagons in operation, thus, guaranteeing a higher operational efficiency of the rail transport.

A completely new area of HoloLens usage is proposed. The Hololens is an augmented reality device, which provides the high precision location information. Such an information is normally used to accurately position holograms within the real space with respect to the viewer (user of HoloLens). The information is precise enough to use it for reporting the position for the purpose of autonomous driving. Several experiments have been executed in vast areas (20 m x 40 m) in order to find out the potential error coming from vibrations or other effects when moving the HoloLens. The results show that the technology can be used for spaces, which are previously known by the system - pre-scan of the space is needed. The big advantage of the system is its readiness for indoor positioning applications with no additional infrastructure needed, simultaneous localization and mapping, complex space mapping and reached precision. The disadvantage is mainly the costs.

Exposure to electromagnetic field caused by transportation systems is a cause of concern for many people. In public and personal transport there are many sources of electromagnetic field. Plenty of dosimetric analyses of electromagnetic field carried out by various research groups found out very high exposure values in the transport. Although the measured fields in transport remain well below the general limit for public exposure as defined by ICNIRP (1998) standards, they are relatively high compared to other micro-environments in daily life, especially for children seated in the rear seat, as field strengths are comparatively high there and children are a sensitive part of the population. How long-term effects of these fields affect the human organism and what is the mechanism of action, are questions without known answers. Several studies point to the potential association of various diseases with exposure to electromagnetic field. The key to understanding the effect of the electromagnetic field on the human organism is to reveal the mechanism of action of the field.

The article presents and describes results of research in determination of the aircraft positioning accuracy with use of the GPS and EGNOS satellite systems in the air navigation. The article, in particular, makes a comparison of the designated aircraft coordinates in the GPS and EGNOS systems in relation to the reference position, determined from the precision differential RTK-OTF technique. The experimental test was conducted in Slovakia, in the vicinity of Kosice airport. In the test, a trial flight by Cessna aircraft was executed over the village of Bidovce (LZBD) in Slovakia, in East-Central Europe. Within the conducted investigations, the GPS and EGNOS positioning accuracies were determined in real time during an in-flight experimental test. Based on the conducted investigations, it was found that the accuracy of the GPS positioning in the air navigation equals ±10 m throughout the most part of the air test. In the same period the EGNOS positioning accuracy in air navigation is equal to ± 5 m.

New original results are presented on relation between passenger's whole-body vibration (WBV) and longitudinal road unevenness characterised by the International Roughness Index (IRI) in 100-m segments. Measurements were provided in nine different cars of six vehicle categories operated on about 1860 km of road network. Vibration total value based on the root mean square (RMS) of the frequency-weighted acceleration was used to quantify the ride comfort at seat surface and seat base (i.e. vehicle floor) in three orthogonal axes. The relations between passenger's acceleration response, comfort reaction levels according to the ISO 2631-1: 1997 and the IRI road unevenness classes, used by the Slovak Road Administration, were estimated. Results indicated higher WBV by ~ 20 % on the motorways than on the 1st and 2nd class roads in the same IRI road class. Using the same IRI road classes for motorways and the 1st and 2nd class roads seems not to be appropriate from the point of view of the whole-body vibrations.

The article elaborates on measures aimed at increasing the performance of the rail freight transport carried out in the north-south direction. The measures are designed based on the implemented analyses focused on the analysis of the current situation of international trade and development of international transport as well as the analysis of the current situation of the European transport infrastructure. The north-south direction was selected due to the enormous increase of the transit road transportation.

The aim of this paper was to determine the effect of surface roughness of cavitation generators made from two different materials: P265GH steel, with a ferritic-pearlitic structure, and X2CrNi18-9 (304L) steel with an austenitic structure on the mass loss and cavitation wear. Cavitation generators were tested in the conditions of cavitation wear environment continuously for 500 PMHs in a specially designed and constructed author's stream and flow device. Based on the carried out experiments was confirmed that the highest mass loss - 0.1752 g is seen for a sample of P265GH steel wet sanded with paper with the grain size of 1000. The smallest mass loss was recorded for the cavitation generator made of X2CrNi18-9 (304L) steel, sanded with sandpaper with the grain size of 2500. Certainly, the smallest number of cavitation wear effects was found for a cavitation generator made of austenitic steel X2CrNi18-9 (304L). Few places were identified based on macroscopic photographs, especially near the edges of the straight-through openings, but their number was much smaller than for the ferritic-pearlitic steel, which is associated most of all with the properties of austenitic chromium - nickel steel.

Propeller shafts of the vehicle's drive transmit a torque to relatively large distances. The shafts are basically long and slender and must be dimensioned not only in terms of torsional stress, but it is also necessary to monitor their resistance to lateral vibration.In the paper, a simple model (of the solved problem) is constructed by the method of physical discretization, which is evident from the nature of the centrifugal force fields' influence on the spectral properties of the shaft. An analytical solving of speed resonances prop shafts test model (whose aim is to obtain values for verification subsequently processed models based on the transfer-matrix method and the finite element method) is performed.

Geometrical discontinuities in mechanical components are detrimental for the mechanical properties of the product itself. Actually, in proximity of such features, the stress increases due to the stress concentration factor, that in the case of a circular hole is equal to 3. Several solutions have been proposed to reduce the stress concentration value. In the present article, the application of a particular porous pattern that can be obtained by laser cutting with the appropriate finishing requirements is introduced in order to modify the local stress field and reduce the stress concentration value near the hole boundary.

The natural frequencies and mode shapes are unique characteristics of each mechanical structure. Their prediction is a crucial part of each dynamic experimental measurement. However, the proper identification of higher natural frequencies and mode shapes can be a problem, especially for big structures such as bridges. The reason is the need to excite the bridge in such a way that it responds in a free-vibrations mode shape. This paper describes three various sources of excitations, which are used to identify the modal characteristics of the pre-stressed concrete bridge. The impulse excitation, traffic load and ambient vibration are used and analyzed. In the case of the loading by a force impulse, modal shapes are also obtained. The study shows that the intensity and kind of the excitation has a noticeable impact on identification of modal frequencies. Finally, the results of the experimental measurements are used to calibrate the numerical model.

The paper is focused on the influence of driving behaviour on fuel consumption and the subsequent environmental impacts. The main issue is to estimate the economic and environmental costs connected with the forced deceleration or stopping and the subsequent acceleration of a motor vehicle in urban traffic. Authors introduce a physical model of a vehicle with variable parameters that allows the calculation of economic and ecological losses in congestions on the basis of data generated by an arbitrary floating car. The losses include the lost kinetic energy of a vehicle during the forced braking, accelerated degradation of vehicle components, the loss of time of drivers and passengers and the increased ecological footprint. Energetic costs are estimated from the vehicle engine efficiency with which the fuel energy is transformed during an acceleration to kinetic energy of a vehicle lost during braking. Further, these costs are estimated from fuel calorific value and fuel price. Costs resulting from the degradation of vehicle components are estimated from their average stated lifetime.

The submitted paper deals with designing routes of the vehicles, which provide the transport network services. We limit our focus to such tasks, where the priority is the edge service in the transport network and the initial problem is finding an Eulerian path. Regarding to real-life problems, this contribution presents such procedure of solving, which takes into account both the existence of a mixed transport network containing one-way roads and the existence of a wider transport network. In this network, there are only selected edges with possibility of the effective passages. This problem can be solved by the modified Rural Postman Problem assuming the strongly connected network. Linear programming is a suitable tool for designing optimal routes of service vehicles.

Conveyor belts with woven plastic belts, aimed for general applications, are very economical transporting means for longer distances. During the operation, the conveyor belts are subjected to various mechanical loadings. The consequences of those loadings are increased stretching of the belt and change of its tensile strength, which negatively affect the proper functioning of the transporter. To avoid the irregularities in the conveyor belt's operation, the tensile properties of the two plastic woven belts were tested (maximal force, maximal extension, breaking force and extension at break). In that way the conditions of the two belts were established. Based on performed experiments the belt that is more suitable for application in the transporter was defined.

The aim of this paper is to compare economic and operational aspects in the transition from direct road transport to unaccompanied CT using intermodal road semitrailers. A comparison of specifications of transport units was carried out as well as the risk assessment, considering the probability of a critical situation occurrence. Both of these factors are key for the final decision making. As a main part of this research paper, a comparative case study was conducted. For the purposes of this comparison, data from actual transport orders were used on a route starting in the Czech Republic, going through the industrial Northwest of Germany and then to Belgium and the Netherlands. As a result of this research, the direct cost of road transport and CT were compared considering the lifespan of the used equipment. Besides that, the investment cost for a road carrier to enter the CT system was quantified, which is essential for the CT system development.

Developing the structure of geodatabase and knowledge base to provide quantitative mapping of land suitability for cultivation the main crops has been shown in the research. The general model and catalogs of knowledge base were designed that are structuring and formalizing information for creating thematic and complex maps and geomodels. The real world spatial problems give rise to multi-criteria decision-making based on geographical information systems (GIS). The GIS environment provides both aggregation and spatial analysis of various georeferenced data. In this paper, the two approaches of multi-criteria evaluation (MCE) are represented - overlaying with the AND operation and the lowest score assignment on one criterion. An example of multi-attribute decision analysis is done using criteria for the crop suitability assessment. A comparison of those two approaches has been made, based on results of the land-use suitability mapping for the study crops - winter wheat, sunflower and corn. The results demonstrated that at certain locations, a range of criteria values, according to the AND operations had the lower applicability and less flexibility than according to the second approach, based on the lowest score assignment on one criterion. Designed maps characterize the threshold status of the soil quality to provide yields of studied crops on certain areas. A set of land suitability maps, designed as quantitative models of integration of environmental, soil and climatic conditions, would be very effective to manage the complex decisions under the crop cultivation.

The capacity calculation procedure for unsignalized intersections is based on the gap-acceptance theory in most of existing capacity regulations and it relies on one of the important parameters - critical gap. However, the capacity calculation procedure and values of critical gaps according to these regulations are valid only for intersections with standard right-of-way (major street leading straight). Nevertheless, in Slovakia, intersections with bending right-of-way (major street not leading straight, but bending) can be encountered. The specific mode of right-of-way results in different priority ranks of traffic movements (set by traffic rules of driving), more complicated traffic situation and therefore, different driver behaviour characteristics. To examine the gap acceptance behaviour of drivers under these specific conditions, an unsignalized four-leg intersection with bending right-of-way located in an urban area of Zilina, Slovakia, was selected. Three different methods (Raff, Wu, and MLM Troutbeck) were used for critical gap estimation from the field data. In the article, results of critical gaps for three through movements of different priority rank (major-street through movement of Rank 2 and minor-street through movements of Rank 3 and 4) are presented. The results show, that the values of critical gaps differ depending on the method by about 3-5 % only, which is not significant. Troutbeck ´s MLM method gives the highest values. The priority rank of movement has the greatest impact on the result. The values of critical gap for major-street through movement of Rank 2 are the smallest; they are approximately 1.3-2.1 s smaller than the values for minor-street through movements of Rank 3 or 4. The highest values of critical gap have been estimated for minor-street through movement of Rank 4 and they are higher compared to the current Slovak regulations TP 102 values for the same priority rank.

The composite alumina-titania coatings have been widely used in industry fields to protect metallic components from wear, corrosion and thereby prolonging their service time. This paper presents an analysis of the microstructure and mechanical properties of Al2O3-TiO2 composite coatings, plasma sprayed on steel substrates from feedstocks containing various concentrations of the TiO2 powder. The coatings revealed lamellar microstructure, formed by the rapid solidification of molten droplets of the powder on previously deposited splats. The main phase identified in the coatings was γ-Al2O3 phase, the others were TiO2 and α-Al2O3, as well as amorphous phase. The results indicated significant improvement of hardness, Young's modulus and fracture resistance of coatings with an increase in TiO2 from 3 wt. % to 13 wt. %. The friction coefficient was found to be the same for both coatings.

This contribution deals with the selective laser melting (SLM), which is one of the additive manufacturing (AM) technologies enabling the production of complex parts from metal powder, layer-by-layer wise. This technology uses laser as source of energy to melt a powder to compact state. Properties of final products can be significantly influenced by the process parameters and post-fabricated heat treatments. The purpose of this study is to determine the effect of a heat treatment on properties of the Ti6Al4V alloy specimens manufactured by Eosint M280 machine by the SLM. Three sets of specimens, treated at different temperatures (730 ˚C, 900 ˚C, 1200 ˚C), resulting in a different structure, associated mechanical and fatigue properties, were investigated.

When the robustness of a public service system design is tested, we can often use scenarios where possible random failures can occur and they can influence the time the service is accessible which is provided for system users. The construction of a suitable scenario is based on the choice of links of the transportation network which influence the system performance in a substantial way. In such scenarios one or multiple arcs can be affected by this failure. In our contribution we present characteristics of pairs of critical arcs that can be used to develop an algorithm for the creation of critical scenarios.