CTU Open Journal Systems (Czech Technical University, Prague / České vysoké učení technické v Praze)
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Influence of laser beam welding parameters on local mechanical properties of duplex stainless steel joints
Get PDFDuplex stainless steels (DSS) are dual-phase alloys consisting of austenitic and ferritic phases in the microstructure. DSS provide an ideal compromise between mechanical properties and corrosion resistance. Welding of DSS leads to a change in the ferrite/austenite ratio in the microstructure and to degradation of the properties of the weld joints. Therefore, it is very important to control the microstructure of the weld joint directly during the welding process. An innovative method of laser welding applying a dual beam was used. By spreading the energy of the laser beam over two spots, additional heat is introduced into the weld, which ensures a slowdown in the cooling rate of the DSS and possibly ensures the desired ratio of ferrite and austenite in the microstructure. The influence of laser welding parameters and energy distribution of the dual beam on the fusion zone (FZ) geometry, resulting microstructure and mechanical properties of the weld joints was monitored. The tensile and shear strength was measured. The coefficient of proportionality between shear and tensile strength was calibrated to be as 1.38 ± 0.01
Mechanical properties of dental fillings with nanoparticles
Get PDFNanoparticles represent an innovative direction in dentistry that offers several possibilities for improving the physical-chemical properties of dental materials. Moreover, they may help to reduce tooth sensitivity and prevent the recurrence of tooth caries with their antibacterial properties. Particular attention is given to the significant potential of nanoparticles in enhancing the mechanical properties of dental fillings. Our aim was to use diamond nanoparticles to modify dental fillings based on glass ionomer cement (GIC) and evaluate the effects of nanoparticles on the hardness, strength, wear resistance, and surface texture of the composite. Results suggest that modification of GIC using diamond nanoparticles can be an effective method for improving mechanical properties and may lead to the development of improved materials for dentistry
Optimization of FIB milling procedure for micromechanical testing of cement pastes
Get PDFThis study focuses on optimizing the Focused Ion Beam (FIB) preparation process for micro-beams made from cement paste prepared from Portland cement CEM I-42.5R, which includes four phases: inner and outer products, Portlandite, and residual clinker. The effects of the primary electron beam, focused ion beam, image drift, imaging issues, and sample moisture cycling were investigated. Recommendations on specific fabrication procedures and FIB milling parameters, such as accelerating voltage, probe current, and time, were provided
Passive safety of light vehicles – effect of speed on the behavior of the vehicle frame structure
Get PDFDue to growing concerns about the climate change situation, an increasing number of restrictions are being introduced. One of them is the shift towards smaller and lighter vehicles that are less demanding to produce, operate, and subsequently recycle. These are specifically L6 and L7 vehicles (four-wheelers called quadricycles). In addition, even for these vehicles, there is an attempt to make their operation even more environmentally sustainable by introducing government regulations on the powertrain, which will have to be purely electric from 2035. However, the growing popularity of these vehicles has one major drawback: safety. In the framework of the urban electric vehicle project located at the Faculty of Transportation Sciences, CTU in Prague, from the already mentioned category, safety is one of the main topics we want to address. This paper discusses the passive safety of quadricycles and the role of FEM simulations throughout the design and development phase of vehicles. The main objective is to validate the main frame of the developed vehicle at an extensive range of impact velocities. In this way, the behavior of the proposed front crumple zone design and their roles in frontal impact can be determined. The metrics to be monitored are, for example, the maximum accelerations on the structure in each part of the frontal crumple zone or the preservation of the survival space
Safety aspects of e-cars charging at railway stations
Get PDFThe article focuses on introducing e-cars in the Czech Republic and the safety aspects of electric cars, particularly when charging at railway stations. Safety aspects are comprehensively linked to the charging of electric vehicles, where maintaining the balance of the electrical network is crucial to prevent asymmetric loading. The article’s primary aim is to inform readers about the introduction of railway station charging stations and highlight the proactive measures taken to address possible technical problems that can arise during recharging. Fire intervention is a key part of the safety plan, ready to be deployed when an electric vehicle catches fire and poses a risk to the surroundings
Investigation of the effect of elbow pipes of Ti6Al4V, 304 stainless steel, AZ91 materials on erosion corrosion by finite element analysis
Get PDFCorrosion is the degradation of metals caused by chemical or electrochemical reactions with their environment. As a result of these reactions, undesirable conditions occur in the physical, chemical, mechanical and electrical properties of metals. These conditions cause parts made of metallic materials to become unusable. Erosion corrosion is one of the most common types of corrosion in fluid transfer. There are several methods for preventing erosion corrosion. First of all, some precautions should be taken to prevent wear. Intervention is very important in terms of cost, especially at the design stage. Measures such as wide angle bends, wall thickness of wear-resistant material and corrosion allowance can be taken, especially in applications where the flow direction needs to be changed. The aim of this study was to determine the effect of liquid fluid on erosion corrosion in Ti6Al4V, 304 stainless steel and MgAz91 elbow pipes by using the computer aided and finite element based AnsysWorkbench Explicit Dynamics module. For the design of the elbow pipe, SolidWorks was used for 3D studies. In the analysis of the pipe, the suitability of the pipe for the 3D model was examined. The effect of fluid rotation on the pipe walls and the effect of the pipe material on the flow along the pipe were determined. The standard k-e model based on the velocity-pressure relationship in continuous and steady flow was used for the flow calculations. The flow simulation showed that for all models the flow accumulation after rotation was more concentrated on the opposite walls of the pipe, as expected. The results obtained showed that the deformation in MgAZ91 material had the highest value at 9.14 × 10−8 mm. This situation has been interpreted to mean that it may vary depending on the flow rate automation. Designs on the old designs in the erosion structure of the liquid that occurs in the pipes with a new product design in the analysis design
Development and causes of migration in lagging regions in the years 2017–2021: a case study of the Slovak Republic
Get PDFMigration represents a process where people leave their homes for various reasons. The aim of the article is to evaluate the level and development of migration in Slovakia and to identify its causes in the Gemer region, which is among the least economically productive regions of Slovakia. We quantified the development and level of migration based on secondary data through selected analytical indicators of migration. We determined the motivations of the residents of the Gemer region to migrate using a questionnaire survey. Until 2004, Slovakia was an emigration country, but in recent years it has turned into a destination country. However, the situation is not the same for all regions of the country. A negative migration balance persists in the Gemer region, although restrictions related to the coronavirus pandemic have slowed this trend. We found that up to 21 % of respondents from the region migrate for work. Up to 45 % of respondents want to move out of the region, while in 64 % of cases the migration is motivated by economic reasons. The opinion on migration is influenced by the gender of the respondent but is not related to the level of education achieved
Methodology for measuring the potential of a tourism destination in relation to sustainable local tourism product development
Get PDFTourism is very strongly associated with the potential of the area, including the society, in which the tourism activities take place. This potential is often fragmented and it depends on the skills of local actors, stakeholders, and tourism management structures to discover and connect it effectively. And it does not matter whether the potential is tangible or intangible, natural or cultural. The potential of each territory is unique and needs to be summarized, measured, evaluated, and categorized for its effective and sustainable use.This article presents the first part of a methodology for the creation of a local tourism product focusing on the measurement of potential. The methods used in this process are based on decision analysis and process management methods. The methodology is addressed to all tourism actors in each destination, in particular managers of destination management organizations, local authorities, or other initiating entities. The Ministry of Regional Development certified the Methodology for the creation of a local tourism product and recommended its use to municipalities and tourism destinations
The use of concrete slurry waste to improve the properties of the stabilised soil
Get PDFIt is often necessary to use stabilising additives during construction to improve the resulting soil properties to ensure the good quality of civil engineering structures. These additives are often produced at high temperatures and with a high carbon footprint. This paper focuses on soil stabilization with waste concrete slurry, which is produced during the production of fresh concrete. The selected clay soil was stabilized with cement and CSW at 2, 4, and 6 % by weight of soil. Compressive strength, the resistance to freezing and thawing, Initial bearing index (IBI), and California bearing capacity (CBR) were monitored. The research did not confirm better performance of CSW binder even at higher dosage compared to cement, which was due to the high water content of the mixtures. Positive results were achieved especially in Freez-Thaw resistance
Measurement of asphalt concrete base thickness using ultrasonic pulse echo
Get PDFThis paper deals with the description and use of one of the up-to-date NDT method, the ultrasonic pulse echo, to determine the thickness of an asphalt concrete model. In the article, the authors explain the principle of the method and the limits of its use. Furthermore, attention is also paid to the influence of the shape and design of the back wall of the tested elements and the speed of propagation of ultrasonic waves. The research is part of a larger work, defect analysis and implementation of Whitetopping technology in the Czech Republic