16168 research outputs found
Sort by
Study of geometry of the broaching tool for plastic processing.
No full textThe thesis provides a comprehensive analysis of thermoplastics and thermosets, with a focus on how their properties affect machinability indicators when cutting tools are used. It was determined that the cutting edge angles, as well as the radius of the tool edges and corners, have a significant impact on tool wear rate and the surface quality of the workpieces. The importance of materials and coatings used in the production of cutting tools was further discussed. Additionally, the numerical methods applied to solve machining problems for plastics were identified. Based on further theoretical analysis, a cutting tool study was conducted using polyacetal as the material being machined. For this study, cutting tool prototypes manufactured by company X were used. The edges and top radii of the prototypes were measured and later evaluated through numerical analysis. During the numerical analysis, ten different mathematical models were created, each with different front and back angles. To more accurately describe the characteristics of the POM-C material used by company X, tensile tests were performed on the samples, which allowed the determination of the yield strength. After defining the characteristics of both the tool and the workpiece material, a numerical analysis was conducted for each tool geometry model. A smoothed particle hydrodynamics (SPH) model was applied to obtain results, aiming to identify which tool geometry is the most effective when machining POM-C plastic. In the economic analysis, the cost of the improved cutting tool was calculated and compared with a cutting tool from the „HASS“ manufacturer, designed for machining steep angles. It was found that the improved cutting tool developed by company X has the potential to be economically superior to market competitors' products. However, additional experimental studies would be needed to confirm it. Furthermore, in terms of ecological sustainability, plastic recycling methods (mechanical, chemical, energy, and biological) and their significance in the industry were discussed. In conclusion, this thesis provides valuable insights into the potential for improving tool geometry efficiency and the research methods that could help enhance the operational properties of tools and the quality of machined workpieces
Strength study of the steel frame of the hangar.
No full textIn the scientific literature analysis section, articles written by foreign researchers on steel hangar structures, connections, and loads applied to buildings were reviewed. The articles describe the interaction between steel structures and the environment, as well as the environmental effects on the strength of steel structures. The scientific articles evaluate the loads affecting the steel hangar based on its location and position within the plot. In the master's thesis, the loads impacting the steel hangar are described and assessed based on its location and position within the plot. The acting loads include: self-weight, snow, wind, and usage. Two combinations of loads are established. In the first combination, snow load is prioritized, while in the second, wind load takes precedence. In the research section, after load evaluation, 3D model calculations are performed on the Autodesk RSA platform to assess the most utilized frame, which is then subjected to further analysis. After identifying the most utilized frame, located in the middle of the hangar, the study continues by examining the impact of changing the steel grade, using S235, S355, and S450 grade structures. To evaluate the structures, column graphs are presented, illustrating the relationship between the structure's mass and the steel grade. An investigation is carried out to observe how the structure's mass and utilization factors change when modifying the types of structural joints. Stiff and hinged joints are assessed, keeping the column-to-foundation joint rigid in all cases. The utilization factors and structural mass are evaluated while changing the frame spacing to 2, 4, and 6 meters. A column graph is provided for the scenario when the entire hangar model is analyzed, depending on the number of frames installed at varying spacings. In this study, the structures are evaluated using frames with HEA, HEB, and HEM cross-sections. Research object – frame of the hangar. Aim of the work – to analyze the strenght of the steel frame of the hangar. Objectives of the work: 1 Perform an analysis of scientific sources of the strenght testing of steel structures; 2 Determine the dependence of the strength of a frame hangar on the cross-sections of the profiles used; 3 Determine the dependence of the strength of a frame hangar on the materials used. The master‘s thesis consists of: summaries in Lithuanian and English, an introduction, 2 chapters, conclusions, and a list of references. The thesis is comprised of 58 pages
Analysis of heat pumps for efficient use in public buildings.
No full textThe aim of this master thesis is to analyse heat pumps to use them more efficient and to increase their applicability in public buildings in small towns. In Lithuania, one of the most popular heating methods for public buildings is district heating, due to economic and ecological aspects. However, not all smaller settlements and villages in Lithuania are equipped with heat network infrastructure, so heat pumps could be an excellent alternative to solid fuel boilers, which use polluting fuels and require permanent maintenance staff. The most popular “air to water” heat pumps on the market today have lower installation costs and require less installation space compared to “ground to water” and “water to water” heat pumps. However, the efficiency of these types of heat pumps decreases as the outdoor air temperature drops. “Ground to water” and “water to water” heat pumps are more efficient, with SCOP values of 5.6 or more, and geothermal boreholes have a lifetime of up to 50 years but require a higher investment for installation. Two energy efficient science buildings, class A+ and class B, were selected as the subject of the study. An analysis of the efficiency of the heat pumps as well as an environmental and economic analysis with the additional inclusion of district heating was carried out. The results of the study show that using heat pumps in combination with solar electricity is the best choice from an economic and environmental point of view. In public buildings, geothermal heating is up to 30-47 % more efficient with solar power, depending on the energy efficiency class of the building, with up to 32 % less CO2 emissions, but with a total 20-year cost of heating of the building up to 5 % more than “air to water” heat pumps
Application of the simulation model in determining the most suitable evacuation route from the construction site.
No full textIn the Master's thesis, a study was carried out in which a simulation game was developed to compare evacuation routes. The game is a tool for collecting data on human behaviour and at the same time a tool for occupational safety training. The study develops a methodology for using panoramic photographs to create a realistic game environment. The panoramic photos were converted into the game development engine “CoSpaces Edu”. The study collected data on the evacuation route choices of respondents in a simulation game. The analysis of the collected data led to the determination of the evacuation time and the preferred evacuation route for people
Fifth Industrial Revolution factors enabling Circular Business Models in companies in the Plastics Sector.
No full textThis master's thesis examines the Factors of the Fifth Industrial Revolution Enabling Circular Business Models in Plastic Sector Companies. The world's annual consumption of plastic and the amount of waste generated are so high that various regulations and documents need to be addressed. The Paris Agreement, European Green Deal, Sustainable Development Goals et al. name the actions that must be taken to reduce global pollution. This is becoming very important for companies now, because they must implement the actions listed, otherwise they will receive large fines or have to stop their activities. Circular business models should replace the classic linear business model in the plastics industry to achieve the set global goals. To enable circular business models, companies still face various challenges. They can use the Factors of the Fifth Industrial Revolution, which, together with technology, would enable Circular Business Models. The subject of the master's thesis is those Factors of the Fifth Industrial Revolution that enable Circular Business Models, and the goal of the thesis is to reveal them in Plastic Sector Companies. The project reveals the problems of the Factors of the Fifth Industrial Revolution and Circular Business Models, and theoretical argumentation is presented. Based on the literature, a theoretical model has been developed, describing how the Factors of the Fifth Industrial Revolution Enable Circular Business Models in Plastic Sector Companies. Two circular business models are examined - circular supply and resource recovery, which are most suitable for the plastics industry and three main principles of the Fifth Industrial Revolution are attributed: human-centricity, sustainability and resilience. To substantiate the theoretical model, a research methodology was developed and a qualitative research method - semi-structured interviews, which consisted of six company representatives, was selected. After empirical evaluation of the developed theoretical model, the model was partially confirmed. This result is based on the fact that respondents had little knowledge about the Fifth Industrial Revolution and found it difficult to link the Factors of the Fifth Industrial Revolution with the Enabling of Circular Business Models. The research results revealed that respondents could link the processes implemented in their companies with the factors of the Fifth Industrial Revolution: human-centricity, sustainability and resilience and circular business models: circular supply and resource recovery, but only when they were more widely disclosed. The theoretical model also highlighted circular economy ecosystems and only one of the companies significantly applied the ecosystem of the material flow industry ecosystem
Detailed determination of delamination parameters in a multilayer structure using asymmetric lamb wave mode /
No full textA signal-processing algorithm for the detailed determination of delamination in multilayer structures is proposed in this work. The algorithm is based on calculating the phase velocity of the Lamb wave A0 mode and estimating this velocity dispersion. Both simulation and experimental studies were conducted to validate the proposed technique. The delamination having a diameter of 81 mm on the segment of a wind turbine blade (WTB) was used for verification of the proposed technique. Four cases were used in the simulation study: defect-free, delamination between the first and second layers, delamination between the second and third layers, and defect (hole). The calculated phase velocity variation in the A0 mode was used to determine the location and edge coordinates of the delaminations and defects. It has been found that in order to estimate the depth at which the delamination is, it is appropriate to calculate the phase velocity dispersion curves. The difference in the reconstructed phase velocity dispersion curves between the layers simulated at different depths is estimated to be about 60 m/s. The phase velocity values were compared with the delamination of the second and third layers and a hole drilled at the corresponding depth. The obtained simulation results confirmed that the drilled hole can be used as a defect corresponding to delamination. The WTB sample with a drilled hole of 81 mm was used in the experimental study. Using the proposed algorithm, detailed defect parameters were obtained. The results obtained using simulated and experimental signals indicated that the proposed new algorithm is suitable for the determination of delamination parameters in a multilayer structure
Investigation of crack propagation in locally thermal-treated cast iron /
No full textCyclic failure problems in layered ductile iron are evident in a wide range of elements in transportation and mining equipment and depend on production technology and operating conditions. The aim of this study was to analyze the effect of residual stresses on the behavior of cyclic and static failure. The stress intensity factor, crack initiation, propagation patterns, static tension diagrams, and fracture behavior of compact tension (CT) specimens were determined. The samples used in this study were made from base cast iron, some of which were subjected to a special localized heat treatment. Experimental and analytical methods were used to conduct this study. The experiments were performed using original testing methods that adhered to the American Society for Testing and Materials (ASTM) regulations. The deformations of the partially heat-treated specimens due to residual stresses were determined using the grid method. The limiting stress intensity coefficient and the failure threshold under cyclic loading were determined in accordance with ASTM recommendations for various crack depths and openings. The results show that the heat treatment process readily produces residual stresses of different magnitudes, stress redistribution, different structures, and layer positions. Residual stresses affect the crack initiation and propagation. The stress intensity factor depends on the depth of the crack, the position of the layers, and the magnitude of the residual stresses
Evaluation of factors affecting the used car market.
No full textThis work is dedicated to the investigation of the used car market and the evaluation of its influencing factors. Using statistical data and scientific literature, an initial market analysis is conducted, identifying the development of the used car market, trends, market growth scale, the relevance of this market in Lithuania and worldwide, and the factors affecting the market. The factors identified during the study are categorized into microeconomic and macroeconomic groups
Binary supplementary cementitious material from expanded clay production dust and opoka /
No full textGlobal warming is a critical issue driven largely by the extensive release of greenhouse gases, with the cement industry being one of the biggest contributors to CO2 emissions. A sustainable solution involves the integration of supplementary cementitious materials (SCMs) into cement production, which can mitigate environmental impacts. This study focuses on the effects of binary SCMs, composed of calcined expanded clay kiln dust and opoka, on the hardening and hydration behavior of Portland cement. The analysis used methods such as X-ray diffraction, thermal analysis, calorimetry, and compressive strength testing. The tested dust was thermally activated at 600 °C and the opoka was dried and milled to evaluate its combined influence on the cement properties. Portland cement was substituted with a combination of these two additives. The findings revealed that the two-component mixture exerts a multifaceted impact on the hydration process of Portland cement. The activated expanded clay kiln dust triggers a pozzolanic reaction because of its high reactivity, while the opoka component promotes the development of monocarboaluminates. This binary supplementary cementitious material, derived from opoka and expanded clay kiln dust, proves to be a highly effective substitute, allowing up to 25 wt.% replacement of Portland cement without reducing its compressive strength
Comparison of validity and reliability of manual consensus grading vs. automated AI grading for diabetic retinopathy screening in Oslo, Norway: a cross-sectional pilot study /
No full textBackground: Diabetic retinopathy (DR) is a leading cause of visual impairment worldwide. Manual grading of fundus images is the gold standard in DR screening, although it is time-consuming. Artificial intelligence (AI)-based algorithms offer a faster alternative, though concerns remain about their diagnostic reliability. Methods: A cross-sectional pilot study among patients (≥18 years) with diabetes was established for DR and diabetic macular edema (DME) screening at the Oslo University Hospital (OUH), Department of Ophthalmology, and the Norwegian Association of the Blind and Partially Sighted (NABP). The aim of the study was to evaluate the validity (accuracy, sensitivity, specificity) and reliability (inter-rater agreement) of automated AI-based compared to manual consensus (MC) grading of DR and DME, performed by a multidisciplinary team of healthcare professionals. Grading of DR and DME was performed manually and by EyeArt (Eyenuk) software version v2.1.0, based on the International Clinical Disease Severity Scale (ICDR) for DR. Agreement was measured by Quadratic Weighted Kappa (QWK) and Cohen's Kappa (κ). Sensitivity, specificity, and diagnostic test accuracy (Area Under the Curve (AUC)) were also calculated. Results: A total of 128 individuals (247 eyes) (51 women, 77 men) were included, with a median age of 52.5 years. Prevalence of any vs. referable DR (RDR) was 20.2% vs. 11.7%, while sensitivity was 94.0% vs. 89.7%, specificity was 72.6% was 83.0%, and AUC was 83.5% vs. 86.3%, respectively. DME was detected only in one eye by both methods. Conclusions: AI-based grading offered high sensitivity and acceptable specificity for detecting DR, showing moderate agreement with manual assessments. Such grading may serve as an effective screening tool to support clinical evaluation, while ongoing training of human graders remains essential to ensure high-quality reference standards for accurate diagnostic accuracy and the development of AI algorithms