Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
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TWO-STEP-SCALING APPROACH TO SIZE EFFECT MODELING OF FRACTURE TOUGHNESS IN DBT REGION
No full textThis abstract outlines a strategy designed to offer estimates of fracture toughness using the Weibull cumulative distribution function (CDF) within the ductile to brittle transition (DBT) region. The size-effect modeling encompasses the dynamic interplay between brittle and ductile damage/fracture micromechanisms, which coexist in varying proportions within the DBT region depending on temperature. The inherent variability is tackled by employing a 3P-Weibull CDF. Application of the two-step-scaling (2SS) rest upon two scaling conditions along the CDF abscissa and ordinate (governed by the scaling parameters κ and ξ, respectively). The two scaling premises define in the scaled space the size-independent Weibull scale parameter (η⁎) and the common CDF slope S⁎ (i.e., the common PDF (probability density function) maxima), respectively. These two constancy conditions stem from the power law, intricately connected to Weibull statistics. This physically plausible power-law scaling is influenced by the traditional concept that the stress at the crack tip increases proportionally to the crack length raised to a power, establishing a connection between weakest link theory (WLT) and the Weibull statistics. When employing the 2SS scheme, the Weibull CDF adopts a modified WLT form. Finally, temperature-influenced DBT displays resemblances to behavior controlled by strain rates, particularly in scenarios of extreme loading causing shock waves that trigger nearly simultaneous activation of dominant nucleation kernels—an occurrence also witnessed at cryogenic temperatures
Efficiency Analysis of Fragmentation Warheads Through Advanced Modeling Techniques: Experimental and Numerical Study
No full textThis research investigates the efficiency of fragmentation warheads through a comprehensive comparison of numerical and analytical modeling techniques, supplemented by arena tests. Advanced numerical models developed within Ansys Autodyn, alongside the mean area of effectiveness software, demonstrate robust capabilities in predicting warhead-soft target interactions. Our numerical model is supplemented with a complex analytical model, and the integration of these two approaches addresses a significant research gap by providing a thorough evaluation of warhead efficiency. This integrated model serves as a valuable tool for warhead design and optimization. Validated with experimental results, the simulation outcomes show excellent agreement with the arena test data, confirming the accuracy and reliability of the developed models. This study explicitly addresses key research gaps, including the integration between experimental and numerical analyses, the gap between explosive propulsion and the determination of efficiency, and the need for a comprehensive tool for warhead design and optimization. By exploring various warhead design configurations and initiation methods, the research offers critical insights for optimizing warhead performance. Notably, nonuniform barrel-shaped warheads exhibit a wider fragment distribution, significantly improving weapon-target interactions, particularly at lower impact angles. The study delves into the key parameters influencing warhead performance, providing detailed justifications for their selection and evaluating the sensitivities of these parameters on the results. This analysis underscores the importance of choosing appropriate parameters for accurate predictions and effective warhead design. In addition, the research highlights the original achievements in overcoming major difficulties and challenges in the field, such as integrating complex numerical and analytical models for comprehensive evaluation. The findings contribute to the advancement of fragmentation warhead design, offering designers reliable tools and guidelines to enhance lethality and efficiency in weapon-target engagements. Future work aims to expand the software’s capabilities to include diverse targets, fragment types, and interaction geometries, further advancing the field of fragmentation warhead design. By addressing the gaps and challenges identified, this research paves the way for more effective and optimized warhead configurations, enhancing their overall performance and impact
Cavitation resistance of refractory coatings
No full textIn this study, the resistance to the cavitation effect of three types of refractory samples based on
talc with the addition of 10%, 15% and 20% cordierite was investigated. Talc has a fine structure,
low hygroscopicity, insensitivity to temperature changes, low coefficient of thermal conductivity,
low coefficient of linear thermal expansion, great ability to stick and coat surfaces, good
grindability, low hardness. Cordierite has high refractoriness, high hardness, high density, low
value of dielectric constant, low coefficient of thermal conductivity, low coefficient of linear
thermal expansion, high resistance to thermal shock, relatively high melting temperature with the
possibility of application up to 1380°C, high inertness towards liquid metal. Cordierite was added
in order to improve properties, primarily to increase resistance to the effect of cavitation. The
prepared mixtures of refractory powders were pressed under a pressure of 1 MPa and sintered at
1200°C.To evaluate the cavitation resistance properties of the investigated refractory samples, the
ultrasonic vibration method with a stationary sample was applied. The change in the mass of the
samples as a function of the cavitation time was monitored and the cavitation speed was
determined. The formation and development of damage to the surface of the samples was
monitored using a scanning electron microscope. The mechanism of degradation and resistance to
the effect of cavitation of the tested samples was monitored by measuring the mass loss and
morphological analysis of the pits formed on the surface of the tested samples. Research has
shown that the addition of cordierite in the composition of the tested samples based on talc
significantly improves the properties of resistance to the effect of cavitation
New protective coatings based on pyrophyllite and zirconium silicate
No full textThe paper presents the results of the synthesis and characterization of refractory coatings based
on pyrophyllite (80%) and zirconium silicate (20%) with a binder based on epoxy resin intended
for the protection of metal and non-metal constructions and parts of equipment in industry.
Samples of refractory fillers were subjected to micronizing grinding to the filler grain size:
pyrophyllite 20μm and zirconium silicate 15μm. This achieved a good alignment of the filler
particles with each other. XRD, SEM, and optical microscopy methods were used to characterize
the obtained fillers. The optimal composition of protective coatings and the procedures for their
production were determined by testing. The ultrasonic vibration method with a stationary sample
according to the ASTM G32 standard was used to characterize the obtained coatings. The aim of
the test was to determine the quality of the coating and the possibility of application for the
protection of metal surfaces in conditions of wear, corrosion, cavitation, and elevated
temperatures. The quality of the coating was evaluated based on the value of the cavitation speed
and the analysis of the formation and development of damage to the surface of the samples under
the effect of cavitation. Based on the measurement of mass loss during the test under the effect of
cavitation, the cavitation speed was determined (V = 0.31 mg/min), and the morphology of the
damaged surfaces was analyzed by recording the surface of the coating on a scanning electron
microscope. It was established that mass losses and the formation of pits on the surface of the
coating were small and that the surface damage was 16.5%, which shows that the tested coating
samples have satisfactory cavitation resistance. The tested coatings based on pyrophyllite and
zirconium silicate can be applied to protect metallic surfaces in conditions where moderate
cavitation effects are expected
The Examples of Machine Vision in Agriculture
No full textMachine vision has been involved in the research and
practical application of various phases of agricultural production
since several decades ago. It includes classic image processing
techniques that use different color spaces, as well as hyperspectral
imaging, which can encompass near and far infrared, UV and X-
rays. Apart from classic machine vision methods, the application
of artificial neural networks and machine learning (especially deep
learning) is currently causing considerable improvement in
agricultural research and practice. In this paper, the principles of
the selection of the different machine vision methods in different
agricultural applications is considered. Special attention is paid to
the examples of the applications of convolutional neural networks
in sorting of agricultural products
A flexible programming and verification methodology for reconfigurable CNC woodworking machine
No full textAn advanced flexible programming methodology for CNC woodworking machines was developed. As the research starting base, a three-axis CNC woodworking machine was used. The developed methodology is proposed for programming, simulation, postprocessing, and machining by woodworking machine. This flexible programming method integrates the standard programming based on CAD, CAD/CAM systems, and STEP-NC protocol through different output files, enabling data interoperability during the realization of the machining tasks. The control system for the machine is configured based on the open-architecture software LinuxCNC to verify the flexible programming method and the results obtained. Programming verification was realized by simulation on a configured virtual machine in different programming environments and finally on a virtual machine integrated with the control system. The results obtained from the study were evaluated comparatively
WAVELET TRANSFORM PACKET FOR SIGNAL ANALYSIS USING STANDARD DEVIATION AND SIGNAL SPECTRUM
No full textThe paper presents the research results and the possibilities of applying the standard deviation and amplitude spectrum for chatter vibration detection using the wavelet transform packet as a tool for signal decomposition that was recorded during machining. An analysis of the signal spectrum was additionally performed, which is represented by a spectrogram. Two experiments were performed, where the cutting force signal and acceleration signal, recorded during the machining processes, were analyzed. The recorded signals were decomposed using the wavelet transform packet with the mother wavelet 'db4', and then the standard deviation in the time domain and the amplitude spectrum in the frequency domain were calculated for each level of the decomposed signal. The application of wavelets in this study is intended to enable a better assessment of the quality of standard deviation and amplitude spectrum in chatter vibration detection
Implementation of a cutting forces model through virtual simulation of machining process
No full textThis paper presents the development of a methodology for monitoring the part machining process on CNC machine tools
using a virtual machine model in the MATLAB/Simulink environment. The focus is on monitoring the components of cutting
forces that occur during the milling process. A vertical milling machine was used for model validation. By integrating
the existing cutting force model and the virtual machine model in MATLAB/Simulink, the visualization of real-time cutting
force values, which depend on the change of the current engagement map along the programmed toolpath, is enabled. The
development of the presented simulation environment forms the basis for the implementation of new functions in G-code,
contributing to the stability and optimization of the machining process
Average Velocity Field Downstream Distributions in the Free Turbulent Swirling Jet Generated by the Axial Fan Impeller with Twisted Blades
No full textThis is an extended abstract published in the Booklet of abstracts of the “2nd International Conference on Mathematical Modelling in Mechanics and Engineering”, Belgrade, 12.-14. September 2024