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Experimental characterization and phase-field damage modeling of ductile fracture in AISI 316l
Vladimir Dunić, Nenad Gubeljak, Miroslav Živković, Vladimir Milovanović, Darko Jagarinec, Nenad Djordjevic, 2024, izvirni znanstveni članek

Opis: ) Modeling and characterization of ductile fracture in metals is still a challenging task in the field of computational mechanics. Experimental testing offers specific responses in the form of crack-mouth (CMOD) and crack-tip (CTOD) opening displacement related to applied force or crack growth. The main aim of this paper is to develop a phase-field-based Finite Element Method (FEM) implementation for modeling of ductile fracture in stainless steel. (2) A Phase-Field Damage Model (PFDM) was coupled with von Mises plasticity and a work-densities-based criterion was employed, with a threshold to propose a new relationship between critical fracture energy and critical total strain value. In addition, the threshold value of potential internal energy—which controls damage evolution—is defined from the critical fracture energy. (3) The material properties of AISI 316L steel are determined by a uniaxial tensile test and the Compact Tension (CT) specimen crack growth test. The PFDM model is validated against the experimental results obtained in the fracture toughness characterization test, with the simulation results being within 8% of the experimental measurements.
Ključne besede: phase-field damage modeling, ductile fracture, crack-tip opening displacement, crack growth, resistance curve, finite element method, simulations
Objavljeno v DKUM: 19.09.2024; Ogledov: 0; Prenosov: 9
.pdf Celotno besedilo (3,84 MB)
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3.
Mechanical behaviour of photopolymer cell-size graded triply periodic minimal surface structures at different deformation rates
Yunus Emre Yilmaz, Nejc Novak, Oraib Al-Ketan, Hacer Irem Erten, Ulas Yaman, Anja Mauko, Matej Borovinšek, Miran Ulbin, Matej Vesenjak, Zoran Ren, 2024, izvirni znanstveni članek

Opis: This study investigates how varying cell size affects the mechanical behaviour of photopolymer Triply Periodic Minimal Surfaces (TPMS) under different deformation rates. Diamond, Gyroid, and Primitive TPMS structures with spatially graded cell sizes were tested. Quasi-static experiments measured boundary forces, representing material behaviour, inertia, and deformation mechanisms. Separate studies explored the base material’s behaviour and its response to strain rate, revealing a strength increase with rising strain rate. Ten compression tests identified a critical strain rate of 0.7 s−1 for “Grey Pro” material, indicating a shift in failure susceptibility. X-ray tomography, camera recording, and image correlation techniques observed cell connectivity and non-uniform deformation in TPMS structures. Regions exceeding the critical rate fractured earlier. In Primitive structures, stiffness differences caused collapse after densification of smaller cells at lower rates. The study found increasing collapse initiation stress, plateau stress, densification strain, and specific energy absorption with higher deformation rates below the critical rate for all TPMS structures. However, cell-size graded Primitive structures showed a significant reduction in plateau and specific energy absorption at a 500 mm/min rate.
Ključne besede: cellular materials, triply periodical minimal surface, photopolymer, mechanical properties, strain rate, experimental compressive testing, computer simulations
Objavljeno v DKUM: 22.05.2024; Ogledov: 216; Prenosov: 19
.pdf Celotno besedilo (9,33 MB)
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Numerical simulations of the flow and aerosol dispersion in a violent expiratory event : Outcomes of the “2022 International Computational Fluid Dynamics Challenge on violent expiratory events
Jordi Pallares, Alexandre Fabregat Tomas, Akim Lavrinenko, Hadifathul Akmal bin Norshamsudin, Gabor Janiga, David Frederick Fletcher, Kiao Inthavong, Marina Zasimova, Vladimir Ris, Nikolay Ivanov, Robert Castilla, Pedro Javier Gamez-Montero, Gustavo Raush, Hadrien Calmet, Daniel Mira, Jana Wedel, Mitja Štrakl, Jure Ravnik, Douglas Hector Fontes, Francisco José De Souza, Cristian Marchioli, Salvatore Cito, 2023, izvirni znanstveni članek

Opis: This paper presents and discusses the results of the “2022 International Computational Fluid Dynamics Challenge on violent expiratory events” aimed at assessing the ability of different computational codes and turbulence models to reproduce the flow generated by a rapid prototypical exhalation and the dispersion of the aerosol cloud it produces. Given a common flow configuration, a total of 7 research teams from different countries have performed a total of 11 numerical simulations of the flow dispersion by solving the Unsteady Reynolds Averaged Navier–Stokes (URANS) or using the Large-Eddy Simulations (LES) or hybrid (URANS-LES) techniques. The results of each team have been compared with each other and assessed against a Direct Numerical Simulation (DNS) of the exact same flow. The DNS results are used as reference solution to determine the deviation of each modeling approach. The dispersion of both evaporative and non-evaporative particle clouds has been considered in 12 simulations using URANS and LES. Most of the models predict reasonably well the shape and the horizontal and vertical ranges of the buoyant thermal cloud generated by the warm exhalation into an initially quiescent colder ambient. However, the vertical turbulent mixing is generally underpredicted, especially by the URANS-based simulations, independently of the specific turbulence model used (and only to a lesser extent by LES). In comparison to DNS, both approaches are found to overpredict the horizontal range covered by the small particle cloud that tends to remain afloat within the thermal cloud well after the flow injection has ceased.
Ključne besede: numerical simulations, computational fluid dynamics
Objavljeno v DKUM: 28.03.2024; Ogledov: 456; Prenosov: 458
.pdf Celotno besedilo (8,63 MB)
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6.
Robotic bin-picking : benchmarking robotics grippers with modified YCB object and model set
Tone Lerher, Primož Bencak, Luka Bizjak, Darko Hercog, Boris Jerman, 2023, objavljeni znanstveni prispevek na konferenci

Opis: Robotic bin-picking is increasingly important in the order-picking process in intralogistics. However, many aspects of the robotic bin-picking process (object detection, grasping, manipulation) still require the research community's attention. Established methods are used to test robotic grippers, enabling comparability of the research community's results. This study presents a modified YCB Robotic Gripper Assessment Protocol that was used to evaluate the performance of four robotic grippers (twofingered, vacuum, gecko, and soft gripper). During the testing, 45 objects from the modified YCB Object and Model Set from the packaging categories, tools, small objects, spherical objects, and deformable objects were grasped and manipulated. The results of the robotic gripper evaluation show that while some robotic grippers performed substantially well, there is an expressive grasp success variation over diverse objects. The results indicate that selecting the object grasp point next to selecting the most suitable robotic gripper is critical in successful object grasping. Therefore, we propose grasp point determination using mechanical software simulation with a model of a two-fingered gripper in an ADAMS/MATLAB cosimulation. Performing software simulations for this task can save time and give comparable results to real-world experiments.
Ključne besede: intralogistics, robotic bin-picking, YCB protocol, robotic gripper evaluation, mechanical software simulations, performance analysis
Objavljeno v DKUM: 21.03.2024; Ogledov: 298; Prenosov: 11
.pdf Celotno besedilo (773,38 KB)
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7.
Introduction to the Computer Simulations : Script
Nejc Novak, Matej Borovinšek, Matej Vesenjak, Zoran Ren, 2024

Opis: The script entitled „Introduction to the computer simulations“ in the field of Engineering Computer Simulations is intended as a study aid in the lectures of the courses Engineering Computer Simulations for foreign students at the University of Maribor and for students at Kumamoto University, Japan. It explains all the material that students must master in these subjects, and is consistent with the subject curriculum. The basics of computational simulations, based on the Finite Element Method, are given from the theoretical basics to step-by-step preparation of simple computational models and their analysis in PrePoMax software.
Ključne besede: computational simulations, solid mechanics, Finite Element Method, designing, numerical methods
Objavljeno v DKUM: 12.03.2024; Ogledov: 414; Prenosov: 42
.pdf Celotno besedilo (7,73 MB)
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8.
Vibration fatigue analysis of two different variants of oil suction pipes
Marko Zadravec, Srečko Glodež, Christian Buzzi, Peter Brunnhofer, Martin Leitner, Janez Kramberger, 2024, izvirni znanstveni članek

Opis: In order to reduce the overall mass of the product, an improved variant of the engine oil suction pipe in hybrid design is developed and analysed as part of this paper. The vibration fatigue analysis of a simple all-metal suction pipe and the new hybrid suction pipe variant is derived using computer FEA simulations and vibration measurements on the shaker. The hybrid design of the technical components makes it possible to combine different types of materials in order to achieve the best possible properties and behaviours for the components under the influence of external loads. In our case, we combine a suction pipe made of S235JR mild steel with a 3D-printed polyamide intake funnel featuring a grid designed to prevent particles from entering the engine’s lubrication circuit. This design reduces the mass and shifts the centre of gravity closer to the attachment point of the pipe, as well as to the engine crankcase, which has a positive effect on the values of natural frequencies and vibration amplitudes. The main objective of such a hybrid suction pipe is precisely to reduce vibrations, and thus extend the service life of the components.
Ključne besede: oil suction pipe, vibration fatigue, failure analyses, experimental testing, numerical simulations
Objavljeno v DKUM: 26.02.2024; Ogledov: 641; Prenosov: 639
.pdf Celotno besedilo (6,90 MB)
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9.
Exploring the possibilities of adjusting gensets to NATO requirements
Dejan Barešić, Željko Hederić, Miralem Hadžiselimović, 2019, izvirni znanstveni članek

Opis: Stationary and mobile gensets are used in the Armed Forces of the Republic of Croatia. In this research, priority was given to mobile gensets which have a variety of uses. In addition to being used in the Republic of Croatia, the mobile gensets are also used in international military operations in various modes of operation. Therefore, it is necessary to be very familiar with their characteristics and the possibility of adjusting them to NATO requirements. For the purpose of the adjustment, a test was performed on a P-B40.R1 genset. A model that simulates the genset behaviour with different tested fuels was developed. The investigated genset, together with some others, was introduced into the Armed Forces pursuant to the Product Quality Protocol that was in force during the 1990s. The Protocol did not cover all requirements and recommendations for the genset operation in an international military environment. Therefore, research was conducted, which has resulted in the adjustment of the equipment and in the harmonisation of the Product Quality Protocol with the ISO standard and NATO requirements. When adjusting the materiel, special emphasis is given to defining certain genset types that are able to use the modified F-34 kerosene-type fuel instead of diesel fuel. The F-34 fuel is obtained from kerosene used in aviation; this fuel can be easily obtained in international military operations where the tendency is to use the same type of fuel for airplanes, vehicles, and diesel engine equipment. When F-34 is used as the genset fuel, the quality of the generated electrical energy might be reduced. For the purpose of bringing the output characteristics of the generator within prescribed limits, simulations were performed both with and without the tuning of the regulation parameters.
Ključne besede: genset, F-34 fuel, regulator adjustment, simulations
Objavljeno v DKUM: 22.02.2024; Ogledov: 227; Prenosov: 22
.pdf Celotno besedilo (1,24 MB)
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10.
Cavitation erosion modelling : comparison of different driving pressure approaches
Luka Kevorkijan, Marko Pezdevšek, Ignacijo Biluš, Gorazd Hren, 2023, izvirni znanstveni članek

Opis: In this paper we compared different driving pressure approaches to calculate the cavitation potential energy from a source, which is transferred to a surface. The first approach used the reference pressure, the second approach used the pressure calculated at each timestep with no averaging, the third approach used the averaged pressure values from all timesteps included in one shedding cycle, and the last approach used pressure values from the steady state simulations results. The results show that for all formulations the averaged pressure values and steady state pressure values give similar results in terms of mean potential power distribution on the hydrofoil surface as in absolute values. The reference pressure approach gave similar results for the derivative and divergence formulation while for the source term the mean potential power distribution on the hydrofoil surface differs and the maximums were near the leading edge. The approach where we used no pressure averaging gave adequate results in terms of mean potential power distribution but differs from other approaches in absolute values which were considerably lower for all potential power formulations.
Ključne besede: cavitation, erosion potentional, driving pressure, numerical simulations
Objavljeno v DKUM: 21.02.2024; Ogledov: 400; Prenosov: 26
.pdf Celotno besedilo (796,29 KB)
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