Modelování indentačních testů metodou konečných prvků a aplikace modelu neuronových sítí

The diploma work investigates the Instrumented Indentation Test (IIT) modelling with Finite Element Method (FEM) and Neural Network (NN). The final goal is to create a NN that can evaluate the experimental data from a physical IIT in such a way to directly calibrate a suitable plasticity model. The study is conducted on an austenitic stainless steel SS304L which is a challenge for IIT. To achieve the goal, IIT is performed on a SS304L specimen to obtain the indenting depth versus the reaction force the material exerts on the indentation ball. Besides, tensile tests with Digital Image Correlation (DIC) on the same material are performed to obtain the tensile stress-strain curve, from which parameters of a constitutive model can be identified. The results from IIT and tensile test are then used to establish a FEM model. Using the FEM model, several IITs can be simulated to create a dataset for NN training in the range of austenitic steels. This dataset is fed into a NN and numerical experiments are done to find an optimal architecture for the final goal. The thesis proposes a framework and proves its feasibility considering Armstrong-Frederick hardening model with three parameters. All the data and identified challenges are reported and discussed.Diplomová práce zkoumá modelování instrumentovaného indentačního testu (IIT) s využitím metody konečných prvků (MKP) a neuronových sítí (NN). Cílem práce je vytvořit NN, která bude schopna vyhodnotit experimentální data z realizovaného IIT takovým způsobem, aby přímo kalibrovala vhodný model plasticity. Studie je prováděna na austenitické nerezové oceli SS304L, která představuje výzvu pro IIT. K dosažení cíle je proveden IIT na vzorku SS304L k získání závislosti hloubky zatlačení na reakční síle, kterou materiál vyvíjí na vtlačovanou kuličku. Kromě toho jsou na stejném materiálu provedeny tahové zkoušky s digitální korelací obrazu (DIC) k získání tahové deformační křivky, z které lze identifikovat parametry konstitutivního modelu. Výsledky z IIT a tahové zkoušky jsou poté použity k vytvoření MKP modelu. S využitím FEM modelu lze simulovat několik IIT a vytvořit tak soubor dat pro trénování NN v rozsahu austenitických ocelí. Tento soubor dat je vložen do NN. K nalezení optimální architektury pro dosažení finálního cíle jsou provedeny numerické experimenty. Práce navrhuje rámec a dokazuje jeho proveditelnost při uvažování Armstrong-Frederickova modelu zpevnění se třemi parametry. Všechna data a zjištěné výzvy jsou zaznamenány a diskutovány.330 - Katedra aplikované mechanikyvýborn

Outage performance analysis of non-orthogonal multiple access systems with RF energy harvesting

Non-orthogonal multiple access (NOMA) has drawn enormous attention from the research community as a promising technology for future wireless communications with increasing demands of capacity and throughput. Especially, in the light of fifth-generation (5G) communication where multiple internet-of-things (IoT) devices are connected, the application of NOMA to indoor wireless networks has become more interesting to study. In view of this, we investigate the NOMA technique in energy harvesting (EH) half-duplex (HD) decode-and-forward (DF) power-splitting relaying (PSR) networks over indoor scenarios which are characterized by log-normal fading channels. The system performance of such networks is evaluated in terms of outage probability (OP) and total throughput for delay-limited transmission mode whose expressions are derived herein. In general, we can see in details how different system parameters affect such networks thanks to the results from Monte Carlo simulations. For illustrating the accuracy of our analytical results, we plot them along with the theoretical ones for comparison

Outage probability analysis for hybrid TSR-PSR based SWIPT systems over log-normal fading channels

Employing simultaneous information and power transfer (SWIPT) technology in cooperative relaying networks has drawn considerable attention from the research community. We can find several studies that focus on Rayleigh and Nakagami-m fading channels, which are used to model outdoor scenarios. Differing itself from several existing studies, this study is conducted in the context of indoor scenario modelled by log-normal fading channels. Specifically, we investigate a so-called hybrid time switching relaying (TSR)-power splitting relaying (PSR) protocol in an energy-constrained cooperative amplify-and-forward (AF) relaying network. We evaluate the system performance with outage probability (OP) by analytically expressing and simulating it with Monte Carlo method. The impact of power-splitting (PS), time-switching (TS) and signal-to-noise ratio (SNR) on the OP was as well investigated. Subsequently, the system performance of TSR, PSR and hybrid TSR-PSR schemes were compared. The simulation results are relatively accurate because they align well with the theory

Outage and bit error probability analysis in energy harvesting wireless cooperative networks

This study focuses on a wireless powered cooperative communication network (WPCCN), which includes a hybrid access point (HAP), a source and a relay. The considered source and relay are installed without embedded energy supply (EES), thus are dependent on energy harvested from signals from the HAP to power their cooperative information transmission (IT). Taking inspiration from this, the author group investigates into a harvest-then-cooperate (HTC) protocol, whereas the source and the relay first harvest the energy from the AP in a downlink (DL) and then collaboratively work in uplink (UL) for IT of the source. For careful evaluation of the system performance, derivations of the approximate closed-form expression of the outage probability (OP) and an average bit error probability ( ABER) for the HTC protocol over Rayleigh fading channels are done. Lastly, the author group performs Monte-Carlo simulations to reassure the numerical results they obtained.Web of Science255746

Residual stress build-up in aluminum parts fabricated with SLM technology using the bridge curvature method

In metal 3D printing with Selective Laser Melting (SLM) technology, due to large thermal gradients, the residual stress (RS) distribution is complicated to predict and control. RS can distort the shape of the components, causing severe failures in fabrication or functionality. Thus, several research papers have attempted to quantify the RS by designing geometries that distort in a predictable manner, including the Bridge Curvature Method (BCM). Being different from the existing literature, this paper provides a new perspective of the RS build-up in aluminum parts produced with SLM using a combination of experiments and simulations. In particular, the bridge samples are printed with AlSi10Mg, of which the printing process and the RS distribution are experimentally assessed with the Hole Drilling Method (HDM) and simulated using ANSYS and Simufact Additive. Subsequently, on the basis of the findings, suggestions for improvements to the BCM are made. Throughout the assessment of BCM, readers can gain insights on how RS is built-up in metallic 3D-printed components, some available tools, and their suitability for RS prediction. These are essential for practitioners to improve the precision and functionality of SLM parts should any post-subtractive or additive manufacturing processes be employed.Web of Science1517art. no. 605

Comprehensive view of topological optimization scooter frame design and manufacturing

The combination of topology optimization (TO) and 3D printing has revolutionized the way components are designed and fabricated. In view of this, this manuscript presents a TO workflow considering the frame of a scooter. In particular, TO is employed to redesign the scooter frame based on a commercial one. The topologically optimized frame is then fabricated with stainless steel 316L utilizing the selective laser melting (SLM) method. In particular, technical obstacles encountered during the process and according solutions are recorded. Given the herein notes, readers who are working with the two technologies can anticipate the technical problems and deliver more effective solutions should any of them arise.Web of Science137art. no. 120

Abrasive surface finishing on SLM 316L parts fabricated with recycled powder

Improving the surface roughness quality of 3D printed components, especially metallic ones, which are fabricated from the selective laser melting (SLM) method, has drawn enormous attention from the research community. It should be noted that various studies on this topic have reported that precise surface roughness results can be obtained with various techniques that are indeed not cost-effective. Differing itself from these studies, this manuscript investigates an economical solution for fabricating and surface treating SLM components. Specifically, the inspected specimens were printed with recycled 316L stainless steel powder and treated solely with two abrasive surface finishing methods. In the manuscript, two scanning strategies namely meander and stripes, and three types of surfaces were investigated. Subsequently, their 2D and 3D surface roughness results were elaborated. After the proposed herein abrasive treatment, 3D surface roughness arithmetical mean height of a surface (Sa) value of 0.9 mu m can be achieved.Web of Science116art. no. 286

Topology optimization of the clutch lever manufactured by additive manufacturing

This article aims to review a redesign approach of a student racing car’s clutch lever component, which was topologically optimized and manufactured by Additive Manufacturing (AM). Finite Element Method (FEM) analysis was conducted before and after a Topology Optimization (TO) process in order to achieve equivalent stiffness and the desired safety factor for the optimized part. The redesigned clutch lever was manufactured by using AM–Selective Laser Melting (SLM) and printed from powdered aluminum alloy AlSi10Mg. The final evaluation of the study deals with the experimental test and comparison of the redesigned clutch lever with the existing part which was used in the previous racing car. Using TO as a main redesign tool and AM brought significant changes to the optimized part, especially the following: reduced mass of the component (10%), increased stiffness, kept safety factor above the 3.0 value and ensured the more aesthetic design and a good surface quality. Moreover, using TO and AM gave the opportunity to consolidate multi-part assembly into a single component manufactured by one manufacturing process that reduced the production time. The experimental results justified the simulation results and proved that even though the applied load was almost 1.5× higher than the assumed one, the maximum von Mises stress on the component was still below the yield limit of 220 MPa.Web of Science169art. no. 351

Návrh a numerická simulace tlumiče nárazu

The main objective of this thesis is develop an Impact Attenuator for the car racing Formula Student competition by designing and performing Crash test simulation numerically. The thesis studies into the rules and requirements of Formula Student for the car design with the emphasis on the Impact Attenuator. A number of designs made of Aluminum Honeycomb material are proposed and tested using Finite Element Method. The data from the simulations is then evaluated and recommendations for further works are stated.The main objective of this thesis is develop an Impact Attenuator for the car racing Formula Student competition by designing and performing Crash test simulation numerically. The thesis studies into the rules and requirements of Formula Student for the car design with the emphasis on the Impact Attenuator. A number of designs made of Aluminum Honeycomb material are proposed and tested using Finite Element Method. The data from the simulations is then evaluated and recommendations for further works are stated.330 - Katedra aplikované mechanikyvýborn

SCFF23 : From Smart City to Smart Factory for Sustainable Future : conceptual framework, scenarios and multidiscipline perspectives : International Conference

The international conference SCFF23 is organized for researchers, experts, and students to share their vision about the future under the concept of “From Smart City to Smart Factory for Sustainable Future” from multidiscipline perspectives. The aim of the conference is to provide an opportunity for participants with different expertise to meet up and share their knowledge, disruptive ideas, solutions to existing problems that hinder us from moving forward to more modern and sustainable life using technologies. The conference facilitates mutual exchanges of experiences and establishment of long-lasting international cooperations. The scope of the conference includes discussions about Innovative and Sustainable technologies, solutions, and frameworks for applications of state-of-the-art technologies to Smart City and Smart Factory.Ostrav