Using the fracture mechanics parameters in assessment of integrity of rotary equipment

In this paper is presented the principle of application of fracture mechanics parameters in determining the integrity of rotary equipment. The behavior of rotary equipment depends on presence of cracks and basically determines the integrity and life of such equipment. The locations of stress concentration (i.e. radius changes) represent a particular problem in rotary equipment, and they are the most suitable places for the occurrence of microcracks i.e. cracks due to fatigue load. This problem is most common in the shaft of relatively large dimensions, for example, turbine shafts in hydropower plants made of high-strength carbon steel with relatively low fracture toughness, and relatively low resistance to crack formation and growth. Having in mind that rotary equipment represents the great risk in the exploitation, whose occasional failures often had severe consequences, it is necessary detail study of their integrity. For this purpose, it is necessary application of parameters of linear-elastic fracture mechanics, such as stress intensity factor, which range defines the rate of crack growth (Parisian law), and its critical value (fracture toughness) determines the critical crack length. The procedures for determining the critical crack length will be described using the fracture mechanics parameters

Development and optimization of aluminum nanocomposites for production of tribological elements

Rezime: Pri razvoju i proizvodnji novih materijala i elemenata eksperiment ima značajnu ulogu. Pristup eksperimentalnom istraživanju ne može se zamisliti bez upotrebe dizajna eksperimenta čijom primenom se pristupa sistematskom načinu planiranja eksperimenta, izvođenju i interpretaciji rezultata eksperimenata. Za potrebe ovog rada su razvijeni, a u radu su analizirani novi nanokompoziti sa A356 osnovom ojačani SiC i Al2O3 nanočesticama različitih veličina i sadržaja. U okviru ispitivanja određene su i prikazane fizičke i mehaničke karakteristike nanokompozita. U radu su sprovedena tribološka ispitivanja primenom dizajna eksperimenta za prvu seriju materijala koji do trenutka proizvodnje nisu bili predmet ranijih istraživanja. Nanokompoziti su proizvedeni sa malim masenim sadržajem ojačavajućih nanočestica primenom modifikovanog kompokasting procesa. Ostvareni eksperimentalni rezultati prvom serijom materijala ukazali su na pravac i tok razvoja nanokompozita sa novim sadržajem ojačavača. Druga faza istraživanja nanokompozita je usmerena na tribološka ispitivanja jer se prvom serijom materijala dokazalo da nije ostvareno značajno poboljšanje u mehaničkim i tribološkim karakteristikama nanokompozita. Izvršena je analiza pohabanih površina nanokompozita što je od velikog značaja za praktičnu primenu ovih materijala. Primenom optimizacionih metoda izvršena je višekriterijumska optimizacija i određena optimalna kombinacija faktora kojom se postižu najbolje karakteristike nanokompozita. Na osnovu eksperimentalnih istraživanja ostvarenih u ovoj disertaciji može se zaključiti da su ostvarena poboljšanja u mehaničkim i tribološkim karakteristikama nanokompozita u poređenju sa osnovnom legurom. Područje primene aluminijumskih nanokompozita neprekidno se širi s obzirom na kombinaciju svojstava koja se mogu postići dodavanjem različitih ojačavača. Dobijene karakteristike razvijenih nanokompozita omogućavaju njihovo korišćenje pri modeliranju i naponsku analizu različitih mašinskih elemenata u CAD softveru. Izvršena je numerička analiza zupčastih parova i ustanovljeno je da se maksimalne vrednosti ekvivalentnog napona javljaju u podnožju zubaca spregnutih zupčanika. Primenom nanokompozita za izradu zupčastog para može se postići veći prenos snage u odnosu na zupčasti par izrađen od osnovne legure, zatim smanjuje se pojava inicijalnih prslina, masa prenosnika, i nivo buke i vibracije u zupčastim prenosnicima manjih snaga, a povećava se njihova otpornost na habanje.Abstract: The experiment has a significant role in the development and production of new materials and machine elements. An approach to experimental research cannot be imagined without design of experiment usage, which repesents a systematic way of planning an experiment, performing and interpreting the experiments results. For the purposes of this thesis, new nanocomposites with A356 base reinforced with SiC and Al2O3 nanoparticles of different sizes and contents were developed and analyzed. Within this research, the physical and mechanical characteristics of nanocomposites were determined and presented. Tribological tests were performed using the design of experiment for the first series of materials that were not the subject of previous research, in today’s literature sources, until the time of production. Nanocomposites were produced with a low mass content of reinforcing nanoparticles using a modified compocasting process. The achieved experimental results with the first series of materials indicated the direction and course of development of nanocomposites with a new content of reinforcements. The second phase of nanocomposite research is focused on tribological tests because the first series of materials didn’t proved the significant improvement in the mechanical and tribological characteristics of nanocomposites is achieved. The analysis of worn surfaces of nanocomposites was performed, which is of great importance for the practical application of these materials. By applying optimization methods, multicriteria optimization was performed and the optimal combination of factors was determined for which gives the nanocomposites of the best characteristics. Based on the experimental research achieved in this dissertation, it can be concluded that improvements have been made both in the mechanical and tribological characteristics of nanocomposites compared to the base alloy. Application field of aluminum nanocomposites is constantly expanding due to the combination of properties that can be achieved by adding different reinforcements. The obtained characteristics of the developed nanocomposites enable their usage in modeling and stress analysis of various machine elements in CAD software. Stress analysis of gear pairs was performed and it was concluded that the maximum values of equivalent stress occur at the base of the teeth of the coupled gears. The use of nanocomposites for the production of gear pair can achieve a higher power transmission compared to the gear pair made of base alloy, then reduces the occurrence of initial cracks, gear mass, and noise and vibration levels in gears of lower power, and increases their wear resistance

Object Detection and Tracking in Cooperative Multi-Robot Transportation

Contemporary manufacturing systems imply the utilization of autonomous robotic systems, mainly for the execution of manipulation and transportation tasks. With a goal to reduce transportation and manipulation time, improve efficiency, and achieve flexibility of intelligent manufacturing systems, two or more intelligent mobile robots can be exploited. Such multi-robot systems require coordination and some level of communication between heterogeneous or homogeneous robotic systems. In this paper, we propose the utilization of two heterogeneous robotic systems, original intelligent mobile robots RAICO (Robot with Artificial Intelligence based COgnition) and DOMINO (Deep learning-based Omnidirectional Mobile robot with Intelligent cOntrol), for transportation tasks within a laboratory model of a manufacturing environment. In order to reach an adequate cooperation level and avoid collision while moving along predefined paths, our own developed intelligent mobile robots RAICO and DOMINO will communicate their current poses, and object detection and tracking system is developed. A stereo vision system equipped with two parallelly placed industrial-grade cameras is used for image acquisition, while convolutional neural networks are utilized for object detection, classification, and tracking. The proposed object detection and tracking system enables real-time tracking of another mobile robot within the same manufacturing environment. Furthermore, continuous information about mobile robot poses and the size of the bounding box generated by the convolutional neural network in the process of detection of another mobile robot is used for estimation of object movement and collision avoidance. Mobile robot localization through time is performed based on kinematic models of two intelligent mobile robots, and conducted experiments within a laboratory model of manufacturing environment confirm the applicability of the proposed framework for object detection and collision avoidance

Image Clasiffication Based on Convolutional Neural Networks

Razvoj tehnologija obrade slike otvara nove perspektive i doprinosi povećanju produktivnosti i kvaliteta širokog spektra industrijskih aplikacija. Klasifikacija slike spada u grupu najkompleksnijih procesa u oblasti digitalne obrade slike, a predstavlja dodeljivanje klase (iz prethodno definisanog skupa) slici koja se posmatra. U okviru ovog rada, klasifikacija slike koristi se u cilju određivanja orijentacije prizmatičnog dela. Predložena metoda klasifikacije zasnovana je na primeni konvolucionih neuronskih mreža (CNN - engl. Convolutional Neural Network). U zavisnosti od vrste ulaza koji se dovodi CNN-u, razmatrana su dva pristupa: prvi pristup podrazumeva preprocesiranje slike i izdvajanje obeležja baziranih na detekciji ivica; dok drugi pristup koristi sirove podatke (bez prethodno izdvojenih obeležja). Metod klasifikacije testiran je u realnom vremenu na eksperimentalnoj instalaciji baziranoj na Raspberry Pi platformi