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1

Automatic Crack Detection Using Weakly Supervised Semantic Segmentation Network and Mixed-Label Training Strategy

Zhang Shuyuan, Xu Hongli, Zhu Xiaoran, Xie Lipeng

Foundations of Computing and Decision Sciences

|

2024

|

Vol. 49, No. 1

95--118

EN

Automatic crack detection in construction facilities is a challenging yet crucial task. However, existing deep learning (DL)-based semantic segmentation methods for this field are based on fully supervised learning models and pixel-level manual annotation, which are time-consuming and labor-intensive. To solve this problem, this paper proposes a novel crack semantic segmentation network using weakly supervised approach and mixed-label training strategy. Firstly, an image patch-level classifier of crack is trained to generate a coarse localization map for automatic pseudo-labeling of cracks combined with a thresholding-based method. Then, we integrated the pseudo-annotated with manual-annotated samples with a ratio of 4:1 to train the crack segmentation network with a mixed-label training strategy, in which the manual labels were assigned with a higher weight value. The experimental data on two public datasets demonstrate that our proposed method achieves a comparable accuracy with the fully supervised methods, reducing over 65% of the manual annotation workload.

2

Wykrywanie pęknięć hartowniczych w stali łożyskowej 100Cr6 metodą prądów wirowych

Kondej Adam, Jończyk Sylwester, Lasota Piotr

Welding Technology Review

|

2023

|

R. 95

87--93

PL

W artykule opisano wyniki badań w zakresie identyfikacji i lokalizacji pęknięć hartowniczych w stali łożyskowej 100Cr6 z wykorzystaniem autorskiego urządzenia kontrolno-pomiarowego do badań nieniszczących metodą prądów wirowych Wirotest M2 oraz automatycznego stanowiska AutoWir-S1. Do badań zastosowano głowicę stykową o częstotliwości 861 kHz. System rejestrował zmiany amplitudy napięcia oraz częstotliwości rezonansowej. Wyraźny spadek wartości obydwu parametrów wskazywał na obecność nieciągłości. Efekt krawędziowy powodował wzrost amplitudy napięcia oraz spadek częstotliwości, jednakże zmiany te nie wpłynęły na detekcję pęknięć. Najmniejsze wykryte pęknięcie charakteryzowało się maksymalną szerokością około 20 μm i było niewidoczne okiem nieuzbrojonym. Uzyskane wykresy powierzchniowe jednoznacznie obrazują przebieg oraz lokalizację poszczególnych nieciągłości.

EN

The article describes the results of research on the identification and localization of quenching cracks in 100Cr6 bearing steel using a proprietary non-destructive testing device based on the eddy current method called Wirotest M2 and an automatic stand AutoWir-S1. A surface probe with a frequency of 861 kHz was used for the tests. The system recorded changes in voltage amplitude and resonant frequency. A significant decrease in both parameters indicated the presence of discontinuities. The edge effect caused an increase in voltage amplitude and a decrease in frequency, but these changes did not affect crack detection. The smallest detected crack had a maximum width of about 20 μm and was invisible by the unaided eye. The obtained surface charts clearly illustrate the course and localization of individual discontinuities.

3

Coda wave interferometry for monitoring the fracture process of concrete beams under bending test

Knak Magdalena, Wojtczak Erwin, Rucka Magdalena

Bulletin of the Polish Academy of Sciences. Technical Sciences

|

2023

|

Vol. 71, nr 3

art. no. e144118

EN

Early detection of damage is necessary for the safe and reliable use of civil engineering structures made of concrete. Recently, the identification of micro-cracks in concrete has become an area of growing interest, especially when it comes to using wave-based techniques. In this paper, a non-destructive testing approach for the characterization of the fracture process was presented. Experimental tests were performed on concrete beams subjected to mechanical degradation in a 3-point bending test. Ultrasonic waves were registered on a specimen surface by piezoelectric transducers located at several points. Then, the signals were processed taking advantage of wave scattering due to micro-crack disturbances. For early-stage damage detection, coda wave interferometry was used. The novelty of the work concerns the application of the complex decorrelation matrix and the moving reference trace approach for better distinguishment of sensors located in different parts of a crack zone. To enhance coda wave-based damage identification results, optical imaging of crack development was performed by means of digital image correlation measurement. The results obtained showed that the coda wave interferometry technique can be successfully used as a quantitative measure of changes in the structure of concrete. The results also indicated that the course of decorrelation coefficient curves enabled the identification of three stages during degradation, and it depended on the location of acquisition points versus the crack zone.

4

A study on microbial self-healing concrete using expanded perlite

Amjad Usama Bin, Siddique Muhammad Shahid, Shahid Taha, Ahmed Iftikhar, Alogla Saleh M., Ahmad Jawad

Bulletin of the Polish Academy of Sciences. Technical Sciences

|

2023

|

Vol. 71, nr 5

art. no. e146475

EN

The increasing concern for the safety and sustainability of structures is calling for the development of smart self-healing materials and preventive repair methods. This research is carried out to investigate the extent of self-healing in normal-strength concrete by using Sporosarcina aquimarina – NCCP-2716 immobilized in expanded perlite (EP) as the carrier. The efficacy of crack-healing was also tested using two alternative self-healing techniques, i.e. expanded perlite (EP) concrete and direct introduction of bacteria in concrete. A bacterial solution was embedded in EP and calcium lactate pentahydrate was added as the nutrient. Experiments revealed that specimens containing EP-immobilized bacteria had the most effective crack-healing. After 28 days of healing, the values of completely healed crack widths were up to 0.78 mm, which is higher than the 0.5 mm value for specimens with the direct addition of bacteria. The specimen showed a significant self-healing phenomenon caused by substantial calcite precipitation by bacteria. The induced cracks were observed to be repaired autonomously by the calcite produced by the bacteria without any adverse effect on strength. The results of this research could provide a scientific foundation for the use of expanded perlite as a novel microbe carrier and Sporosarcina aquimarina as a potential microbe in bacteria-based self-healing concrete.

5

Industrial Application of Surface Crack Detection in Sheet Metal Stamping Using Shift-and-Add Speckle Imaging

Świłło Sławomir, Cacko Robert

Advances in Science and Technology. Research Journal

|

2023

|

Vol. 17, no 5

220--235

EN

The sheet metal surface crack detection during manufacturing is an essential issue because of both the product quality and process productivity. Development of solutions to eliminate defective products during the metal forming process is crucial for the smooth production and for developing an appropriate tool geometry in the initial phase of the process. Currently, the methods of surface crack detection used in the industry are mostly related to visual inspection. These are methods that require operators of industrial facilities considerable attention and effort to capture emerging discontinuities on the sheet metal surface. Also, this situation results increase in the duration of the specific operations of stamping and significantly reduces productivity. Therefore, an industrial application of a non-contact laser technique that simultaneously provides the results of the speckle imaging is presented. The authors demonstrate a specially designed machine vision system along with experimental tools for the stamping operation. Proposed solution uses the phenomenon of speckle pattern that appears in the image of the investigated sheet surface produced by the laser beam emission. In this method, coherent laser light is emitted to the surface, where a speckle pattern is generated due to scatter reflection from the sheet metal surface and then, shift-and-add technique and image processing is applied. The proposed measurement technique consists, initially, of making a sequence of images of the tested object for the moving surface of the sheet. Secondly, the object's displacement quantity in each image is determined, and the position is corrected. The test object in each image is moved to the starting position, and all images are superimposed. It allows to obtain a high-quality image with visible surface defects. Finally, the dynamically changing speckle pattern intensity is evaluated using Gaussian-of-Laplacian edge detection to investigate a surface crack location due to the surface discontinues and light scattering. This process is recommended for machine vision imaging of distant objects, which works well in industrial conditions as well as online analysis. Also, from the speckle size measurement, an experimental procedure is employed to verify the best condition for vision system resolution.

6

Advanced communication system: for the survey of rail tracks to improve safety of rail transportation

Yadav A. K., Szpytko J.

Journal of KONES

|

2017

|

Vol. 24, No. 2

315--322

EN

Railway transportation is a backbone of any country for transporting people and cargo. At present Indian railway is the largest network in Asia. So that safety is always big concern. Here in this article low cost railway track surveillance and monitoring system is proposed which will identify drastic and minor changes into the railway track. It consist a high-resolution CMOS camera mounted on robot. It is designed like: it can easily roll on railway track. In case of any obstacle or train coming on track, robot folds itself and provides a path to pass the train. It is controlled by wireless control system, which can be operated from remote location or station. For accurate results, a live video streaming is done to the remote station for future references and comparison of results. On the assembly of robot, a GPS (Global Positioning System) is mounted to know the location of robot on the rail track. An obstacle detector sensor is also mounted on the front of the robot to detect any coming obstacle. In this article ultrasonic method (Non-Destructive Method) is also explained to detects presence of cracks on rail track in real time. Overall, power utilization of this system will be very low by operating this system by solar power. Signal processing and wireless communication system is used as technology, which cuts off the overall cost. By implementing this surveillance system, we can improve the safety parameters of Indian railway by minimizing the errors and reducing the time and cost.

7

A method of fatigue strength testing of wheel rim fragments at the production process stage

Rychlik A., Kozubel W.

Journal of KONES

|

2016

|

Vol. 23, No. 1

289--296

EN

The paper describes a method of accelerated fatigue strength testing of elements with the use of inertia forces. The presented test method is dedicated to the selected materials, constructions and joints used in the production of wheel rims for motor vehicles, tractors and special vehicles. The analysis of the fatigue process in machinery components and the evaluation of its state in terms of product quality control can be divided into: quasi-static analysis, resonance analysis, and the one generally used today – virtual fatigue analysis. Virtual analysis is applicable to new components and/or structures released to production according to the concept based on the interaction of theoretical and working models in the context of service life prediction. The purpose of this paper is to present a tool for examination, and a method allowing the identification of the beginning of the fatigue cracking process in structural components. The demonstrated method belongs to the destructive testing group. Cracking process analysis and identification is based on a multiparameter analysis of vibration signals in the amplitude-frequency domain. Inertia force is used in the test piece destruction process. The discussed method is applicable to a wide range of fatigue tests for structural components in the quality control process for materials and combinations of these materials. The method has been employed in the production of low-speed and special machinery wheel rims by Polkar Warmia Ltd.

8

Opracowanie techniki wykrywania pęknięć podczas kształtowania przemysłowego blach

Świłło S., Cacko R., Czyżewski P., Chorzępa W.

Hutnik, Wiadomości Hutnicze

|

2016

|

Vol. 83, nr 1

8--12

PL

Przedstawiona został aplikacja przemysłowa detekcji pęknięć podczas kształtowania blach karoseryjnych. Zaproponowane przez autorów rozwiązanie wykorzystuje zjawisko optyczne plamkowania powstałe na badanej powierzchni w wyniku emisji wiązki światła laserowego. Rozpoznawanie obrazu pęknięcia odbywa się poprzez porównanie obrazów z defektem i bez defektu. Realizacja pomiarów odbywa się z wykorzystaniem systemu wizyjnego umożliwiającego transmisję zarejestrowanego obrazu i dalszą jego obróbkę numeryczną. Cały proces rejestracji obrazu i jego analizy odbywa się w czasie rzeczywistym dzięki zastosowaniu szybkiego procesu obróbki obrazu przetwarzanego w środowisku Matlab. Do tych celów został opracowany specjalny system wizyjny wraz ze stanowiskiem modelowym do testowania zaproponowanego rozwiązania. Na zaprojektowanym stanowisku badaniom poddawany jest na przemian wyrób wadliwy i prawidłowy z odpowiednio zaplanowanym sposobem pomiaru symulującym realizację rzeczywistych warunków procesu kształtowania plastycznego.

EN

The industrial application of crack detection in stamped auto-parts is presented. Solution proposed by the authors uses the phenomenon of speckle pattern occuring on the investigated surface by the laser beam emission. Crack image recognition is achieved through a comparison of two images: one with the defect and the other without it. The measurements are performed using a vision system allowing for transmission of the recorded image and further its numerical processing. The whole process of image acquisition and analysis is performed in real time through the image processing in Matlab software environment. For these purposes a special vision system along with the test rig allowing to test the proposed solution have been developed. On the designed measuring stack-up alternately the failed and correct components are measured with appropriately planned schedule simulating the real process of metal/component forming.

9

Bi-axial Neutral Axis Tracking for Crack Detection in Wind Turbine Towers

Soman R., Malinowski P., Ostachowicz W.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2015

|

Vol. 19, No 3

223--235

EN

This work concentrates on Structural Health Monitoring (SHM) of a wind turbine tower. The paper investigates the use of a decision level data fusion based on bi-axial tracking of change in the neutral axis (NA) position for damage detection in wind turbine towers. A discrete Kalman Filter (KF) is employed for the estimation of the NA in the presence of measurement noise from the strain sensors. The KF allows data fusion from the strain sensors and the yaw mechanism for the accurate estimation of the NA. Any change in the NA position may be used for detecting and locating the damage. The tan inverse of the ratio of the change in the NA along two perpendicular axes is taken and used for the localization. The study was carried out on a simulated finite element (FE) model of a wind turbine tower with a surface crack. The sensitivity studies carried out on the structure in terms of different crack sizes, crack locations and crack orientations indicate that the methodology is robust enough to detect the crack under different operational loading conditions.

10

Technologia EMAT w zastosowaniu do diagnostyki gazociągów wysokiego ciśnienia

Witek M., Szałęga M.

Gaz, Woda i Technika Sanitarna

|

2015

|

Nr 11

387--392

EN

Gas transmission pipelines are commonly inspected by in-line tools equipped with sensors for nondestructive testing. EMAT inspection technology, designed for detection of stress corrosion cracking, is also sensitive to areas of disbanded coating and other crack-like features. An electromagnetic acoustic transducer is used for contactless generating and receiving waves using electromagnetic phenomena. Second part of this publication presents a summary of calculation of the high pressure pipeline with wall defect like longitudinal semi-elliptical crack. The calculations are based on standard BS 7910:2005, which describes the influence of cracks on the pipeline maximum operating pressure.

PL

Gazociągi wysokiego ciśnienie są powszechnie badane przez tłoki do inspekcji wewnętrznej, wyposażone w czujniki służące do diagnostyki stanu ścianki gazociągu. Technologię EMAT zaprojektowano w celu wykrywania skutków korozji naprężeniowej, odspojeń zewnętrznej powłoki izolacyjnej, a także pęknięć materiału stalowego. Elektromagnetyczny przetwornik akustyczny, służy do bezkontaktowego tworzenia i odbioru fal powstałych w skutek zjawisk elektromagnetycznych. W drugiej części publikacji zostały przedstawione obliczenia gazociągu wysokiego ciśnienia z defektem typu pęknięcie wzdłużne półeliptyczne ścianki. Zastosowano algorytm obliczeniowy wg standardu BS 7910:2005 dla oceny istotności przykładowych defektów, pozwalający stwierdzić wpływ pęknięcia na maksymalne ciśnienie robocze gazociągu.

11

Application of resistive ladder sensor for detection and quantification of fatigue cracks in aircraft structure

Kurnyta A.

Pomiary Automatyka Robotyka

|

2013

|

R. 17, nr 2

558-563

EN

The paper presents preliminary laboratory verification of resistive ladder sensor application. The sensor, which is akin to foil strain gage, can be used for detection and length quantification of fatigue cracks. Special measurement circuit for data acquisition was developed and test specimens were prepared. Afterwards, laboratory tests on fatigue-testing machine were elaborated to explore utility and reliability of proposed method for crack detection. After analysis of acquired data, some observation and conclusion were drawn, especially about electronic circuit. Modifications in measurement system were described and simulated in Micro-Cap - an electronic circuit analysis program. The paper is concluded with summary from laboratory tests and simulations.

PL

W artykule przedstawiono wstępne badania laboratoryjne aplikacji rezystancyjnego czujnika drabinkowego. Czujnik, podobny do tensometru foliowego, może zostać użyty do wykrywania i określania długości pęknięć zmęczeniowych. Zaprojektowano specjalny układ pomiarowy do akwizycji danych, oraz przygotowano próbki. Następnie przeprowadzono badania na maszynie zmęczeniowej w celu poznania użyteczności i niezawodności zaproponowanej metody detekcji pęknięć. Po przeanalizowaniu danych pomiarowych wysunięto wnioski i spostrzeżenia, dotyczące zwłaszcza układu elektronicznego. Opisano proponowane modynkacje układu oraz przedstawiono symulacje w programie Micro-Cap - programie do analizy układów elektronicznych. Artykuł podsumowano wnioskami z badan laboratoryjnych i symulacyjnych.

12

Preliminary Verification of Selected Solutions for Crack Detection

Kurnyta A., Reymer P.

Fatigue of Aircraft Structures

|

2012

|

Iss. 4

58--63

EN

Throughout its service life an aircraft is subjected to varying loads. Because of those periodically appearing stresses, undesirable and irreversible changes in structure may occur. As a consequence, cracks are formed, which reduce aircraft structural strength, significantly affecting structural integrity. For that reason, intensive research works are carried out around the world to develop innovative and reliable methods for detection of cracks initiation and propagation. This paper presents two methods of crack detection. One of them uses wireless polymer gages for determining deformation in a test region. The other one uses electrical, resistive ladder sensors for detection of cracks and their length determination.

13

Fractal Dimension-Based Crack Identification Technique of Composite Beams for On-Line SHM Systems

Katunin A.

Machine Dynamics Research

|

2010

|

Vol. 34, No. 2

60-69

EN

Due to the required high reliability of many responsible engineering constructions the structural health monitoring (SHM) systems must work in the on-line mode. Therefore, it is necessary to develop new fault detection techniques for improving faults detectibility and simultaneously to reduce the processing time of fault detection. In the present paper the crack identification technique based on the fractal dimension of composite beams was discovered. For the analysis the finite element method (FEM)-based simulation modal data were considered. The fractal dimension of obtained normal modes of the composite beam was estimated based on Higuchi's algorithm. Next, the displacement data were noised with various levels for simulating the real measurement conditions and the crack detectibility was determined for various crack depths. Obtained results show that proposed technique could be used in practical on-line SHM systems due to its noise robustness, simplicity and low time-consuming processing.

14

A novel LBP based methods for pavement crack detection

Hu Y., Zhao C. X.

Image Processing & Communications

|

2009

|

Vol. 14, no 4

5-12

EN

The local binary pattern (LBP) is a gray-scale and rotation invariant operator, and has been proved to be theoretically very simple, yet computational efficient approach for texture classification. As for the irregular texture surface image, like pavement surface image, the original LBP performs not good enough for practical purposes. First, threshold in plain area often cause mismatch in local structure. Second, nonuniform patterns were directly merged into one pattern will discards large amount of texture information represented by these patterns. In this paper, a novel LBP based operator for pavement crack detection is proposed. In our approach, local neighbors are classified into smooth area and rough area, segmentation only performed in rough area to catch local structure information. And then, local patterns are regrouped and a lookup table is created for fast implement. With these methods, the proposed approach detects cracks well and becomes more robust against noise. Experiments on the pavement surface image show the good performance of this new LBP based operator. More importantly, because of its simplicity, online implementation is possible as well.

15

Crack detection in beam like structures. Part I. Identification of crack location

Majkut L.

Diagnostyka

|

2008

|

nr 2(46)

17-20

EN

This paper deals with detection of a transverse crack location in beam like structure. An input quantity for detection a natural mode of vibrations was chosen. The crack is substituted by rotational spring, which flexibility is calculated by using Castigliano theorem and laws of the fracture mechanics. Based on this model of crack the first natural mode of Bernoulli-Euler beam was determined then analysed. The modal assurance criterion (MAC coefficients) were determined as a function of crack depth and location. These quantities can be used for crack detection in beam like structures. In order to crack location the discrete and continuous wavelet analysis of mode shapes was used.

PL

W pracy opisano pewien sposób detekcji pęknięcia oraz identyfikacji jego lokalizacji. Jako wielkości wejściowe procesu identyfikacji wybrano wektory własne belki z pęknięciem. Jako model pęknięcia przyjęto przegub sprężysty, którego podatność wyznaczono na podstawie praw mechaniki pękania i twierdzenia Castigliano. Wykorzystując taki opis pęknięcia wyznaczono wektory własne pękniętej belki opisanej modelem Bernoulliego-Eulera. Wyznaczono współczynniki MAC (modal assurance criterion) w funkcji głębokości i miejsca pęknięcia. Wielkości te pozwalają jedynie na detekcję pęknięcia. W celu wyznaczenia lokalizacji uszkodzenia wykorzystano dyskretną i ciągłą analizę falkową wektorów własnych.

16

Continuous one-dimensional elastic macro-elements as a natural alternative crack detection tool to the spectral finite element method

Szolc T.

Archives of Mechanics

|

2007

|

Vol. 59, nr 6

473-499

EN

In the paper the wave method of fault identification in rods, shafts and beams is proposed. This method is based on dynamical models consisting of structural macroelements with continuously distributed inertia!-visco-elastic properties, represented by individual segments of the investigated objects. The fault detection and identification reduces to simulations of diagnostic wave propagation and wave reflections in these models. These simulations are performed directly in time domain by means of analytical solutions of the partial differential equations of motion. In the computational examples, reflected waves were sought in the cracked cantilever rod and beam. These results have been compared with the analogous findings obtained by other authors, using the spectral finite element method. The natural continuous character of the applied elastic macro-elements enables us to apply a straightforward simulation of wave effects, which makes the proposed approach a promising and effective tool for fault identification in various structures and mechanical systems.

17

Crack detection on beams by time-frequency analysis of transient flexural waves

Apostoloudi A., Douka E., Hadjileontiadis L. J., Rekanos I. T., Trochidis A.

Archives of Acoustics

|

2007

|

Vol. 32, No. 4

941--954

EN

A method for crack detection in beams by time-frequency analysis of flexural waves is described. Two different time-frequency representations, namely the continuous wavelet transform and the smoothed pseudo-Wigner distribution are employed. Simulated and measured exural waves in a cracked beam are analysed and both the location and size of the crack are accurately determined. The location of the crack is estimated using the arrival time of reflected waves with different group velocities. The ratio of the reflected wave energy to the incident wave one is calculated and used as an indicator of the crack size. Wave experiments in a slender brass beam are in good agreement with predictions verifying the effciency of the method. In view of the results obtained, the advantages and shortcomings of the time-frequency representations employed are presented and discussed.

18

Acoustical diagnostics of cracks in beam like structures

Majkut L.

Archives of Acoustics

|

2006

|

Vol. 31, No. 1

17-28

EN

In this paper, the acoustical symptoms of a constructional element with an edge non-propagating crack on the example of a cantilever beam are searched. In this work the influence of a crack on flexural natural frequency was analysed. The crack is substituted by a rotational spring, which flexibility is calculated using the Castigliano theorem and the laws of the fracture mechanics. In this work the changes in the first and second natural frequency of the flexural vibrations are showed as a function of location and depth of the crack. The acoustic signal measured with a microphone placed above the beam is used for diagnostic systems. Changes in the natural frequency cannot be used for the identification of a small crack (the depth is less than 10% of beam height). For the detecting of a smaller crack, the effect of coupled different modes of vibration is presented. The paper presents a modelling and analysis algorithm for cracked Euler-Bernoulli beams by considering the coupling between the bending and axial vibration modes. The analysis of the coupled vibrations showed that additional resonance frequencies appeared in the acoustic spectrum.

19

Crack detection by the topological gradient method

Amstutz S., Horchani I., Masmoudi M.

Control and Cybernetics

|

2005

|

Vol. 34, no 1

81-101

EN

The topological sensitivity analysis consists in studying the behavior of a shape functional when modifying the topology of the domain. In general, the perturbation under consideration is the creation of a small hole. In this paper, the topological asymptotic expansion is obtained for the Laplace equation with respect to the insertion of a short crack inside a plane domain. This result is illustrated by some numerical experiments in the context of crack detection.

20

Diagnostyka kontrolna węglowego młyna kulowego

Barczewski R., Zielnica M.

Zeszyty Naukowe Politechniki Poznańskiej. Budowa Maszyn i Zarządzanie Produkcją

|

2004

|

Nr 1

137-146

PL

W artykule przedstawiono zagadnienia diagnostyki kontrolnej węglowego młyna kulowego, a w szczególności stalowych kuł - podstawowych elementów zespołu mielącego. Standardowa procedura kontroli kuł, obejmująca ważenie, pomiar oraz próbę toczenia, nie gwarantuje wykrywania wad strukturalnych i materiałowych (np. pęknięć i porowatości). Zastosowanie innych metod badań nieniszczących, jak radiologia, defektoskopia ultradźwiękowa, metody wizualne do detekcji wad, do obiektu sferycznego nie zawsze jest możliwe i ekonomicznie uzasadnione. Zaproponowano alternatywną metodę badania kuł. Dodatkowa wstępna klasyfikacja została oparta na analizie parametrów drgań swobodnych. Analiza dynamiczna uzyskanego metodą elementów skończonych modelu kuli oraz badania doświadczalne wykazały, że dominujące składowe w widmie drgań swobodnych odpowiadają dziesiątemu i dwunastemu modowi drgań. Zmniejszenie grubości ścianki kuli powoduje wzrost częstotliwości odpowiadającej dziesiątej postaci drgań, która jednak jest mało wrażliwa na występowanie pęknięć. Wykrywanie pęknięć kuli może być oparte na analizie zmian częstotliwości dwunastego modu. W artykule przedstawiono również uproszczony algorytm przetwarzania sygnału drganiowego stosownego w procedurze preselekcji kuł.

EN

The paper presents problems of testing diagnostics of coal ball mill, especially steel balls which are major elements of the milling unit. Standard testing procedure of the balls including: the weighting and measuring as well as rolling test does not guarantee the detection of structural and material failures (i.e. cracks, porosity). Application of other NDT methods, like radiology, ultrasonic testing, visual inspection, to failures detection in spherical object is not always possible and economically justified. Therefore, the alternative test procedure of balls has been proposed. An additional initial classification of balls for the following detailed tests have been based on the analysis of free vibration parameters. The dynamic analysis of the FEM model of the ball and experiments show that frequencies of the dominant components in free vibration spectrum correspond to tenth (f!0) and twelfth (f,2) vibration mode. Decrease of the thickness of the ball wall cause increase of f]0 frequency value which is less sensitive on crack presence.. Detection of ball cracks can be based on the analysis of frequency changes of the twelfth vibration mode. Also the paper presents a simplified algorithm of the vibration signal processing used in the ball preselection procedure.