Mirosław Witoś

Diagnosis of Supporting Structures of HV Lines Using Magneto-Mechanical Effects

This paper concerns the idea of using magneto-mechanical effects in prophylactic activities to reduce the risk of occurrence of an extensive blackout on high voltage (HV) lines. The subject matter of the paper is related to the event from April 8, 2008, which deprived approximately 600,000 recipients from 18 cities of the West Pomeranian voivodeship of power and caused millions in losses for the national economy. In theoretical considerations, the idea of diagnosing the technical state and level of effort of steel power line towers using the metal magnetic memory method (MMM) is presented, with a consideration of the methodology for obtaining a reference signal from the external magnetic field. The capabilities of the MMM method have been illustrated by examples of active and passive experiments. Finally, the authors indicated the need of IT support of MMM data analysis using a 3D model of the predicted distribution of the magnetic field in the vicinity of the tested object.

The Reference Signal of Geomagnetic Field for MMM Expert Systems

The first step of a methodological approach to the validation of the metal magnetic memory (MMM) method in non-destructive testing (NDT) applications and in systems used for the diagnosis of early stages of material fatigue in mechanical constructions (structural health monitoring, SHM, and prognosis health management, PHM) has been presented in the paper. The study is focused on the properties of the external natural source of magnetisation of the object under MMM examination and the impact of its components. The precise data of the Earths geomagnetism measurements (from ground stations and satellites) and the revised model of the Earths magnetism can be applied in order to calibrate high sensitive magnetic field sensors, validate measurement results and extend the functional capacity of the MMM method.

Compressor Blade Fatigue Diagnostics and Modelling with the Use of Modal Analysis

Compressor Blade Fatigue Diagnostics and Modelling with the Use of Modal Analysis This paper investigates the diagnostic and research aspects of the compressor blade fatigue. The authors have reviewed the characteristics of different modes of metal blade fatigue (LCF, HCF, VHCF). The polycrystalline defects and impurities influencing the fatigue, along with their related surface finish techniques, have been taken into account. The experimental methods of structural health assessment have been considered. The Tip Timing (TTM), Experimental Modal Analysis (EMA) and Metal Magnetic Memory (MMM) provide information on the damage of the diagnosed object (compressor blade). It has been proven that the shape of resonance characteristics gives an ability to determinate if fatigue or a blade crack is concerned. Early damage symptoms, i.e. modal properties of material strengthening and weakening phases have been described. The experimental verification of the FEM model is presented based on a large body of experimental data collected by the author.

SELECTION OF TRANSFORMER SHEETS USING AN IMPEDANCE METHOD

Different grades of electric steel may appear side by side at the stage of production and repair of transformers. The magnetic parameters of electric steels are also very sensitive to residual stresses and overheating. A handy method to verify the steel grade and the direction of anisotropy is needed. The article presents the impedance method. applied to control magnetic parameters of transformer sheets. The described methods are a complement to the standardized control methods (i.e. EN 60404-2, IEC 60404-3, IEC-60404-10) of transformer sheets applied by the producers and laboratory methods. The theoretical basis of the NDT method is presented. Then, the results of impedance tests carried out on 5 different samples are presented. The obtained results have been verified by single sheet tester (SST) and magneto-optical Kerr effect (MOKE) methods. It has been presented that the impedance measurements of the material might be used in non-destructive tests to quickly and cheaply evaluate the microstructure quality (e.g. selection of transformer sheets), the influence of mechanical and thermal stresses and the processes of fatigue degradation.

Magneto-Mechanical Effects in NDE & SHM Applications

The paper presents the theoretical and experimental results from evaluating the early phase of material fatigue and discusses the issues concerning the example of two object classes: supporting structures and shaft working under real environmental conditions. In theoretical considerations, the Hall-Petch and Bailey-Hirsch relationships between microstructure and mechanical parameters are given. Magneto-mechanical effects and the magnetic passive observer have been used for evaluating the early phase of material fatigue. The Metal Magnetic Memory method of structural health assessment was verified and the potential for a reliable diagnosis of damage to the ferromagnetic material at the 1st and 2nd stage was confirmed.

The MMM Expert System: From a Reference Signal to The Method Validation

Abstract This paper presents the first step in the methodological approach to the validation of the metal magnetic memory (MMM) method in the non-destructive testing (NDT) applications and in the systems used for diagnosis of early stages of material fatigue in mechanical constructions (structural health monitoring, SHM, and prognosis health management, PHM). The study is focused on the properties of the external natural source of magnetisation of the object under MMM examination and the impact of the magnetisation components. The precise data obtained from measurements of the Earths geomagnetism (from ground stations and satellites) and the revised model of the Earths magnetism can be applied in order to calibrate high sensitivity magnetic field sensors, validate the measurement results and extend the functional capacity of the MMM method.