Fracture and Fatigue of Materials and Structures

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Authors: Wojciech Blażejewski, Pawel Gasior, Jerzy Kaleta, Radosław Rybczyński
Abstract: In this paper a study of damage accumulation evaluation of highly stressed composite layer using acoustic emission method and local strain measurements by optical fiber based sensors in form of Fiber Bragg Grating (FBG) is presented. The study was carried out using composite NOL-ring specimens. These kind of specimens can simulate behavior of the cylindrical part of the pressure vessel. Quasistatic and creep tests of CFRC made NOL specimens were performed. It has been shown that there is a correlation between changes in the strain field of composite material, detected by FBG optical sensors, and changes in acoustic emission signals. The possibility of a kind of calibration of composite material strain state monitoring system by AE measurements and at the same time evaluation of damage accumulation was confirmed.
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Authors: Miroslaw Bocian, Jerzy Kaleta, Daniel Lewandowski, Michał Przybylski
Abstract: Abstract. The paper presents test stand designed for testing magnetorheological composites (MRC) under dynamic loading, together with the method for obtaining damping characteristics of the tested material. The test stand is based on Single-Degree-Of-Freedom system excited with use of modal hammer. The MRC is stimulated with use of double circular dipolar Halbach array based on neodymium magnets. The analysis of the experimental results is performed with use of the half-power method and the circle-fit method. results presented in the paper show usefulness of the test stand and of the method for obtaining damping parameters of the MRC. The results present change in the damping character of the material under variable magnetic field.
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Authors: Ewelina Böhm, Tadeusz Łagoda
Abstract: The paper presents an analysis of aluminium and its alloys in terms of fatigue strength. The paper contains information in terms of cyclic fatigue tests of aluminium alloys. On the basis of available literature data, Basquin fatigue characteristics have been designated. On their basis a comparison between chosen fatigue characteristics of aluminium alloys with different chemical composition and element percentage in the substance have been done.
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Authors: Dariusz Boroński
Abstract: This paper presents possibilities of determination of a material fatigue life for particular laser weld zones using specimens of micrometer dimensions. An original research system MFS developed at the University of Technology and Life Sciences in Bydgoszcz has been used whose research possibilities have been illustrated on the example of fatigue life tests of welds made of steel S 355J2G3.
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Authors: Dariusz Boroński, Robert Sołtysiak, Tomasz Giesko, Tomasz Marciniak, Zbigniew Lutowski, Sławomir Bujnowski
Abstract: In this paper, the possibilities of detection and measurement of fatigue crack length in welded joints made of steel of duplex type, have been presented. In the investigations there has been used an original research system FatigueVIEW employing advanced optoelectronic techniques and numerical methods of image analysis. The proposed approach enables analysis of the fatigue crack growth during fatigue tests and after their finishing in off-line mode.
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Authors: Michał Burak, Dariusz Skibicki, Michał Stopel
Abstract: The article presents calculations of fatigue life acc. to CDM model performed analytically and in program LS-DYNA with the model implemented there. On the basis of comparison of the obtained results with experimental fatigue lives, the possibility of estimation of fatigue life in LS-DYNA program acc. to CDM model was evaluated.
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Authors: Marek Cieśla, Jerzy Herian, Grzegorz Junak
Abstract: The elements of railway turnouts made from rail sections of R260 high carbon steel must have a high resistance to abrasive and contact fatigue wear, as well as a good resistance to cracking under service loads. These mechanical properties largely determine the suitability of steel for use as railway track components. In this study, two groups of specimens were subjected to tests of mechanical properties and metallurgical analyses. The first group included material obtained from the hot-rolled block section, the rolling end temperature being Tkw = 950°C, while the second group was material after the rolling process with the subsequent 20-minute isothermal annealing at a temperature of 480°C. The microstructure of tested materials (Rm, Rp0.2, A5, Z, HB) was characterized, and their basic mechanical properties and fracture toughness in the KIc plane strain condition were determined. Also the effect of temperature, ranging from-80°C to 100°C, on the KCU impact toughness of R260 steel was established. Based on the SEM observation using the Hitachi S-3400N scanning microscope, it was found that pearlitic structure with a varied distance between cementite plates, equal to 0.29 μm and 0.09 μm, respectively, appears in the hot-rolled R260 steel and in the steel subjected to additional isothermal annealing treatment. The impact of pearlite morphology on the cracking characteristics and basic mechanical properties of materials was analyzed. It was found that at room temperature, the higher fracture toughness (KIc = 66.4 MPa·m1/2) is shown by the steel after isothermal annealing at 480°C, in which less distance between the plates of cementite has been observed in the perlite. The fracture toughness of R260 steel after hot rolling at 950°C was KIc = 48.3 MPa·m1/2. As in the case of fracture toughness, the impact strength of R260 steel after isothermal annealing was significantly greater than the impact strength of steel only after hot rolling. The determined cracking characteristics of R260 steel make it possible to determine the effect of heat treatment on the formation of microstructure and material properties, which determine the service life of rail sections.
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Authors: Kamila Czajkowska, Piotr Czarnocki, Zbigniew Lorenc
Abstract: Fatigue delamination of CF unidirectional laminates made of low temperature and vacuum bag cured prepreg, (out of autoclave-OOA), with MTM46 epoxy system was investigated under Mode II loading condition and the coefficients of the corresponding Paris equations were determined. The tests were carried out with the use of ENF beam specimens under displacement controlled conditions and at room temperature with the frequency, f=5Hz, and cycle parameter R=0.1. The crack length, a, was calculate based on the specimen compliance changes. For each specimen, for the entire range of load cycles, i.e. 1 nnmax, the a (n) relationship was approximated with the help of a single sigmoidal function and then the da/dn (n) relationship was determined. In addition, for the comparison purpose the 7-point approximation procedure recommended by ASTM E647 for the same purpose was applied. The differences in results produced by both the data reduction variants were presented for important variants stages and discussed.
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Authors: Józef Drewniak, Jacek Rysiński
Abstract: In this paper, the analytical method of fatigue life estimation of gear teeth is proposed. The computational model of fatigue damage accumulation was built using the adequate NASGRO 2/3 formula, moreover Formans and Paris-Erdogans laws were utilized for comparison. The ranges of stress intensity factor were determined using the boundary element method.
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