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1
EN
The paper presents test results concerning the service life of fillet welds made in steel S355. In addition, the article discusses the initiation and growth of fatigue cracks in specimens subjected to bending with torsion. The tests were performed in relation to constant stress ratio R = -1 and 0. The results presented in the article take into account the effect of the technological treatment on the service life of the specimens. The tests revealed longer service life of the specimens not subjected to the technological treatment, both when R = -1 and 0.
PL
Przedstawiono wyniki badań trwałości, inicjacji oraz wzrostu pęknięć zmęczeniowych próbek ze stali S355 ze spoinami pachwinowymi, poddanych zginaniu ze skręcaniem. Badania przeprowadzono przy stałej wartości współczynnika asymetrii cyklu R = - 1 oraz 0. Prezentowane wyniki uwzględniają wpływ zabiegu technologicznego na trwałość badanych próbek. Stwierdzono większą trwałość zmęczeniową próbek bez zabiegu technologicznego, zarówno dla R = -1 jak i R = 0.
EN
Purpose: The aim of the proposed research is to create a calculation model of surface fatigue crack growth at the axle of railway wheelset working under operational loads. Design/methodology/approach: The energy approach of the fracture mechanics was used to formulate the calculation model of fatigue crack propagation at the wheelset axle surface. The method of least squares was used to determine the investigated material mechanical constants that the kinetic equations of the calculation model contain. The system of differential equations of crack growth kinetics was solved numerically using the Runge-Kutta method. Findings: On the basis of the energy approach of the fracture mechanics the calculation model of fatigue macrocrack growth in three-dimensional elastic-plastic body in case of a mixed-mode I+II+III macromechanism of fracture has been built. On the basis of the created calculation model, the kinetics of the growth of fatigue cracks was investigated both in the middle part of the wheelset axle and in the axle journal. Research limitations/implications: The results obtained on laboratory specimens should be tested during a real railway wheelset axle investigation. Practical implications: The created calculation model can be used in practice to formulate method of residual lifetime estimation of railway wheelset axle. Originality/value: It was shown, that surface crack kinetics depends not only on the crack initial area but also significantly depends on the crack edge geometry and comparatively small crack-like defects at the wheelset axle surface can reach critical sizes in comparatively short run. It has been found that mechanical shear stresses caused by the weight of the loaded railway wagon in the cross section of the wheelset axle journal can significantly accelerate the growth of the transverse fatigue crack at the axle surface, reducing the period of crack subcritical growth by about 20%.
EN
A high resolution sensor of linear displacements has been elaborated for diagnosing the size of the crack tip opening in standard test specimens. Based on the data measured during fatigue crack growth resistance tests of a wheel steel heat treated after various modes, calculations of the strain and energy parameters of local fracture were performed for the corresponding variants of treatment, and fatigue crack growth rate diagrams were constructed using different approaches of fatigue fracture mechanics. It was established that the diagrams obtained using the strain and energy approaches are more sensitive to material microstructure and its mechanical properties than the traditional diagrams obtained using the stress approach. Based on the parameters of the fatigue crack growth resistance estimated using the strain and energy approaches, the effective diagnostics and the best heat treatment mode for the wheel steel was developed. It comprises the stages of isothermal quenching and tempering at a temperature of 500 °С, providing the highest fatigue fracture toughness of the steel.
PL
Opracowano czujnik przemieszczeń liniowych o podwyższonej czułości dla diagnozowania rozwartości szczeliny na podstawie określenia odkształceń i energetycznych parametrów uszkodzenia lokalnego. W oparciu o różne podejścia mechaniki zniszczenia zmęczeniowego zostały skonstruowane diagramy prędkości propagacji pęknięć zmęczeniowych w stali koła kolejowego po różnych rodzajach obróbki cieplnej. Ustalono, że diagramy odporności na pękanie, otrzymane według odkształceniowego lub energetycznego podejścia, są bardziej wrażliwe do strukturalnych i mechanicznych własności materiałów w porównaniu z tradycyjnymi diagramami otrzymanymi według podejścia siłowego. Pokazano zalety odkształceniowego i energetycznego podejścia w porównaniu z podejściem siłowym w zakresie optymalizacji charakterystyk odporności materiałów na pękanie. Dokonano skutecznej diagnostyki stanu technicznego materiału oraz optymalizacji obróbki cieplnej stali kół kolejowych. Ustalono, że hartowanie izotermiczne z odpuszczaniem przy temperaturze 500°C zapewnia najwyższą odporność stali na pękanie.
EN
In practice for all metallic materials, damage by fatigue usually takes in two steps, the appearance of an initial crack which then grows as a function of the present microstructure. The objective of this study is to identify the elements influencing the fatigue crack growth rate on aluminum alloys of different microstructures. Characterization tests and microstructural analysis on 2024-T3, 5083-H22, 6082-T6 and 7075-T6 shades have been carried out. Based on the experimental results obtained, AA7075-T6 has the best fatigue crack rate resistance which is explained by its behavior as well as the nature and dispersive distribution of the secondary element.
EN
In practice for all metallic materials, damage by fatigue usually takes in two steps, the appearance of an initial crack which then grows as a function of the present microstructure. The objective of this study is to identify the elements influencing the fatigue crack growth rate on aluminum alloys of different microstructures. Characterization tests and microstructural analysis on 2024-T3, 5083-H22, 6082-T6 and 7075-T6 shades have been carried out. Based on the experimental results obtained, AA7075-T6 has the best fatigue crack rate resistance which is explained by its behavior as well as the nature and dispersive distribution of the secondary element.
EN
The aim of this study is to investigate the fatigue crack growth behavior with post weld heat treatments (T4) on transverse tungsten inert gas-welded Aluminum alloy 6013. All fatigue tests have been carried out using center cracked tension specimens at ambient temperature under a stress ratio of R = 0.3. The results revealed that various time of aging in T4 affects its mechanical properties, also the fatigue crack growth behavior as well. It has been observed that in the heat treated samples the crack growth rate is lower than that in the as-welded sample, but higher than the rate in the base metal. To be more specific, samples with 18 hours aging exhibit the highest tensile strength and fatigue resistance compared to the other heat treated samples. The probability assessment has also been used to determine the fatigue crack growth rate and a good linearity has been found.
EN
In a martensitic-bainitic microalloyed steel, the effect of hydrogen on fatigue crack growth was studied using rotary bending fatigue tests. The steel was subjected to a rapid thermal cycle to get a microstructure similar to that which would be formed within the coarse-grained heat-affected zone of a weld. Crack growth was monitored as a function of the number of cycles applied during fatigue tests on three types of specimens: 1) those without hydrogen charge, 2) those charged with hydrogen and 3) those charged with hydrogen which was then discharged through low-temperature heat treatment. All types showed persistent slip marks, and cracks propagated along high-shear-stress planes. In the presence of hydrogen, crack growth was affected by microstructural defects caused by the hydrogen charging process, and the persistent slip marks developed in an area closer to the crack tip and crack path. On the contrary, without hydrogen, crack growth occurred perpendicular to the applied force, and the persistent slip marks were fewer in number and further from the crack tip and crack path. This indicates that the plasticity increased (i.e., the damage that occurred in the presence of hydrogen matched the hydrogen-enhanced local plasticity mechanism).
EN
The article presents the maps of xx stress component and compares values of analytical and numerical calculations for the stress intensity factor range of welded specimens with fillet welds which subjected to cyclic bending. The tests were performed under constant value of moment amplitude Ma = 9.20 Nm and stress ratio R = σmin/ σmax = -1. The specimens were made of drag steel rod S355. The specimens were solid and welded. The numerical models were simulated with ABAQUS suite and numerical calculations performed with FRANC3D software.
EN
This paper describes fatigue cracks growth in three different bimetallic made by explosive cladding. In any case, it was the same base material - carbon steel P355NH, and clad materials are: austenitic stainless steel 316L, 254SMO and super duplex (50% ferritic structure, 50% of the austenitic structure). Specimens of rectangular cross-section was subje ted to fatigue bending with of the stress mean value equal zero and of constant amplitude equal to 19.41 N•m. The crack propagation was measured using a portable microscope with a micrometer located on the fatigue stand.
EN
Over the last 60 years, several models have been developed governing different zones of fatigue crack growth from the threshold zone to final failure. The best known model is the Paris law and a number of its based on mechanical, metallurgical and loading parameters governing the propagation of cracks. This paper presents an analytical model developed to predict the fatigue crack propagation rate in the Paris regime, for different material properties, yield strength (σy), Young’s modulus (E) and cyclic hardening parameters (K’, n’) and their influence by variability. The cyclic plastic deformation at a crack tip or any other cyclic hardening rule may be used to reach this objective, for to investigate this influence, these properties of the model are calibrated using available experimental data in the literature. This FCGR model was validated on Al-alloys specimens under constant amplitude load and shows good agreement with the experimental results.
EN
Corrosion fatigue crack growth studies were conducted on eccentrically-loaded single edge notch tension specimens made of SA 333 Gr. 6 and SA 516 Gr. 70 carbon steels in water environment. The experiments were conducted using a ±250 kN capacity Universal Testing Machine under constant amplitude sinusoidal loading at a test frequency of 0.50 Hz and stress ratio of 0.1. The fabrication of test specimens and the experiments were carried out based on ASTM E 647 and ASTM E 1820. The crack initiation and growth were monitored and images were captured by using a digital camera at regular intervals of fatigue cycles. By using these images, the length of crack was measured. The tests were terminated when the uncracked portion of the specimens was insufficient to take further load. Crack growth rate and stress intensity factor range values were evaluated at incremental values of loading cycles and crack length. Using the crack growth rate vs. stress intensity factor range plots, best fit curves following power law in the form of Paris’ equation were obtained.
EN
A method of calculating stress intensity factors, using point-load weight function, for twodimensional surface cracks subjected to rotary bending, applied to circular objects is described in the paper. The research has regarded planar cracks in finite circular bodies, which may occur e.g. in shaft cross sections of belt-driven machines. This type of drive is widely spread in the technological lines, therefore the research on improving its fatigue durability is crucial for development of this branch of industry. One of a few advantages of the method which has been applied is the possibility to evaluate stress intensity factor (SIF) values precisely in a quick and simple way. The paper shows the computation for various parameters of shape and size of shafts and cracks. The presented method usually yields conservative results compared to reference values obtained for the same configurations with the finite element method, which gives a good perspective to use such calculated SIFs for life assessment. Checking of these possibility is an essential issue of the work described in the paper.
13
EN
2524-T3 aluminum alloy sheets with different grain sizes (13 μm, 59 μm, 178 μm, 355 μm, 126 μm, and 87 μm) were prepared using methods such as rolling and annealing. The microstructures and mechanical properties of the 2524-T3 aluminum alloy sheets were studied using optical microscopy (OM), scanning electron microscopy (SEM), and tensile and fatigue crack growth (FCG) rate tests. The grain size had a significant effect on the fatigue crack growth (FCG) rate. Alloys with grain sizes between 50 and 100 μm exhibited high fatigue crack propagation resistances and the lowest FCG rates (da/dN = 1.05–1.45 × 10−3 mm/cycle at ΔK = 30 MPa m1/2). Microstructural observations revealed that fatigue cracks propagated more tortuously in the alloy with grain sizes within the range of 50–100 μm. This result is attributed to the combined effects of grain boundaries, crack deflection, fracture surface roughness-induced crack closure, and plasticity-induced crack closure.
EN
The paper presents an analysis of the state of stress and crack tip opening displacement (strain) in specimens with rectangular cross-section subjected to torsion and combined bending with torsion. The specimens were made of the EN AW-2017A aluminium alloy. The specimens had an external unilateral notch, which was 2 mm deep and its radius was 22.5 mm. The tests were performed at constant moment amplitude MT=MBT= 15.84 N.m and under stress ratio R= -1. The exemplary results of numerical computations being obtained by using the FRANC3D software were shown in the form of stress and crack tip opening displacement (CTOD) maps. The paper presents the differences of fatigue cracks growth under torsion and bending with torsion being derived by using the FRANC3D software.
EN
Effects of variables related to design and production of riveted lap joints representative of longitudinal sheet connections for a pressurized transport aircraft fuselage were experimentally investigated. The specimens from an aircraft Al alloy D16 Alclad sheets of three different thicknesses (1.9, 1.2 and 0.8 mm) were assembled under load control using round head rivets and rivets with the compensator from a P24 Al alloy. For the joints from 1.9 mm thick sheets fatigue tests indicated a dependency of the crack initiation site and crack path on the squeeze force level and on the rivet type. At the same time, increasing the squeeze force led to improved fatigue properties of the joints, specimens assembled using the rivets with the compensator showing fatigue lives consistently longer than joints with the round head rivets. All observed trends have been explained based on hole expansion and load transfer measurements. For thin sheets connected using the round head rivets, local deformations and indentations under the driven rivet head promoted crack initiation and failure in the adjacent sheet. Fatigue test results indicated that the detrimental effect of this type imperfections could outweigh the benefits associated with a decrease in secondary bending due to thinning the sheets. The rivets with the compensator were observed to cause significant local imperfections beneath the manufactured head, which adversely affected the joint fatigue performance.
PL
Sposób zniszczenia i wytrzymałość zmęczeniowa połączeń zakładkowych stosowanych w lotnictwie zależy od wielu czynników technologicznych i konstrukcyjnych, a w szczególności od rodzaju nitu i siły jego zakuwania oraz grubości łączonych blach. W artykule omówiono te zagadnienia na przykładzie blach o różnych grubościach z lotniczego stopu aluminium D16, połączonych zakładkowo za pomocą nitów z łbem kulistym ze stopu PA24. Próbki połączeń poddawane były stałoamplitudowym obciążeniom zmęczeniowym przy różnych poziomach naprężeń nominalnych. Wykazano, że wraz ze wzrostem siły zakuwania nitów rośnie trwałość zmęczeniowa połączenia, a tor pęknięcia oddala się od przekroju netto blachy. Zaobserwowano, że pęknięcia zmęczeniowe pojawiają się w blasze, w której ekspansja otworów nitowych jest mniejsza, co z kolei zależy od rodzaju nitu. Trendy te wyjaśniono na podstawie wyników pomiarów ekspansji otworów nitowych wypełnionych nitami zakutymi przy użyciu różnych sił oraz z uwzględnieniem wyznaczonego eksperymentalnie względnego udziału poszczególnych rzędów nitów w transferze obciążenia. Stwierdzono, że nity z kompensatorem nie są odpowiednie do łączenia cienkich blach; w trakcie zakuwania powstają znaczne deformacje złącza obniżające jego własności zmęczeniowe.
PL
Artykuł zawiera wyniki badań doświadczalnych na próbkach o przekroju prostokątnym wykonanych ze stali 10HNAP (S355J2G1W). Stosunek wysokości próbki do szerokości wynosił 1,5. Badania na zginanie ze skręcaniem prowadzone były przy stosunku amplitudy momentów zginającego do skręcającego M[ag]/M[as] = 0,47; 0,94; 1,87 i częstotliwości obciążenia 26,5 Hz. Całkowity moment M[(t)]=[pierwiastek]M[s][^2](t) + M[g][^2](t) indukowano siłami na ramionach o długości 0,2 m. Jednostronnie utwierdzone próbki badano przy cyklicznym zginaniu ze skręcaniem przy różnych amplitudach momentu zginającego M[ag] = 5,64; 10,17; 15,38 N x m i momentu skręcającego M[as] = 8,23; 10,89, 12,08 N x m. Rozwój ścieżek pękania był obserwowany na powierzchni próbki metodą optyczną.
EN
The paper presents the experimental results concerning fatigue crack paths in the plate specimens made of 10HNAP (S355J2G1W) steel. The specimens have rectangular cross sections of the ratio of height to width equal to 1.5. The tests were realized at a fatigue test stand MZGS-100Ph where the ratio of torsion moment to bending moment was M[B](t)/M[T](t) = 0.47, 0.94, 1.87 and loading frequency was 26.5 Hz. The total moment M[(t)]=[ square root]M[s][^2](t) + M[g][^2](t) was generated by force on the arm 0.2 m in length. Unilaterally restrained specimens were subjected to cyclic bending with torsion with the different amplitudes of bending moment M[aB] = 5.64, 10.17, 15.38 N x m and torsion moment M[aT] = 8.23, 10.89, 12.08 N x m. Crack paths was observed on the specimen surface with the optical method.
EN
A strip yield model implementation by the present authors is applied to predict fatigue crack growth observed in structural steel specimens under various constant and variable amplitude loading conditions. Attention is paid to the model calibration using the constraint factors in view of the dependence of both the crack closure mechanism and the material stress-strain response on the load history. Prediction capabilities of the model are considered in the context of the incompatibility between the crack growth resistance for constant and variable amplitude loading.
PL
Opracowany przez Autorów model pasmowego płynięcia został zastosowany do prognozowania rozwoju pęknięć zmęczeniowych obserwowanych w badaniach zmęczeniowych próbek ze stali konstrukcyjnych w warunkach obciążeń stało- i zmiennoamplitudowych. Skoncentrowano się głównie na kalibracji modelu przy użyciu odpowiednio dobranych współczynników skrępowania uwzględniających zarówno mechanizm zamykania się pęknięcia jak i naprężeniowo-odkształceniową charakterystykę materiału właściwą dla danej historii obciążenia. Wyniki prognoz przy użyciu tak skalibrowanego modelu zostały poddane gruntownej ocenie z uwzględnieniem różnic w rozwoju pęknięć obserwowanych w przypadku obciążeń stało- i zmiennoamplitudowych.
EN
The paper is focused on the calibration of the strip yield (Dugdale) model for crack growth predictions for structural steel. This is achieved by imposing appropriate constraints on yielding the strip elements. To avoid a fortuitous, i.e. physically unjustified choice of the constraint factors, a novel concept for their selection is proposed, namely matching the experimentally observed and predicted by the model cyclic stress-strain behaviour at the crack tip. The approach is shown to yield satisfactory prediction results on crack growth under constant amplitude loading and after application of an overload cycle.
PL
W artykule skupiono się na kalibracji modelu pasmowego płynięcia do prognozowania rozwoju pęknięć zmęczeniowych w stali konstrukcyjnej, stosując odpowiednie współczynniki skrępowania. W oparciu o wcześniejsze analizy stwierdzono, że w przypadku tego materiału adekwatne przewidywanie trendów eksperymentalnych we wzroście pęknięć zmęczeniowych wymaga zastosowania trzech niezależnych współczynników skrępowania modyfikujących granice plastyczności odpowiednio dla rozciąganych i ściskanych elementów pasma plastycznego przed frontem pęknięcia, oraz ściskanych elementów za jego frontem. W takim przypadku jednak, wymagany poziom otwarcia pęknięcia możliwy jest do osiągnięcia przy wielu kombinacjach tych współczynników. Zaproponowano więc, by dodatkowym kryterium ich doboru była zgodność między wyznaczoną eksperymentalnie a symulowaną przy użyciu modelu lokalną cykliczną odpowiedzią materiału. Pokazano, że tak skalibrowany model dobrze opisuje w sensie ilościowym trendy eksperymentalne we wzroście pęknięć zmęczeniowych w stali konstrukcyjnej przy obciążeniu stałoamplitudowym oraz po pojedynczym przeciążeniu.
EN
Long-time operating parts from old bridges (particularly erected at the turn of 19th and 20th century) show inclination to the brittle fracture. This type of fracture is initiated as a result of the degrading processes intensity. Structural degrading processes participate into the basic mechanical properties - it is particularly visible in the puddled steel. These processes consist in progressive decomposition of the bainite and pearlite area into carbides and nitrides. The separation of nitrides and carbides inside ferrite grain (and of course onto boundary) is also taken into account. In this paper, the investigation results related to registration fatigue crack growth rate have been presented. For the examination, a part of Piaskowy Brigde in Wroclaw (erected in 1861) was used. The differences in kinetics of fatigue crack growth are also presented. A new energy model has been reminded in the last part of the paper. The main advantages in description of fatigue crack growth have been determined due to a new critical quantity - the energy parameter deltaH [J/m2
PL
Długotrwale eksploatowane stale mostowe, szczególnie pochodzące z konstrukcji wzniesionych na przełomie XIX/XX wieku, wykazują skłonność do kruchego pękania. Kruche pękanie inicjowane jest na skutek intensyfikacji procesów degradacyjnych - degradacji strukturalnej oraz degradacji wytrzymałościowej podstawowych własności mechanicznych (zwłaszcza stale zgrzewne). Procesy degradacyjne polegają w ogólności na postępującym rozpadzie perlitu, wydzieleniach węglików i azotków, zarówno na granicach jak i wewnątrz ziarn. W pracy przedstawiono wyniki badań takich stali mostowych (pochodzących głównie z mostu Piaskowego we Wrocławiu rok bud. 1861) z punktu widzenia metod mechaniki pękania. W wyniku badań otrzymano wykresy kinetyki pękania zmęczeniowego, zgodnie z założeniami norm. Dzięki zastosowaniu kryterium energetycznego wyznaczono również nowy typ wykresu kinetyki pękania zmęczeniowego, bazujący na energii dyssypowanej w każdym cyklu widma obciążenia cyklicznego.
EN
In the paper, the influence of the notch radius on changes of the [delta]J parameter under low and high-cycle fatigue is discussed. The tests were carried out on plates made of FeP04-UNI 8092 deep-drawing steel. The specimens were characterised by double symmetric lateral notches with the notch root radius ranging from 0.2mm to 10mm. The MTS 809 servo-hydraulic device was used for tests performed at the Department of Management and Engineering in Vicenza (Padova University). All fa- tigue tests were performed under force control, by imposing a constant value of the nominal load ratio, R = 0, and a load amplitude Pa = 6 and 7 kN (which corresponded to the nominal amplitude of normal stresses a = 100, 117MPa before the crack initiation). The test frequency ranged from 13 and 15Hz.
PL
W pracy przedstawiono wpływ promienia karbu na zmiany parametru [delta]J podczas badań wykonywanych w zakresie niskiej i wysokiej liczby cykli zmęczeniowych. Badaniom poddano próbki płaskie wykonane ze stali FeP04-UNI 8092. Próbki charakteryzowały się dwustronnymi symetrycznymi zewnętrznymi karbami z promieniami dna karbu w zakresie od 0,2 do 10mm. Wyniki badań prezentowane w pracy wykonywano na maszynie hydraulicznej MTS 809 w Department of Management and Engineering w Vicenzy (Universytet w Padwie).Wszystkie badanie zmęczeniowe były wykonywane przy obciążeniu z kontrolowaną siłą przy stałej wartości współczynnika asymetrii cyklu R = 0 i amplitudzie obciążenia Pa = 6 i 7 kN (która korespondowała z nominalną amplitudą naprężenia normalnego a = 100, 117MPa przed inicjacją pęknięcia). Badania wykonywano w zakresie częstotliwości obciążenia 13 i 15Hz.
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