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EN
The increasing share of renewables in electricity production adversly affects the operation of thermal plants, including steam turbine units. Intermittency of renewable sources results in high variability of steam turbine operating conditions, which together with the inherent scatter of turbine operating parameters significantly complicates their lifetime assessment. The paper presents a concept of lifetime monitoring system in scope of creep-fatigue damage. The system is based on online and offline calculations, performs online analysis of measurement data and takes into account the results of material tests. Functionality of the system main modules is described and mathematical models suitable for online calculations are presented. A general concept of hardware configuration for the system is proposed as well.
PL
Wzrastający udział odnawialnych źródeł energii w produkcji prądu ma niekorzystny wpływ na pracę elektrowni cieplnych, w tym bloków parowych. Niestabilność źródeł odnawialnych skutkuje dużą zmiennością warunków pracy turbin parowych, co w połączeniu z nieodłącznym rozrzutem parametrów pracy turbin w znaczący sposób komplikuje ocenę ich żywotności. W artykule przedstawiono koncepcję systemu monitorowania żywotności w zakresie zużycia zmęczeniowo-pełzaniowego. System ten oparty jest na obliczeniach w trybie online i offline, wykonuje na bieżąco analizę danych pomiarowych oraz uwzględnia wyniki badań materiałowych. Omówione zostały funkcje głównych modułów systemu wraz z propozycją modeli matematycznych odpowiednich do obliczeń w trybie online. Zaproponowano również ogólną koncepcję konfiguracji sprzętowej systemu.
2
Content available Modelling the time-dependent behaviour of soft soils
EN
Time dependence of soft soils has already been thoroughly investigated. The knowledge on creep and relaxation phenomena is generally available in the literature. However, it is still rarely applied in practice. Regarding the organic soils, geotechnical engineers mostly base their calculations on the simple assumptions. Yet, as presented within this article, the rate-dependent behaviour of soft soils is a very special and important feature. It influences both the strength and the stiffness of a soil depending on time. It is, thus, significant to account for time dependence in the geotechnical design when considering the soft soils. This can result in a more robust and economic design of geotechnical structures. Hence, the up-to-date possibilities of regarding creep in practice, which are provided by the existing theories, are reviewed herein. In this article, we first justify the importance of creep effects in practical applications. Next, we present the fundamental theories explaining the time-dependent behaviour of organic soils. Finally, the revision of the existing constitutive models that can be used in numerical simulations involving soft soils is introduced. Both the models that are implemented in the commercial geotechnical software and some more advanced models that take into account further aspects of soft soils behaviour are revised. The assumptions, the basic equations along with the advantages and the drawbacks of the considered models are described.
PL
W artykule pokazano możliwość zastosowania metod metalograficznych do oceny stopnia uszkodzenia wewnętrznego stali chromowo-molibdenowych eksploatowanych w warunkach pełzania. Wykorzystanie obrazów struktur metalograficznych uzyskanych w wyniku badań w skaningowym mikroskopie elektronowym lub w mikroskopie konfokalnym pozwala zaklasyfikować materiał pod względem stopnia uszkodzenia wewnętrznego. Stanowi ono jedno z istotnych kryteriów dopuszczenia elementu do dalszej eksploatacji lub też podstawę do wymiany elementu instalacji ze względu na zbyt duże jego zniszczenie w wyniku równoczesnego działania podwyższonej temperatury i naprężenia.
EN
The article presents the possibility of using metallographic methods to assess the degree of internal damage to chromium-molybdenum steels operated in creep conditions. Using images of metallographic structures obtained as a result of scanning electron microscopy or confocal microscopy enables classifying a material in terms of the internal damage degree. It is one of the important criteria for approving an element for further operation or is the basis for replacing the element of an installation due to its excessive destruction as a result of the simultaneous action of elevated temperature and stress.
PL
Przedstawiono sposób wyznaczania trwałości resztkowej i resztkowej trwałości rozporządzalnej na podstawie skróconych prób pełzania dla różnych poziomów temperatury wyższej od eksploatacyjnej i przy poziomie naprężenia odpowiadającego eksploatacyjnemu. Zaproponowano sposób wyznaczania udziału trwałości rozporządzalnej w trwałości oraz wyznaczanie czasu bezpiecznej eksploatacji poza obliczeniowy.
EN
The creep test is one of the important approaches to determining some mechanical properties of composite materials. This study was carried out to investigate the creep behaviour of an epoxy composite material that was reinforced with Y2O3 powder at weight ratios of 2%, 7%, 12%, 17% and 22%. Each volume ratio was subjected to five loads over the range of 1N to5N at a constant temperature of 16 ± 2°C. In this work, creep behaviour, stress and elasticity modulus were studied through experimental and numerical analyses. Results showed that increasing the weight ratio of Y2O3 powder enhanced creep characteristics.
EN
In this study, to investigate effects of rhenium addition on the microstructures and mechanical properties, 15Cr-1Mo ODS ferritic steels with rhenium additions were fabricated by the mechanical alloying, hot isostatic pressing, and hot rolling processes. Unremarkable differences on grain morphologies and nano-oxide distributions were estimated in the microstructure observations. However, the ODS ferritic steels with 0.5 wt.% rhenium showed higher tensile and creep strengths at elevated temperature than that without rhenium. It was found that rhenium is very effective to improve the mechanical properties.
EN
The long-term impact on creep, drying shrinkage, and permeation characteristics of an innovative concrete produced with manufactured geopolymer coarse aggregate (GPA) has been investigated and compared with quarried Basalt aggregate concrete. Microstructure and pore-structure development up to 1 year were examined through scanning electron microscopy, nanoindentation, and X-ray computed tomography. Compressive strength and elastic modulus of GPA concrete varied from 34.6 to 50.8 and 18.5 to 20.5 GPa, respectively, between 28 and 365 days. The 1-year creep strain of GPA concrete was 747 microstrain while the calculated creep coefficient was 0.97, which is significantly lower than the creep coefficient predicted by AS 3600 and CEB-FIP models. Moreover, the 365-day drying shrinkage is 570 microstrain, which is also lower than the maximum permissible limit specified by AS3600. The GPA concrete displayed high water absorption, but lower air and water permeability compared to Basalt aggregate concrete. This is attributed to a porous surface layer with large number of capillaries increasing the water absorption of GPA concrete through capillary suction. The discontinuity in the pore network coupled with a condensed interfacial transition zone formed in GPA concrete could be the reason for lower permeability. Overall, the long-term performance of the GPA demonstrates a potential as a lightweight coarse aggregate for concrete, with the added advantage of reducing the environmental impact utilizing fly ash from coal-fired power generation.
EN
In the present paper, we have studied the temperature and pressure dependent creep stress analysis of spherical shell. The review is critical to enhance the warm resistance of spherical shells in high-temperature conditions. The effect of different parameters was studied and it was noticed that the parameter n has a significant influence on the creep stresses and strain rates. Creep stresses and strain rates are ascertained on the premise of summed up strain measures and Seth’s transition hypothesis. This investigation is completed to demonstrate the impacts of temperature on the creep stresses and strain rates in the spherical shell. The resulting quantities are computed numerically and depicted graphically. It has been watched that the spherical shell made of an incompressible material is on more secure side of configuration when contrasted with the shell made of a compressible material.
9
Content available remote Effect of magnitude of sustained loading on the long-term deflection of RC beams
EN
The paper investigates the influence of the magnitude of sustained loading and tension steel percentage on the creep and shrinkage deflections of the reinforced concrete (RC) beams of different concrete grades. The magnitude of sustained loading was taken as 25% and 50% of the first crack load. Three concrete grades of 45, 35 and 25 MPa and two tension steel percentages of 0.77% and 1.21% were used. The long-term deflection was measured under the sustained four-point bending at the ages of 1, 3, 7, 14, 21, 30, 60, 90, 120 and 150 days. The shrinkage deflection of RC beams for the three concrete grades was measured at the same ages on specimens under their own weight. Based on the experimental investigations author's earlier model was extended to predict the total deflection due to creep and shrinkage of RC beams for varying magnitudes of sustained loading, and different compres-sive strengths of concrete.
EN
Prestress losses are usually calculated by bringing the tendons in the cross-section to the single resultant tendon. This solution is correct only for tendons concentrated in one part of the cross-section, while with their wider distribution, for example after the use of upper tendons, it may result in underestimation of losses in the lower tendons and overestimation in the upper tendons. The paper presents formulae to determine time dependent prestress losses separately for the top and bottom tendons of a pretensioned concrete member. Furthermore, variations of stress in the prestressing steel are analysed for two pretensioned concrete members to evaluate the possibility of using the equation (5.46) from the Eurocode 2 for the resultant tendon instead of the deduced formulae. The aim of this study is to show how great the error of estimated loss of prestressing force on the basis of several typical prestressed concrete sections can be.
EN
This paper presents the review on available approaches to predicting consolidation settlement of cohesive soils. The progress of deformation in clays is visualized as the combination of hydrodynamic and rheological processes. The first part deals with infinitesimal consolidation theories. The second part is a review of finite strain solutions that describe consolidation of soils. Non-linear one-dimensional consolidation of a thin and thick clay deposit considering linear void ratiolog effective stress relationship, self-weight of soil, constant volume (1+void ratio), thickness of clay layer and coefficient of consolidation also were considered. This aspects was illustrated for different cases on the basis of variations of degree of consolidation obtained both for settlements and dissipation of excess pore water pressures. In addition attention was paid to non-linearity ofpermeability and compressibility during consolidation course, variablity of coefficient of consolidation and time-dependent soil response.
EN
This paper presents the results of material tests of repair welded joints carried out for samples of materials taken from high pressure steam pipelines after over 200,000 operating hours in creep conditions, made of the 13HMF steel (14MoV6-3). The aim of the study was to assess the mechanical properties and changes in the structure of repair welded joints (new material + material after use), including the original material, heat affected zone and the weld, occurring as a result of the welding process and heat treatment after welding.
PL
W niniejszym opracowaniu zaprezentowano wyniki badań materiałowych przykładowych naprawczych złączy spawanych wykonanych na próbkach materiałów pobranych z rurociągów pary wysokoprężnej po przepracowaniu 200 tysięcy godzin pracy w warunkach pełzania, wykonanych ze stali 13HMF (14MoV6-3). Celem badań była ocena właściwości mechanicznych oraz zmian struktury naprawczych złączy spawanych (materiał nowy + materiał po eksploatacji) obejmujących materiał rodzimy, strefę wpływu ciepła i spoinę, zachodzących na skutek procesu spawania i przeprowadzonej obróbki cieplnej po spawaniu.
13
PL
Wartości parametrów mechanicznych drewna zmniejszają się w czasie pod wpływem działania obciążeń zewnętrznych. Redukcja nośności zależy od typu obciążenia i od klasy drewna. Ze względu na obciążenie długotrwałe, przy wysokich poziomach naprężeń, występują efekty redukcji wytrzymałości zwane pełzaniem. W artykule przedstawiono kalibrację współczynnika modyfikacji kmod za pomocą metod probabilistycznych. Pod uwagę wzięto trzy modele zniszczenia: Gerhardsa, Barretta-Foschi oraz Foschi-Yao. Parametry w tych modelach przyjęto zgodnie z metodą największej wiarygodności, wykorzystując dane istotne dla polskiego drewna konstrukcyjnego. Parametry obciążenia śniegiem zostały oszacowane na podstawie danych meteorologicznych. Dane zawierają obciążenie śniegiem polskich stref górskich: Zakopanego, Świeradowa i Leska z przeszło 45 lat. Do oceny niezawodności wykorzystano reprezentatywne stany krótko- i długoterminowe. Następnie dokonano estymacji współczynnika kmod dotyczącego polskich warunków górskich.
EN
The values of mechanical parameters of wood decrease in time under the influence of external loads. It depends on the type of load and timber. Due to long term loading at high stress ratio levels, there are strength reduction effects, referred to as creep-rupture effects. The paper presents the calibration of the modification factor kmod using probabilistic methods. Three damage accumulation models are considered: Gerhards, Barrett- Foschi and Foschi-Yao. The parameters in this models are fitted by the Maximum Likelihood Method using the data relevant for Polish structural timber. The snow load process parameters have been estimated based on Polish snow data over 45 years from mountain zones: Zakopane, Świeradów and Lesko. Representative short-and long-term states are used for evaluate the reliability. Then, the kmod coefficient was estimated for Polish mountain zones.
EN
The paper presents an attempt of application of the acoustic birefringence coefficient for early stage degradation assessment of Inconel 718 nickel superalloy after short-term creep. It is shown that it can serve as a good damage sensitive parameter and, moreover, it can be well correlated with hardness variation.
PL
Przedstawiono uaktualnione wytyczne stosowania i projektowania wgłębnego mieszania gruntu na mokro, oparte na polskich doświadczeniach. Szczególną uwagę zwrócono na właściwości i zasady projektowania cementogruntu, które mają podstawowe znaczenie. Wykonawcze aspekty mieszania gruntu uwzględniono tylko w zakresie ich wpływu na projektowanie.
EN
Presented are updated recommendations of wet deep soil mixing implementation and design, with reference to Polish practice. Particular attention has been paid to the properties and principles of design of stabilised soil. Aspects related to the execution of soil mixing are only taken into account in terms of their influence on design.
PL
W pracy przeprowadzono analizę możliwej przyczyny występowania samoczynnego zapłonu mieszanki paliwowo-powietrznej lotniczego silnika spalinowego obciążonego mocą maksymalną podczas badań na hamowni silnikowej. Takie objawy niepoprawnej pracy silnika mogą występować także w locie samolotu i śmigłowca. W celu wyjaśnienia przyczyny niepoprawnej pracy silnika zastosowano nieliniową analizę metodą elementów skończonych. Określono dyskretny model uproszczonego układu zespołu cylindra silnika obejmujący kadłub i tuleję cylindrową. W analizie numerycznej uwzględniono zarówno siłę mechaniczną, wynikającą z obciążenia zaciskiem tulei cylindrowej w kadłubie jak i obciążenie ciśnieniem czynnika roboczego oraz obciążenie nierównomiernym polem temperatury. Przemieszczenia i naprężenia w tulei i kadłubie obliczono metodą elementów skończonych za pomocą systemu PATRAN oraz systemem ABAQUS. Wynikło to z konieczności uwzględnienia silnej anizotropii właściwości tulei cylindrowej z żeliwa szarego podczas rozciągania i ściskania. Geometrię części modelowano elementami płaskimi o topologii czterowęzłowej z elementami kontaktowymi dwuwymiarowymi sprzęgającymi. Analitycznie wyznaczono także naprężenia zginające w zespole cylindra wywołane obciążeniem bocznym tłoka silnika poprzez uwzględnienie ciśnienia czynnika roboczego, sił masowych i siły tarcia. Obciążenie ciśnieniem i temperaturą zespołu cylindra określono w wyniku badań stanowiskowych silnika. Charakterystyki materiałowe żeliwa szarego i żaroodpornego stopu aluminium wyznaczono doświadczalnie. Wyniki nieliniowej analizy statycznej naprężeń i odkształceń dla połączenia tuleja cylindrowa-kadłub wykazały, że w obszarze zwrotu zewnętrznego pierścieni tłokowych wystąpiły wysokie naprężenia i odkształcenie plastyczne tulei cylindrowej, wywołujące brak styku połączenia tych elementów. Zakłóca to przepływ ciepła z tulei cylindrowej do kadłuba i stwarza możliwość niekontrolowanego zapłonu mieszanki paliwowo-powietrznej. W silniku istnieje konieczność stosowania zacisku średnicowego tulei w cylindrze w granicach 0.21÷0.42 mm, co wynika z rozszerzalności cieplnej elementów w warunkach jego pracy z maksymalną prędkością obrotową i obciążenia maksymalną mocą. Połączenie skurczowo-rozprężne tulei z cylindrem dla największego zacisku powoduje odkształcenie plastyczne żeliwa szarego tulei cylindrowej. Wymagana jest zmiana gatunku lub rodzaju żeliwa o wytrzymałości doraźnej powyżej 400 MPa.
EN
The paper analyzes the possible cause of self-ignition of air-fuel mixture in spark-ignition internal combustion engine loaded with maximum power during tests on the engine dynamometer stand. It leads to incorrect engine operation and may also occur during the flight of an aircraft or helicopter. In order to explain the cause of incorrect engine operation, a non-linear analysis using the finite element method was applied. A discreet model of a simplified engine cylinder assembly system comprising a cylinder body and the liner was determined. The numerical analysis includes both the mechanical force resulting from loading the cylinder liner clamp in the body as well as the pressure of the working medium pressure and the load on the non-uniform temperature field taken from engine test-bed measurements. The results of nonlinear static analysis of stresses and strains for the cylinder body-liner connection have shown that in the area of TDC where outer piston ring turns back, high stresses and plastic deformation of the cylinder liner occurr, causing a lack of contact between these elements. This disrupts the heat transfer from the cylinder liner to the cylinder body and creates the possibility of uncontrolled ignition of the fuel-air mixture.
EN
The effect of cobalt aluminate inoculant addition and melt-pouring temperature on the structure and mechanical properties of Ni-based superalloy was studied. The first major move to control the quality of investment cast blades and vanes was the control of grain size. Cobalt aluminate (CoAl2 O4 ) is the most frequently utilized inoculant in the lost-wax casting process of Ni-based superalloys. The inoculant in the prime coat of moulds and pouring temperature play a significant role in grain size control. The finest surface grains were obtained when the internal surface of shell mould was coated with cobalt aluminate and subsequently pouring was at 1480°C. The influence of selected casting parameters and inoculant addition on mechanical properties was investigated on the basis of tensile, creep and hardness testing. The effect of grain refinement on mechanical properties were consistent with established theories. Tests conducted at ambient temperature indicated a beneficial effect of grain refinement both on tensile strength and hardness. In contrast at elevated temperature during creep, the reverse trend was observed.
EN
This paper presents the results of a numerical simulation of a slope deformation process. The landslide slope “Grabina” inKoronowo near Bydgoszcz (Poland) serves as an example.Aslope profile located in the central part of the slope, between the main scarp and the toe of the landslide, was selected. The average dip of the slope is about 10, and its length is approximately 55 m. Elasticity, plasticity and viscosity properties were taken into account in the model of the soil mass that composes the slope. The visco-elastic properties are described by the Burgers model (Mainardi and Spada 2011), and the plastic ones by the Coulomb-Mohr law.Anumerical simulation was carried out by the computer code FLAC2D in the plane strain state with the assumption of the Lagrange routine. The model was discretized taking into account the results of inclinometric measurements, which proved that the slide movement was concentrated in a narrow loam zone of 0.5–1.0 m thickness. No tests of the viscosity parameters were performed, so they were determined by the back analysis and a trial and error method. The calculation results were verified by comparison with the displacement measured by the inclinometric method in three boreholes. The analysis performed demonstrated the possibility of approximating and forecasting landslide displacements by the combined Burgers and Coulomb-Mohr models.
EN
The paper presents a new method of lifetime calculations of steam turbine components operating at high temperatures. Component life is assessed on the basis of creep-fatigue damage calculated using long-term operating data covering the whole operating period instead of representative events only. The data are analysed automatically by a dedicated computer program developed to handle big amount of process data. Lifetime calculations are based on temperature and stress analyses performed by means of finite element method and using automatically generated input files with thermal and mechanical boundary conditions. The advanced lifetime assessment method is illustrated by an example of lifetime calculations of a steam turbine rotor.
EN
The paper presents the results of examination of microhardness of chemical coatings Ni-P, applied on samples of aluminium alloy for plastic processing AW-7075. The examinations have been performed on samples with three different thicknesses of the Ni-P coatings; next the influence of their thickness on the depth of material penetration by the indenter under load, as well as its influence on creep, increase of Martens hardness and on the Young’s modulus of the system of the coating with the substrate material. Hardness measurements have been performed with the use of PICODENTOR HM500 nanohardness tester (Vickers). The purpose of the examination of Ni-P coating deformation without dispersion phases is analysis of their mechanical properties in respect of the possibility of technical applications on the aluminium alloy AW-7075 (among others, by the selection of optimum thicknesses on hard aluminium alloy), as well as the determination of the possibility of applying dispersion phases in order to improve their properties.
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