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EN
The paper evaluates the causes related to the fatigue damage in a conveyor slide plate, exposed to high-frequency cyclic loads. The plate was made of 1.4301 acid-resistant steel. The fractography showed that the plate failure was caused by fatigue crack. A nonlinear analysis of plate deformation was conducted using the finite element method (FEA) in LS-Dyna software. The maximum normal stresses in the plate fracture were used in further analysis. A “fatigue limit” calculated initially using a FITNET procedure was above the maximum stress calculated using FEA. It indicates that the structural features of the plate were selected correctly. The experimental test results for 1.4301 acid-resistant steel were described using a probabilistic Weibull distribution model. Reliability was determined for the obtained S-N curve at 50% and 5% failure probability allowing for the selected coefficients (cycle asymmetry, roughness, variable load) and the history of cyclic loading. Cumulative damage was determined using the Palmgren-Miner hypothesis. The estimated fatigue life was similar to the actual value determined in the operating conditions for the S-N curve at 5% failure probability. For engineering calculations, the S-N curve at max. 5% failure probability is recommended.
EN
Tooth fracture is the most dangerous form of gear wear that excludes the gear from further use. In order to counteract the occurrence of this type of damage, it is very important to properly design the toothed gear. To calculate the gear tooth bending strength, a strength parameter called the nominal stress number σFlim is necessary. ISO 6336-5:2003(E) and available material databases provide σFlim values for the most popular engineering materials used for gears, including those for case-hardened steels. There is, however, no data for a new generation of nanostructured engineering materials, which are the subject of research conducted at the Tribology Department of ITeE – PIB. The σFlim parameter is most often determined in cyclic fatigue tests on toothed gears with specially selected tooth geometry. In order to determine the above strength parameter, a pulsator (symbol T-32) was developed and manufactured at ITeE-PIB in Radom. The article presents a new device, research methodology, and the results of verification tests for case-hardened steel 18CrNiMo7-6, confirming the correctness of the adopted design assumptions and the developed research methodology. The results of tooth bending fatigue tests are the basis for the selection of a new engineering material dedicated to gears, which later undergoes tribological testing.
PL
Złamanie zęba u podstawy jest najbardziej niebezpieczną formą zużycia kół zębatych wykluczającą je z dalszej eksploatacji. W celu przeciwdziałania wystąpieniu tego rodzaju uszkodzenia bardzo istotne jest właściwe zaprojektowanie koła zębatego. Do obliczeń wytrzymałościowych kół zębatych na złamanie zęba niezbędny jest parametr wytrzymałościowy zwany granicą zmęczenia σFlim. Norma ISO 6336–5:2003(E), a także dostępne bazy materiałowe podają wartości σFlim dla najbardziej popularnych materiałów wykorzystywanych na koła zębate, w tym dla stali nawęglanych. Brak jest jednak jakichkolwiek danych dla nowej generacji nanostrukturalnych materiałów konstrukcyjnych, które są przedmiotem badań prowadzonych w Zakładzie Tribologii ITeE – PIB. Parametr σFlim wyznacza się najczęściej w badaniach pulsacyjnych na kołach zębatych o specjalnie dobranej geometrii uzębienia. W celu wyznaczenia powyższego parametru wytrzymałościowego w ITeE – PIB w Radomiu opracowano i wytworzono pulsator (o symbolu T–32). W artykule przedstawiono nowe urządzenie, metodykę badawczą oraz wyniki badań weryfikacyjnych dla stali konstrukcyjnej 17HNM – nawęglanej i hartowanej, potwierdzające poprawność przyjętych założeń konstrukcyjnych i opracowanej metodyki badawczej. Wyniki badań zmęczeniowych stanowią podstawę wyboru nowego materiału konstrukcyjnego dedykowanego na koła zębate, które później poddaje się przekładniowym badaniom tribologicznym.
3
Content available Accuracy of determined S-N curve by selected models
EN
The study shows models defining the relationship between the fatigue life and the stress amplitude. The first models have been developed at the beginning of the 20th century; however, new models are still being developed. The author decided to compare the most commonly used model, i.e. a linear regression model and the two models discussed in ISO-12107. The comparison also included some recently developed models, i.e. Strohmeyer, Basenaire, Castillo et al., Kohout and Vechet, Leonetti et al., and Pasual and Meeker model, including its modified version. The fatigue data for S355J2+C and AISI 1045 steel were used for the comparison. The best estimate of the fatigue life was obtained by using the modified Pasual and Meeker model.
EN
An experimental study was carried out on the fatigue behaviour of multi-axial warp-knitted fabric composites. Composite samples reinforced with multi-axial warp-knitted fabric/matrix were manufactured by the vacuum-assisted resin transfer moulding method. Tensile-tensile fatigue cycling was carried out at different load levels, and S-N curves, tensile stress-strain curve and stiffness degradation of the multi-axial composite samples were obtained. Finally post-fatigue tensile tests were done at a stress level of 75%, at the stages of 1/3N and 2/3N, and the equivalent residual strength and stiffness degradation were obtained.
PL
Dokonano oceny właściwości mechanicznych i zmęczeniowych kompozytowych dzianin wieloosiowych. Kompozyty wzmocnione dzianiną wieloosiową wytworzono przy zastosowaniu próżniowej metody formowania. Dokonano oceny zmęczenia materiału i właściwości wytrzymałościowych przy różnych poziomach obciążenia. Przedstawiono krzywe S-N, krzywą naprężenie-odkształcenie i degradację sztywności wieloosiowych próbek kompozytowych. Wykonano również testy zmęczenia materiału przy poziomie naprężenia 75%, w etapach 1/3N i 2/3N. Omówiono równoważną wytrzymałość szczątkową i degradację sztywności kompozytowych dzianin wieloosiowych.
EN
The paper presents two approaches of determining S-N fatigue characteristics. The first is a commonly used and well-documented approach based on the least squares method and staircase method for limited fatigue life and fatigue limit, accordingly. The other approach employs the maximum likelihood method. The analysis of the parameters obtained through both approaches exhibited minor differences. The analysis was performed for four steel construction materials, i.e. C45+C, 45, SUS630 and AISI 1045. It should be noted that the quantity of samples required in the second approach is significantly smaller than with the first approach, which translates into lower duration and costs of tests.
EN
The study presents two approaches to plotting an S-N curve based on the experimental results. The first approach is commonly used by researchers and presented in detail in many studies and standard documents. The model uses a linear regression whose parameters are estimated by using the least squares method. A staircase method is used for an unlimited fatigue life criterion. The second model combines the S-N curve defined as a straight line and the record of random occurrence of the fatigue limit. A maximum likelihood method is used to estimate the S-N curve parameters. Fatigue data for C45+C steel obtained in the torsional bending test were used to compare the estimated S-N curves. For pseudo-random numbers generated by using the Mersenne Twister algorithm, the estimated S-N curve for 10 experimental results plotted by using the second model, estimates the fatigue life in the scatter band of the factor 3. The result gives good approximation, especially regarding the time required to plot the S-N curve.
EN
This paper presents analytical methods for determination of the curve for a high-cycle fatigue. It has been found based on qualitative and quantitative verification that the error introduced by these methods can be as large as 3-fold length of the experimental life. In addition, the wrong result can lay on either the safe or the unsafe side with equal probability. Therefore, an analytical-and-experimental (hybrid) method has been proposed. Verification of computed characteristics vs. experimental data demonstrated that the “proprietary” proposal reduced the error. In addition, an approximate error depending on the number of experiments has been determined based on the computations.
EN
The article collates guidelines concerning experimental construction of the S-N fatigue curves within a limited fatigue life range. An attempt is made to compare these guidelines, based on experimental data recorded during rotating bending of a notched specimen made of 42CrMo4. The recorded differences in fatigue life values between the constructed curves reach the maximum of 12.2%. According to the above guidelines, the number of tests in particular test series varies from 6 to 28. Based on the performed analysis a conclusion was made that the increase in the number of tests leads to the increase of accuracy but, on the other hand, remarkably increases the time of the experiment and, consequently, its cost. In this context, it is the research worker who, taking into account a possible future use of the fatigue curve, should individually decide about its accuracy.
9
Content available remote Application of mini specimens to high-cycle fatigue tests
EN
Determining complete material fatigue characteristics (S-N curve) is time-consuming and very expensive. Searching for faster procedures of determining the S-N curve, one can use approximate methods which are burdened with qualitative and quantitative error. Such characteristics differ from the real experimental studies results. Yet another method involves the use of mini specimens; the specimens the dimensions of which are lower than the normative sample. It allows for performing tests using much cheaper test stands. In the specimens researched there is a size effect which is broadly discussed in the available literature. The present work offers a review of the current theoretical knowledge on the size effect. There was analysed the geometry of mini specimens applied in experimental studies. Selected works with the use of mini specimens have been reviewed. Areas have been defined in which the mini specimen application is justifiable.
EN
Operated helicopter is submitted to varying loads spectrum. Important, for the sake of assurance structure integrity, is definition of the actual value of loads which act on individual structure element. The object of this analysis was the Mi-24 helicopter swashplate lever arm. Life estimation of this element with analytical method, for the sake of complicated geometry, can be problematical. It would be necessary to use considerable generalization which would certainly decrease results reliability. Numerical analysis allows one to create arbitrary shapes but it is necessary to properly define boundary condition. These work presents methodology for determining fatigue life of the structure element with use of strain gauges, which serve to define the real flight loads. Next step was to determine accurate element shape with the aid of 3D scanner ATOSIII. Geometry was imaged in CAD/CAM environment. After importing the geometry model to MSC.Patran the numerical model was developed. The analysis was done in the scope of linear static analysis. Estimation of fatigue life was done with the aid of MSC.Fatigue computer program. Fatigue life was estimated according to the Palmgren's - Miner's cumulation damage rule. Test was done in order to define potential fatigue damage sites and defining fatigue life of element. That allows verifying plane overhaul life and fully using helicopters potential next to keeping requested level of safety.
PL
Warunki losowych stanów naprężenia są bardzo często powodują powstawania pęknięć zmęczeniowych elementów maszyn i konstrukcji mechanicznych pod wpływem obciążeń eksploatacyjnych. Celem niniejszej pracy jest porównanie trwałości obliczeniowych z eksperymentalnymi badań zmęczeniowych wykonanych w warunkach jednoosiowego losowego satnu naprężenia próbek wykonanych ze stali 18G2A. Badania prowadzono na próbkach płaskich o zmiennym przekroju w części pomiarowej, wykonanych zgodnie z zaleceniami normy [1]. Parametry obróbki mechanicznej były tak dobrane, że zabezpieczały próbki przed powstawaniem przypaleń szlifierskich, pęknięć i innych wad powierzchniowych oraz ograniczały do minimum zgniot powierzchniowy. Materiałem wyjściowym do produkcji próbek była blacha o grubości 10 mm walcowana wzdłuż (w) i w poprzek (wp).
EN
The paper contains considerations on fatigue life determined on the basis of tests performed under uniaxial stress state. Specimens made of 18G2A steel were tested. The calculated fatigue lives were compared with those obtained from the tests. The calculations were performed according to the S-N characteristic (the Wöhler curve) plotted according to the ASTM standard, and in the scatter for the assumed significance level 5%, typical for fatigue tests. The results of calculations conform with the experimental results within all the range.
PL
Celem pracy było oszacowanie trwałości zmęczeniowej węzłów siłowych skrzydła samolotu Su-22. Powyższy cel zrealizowano, wykonując kompleksowe badania obejmujące między innymi analizę profilu eksploatacji samolotów, pomiary tensometryczne podczas lotów oraz modelowanie numeryczne. W niniejszej pracy przedstawiono zarys działań realizowanych w poszczególnych fazach badań. Opisano zarówno stosowane metody obliczeniowe, jak i sprzęt pomiarowy. Obliczenia trwałości wykonano metodą krzywej S-N na podstawie rzeczywistego widma obciążeń, stanu naprężenia wyznaczonego podczas obliczeń numerycznych.
EN
Assessment of the fatigue life of the Su-22 wing-root joint was rhe purpose of the work. Numerous tasks have been carried out, e.g., operational profile analysis, flight tests, stress measurement, as well as numerical calculations. The general algorithm of this complex work was presented in this paper. The applied methods and instrumentation were described. Fatigue life calculations was carried out using idea of S-N safe curve based on the real load spectrum and on the stress distribution calculated by meas of FE technique.
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