Zmęczenie materiału to jeden z najczęstszych powodów uszkodzeń istniejących stalowych mostów kolejowych, zwłaszcza nitowanych. Dlatego procedura oceny trwałości zmęczeniowej jest jedną z najistotniejszych w kompleksowej ocenie nośności i trwałości istniejących mostów. Niezawodna ocena trwałości zmęczeniowej jest zazwyczaj decydująca przy szacowaniu przydatności eksploatacyjnej mostu. W pracy przedstawiono przykład oceny trwałości zmęczeniowej kratownicowego mostu kolejowego, bazującej na europejskiej procedurze opartej na Eurokodach. Procedura wykorzystuje metodę bezwarunkowej żywotności zmęczeniowej w konwencji naprężeń nominalnych. Ocena trwałości zmęczeniowej wykazała, że trwałość zmęczeniowa konstrukcji stalowej mostu jest już praktycznie wyczerpana, a dalsza żywotność zmęczeniowa konstrukcji jest zerowa. Biorąc pod uwagę wyniki przeprowadzonej oceny mostu kolejowego jednoznacznie wykazano, że istniejąca konstrukcja stalowa nie nadaje się do wykorzystania w planowanej modernizacji / przebudowie mostu oraz do dalszej eksploatacji w planowanym 50-letnim okresie życia technicznego konstrukcji.
EN
Fatigue is one of the most often reasons for failure in existing steel bridges, particularly with riveted structure. Therefore fatigue assessment is always the most important part of the complex evaluation of existing steel bridges. The reliable fatigue assessment is often decisive in the estimation of the remaining service life of a bridge. The example of a comprehensive fatigue assessment of 100 years old riveted truss railway bridge, based on European procedures and codes, has been presented in the paper. The applied procedure is based on the safe life method in the convention of nominal stresses. The bridge assessment revealed, that the remaining fatigue strength was almost exhausted and the further service life of the bridge was close to zero. Taking into account the assessment results it was also revealed, that the existing riveted truss superstructure was not suitable for further use in the railway bridge after its rehabilitation, which aimed to extend the bridge service life by the next 50 years.
Using original cold-formed rivets in repairs of airframes of helicopters is difficult due to no access to inside parts of the airframe. Thus, the main aim of the study was to investigate the possibility to use the blind rivets or hybrid joints by verification the fatigue performance of such joints that must be better than with original rivets. Riveted and hybrid joints have been experimentally tested under static and fatigue loads. Furthermore, numerical calculations of stress distribution for strapped joint have been conducted. The test results covered fatigue life of lap joints and models of repaired airframe sheets using ordinary mushroom head rivets ref. 3558A-4-10, titanium driven blind bolts with pin, ref. MBF2110AB-05-150 and modified hybrid joints. Using titanium driven blind bolts with pin instead of ordinary hammer-bucked rivets, can improve the fatigue life of element made of aluminum alloy AW 2024T3. There are advantages of replacing riveted joints with modified hybrid (rivet & adhesive) joints in threefold increase in fatigue life of repaired airframe structures.
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W pracy przedstawiono wyniki badań eksperymentalnych, których celem była ocena możliwości zastąpienia w połączeniach konstrukcji lotniczych nitów typu solid nitami jednostronnymi. Ponieważ nity jednostronne, w przeciwieństwie do nitów typu solid, składają się z wielu elementów, w ocenie jako kryterium porównawcze przyjęto nie tylko nośność połączeń, ale również odporność na zjawisko samoczynnego demontażu elementów nitów jednostronnych poddanych zmiennemu obciążeniu. W badaniach zmęczeniowych stwierdzono, że istnieje możliwość zastąpienia nitów typu solid nitami jednostronnymi, ale trwałość zmęczeniowa połączeń jednozakładowych połączeń zależy istotnie od miejsca zerwania trzpienia nita jednostronnego w procesie jego spęczania.
EN
The paper presents the results of experimental research, the aim of which was to assess the possibility of replacing rivets with solid one-sided rivets in connections of aircraft structures. Because one-sided rivets, in contrast to solid rivets, consist of many elements, the evaluation as a comparative criterion assumes not only the load capacity of connections, but also the resistance to the phenomenon of automatic dismantling of one-sided rivets subjected to a variable load. In fatigue tests, it was found that there is a possibility of replacing rivets with solid one-sided rivets, but the fatigue life of joints of one-sided joint connections depends significantly on the place of rupture of the one-sided blind pin in its heading process.
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W pracy przedstawiono wyniki badań właściwości wytrzymałościowych przeprowadzonych w próbie rozciągania dla połączeń klejowych, nitowych i klejowo-nitowych blach ze stopu aluminium EN AW-5754. Zastosowano dwie najbardziej rozpowszechnione metody wykonywania połączeń nierozłącznych, jakimi są klejenie i nitowanie oraz dodatkowo badaniom poddano połączenia powstałe z zastosowania obu metod. W procesie nitowania zastosowano pojedynczy nit zrywalny, wykonany ze stopu aluminium. W procesie klejenia wykorzystano klej epoksydowy dwuskładnikowy Epidian 57/PAC/1:1. Powierzchnię do procesu klejenia przygotowano poprzez ręczną obróbkę mechaniczną papierem ściernym P320 oraz odtłuszczanie środkiem Loctite 7063. Proces utwardzania połączeń klejowych przebiegał w temperaturze otoczenia. Analizowane połączenia poddano badaniom niszczącym, zgodnie z normą ISO 4587, na maszynie wytrzymałościowej Zwick/Roell Z150. Na podstawie wyników badań zauważono, że lepszą nośnością charakteryzowały się połączenia klejowe, jednak wynik ten nie odbiegał znacząco od wartości wytrzymałości połączenia klejowo-nitowego. Najmniej korzystnymi wynikami charakteryzowały się połączenia nitowe, co mogło być skutkiem zastosowania pojedynczego nitu.
EN
The paper presents results of a tensile test for adhesive, rivets and adhesive-riveted aluminum sheet EN AW-5754 joints. Values of strength and destructive force were presented. Due to its characteristics of used in research material finds application in almost all industries, precisely because the focus was on correctness of the technology made joints and the mechanical properties which characterized the resulting joints. Two of the most popular methods for performing permanent joints was used – bonding and riveting and hybrid of these two method. In riveting a single rivet made of an aluminum alloy was used. The holes for the rivets were previously drilled. In bonding process of the adhesive used was a two-component adhesive consisting of epoxy resin Epidian 57 and hardener PAC prepared in a stoichiometric ratio of 1:1. The sandpaper P320 machining process and degreasing with Loctite 7063 was used to surface treatment of surfaces adherends. The curing process was performed at ambient temperature. Analysed joints were destructive tested, in accordance with ISO 4587, on testing machine Zwick / Roell Z150.Based on the results observed that a better load capacity characterized by adhesive joints, but this result was similar with the load capacity of the joint adhesive-riveted. The least positive results were characterized by riveted joints, which could be due to the use of a single rivet.
Tension fields are shown to have an influence on surface pressure and on material deformation in the riveted joints in thin walled structures and particularly in semistressed skin structures. Stresses and materials displacements were analyzed in the riveted joints performing under such conditions. Special attention has been attached to estimation of the microslips occurring between rivets and holes. A thin plate panel has been used for the test sample, which under effort condition revealed tension fields.
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W pracy przedstawiono analizę porównawczą nośności, stosowanych w przemyśle lotniczym, połączeń nitowych wykonywanych z zastosowaniem nitów pełnych, nitów do zabudowy jednostronnej, nitów typu Lock-bolt oraz elementów złącznych typu Hi-lok. Badania wykazały, że połączenia wykonane nitami pełnymi posiadały nośność 20243 N, nitami do zabudowy jednostronnej 28687 N, nitami typu Lock-bolt 28281 N, łącznikami typu Hi-lok 27264 N. Nowe sposoby wykonywania połączeń nitowych zapewniają uzyskanie nośności o 35 – 42% większej od połączeń tradycyjnych.
EN
The paper presents a comparative analysis of the following issues: load capacity used in the aerospace industry, riveted joints made with application of solid rivets, blind rivets, the Lock-bolt type rivets and Hi-lok type fasteners. Studies show that the load capacity of joints made with application of solid rivets is 20243 N, and for blind rivets is: 28687 N, Lock-bolt type rivets: 28281 N, and Hi-lok type fasteners: 27264 N. As a result, new procedures designed for the riveted joints lead to the increased strength of 35 – 42% than for the traditional joints.
The article presents the analysis of the structure of the load capacity of riveted joints. For the four joining systems the lap joint specimens were made and tested in the shearing test. The joints were prepared for the three combinations of the DC01 steel and EN AW- 5754 aluminium alloy sheets with the thickness of 2mm. On the basis of the obtained load-elongation diagram tensile shear test curves, the basic parameters defined in the ISO/DIS 12996 standard were determined. In the case of the conventional riveted joints the maximum load capacity of the joint is determined by the strength of the fastener. For the joints with aluminium-steel blind rivet , the load capacity of the joint was on the strength limit of the rivet tubular part and on the strength limit of the sheet material. The strength of the SSPR joint is determined by the mechanical properties of the material of the joined sheets. From all sheets and rivet specimens arrangements the highest load capacity of the joint was obtained for the DC01 sheet material joints, and the lowest load capacity of the joint was obtained for the EN AW-5754 sheet material joints.
Sheet metal parts are widely used in airframes. Most sheet metal parts used in aircraft assembly are joined using rivets. A number of riveting parameters directly influence fatigue properties of a structure. These include a rivet length, driven head diameter, tolerance of a rivet hole and a rivet shank diameter, and a protective layer among others. Unfavourable selection or change of these parameters can lead to stress concentrations and early crack nucleation. Crack growth can cause failure of a whole structure. The selection of the riveting process parameters is usually described in a company’s internal instruction (process specifications). Some parameters can be defined in an aircraft's technical specifications. Riveting instructions among other production documentation are part of a company's closely guarded know-how. The author obtained access to two riveting instructions used in Poland and three such documents used in western Europe. The author was permitted to publish the comparison of the parameters from these documents but he is not supposed to reveal any other information. For the reasons stated above, the following cryptonyms were used in the article: Poland-1, Poland-2, West-1, West-2 and West-3. The quality of a joint also depends on rivets parameters that are defined in rivets standards. For this reason, selected rivets defined in the Polish and Russian industry standards as well as western standards are compared in this paper. Tolerances of a rivet and a hole diameter, clearances between a rivet and a hole, rivet lengths anticipated for driven head formation as well as driven head dimensions are taken into account.
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W pracy przedstawiono wyniki badań eksperymentalnych, których celem było określenie trwałości zmęczeniowej połączeń mechanicznych i klejowo-mechanicznych (hybrydowych). Do łączenia elementów wykorzystano połączenia nitowe oraz połączenia śrubowe. Stwierdzono, że trwałość zmęczeniowa połączeń jednozakładowych zależy od sił nacisku powstających w czasie montażu połączenia oraz że zastosowanie do łączenia elementów śrubowych (w tym Hi-Loków) powoduje wzrost trwałości zmęczeniowej połączeń. Potwierdzono, że zastąpienie połączeń mechanicznych połączeniami klejowo-mechanicznymi może mieć pozytywny wpływ na trwałość zmęczeniową połączeń, ale pod warunkiem ograniczenia nacisków w czasie ich montażu.
EN
This paper presents the results of experimental studies aimed at determining the fatigue life of mechanical and adhesive-mechanical (hybrid) joints. The joints were prepared with the use of rivets and screws. The results shown that the fatigue life of single lap joints depends on the pressure forces generated during the joint assembling. Furthermore, the use of screws (including Hi-Lok fasteners) for jointing elements increases the fatigue life of the joints. It confirms that the replacement of mechanical joints by adhesive-mechanical joints may have a positive impact on fatigue life of the joints, by reducing pressure forces during the joints assembling.
W artykule przedstawiono wyniki badań eksperymentalnych oraz analiz numerycznych MES związane z procesem zakuwania nitu. Analizie poddano stosowane w polskim przemyśle lotniczym nity z łbem kulistym z materiału PA24 oraz blachy ze stopu D16CzATW. Zbadano, jak siła nitowania wpływa na charakterystyczne wymiary zakuwki oraz ekspansję otworu nitowego, a następnie uzyskane wyniki porównano z wynikami analiz MES. Ponieważ dotychczas stosowane metody pomiaru ekspansji otworu mogą być obarczone błędem, opracowano własną metodę pomiaru, cechującą się większą dokładnością. Zbadano, jak przyjęty w analizach MES model materiału nitu wpływa na jakość otrzymywanych wyników. Wykazano, że wierne odtworzenie procesu nitowania w MES wymaga odpowiedniego zdefiniowania modeli materiałowych stosowanych w tych analizach. Ponadto określono wpływ siły zakuwania nitu na rozkład oraz wielkość resztkowych naprężeń promieniowych i obwodowych wokół otworu nitowego.
EN
Experimental results and numerical FE analysis related to the riveting process are considered in the paper. The research has focused on the round head rivet and D16CzATW sheet material used by Polish aircraft manufacturers. The effect of rivet squeeze force on the rivet driven head dimensions and rivet hole expansion was experimentally investigated and the results were compared with the FE results. In view of an insufficient accuracy of hole expansion measurement methods used so far, a novel more accurate measurement technique developed by the present authors has been applied. FE results were obtained for various models of the rivet material. It was shown that an adequate numerical modelling of the rivet installation is conditioned by appropriate assumptions about the constitutive characteristics of the rivet material. The impact of the squeeze force on distributions and values of residual stresses generated by riveting was also determined.
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.
Evaluation of the fatigue load, the rivet squeezing force, the velocity of rivet close up and the hole diameter before sizing (after drilling) effect on the fatigue life of specimens with sized and riveted hole was presented in this paper. The work contains two parts. Design of experiment and the results of the fatigue tests performed by the described experiment plan was presented in the first part. The statistical analyses and examples of using the mathematical model of the experimental unit were presented in the second part.
Evaluation of the fatigue load, the rivet squeezing force, the velocity of rivet close up and the hole diameter before sizing (after drilling) effect on the fatigue life of specimens with sized and riveted hole was presented in this paper. The work contains two parts. Design of experiment and the results of the fatigue tests performed by the described experiment plan was presented in the first part. The statistical analyses and examples of using the mathematical model of the experimental unit were presented in the second part.
The X-ray diffraction method is the best, widely available, non-destructive measurement method used to determine the residual and load stresses in crystalline materials. This method can be applied without any limitations to flat specimens. Depending on the equipment geometry, the type of material and geometry of the specimen, there are many limitations, restrictions and recommendations which have to be fulfilled to obtain reliable results. This was the reason for working out a methodology for X-ray diffraction stress measurements for riveted specimens.The first case to analyze is the necessity of choosing an X-ray tube suitable for the specimen material which will give the diffraction peaks in the range of 2Θ angles between 120° and 180°. Afterwards it is crucial to make the best selection of Bragg's angle 2Θ. In the vast majority of cases the best selection is the possibly biggest 2Θ angle because of the best accuracy of the measurement. However, for example for aluminum alloys (for CrKα radiation), this choice is not so obvious. It is much more convenient to perform measurements not for the highest diffraction angle. The best selection in this case is 2Θ=139,3°, and not 156,7°. Other selections which are necessary to be made before measurements are the collimator diameter, time of exposure, ψ tilts and φ oscillations. The proper selection of these parameters is crucial for the fast and efficient performing of measurements and for obtaining reliable results. Before performing the measurement, especially in the case of the specimen with complicated geometry (for example in the case of riveted specimens made of aluminum alloys), it is necessary to analyze the results obtained paying special attention to the possibility of the appearing of the rivet head/driven rivet head shadow during the measurement. The work describes differences between the X-ray stress measurement results obtained without any interference and the results received after eliminating the selected diffraction peaks for which the shadow of rivet head/driven rivet head has appeared.
The goal of the project was to increase the fatigue life of the riveted joints in order to achieve an increase in the aircraft service life, a smaller number of inspections and, consequently, lower aircraft operating costs. This goal was achieved by the analysis and optimization of the riveting process as well as by improving the fatigue life prediction methods (crack initiation and propagation). The project outcomes enable a more precise fatigue life estimation and an increase in Time Before Overhaul (TBO) for currently used aircraft, as well as optimize the design of new aircraft from the fatigue point of view.
The aim of the project was to improve fatigue performance of riveted joints in airframes. Fatigue strength of a joint depends on structural, material and manufacturing factors. The project involved numerical and experimental analysis of material factors and manufacturing imperfections. The paper deals with the analysis of material structure and properties by means of the optical and SE methods. Static monotonic tests for sheet and rivet materials were carried out. ARAMIS optical system was used for the study of deformation and strain fields in the material during loading. This tool offers the possibility of a non-contact measurement with 3D image correlation methods (digital image correlation, DIC) using high-resolution digital CCD cameras. In ductile materials (such as aluminium alloy), subjected to appropriate loading conditions, voids may form, which grow and coalesce leading to crack formation and potential failure. A micro crack may be initiated at the inclusion particles and then voids grow around it. Experimental studies showed that these processes are strongly influenced by hydrostatic stress (Gurson’s material model). SEM analysis of material structure was carried out after performing static tests. In the paper, the authors present the influence of a material model on the results of numerical simulation of the tensile loaded samples with open and riveted holes. The application of Gurson’s material model allows observation of crack growth in the sample cross-section and determination of the sheet rupture as the moment when constraint force decreases to zero (material separation occurs).
Riveting is the most commonly used method of joining sheet metal components of the aircraft structure. The riveted joints are critical areas of the aircraft structure due to severe stress concentrations and effects such as fretting and secondary bending. The most spectacular and wellknown evident of this was the accident of Boeing B737 of Aloha Airline in 1988, when during the flight at altitude of 7300 m a large part of fuselage skin was removed due to explosive decompression. The investigation showed that the reason for this accident was widespread fatigue damage of riveted joints. This accident was an impulse for establishing many research programs around the world focused on fatigue of riveted joints.
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W pracy zawarto wyniki badań nad możliwością zastąpienia tradycyjnych połączeń nitowych z nitem zakuwanym i zrywalnym nowymi połączeniami z użyciem nitu samowykrawającego. Dla czterech różnych systemów scalania wykonano połączenia z blach stalowych DC01 oraz stopu aluminium AW-5754 o grubości 2 mm. Przeanalizowano zachowanie się owych połączeń podczas przenoszenia obciążenia stycznego oraz normalnego. Eksperymentalnie zbadano wpływ układu materiału połączonych warstw na przebieg krzywej ścinania dla różnych systemów nitowania.
EN
In this paper investigation results of the possibility to replace traditional riveted joints with a blind rivet and blind hermetic rivet with the new solution of using solid self-piercing rivet is presented. The connection for the four different joining systems was made from DC01sheet steel and AW-5754 aluminum alloy sheet 2 mm thick. The behavior of these connections when moving the tangential and normal loads was analyzed. The effect of layers of connected material on the shear curve for different systems riveting was experimentally investigated.
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W artykule przedstawiono technologię montażu szwów w konstrukcjach lotniczych z wewnętrznym hermetykiem, których nitowanie celowo wykonuje się w okresie przed utwardzeniem hermetyku (w czasie jego żywotności).
EN
Article covers joint assembly process for aviation structures with seam sealant, riveting of which is reasonable to fulfill while sealant is spreadable.
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The article presents comparative analysis of destructive force values for adhesive, adhesive-riveted and titanium alloy riveted joints, widely applied in aircraft industry. The analysis was conducted for three types of assembly joints: adhesive, adhesive-riveted and riveted. The two joints variants considered differed in the length of the lap, the number and the distribution of rivets. The riveted and adhesive-riveted joints tested included two or five rivets. Moreover, two lap lengths were applied for all the tested joint types (adhesive, adhesive-riveted, riveted), 16 and 32 mm. In the case of single-riveted joints (2 rivets) the lap length was 16mm, while for the other sample (5 rivets) - 32 mm. The results of the tests led to observe the increase of the destructive force value in the case of adhesive joints with the increase of the lap length. The observation was not dissimilar for the riveted and adhesive-riveted joints. The comparison of the three joint types of equal lap length indicated that the destructive force value for adhesive-riveted and riveted joints difference was negligible, while lower values could be observed in the case of adhesive joints.
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