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1

Research on the Degradation Process of Railway Rails Due to Lifespan Exceeding

Berbecaru Andrei-Constantin, Coman George, Ciucă Sorin, Gherghescu Ioana-Arina, Sohaciu Mirela, Grădinaru Catalin, Predescu Cristian

Archives of Metallurgy and Materials

|

2022

|

Vol. 67, iss. 2

535--540

EN

The paper presents the impact of exceeding the railway rails lifespan which usually causes a railway structural failure, thus an accident. The research highlights the rails’s high degradation, especially on the running area, consisting in 60-70% weight loss by advanced wear of the rail, followed by fatigue fracture caused by alternating cyclic stresses that initiates the crack and also by tensile stresses resulting in the crack growth. The chemical composition, structural and mechanical properties were analyzed in order to establish the causes that led to the railway rails rupture.

2

Effect of non-zero mean stress bending-torsion fatigue on fracture surface parameters of 34CrNiMo6 steel notched bars

Macek Wojciech, Szala Mirosław, Trembacz Jarosław, Branco Ricardo, Costa José

Production Engineering Archives

|

2020

|

Vol. 26, Iss. 4

167--173

EN

Modern methods of testing materials require the use of the latest technologies and combining measurement and calculation methods. It is important to find a quantitative way of describing, among other things, the failures so that it can help to design with high accuracy. This paper studies loading orientations on crack shape and fracture surface changes. The advantage of the entire fracture surface method is simplicity and applicability in studies on other materials, shapes and loadings. A higher values of fracture surface parameters (Sx, Vx) was observed in failure specimens with lower σ/τ (B/T) ratios. It has been observed that largest crack lengths with a small number of cycles occur for loading combinations different then B=T. As well as analyzed surface parameters Sx, Vx, are higher for larger number of cycles to crack initiation (Ni) values.

3

Fatigue characteristics of materials used in transport industry applications

Belan Juraj, Kuchariková Lenka, Mazur Magdalena, Tillová Eva, Chalupová Mária

System Safety : Human - Technical Facility - Environment

|

2019

|

Vol. 1, nr 1

810--818

EN

Designers have a major interest about fatigue properties of materials used in transport industry. Each component in transport works under alternating stress. From this point of view the fatigue properties are important for single parts lifetime resulting into safety of whole components as cars and airplanes what leads to safety on the roads or air and have influence on human life as well. Therefore this paper deals with fatigue properties of wrought Inconel alloy IN 718 and aluminum cast alloy AlSi9Cu3. Both materials were put on fatigue push – pull test, but Ni – based IN 718 alloy at frequency of loading around 20 000 kHz (High Frequency High Cycles Fatigue) and aluminum alloy AlSi9Cu3 at frequency of loading around 80 Hz (Low Frequency High Cycles Fatigue). These parameters were chosen with respect of usage such materials for production of components used in transport industry applications. Results after fatigue tests are presented as Wohler curve. For prediction of source of fracture the SEM fractography analysis of fatigue fracture surfaces was made.

4

The researches of influence of strengthening on fatigue strength of aluminium wires for OHL conductors

Jurkiewicz Bartosz, Smyrak Beata, Zasadzinska Malgorzata, Franczak Krystian, Strzepek Pawel

Archives of Civil and Mechanical Engineering

|

2019

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Vol. 19, no. 3

862--870

EN

The traditional overhead conductors (OHL conductors) are made from a high strength steel core and several layers of aluminium wires. Operating conditions under variable stress derived from von Karman vortices leads to fatigue cracking of the outer layer of wires, first of the outer layer, and then the inner layers. The dynamic component of tension, dependent on the static tension of the wire, its geometric construction and rigidity (the number and diameter of the wires, the coil angle), lead to fatigue destruction of the wires. The conse-quence of this is the gradual degradation of the conductor as a whole, which is a decrease in the electrically active cross-section, and as a result of overheating, also in its mechanical properties. The ultimate effect is breaking of the conductor and a fault of the power line. The subject of the paper concerns fatigue strength tests of cold-drawn commercially pure aluminium wires in different temper of strain hardening. The paper attempts to describe fatigue strength, research methodology, description of a research stand. Based on study results and their analysis, conclusions were formulated concerning the differentiation of fatigue strength and EN AW-1370 wires used for overhead power conductors.

5

Influence of microstructure on fatigue fracture of Ti–2.5Cu alloy

Hepner M., Rozumek D.

Inżynieria Materiałowa

|

2018

|

Vol. 39, nr 2

84--89

EN

The paper presents the test results obtained for fatigue crack growth in Ti–2.5Cu alloy subjected to bending in notched specimens. The tested specimens were subjected to various variants of heat treatment. The tests were performed at the fatigue test stand MZGS-100 under loading frequency 28.4 Hz. The study was conducted for a constant amplitude of moment Ma = 11.2 N∙m and different values of stress ratio R = –1 and 0. Influence of the microstructure on the crack paths in plane specimens was observed. The propagation of the main crack in the two-phase structure takes place both transcrystallinely through α phase grains and through the boundaries of the grains in metastable phase precipitation areas, whereas the propagation of the side cracks takes place along the precipitates of the coniferous phase. In the material after supersaturation and ageing at a temperature of 415°C, after Nf = 12 000 cycles (R = 0), no side cracks were observed, and the main crack develops in both phases that form the microstructure shown in Figure 10. A different fracture mechanism occurs for the material after supersaturation and ageing (Nf = 11 000 cycles) at a temperature of 760°C. In this case, an irregular path of the main crack is observed, whose direction in the micro-areas is determined by the precipitates of the intermetallic phase (Fig. 11). From the beginning of the main crack and along its entire length, numerous side cracks develop that are over 150 μm in length. The components of the structure that facilitate the propagation of cracks and determine their direction are clusters of Ti2Cu precipitates on the boundaries of α phase. In case of this alloy, the impact of the mean stress value during cyclic testing decreases fatigue life considerably.

PL

Celem pracy była ocena trwałości zmęczeniowej stopu Ti–2,5Cu (IMI230) po różnej obróbce cieplnej oraz określenie różnic w mechanizmie propagacji pęknięć zmęczeniowych uwarunkowanych odmienną mikrostrukturą.

6

Identification of the cause of the stem neck fracture in the hip joint endoprosthesis

Ryniewicz A. M., Bojko Ł., Ryniewicz A., Pałka P., Ryniewicz W.

International Journal of Applied Mechanics and Engineering

|

2018

|

Vol. 23, no. 1

223--234

EN

Endoprosthesis stem fractures are among the rarest complications that occur after hip joint arthroplasty. The aim of this paper is to evaluate the causes of the fractures of the Aura II stem neck, which is an element of an endoprosthesis implanted in a patient. In order to achieve it, a radiogram was evaluated, the FEM analysis was carried out for the hip joint replaced using the Aura II prosthesis and scanning tests as well as a chemical analysis were performed for the focus of fatigue. The tests performed indicate that the most probable causes leading to the fatigue fracture of the Aura II stem under examination were material defects in the process of casting and forging (forging the material with delamination and the presence of brittle oxides and carbides) that resulted in a significant reduction of strength and resistance to corrosion. In the light of an unprecedented stem neck fracture, this information should be an indication for non-destructive tests of ready-made stems aiming to discover the material and technological defects that may arise in the process of casting and drop forging.

7

Variable surface temperature distribution as a criticality indicator of the self-heating effect in composites

Katunin A.

Advances in Materials Science

|

2018

|

Vol. 18, nr 1(55)

5--12

EN

Since self-heating effect may significantly intensify structural degradation, it is essential to investigate its criticality, i.e. the temperature value at which fatigue fracture is initiated. In this paper, a new and sensitive criticality indicator based on evaluation of evolution of surface temperature distribution was proposed and experimentally validated. It was shown that comparing to other measurement techniques the presented approach allows for precise evaluation of the critical value of the self-heating temperature. The properly determined critical value may be helpful both during design and operation of elements made of polymers and polymeric composite.

8

Fatigue growth analysis of multiple coplanar crack using real and substitute crack contour

Grabowski P., Jankowiak A.

Zeszyty Naukowe Instytutu Pojazdów / Politechnika Warszawska

|

2017

|

z. 4/113

51--62

EN

Structural components of construction machinery often contain cracks or crack-like defects initiated at notches under service cycling loading. The notches most exposed to the fatigue degradation process are often welded joints. It is caused by the fact that those joints usually contain initial imperfections (e.g. internal flaws and defects), which may start to grow during the machine’s operation. In many types of machines, those cracks can decide on the process of material destruction and overall operating time. In order to determine the time spent on the stable fatigue growth of such cracks, the crack growth analysis needs to be carried out. The results of such analyses may be very helpful in estimating overall fatigue durability of welded structures. Because of imperfections occurring during a manufacturing process, welded joints are often the locations where multiple cracks may be observed, which means more than one crack growing in one plane. In most cases, for fatigue growth analyses of such cracks, commonly used are the procedures that suggest to replace real crack contours with one substitute contour. Those substitute contours are usually regular shapes (circular, elliptical) that cover the whole considered group of cracks or the major part of their real total area. Furthermore, using such type of a substitute contour allows you to analyze a single crack growth with available methods (e.g. well-known analytical solutions). However, this approach can result in conservative fatigue life assessments. In some cases the level of above mentioned conservatism is very hard to determine, which may result in overdesigning of particular components of the structure (either its dimensions or total weight of the structure), which often is unacceptable from economical point of view. The paper presents selected cases of fatigue growth analyses of multiple cracks, with the usage of method that requires substituting group of cracks with idealized single contour. Some variations of substitute contours are considered. The results are compared to the ones obtained during analyzes of real crack contours. During the assessments of substitute cracks also an attempt to estimate the level of conservatism was taken. The analyses were done for cracks undergoing tensile loading (Mode I) with uniform stress distribution.

PL

Elementy konstrukcji nośnych maszyn roboczych często zawierają pęknięcia lub szczelinopodobne wady inicjujące się w węzłach konstrukcyjnych (karbach) pod działaniem obciążeń eksploatacyjnych. Najbardziej narażone na degradację zmęczeniową węzły konstrukcji nośnych to z reguły połączenia spawane. Jest to spowodowane faktem, że zawierają one po-technologiczne niedoskonałości (wady, niezgodności spawalnicze), które mogą się powiększać w trakcie eksploatacji maszyny. W wielu przypadkach może to decydować o zniszczeniu materiału i całkowitej trwałości elementu. Aby wyznaczyć czas stabilnego wzrostu takich wad, musi być przeprowadzona analiza wzrostu pęknięcia. Wyniki takiej analizy są istotne dla oszacowania całkowitej trwałości zmęczeniowej spawanych konstrukcji nośnych. Niedoskonałości procesów wytwarzania sprzyjają występowaniu wielokrotnych, (czyli więcej niż jednej w tej samej płaszczyźnie) wad czy pęknięć w połączeniach spawanych. Zazwyczaj w takich sytuacjach, przy analizie wzrostu pęknięć zmęczeniowych, stosuje się procedury zastępowania grupy rzeczywistych pęknięć pojedynczą szczeliną zastępczą. Te zastępcze kontury szczelin mają zazwyczaj regularny kształt (kołowy, eliptyczny), który obejmuje całą grupę pęknięć lub zasadniczą część ich sumarycznego pola powierzchni. Zastosowanie szczeliny zastępczej o wyidealizowanym kształcie pozwala na analizę wzrostu pęknięcia z wykorzystaniem dostępnych metod (np. znanych rozwiązań analitycznych). Podejście takie może jednakże prowadzić do istotnego niedoszacowania trwałości zmęczeniowej. W wielu przypadkach poziom tego konserwatyzmu jest niezwykle trudny do określenia, co może skutkować np. przewymiarowaniem elementów konstrukcji nośnej (zarówno w ujęciu wymiarowym, jak i masowym), co najczęściej jest nie do przyjęcia z ekonomicznego punktu widzenia. W pracy przedstawiono wybrane przypadki analiz wzrostu wielokrotnych pęknięć zmęczeniowych, wykonanych metodą zastąpienia pary współpłaszczyznowych pęknięć wyidealizowaną szczeliną zastępczą. Rozpatrzono kilka szczelin zastępczych o różnych kształtach. Wyniki porównano do wyników analizy wzrostu dwóch rzeczywistych pęknięć. W ramach analiz wzrostu dla szczelin o kształtach zastępczych podjęto próbę oszacowania skali konserwatyzmu takiego oszacowania. Analizy przeprowadzono dla pęknięć poddanych działaniu rozciągania przy równomiernym rozkładzie naprężeń (Mode I).

9

A Fatigue Fracture Study on TDCB Aluminum Foam Specimen of Type Mode III Bonded with Adhesive

Lee J. H., Cho J. U.

Archives of Metallurgy and Materials

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2017

|

Vol. 62, iss. 2B

1359--1362

EN

This paper studies the characteristics of junction structure of closed-cell type aluminum foam, which is generally used as a shock absorber. TDCB specimens were designed for mode III type with thickness as a variable and performed a fatigue experiment on them by thickness. As the result, the load value of all specimens peaks under 0 to 25 cycles and decreases as the cycles increase. As the specimen thickens by 10 mm, the maximum load value is 1.2 times. When the thickness increases by 20 mm, the maximum value increases by 1.5 times. This study result can be utilized by investigating the mechanical characteristics of TDCB specimens for mode III type under fatigue loading conditions systematically and efficiently.

10

Microdamage distribution in fatigue fractures of bone allografts following gamma-ray exposure

Presbítero G., Hernandez-Rodríguez M. A. L., Contreras-Hernandez G. R., Vilchez J. F., Susarrey O., Gutiérrez D.

Acta of Bioengineering and Biomechanics

|

2017

|

Vol. 19, no. 4

43--53

EN

Although clear evidence of significant differences in bone properties have been extensively studied, results vary under the ranges usually used for sterilization purposes (25-35 kGy). Hence, the aim of this work was the study of the mechanical properties and microdamage development of human bones used as allografts following gamma-ray exposure, followed by an extensive statistical analysis of microdamage effects in fatigue behaviour. Methods: Specimens of the cortical region of human femurs were exposed to 15-25 kGy and 26-30 kGy radiation levels, then they were subjected to compression fatigue tests until fracture. The fatigue life was determined in relation to the radiation level, and the evolution of microdamage was assessed through fluorescence microscopy in order to calculate characteristic lengths of microcracks. Results: Significant differences in fatigue life were detected (p < 0.05) between non-radiated (control) and radiated specimens, resulting in a drastic 89.2% fatigue life reduction of the 15-25 kGy group, and 95.3% in the 26-30 kGy group in comparison to the control. Microdamage analysis showed a considerable increase in microcrack lengths when bone was exposed to gamma radiation, which may indicate that bones used as allografts could fracture at some point when subjected to in vivo loading conditions. Conclusions: The results of our research indicate that, even if a range of 15-25 kGy is suggested to sterilize bone allografts, such practice needs to be reconsidered. In addition, with use of Weibull distribution, this work describes the conditions in which microcracks grow towards the fracture of bones in relation to the decrease in their mechanical properties.

11

Preliminary evaluation of possibility of coplanar multiple cracks growth modelling with usage of two-dimensional weight function

Grabowski P., Jankowiak A.

Zeszyty Naukowe Instytutu Pojazdów / Politechnika Warszawska

|

2016

|

z. 4/108

129--146

EN

Structural components of construction machinery are subjected to fatigue degradation, caused mainly by operating conditions. The most sensitive to the phenomenon are welded joints of the structure, where cracks can often initiate. They might be decisive for whole structure’s fatigue resource, so modeling those basing on real operational loading should be considered as an essential part of whole machine’s fatigue resource assessment. In such welded joints may occur more than one two-dimensional crack in a planar section (initiated and propagating of internal flaws after welding process). This paper tries to give the preliminary answer the question about possibility to apply two-dimensional weight function (WF2D) for calculation of stress intensity factors’ values for multiple, coplanar cracks and to model their growth.

PL

Konstrukcje nośne maszyn roboczych, z uwagi na warunki eksploatacji, są narażone na degradację zmęczeniową. Szczególnie wrażliwe na nią są węzły spawane występujące w połączeniach poszczególnych elementów, gdzie często inicjują się pęknięcia zmęczeniowe. To one w dużej mierze decydują o trwałości zmęczeniowej węzłów konstrukcyjnych, a zatem modelowanie ich wzrostu w oparciu o rzeczywiste obciążenia eksploatacyjne stanowi istotny element oceny zasobu eksploatacyjnego maszyny. W rzeczywistych spawanych węzłach konstrukcyjnych, w jednej płaszczyźnie przekroju może występować więcej niż jedno pęknięcie dwuwymiarowe (zainicjowanie pęknięć i ich propagacja może nastąpić np. z występujących w tej płaszczyźnie niezgodności spawalniczych). Niniejsze opracowanie stanowi próbę sprawdzenia możliwości zastosowania metody dwuwymiarowej funkcji wagowej (WF2D) do wyznaczania współczynników intensywności naprężeń dla współpłaszczyznowych pęknięć wielokrotnych i modelowania ich wzrostu.

12

Influence of 65G steel microstructure on crack faces friction factor under mode II fatigue fracture

Ivanytskyj Y. L., Lenkovskiy T. M., Molkov Y. V., Kulyk V. V., Duriagina Z. A.

Archives of Materials Science and Engineering

|

2016

|

Vol. 82, nr 2

49--56

EN

Purpose: The aim of the paper is to evaluate the dependence of microstructure parameters, strength and plasticity of steel on crack faces friction factor. Design/methodology/approach: The specimens for the investigation were cut out from the 10 mm thick hot-rolled plate of 65G steel used as a model material for fatigue and durability testing of whole-rolled railway wheels. The mechanical characteristics of the steel were determined according to the state standard using cylindrical specimens of diameter 5 mm and effective length 50 mm. The specimens were heat-treated at the mentioned conditions. Fatigue testing under mode II loading was carried out on a special rigid loading machine in the standard laboratory conditions at symmetric sinusoidal cycle with a frequency of 12 Hz in the range of fatigue crack growth rates da/dN = 5∙10⁻⁸…5∙10⁻⁷ m/cycle until its reaches relative length l/b ≥ 0.8. The obtained microsections were investigated using the optical metallographic microscope Neophot 9 equipped with a digital camera Nikon D50 and electronic scanning microscope Zeiss EVO 40XVP. Hardness of the specimens with different microstructure was determined using durometer TK-2. The crack faces friction factor was determined using original device for fractured surfaces sliding under certain compression force realization. Findings: The dependences of microstructure parameters, strength and plasticity of steel on crack faces friction factor are obtained. Research limitations/implications: The investigation of the influence of microstructure parameters, strength and plasticity of real wheel steels on crack faces friction factor at the mode II fatigue crack growth will be carried out. Practical implications: The value of crack faces friction factor have strong impact on stress intensity at the crack tip and must be taken into account at crack growth rates curves plotting. Originality/value: Mode II fatigue crack faces friction factor of steel is firstly experimentally determined.

13

Fatigue Life Supervision of Structural Components of Open-Pit Machines

Grabowski P., Jankowiak A., Król R.

Machine Dynamics Research

|

2015

|

Vol. 39, No. 4

73-84

EN

Structural components of open-pit machines are exposed to fatigue degradation caused by operational loading. Those machines are usually manufactured in piece production and their usage is very intensive. This paper presents the procedure based on the exploitation strategy of such machines according to their technical condition in notches (like welded joints, etc.). Loading data were acquired on the real open-pit machine – KWK 910 excavator.

14

Numeryczna analiza naprężeń w zaworze wydechowym silnika tłokowego pracującym w warunkach obciążenia termo-mechanicznego

Witek L.

Logistyka

|

2015

|

nr 4

6681--6688, CD2

PL

Niniejsza praca opisuje wpływ różnych rodzajów obciążeń na rozkład naprężeń zaworu grzybkowego silnika z zapłonem samoczynnym. W celu rozwiązania zdefiniowanego problemu naukowego zbudowany został model geometryczny oraz uproszczony model dyskretny układu zaworowego. W pracy uwzględniono dwa rodzaje obciążeń: mechaniczne (od siły ugięcia sprężyny, po zamknięciu zaworu) oraz cieplne (od nierównomiernego nagrzania) W pierwszej części pracy analizowano przypadki obciążeń działających niezależnie, co pozwoliło na ocenę wpływu obciążeń składowych na poziom wytężenia materiału zaworu. Rezultaty analizy numerycznej wykazały, że największy wpływ na poziom naprężeń w zaworze ma obciążenie termiczne wynikające z niejednorodnego pola temperatury. W pracy analizowano także naprężenia pochodzące od wszystkich obciążeń działających równocześnie. W ostatniej części pracy sformułowano wnioski końcowe oraz wskazano kierunki dalszych badań.

EN

This paper presents the influence of different kinds of loads on the stress distribution in the valve of combustion engine. In order to solve the research problem, both the geometrical and the discrete model of valve system were defined. Two types of load were taken into consideration: the mechanical load (from valve spring, after valve close) and the thermal load (from non-uniform temperature distribution). In first part of work a separated loads were considered. Results of numerical analysis showed that the most significant influence on the stress levels in the valve has the thermal load related to non-uniform temperature field. In the last part of work the influence of complex thermo-mechanical load on stress state of valve were considered. Results of work showed that the operational stress has a small values. In summary of the work an interesting conclusions were formulated.

15

Case study and failure analysis of a total hip stem fracture

Mierzejewska Ż. A.

Advances in Materials Science

|

2015

|

Vol. 15, nr 2(44)

5--13

EN

A total hip replacement is a procedure that requires removal of the affected joint lesions and replacing it with artificial elements. Nevertheless, like any invasive surgery, it is associated with the risk of complications, including joint infection, fracture of the bone during and after surgery, scarring and limitation of motion of the hip, and loosening of the prosthesis. In this work we present and describe the results of its investigations. In order to determine the mechanism of failure, a broken stem components were analyzed by means of macroscopic and microscopic observations and hardness measurements. The hardness, microstructure and chemical composition of the broken part of the hip stem were analyzed. Microscopic examination revealed numerous defects in material. Among them are pores and emptiness, located on the outskirts of the tested samples and a plurality of micro-cracking, debonding and delamination of the material due to the overloading of a fatigue character. There were no changes caused by intergranular corrosion or pitting, which may indicate for an even distribution of the major alloying components such as chromium and nickel. Observations of the material by using scanning electron microscopy (SEM), clearly proved that the destruction was caused by material fatigue. The investigation showed that the crack had originated due to a high stress concentration on the lateral corner section of the stem. Large surface of the fatigue crack zone area indicated for small stresses and small crack propagation velocities. There was a clear correlation between the grain size of the steel hardness. The results of hardness test revealed a significant increase hardness of stem in relation to the normative values. In addition, the measured average grain size is less than the standard accepted. Using Solid Works simulation and FEM a model of the stem was created and analyzed in terms of strength and rated the distribution of the generated stress. The finite-element analysis confirmed that there is the highest stress concentration in the middle of the stem.

16

Some Remarks on the Crack Growth Analysis in Structural Components under Service Loading

Grabowski P., Jankowiak A.

Machine Dynamics Research

|

2014

|

Vol. 38, No. 2

17-26

EN

Structural components of construction machinery and open-pit machines often contain cracks or crack-like defects initiated at notches under service cycling loading. Those cracks can decide on the process of material destruction. In order to determine the time spent on the stable fatigue growth of such cracks, the crack growth analysis needs to be carried out. One of the most important issues in the crack growth analysis is acquisition of straining history and preparation of its spectrum for fatigue calculations. However, durability forecasts may substantially differ one from another, depending on the type of applied assumptions and simplifications (i.e. calculations in the loading blocks and their sequence or taking into account the mean stress). The paper presents the selected aspects of the fatigue crack growth analysis carried out with the use of the service loading acquired on the real open-pit machine - KWK 910 excavator.

17

Failure analysis of a femoral hip stem made of stainless steel after short time of exposure

Mierzejewska Ż. A., Oksiuta Z.

Acta Mechanica et Automatica

|

2014

|

Vol. 8, no. 3

146--150

EN

This paper describes a case study summarising the failure analysis of a stainless steel femoral stem, which failed prematurely within 36 months of exploitation in human body. In order to determine the mechanism of failure, a broken stem component were analyzed by means of macroscopic and microscopic obserwations and hardness measurements. Metallurgical obserwations revealed that the tested material does fulfill ASTM requirements. Scanning electron microscopy images revealed the presence of stress-induced cracking. The results of the hardness revealed significant nonuniformity from the surface towards the inner part of the stem. It is assumed that any discontinuity or defect on the fracture surface of the stem acted as preferential site for a crack nucleation and propagation by fatigue until the cross section of stem was not able to sustain a load generated by a patient.

18

Analiza fraktograficzna przełomów zmęczeniowych łopatek silników lotniczych

Babul T.

Inżynieria Powierzchni

|

2012

|

nr 1

20-26

PL

W artykule zamieszczono analizę wyników badań fraktograficznych łopatek sprężarki silnika lotniczego wykonane ze stopów Inconel po badaniach wytrzymałości zmęczeniowej. Badania zmęczeniowe prowadzono w warunkach zginania dla współczynnika asymetrii cyklu R = -1 za pomocą maszyny typu Schenck. Omówiono typowe mechanizmy oraz przełomy zmęczeniowe występujące podczas symetrycznego obciążania cyklicznego łopatek.

EN

This paper presents the analysis of fractographic test results of compressor blades in aircraft engine, manufactured from Inconel alloys after fatigue strength tests. Fatigue strength examinations were performed in bending conditions, with stress rado R = - 1 with the use of Schenck type machine. There are also described some typical mechanisms and fatigue fractures which occur during the symmetric cyclic load of blades.

19

Numerical Simulation of Fatigue Fracture of the Turbine Disc

Witek L.

Fatigue of Aircraft Structures

|

2012

|

Iss. 4

114--122

EN

This paper presents the results of the crack propagation analysis of an aircraft engine turbine disc. In the first part of the work the finite element method was used for calculation of the stress state and the stress intensity factor (SIF, KI, K-factor) in the turbine disc with an embedded quarter-elliptical corner crack, subjected to low-cycle thermo-mechanical fatigue. To refine the K-factor calculation, specially degenerated finite elements were used. These elements provide stress singularity suitable for the linear-elastic material of the disc. The performed calculations yielded the stress intensity factor KI for different crack sizes. Subsequently, ΔK parameter was determined as a difference of the KI values calculated for the turbine’s speeds equal to 6373 and 14200 RPM. Based on the Paris-Erdogan equation and the obtained ΔK values, the fatigue crack growth plot for the turbine disc subjected to complex thermo-mechanical loads was determined.

20

Finite element stress analysis of forging dies to improve their fatigue life

Dehghani K., Jafari A.

Materials Science Poland

|

2010

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Vol. 28, No. 1

139--152

EN

The forging dies, and in a particular case a bolt die, were stress analyzed by the finite element method. Two possible modes of die failure, due to hoop and axial stresses, were investigated. The critical zones of highly concentrated stresses have been identified. Several approaches were studied to overcome the tensile stresses that result in a premature failure of a forging die. The results of the finite element simulations show that generating the compressive or negative stresses, as produced by the techniques applied, can completely remove, or at least significantly reduce the detrimental tensile stresses generated/ during forging. This can readily improve the fatigue life of dies. Numerical stress analysis was performed on critical elements lying in the transition zone of dies. Finally, advanced numerical methods, especially the finite element method, were used to determine the optimum mean stress and the optimum alternative stress as well as to analyze the compressive negative stresses generated by the applied techniques. The ABAQUS software was used for the finite element simulation. The optimum mean stress and the optimum alternative stress at the most critical finite element were determined to be 140-150 and 34-38 MPa, respectively.