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1

Investigation of low- and high-cycle fatigue in Al 2024-T4 alloy

Kłysz Sylwester

Technical Sciences / University of Warmia and Mazury in Olsztyn

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2020

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nr 23(4)

309--321

EN

The article presents the results of low- (LCF) and high-cycle fatigue (HCF) analyses of 2024-T4 aluminum alloy which is used in aircraft construction, mainly for highly loaded structural components, including for plating, fuselage frames and rotor blade girders in helicopters. The alloy is used in structures where a high strength-to-weight ratio and high fatigue resistance are required. However, the alloy is poorly weldable and has low corrosion resistance. The tests were performed on hourglass and cylindrical samples with parallel and perpendicular orientation relative to the rolling direction. Samples for analysis were obtained from the production line of PZL-130 Orlik TC-II trainer aircraft. The results of the analysis were described by Manson- -Coffin and Morrow equations.

2

Stress-life curve for high and low cycle fatigue

Kurek Andrzej, Kurek Marta, Łagoda Tadeusz

Journal of Theoretical and Applied Mechanics

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2019

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Vol. 57 nr 3

677--684

EN

The paper contains a proposal of a new model for the stress-life curve. The new model reflects the nature of the stress curve occurring under current conditions, which means its shape of an inclined letter S. It can be used for both low and high cycle fatigue. Verification of the proposed model was performed on experimental results of ten various materials from three main types that are low-alloy, high-alloy and non-alloy steels.

3

Accuracy of determined S-N curve by selected models

Strzelecki Przemysław

Journal of Theoretical and Applied Mechanics

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2019

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Vol. 57 nr 4

859--868

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.

4

Analysis of the mechanism of fatigue failure of the Refill Friction Stir Spot Welded overlap joints

Kubit Andrzej, Trzepiecinski Tomasz, Bochnowski Wojciech, Drabczyk Mateusz, Faes Koen

Archives of Civil and Mechanical Engineering

|

2019

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Vol. 19, no. 4

1419--1430

EN

The aim of this work is the experimental investigation of fatigue failure in Refill Friction Stir Spot Welding joints. The specimens for the fatigue analysis were made of 0.8-mm-thick and 1.6-mm-thick 7075-T6 aluminium alloy which is used to fabricate aircraft fuselages con-sisting of a plate skin with a stiffening stringer. The load capacity of joints was determined by tensile/shear tests. Fatigue tests were carried out on an Instron E10000 testing machine at room temperature. High-cycle fatigue tests were carried out under the following conditions: a limited number of cycles equal to 2 _ 106, a frequency of 50 (Hz), and a coefficient of stress cycle R = 0.1. Microstructural features of fatigue fractures for different levels of variable load were examined using Scanning Electron Microscopy micrographs. The analysis of the fatigue fractures reveals that the Alclad layer at the bottom of the weld is a kind of structural notch and in this situation can be the location of the initiation of fatigue cracking. It was found that fracture mechanism depends on the value of load amplitude. Analysis of the SEM micrographs of fatigue fractures shown that the thermo-mechanically affected zone and heat affected zone are sources of fatigue failure.

5

Fatigue lifetime of 20MnV6 steel with holes manufactured by various methods

Bokůvka O., Jambor M., Trško L., Nový F., Lisiecka B.

Production Engineering Archives

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2018

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Vol. 19

3--5

EN

In this paper, the authors publish their own experimental results of the examination of the different holes (milled, drilled and drilled + shot peened) on the fatigue lifetime of 20MnV6 steel. The experiments were carried out at low-frequency loading (f = 10 Hz, pulsating tension loading) in the region from N = 2×105 up to N = 2×106 cycles. The best fatigue properties were obtained in the parts with drilled + shot peened holes.

6

Analysis of selected mathematical models of high-cycle S-N characteristics

Strzelecki P., Sempruch J., Tomaszewski T.

Technical Sciences / University of Warmia and Mazury in Olsztyn

|

2017

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nr 20(3)

227--240

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.

7

Size effect in high-cycle fatigue

Tomaszewski T., Sempruch J.

Journal of Machine Construction and Maintenance - Problemy Eksploatacji

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2017

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no. 1

29--35

EN

The paper describes size effect in reference to available empirical and analytical models. The size effect of an object on strength properties was classified from 3 perspectives: statistical, geometrical, and technological. The following part of the paper identifies a verification method that has been supplemented by proprietary experimental test results obtained for a minispecimen made of aluminium alloy EN AW-6063.

PL

Artykuł przedstawia efekt skali w odniesieniu do dostępnych modeli empirycznych i analitycznych. Wpływ efektu skali na wytrzymałość zmęczeniową obiektu został sklasyfikowany z trzech różnych perspektyw: statystycznej, geometrycznej oraz technologicznej. W artykule zidentyfikowano metodę weryfikacji, która została uzupełniona przez wyniki badań eksperymentalnych dla minipróbki stopu aluminium EN AW-6063.

8

Verification of analytical models of the S-N curve within limited fatigue life

Strzelecki P., Sempruch J.

Journal of Theoretical and Applied Mechanics

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2016

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Vol. 54 nr 1

63--73

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.

9

Fatigue Characteristics of Selected Light Metal Alloys

Cieśla M., Junak G., Marek A.

Archives of Metallurgy and Materials

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2016

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Vol. 61, iss. 1

271--274

EN

The paper addresses results of fatigue testing of light metal alloys used in the automotive as well as aerospace and aviation industries, among others. The material subject to testing comprised hot-worked rods made of the AZ31 alloy, the Ti-6Al-4V two-phase titanium alloy and the 2017A (T451) aluminium alloy. Both low- and high-cycle fatigue tests were conducted at room temperature on the cycle asymmetry ratio of R=-1. The low-cycle fatigue tests were performed using the MTS-810 machine on two levels of total strain, i.e.Δεc= 1.0% and 1.2%. The high-cycle fatigue tests, on the other hand, were performed using a machine from VEB Werkstoffprufmaschinen-Leipzig under conditions of rotary bending. Based on the results thus obtained, one could develop fatigue life characteristics of the materials examined (expressed as the number of cycles until failure of sample Nf) as well as characteristics of cyclic material strain σa=f(N) under the conditions of low-cycle fatigue testing. The Ti-6Al-4V titanium alloy was found to be characterised by the highest value of fatigue life Nf, both in lowand high-cycle tests. The lowest fatigue life, on the other hand, was established for the aluminium alloys examined. Under the high-cycle fatigue tests, the life of the 2017A aluminium and the AZ31 magnesium alloy studied was determined by the value of stress amplitude σa. With the stress exceeding 150 MPa, it was the aluminium alloy which displayed higher fatigue life, whereas the magnesium alloy proved better on lower stress.

10

Comparing guidelines concerning construction of the S-N curve within limited fatigue life range

Strzelecki P., Sempruch J., Nowicki K.

Polish Maritime Research

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2015

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nr 3

67--74

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.

11

Trwałość wysokocyklowa stopów metali lekkich

Cieśla M., Marek A.

Hutnik, Wiadomości Hutnicze

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2015

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Vol. 82, nr 8

546--548

PL

Praca dotyczy badań zmęczenia wysokocyklowego przerabianych plastycznie stopów metali lekkich, mających zastosowanie między innymi w technice lotniczej. Przydatność stopów metali lekkich na elementy konstrukcyjne urządzeń determinowana jest, oprócz ich niskiej gęstości, także szeregiem korzystnych właściwości mechanicznych, a w przypadku zastosowań na elementy środków transportu dodatkowo dobrą wytrzymałością zmęczeniową. Materiał do badań stanowiły pręty po przeróbce plastycznej na gorąco ze stopów magnezu AZ31 i AZ61, dwufazowego stopu tytanu Ti-6Al-4V oraz stopu aluminium 2017A (T451). Do badań zmęczenia wysokocyklowego w warunkach zginania obrotowego przy współczynniku asymetrii cyklu R= −1 wykonano próbki walcowe o średnicy d0=8 mm. Przeprowadzono próby w zakresie ograniczonej wytrzymałości zmęczeniowej. Na podstawie uzyskanych wyników opracowano charakterystyki trwałości zmęczeniowej badanych materiałów. W badaniach zmęczenia wysokocyklowego największą trwałość wykazał stopu tytanu Ti-6Al-4V.

EN

The paper refers to the research on high-cycle fatigue of wrought light metal alloys, applied, inter alia, in the aviation technology. Usefulness of the light metal alloys for various structural components is determined, apart from their low density, by a number of favourable mechanical properties and in the case of their use for components of transport means - additionally by good fatigue strength. The material for the research consisted of hot-worked rods made of AZ31 and AZ61 magnesium alloys, Ti-6Al-4V two-phase titanium alloy and 2017A (T451) aluminium alloy. Cylindrical specimens with a diameter of d0 = 8 mm were made for the fatigue test under high-cycle rotary bending conditions with the cycle asymmetry coefficient R = −1. The tests were carried out for a limited fatigue strength range. Based on the obtained results, fatigue life characteristics of the tested materials were drawn up. It was found that the Ti-6Al-4V alloy has the longest fatigue life.

12

Wyznaczenie charakterystyki zmęczeniowej materiału profili aluminiowych z wykorzystaniem minipróbek

Tomaszewski T., Sempruch J.

Przegląd Mechaniczny

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2014

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nr 4

28--31

PL

Szerokie zastosowanie profili kształtowych niesie ze sobą konieczność określenia własności zmęczeniowych materiału, z którego są produkowane. W wyniku procesu produkcyjnego takich profili, materiał wejściowy poddawany jest znacznym odkształceniom plastycznym i wpływowi ciepła. Skutkuje to koniecznością prowadzenia badań na gotowych elementach, z których niemożliwe jest pobranie próbki normatywnej. W pracy opisano metodykę badań zmęczeniowych (geometria próbki, obciążenia, stanowiska badawcze, analiza wyników) z wykorzystaniem minipróbek możliwych do pobrania z profili kształtowych.

EN

A vast application of shape profiles brings the need to determine the fatigue properties of the materiał they are produced from. As a result of the production processes of such profiles, the initial materiał was exposed to considerable plastic deformations and the effect of heat. It results in the need of performing tests with finished components from which it is impossible to sample a normative specimen. The paper describes the fatigue testing methodology (specimen geometry, loads, testing stand, analysis of the results) in the use of mini specimens which can be taken from shape profiles.

13

Zakres normalizacji warunków badań zmęczeniowych minipróbek

Tomaszewski T., Sempruch J.

Postępy w Inżynierii Mechanicznej

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2014

|

nr 3(2)

59--66

PL

W pracy scharakteryzowano procedurę prowadzenia badań zmęczeniowych w oparciu o normy. Przedstawiono geometrię próbek gładkich, warunki prowadzenia badań i opis wyników w formie charakterystyki zmęczeniowej σa-N. Jako praktyczną możliwość rozszerzenia zakresu identyfikacji własności zmęczeniowych materiału zaproponowano metodykę badań na minipróbkach.

EN

The paper was characterized procedure for conducting fatigue tests based on the standards. The geometry of the smooth specimens, conditions of tests and description of the results (fatigue characteristics σa-N) was presented. As a practical opportunity to extend the scope of the identification of fatigue properties of the material proposed methodology for testing the mini specimens.

14

Wykorzystanie minipróbek do wyznaczania trwałości i wytrzymałości zmęczeniowej materiałów konstrukcyjnych

Tomaszewski T., Sempruch J.

Postępy w Inżynierii Mechanicznej

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2014

|

nr 4(2)

45--54

PL

W pracy przedstawiono metodykę prowadzenia badań do wyznaczania własności zmęczeniowych materiału z wykorzystaniem minipróbek. Sformułowano hipotezy badawcze i metodykę badań. Wyniki analizowano w zakresie wpływu efektu skali.

EN

This paper presents the research methodology for determining the fatigue properties of the material with the use of mini specimens. The hypotheses and research methodology were formulated. The results of size effect were analyzed.

15

Verification of selected models of the size effect based on high-cycle fatigue testing on mini specimens made of EN AW-6063 aluminum alloy

Tomaszewski T., Sempruch J., Piątkowski T.

Journal of Theoretical and Applied Mechanics

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2014

|

Vol. 52 nr 4

883--894

EN

The study presents several cases where use of specimens with reduced overall dimensions, i.e. mini specimens in the course of fatigue tests is advantageous. The high-cycle fatigue tests based on a developed method have been performed on mini specimens and normative specimens (comparative tests). The tests have been conducted on EN AW-6063 aluminum alloy specimens. A correction coefficient determined as a result of monotonic tests and selected models of the size effect have been critically assessed based on the test results. A statistical Weibull’s weakest link model and a monofractal approach based on a fractal dimension have been verified.

16

Metodyka badań zmęczeniowych z wykorzystaniem minipróbek - stanowisko, próbki, obciążenia i weryfikacja dla stopu EN AW-6063

Tomaszewski T., Sempruch J.

Inżynieria i Aparatura Chemiczna

|

2013

|

Nr 2

120-121

PL

Weryfikacja własności cyklicznych materiału w wielu przypadkach jest to niemożliwa z uwagi na ograniczenia wymiarowe badanych obiektów. Wówczas jednym z rozwiązań jest prowadzenie badań wykorzystujących próbkę mniejszą. W pracy przedstawiono badania porównawcze próbek normatywnych i minipróbek. Nieznacznie większy rozrzut wyników dla minipróbki w stosunku do próbki normatywnej sugeruje wiarygodność proponowanej metodyki.

EN

Verification of material cyclic properties is not possible in many cases due to size limitations of tested objects. One possible solution is to conduct tests which would consider the smaller specimens. This paper presents a comparative study of normative and mini-specimens. Slightly higher spread of results obtained for mini-specimens compared to normative specimens suggests reliability of proposed methodology.

17

The conception of energetic investigations of the multisymptom fatigue of the simple mechanical system' constructional materials

Korczewski Z.

Journal of Polish CIMAC

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2012

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Vol. 7, no 1

99-107

EN

The article presents the basic assumptions of the research project aimed, as the main scientific purpose, an identification of the slow-changeable energy processes surrounding the high-cycle fatigue of constructional materials within the plain mechanical system, especially the marine one, for diagnostic purposes. There is foreseen an application of alternative diagnostic methods based on energetic observations of the multi-symptom, continuous and irreversible alterations of the fatigue state within the material and construction of the elements transmitting the stream of mechanical energy from the propulsion engine to the propeller. Such methods will represent an essential supplement of already existing diagnosing systems of marine engines as well as marine propulsions. Only then an implementation of the condition based maintenance within the marine propulsion operation can be seen fit to approve. Second part of the paper demonstrates the results of preliminary experimental investigations conducted on the Schenck fatigue machine. The machine has been especially adapted for the purposes of the planned energy research and equipped with measuring apparatus of vibration, acoustic emission and thermal emission.

18

Investigating the size effect for the small-dimension specimens made from the EN AW-6063 aluminium alloy

Tomaszewski T., Sempruch J., Piątkowski T.

Journal of Polish CIMAC

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2012

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Vol. 7, no 3

339-346

EN

The paper concerns the size effect on fatigue life and fatigue strength. As for the mini specimens, smaller than the normative specimens, they show an increase in fatigue life with a decrease in the object cross-section area. Theoretically the calculational models assume a lack of sensitivity of the aluminum alloys to changes in the crosssection size, which is contrary to the experimental tests. The paper has been an attempt at determining the size effect for EN AW-6063 aluminum alloy mini specimens. Monotonic and fatigue tests were made. There were observed correlations of the results for the coefficient of material sensitivity to change in the cross-section. The results have made it possible to define the relationship of the ultimate tensile strength and fatigue strength for the specimens of various size.

19

Fatigue strength of MAR-M509 alloy with structure refined by rapid crystallization

Mróz M., Orłowicz W., Tupaj M., Trytek A.

Archives of Foundry Engineering

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2010

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Vol. 10, iss. 3

119--122

EN

This study presents test results of high-cycle (N>2⋅107) fatigue bending strength of MAR-M-509 cobalt alloy samples, as cast and after surface refining with a concentrated stream of heat. Tests were conducted on samples of MAR-M59 alloy casts, obtained using the lostwax method. Cast structure refining was performed with the GTAW method in argon atmosphere, using the current I = 200 A and electrical arc scanning velocity vs = 250 mm/min. The effect of rapid crystallization occurring after the fusion process is refinement of the MAR-M509 alloy cast microstructure and significant improvement in bending fatigue strength.

20

On the fatigue-critical amplitude of random-amplitude stress

Kolenda J.

Polish Maritime Research

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2007

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nr 2

9-11

EN

Uniaxial non-zero mean stress of constant circular frequency in the high-cycle fatigue regime is considered. It is assumed that equation of the S-N curve and modified Soderberg equation are applicable. For constant-amplitude stress, the fatigue-critical stress amplitude is defined as that which leads to failure during the required design life. For random-amplitude stress, expected values of the fatigue-critical stress amplitude and total fatigue damage accumulated during the required design life are estimated. It is found that the probability of fatigue failure is equal to the probability of exceedance of the fatigue-critical stress amplitude. As an example, for stationary random stress the equivalent random-amplitude stress and probability of fatigue failure are determined.