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1

A FCG Model and the Graphical User Interface Under Matlab for Predicting Fatigue Life: Parametric Studies

Kebir Tayeb, Correia José A.F.O., Benguediab Mohamed, Imad Abdellatif

Fatigue of Aircraft Structures

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2021

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Iss. 13

116--139

EN

The focus of this research work was predicting the fatigue life of mechanical components used for industrial and transport systems. To understand how the phenomenon of fatigue occurs in a material, the fatigue crack growth is studied. The purpose of this work was to create a graphical user interface (GUI) under Matlab to allow researchers to conduct the parametric studies of fatigue crack propagation to predict fatigue life. In this work, three models for fatigue crack propagation were used: those of Paris, Walker and Forman in order to study the three parameters: the Paris exponent m, load ratio R and hardness KIC, respectively. In addition, a novel model FCG was developed to study the influence of the hardening parameters (K′, n′) on fatigue crack propagation. The comparison of the simulation results with those in the literature shows good agreement.

2

Influence of the cyclic hardening model on the results of the numerical analysis of fatigue life on example of the compressor blade

Bednarz Arkadiusz

Journal of KONES

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2019

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Vol. 26, No. 2

7--14

EN

The main goal of the presented work is to determine the impact of the cyclic hardening model on the numerical results of the ε-N fatigue test. As an object of study, compressor blade (from PZL-10W helicopter engine) was used. The examined blade was made of EI-961 alloy. In numerical analysis, a geometrical model of the blade with a preliminary defect was created. Geometrical defect – V-notch was created on the leading edge. This defect was introduced in order to weaken the structure of the element and the possibility of observing the crack initiation process (in experimental tests). Material data to ε-N analysis, based on Manson-Coffin-Basquin equation, were estimated for Mitchell’s model. This model was built based on strength data provided by the steel producer. Based on three different models of cyclic hardening (Manson, Fatemi, and Xianxin), a number of load cycles were calculated. Load cycle during numerical analysis was represented as resonance bending with an amplitude of displacement equal to A = 1.8 mm. Obtained results were compared with experimental data. Additionally, the analytical model of ε-N fatigue (depending on the cyclic hardening) was prepared. All the work carried out has been summarized by a comprehensive comparative analysis of the results. Obtained results and dependencies can be used in the selection of an appropriate model of cyclic hardening in further fatigue tests of many aerospace elements.

3

Effect of cyclic hardening on stress relaxation in SUS316HTP under creep-fatigue loading at 700ºC: experiments and simulations nobutada

Ohno N., Sasaki T., Shimada T., Tokuda K., Yoshida K., Okumura D.

Journal of Theoretical and Applied Mechanics

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2018

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Vol. 56 nr 2

497--510

EN

Cyclic hardening and stress relaxation experiments of SUS316HTP were performed under creep-fatigue loading with tensile strain holding at 700ºC. Experiments revealed that under strain holding, the slow stress-relaxation stage satisfying Norton’s law with slight cyclic hardening followed a rapid stress-relaxation stage that was noticeably affected by cyclic hardening. This suggests that in the slow stress-relaxation stage, inelastic deformation mechanisms different from that of viscoplasticity occurred. Experiments were simulated using a cyclic viscoplastic-creep model in which the inelastic strain-rate was decomposed into viscoplastic and creep components that were affected differently by cyclic hardening. The simulation accurately reproduced the experiments.

4

Problem of cyclic hardening or softening in metals under programmed loading

Mroziński S., Szala J.

Scientific Problems of Machines Operation and Maintenance

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2010

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Vol. 45, nr 4

83-96

PL

Zjawisko cyklicznego umocnienia lub osłabienia metali i ich stopów jest znane od ponad 40 lat. Mimo tak długiego okresu badań brak jest ogólnego opisu uniwersalnych modeli tych zjawisk. Podstawą w ich ocenie są badania doświadczalne prowadzone w warunkach obciążeń sinusoidalnych stałoamplitudowych. Wyróżnia się badania ze stałą amplitudą naprężenia lub stałą amplitudą odkształcenia. Warunki te nie są równoważne w zakresie obciążeń, w których nie obowiązuje prawo liniowej zależności naprężenia od odkształcenia. Zagadnienie cyklicznego umocnienia lub osłabienia metali oraz ich stopów istotnie komplikuje się w przypadku zmiennoamplitudowych obciążeń, które są charakterystyczne dla obciążeń eksploatacyjnych elementów konstrukcyjnych. W pracy opisano badania własności cyklicznych trzech stopów metali: stopu aluminium PA7 silnie umacniającego się cyklicznie, stali stopowej 30HGSA- podlegającej silnemu cyklicznemu osłabieniu oraz stali konstrukcyjnej C45, która w zależności od poziomu obciążenia ulega cyklicznemu osłabieniu lub cyklicznemu umocnieniu. Badania przeprowadzono w warunkach programowanych obciążeń ze stopniowo rosnącą amplitudą naprężenia.

EN

Problem of cyclic hardening or softening in metals and their alloys has been known for over 40 years. Despite such a long period of time there is lack of the universal models describing these processes. The basis of their valuation are experimental tests carried out under constant amplitude sinusoidal loadings. The tests can be performed under constant stress amplitude or constant strain amplitude. These conditions are not equivalent for the range of loadings, where the law of the linear relation of stress from strain is not valid. The problem of the cyclic hardening or softening in metals and their alloys becomes significantly complex in the case of variable amplitude loadings, typical for operating loadings of construction elements. In the paper there was described the investigating of cyclic properties of three alloys: PA7 aluminium alloy strongly hardening cyclically, 30HGSA alloy steel strongly softening cyclically and C45 constructional steel which, depending on loading level, undergoes cyclic softening or cyclic hardening. The tests were carried out under programmed loadings with gradually increasing stress amplitude.

5

Application of the cyclic plasticity hardening law to metal forming

Muszka K., Perzyński K., Madej Ł.

Computer Methods in Materials Science

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2008

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Vol. 8, No. 4

165-170

EN

Creation of a robust numerical model of the low cyclic plastic deformation is essential for predicting inhomogeneities occurring during strain path change. Application of such model to simulate various simple plastometric tests (three point bending or tension/compression) is the main subject of the present work. To take this effect into account, a nonlinear isotropic/kinematic hardening material model is considered and all the results are compared with those obtained for the conventional isotropic hardening model. Observed differences in strain and stress distribution are discussed in details. Finally, based on this analysis, conclusions regarding the possibility to apply investigated tests in identification of the material model parameters through the inverse analysis are drawn.

PL

Przygotowanie odpowiedniego modelu numerycznego, opisującego zachowanie materiału poddanego nisko-cyklicznym odkształceniom plastycznym jest kluczowe dla prawidłowego przewidywania niejednorodności wynikających ze zmiany drogi odkształcenia podczas rzeczywistych procesów przeróbki plastycznej metali. Głównym celem prezentowanej pracy jest dyskusja możliwości wykorzystania takich modeli do symulacji prostych testów plastometrycznych (trójpunktowego zginania i cyklicznego rozciągania/ściskania). Aby w pełni uwzględnić wpływ odkształceń cyklicznych, w symulacjach wykorzystano izotropowo-kinematyczny model umocnienia, a wyniki porów-nano z tymi, uzyskanymi z zastosowaniem konwencjonalnego modelu izotropowego. Szczegółowej dyskusji poddano zaobserwowane różnice w rozkładach odkształceń i naprężeń. Bazując na tej analizie, podano wnioski dotyczące możliwości wykorzystania prezentowanych testów plastometrycznych do identyfikacji parametrów modeli dla odkształceń cyklicznych z wykorzystaniem analizy odwrotnej.