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11 pages, 9895 KiB

Open AccessArticle

Effect of Fine Particle Peening Using Hydroxyapatite Particles on Rotating Bending Fatigue Properties of β-Type Titanium Alloy

by Yuki Nakamura, Koichiro Nambu, Toshikazu Akahori, Toshihiro Shimizu and Shoichi Kikuchi

Appl. Sci. 2021, 11(9), 4307; https://doi.org/10.3390/app11094307 - 10 May 2021

Cited by 5 | Viewed by 1958

Abstract

Fine particle peening (FPP) using hydroxyapatite (HAp) shot particles was performed to improve the fatigue strength and form a HAp transfer layer on a beta titanium alloy (Ti–22V–4Al). The surface microstructures of the FPP-treated specimen were characterized using scanning electron microscopy, micro-Vickers hardness [...] Read more.

Fine particle peening (FPP) using hydroxyapatite (HAp) shot particles was performed to improve the fatigue strength and form a HAp transfer layer on a beta titanium alloy (Ti–22V–4Al). The surface microstructures of the FPP-treated specimen were characterized using scanning electron microscopy, micro-Vickers hardness testing, energy dispersive X-ray spectrometry, X-ray diffraction, and electron backscattered diffraction. A HAp transfer layer with a thickness of 5.5 μm was formed on the surface of the Ti–22V–4Al specimen by FPP. In addition, the surface hardness of the Ti–22V–4Al was increased, and high compressive residual stress was generated on the specimen surface by FPP. Rotating bending fatigue tests were performed at room temperature in laboratory air over a wide cycle-life region (10³–10⁹ cycles). In the long cycle-life regime, the fatigue strength at 10⁷ cycles of the FPP-treated specimen became higher than that of the untreated specimen. This result is attributed to the formation of a work-hardened layer with high compressive residual stress by FPP. However, the fatigue strength was not improved by FPP in the short cycle-life regime, because fatigue cracks were initiated at surface defects formed during the FPP process. The fatigue fracture mode of the FPP-treated specimens shifted from surface-initiated fracture to subsurface-initiated fracture at a stress amplitude level of 600 MPa. Full article

(This article belongs to the Special Issue Advances in Very-High-Cycle Fatigue)

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17 pages, 24041 KiB

Open AccessArticle

Experimental Evidence of Specimen-Size Effects on EN-AW6082 Aluminum Alloy in VHCF Regime

by Stefano Invernizzi, Francesco Montagnoli and Alberto Carpinteri

Appl. Sci. 2021, 11(9), 4272; https://doi.org/10.3390/app11094272 - 08 May 2021

Cited by 17 | Viewed by 2454

Abstract

The present paper investigates the influence of the specimen size of EN-AW6082 wrought aluminium alloy subjected to very high cycle fatigue (VHCF) tests. The hourglass specimens were tested under fully reversed loading condition, up to 10⁹ cycles, by means of the ultrasonic [...] Read more.

The present paper investigates the influence of the specimen size of EN-AW6082 wrought aluminium alloy subjected to very high cycle fatigue (VHCF) tests. The hourglass specimens were tested under fully reversed loading condition, up to 10⁹ cycles, by means of the ultrasonic fatigue testing machine developed by Italsigma^® (Italy). Three specimens groups were considered, with a diameter in the middle cross-section ranging from 3 mm up to 12 mm. The stress field in the specimens was determined numerically and by strain gauge measurements in correspondence of the cross-section surface. The dispersion of experimental results has been accounted for, and data are reported in P-S-N diagrams. The decrease in fatigue resistance with increasing specimen size is evident. Theoretical explanation for the observed specimen-size effect is provided, based on Fractal Geometry concepts, allowing to obtain scale independent P-S*-N curves. The fatigue life expectation in the VHCF regime of the EN-AW6082 aluminium alloy full-scale components is rather overestimated if it is assessed only from standard small specimens of 3 mm in diameter. Experimental tests carried out on larger specimens, and a proper extrapolation, are required to assure safe structural design. Full article

(This article belongs to the Special Issue Advances in Very-High-Cycle Fatigue)

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15 pages, 6871 KiB

Open AccessFeature PaperArticle

Proposal of a Probabilistic Model on Rotating Bending Fatigue Property of a Bearing Steel in a Very High Cycle Regime

by Tatsuo Sakai, Akiyoshi Nakagawa, Yuki Nakamura and Noriyasu Oguma

Appl. Sci. 2021, 11(7), 2889; https://doi.org/10.3390/app11072889 - 24 Mar 2021

Cited by 4 | Viewed by 2083

Abstract

In S-N diagrams for high strength steels, the duplex S-N curves for surface-initiated failure and interior inclusion-initiated failure were usually confirmed in the very high cycle regime. This trend is more distinct in the loading type of rotating bending, due to the stress [...] Read more.

In S-N diagrams for high strength steels, the duplex S-N curves for surface-initiated failure and interior inclusion-initiated failure were usually confirmed in the very high cycle regime. This trend is more distinct in the loading type of rotating bending, due to the stress distribution across the section. In the case of interior failure mode, the fish-eye is usually observed on the fracture surface and an inclusion is also observed at the center of the fish-eye. In the present work, the authors attempted to construct a probabilistic model on the statistical fatigue property in the interior failure mode, based on the distribution characteristics of the location and the size of the interior inclusion at the crack initiation site. Thus, the P-S-N characteristics of the bearing steel (SUJ2) in the very high cycle regime were successfully explained. Full article

(This article belongs to the Special Issue Advances in Very-High-Cycle Fatigue)

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17 pages, 8305 KiB

Open AccessFeature PaperArticle

Initiation and Propagation Processes of Internal Fatigue Cracks in β Titanium Alloy Based on Fractographic Analysis

by Gaoge Xue, Takashi Nakamura, Nao Fujimura, Kosuke Takahashi and Hiroyuki Oguma

Appl. Sci. 2021, 11(1), 131; https://doi.org/10.3390/app11010131 - 25 Dec 2020

Cited by 6 | Viewed by 2317

Abstract

Uniaxial fatigue tests were conducted for a β titanium alloy Ti-22V-4Al up to a very high cycle fatigue (VHCF) regime. The initiation and propagation processes of the internal fatigue cracks were investigated using 3D fractographic analysis. Multiple facets were observed at the crack [...] Read more.

Uniaxial fatigue tests were conducted for a β titanium alloy Ti-22V-4Al up to a very high cycle fatigue (VHCF) regime. The initiation and propagation processes of the internal fatigue cracks were investigated using 3D fractographic analysis. Multiple facets were observed at the crack initiation site. Three facet initiation models were proposed based on the surface appearances and the 3D facet bonding patterns of the multiple facets, and the major facet was determined to be the true crack initiation site. Using the size of the major facet, a Tanaka–Akiniwa model, which can determine the material constants for the Paris law using only conventional fatigue tests, was applied to reveal the propagation process of the internal cracks. A reverse fatigue life prediction was also conducted to evaluate the accuracy of the material constants obtained using the Tanaka–Akiniwa model. When the facet initiation models were applied, the predictions showed less deviation and better agreement than when the facet initiation process was not considered. The findings of this study indicate that the formation of multiple facets in β titanium alloys is sequential rather than simultaneous. Full article

(This article belongs to the Special Issue Advances in Very-High-Cycle Fatigue)

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14 pages, 9881 KiB

Open AccessArticle

Ultrasonic Fatigue Device and Behavior of High-Temperature Superalloy Inconel 718 with Self-Heating Phenomenon

by Mengxiong Zhao, Tieying Wu, Zhenhua Zhao, Lulu Liu, Gang Luo and Wei Chen

Appl. Sci. 2020, 10(23), 8761; https://doi.org/10.3390/app10238761 - 07 Dec 2020

Cited by 1 | Viewed by 2245

Abstract

Ultrasonic resonance fatigue test method at 20 kHz related to the very high cycle fatigue (VHCF) aims to accelerate a time-consuming experiment. In this paper, an ultrasonic fatigue device with a data acquisition system was improved for monitoring and recording the data from [...] Read more.

Ultrasonic resonance fatigue test method at 20 kHz related to the very high cycle fatigue (VHCF) aims to accelerate a time-consuming experiment. In this paper, an ultrasonic fatigue device with a data acquisition system was improved for monitoring and recording the data from fatigue tests in which self-heating phenomenon exists. Symmetric tension-compression sinusoidal vibrating mode (R = −1) was observed in this study. VHCF behavior and mechanism of Inconel 718 were carried out using this device. It was concluded that more than 99% of fatigue life is consumed in initiation duration. Specimen temperature increase was not a decisive factor in VHCF strength for Inconel 718, as long as it was far less than the design temperature limitation. A single initiation site existed at the subsurface facet or grain cluster, observed from scanning electron microscope (SEM) micrographs. Quasi-cleavage fracture in transgranular ductile mode emerged and then tended to trace grain boundaries in an intergranular manner by cleavage-dominated mixed mode. Full article

(This article belongs to the Special Issue Advances in Very-High-Cycle Fatigue)

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18 pages, 12779 KiB

Open AccessArticle

Very-High-Cycle Fatigue and Charpy Impact Characteristics of Manganese Steel for Railway Axle at Low Temperatures

by Byeong-Choon Goo, Hyung-Suk Mun and In-Sik Cho

Appl. Sci. 2020, 10(15), 5042; https://doi.org/10.3390/app10155042 - 22 Jul 2020

Cited by 4 | Viewed by 2775

Abstract

Railway vehicles are being exposed with increasing frequency to conditions of severe heat and cold because of changes in the climate. Trains departing from Asia travel to Europe through the Eurasian continent and vice versa. Given these circumstances, the mechanical properties and performance [...] Read more.

Railway vehicles are being exposed with increasing frequency to conditions of severe heat and cold because of changes in the climate. Trains departing from Asia travel to Europe through the Eurasian continent and vice versa. Given these circumstances, the mechanical properties and performance of vehicle components must therefore be evaluated at lower and higher temperatures than those in current standards. In this study, specimens were produced from a commercial freight train axle made of manganese steel and subjected to high-cycle fatigue tests at −60, −30, and 20 °C. The tests were conducted using an ultrasonic fatigue tester developed to study fatigue at low temperatures. Charpy impact testing was performed over the temperature range of −60 to 60 °C to measure the impact absorption energy of the axle material. The material showed a fatigue limit above 2 million cycles at each temperature; the lower the test temperature, the greater the fatigue limit cycles. The impact absorption energy at −60 °C was 81% less compared to the value at 20 °C. The axle material became completely brittle in the temperature range of −30 to −40 °C. Full article

(This article belongs to the Special Issue Advances in Very-High-Cycle Fatigue)

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12 pages, 3809 KiB

Open AccessFeature PaperArticle

Ultrasonic VHCF Tests on Very Large Specimens with Risk-Volume Up to 5000 mm³

by Andrea Tridello, Davide Salvatore Paolino and Massimo Rossetto

Appl. Sci. 2020, 10(7), 2210; https://doi.org/10.3390/app10072210 - 25 Mar 2020

Cited by 17 | Viewed by 2536

Abstract

The research on the size-effects in Very-High-Cycle Fatigue (VHCF) has recently drawn the attention of several scholars. The fatigue cracks in VHCF originate from the largest defect present within the loaded material volume (risk-volume) and the larger the risk-volume, the larger the probability [...] Read more.

The research on the size-effects in Very-High-Cycle Fatigue (VHCF) has recently drawn the attention of several scholars. The fatigue cracks in VHCF originate from the largest defect present within the loaded material volume (risk-volume) and the larger the risk-volume, the larger the probability of critical defects affecting the VHCF response (size-effect). Many models have been proposed in the literature to deal with size-effects in VHCF. However, the proposed models cannot be validated on full-scale components, since VHCF tests are typically carried out with ultrasonic fatigue testing machines. The authors have proposed a specimen geometry, the so-called Gaussian specimens, to enlarge as much as possible the risk-volume in ultrasonic VHCF tests. In this study, fully reversed tension–compression ultrasonic VHCF tests up to 10⁹ cycles were carried out on AISI H13 steel Gaussian specimens with a risk-volume of 5000 mm³, two times larger than the largest tested in the literature. The stress distribution and the absence of bending loads were verified with strain gages, proving that VHCF tests on risk-volumes of 5000 mm³ can be reliably carried out. Ultrasonic VHCF tests were also carried out on small hourglass specimens, confirming that larger risk-volumes allow for a more reliable design against VHCF failures. Full article

(This article belongs to the Special Issue Advances in Very-High-Cycle Fatigue)

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Review

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27 pages, 5797 KiB

Open AccessFeature PaperReview

Properties of the Fine Granular Area and Postulated Models for Its Formation during Very High Cycle Fatigue—A Review

by Jan Patrick Sippel and Eberhard Kerscher

Appl. Sci. 2020, 10(23), 8475; https://doi.org/10.3390/app10238475 - 27 Nov 2020

Cited by 17 | Viewed by 2358

Abstract

Understanding the mechanisms leading to very high cycle fatigue is necessary to make predictions about the behavior under various conditions and to ensure safe design over the whole lifetime of high-performance components. It is further vital for the development of possible measures to [...] Read more.

Understanding the mechanisms leading to very high cycle fatigue is necessary to make predictions about the behavior under various conditions and to ensure safe design over the whole lifetime of high-performance components. It is further vital for the development of possible measures to increase the very high cycle fatigue strength. This review therefore intends to give an overview of the properties of the fine granular area that have been observed so far. Furthermore, the existing models to describe the early crack initiation and crack growth within the very high cycle fatigue regime are outlined and the models are evaluated on the basis of the identified fine granular area properties. The aim is to provide an overview of the models that can already be considered refuted and to specify the respective open questions regarding the other individual models. Full article

(This article belongs to the Special Issue Advances in Very-High-Cycle Fatigue)

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