Estimation of Fatigue Crack Growth Rate in Heat-Resistant Steel by Processing of Digital Images of Fracture Surfaces

The micro- and macroscopic fatigue crack growth (FCG) rates of a wide class of structural materials were analyzed and it was concluded that both rates coincide either during high-temperature tests or at high stress intensity factor (SIF) values. Their coincidence requires a high level of cyclic defo...

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Autores principales:	Pavlo Maruschak, Roman Vorobel, Oleksandra Student, Iryna Ivasenko, Halyna Krechkovska, Olena Berehulyak, Teodor Mandziy, Lesia Svirska, Olegas Prentkovskis
Formato:	article
Lenguaje:	EN
Publicado:	MDPI AG 2021
Materias:	34KhN3M steel long-term operation degradation fatigue crack growth rate fractography fatigue striations Mining engineering. Metallurgy TN1-997
Acceso en línea:	https://doaj.org/article/b9d70e1a02714f5d80e4d19cd38c9d5b
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spelling	oai:doaj.org-article:b9d70e1a02714f5d80e4d19cd38c9d5b2021-11-25T18:21:51ZEstimation of Fatigue Crack Growth Rate in Heat-Resistant Steel by Processing of Digital Images of Fracture Surfaces10.3390/met111117762075-4701https://doaj.org/article/b9d70e1a02714f5d80e4d19cd38c9d5b2021-11-01T00:00:00Zhttps://www.mdpi.com/2075-4701/11/11/1776https://doaj.org/toc/2075-4701The micro- and macroscopic fatigue crack growth (FCG) rates of a wide class of structural materials were analyzed and it was concluded that both rates coincide either during high-temperature tests or at high stress intensity factor (SIF) values. Their coincidence requires a high level of cyclic deformation of the metal along the entire crack front as a necessary condition for the formation of fatigue striations (FS). Based on the analysis of digital fractographic images of the fatigue fracture surfaces, a method for the quantitative assessment of the spacing of FS has been developed. The method includes the detection of FS by binarization of the image based on the principle of local minima, rotation of the highlighted fragments of the image using the Hough transform, and the calculation of the distances between continuous lines. The method was tested on 34KhN3M steel in the initial state and after long-term operation (~3 × 10<sup>5</sup> h) in the rotor disk of a steam turbine at a thermal power plant (TPP). Good agreement was confirmed between FCG rates (both macro and microscopic, determined manually or using digital imaging techniques) at high SIF ranges and their noticeable discrepancy at low SIF ranges. Possible reasons for the discrepancy between the micro- and macroscopic FCG rates at low values of the SIF are analyzed. It has also been noted that FS is easier to detect on the fracture surface of degraded steel. Hydrogen embrittlement of steel during operation promotes secondary cracking along the FS, making them easier to detect and quantify. It is shown that the invariable value of the microscopic FCG rate at a low SIF range in the operated steel is lower than observable for the steel in the initial state. Secondary cracking of the operated steel may have contributed to the formation of a typical FS pattern along the entire crack front at a lower FCG rate than in unoperated steel.Pavlo MaruschakRoman VorobelOleksandra StudentIryna IvasenkoHalyna KrechkovskaOlena BerehulyakTeodor MandziyLesia SvirskaOlegas PrentkovskisMDPI AGarticle34KhN3M steellong-term operationdegradationfatigue crack growth ratefractographyfatigue striationsMining engineering. MetallurgyTN1-997ENMetals, Vol 11, Iss 1776, p 1776 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	34KhN3M steel long-term operation degradation fatigue crack growth rate fractography fatigue striations Mining engineering. Metallurgy TN1-997
spellingShingle	34KhN3M steel long-term operation degradation fatigue crack growth rate fractography fatigue striations Mining engineering. Metallurgy TN1-997 Pavlo Maruschak Roman Vorobel Oleksandra Student Iryna Ivasenko Halyna Krechkovska Olena Berehulyak Teodor Mandziy Lesia Svirska Olegas Prentkovskis Estimation of Fatigue Crack Growth Rate in Heat-Resistant Steel by Processing of Digital Images of Fracture Surfaces
description	The micro- and macroscopic fatigue crack growth (FCG) rates of a wide class of structural materials were analyzed and it was concluded that both rates coincide either during high-temperature tests or at high stress intensity factor (SIF) values. Their coincidence requires a high level of cyclic deformation of the metal along the entire crack front as a necessary condition for the formation of fatigue striations (FS). Based on the analysis of digital fractographic images of the fatigue fracture surfaces, a method for the quantitative assessment of the spacing of FS has been developed. The method includes the detection of FS by binarization of the image based on the principle of local minima, rotation of the highlighted fragments of the image using the Hough transform, and the calculation of the distances between continuous lines. The method was tested on 34KhN3M steel in the initial state and after long-term operation (~3 × 10<sup>5</sup> h) in the rotor disk of a steam turbine at a thermal power plant (TPP). Good agreement was confirmed between FCG rates (both macro and microscopic, determined manually or using digital imaging techniques) at high SIF ranges and their noticeable discrepancy at low SIF ranges. Possible reasons for the discrepancy between the micro- and macroscopic FCG rates at low values of the SIF are analyzed. It has also been noted that FS is easier to detect on the fracture surface of degraded steel. Hydrogen embrittlement of steel during operation promotes secondary cracking along the FS, making them easier to detect and quantify. It is shown that the invariable value of the microscopic FCG rate at a low SIF range in the operated steel is lower than observable for the steel in the initial state. Secondary cracking of the operated steel may have contributed to the formation of a typical FS pattern along the entire crack front at a lower FCG rate than in unoperated steel.
format	article
author	Pavlo Maruschak Roman Vorobel Oleksandra Student Iryna Ivasenko Halyna Krechkovska Olena Berehulyak Teodor Mandziy Lesia Svirska Olegas Prentkovskis
author_facet	Pavlo Maruschak Roman Vorobel Oleksandra Student Iryna Ivasenko Halyna Krechkovska Olena Berehulyak Teodor Mandziy Lesia Svirska Olegas Prentkovskis
author_sort	Pavlo Maruschak
title	Estimation of Fatigue Crack Growth Rate in Heat-Resistant Steel by Processing of Digital Images of Fracture Surfaces
title_short	Estimation of Fatigue Crack Growth Rate in Heat-Resistant Steel by Processing of Digital Images of Fracture Surfaces
title_full	Estimation of Fatigue Crack Growth Rate in Heat-Resistant Steel by Processing of Digital Images of Fracture Surfaces
title_fullStr	Estimation of Fatigue Crack Growth Rate in Heat-Resistant Steel by Processing of Digital Images of Fracture Surfaces
title_full_unstemmed	Estimation of Fatigue Crack Growth Rate in Heat-Resistant Steel by Processing of Digital Images of Fracture Surfaces
title_sort	estimation of fatigue crack growth rate in heat-resistant steel by processing of digital images of fracture surfaces
publisher	MDPI AG
publishDate	2021
url	https://doaj.org/article/b9d70e1a02714f5d80e4d19cd38c9d5b
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Estimation of Fatigue Crack Growth Rate in Heat-Resistant Steel by Processing of Digital Images of Fracture Surfaces

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