The kinetics and mechanism of fatigue crack growth in iron

Romaniv, O. N.; Shur, E. A.; Tkach, A. N.; Simin'kovich, V. N.; Kiseleva, T. N.

doi:10.1007/bf00722905

Cited by 8 publications

(4 citation statements)

References 12 publications

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“…A similar result for the constant values of pressure and a wide range of P was experimentally obtained in [55]. Good agreement between the values of the coefficients A and n with the published data [71] and a satisfactory approximation of the experimental results confirm the correctness of the approach adopted for the study of porous iron.…”

Section: Influence Of Pores On the Friction And Wear Of Ironsupporting

confidence: 83%

Model of Fracture, Friction, and Wear Phenomena of Porous Iron

Шацов

Ryaposov

Larinin

2011

Advances in Tribology

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Mechanical and tribotechnical features of powdered materials are strongly influenced by pore volume, fracture character, impurities, alloying, concentration inhomogeneity, friction conditions, and other factors. Pores also have influence on acceleration of diffusion processes and reduce undercooled austenite resistance. Annealed in hydrogen, ultra pure iron powder was used to study porous iron features. Toughness fracture and tribotechnical features had nonmonotonic dependence from porosity different from all known dependences got from technical iron powders. Researches brought out the fact that in process of porosity reduction by pressing and annealing cycles, the average dimension of porous is changed. According to the analysis of porous structure were created models of friction, wear, and fracture of pure porous iron.

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Section: Influence Of Pores On the Friction And Wear Of Ironsupporting

confidence: 83%

Model of Fracture, Friction, and Wear Phenomena of Porous Iron

Шацов

Ryaposov

Larinin

2011

Advances in Tribology

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“…Dislocations are accumulated in the form of stable slip bands typical of silicon and cz-iron [15,16]. According to [12], only the shear component of stresses forms the band dislocation structure (BDS) near the crack tip and separate cracks are initiated on the boundaries of the bands. The material between these cracks ruptures under the action of normal stresses and they merge with the main crack propagating along the BDS boundaries, where the density of dislocations is maximum.…”

Section: Fractography Of Fatigue Cracks In the Degraded Materialsmentioning

confidence: 99%

“…3a). This shape of the fracture surface corresponds to a dislocation slip-band structure [12][13][14] formed in the prefracture zone under cyclic loading. Dislocations are accumulated in the form of stable slip bands typical of silicon and cz-iron [15,16].…”

Section: Fractography Of Fatigue Cracks In the Degraded Materialsmentioning

confidence: 99%

Effect of high-temperature degradation of heat-resistant steel on the mechanical and fractographic characteristics of fatigue crack growth

Student¹,

Dudziński²,

Nykyforchyn³

et al. 1999

Mater Sci

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We study the influence of degradation of 12KhlMF heat-resistant steel under service and laboratory conditions on the variation of the threshold characteristics of its crack resistance and fractographic characteristics of the near-threshold growth of a fatigue crack. It is shown that hydrogen dissolved in the metal intensifies its cracking in the prefracture zone, first, along the grain boundaries and then, when the time of contact between the metal and hydrogenating media becomes sufficiently large, along the boundaries of subgrains, which leads to a stable decrease in the effective threshold Kthet" f. The process of fragmentation of the damaged metal by secondary cracks is a typical feature of crack growth with the threshold rate. The longer the contact of the metal with the hydrogenating medium, the lower the growth rate for which the fracture surface contains fatigue grooves and the larger the opening displacement of crack lips decorating these grooves. Hydrogen also facilitates the shift of the regions of tunnel crack growth relative to the corresponding areas on the conjugated fracture surfaces and, thus, increases the level of K~hcl. The actions of the factors Ktheff and Kthcl are mutually compensating and, therefore, it is impossible to determine the actual influence of hydrogen on the cyclic crack-growth resistance of the damaged metal by analyzing only the value of gth.Cyclic loading is one of the most dangerous factors affecting the durability of power, chemical, and oil equipment. Moreover, this equipment often operates in aggressive hydrogen-containing media. The long-term operation of equipment under the combined action of cyclic loading, high temperature, and hydrogen-containing media leads to the degradation of the materials properties as compared with its original state [1,2].The analysis of fracture surfaces is extensively used (as a procedure of investigation and detection of defects) for the determination of the causes of failures. This method is based on the fact that the direction of crack growth reflects the weakest place in the material and, thus, determines the most thermodynamically favorable fracture mechanism. In the fracture surface, one can see the history of fracture and its analysis enables one to find the most significant fracture mechanisms and relate them to various mechanical, microstructural, corrosion, and thermal effects. The fractographic investigations of laboratory specimens tested under known conditions and loading modes can also be used to clarify the causes of in-service failures in industry [3].The detrimental effect of high temperature on the process of fatigue crack growth (FCG) in heat-resistant steels is discussed in [4][5][6]. It is shown that the threshold characteristics of FCG reflect changes in the material caused by its degradation. However, only the effective threshold range of the stress intensity factor (SIF) responsible for the effect of crack closure always decreases as the degree of degradation of the metal increases.In the present work, we study and co...

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“…The lack of an unambiguous correlation between the experimentally determined FCG rate for a macrocrack and one more, obtained under the assumption of the formation of a separate FS in each loading cycle, was also demonstrated by the example of technically pure iron (ARMCO-Fe) [44], low carbon steel [45], alloy of iron with 3.7% Si [46], magnesium alloy IMB6 [47] and coarse-grained nickel of high purity [48].…”

Section: Introductionmentioning

confidence: 99%

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

Maruschak

Vorobel

Student

et al. 2021

Metals

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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 × 105 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.

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The kinetics and mechanism of fatigue crack growth in iron

Cited by 8 publications

References 12 publications

Model of Fracture, Friction, and Wear Phenomena of Porous Iron

Model of Fracture, Friction, and Wear Phenomena of Porous Iron

Effect of high-temperature degradation of heat-resistant steel on the mechanical and fractographic characteristics of fatigue crack growth

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

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