Study on fatigue crack initiation and propagation from forging defects

Varfolomeev, Igor; Moroz, S.; Siegele, Dieter; Kadau, Kai; Amann, Christian

doi:10.1016/j.prostr.2017.11.100

Cited by 7 publications

(7 citation statements)

References 1 publication

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“…We applied fatigue loading vertically using the same load-controlled simulation technique described in section 2, but with a different stress level of 800 MPa. In our 2D simulation cell this is resulting in plane strain comparable loading conditions, which is also comparable to the condition present in specimen-based tests [5,23], as well as in large rotor forgings including small flaws or cracks. Here, we considered aluminum oxide as discontinuous inclusions.…”

Section: Computational Modelsupporting

confidence: 70%

“…Material properties used in this model for inclusions and rotor steel matrix are shown in Table 3 for temperatures of 20, 350 and 450°C. Details on the inclusions and rotor steel can be found in Varfolomeev et al [5] and Radaelli et al [23]. [27] 1.89 0.2 8000…”

Section: Computational Modelmentioning

confidence: 99%

“…These inclusions can range from several micrometers to a few hundred micrometers in diameter [3] depending on the specifics of the manufacturing processes and materials involved. If these clusters are large enough, typically a millimeter or larger, then they might be detected by ultrasonic testing [4][5][6]. These unavoidable manufacturing imperfections need to be accounted for in engineering life prediction methods, for both new apparatus and service applications.…”

Section: Introductionmentioning

confidence: 99%

“…The fatigue crack growth can be described by established engineering fracture mechanics [5,[7][8][9]. However, no established engineering method is readily available for the nucleation process, as it critically depends on the details of the flaw structure and properties.…”

Section: Introductionmentioning

confidence: 99%

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Crack nucleation at forging flaws studied by non-local peridynamics simulations

Karim

Kadau

Narasimhachary

et al. 2021

Mathematics and Mechanics of Solids

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We present a computational study and framework that allows us to study and understand the crack nucleation process from forging flaws. Forging flaws may be present in large steel rotor components commonly used for rotating power generation equipment including gas turbines, electrical generators, and steam turbines. The service life of these components is often limited by crack nucleation and subsequent growth from such forging flaws, which frequently exhibit themselves as non-metallic oxide inclusions. The fatigue crack growth process can be described by established engineering fracture mechanics methods. However, the initial crack nucleation process from a forging flaw is challenging for traditional engineering methods to quantify as it depends on the details of the flaw, including flaw morphology. We adopt the peridynamics method to describe and study this crack nucleation process. For a specific industrial gas turbine rotor steel, we present how we integrate and fit commonly known base material property data such as elastic properties, yield strength, and S-N curves, as well as fatigue crack growth data into a peridynamic model. The obtained model is then utilized in a series of high-performance two-dimensional peridynamic simulations to study the crack nucleation process from forging flaws for ambient and elevated temperatures in a rectangular simulation cell specimen. The simulations reveal an initial local nucleation at multiple small oxide inclusions followed by micro-crack propagation, arrest, coalescence, and eventual emergence of a dominant micro-crack that governs the crack nucleation process. The dependence on temperature and density of oxide inclusions of both the details of the microscopic processes and cycles to crack nucleation is also observed. The results are compared with fatigue experiments performed with specimens containing forging flaws of the same rotor steel.

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Section: Computational Modelsupporting

confidence: 70%

Section: Computational Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Crack nucleation at forging flaws studied by non-local peridynamics simulations

Karim

Kadau

Narasimhachary

et al. 2021

Mathematics and Mechanics of Solids

Self Cite

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“…The CIVA software package (EXTENDE S.A., Massy, France) was used to optimize the phase field. The three test samples described in the source [ 8 ] were taken from the material so that the UT indications were in the middle of the cross-section. The samples were then subjected to cyclic loading by applying tensile stresses of different magnitudes and different stress ratios.…”

Section: Introductionmentioning

confidence: 99%

Investigation of Forging Metal Specimens of Different Relative Reductions Using Ultrasonic Waves

2021

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Forgings produced in industry are an irreplaceable basis for subsequent elaborating on machine tools. The quality of the semi-finished product produced by forging is a necessary prerequisite for ensuring the final quality of the final product because the forging can produce some defects. The presented paper is aimed at investigation of selected characteristics of forging steel specimens for various levels of their relative reduction. Ultrasound testing belongs to methods for investigation of structure changes, including defects. Experimental investigation, using both the attenuation and velocity measurements, verify that the reduction of specimens’ material can have an effect on the propagation of ultrasound waves passing through the specimen body. The procedure of steel samples forging corresponds accordingly to the process of their hardening. The increase of toughness after relative reduction of forging in the range of 10–50% is with highest probability caused by the strength matrices development due to the relatively important deformation hardening. It is evident that the deformation hardening is almost the same after every 10% addition of relative reduction. Experiments are supplemented by Barkhausen noise detection and metallographic characteristics of the samples. While differences between the Barkhausen noise values are in principle relatively small and significant differences are only in the values of the position of the envelope, there is maximum coincidence with ultrasonic investigation.

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