Probabilistic Fracture Mechanics for Heavy-Duty Gas Turbine Rotor Forgings

Kadau, Kai; Gravett, Phillip W.; Amann, Christian

doi:10.1115/1.4038524

Cited by 12 publications

(4 citation statements)

References 13 publications

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“…Also, the stochastic nature of crack nucleation processes should be considered, either explicitly by modeling microstructural variations and properties, or by adding stochastic terms in the governing equations. This could directly support probabilistic engineering design and modeling [1, 2].…”

Section: Discussionmentioning

confidence: 99%

“…Despite several advances in manufacturing and inspection technologies, unavoidable small manufacturing imperfections such as forging flaws can still be present in large components and need to be accounted in an engineering design process and life prediction methods [1]. These inclusions are typically small clusters of non-metallic inclusions (NMIs) such as mixed oxides including CaO, MgO, and Al 2 O 3 particles [2] that are embedded in the metal matrix.…”

Section: Introductionmentioning

confidence: 99%

“…These unavoidable manufacturing imperfections need to be accounted for in engineering life prediction methods, for both new apparatus and service applications. To address this topic, a series of expensive destructive tests has been performed, in which the fatigue life of forging flaws as well as the microscopic structure of different sized flaws under realistic engine conditions have been measured [1, 5]. In these studies, the life cycle of the flaw N total , or the process of failure originating from flaws arising from forging or other manufacturing processes, is described by a crack nucleation phase enduring N nuc cycles and a subsequent fatigue crack growth phase N FM :…”

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: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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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“…Besides forging flaw crack growth, low‐cycle fatigue (LCF) crack initiation and subsequent growth is another possible source for rotor burst . That is why research activities have taken probabilistic LCF modelling approaches for rotor steels and forged Ni‐base superalloys into their focus .…”

Section: Introductionmentioning

confidence: 99%

Evaluation of component‐similar rotor steel specimens with a local probabilistic approach for LCF

Mäde

Kumar²,

Schmitz

et al. 2019

Fatigue Fract Eng Mat Struct

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Lately, a successful validation of a combined size and gradient effect modelling approach in a local probabilistic framework for LCF was published. A second validation study is here presented using LCF data of component‐similar specimens made of forged X12CrMoWVNbN10‐1‐1. It is found that a reasonable LCF crack initiation life prediction can be achieved by the local probabilistic model using single batch material parameters. However, the material parameters obtained from mixed batch LCF test data overestimate the actual material inherent LCF life scatter. Consequently, the size effect shift is pronounced too much, and the LCF life is predicted beyond crack initiation. Estimating the material parameters from a single batch data set instead results in a much less dispersed LCF life distribution and an approximately correct size effect shift. The predicted median Wöhler curve then corresponds to borehole‐specimen lives for initial cracks at the detection threshold. A reasonable prediction of technically relevant crack sizes in such inhomogeneous components requires additional modelling of stress gradient effects.

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