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Sedlak, M., Alfredsson, B. & Efsing, P. (2019). A coupled diffusion and cohesive zone model for intergranular stress corrosion cracking in 316L stainless steel exposed to cold work in primary water conditions. Engineering Fracture Mechanics, 217, Article ID UNSP 106543.
Open this publication in new window or tab >>A coupled diffusion and cohesive zone model for intergranular stress corrosion cracking in 316L stainless steel exposed to cold work in primary water conditions
2019 (English)In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 217, article id UNSP 106543Article in journal (Refereed) Published
Abstract [en]

A multi-physics model was developed to simulate intergranular stress corrosion cracking (IGSCC) in austenitic stainless steel. The model is implicit, coupled with a segregated solution scheme including a diffusion equation based on Fick's second law and a cohesive zone description for the fracture mechanics part. The degradation is modelled with an anodic slip-dissolution equation that uses the effective cohesive traction and concentration as the main parameters. The diffusivity in Fick's second law creates a moving boundary. The cohesive zone is modelled using the PPR model with extended degradation properties using the degradation parameter chi. The model was evaluated against experiments on the effects of cold work on IGSCC. The model showed good agreements for both shifting amount of cold work, illustrated by only changing the yield stress in the bulk material and for shifting the stress intensity factor. The model versatility was also shown by simulating IGSCC in Alloy 600, also with good agreements. The change in the bulk material made crack propagation more disadvantageous for the lower yield stress where the crack blunts, creates more plastic strain and lowers the cohesive traction. The model predicts that cold work of the bulk material creates a faster crack growth velocity due to lower amount of plastic deformation in the bulk and higher cohesive traction. The higher crack growth rate is a coupled effect of both fracture and oxidation properties.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2019
Keywords
Cohesive zone model, Fracture mechanics, Diffusion, Anodic dissolution, Multi-physics, Finite element model
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-256256 (URN)10.1016/j.engfracmech.2019.106543 (DOI)000477821300001 ()2-s2.0-85069557939 (Scopus ID)
Note

QC 20191022

Available from: 2019-10-22 Created: 2019-10-22 Last updated: 2019-10-22Bibliographically approved
Boåsen, M., Stec, M., Efsing, P. & Faleskog, J. (2019). A generalized probabilistic model for cleavage fracture with a length scale - Influence of stress state and application to surface cracked experiments.
Open this publication in new window or tab >>A generalized probabilistic model for cleavage fracture with a length scale - Influence of stress state and application to surface cracked experiments
2019 (English)Report (Other academic)
Abstract [en]

A probabilistic model for the cumulative probability of failure by cleavage fracture with a material related length scale is further developed in this study. A new generalized effective stress measure is proposed, based on a normal stress decomposition of the stress tensor, capable of describing a state of normal stress in the range from the mean stress to the maximum principal stress. The effective stress measure associated with a material point is evaluated from the stress tensor averaged over the material related length scale. The model is shown to be well capable to predict both the fracture toughness at loss of both in-plane and out-of-plane constraint by model application to two different datasets from the open literature. The model is also shown to be well capable of predicting the probability of failure of discriminating experiments on specimens containing semi-elliptic surface cracks. A comparison where the master curve methodology is used to predict the probability of failure of the experiments is also included.

Publisher
p. 38
Series
TRITA-SCI-RAP ; 2019:001
Keywords
Cleavage fracture, Brittle fracture, Non-local stress, Weakest link, Semi elliptic surface crack;
National Category
Applied Mechanics
Research subject
Solid Mechanics; Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-246032 (URN)
Funder
Swedish Radiation Safety Authority
Note

QC 20190312

Available from: 2019-03-11 Created: 2019-03-11 Last updated: 2019-03-12Bibliographically approved
Boåsen, M., Stee, M., Efsing, P. & Faleskog, J. (2019). A generalized probabilistic model for cleavage fracture with a length scale - Influence of stress state and application to surface cracked experiments. Engineering Fracture Mechanics, 214, 590-608
Open this publication in new window or tab >>A generalized probabilistic model for cleavage fracture with a length scale - Influence of stress state and application to surface cracked experiments
2019 (English)In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 214, p. 590-608Article in journal (Refereed) Published
Abstract [en]

A probabilistic model for the cumulative probability of failure by cleavage fracture with a material related length scale is further developed in this study. A new generalized effective stress measure is proposed, based on a normal stress decomposition of the stress tensor, capable of describing a state of normal stress in the range from the mean stress to the maximum principal stress. The effective stress measure associated with a material point is evaluated from the stress tensor averaged over the material related length scale. The model is shown to be well capable to predict both the fracture toughness at loss of both in-plane and out-of-plane constraint by model application to two different datasets from the open literature. The model is also shown to be well capable of predicting the probability of failure of discriminating experiments on specimens containing semi-elliptic surface cracks. A comparison where the master curve methodology is used to predict the probability of failure of the experiments is also included.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2019
Keywords
Cleavage fracture, Brittle fracture, Non-local stress, Weakest link, Semi-elliptic surface crack
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-252591 (URN)10.1016/j.engfracmech.2019.03.041 (DOI)000467694000040 ()
Note

QC 20190611

Available from: 2019-06-11 Created: 2019-06-11 Last updated: 2019-06-11Bibliographically approved
Huotilainen, C., Ivanchenko, M., Ehrnsten, U. & Efsing, P. (2019). Electrochemical investigation of in-service thermal aging in two CF8M cast stainless steels. Journal of Nuclear Materials, 520, 34-40
Open this publication in new window or tab >>Electrochemical investigation of in-service thermal aging in two CF8M cast stainless steels
2019 (English)In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 520, p. 34-40Article in journal (Refereed) Published
Abstract [en]

In-service thermal aging of CF8M cast austenitic stainless steel was investigated in materials removed from the steam generator inlet and crossover elbows of the Ringhals 2 pressurized water reactor nuclear power plant unit after approximately 92kh of full operating time. The thermal aging of these materials was investigated using the double loop electrochemical potentiokinetic reactivation method, coupled with indentation hardness measurements and microstructural characterizations, to identify correlations between the electrochemical behavior and traditional methods of investigating thermal aging embrittlement effects in cast stainless steels. While this electrochemical method can be easily employed to quantify thermal aging effects in materials aged at higher temperatures (e.g. greater than 350 degrees C), this study highlights the difficulties encountered when electrochemically evaluating the aging of materials exposed to nuclear power plant operating conditions. 

Place, publisher, year, edition, pages
Elsevier, 2019
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-252958 (URN)10.1016/j.jnucmat.2019.04.001 (DOI)000468520500005 ()2-s2.0-85064254951 (Scopus ID)
Note

QC 20190611

Available from: 2019-06-11 Created: 2019-06-11 Last updated: 2019-06-11Bibliographically approved
Sedlak, M., Alfredsson, B. & Efsing, P. (2018). A cohesive element with degradation controlled shape of the traction separation curve for simulating stress corrosion and irradiation cracking. Engineering Fracture Mechanics, 193, 172-196
Open this publication in new window or tab >>A cohesive element with degradation controlled shape of the traction separation curve for simulating stress corrosion and irradiation cracking
2018 (English)In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 193, p. 172-196Article in journal (Refereed) Published
Abstract [en]

A cohesive element with extended environmental degradation capability was developed and implemented into an Abaqus user element. The element uses a virgin and a fully degraded Traction Separation Law (TLS) as input. The use of the potential based PPR model enables flexibility in the softening shapes for both TSL. When the element is degraded, the TSL gradually goes from the shape of the virgin material to the fully degraded TSL shape. This transition was made with a new parameter. that can govern a more ductile or brittle crack growth behaviour at degradation. The effect on the plastic zone due to changing the softening shape is shown, where the convex shaped softening TSL gives higher plastic dissipation and larger plastic zones than the concave and more brittle TSL. The new degradation method was evaluated against a Hydrogen Embrittlement (HE) experiment showing improved agreement with the experiment compared to the literature. The effect of different susceptibility zones at the crack tip was also investigated, showing that a uniform degradation throughout the susceptible zone is more influenced by the. parameter than a triangular susceptible zone.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2018
Keywords
Traction separation law, Intergranular stress corrosion cracking, PPR potential-based, User element, Hydrogen embrittlement
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-225695 (URN)10.1016/j.engfracmech.2018.02.011 (DOI)000427918000013 ()2-s2.0-8504238535 (Scopus ID)
Note

QC 20180411

Available from: 2018-04-11 Created: 2018-04-11 Last updated: 2018-05-22Bibliographically approved
Lindgren, K., Boåsen, M., Stiller, K., Efsing, P. & Thuvander, M. (2018). Cluster formation in in-service thermally aged pressurizer welds. Journal of Nuclear Materials, 504, 23-28
Open this publication in new window or tab >>Cluster formation in in-service thermally aged pressurizer welds
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2018 (English)In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 504, p. 23-28Article in journal (Refereed) Published
Abstract [en]

Thermal aging of reactor pressure vessel steel welds at elevated temperatures may affect the ductile-to-brittle transition temperature. In this study, unique weld material from a pressurizer, with a composition similar to that of the reactor pressure vessel, that has been in operation for 28 years at 345 °C is examined. Despite the relatively low temperature, the weld becomes hardened during operation. This is attributed to nanometre sized Cu-rich clusters, mainly located at Mo- and C-enriched dislocation lines and on boundaries. The welds have been characterized using atom probe tomography, and the characteristics of the precipitates/clusters is related to the hardness increase, giving the best agreement for the Russell-Brown model.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Atom probe tomography, Precipitation, RPV steel, Thermal aging
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-224810 (URN)10.1016/j.jnucmat.2018.03.017 (DOI)000430050900003 ()2-s2.0-85043976074 (Scopus ID)
Note

QC 20180327

Available from: 2018-03-27 Created: 2018-03-27 Last updated: 2019-09-20Bibliographically approved
Bjurman, M., Lindgren, K., Thuvander, M., Ekström, P. & Efsing, P. (2018). Microstructural evolution of welded stainless steels on integrated effect of thermal aging and low flux irradiation. In: 18th International Conference on Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors, 2017: . Paper presented at 18th International Conference on Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors, 2017, Portland, United States, 13 August 2017 through 17 August 2017 (pp. 703-710). Springer International Publishing, Part F11
Open this publication in new window or tab >>Microstructural evolution of welded stainless steels on integrated effect of thermal aging and low flux irradiation
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2018 (English)In: 18th International Conference on Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors, 2017, Springer International Publishing , 2018, Vol. Part F11, p. 703-710Conference paper, Published paper (Refereed)
Abstract [en]

The combined effect of thermal aging and irradiation on cast and welded stainless steel solidification structures is not sufficiently investigated. From theory and consecutive aging and irradiation experiments, the effect of simultaneous low rate irradiation and thermal aging is expected to accelerate and modify the aging processes of the ferrite phase. Here, a detailed analysis of long-term aged material at very low fast neutron flux at LWR operating temperatures using Atom Probe Tomography is presented. Samples of weld material from various positions in the core barrel of the Zorita PWR are examined. The welds have been exposed to 280–285 °C for 38 years at three different neutron fluxes between 1 × 10−5 and 7 × 10−7 dpa/h to a total dose of 0.15–2 dpa. The aging of the ferrite phase occurs by spinodal decomposition, clustering and precipitation of e.g. G-phase. These phenomena are characterized and quantitatively analyzed in order to understand the effect of flux in combination with thermal aging.

Place, publisher, year, edition, pages
Springer International Publishing, 2018
Keywords
Irradiation, Spinodal decomposition, Stainless steel, Thermal aging, Weld ferrite
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-224267 (URN)10.1007/978-3-319-68454-3_54 (DOI)000456874000054 ()2-s2.0-85042420655 (Scopus ID)9783319684536 (ISBN)
Conference
18th International Conference on Environmental Degradation of Materials in Nuclear Power Systems - Water Reactors, 2017, Portland, United States, 13 August 2017 through 17 August 2017
Note

QC 20180315

Available from: 2018-03-16 Created: 2018-03-16 Last updated: 2019-02-19Bibliographically approved
Shen, R. R. & Efsing, P. (2018). Overcoming the drawbacks of plastic strain estimation based on KAM. Ultramicroscopy, 184, 156-163
Open this publication in new window or tab >>Overcoming the drawbacks of plastic strain estimation based on KAM
2018 (English)In: Ultramicroscopy, ISSN 0304-3991, E-ISSN 1879-2723, Vol. 184, p. 156-163Article in journal (Refereed) Published
Abstract [en]

Plastic strain estimation using electron backscatter diffraction (EBSD) based on kernel average misorientation (KAM) is affected by random orientation measurement error, EBSD step length, choice of kernel and average grain size. These sensitivities complicate reproducibility of results between labs, but it is shown in this work how these drawbacks can be overcome. The modifications to KAM were verified against a similar misorientation metric based on grain orientation spread (GOS), which does not show sensitivity to these factors. Both metrics were used in parallel to estimate the plastic strain distribution in Alloy 690 heat affected zones from component mockups, and showed the same results where the grain size was correctly compensated for.

Place, publisher, year, edition, pages
Elsevier B.V., 2018
Keywords
Electron backscatter diffraction, Heat affected zone, Kernel average misorientation, Nickel-base alloy, Plastic deformation, Backscattering, Corrosion, Diffraction, Electron diffraction, Grain size and shape, Average grain size, Electron back scatter diffraction, Kernel average misorientation (KAM), Mis-orientation, Nickel base alloys, Random orientations, Reproducibilities, Strain distributions
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-216802 (URN)10.1016/j.ultramic.2017.08.013 (DOI)000415650200018 ()2-s2.0-85029088686 (Scopus ID)
Note

Export Date: 24 October 2017; Article; CODEN: ULTRD; Correspondence Address: Shen, R.R.; Department of Solid Mechanics, KTH Royal Institute of Technology, Teknikringen 8D, Sweden; email: rshen@kth.se; Funding details: Vattenfall; Funding text: The authors wish to extend their gratitude to Vattenfall, Fortum and Uniper who funded this work, and to the Electric Power Research Institute (EPRI) and Torsten Pedersen at Ringhals AB for supplying the mockups used in this work. QC 20171205

Available from: 2017-12-05 Created: 2017-12-05 Last updated: 2018-02-15Bibliographically approved
Efsing, P. & Ekstrom, P. (2018). Swedish RPV Surveillance Programs. In: Server, WL Brumovsky, M (Ed.), INTERNATIONAL REVIEW OF NUCLEAR REACTOR PRESSURE VESSEL SURVEILLANCE PROGRAMS: . Paper presented at Workshop on Nuclear Reactor Pressure Vessel Surveillance Programs, JUN 29, 2016, Chicago, IL (pp. 219-231). ASTM INTERNATIONAL
Open this publication in new window or tab >>Swedish RPV Surveillance Programs
2018 (English)In: INTERNATIONAL REVIEW OF NUCLEAR REACTOR PRESSURE VESSEL SURVEILLANCE PROGRAMS / [ed] Server, WL Brumovsky, M, ASTM INTERNATIONAL , 2018, p. 219-231Conference paper, Published paper (Refereed)
Abstract [en]

Because the reactors of the Swedish reactor program were erected over a limited period of time, there are significant similarities regarding used materials and manufacturing methods between the different units. Each individual plant is supplied with a plant-specific surveillance program that reflects the materials utilized in the belt-line area form the start of operation. The programs were originally based on U.S. Nuclear Regulatory Commission guidance and supported by ASTM codes and standards, and the reactors were originally constructed for an estimated operating time of 40 years. The programs have been updated to reflect the fact that current planning calls for up to 60 years of operation for several of the most recent plants. The surveillance programs are to be validated and accepted by the Swedish Radiation Safety Authority.

Place, publisher, year, edition, pages
ASTM INTERNATIONAL, 2018
Series
American Society for Testing and Materials Selected Technical Papers, ISSN 0066-0558 ; 1603
Keywords
surveillance programs, reactor pressure vessel steel, long-term operation, regulations
National Category
Production Engineering, Human Work Science and Ergonomics
Identifiers
urn:nbn:se:kth:diva-234212 (URN)10.1520/STP160320170012 (DOI)000441706500011 ()2-s2.0-85050157779 (Scopus ID)978-0-8031-7651-5 (ISBN)
Conference
Workshop on Nuclear Reactor Pressure Vessel Surveillance Programs, JUN 29, 2016, Chicago, IL
Note

QC 20180905

Available from: 2018-09-05 Created: 2018-09-05 Last updated: 2018-09-05Bibliographically approved
Boåsen, M., Efsing, P. & Ehrnstén, U. (2017). On flux effects in a low alloy steel from a Swedish reactor pressure vessel. Journal of Nuclear Materials, 484, 110-119
Open this publication in new window or tab >>On flux effects in a low alloy steel from a Swedish reactor pressure vessel
2017 (English)In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 484, p. 110-119Article in journal (Refereed) Published
Abstract [en]

This study aims to investigate the presence of Unstable Matrix Defects in irradiated pressure vessel steel from weldments of the Swedish PWR Ringhals 4 (R4). Hardness tests have been performed on low flux (surveillance material) and high flux (Halden reactor) irradiated material samples in combination with heat treatments at temperatures of 330, 360 and 390 °C in order to reveal eventual recovery of any hardening features induced by irradiation. The experiments carried out in this study could not reveal any hardness recovery related to Unstable Matrix Defects at relevant temperatures. However, a difference in hardness recovery was found between the low and the high flux samples at heat treatments at higher temperatures than expected for the annihilation of Unstable Matrix Defects–the observed recovery is here attributed to differences of the solute clusters formed by the high and low flux irradiations.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Defects, Hardness, Heat treatment, High strength steel, Irradiation, Pressure vessels, Pressurized water reactors, Recovery, High flux, Irradiated materials, Low flux, Matrix defects, Pressure vessel steels, Reactor Pressure Vessel, Solute cluster, Weldments, Alloy steel
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-201957 (URN)10.1016/j.jnucmat.2016.11.026 (DOI)000393246300014 ()2-s2.0-85002170882 (Scopus ID)
Note

QC 20170303

Available from: 2017-03-03 Created: 2017-03-03 Last updated: 2017-11-29Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-1498-5691

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