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Publications (5 of 5) Show all publications
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
Dahlberg, C. F. O. & Boåsen, M. (2019). Evolution of the length scale in strain gradient plasticity. International journal of plasticity, 112, 220-241
Open this publication in new window or tab >>Evolution of the length scale in strain gradient plasticity
2019 (English)In: International journal of plasticity, ISSN 0749-6419, E-ISSN 1879-2154, Vol. 112, p. 220-241Article in journal (Refereed) Published
Abstract [en]

An equivalence is assumed between a microstructural length scale related to dislocation density and the constitutive length scale parameter in phenomenological strain gradient plasticity. An evolution law is formed on an incremental basis for the constitutive length scale parameter. Specific evolution equations are established through interpretations of the relation between changes in dislocation densities and increments in plastic strain and strain gradient. The length scale evolution has been implemented in a 2D-plane strain finite element method (FEM) code, which has been used to study a beam in pure bending. The main effect of the length scale evolution on the response of the beam is a decreased strain hardening, which in cases of small beam thicknesses even leads to a strain softening behavior. An intense plastic strain gradient may develop close to the neutral axis and can be interpreted as a pile-up of dislocations. The effects of the length scale evolution on the mechanical fields are compared with respect to the choice of length evolution equation.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2019
Keywords
Length scale evolution, Strain gradient plasticity, Size effects, Dislocation mean free path, Dislocation microstructure
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-241186 (URN)10.1016/j.ijplas.2018.08.016 (DOI)000454468400013 ()2-s2.0-85053428373 (Scopus ID)
Note

QC 20190121

Available from: 2019-01-21 Created: 2019-01-21 Last updated: 2019-03-11Bibliographically 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
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/0000-0002-8408-8489

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