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Dahlberg, Carl F. O.ORCID iD iconorcid.org/0000-0002-9509-2811
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Publications (10 of 31) Show all publications
Fischer, T., Zhou, T., Dahlberg, C. F. O. & Hedström, P. (2024). Relating stress/strain heterogeneity to lath martensite strength by experiments and dislocation density-based crystal plasticity. International journal of plasticity, 174, Article ID 103917.
Open this publication in new window or tab >>Relating stress/strain heterogeneity to lath martensite strength by experiments and dislocation density-based crystal plasticity
2024 (English)In: International journal of plasticity, ISSN 0749-6419, E-ISSN 1879-2154, Vol. 174, article id 103917Article in journal (Refereed) Published
Abstract [en]

To enhance the fundamental understanding for micromechanical lath martensite deformation, the microstructure as well as macro- and microscopic tensile properties of as -quenched 15-5 PH stainless steel are systematically analysed depending on the austenitisation temperature. Based on electron backscatter diffraction (EBSD) and backscattered electron (BSE) analysis, it is noted that the martensite morphology alters from a less defined to a more clearly defined parallel arrangement of the block and lath structure with increasing temperature. For an indepth quantification of the hierarchical boundary strengthening contributions in relation to local stress/strain heterogeneity, separate high-fidelity virtual microstructures are realised for the different scales (prior austenite grains, packets and blocks). This is consistent with the materials transformation process. The virtual microstructures are simulated employing the crystal plasticity finite element method (CPFEM) adapted for handling high dislocation density and encompassing all relevant strengthening mechanisms by boundaries, dislocations and solute atoms. While accurately capturing the measured size -dependent stress-strain behaviour, the simulations reveal in line with the experiments (Hall-Petch) that blocks are the most effective dislocation motion barrier, causing increased strain hardening and stress/strain heterogeneity. Furthermore, since strain localisation is predicted strongest in the distinct block structure, the experimentally observed early plastic material yielding is thought to be favoured here.

Place, publisher, year, edition, pages
Elsevier BV, 2024
Keywords
Martensite, Microstructure, EBSD, Mechanical properties, Modelling
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:kth:diva-344969 (URN)10.1016/j.ijplas.2024.103917 (DOI)001183361400001 ()2-s2.0-85184992541 (Scopus ID)
Note

QC 20240404

Available from: 2024-04-04 Created: 2024-04-04 Last updated: 2024-04-04Bibliographically approved
Subasic, N., Alfredsson, B., Dahlberg, C. F. O., Öberg, M. & Efsing, P. (2023). Mechanical Characterization of Fatigue and Cyclic Plasticity of 304L Stainless Steel at Elevated Temperature. Experimental mechanics, 63(8), 1391-1407
Open this publication in new window or tab >>Mechanical Characterization of Fatigue and Cyclic Plasticity of 304L Stainless Steel at Elevated Temperature
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2023 (English)In: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 63, no 8, p. 1391-1407Article in journal (Refereed) Published
Abstract [en]

Background: The mechanical characterization of the cyclic elastoplastic response of structural materials at elevated temperatures is crucial for understanding and predicting the fatigue life of components in nuclear reactors. Objective: In this study, a comprehensive mechanical characterization of 304L stainless steel has been performed including metallography, tensile tests, fatigue tests, fatigue crack growth tests and cyclic stress-strain tests. Methods: Isothermal tests were conducted at both room temperature and 300 °C for both the rolling direction and the transverse direction of the hot rolled steel. Mechanical properties were extracted from the uniaxial experiments by fitting relevant material models to the data. The cyclic plasticity behavior has been modelled with a radial return-mapping algorithm that utilizes the Voce nonlinear isotropic hardening model in combination with the Armstrong-Frederick nonlinear kinematic hardening model. The plasticity models are available in commercial FE software and accurately capture the stabilized hysteresis loops, including a substantial Bauschinger effect. Results: The material exhibits near isotropic properties, but its mechanical performance is generally reduced at high temperatures. Specifically, in the rolling direction, the Young’s modulus is reduced by 16 % at 300 °C, the yield strength at 0.2 % plastic strain is lower by 23 %, and the ultimate tensile strength is lower by 30 % compared to room temperature. Fatigue life is also decreased, leading to an accelerated fatigue crack growth rate compared to room temperature. A von Mises radial return mapping algorithm proves to be effective in accurately modelling the cyclic plasticity of the material. The algorithm has also been used to establish a clear correlation between energy dissipation per cycle and cycles to failure, leading to the proposal of an energy-based fatigue life prediction model. Conclusions: The material exhibits reduced mechanical performance at elevated temperatures, with decreased monotonic strength, compared to room temperature. Fatigue life is also compromised, resulting in accelerated fatigue crack growth. The material’s hardening behavior differs at room temperature and elevated temperature, with lower peak stress values observed at higher temperatures. The radial return mapping algorithm can be used to determine the dissipated energy per cycle which together with fatigue testing has been used to propose a low cycle fatigue life prediction model at both temperatures.

Place, publisher, year, edition, pages
Springer Nature, 2023
Keywords
Cyclic properties, Fatigue strength, Plasticity, Return mapping algorithm, Stainless steel
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-349870 (URN)10.1007/s11340-023-00992-5 (DOI)001065130000002 ()2-s2.0-85170541942 (Scopus ID)
Note

QC 20240704

Available from: 2024-07-04 Created: 2024-07-04 Last updated: 2024-07-04Bibliographically approved
Fischer, T., Dahlberg, C. F. O. & Hedström, P. (2023). Sensitivity of local cyclic deformation in lath martensite to flow rule and slip system in crystal plasticity. Computational materials science, 222, 112106, Article ID 112106.
Open this publication in new window or tab >>Sensitivity of local cyclic deformation in lath martensite to flow rule and slip system in crystal plasticity
2023 (English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 222, p. 112106-, article id 112106Article in journal (Refereed) Published
Abstract [en]

The prediction of the cyclic deformation behaviour in lath martensite-based high-strength steels requires constitutive models that reflect the local stress and strain fields as accurately as possible. At the same time, the constitutive models should act as efficiently as possible in order to achieve the required high number of cycles in a finite time. Only few research works have studied the sensitivity of the local cyclic deformation in lath martensite to the power law-based flow rule (Hutchinson or Chaboche-Cailletaud) and the active body-centred cubic (bcc) slip systems ({110}(111) and {112}(111)) in the crystal plasticity finite element method (CPFEM). This paper, therefore, aims to provide some guidance in the selection of suitable flow rule and slip systems. Based on full-field micromechanical modelling of a medium-carbon steel under symmetric strain-controlled cyclic loading, it can be shown that the two most commonly used flow rules according to Hutchinson and Chaboche-Cailletaud are equally capable of predicting the local stress and strain distributions within the hierarchical martensitic microstructure. However, using the Hutchinson flow rule increases the computational performance for the quasi-rate-independent problem considered here. The local distributions found differ strongly from those in the parent austenitic microstructure. If plastic deformation is assumed not only on the slip systems {110}(111), as often done, but also on the {112}(111) type, a redistribution of the bimodal distributed local stresses occurs at a significantly lower stress level. The unimodal distributed local strains are less affected by this. In addition, it is found that slightly different critical resolved shear stress (CRSS) values for both slip system types influence the local stress and strain distributions less severely than the additional plastic slip activation in the material.

Place, publisher, year, edition, pages
Elsevier BV, 2023
Keywords
Lath martensite, Microstructure, Fe-C alloys, Crystal plasticity, Micromechanics
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-325591 (URN)10.1016/j.commatsci.2023.112106 (DOI)000952187600001 ()2-s2.0-85149438360 (Scopus ID)
Note

QC 20230412

Available from: 2023-04-12 Created: 2023-04-12 Last updated: 2023-12-07Bibliographically approved
Fischer, T., Xiang, S., Dahlberg, C. F. O. & Hedström, P. (2022). Creep-fatigue properties of austenitic cast iron D5S with tension and compression dwell: A dislocation density-based crystal plasticity study. Materials Science & Engineering: A, 860, 144212, Article ID 144212.
Open this publication in new window or tab >>Creep-fatigue properties of austenitic cast iron D5S with tension and compression dwell: A dislocation density-based crystal plasticity study
2022 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 860, p. 144212-, article id 144212Article in journal (Refereed) Published
Abstract [en]

To predict and better understand the creep-fatigue behaviour of austenitic cast iron D5S under tension and compression dwell at 800 degrees C, a physics-based crystal plasticity model that describes the complex rate-and temperature-dependent deformation of the material as a function of the dislocation density is implemented. In addition to the tension and compression dwell direction, the effect of three different dwell times (30, 180 and 600 s) on the creep-fatigue properties is investigated. The dislocation density-based crystal plasticity simulations are compared to experimental tests from a prior work. While relaxation tests and low-cycle fatigue (LCF) tests without dwell assist in systematically identifying the material parameters, creep-fatigue (CF) data is used to validate the predictions. The virtual testing is performed on a large-scale representation of the actual test specimen with a polycrystalline structure. To analyse the fatigue damage mechanism, small-scale predictions are also conducted using a micromechanical unit cell approach. Here, a single graphite nodule frequently found in the material is embedded into the austenitic matrix. In the present work, a close agreement is achieved between the predicted CF behaviour and the experimental results. Consistent with the experimental findings, the simulation results show that the addition of compression dwell leads to an uplift of the overall tensile stress level, which significantly reduces the fatigue life of the material. The unit cell studies demonstrate that during this uplift, a strong localisation of stresses and strains arises at the graphite/matrix interface, triggering the nucleation and growth of cavities and/or debonding.

Place, publisher, year, edition, pages
Elsevier BV, 2022
Keywords
Creep-fatigue, Dwell-fatigue, Ductile cast iron, Crystal plasticity, Dislocation density
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-323017 (URN)10.1016/j.msea.2022.144212 (DOI)000894180200002 ()2-s2.0-85142157705 (Scopus ID)
Note

QC 20230112

Available from: 2023-01-12 Created: 2023-01-12 Last updated: 2023-12-07Bibliographically approved
Van Tran, K., Woracek, R., Kardjilov, N., Markoetter, H., Abou-Ras, D., Puplampu, S., . . . Manke, I. (2022). Torsion of a rectangular bar: Complex phase distribution in 304L steel revealed by neutron tomography. Materials & design, 222, Article ID 111037.
Open this publication in new window or tab >>Torsion of a rectangular bar: Complex phase distribution in 304L steel revealed by neutron tomography
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2022 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 222, article id 111037Article in journal (Refereed) Published
Abstract [en]

Metastable austenitic stainless steel (304L) samples with a rectangular cross-section were plastically deformed in torsion during which they experienced multiaxial stresses that led to a complex martensitic phase distribution owing to the transformation induced plasticity effect. A three-dimensional character-ization of the phase distributions in these cm-sized samples was carried out by wavelength-selective neutron tomography. It was found that quantitatively correct results are obtained as long as the samples do not exhibit any considerable preferential grain orientation. Optical microscopy, electron backscatter diffraction, and finite element modeling were used to verify and explain the results obtained by neutron tomography. Altogether, neutron tomography was shown to extend the range of microstructure charac-terization methods towards the meso-and macroscale.

Place, publisher, year, edition, pages
Elsevier BV, 2022
Keywords
Neutron tomography, Phase distribution, Rectangular cross-section, Torsion, Geometrical effect
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-320481 (URN)10.1016/j.matdes.2022.111037 (DOI)000862773300004 ()2-s2.0-85135925542 (Scopus ID)
Note

QC 20221026

Available from: 2022-10-26 Created: 2022-10-26 Last updated: 2022-10-26Bibliographically approved
Boåsen, M., Dahlberg, C. F. O., Efsing, P. & Faleskog, J. (2021). A weakest link model for multiple mechanism brittle fracture — Model development and application. Journal of the mechanics and physics of solids, 147, Article ID 104224.
Open this publication in new window or tab >>A weakest link model for multiple mechanism brittle fracture — Model development and application
2021 (English)In: Journal of the mechanics and physics of solids, ISSN 0022-5096, E-ISSN 1873-4782, Vol. 147, article id 104224Article in journal (Refereed) Published
Abstract [en]

A multiple mechanism weakest link model for intergranular and transgranular brittle fracture is developed on the basis of experimental observations of a thermally aged low alloy steel. The model development is carried out in tandem with micro mechanical analysis of grain boundary cracking using crystal plasticity modeling of polycrystalline aggregates with the purpose to inform the weakest link model. The fracture modeling presented in this paper is carried out by using a non-local porous plastic Gurson model where the void volume fraction evolution is regularized over two separate length scales. The ductile crack growth preceding the final brittle fracture is well predicted using this type of modeling. When applied to the brittle fracture tests, the weakest link model predicts the fracture toughness distribution remarkably well, both in terms of the constraint and the size effect. Included in the study is also the analysis of a reference material.

Place, publisher, year, edition, pages
Elsevier BV, 2021
Keywords
Brittle fracture, Cleavage fracture, Crystal plasticity, Intergranular, Transgranular, Weakest link
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-291149 (URN)10.1016/j.jmps.2020.104224 (DOI)000612236400011 ()2-s2.0-85097054128 (Scopus ID)
Note

QC 20210303

Available from: 2021-03-03 Created: 2021-03-03 Last updated: 2022-06-25Bibliographically approved
Dahlberg, C. F. O., Faleskog, J. & Larsson, P.-L. (2021). Correlation of Global Quantities at Material Characterization of Pressure-Sensitive Materials Using Sharp Indentation Testing. LUBRICANTS, 9(3), Article ID 29.
Open this publication in new window or tab >>Correlation of Global Quantities at Material Characterization of Pressure-Sensitive Materials Using Sharp Indentation Testing
2021 (English)In: LUBRICANTS, ISSN 2075-4442, Vol. 9, no 3, article id 29Article in journal (Refereed) Published
Abstract [en]

Correlation of sharp indentation problems is examined theoretically and numerically. The analysis focuses on elastic-plastic pressure-sensitive materials and especially the case when the local plastic zone is so large that elastic effects on the mean contact pressure will be small or negligible as is the case for engineering metals and alloys. The results from the theoretical analysis indicate that the effect from pressure-sensitivity and plastic strain-hardening are separable at correlation of hardness values. This is confirmed using finite element methods and closed-form formulas are presented representing a pressure-sensitive counterpart to the Tabor formula at von Mises plasticity. The situation for the relative contact area is more complicated as also discussed.

Keywords
indentation hardness, plastic contact, contact area, contact mechanics, finite-element method
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-292962 (URN)10.3390/lubricants9030029 (DOI)000633851300001 ()2-s2.0-85102757992 (Scopus ID)
Note

QC 20210419

Available from: 2021-04-19 Created: 2021-04-19 Last updated: 2022-06-25Bibliographically approved
Boåsen, M., Dahlberg, C. F. O., Efsing, P. & Faleskog, J. (2020). A weakest link model for multiple mechanism brittlefracture - Model development and application.
Open this publication in new window or tab >>A weakest link model for multiple mechanism brittlefracture - Model development and application
2020 (English)Report (Other academic)
Abstract [en]

A multiple mechanism weakest link model for intergranular and transgranularbrittle fracture is developed on the basis of experimental observations in a thermallyaged low alloy steel. The model development is carried out in tandemwith micro mechanical analysis of grain boundary cracking using crystal plasticitymodeling of polycrystalline aggregates with the purpose to inform theweakest link model. The fracture modeling presented in this paper is carriedout by using a non-local porous plastic Gurson model where the void volumefraction evolution is regularized over two separate length scales. The ductilecrack growth preceding the nal brittle fracture is well predicted using this typeof modeling. When applied to the brittle fracture tests, the weakest link modelpredicts the fracture toughness distribution remarkably well, both in terms ofthe constraint and the size eect. Included in the study is also the analysis of areference material.

Publisher
p. 46
Series
TRITA-SCI-RAP ; 2020:005
National Category
Applied Mechanics
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:kth:diva-279001 (URN)
Note

QC 20200812

Available from: 2020-08-10 Created: 2020-08-10 Last updated: 2024-03-18Bibliographically approved
Dahlberg, C. F. O. & Ortiz, M. (2020). Size Scaling of Plastic Deformation in Simple Shear: Fractional Strain-Gradient Plasticity and Boundary Effects in Conventional Strain-Gradient Plasticity. Journal of applied mechanics, 87(3), Article ID 031017.
Open this publication in new window or tab >>Size Scaling of Plastic Deformation in Simple Shear: Fractional Strain-Gradient Plasticity and Boundary Effects in Conventional Strain-Gradient Plasticity
2020 (English)In: Journal of applied mechanics, ISSN 0021-8936, E-ISSN 1528-9036, Vol. 87, no 3, article id 031017Article in journal (Refereed) Published
Abstract [en]

A recently developed model based on fractional derivatives of plastic strain is compared with conventional strain-gradient plasticity (SGP) models. Specifically, the experimental data and observed model discrepancies in the study by Mu et al. (2016, "Dependence of Confined Plastic Flow of Polycrystalline Cu Thin Films on Microstructure," MRS Com. Res. Let. 20, pp. 1-6) are considered by solving the constrained simple shear problem. Solutions are presented both for a conventional SGP model and a model extension introducing an energetic interface. The interface allows us to relax the Dirichlet boundary condition usually assumed to prevail when solving this problem with the SGP model. We show that the particular form of a relaxed boundary condition does not change the underlying size scaling of the yield stress and consequently does not resolve the scaling issue. Furthermore, we show that the fractional strain-gradient plasticity model predicts a yield stress with a scaling exponent that is equal to the fractional order of differentiation.

Place, publisher, year, edition, pages
ASME, 2020
Keywords
constitutive modeling of materials, mechanical properties of materials, plasticity
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-272903 (URN)10.1115/1.4045872 (DOI)000525406900020 ()2-s2.0-85101878408 (Scopus ID)
Note

QC 20200526

Available from: 2020-05-26 Created: 2020-05-26 Last updated: 2024-03-15Bibliographically approved
Gudmundson, P. & Dahlberg, C. F. O. (2019). Dislocation based strain gradient plasticity model for prediction of length scale dependent initial yield strength. In: 6th International Conference on Material Modelling (ICCM6): . Paper presented at 6th International Conference on Material Modelling (ICCM6).
Open this publication in new window or tab >>Dislocation based strain gradient plasticity model for prediction of length scale dependent initial yield strength
2019 (English)In: 6th International Conference on Material Modelling (ICCM6), 2019Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

Many experimental studies have shown a plastic strengthening effect for structural length scales approaching microstructural dimensions. Both increases in initial yield strength and strain hardening have been observed. Over the last 30 years different strain gradient plasticity (SGP) theories have been developed in order to capture these length scale dependences. However, up to now no generally accepted theory has emerged. In the present presentation, focus is directed into a physically based SGP model for initiation of plastic deformation.

The plastic behavior is governed by a dissipative part that primarily controls the hardening at moderate plastic strains and an energetic part that is of importance for the initiation of plastic flow. It is shown that a model based on the self-energies of dislocations can be translated into an internal free energy in terms of plastic strain gradients. Similarly, the dissipative part of the model is based on the Taylor model, which also gives a direct connection to dislocation theory.

In this way, a physical connection is made between the SGP framework and dislocation mechanics. It is shown that the same length scale emerges for both the energetic and the dissipative part of the model. Apart from a non-dimensional factor of the order of unity, the length scale can be defined as the Burgers vector divided by the strain for initiation of plastic deformation.

When the structural length scale approaches this microstructural length scale, strengthening effects result. The three-dimensional SGP model is specialized to the simple load cases of tensile tension with a passivation layer that prohibits plastic deformation on the surfaces as well as pure bending with free and fixed boundary conditions for plastic strain. Simulations of initial yield stress for varying thicknesses are compared to experimental observations reported in the literature. It is shown that the model in a good way can capture the length scale dependences. Also upper bound solutions are presented for a spherical void in an infinite volume as well as torsion of a cylindrical rod. The model is as well applied to derive a prediction for the Hall-Petch effect.

Keywords
strain gradient plasticity
National Category
Applied Mechanics
Research subject
Solid Mechanics
Identifiers
urn:nbn:se:kth:diva-255868 (URN)
Conference
6th International Conference on Material Modelling (ICCM6)
Note

QC 20190902

Available from: 2019-08-14 Created: 2019-08-14 Last updated: 2024-03-15Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-9509-2811

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