Analysis of the correlation between micro-mechanical fields and fatigue crack propagation path in nodular cast iron

Tito Andriollo; Yubin Zhang; Søren Fæster; Varvara Kouznetsova

doi:10.1016/j.actamat.2020.02.026

Analysis of the correlation between micro-mechanical fields and fatigue crack propagation path in nodular cast iron

Tito Andriollo (Corresponding author)
, Yubin Zhang
, Søren Fæster
, Varvara Kouznetsova

Research output: Contribution to journal › Article › Academic › peer-review

29 Citations (Scopus)

Abstract

The morphology of the fatigue crack in nodular cast iron has great influence on the material performance under cyclic loading. In contrast to previous phenomenological studies, the present work attempts to unravel a relation between the crack propagation path and the micro-mechanical fields developing at the microstructural level. To this end, a fatigue crack in a compact tension specimen is imaged with X-ray tomography and a new segmentation procedure based on digital volume correlation is used to distinguish the part of the crack growing in the matrix from the graphite nodules. The micromechanical fields surrounding the tip of the notch as well as the tip of the fully developed fatigue crack are estimated via 3D microstructure-resolved finite element models, whose size is maintained small compared to the specimen by using boundary conditions measured in-situ with digital image correlation. The numerical fields are compared to the location of the crack nucleation site as well as to the crack growth direction. A weak correlation is found between the nucleation site and the equivalent plastic strain, suggesting that nucleation is controlled by plasticity occurring at a lower scale. On the other hand, a clear correlation is revealed between the crack growth direction and the direction perpendicular to the maximum principal stress. Based on this result, a mechanism is proposed to explain the step-like features characterizing the shape of the fatigue crack in nodular cast iron.

Original language	English
Pages (from-to)	302-314
Number of pages	13
Journal	Acta Materialia
Volume	188
DOIs	https://doi.org/10.1016/j.actamat.2020.02.026
Publication status	Published - 15 Apr 2020

Funding

This work was carried out within the frame of the project ‘‘Optimised high performance ductile cast iron using 4D X-ray analysis and microstructural modelling’’, Danish Research Council for Independent Research , grant no. 8022-00085B . The authors gratefully acknowledge: Dr. Karl Martin Pedersen and Dr. Sanita Zike from Siemens Gamesa Renewable Energy A/S, for providing the material used in the investigation and performing the tensile monotonic and cyclic tests; Dr. Chaoling Xu and M.Sc. Steffen Rasmussen from Technical University of Denmark, for providing support during the preparation of the specimen and the crack growth test; Ass. Prof. Johan Hoefnagels and M.Sc. Aslan Mohammadpourshoorbakhlou, from Eindhoven University of Technology, for help with the DIC analysis and the meshing toolbox. This work was carried out within the frame of the project ‘‘Optimised high performance ductile cast iron using 4D X-ray analysis and microstructural modelling’’, Danish Research Council for Independent Research, grant no. 8022-00085B. The authors gratefully acknowledge: Dr. Karl Martin Pedersen and Dr. Sanita Zike from Siemens Gamesa Renewable Energy A/S, for providing the material used in the investigation and performing the tensile monotonic and cyclic tests; Dr. Chaoling Xu and M.Sc. Steffen Rasmussen from Technical University of Denmark, for providing support during the preparation of the specimen and the crack growth test; Ass. Prof. Johan Hoefnagels and M.Sc. Aslan Mohammadpourshoorbakhlou, from Eindhoven University of Technology, for help with the DIC analysis and the meshing toolbox.

Funders	Funder number
Eindhoven University of Technology
Danmarks Frie Forskningsfond	8022-00085B
Technical University of Denmark

Keywords

Cast iron
Crack propagation
Digital volume correlation
Fatigue
Micromechanical modeling

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10.1016/j.actamat.2020.02.026

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title = "Analysis of the correlation between micro-mechanical fields and fatigue crack propagation path in nodular cast iron",

abstract = "The morphology of the fatigue crack in nodular cast iron has great influence on the material performance under cyclic loading. In contrast to previous phenomenological studies, the present work attempts to unravel a relation between the crack propagation path and the micro-mechanical fields developing at the microstructural level. To this end, a fatigue crack in a compact tension specimen is imaged with X-ray tomography and a new segmentation procedure based on digital volume correlation is used to distinguish the part of the crack growing in the matrix from the graphite nodules. The micromechanical fields surrounding the tip of the notch as well as the tip of the fully developed fatigue crack are estimated via 3D microstructure-resolved finite element models, whose size is maintained small compared to the specimen by using boundary conditions measured in-situ with digital image correlation. The numerical fields are compared to the location of the crack nucleation site as well as to the crack growth direction. A weak correlation is found between the nucleation site and the equivalent plastic strain, suggesting that nucleation is controlled by plasticity occurring at a lower scale. On the other hand, a clear correlation is revealed between the crack growth direction and the direction perpendicular to the maximum principal stress. Based on this result, a mechanism is proposed to explain the step-like features characterizing the shape of the fatigue crack in nodular cast iron.",

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N2 - The morphology of the fatigue crack in nodular cast iron has great influence on the material performance under cyclic loading. In contrast to previous phenomenological studies, the present work attempts to unravel a relation between the crack propagation path and the micro-mechanical fields developing at the microstructural level. To this end, a fatigue crack in a compact tension specimen is imaged with X-ray tomography and a new segmentation procedure based on digital volume correlation is used to distinguish the part of the crack growing in the matrix from the graphite nodules. The micromechanical fields surrounding the tip of the notch as well as the tip of the fully developed fatigue crack are estimated via 3D microstructure-resolved finite element models, whose size is maintained small compared to the specimen by using boundary conditions measured in-situ with digital image correlation. The numerical fields are compared to the location of the crack nucleation site as well as to the crack growth direction. A weak correlation is found between the nucleation site and the equivalent plastic strain, suggesting that nucleation is controlled by plasticity occurring at a lower scale. On the other hand, a clear correlation is revealed between the crack growth direction and the direction perpendicular to the maximum principal stress. Based on this result, a mechanism is proposed to explain the step-like features characterizing the shape of the fatigue crack in nodular cast iron.

AB - The morphology of the fatigue crack in nodular cast iron has great influence on the material performance under cyclic loading. In contrast to previous phenomenological studies, the present work attempts to unravel a relation between the crack propagation path and the micro-mechanical fields developing at the microstructural level. To this end, a fatigue crack in a compact tension specimen is imaged with X-ray tomography and a new segmentation procedure based on digital volume correlation is used to distinguish the part of the crack growing in the matrix from the graphite nodules. The micromechanical fields surrounding the tip of the notch as well as the tip of the fully developed fatigue crack are estimated via 3D microstructure-resolved finite element models, whose size is maintained small compared to the specimen by using boundary conditions measured in-situ with digital image correlation. The numerical fields are compared to the location of the crack nucleation site as well as to the crack growth direction. A weak correlation is found between the nucleation site and the equivalent plastic strain, suggesting that nucleation is controlled by plasticity occurring at a lower scale. On the other hand, a clear correlation is revealed between the crack growth direction and the direction perpendicular to the maximum principal stress. Based on this result, a mechanism is proposed to explain the step-like features characterizing the shape of the fatigue crack in nodular cast iron.

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KW - Micromechanical modeling

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ER -

Analysis of the correlation between micro-mechanical fields and fatigue crack propagation path in nodular cast iron

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