Publication detail

Quantitative analysis of intrinsic mode III fatigue thresholds in bcc metals

VOJTEK, T. ŽÁK, S. POKLUDA, J.

Original Title

Quantitative analysis of intrinsic mode III fatigue thresholds in bcc metals

English Title

Quantitative analysis of intrinsic mode III fatigue thresholds in bcc metals

Type

journal article in Web of Science

Language

en

Original Abstract

Intrinsic (effective) threshold is a material characteristic important for both engineering and science connected to fatigue crack propagation processes. This paper presents the first attempt to give a quantitative interpretation of the mode III effective threshold. The approach of a local growth mode previously applied to the remote mode II cracks, which led to a prediction of values of the mode II effective threshold in metallic materials, is applied to remote mode III cracks in materials with coplanar shear-mode crack growth (bcc metals). Local mode II stress intensity factors of a zig-zag shaped crack front loaded in the remote mode III were determined by numerical modelling for various angles of in-plane crack front asperities. The results were compared with experimentally measured effective thresholds and geometry of real crack fronts. It was found that for relatively small angles of the in-plane precrack asperities (23° for the ARMCO iron and 25° for niobium) the remote mode III crack propagation can be realized purely by the local mode II growth mechanism. Experimentally measured average angles of asperities on real precrack fronts (25° for the ARMCO iron and 26° for niobium) were very close to those obtained theoretically. This represents a quantitative confirmation of a dominance of the local mode II mechanism previously deduced only qualitatively by observation of fractographical patterns.

English abstract

Intrinsic (effective) threshold is a material characteristic important for both engineering and science connected to fatigue crack propagation processes. This paper presents the first attempt to give a quantitative interpretation of the mode III effective threshold. The approach of a local growth mode previously applied to the remote mode II cracks, which led to a prediction of values of the mode II effective threshold in metallic materials, is applied to remote mode III cracks in materials with coplanar shear-mode crack growth (bcc metals). Local mode II stress intensity factors of a zig-zag shaped crack front loaded in the remote mode III were determined by numerical modelling for various angles of in-plane crack front asperities. The results were compared with experimentally measured effective thresholds and geometry of real crack fronts. It was found that for relatively small angles of the in-plane precrack asperities (23° for the ARMCO iron and 25° for niobium) the remote mode III crack propagation can be realized purely by the local mode II growth mechanism. Experimentally measured average angles of asperities on real precrack fronts (25° for the ARMCO iron and 26° for niobium) were very close to those obtained theoretically. This represents a quantitative confirmation of a dominance of the local mode II mechanism previously deduced only qualitatively by observation of fractographical patterns.

Keywords

effective crack-growth thresholds; modes II and III; growth micromechanisms; metallic materials

Released

01.10.2018

Publisher

Elsevier

ISBN

1879-3452

Periodical

INTERNATIONAL JOURNAL OF FATIGUE

Year of study

115

Number

1

State

GB

Pages from

35

Pages to

41

Pages count

7

Documents

BibTex


@article{BUT152016,
  author="Tomáš {Vojtek} and Stanislav {Žák} and Jaroslav {Pokluda}",
  title="Quantitative analysis of intrinsic mode III fatigue thresholds in bcc metals",
  annote="Intrinsic (effective) threshold is a material characteristic important for both engineering and science connected to fatigue crack propagation processes. This paper presents the first attempt to give a quantitative interpretation of the mode III effective threshold. The approach of a local growth mode previously applied to the remote mode II cracks, which led to a prediction of values of the mode II effective threshold in metallic materials, is applied to remote mode III cracks in materials with coplanar shear-mode crack growth (bcc metals). Local mode II stress intensity factors of a zig-zag shaped crack front loaded in the remote mode III were determined by numerical modelling for various angles of in-plane crack front asperities. The results were compared with experimentally measured effective thresholds and geometry of real crack fronts. It was found that for relatively small angles of the in-plane precrack asperities (23° for the ARMCO iron and 25° for niobium) the remote mode III crack propagation can be realized purely by the local mode II growth mechanism. Experimentally measured average angles of asperities on real precrack fronts (25° for the ARMCO iron and 26° for niobium) were very close to those obtained theoretically. This represents a quantitative confirmation of a dominance of the local mode II mechanism previously deduced only qualitatively by observation of fractographical patterns.",
  address="Elsevier",
  chapter="152016",
  doi="10.1016/j.ijfatigue.2018.04.022",
  institution="Elsevier",
  number="1",
  volume="115",
  year="2018",
  month="october",
  pages="35--41",
  publisher="Elsevier",
  type="journal article in Web of Science"
}