Publication detail

Initiation of fatigue cracks in ultrafine-grained materials in high-cycle fatigue region

FINTOVÁ, S. KUNZ, L.

Original Title

Initiation of fatigue cracks in ultrafine-grained materials in high-cycle fatigue region

English Title

Initiation of fatigue cracks in ultrafine-grained materials in high-cycle fatigue region

Type

journal article in Web of Science

Language

en

Original Abstract

Initiation of fatigue cracks in materials with conventional grain (CG) size was investigated very thoroughly in the past. There is an extensive knowledge on the localization of cyclic plasticity and early crack development; however, it cannot be straightforwardly applied to the ultrafine-grained (UFG) structures with the grain size below 1 micrometer, because the crack initiation mechanisms are related to dislocation structures, which cannot develop in UFG materials simply from the size reasons. The paper brings results of an experimental investigation of the cyclic strain localization and crack initiation by means of focused ion beam technique (FIB). Two substantially different materials as regards the crystallographic structure, namely UFG Cu and magnesium alloy AZ91 processed by equal channel angular pressing (ECAP) were investigated and the observed characteristic features of crack initiation were discussed. The observations bring evidence that in the high-cycle fatigue (HCF) region point defects generated by dislocation activity do play very important role in the fatigue crack initiation process in UFG Cu. Fatigue cracks initiate in slip bands which form in areas of near-by oriented grains and are characteristic by surface relief, consisting of extrusions and intrusions. Point defects and formation of cavities and voids along the active slip planes governs the HCF crack initiation. No grain coarsening and development of specific dislocation structure was observed in the regions of crack initiation in UFG Cu. The mechanism of the crack initiation in AZ91 alloy processed by ECAP was found to be similar to that known from CG alloy. The cracks initiate in cyclic slip bands which forms in individual grains due to their relatively large grain size. The initiated cracks propagate along the slip planes in a crystallographic way which corresponds to the quasicleavage mechanism often reported for CG Mg alloys.

English abstract

Initiation of fatigue cracks in materials with conventional grain (CG) size was investigated very thoroughly in the past. There is an extensive knowledge on the localization of cyclic plasticity and early crack development; however, it cannot be straightforwardly applied to the ultrafine-grained (UFG) structures with the grain size below 1 micrometer, because the crack initiation mechanisms are related to dislocation structures, which cannot develop in UFG materials simply from the size reasons. The paper brings results of an experimental investigation of the cyclic strain localization and crack initiation by means of focused ion beam technique (FIB). Two substantially different materials as regards the crystallographic structure, namely UFG Cu and magnesium alloy AZ91 processed by equal channel angular pressing (ECAP) were investigated and the observed characteristic features of crack initiation were discussed. The observations bring evidence that in the high-cycle fatigue (HCF) region point defects generated by dislocation activity do play very important role in the fatigue crack initiation process in UFG Cu. Fatigue cracks initiate in slip bands which form in areas of near-by oriented grains and are characteristic by surface relief, consisting of extrusions and intrusions. Point defects and formation of cavities and voids along the active slip planes governs the HCF crack initiation. No grain coarsening and development of specific dislocation structure was observed in the regions of crack initiation in UFG Cu. The mechanism of the crack initiation in AZ91 alloy processed by ECAP was found to be similar to that known from CG alloy. The cracks initiate in cyclic slip bands which forms in individual grains due to their relatively large grain size. The initiated cracks propagate along the slip planes in a crystallographic way which corresponds to the quasicleavage mechanism often reported for CG Mg alloys.

Keywords

fatigue cracks initiation, fatigue, AZ91 magensium alloy

RIV year

2014

Released

25.06.2014

Publisher

IOP Publishing Ltd.

Pages from

2

Pages to

5

Pages count

4

BibTex


@article{BUT110659,
  author="Stanislava {Fintová} and Ludvík {Kunz}",
  title="Initiation of fatigue cracks in ultrafine-grained materials in high-cycle fatigue region",
  annote="Initiation of fatigue cracks in materials with conventional grain (CG) size was investigated very thoroughly in the past. There is
an extensive knowledge on the localization of cyclic plasticity and early crack development; however, it cannot be
straightforwardly applied to the ultrafine-grained (UFG) structures with the grain size below 1 micrometer, because the crack initiation
mechanisms are related to dislocation structures, which cannot develop in UFG materials simply from the size reasons.
The paper brings results of an experimental investigation of the cyclic strain localization and crack initiation by means of focused
ion beam technique (FIB). Two substantially different materials as regards the crystallographic structure, namely UFG Cu and
magnesium alloy AZ91 processed by equal channel angular pressing (ECAP) were investigated and the observed characteristic
features of crack initiation were discussed.
The observations bring evidence that in the high-cycle fatigue (HCF) region point defects generated by dislocation activity do
play very important role in the fatigue crack initiation process in UFG Cu. Fatigue cracks initiate in slip bands which form in
areas of near-by oriented grains and are characteristic by surface relief, consisting of extrusions and intrusions. Point defects and
formation of cavities and voids along the active slip planes governs the HCF crack initiation. No grain coarsening and
development of specific dislocation structure was observed in the regions of crack initiation in UFG Cu. The mechanism of the
crack initiation in AZ91 alloy processed by ECAP was found to be similar to that known from CG alloy. The cracks initiate in
cyclic slip bands which forms in individual grains due to their relatively large grain size. The initiated cracks propagate along the
slip planes in a crystallographic way which corresponds to the quasicleavage mechanism often reported for CG Mg alloys.",
  address="IOP Publishing Ltd.",
  chapter="110659",
  doi="10.1016/j.proeng.2014.06.213",
  institution="IOP Publishing Ltd.",
  number="6",
  volume="74",
  year="2014",
  month="june",
  pages="2--5",
  publisher="IOP Publishing Ltd.",
  type="journal article in Web of Science"
}