Publication detail

Near-threshold Fatigue Crack Propagation under Mixed-mode II+III in ARMCO Iron

VOJTEK, T. POKLUDA, J. ŠANDERA, P. HORNÍKOVÁ, J. SLÁMEČKA, K. PIPPAN, R. HOHENWARTER, A.

Czech title

Šíření únavových trhlin ve složeném módu II+III v ARMCO železe v prahové oblasti

English title

Near-threshold Fatigue Crack Propagation under Mixed-mode II+III in ARMCO Iron

Type

conference paper

Language

en

Original abstract

The paper is dedicated to experiments on near-threshold fatigue cracks under mixed-mode II+III in the ARMCO iron. The aim is to find the intrinsic (effective) threshold value of stress intensity factor (SIF) range in the mixed mode II+III and to compare it to those in modes II, III as well as to elucidate the crack growth mechanism. In this paper we only focus on the mixed-mode II+III experiment. Cylindrical bars with circumferential cracked notch were loaded by shear force. The notch is located in the middle of the bar and, therefore, no bending moment is present. Pre-cracks were created by compressive cyclic loading in mode I to obtain smooth fracture surfaces. After the experiment, the specimens were fractured under very low temperature or by cyclic tensile loading. The circumferential crack was loaded by different combination of modes II and III. The SIFs in mode II and III were numerically calculated using FEM. Two simple formulae were used to evaluate the effective mixed-mode SIF. The crack path and the surface topography were studied by means of a 3D reconstruction of fracture surfaces using stereo pairs of SEM images of the fracture surface (stereophotogrammetry in SEM). Differences between crack paths (and associated morphologies) under modes II, III and II+III were analyzed and statistically described in terms of local inclination and twisting angles.

Czech abstract

Článek je věnován experimentům s únavovými trhlinami v prahové oblasti v ARMCO železe. Cílem je nalézt intrinzitní (efektivní) prahové hodnoty rozkmitu faktoru intenzity napětí ve složeném módu II+III a srovnat je s hodnotami pro módy II a III a zároveň také objasnit mechanismus jejich růstu. V tomto článku se zaměřujeme pouze na experiment pro složený mód II+III. Válcové tyčové vzorky s obvodovým vrubem s trhlinou byly zatěžovány ve smyku. Vrub se nacházel uprostřed vzorku, takže nebyl přítomen ohybový moment. Iniciační trhliny byly vytvořeny tlakovým cyklickým zatížením v módu I, aby byly obdrženy hladké lomové plochy. Po experimentu byly vzorky dolomeny za velmi nízké teploty nebo cyklickým zatížením v tahu. Obvodová trhlina byla zatěžována různou kombinací módů II a III. Faktory intenzity napětí v módech II a III byly spočteny numericky pomocí MKP. Dva jednoduché vztahy byly používány pro vyhodnocování efektivních faktorů intensity napětí pro složený mód. Trajektorie šíření trhliny a topografie jejího povrchu byly studovány pomocí 3D rekonstrukce lomových ploch s využitím stereo-párů snímků lomových ploch z řádkovacího elektronového mikroskopu (stereofotogrammetrie v ŘEM). Rozdíly mezi směry šíření trhliny (a s tím spojených morfologií) v módech II, III a II+III byly analyzovány a statisticky popsány pomocí úhlů lokálních odklonů a natočení.

English abstract

The paper is dedicated to experiments on near-threshold fatigue cracks under mixed-mode II+III in the ARMCO iron. The aim is to find the intrinsic (effective) threshold value of stress intensity factor (SIF) range in the mixed mode II+III and to compare it to those in modes II, III as well as to elucidate the crack growth mechanism. In this paper we only focus on the mixed-mode II+III experiment. Cylindrical bars with circumferential cracked notch were loaded by shear force. The notch is located in the middle of the bar and, therefore, no bending moment is present. Pre-cracks were created by compressive cyclic loading in mode I to obtain smooth fracture surfaces. After the experiment, the specimens were fractured under very low temperature or by cyclic tensile loading. The circumferential crack was loaded by different combination of modes II and III. The SIFs in mode II and III were numerically calculated using FEM. Two simple formulae were used to evaluate the effective mixed-mode SIF. The crack path and the surface topography were studied by means of a 3D reconstruction of fracture surfaces using stereo pairs of SEM images of the fracture surface (stereophotogrammetry in SEM). Differences between crack paths (and associated morphologies) under modes II, III and II+III were analyzed and statistically described in terms of local inclination and twisting angles.

Keywords in Czech

složený mód, faktor intenzity napětí, šíření trhliny, ARMCO železo

Keywords in English

mixed mode, stress intensity factor, crack growth, ARMCO iron

RIV year

2012

Released

26.08.2012

Location

Kazan

ISBN

978-5-905576-18-8

Book

19th European Conference on Fracture

Pages from–to

188–193

Pages count

6

BIBTEX


@inproceedings{BUT95956,
  author="Tomáš {Vojtek} and Jaroslav {Pokluda} and Pavel {Šandera} and Jana {Horníková} and Karel {Slámečka} and Reinhard {Pippan} and Anton {Hohenwarter},
  title="Near-threshold Fatigue Crack Propagation under Mixed-mode II+III in ARMCO Iron",
  booktitle="19th European Conference on Fracture",
  year="2012",
  month="August",
  pages="188--193",
  address="Kazan",
  isbn="978-5-905576-18-8"
}