Near-threshold propagation of mode II and mode III fatigue cracks in ferrite and austenite

Abstract The near-threshold behavior of mode II and mode III long fatigue cracks in ferritic (ARMCO iron) and austenitic (X5CrNi18-10) steel were experimentally studied using various samples specially prepared to obtain the effective threshold values ΔKIIeff,th and ΔKIIIeff,th. In both investigated materials, the effective thresholds for mode III were ∼1.7 times higher than those for mode II. Three-dimensional topological data obtained by the examination of fracture surfaces using stereophotogrammetry were utilized to identify crack growth micromechanisms. In austenite, mode I branching of both the mode II and mode III cracks started at the very onset of crack growth. On the other hand, all cracks in ferrite propagated in crystallographically assisted local mixed mode I + II + III with mode II dominance. These experimental results can be understood in terms of crack growth micromechanisms according to a deformation model in ferrite and a decohesion model in austenite. The dissimilarity of growth mechanisms in ferrite and austenite may be attributed to a different number of available slip systems in body-centered cubic and face-centered cubic metals.

[1]  J. Rice,et al.  Slightly curved or kinked cracks , 1980 .

[2]  Otmar Kolednik,et al.  Reconstruction of surface topographies by scanning electron microscopy for application in fracture research , 1996 .

[3]  Wanlin Guo,et al.  Three-parameter K–T–Tz characterization of the crack-tip fields in compact-tension-shear specimens , 2012 .

[4]  Hans Albert Richard,et al.  A loading device for the creation of mixed mode in fracture mechanics , 1983 .

[5]  E. Tschegg,et al.  Sliding mode crack closure and mode III fatigue crack growth in mild steel , 1983 .

[6]  Vikram Deshpande,et al.  Discrete dislocation plasticity and crack tip fields in single crystals , 2001 .

[7]  Pinna,et al.  The preferred fatigue crack propagation mode in a M250 maraging steel loaded in shear , 1999 .

[8]  R. Pippan,et al.  Can pure mode III fatigue loading contribute to crack propagation in metallic materials , 2008 .

[9]  S. Pearson.  Initiation of fatigue cracks in commercial aluminium alloys and the subsequent propagation of very short cracks , 1975 .

[10]  R. Pippan,et al.  On the mechanism of fatigue crack propagation in ductile metallic materials , 2011 .

[11]  On the Mechanism of Factory-Roof Formation , 2010, CP 2013.

[12]  R. Pippan.  THE GROWTH OF SHORT CRACKS UNDER CYCLIC COMPRESSION , 1987 .

[13]  Reinhard Pippan,et al.  A NEW POWERFUL TOOL FOR SURVEYING CLEAVAGE FRACTURE SURFACES , 1997 .

[14]  S. Suresh.  Fatigue of materials , 1991 .

[15]  M. Klesnil,et al.  Fatigue of metallic materials , 1980 .

[16]  R. Ritchie.  Mechanisms of fatigue crack propagation in metals, ceramics and composites: Role of crack tip shielding☆ , 1988 .

[17]  R. Pippan,et al.  The influence of crack length on fatigue crack growth in deep sharp notches , 1987 .

[18]  R. Pippan.  Dislocation emission and fatigue crack growth threshold , 1991 .

[19]  Reinhard Pippan,et al.  Threshold and effective threshold of fatigue crack propagation in ARMCO iron. I, The influence of grain size and cold working , 1991 .

[20]  R. Pippan,et al.  Straightforward comparison of fatigue crack growth under modes II and III , 2008 .

[21]  Y. Murakami.  Metal Fatigue: Effects of Small Defects and Nonmetallic Inclusions , 2002 .

[22]  J. Pokluda,et al.  Micromechanisms of Fracture and Fatigue , 2010 .

[23]  R. Pippan,et al.  Dislocation modelling of fatigue cracks: an overview , 2001 .

[24]  E. Bretscher.  Encyclopædia of Physics , 1958, Nature.

[25]  Vikram Deshpande,et al.  A discrete dislocation analysis of near-threshold fatigue crack growth , 2001, Acta Materialia.

[26]  S. Ohr.  An electron microscope study of crack tip deformation and its impact on the dislocation theory of fracture , 1985 .

[27]  H. Vehoff,et al.  Crack propagation and cleavage initiation in Fe-2.6%-Si single crystals under controlled plastic crack tip opening rate in various gaseous environments , 1980 .

[28]  R. Pippan,et al.  Discrete dislocation modelling of near threshold fatigue crack propagation , 2010 .