Microstructural Interpretation of Effective Fatigue Threshold of Structural Steel

Microstructural Interpretation of Effective Fatigue Threshold of Structural Steel

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In the case of plain strain conditions, the shear misfit of crack flanks causing the rough-ness-induced crack closure is determined by the asymmetry of configurations of crack-wake dislo-cations and by a low value of the size ratio SR (the plastic zone size/the characteristic microstruc-tural distance). The crack wake dislocations produce also the plasticity induced crack closure as a result of a near-tip mismatch perpendicular to crack flanks. These extrinsic shielding effects can be quantitatively estimated according to recently published theoretical concepts [1-3] that were ap-plied to the austenitic steel of Japan provenience in the threshold region of fatigue crack propaga-tion. Related fatigue experiments were based on a standard load shedding technique associated with monitoring of the crack closure level. The surface roughness was analysed by means of the optical chromatography that enables a 3D reconstruction of fracture morphology. Calculated and measured effective threshold values of about 2.2 MPa.m1/2 are practically identical. Total levels of the extrin-sic toughening induced by the austenitic microstructure are rather low when compared to those identified in ferritic- and ferritic-austenitic steels.

In the case of plain strain conditions, the shear misfit of crack flanks causing the rough-ness-induced crack closure is determined by the asymmetry of configurations of crack-wake dislo-cations and by a low value of the size ratio SR (the plastic zone size/the characteristic microstruc-tural distance). The crack wake dislocations produce also the plasticity induced crack closure as a result of a near-tip mismatch perpendicular to crack flanks. These extrinsic shielding effects can be quantitatively estimated according to recently published theoretical concepts [1-3] that were ap-plied to the austenitic steel of Japan provenience in the threshold region of fatigue crack propaga-tion. Related fatigue experiments were based on a standard load shedding technique associated with monitoring of the crack closure level. The surface roughness was analysed by means of the optical chromatography that enables a 3D reconstruction of fracture morphology. Calculated and measured effective threshold values of about 2.2 MPa.m1/2 are practically identical. Total levels of the extrin-sic toughening induced by the austenitic microstructure are rather low when compared to those identified in ferritic- and ferritic-austenitic steels.

Microstructure, Effective Fatigue Threshold, Structural Steel

Microstructure, Effective Fatigue Threshold, Structural Steel

POKLUDA, J.; KONDO, Y.; SLÁMEČKA, K.; KOZÁK, V.; HORNÍKOVÁ, J.; ŠANDERA, P.

2010

02.09.2008

Vutium

Brno

9781617823190

Multilevel Approach to Fracture of Materials, Components and Structures (ECF17)

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2216

2219

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