Mikrostrukturní interpretace efektivní prahové hodnoty kontrukčních ocelí

Microstructural Interpretation of Effective Fatigue Threshold of Structural Steel

článek ve sborníku ve WoS nebo Scopus

en

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.

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.

Mikrostruktura, Efektivní prahová hodnota, konstrukční oceli

Microstructure, Effective Fatigue Threshold, Structural Steel

2008

02.09.2008

Vutium

Brno

9781617823190

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

1

2216–2219

4