Assessment of Extrinsic Crack Tip Shielding in Austenitic Steel near Fatigue Threshold

Assessment of Extrinsic Crack Tip Shielding in Austenitic Steel near Fatigue Threshold

Článek WoS

Asymmetric arrangements of stored crack-wake dislocations and low values of the size ratio SR, the plastic zone size / the characteristic microstructural distance, were found to be of basic importance for the shear misfit of crack flanks causing the roughness-induced crack closure in case of plain strain conditions. The crack wake dislocations produce also the plasticity induced crack closure as a result of a near-tip mismatch perpendicular to crack flanks. According to a recently published theoretical concept, an estimation of these extrinsic shielding effects in the threshold re-gion of fatigue crack propagation was made for austenitic steel of Japan provenience. Related fa-tigue 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 chromatogra-phy 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 extrinsic tough-ening induced by the austenitic microstructure are rather low when compared to those identified in ferritic- and ferritic-austenitic steels.

Asymmetric arrangements of stored crack-wake dislocations and low values of the size ratio SR, the plastic zone size / the characteristic microstructural distance, were found to be of basic importance for the shear misfit of crack flanks causing the roughness-induced crack closure in case of plain strain conditions. The crack wake dislocations produce also the plasticity induced crack closure as a result of a near-tip mismatch perpendicular to crack flanks. According to a recently published theoretical concept, an estimation of these extrinsic shielding effects in the threshold re-gion of fatigue crack propagation was made for austenitic steel of Japan provenience. Related fa-tigue 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 chromatogra-phy 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 extrinsic tough-ening induced by the austenitic microstructure are rather low when compared to those identified in ferritic- and ferritic-austenitic steels.

Assessment, Extrinsic Crack Tip Shielding, Austenitic Steel, Fatigue Threshold

Assessment, Extrinsic Crack Tip Shielding, Austenitic Steel, Fatigue Threshold

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

2010

02.07.2008

1013-9826

Key Engineering Materials (print)

385-387

1

Švýcarská konfederace

49

52

4