Synchrotron 3D characterization of arrested fatigue cracks initiated from small tilted notches in steel
Journal Title: Frattura ed Integrità Strutturale - Year 2015, Vol 9, Issue 33
Abstract
High resolution synchrotron X-ray tomography has been used to obtain 3D images of arrested cracks initiated at small artificial defects located on the surface of cylindrical steel specimens subjected to mode I fatigue loading. These defects consist in small semi-circular slits tilted at 0°, 30° or 60° with respect to the plane normal to the loading axis; all of them had the same defect size, area = 188 μm, where the area denotes the area of the domain defined by projecting the defect on a plane normal to the loading axis. Arrested cracks initiated from the notch were observed for all tilt angles at the surface of samples cycled at the fatigue limit (stress amplitude at which the specimen does not fail after 1×107 cycles). High resolution synchrotron X-ray tomography has been used to obtain 3D images of those small defects and non-propagating cracks (NPC). Despite the fact that steel is a highly attenuating material for X rays, high resolution 3D images of the cracks and of the initiating defects were obtained (0.65 m voxel size). The values of surface crack length measured by tomography are the same as those obtained by optical microscope measurements. The area values present the same tendency as the surface length of NPC, i.e. larger non-propagating cracks areas were observed in the softer steel. In the extreme case of 60º tilted defect, the crack fronts appear much more discontinuous with several cracks propagating in mode I until arrest.
Authors and Affiliations
P. Lorenzino, J. Buffiere, S. Okazaki, H. Matsunaga, Y. Murakami
Plastic zone evolution near a crack tip and its role in environmentally assisted cracking
This paper analyzes the effects of crack tip plastic strains and compressive residual stresses, created by fatigue pre-cracking, on environmentally assisted cracking of pearlitic steel subjected to localized anodic...
A probabilistic interpretation of the Miner number for fatigue life prediction
The Miner number M, used as a tool for lifetime prediction of mechanical and structural components in most of the standards related to fatigue design, is generally accepted as representing a damage stage resultin...
Cf/C composites: correlation between CVI process parameters and Pyrolytic Carbon microstructure
Chemical Vapour Infiltration (CVI) technique has been long used to produce carbon/carbon composites. The Pyrolytic Carbon (Py-C) matrix infiltrated by CVI could have different microstructures, i.e. Rough Laminar...
Electro-mechanical coupled design of self-powered sensing systems and performances comparison through experiments
Recent advances in low-power sensors and electronic components open to innovative strategies in structural monitoring and real-time data processing, in particular for industrial and vehicular fields. Dedicated devi...
Resilience and ductility of Oxy-fuel HAZ cut
Cutting processes affect the material to a deeper or shallower attached-to-the-cut zone. Its microstructure, its hardness and mechanical properties are changed. Also the cutting process introduces surface roughne...