Strain profiling of fatigue crack overload effects using energy dispersive X-ray diffraction

Croft, Mark; Zhong, Z.; Jisrawi, N.; Zakharchenko, I. V.; Holtz, R.L.; Skaritka, J.; Fast, Tobias; Sadananda, K.; Lakshmipathy, M.; Tsakalakos, Thomas

doi:10.1016/j.ijfatigue.2005.06.022

Cited by 81 publications

(76 citation statements)

References 9 publications

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“…Two different families of techniques have been used, namely, synchrotron X-ray diffraction and displacement field measurement either by Digital Image Correlation (DIC) or tracking of individual markers. Synchrotron X-ray diffraction studies allow mapping the crack tip strain field [4][5][6][7]. This method is mainly applied to unloaded samples and it focuses on measurement of the residual strains in the wake and at the tip of a post overload fatigue crack with a rather coarse spatial resolution along the crack front where the strain is averaged through the sample thickness for 1-mm thick samples where plane stress should prevail [7] or sampled every 300 µm to understand the stronger crack retardation observed near the specimen edges [5].…”

Section: Introductionmentioning

confidence: 99%

Influence of closure on the 3D propagation of fatigue cracks in a nodular cast iron investigated by X-ray tomography and 3D volume correlation

et al. 2010

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Synchrotron X-ray tomography was performed during in-situ fatigue crack propagation in two small size specimens made of nodular graphite cast iron. While direct image analysis allows to retrieve the successive positions of the crack front, and to detect local crack retardation, volume correlation enables for the measurement of displacement fields in the bulk of the specimen. The Stress Intensity Factors (SIF) which are extracted from the measured displacement fields and the corresponding local crack growth rate all along the front are in good agreement with published results. In particular, it is possible to link the non propagation

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Section: Introductionmentioning

confidence: 99%

Influence of closure on the 3D propagation of fatigue cracks in a nodular cast iron investigated by X-ray tomography and 3D volume correlation

et al. 2010

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“…The application of synchrotron based energy dispersive X-ray diffraction (EDXRD) to a measurement of local strain fields in the vicinity of fatigue cracks was discussed in a previous article by the authors [1][2]. The technique exploits the high intensity/energy white beam (30-200 KeV) x-rays of the X17 wiggler beamline at the Brookhaven National Synchrotron Light Source (NSLS).…”

Section: Technical Approachmentioning

confidence: 99%

“…The strain variation from position to position in the sample is then determined from the shifts in Bragg peak energy via the relation eh=(Ad/ do)hkl=(AE/ E 0 )hk 1 the a sample is translated through the beam. Here Ad = d-d 0 is the change in the lattice plane spacing, do is the lattice spacing of the stress-free materials, AE = E 0 -E is the corresponding Bragg peak shift and E 0 is the center of gravity of peak of the stress-free material [1][2]. A point far from the crack tip was chosen to determine the E 0 value.…”

Section: Technical Approachmentioning

confidence: 99%

Synchrotron Based X-Ray Strain Mapping in Fatigued Materials Subjected to Overload

Tsakalakos¹,

Croft²,

Zhong³

et al. 2007

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The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing date sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing the burden, to Department of Defense. Washington Headquarters Services, Directorate for Information Operations and Reports t0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington. VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid 0MB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 1. REPORT DATE (D0-MM-YYYY)2. REPORT Fatigue crack growth involves localized fracture at the crack tip, and it intrinsically depends upon the local internal strain/stress fields and accumulated damage in the vicinity of the tip. The purpose of this report is to directly correlate variations in crack growth rate with variations in the relevant local strains around the crack tip. The so-called "overload effect", namely the prominent crack growth rate retardation after a single overload cycle in an otherwise constant amplitude is studied. Our high spatial resolution measurements around fatigue crack are greatly facilitated by indexing our measurements to the fatigue crack itself. This crack based positioning is accomplished by measuring the beam intensity transmitted through the sample, with a transmission detector, so that a radiographic transmission profile can be constructed. Such transmission profiles enabled precise location of the crack and the crack tip in the x-ray beam. SUBJECT Technical Section Technical ObjectivesThe technical objectives of this contract where to use high energy, synchrotron based x-ray diffraction measurements to determine the local strain/stress fields in the vicinity of fatigue crack tips. These strain/stress field measurements were initiated to provide guidance for fundamental modeling of fatigue crack growth. Here it should be noted that such modeling is fundamentally grounded in these local strain/stress fields and that heretofore methods to actually measure these strain fields were essentially nonexistent. (The synchrotron based x-ray diffraction techniques used in this work or developed previously by our group under previous ONR contracts.) The specific focus of this phase of our research was the "overload effect" in which a single cycle overload, in an otherwise constant amplitude fatigued specimen, retards the crack growth rate for a certain number of cycles (or crack length) after the overload (this is described at greater length below). Understanding the overload effect is an important step toward developing models of variable amplitude fatigue loading such as are needed i...

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“…In view of these considerations, blindhole-drilling [34], conventional X-ray [35] and neutron diffraction [36] appear to be not suitable, since they probe regions of millimetre dimensions, which are too large to resolve steep lateral RS gradients. Residual strain measurements with high lateral spatial resolution have been already done in the past using synchrotron XRD, mainly to determine crack-tip strain fields [37][38][39][40]. However, as high energy XRD utilizes small diffraction angles, the very high lateral spatial resolution can usually only be achieved in two orthogonal directions at the centre of bulk specimens.…”

Section: Introductionmentioning

confidence: 99%

High Spatial Resolution Evaluation of Residual Stresses in Shot Peened Specimens Containing Sharp and Blunt Notches by Micro-hole Drilling, Micro-slot Cutting and Micro-X-ray Diffraction Methods

et al. 2016

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The moderately high lateral RS gradients (on the order of tens of MPa/μm) near shot peened notches in conjunction with the shallow treatment depth (some hundreds of microns) limit the application of far-field and/or high resolution synchrotron diffraction residual stress measurement techniques. Recently proposed Focused Ion Beam -Scanning Elecron Microscope -Digital Image Correlation (FIB-SEM-DIC) based micro mechanical stress relaxation methods for the measurement of residual stress at the micron scale became suitable techniques for local evaluation of residual stresses and stress gradients in shot peened specimens. In this paper ultra-high resolution (~0.5-0.8 μm depth and 5-10 μm lateral resolution) mechanical relaxation stress measurements were used to evaluate the stress variation local to individual peening dimples in ceramic (60-120 μm diameter beads) shot peened Al-7075-T651 double notched samples having 0.15, 0.5 and 2.0 mm radii using Micro-Hole Drilling (μHD), Micro-Slot Cutting (μSC) and micro X-ray Diffraction (μXRD) methods. The micron-sized sampling volumes enabled the stress to be evaluated in individual impact craters (dimples) showing significant point-to-point variation (~+/−150 MPa) (with certain dimples even recording tensile stresses). After around 30 μm of layer removal the heavily deformed region had largely been removed and the stress profile became much more homogeneous. At this depth the μHD and μSC results were in good accord with those from μXRD measurements which sample over a much larger volume (~40 μm depth × 50 μm laterally) showing an in-plane compressive stress of around 150 MPa far from the notches with the residual stress rising to about 200 MPa at a blunt (2 mm) notch and 500 MPa for a sharp (0.15 mm) one. Further, these recorded variations of residual stresses were correlated with microstructural features, e.g. grains, networks of sub-surface cracks, intermetallics and highly deformed sub-surface regions, revealed by large volume Serial Sectioning Tomography using Plasma Xe + Focus Ion Beam -Scanning Electron Microscope (PFIB-SEM), EDS and EBSD maps. This allowed for the first time characterize large volume (100 × 66 × 30 μm 3 ) of shot peened regions with resolution of dozens of nanometers and correlate residual stress depth profiles with 3D microstructural features. Finally, in (Benedetti et al. 2016, Int. J. Fatigue) these RS measurements are used to reconstruct the RS field through finite element (FE) analyses.

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Strain profiling of fatigue crack overload effects using energy dispersive X-ray diffraction

Cited by 81 publications

References 9 publications

Influence of closure on the 3D propagation of fatigue cracks in a nodular cast iron investigated by X-ray tomography and 3D volume correlation

Influence of closure on the 3D propagation of fatigue cracks in a nodular cast iron investigated by X-ray tomography and 3D volume correlation

Synchrotron Based X-Ray Strain Mapping in Fatigued Materials Subjected to Overload

High Spatial Resolution Evaluation of Residual Stresses in Shot Peened Specimens Containing Sharp and Blunt Notches by Micro-hole Drilling, Micro-slot Cutting and Micro-X-ray Diffraction Methods

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