Phase contrast stereometry: fatigue crack mapping in 3D

2004 ◽  
Author(s):  
Konstantin I. Ignatiev ◽  
Wah-Keat Lee ◽  
Kamel Fezzaa ◽  
Francesco De Carlo ◽  
Stuart R. Stock
Keyword(s):  
Fatigue Crack ◽  
Phase Contrast ◽  
Crack Mapping

Investigation of Fatigue Crack Propagation in Nickel Superalloy Using Diffraction Contrast Tomography and Phase Contrast Tomography

2014 ◽  
Vol 891-892 ◽  
pp. 923-928 ◽  
Author(s):  
Olivier M.D.M. Messé ◽  
Joel Lachambre ◽  
Andrew King ◽  
Jean Yves Buffière ◽  
Cathie M.F. Rae
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Phase Contrast ◽  
High Energy ◽  
Short Crack ◽  
X Rays ◽  
Post Mortem ◽  
Diffraction Contrast ◽  
Phase Contrast Tomography

Evaluation of superalloy component life in turbine engines requires a detailed understanding of how fatigue crack initiation and short crack propagation contribute to fatigue life. However most investigations have been carried out post-mortem and in two dimensions. New techniques are able to fully resolve cracks propagating in four dimensions (space and time), enabling characterisation of their local environments and allowing a much deeper understanding of fatigue mechanics. Nickel-based superalloys experiencing high cycle fatigue have shown a high sensitivity to microstructure during initiation and short crack propagation. Using high energy X-rays and the combination of Diffraction Contrast Tomography (DCT) and Phase Contrast Tomography (PCT), we followed a fatigue crack initiated from a Focused Ion Beam (FIB) milled notch at room temperature. Analyses have been carried out to fully characterise the crack and its environment. We tracked the evolution of the crack and interactions with the microstructure. Subsequently, post-mortem investigations have been carried out to corroborate results obtained from the tomographs and to provide more local information of fatigue crack propagation.

Comparison of Crack Geometry Determined with Phase Contrast Radiography and with Microtomography

2001 ◽  
Vol 678 ◽  
Author(s):  
S.R. Stock ◽  
K. Ignatiev ◽  
W.K. Lee ◽  
K. Fezzaa ◽  
G.R. Davis ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Phase Contrast ◽  
Thick Plate ◽  
Crack Opening ◽  
Three Dimensional ◽  
Compact Tension ◽  
Crack Geometry ◽  
Projection Images ◽  
Absorption Contrast ◽  
Good Agreement

AbstractX-ray microtomography of the three-dimensional spatial distribution of crack opening as a function of applied load has helped clarify important processes of roughness-induced fatigue crack closure. Fracture mechanics dictates sample geometries which limit the crack opening sensitivity that can be obtained with microtomography, and there is a real need to be able to quantify smaller openings. Synchrotron phase contrast radiographs of an AA 2090 T8E41 (central 2 mm of a 12.7 mm thick plate) compact tension sample show the fatigue crack geometry clearly while absorption contrast radiographs of the same sample have difficulty even detecting the crack. The phase contrast expected in the projection images is determined from the microtomography-derived, three-dimensional crack geometry and compared to that observed experimentally. Good agreement is obtained between the phase contrast radiographs and the expected pattern of contrast.

D062 Fatigue Crack Study Using X-ray Phase Contrast and Multiple Angle Stereometry Methods

2003 ◽  
Vol 18 (2) ◽  
pp. 175-175
Author(s):  
K. Ignatiev ◽  
S. R. Stock
Keyword(s):  
Fatigue Crack ◽  
Phase Contrast ◽  
X Ray

scholarly journals 3-D growth of a short fatigue crack within a polycrystalline microstructure studied using combined diffraction and phase-contrast X-ray tomography

2011 ◽  
Vol 59 (2) ◽  
pp. 590-601 ◽  
Author(s):  
Michael Herbig ◽  
Andrew King ◽  
Péter Reischig ◽  
Henry Proudhon ◽  
Erik M. Lauridsen ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Phase Contrast ◽  
X Ray ◽  
Short Fatigue Crack ◽  
Polycrystalline Microstructure

scholarly journals Cyclic Deformation Induced Residual Stress Evolution and 3D Short Fatigue Crack Growth Investigated by Advanced Synchrotron Tomography Techniques

Materials ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1562
Author(s):  
Benjamin Dönges ◽  
Melanie Syha ◽  
Anne K. Hüsecken ◽  
Ullrich Pietsch ◽  
Wolfgang Ludwig ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Residual Stresses ◽  
Crack Propagation ◽  
Crack Growth ◽  
Cyclic Deformation ◽  
Phase Contrast ◽  
Crack Nucleation ◽  
Short Fatigue Crack ◽  
Phase Contrast Tomography

Diffraction and phase contrast tomography techniques were successfully applied to an austenitic–ferritic duplex stainless steel representing exemplarily a metallic material containing two phases with different crystal structures. The reconstructed volumes of both phases were discretized by finite elements. A crystal plasticity finite-element analysis was executed in order to simulate the development of the experimentally determined first and second order residual stresses, which built up due to the manufacturing process of the material. Cyclic deformation simulations showed the single-grain-resolved evolution of initial residual stresses in both phases and were found to be in good agreement with the experimental results. Solely in ferritic grains, residual stresses built up due to cyclic deformation, which promoted crack nucleation in this phase. Furthermore, phase contrast tomography was applied in order to analyze the mechanisms of fatigue crack nucleation and short fatigue crack propagation three-dimensionally and nondestructively. The results clearly showed the significance of microstructural barriers for short fatigue crack growth at the surface, as well as into the material. The investigation presented aims for a better understanding of the three-dimensional mechanisms governing short fatigue crack propagation and, in particular, the effect of residual stresses on these mechanisms. The final goal was to generate tailored microstructures for improved fatigue resistance and enhanced fatigue life.

Observation of biological macromolecules using various electron microscopic methods

1978 ◽  
Vol 36 (2) ◽  
pp. 170-171
Author(s):  
Mitsuo Ohtsuki ◽  
Michael Sogard
Keyword(s):  
Electron Microscope ◽  
Phase Contrast ◽  
Image Interpretation ◽  
Density Lipoprotein ◽  
Biological Macromolecules ◽  
Contrast Effects ◽  
Biological Structure ◽  
Electron Microscopic ◽  
Structural Investigations ◽  
Staining Techniques

Structural investigations of biological macromolecules commonly employ CTEM with negative staining techniques. Difficulties in valid image interpretation arise, however, due to problems such as variability in thickness and degree of penetration of the staining agent, noise from the supporting film, and artifacts from defocus phase contrast effects. In order to determine the effects of these variables on biological structure, as seen by the electron microscope, negative stained macromolecules of high density lipoprotein-3 (HDL3) from human serum were analyzed with both CTEM and STEM, and results were then compared with CTEM micrographs of freeze-etched HDL3. In addition, we altered the structure of this molecule by digesting away its phospholipid component with phospholipase A2 and look for consistent changes in structure.

Analysis of STEM micrographs of thick objects

1978 ◽  
Vol 36 (2) ◽  
pp. 106-107
Author(s):  
S. Golladay
Keyword(s):  
Inelastic Scattering ◽  
Multiple Scattering ◽  
Mass Distribution ◽  
Cross Sections ◽  
Phase Contrast ◽  
Image Point ◽  
Contrast Effects ◽  
Total Cross Sections ◽  
Elastic And Inelastic Scattering

The theory of multiple scattering has been worked out by Groves and comparisons have been made between predicted and observed signals for thick specimens observed in a STEM under conditions where phase contrast effects are unimportant. Independent measurements of the collection efficiencies of the two STEM detectors, calculations of the ratio σe/σi = R, where σe, σi are the total cross sections for elastic and inelastic scattering respectively, and a model of the unknown mass distribution are needed for these comparisons. In this paper an extension of this work will be described which allows the determination of the required efficiencies, R, and the unknown mass distribution from the data without additional measurements or models. Essential to the analysis is the fact that in a STEM two or more signal measurements can be made simultaneously at each image point.

The Imaging of Crystal Structures and Crystal Defects

1978 ◽  
Vol 36 (3) ◽  
pp. 207-217
Author(s):  
J.M. Cowley
Keyword(s):  
Electron Microscope ◽  
Crystal Structures ◽  
Phase Contrast ◽  
Crystal Defects ◽  
Atom Density ◽  
Lack Of Information ◽  
Spatial Frequencies

The problem of "understandinq" electron microscope imaqes becomes more acute as the resolution is improved. The naive interpretation of an imaqe as representinq the projection of an atom density becomes less and less appropriate. We are increasinqly forced to face the complexities of coherent imaqinq of what are essentially phase objects. Most electron microscopists are now aware that, for very thin weakly scatterinq objects such as thin unstained bioloqical specimens, hiqh resolution imaqes are best obtained near the optimum defocus, as prescribed by Scherzer, where the phase contrast imaqe qives a qood representation of the projected potential, apart from a lack of information on the lower spatial frequencies. But phase contrast imaqinq is never simple except in idealized limitinq cases.

Observation of Phase Contrast Images in STEM and CTEM Modes by Using 100 kV Field Emission Electron Gun

1974 ◽  
Vol 32 ◽  
pp. 390-391
Author(s):  
Y. Harada ◽  
T. Goto ◽  
H. Koike ◽  
T. Someya
Keyword(s):  
Field Emission ◽  
Phase Contrast ◽  
Image Formation ◽  
Fresnel Diffraction ◽  
Experimental Results ◽  
Electron Gun ◽  
Scanning Microscopy ◽  
Emission Electron ◽  
Lattice Images

Since phase contrasts of STEM images, that is, Fresnel diffraction fringes or lattice images, manifest themselves in field emission scanning microscopy, the mechanism for image formation in the STEM mode has been investigated and compared with that in CTEM mode, resulting in the theory of reciprocity. It reveals that contrast in STEM images exhibits the same properties as contrast in CTEM images. However, it appears that the validity of the reciprocity theory, especially on the details of phase contrast, has not yet been fully proven by the experiments. In this work, we shall investigate the phase contrast images obtained in both the STEM and CTEM modes of a field emission microscope (100kV), and evaluate the validity of the reciprocity theory by comparing the experimental results.

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