Three Dimensional Replication of Fatigue Cracks by Vacuum Infiltration for Study of Crack Tip Morphology by Scanning Electron Microscopy

1970 ◽  
Vol 28 ◽  
pp. 402-403
Author(s):  
G. G. Shaw
Keyword(s):  
Fatigue Cracks ◽  
Three Dimensional ◽  
Crack Tip ◽  
Vacuum Infiltration ◽  
Three Dimensions ◽  
New Information ◽  
Crack Tips ◽  
Sheet Sample ◽  
Scanning Electron

I. Introduction: Fatigue investigators have been looking at crack tips by examining the surface and by sectioning the crack. Much useful information has been obtained by these methods, but a look at the complete crack in three dimensions with the tip intact yields much new information. This is especially true when one is able to examine the crack tip in full tension or compression or stages in between, by using the following techniques.II. Vacuum Infiltration in Situ: The crack is generated on a fatigue machine using a sheet sample with a notched central hole. If one desires to replicate in full tension, the machine is stopped in tension and the apparatus shown in Figure 1 is clamped to the sides of the sample.

scholarly journals Damage Adaptive Titanium Alloy by In-Situ Elastic Gradual Mechanism

Materials ◽  
2020 ◽  
Vol 13 (2) ◽  
pp. 406
Author(s):  
Siqian Zhang ◽  
Jing Liu ◽  
Haoyu Zhang ◽  
Jie Sun ◽  
Lijia Chen
Keyword(s):  
Titanium Alloy ◽  
Damage Tolerance ◽  
Three Dimensional ◽  
Crack Tip ◽  
In Situ Stress ◽  
Crack Deflection ◽  
Adaptive Mechanism ◽  
Ultrafine Grained ◽  
Elastic Gradient

Natural materials are generally damage adaptive through their multilevel architectures, with the characteristics of compositional and mechanical gradients. This study demonstrated that the desired elastic gradient can be in-situ stress-induced in a titanium alloy, and that the alloy showed extreme fatigue-damage tolerance through the crack deflection and branch due to the formation of a three-dimensional elastically graded zone surrounding the crack tip. This looks like a perceptive and adaptive mechanism to retard the crack: the higher stress concentrated at the tip and the larger elastic gradient to be induced. The retardation is so strong that a gradient nano-grained layer with a thickness of less than 2 μm formed at the crack tip due to the highly localized and accumulated plasticity. Furthermore, the ultrafine-grained alloy with the nano-sized precipitation also exhibited good damage tolerance.

scholarly journals Three-dimensional in-situ imaging of cracks in concrete using diffuse ultrasound

2017 ◽  
Vol 17 (2) ◽  
pp. 279-284 ◽  
Author(s):  
Yuxiang Zhang ◽  
Eric Larose ◽  
Ludovic Moreau ◽  
Grégoire d’Ozouville
Keyword(s):  
Wind Tunnel ◽  
Multiple Scattering ◽  
Structural Changes ◽  
Imaging Technique ◽  
Three Dimensional ◽  
Three Dimensions ◽  
Thick Wall ◽  
Pressure Changes ◽  
Diffuse Ultrasound

Locadiff, an innovative imaging technique based on diffuse waves, has recently been developed in order to image mechanical changes in heterogeneous, geological, or man-made materials. This manuscript reports the on-site application of Locadiff to locate several pre-existing cracks on an aeronautical wind tunnel made of pre-stressed concrete. Using 32 transducers working at ultrasonic frequencies (80–220 kHz) where multiple scattering occurs, we monitor during 15 min an area of 2.5 m×2.5 m of a 35-cm-thick wall. With the wind tunnel in its routine operation, structural changes around the cracks are detected, thanks to their closing or opening due to slight pressure changes. By mapping the density of such microstructure changes in the bulk of the material, locating three pre-existing cracks is properly performed in three dimensions.

scholarly journals In Situ Examination of moving Crack Tips in Ordered Intermetallics

1998 ◽  
Vol 539 ◽  
Author(s):  
J.K. Heuer ◽  
N.Q. Lam ◽  
P.R. Okamoto ◽  
J.F. Stubbins
Keyword(s):  
Ion Irradiation ◽  
High Stress ◽  
Crack Tip ◽  
Dark Field ◽  
Stress Concentrations ◽  
Moving Crack ◽  
Dark Field Imaging ◽  
Crack Tips ◽  
Similarity And Difference

AbstractRecent studies have shown that high stress concentrations at moving crack tips in the intermetallic compound NiTi can induce a crystalline-to-amorphous (C-A) transformation of the crack tip region. This stress-induced C-A transformation has a temperature dependence and crystallization behavior similar to those of ion irradiation-induced C-A transformation of NiTi. The present study examines if these similarities between stress- and irradiation-induced amorphization hold true for two other intermetallic compounds, CuTi and Ni3Ti. In situ straining was performed in an intermediate-voltage transmission electron microscope. The presence or absence of an amorphous phase was determined by dark field imaging and selected area diffraction of crack tip regions. Crack tips in both CuTi and Ni3Ti were found to remain crystalline upon fracture. The observed absence of stress-induced amorphization in Ni3Ti is consistent with its known absence during irradiation, but the absence in CuTi differs from its known irradiation-induced amorphization behavior. Reasons for the similarity and difference are discussed.

scholarly journals Three Dimensional Growth in GaAs MBE Studied by in-situ Scanning Electron Microscopy.

Hyomen Kagaku ◽  
1998 ◽  
Vol 19 (11) ◽  
pp. 747-751
Author(s):  
Katsuto TANAHASHI ◽  
Yuichi KAWAMURA ◽  
Naohisa INOUE ◽  
Yoshikazu HOMMA
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Three Dimensional ◽  
Dimensional Growth ◽  
Scanning Electron

Technique for Visualizing Subgrain Structure at Fatigue Crack Tips by Ion Etching and Scanning Electron Microscopy

1973 ◽  
Vol 31 ◽  
pp. 86-87 ◽  
Author(s):  
G. G. Shaw ◽  
D. K. Benson
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Fatigue Crack ◽  
Single Crystal ◽  
Fatigue Cracks ◽  
Subgrain Structure ◽  
Ion Etching ◽  
Etch Patterns ◽  
Crack Tips ◽  
Scanning Electron

The subgrain structure in ram size areas adjacent to fatigue cracks has been observed by ion etching followed by scanning electron microscopy. The etch patterns have been definitely identified as subgrain structure resulting from the fatigue strains by direct comparison with channelling electron microscopy. The technique is described as it was applied to a single crystal of aluminum which had been fatigued in Stage I by reversed bending.A 5 mm long section of crystal containing the crack was cut from the fatigue sample by spark machining. This section was sliced into pieces 2 to 3 mm thick, and a slice selected with the crack tip close to its center. The selected slice was placed in a shallow aluminum cup about 2 cm in diameter.

scholarly journals Utilizing broadband X-rays in a Bragg coherent X-ray diffraction imaging experiment

2016 ◽  
Vol 23 (5) ◽  
pp. 1241-1244 ◽  
Author(s):  
Wonsuk Cha ◽  
Wenjun Liu ◽  
Ross Harder ◽  
Ruqing Xu ◽  
Paul H. Fuoss ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Three Dimensions ◽  
X Rays ◽  
X Ray Diffraction ◽  
X Ray ◽  
Individual Crystal ◽  
Sample Motion ◽  
Diffraction Imaging ◽  
Individual Grains

A method is presented to simplify Bragg coherent X-ray diffraction imaging studies of complex heterogeneous crystalline materials with a two-stage screening/imaging process that utilizes polychromatic and monochromatic coherent X-rays and is compatible within situsample environments. Coherent white-beam diffraction is used to identify an individual crystal particle or grain that displays desired properties within a larger population. A three-dimensional reciprocal-space map suitable for diffraction imaging is then measured for the Bragg peak of interest using a monochromatic beam energy scan that requires no sample motion, thus simplifyingin situchamber design. This approach was demonstrated with Au nanoparticles and will enable, for example, individual grains in a polycrystalline material of specific orientation to be selected, then imaged in three dimensions while under load.

Measurement of three-dimensional lung tree structures by using computed tomography

1995 ◽  
Vol 79 (5) ◽  
pp. 1687-1697 ◽  
Author(s):  
S. A. Wood ◽  
E. A. Zerhouni ◽  
J. D. Hoford ◽  
E. A. Hoffman ◽  
W. Mitzner
Keyword(s):  
Computed Tomography ◽  
Three Dimensional ◽  
Three Dimensions ◽  
Central Axis ◽  
Segment Length ◽  
Cross Sectional ◽  
Tree Structures ◽  
Branch Segment ◽  
Tomography Data

A method was devised to computationally segment and measure three-dimensional pulmonary trees in situ. Bronchi and pulmonary vessels were computationally extracted from volumetric computed tomography data based on radiopacity differences between airway wall and airway lumen and between blood and parenchyma, respectively. The tree was reduced to a central axis to facilitate measurement of branch segment length and angle. Cross-sectional area was measured on a reconstructed computed tomography slice perpendicular to this central axis. The method was validated by scanning two Plexiglas phantoms and an intact lung. Reconstructed diameters in the phantoms were accurate for branches > 2 mm. In the lung airway branches between 1 and 2 mm in diameter were often unresolved when their angle of orientation with respect to the axis of the scanner was > 45 degrees. However, if a branch was resolved, its reconstructed diameter was little affected by orientation. This method represents a significant improvement in the analysis of complex pulmonary structures in three dimensions.

In SituScanning Electron Microscope (SEM) Observations of Damage and Crack Growth of Shale

2018 ◽  
Vol 24 (2) ◽  
pp. 107-115 ◽  
Author(s):  
Zhendong Cui ◽  
Weige Han
Keyword(s):  
Electron Microscope ◽  
Crack Growth ◽  
Elastic Recovery ◽  
Three Dimensional ◽  
Crack Tip ◽  
Squeezing Effect ◽  
Initiation Zone ◽  
Bedding Planes ◽  
Crack Tips ◽  
Formation And Evolution

AbstractTo better understand the formation and evolution of hierarchical crack networks in shales, observations of microscopic damage, and crack growth were conducted using anin situtensile apparatus inside a scanning electron microscope. An arched specimen with an artificial notch incised into the curved edge was shown to afford effective observation of the damage and crack growth process that occurs during the brittle fracturing of shale. Because this arched specimen design can induce a squeezing effect, reducing the tensile stress concentration at the crack tip, and preventing the brittle shale from unstable fracturing to some extent. Both induced and natural pores and cracks were observed at different scales around the main crack path or on fractured surfaces. Observations indicate that the crack initiation zone develops around the crack tip where tensile stresses are concentrated and micro/nanoscale cracks nucleate. Crack advancement generally occurs by the continuous generation and coalescence of damage zones having intermittent en echelon microscopic cracks located ahead of the crack tips. Mineral anisotropy and pressure build-up around crack tips causes crack kinking, deflection, and branching. Crack growth is often accompanied by the cessation or closure of former branch cracks due to elastic recovery and induced compressive stress. The branching and interactions of cracks form a three-dimensional hierarchical network that includes induced branch cracks having similar paths, as well as natural structures such as nanopores, bedding planes, and microscopic cracks.

The Application of Scanning Electron Microscopy in the Investigation of Human Gastrointestinal Pathology

1973 ◽  
Vol 31 ◽  
pp. 430-431
Author(s):  
S. Siew
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Three Dimensional ◽  
Morphological Characteristics ◽  
Significant Advance ◽  
Gastrointestinal Pathology ◽  
Transmission Electron ◽  
Three Dimensional Configuration ◽  
Scanning Electron

A significant advance in our knowledge of gastrointestinal pathology has been achieved through endoscopy of the accessible portions of the alimentary tract. This procedure has allowed the evaluation of morphological characteristics of the mucosa by means of direct viewing in situ and through microscopy (light and transmission electron) of biopsies taken from selected areas. The importance of examination of the three dimensional configuration of the mucosal surface has been recognized, particularly in the assessment of the intestinal villi in cases of malabsorption, where it is recommended that the biopsies should be examined first by means of the dissecting microscope. Therefore, there is an obvious indication here for scanning electron microscopy, with its far greater potential.

Characterization of Crack-Tip Dislocations and their Effects on Materials Fracture

2010 ◽  
Vol 654-656 ◽  
pp. 2307-2311
Author(s):  
Kenji Higashida ◽  
Masaki Tanaka ◽  
Sunao Sadamatsu
Keyword(s):  
Single Crystals ◽  
Electron Tomography ◽  
Three Dimensional ◽  
Crack Tip ◽  
Local Stress ◽  
Dimensional Structure ◽  
Three Dimensional Structure ◽  
Scanning Transmission ◽  
Crack Tips ◽  
P Type

Three-dimensional structure of crack tip dislocations were investigated by combining scanning transmission electron microscopy (STEM) and electron tomography (ET) in silicon single crystals. P-type (001) silicon single crystals were employed. <110> cracks were introduced from an indent on the (001) surface. The specimen was heated at 873K in order to introduce dislocations at the crack tips. The specimen was thinned to include the crack tip in the foil by an iron milling machine. STEM-ET observation revealed the three-dimensional structure of crack tip dislocations. Their Burgers vectors were determined by using an invisibility criterion. The local stress intensity factor was calculated using the dislocation characters obtained in the observation in this study, indicating that the dislocations observed were mode II shielding type dislocations.

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