scholarly journals High-Density Distributed Crack Tip Sensing System Using Dense Ultra-Short FBG Sensors

Sensors ◽  
2019 ◽  
Vol 19 (7) ◽  
pp. 1702 ◽  
Author(s):  
Xin Gui ◽  
Zhengying Li ◽  
Xuelei Fu ◽  
Changjia Wang ◽  
Yiming Wang ◽  
...  
Keyword(s):  
Spatial Resolution ◽  
Structural Damage ◽  
Crack Tip ◽  
High Density ◽  
Multiple Cracks ◽  
Detection Distance ◽  
Crack Tips ◽  
Frequency Domain Reflectometry ◽  
Oblique Crack ◽  
The One

Crack generation starts at the crack tip, which bears the highest stress concentration. Under further stress, the crack propagates and leads to severe structural damage. To avoid such damage, the identification of the crack tips, and monitoring of the surrounding stress and strain fields, are very important. In this work, the location of, and strain distribution monitoring around, the crack tip are achieved using a dense ultra-short (DUS) fiber Bragg grating (FBG) array together with an improved optical frequency domain reflectometry (OFDR) interrogator. The adjacent grating interference correlation algorithm helps overcome the limitation on the demodulation precision, which is imposed by the inherently broad reflection spectra of individual ultra-short gratings. High spatial resolution measurement of the strain profile around the crack tip is performed at different levels of induced strain. Furthermore, the vertical-crossed layout is adopted to avoid the omission of cracks, which usually occurs in the case of the one direction layout. We achieve 1 mm spatial resolution and 7.5 m detection distance. Location of a single crack, multiple cracks, and an oblique crack was realized experimentally by locating the crack tips. The experimental results are consistent with the theoretical analysis, verifying the feasibility of the DUS-FBG system for high-density distributed crack tip sensing.

Strip Yield Analysis for Multiple Cracked Sheet With Riveted Stiffeners

1993 ◽  
Vol 115 (4) ◽  
pp. 398-403 ◽  
Author(s):  
T. Nishimura
Keyword(s):  
Plastic Zone ◽  
Stress Singularity ◽  
Fredholm Integral Equations ◽  
Multiple Cracks ◽  
Basic Solution ◽  
Yield Model ◽  
Strip Yield Model ◽  
Crack Tips ◽  
Fictitious Crack ◽  
Crack Tip Opening

An elasto-plastic analysis is conducted based upon a strip yield model for analyzing multiple cracks in a sheet reinforced with riveted stiffeners. Using the basic solution of a single crack and taking unknown fictitious surface tractions and fastener forces, Fredholm integral equations are formulated from the equilibrium condition along multiple cracks in the sheet. In addition compatibility equations of displacements are formulated among the sheet, fasteners and stiffeners. Based upon no stress singularity at the fictitious crack tips, these equations are iteratively solved as a single system of equations. Then the unknown fictitious surface tractions, fastener forces, and plastic zone sizes ahead of the crack tips are determined. The crack tip opening displacements for a multiple cracked sheet with riveted stiffeners are determined from the derived fictitious surface tractions and plastic zone sizes. Four example calculations and predictions are presented.

Over-the-row harvester damage evaluation in super-high-density olive orchard by on-board sensing techniques

2017 ◽  
Vol 8 (2) ◽  
pp. 487-491 ◽  
Author(s):  
J. Martinez-Guanter ◽  
M. Garrido-Izard ◽  
J. Agüera ◽  
C. Valero ◽  
M. Pérez-Ruiz
Keyword(s):  
Structural Damage ◽  
Image Data ◽  
High Density ◽  
Tree Structure ◽  
Light Detection And Ranging ◽  
Olive Grove ◽  
Damage Evaluation ◽  
Olive Fruit ◽  
Before And After ◽  
Extra Stress

New Super-High-Density (SHD) olive orchards designed for mechanical harvesting are increasing very rapidly in Spain. Most studies have focused in effectively removing the olive fruit, however the machine needs to put significant amount of energy on the canopy that could result in structural damage or extra stress on the trees. During harvest, a series of 3-axis accelerometers were installed on the tree structure in order to register vibration patterns. A LiDAR (Light Detection and Ranging) and a camera sensing device were also mounted on a tractor. Before and after harvest measurements showed significant differences in the LiDAR and image data. A fast estimate of the damage produced by an over-the-row harvester with contactless sensing could be useful information for adjusting the machine parameters in each olive grove automatically in the future.

Cycling-induced structural damage/degradation of electrode materials – microscopic viewpoint

2021 ◽  
Author(s):  
Fuqian Yang
Keyword(s):  
Intermetallic Compounds ◽  
Structural Damage ◽  
Electrode Materials ◽  
Crack Tip ◽  
Lithium Ion ◽  
Simple Calculation ◽  
Radius Of Curvature ◽  
Critical Separation ◽  
Analytical Formulas ◽  
Body Potential

Abstract Most analyses of the mechanical deformation of electrode materials of lithium-ion battery in the framework of continuum mechanics suggest the occurring of structural damage/degradation during the de-lithiation phase and cannot explain the lithiation-induced damage/degradation in electrode materials, as observed experimentally. In this work, we present first-principle analysis of the interaction between two adjacent silicon atoms from the Stillinger-Weber two-body potential and obtain the critical separation between the two silicon atoms for the rupture of Si-Si bonds. Simple calculation of the engineering-tensile strain for the formation of Li-Si intermetallic compounds from the lithiation of silicon reveals that cracking and cavitation in lithiated silicon can occur due to the formation of Li-Si intermetallic compounds. Assuming the proportionality between the net mass flux across the tip surface of a slit crack and the migration rate of the crack tip, we develop analytical formulas for the growth and healing of the slit crack controlled by lithiation and de-lithiation, respectively. It is the combinational effects of the state of charge, the radius of curvature of the crack tip and local electromotive force that determine the cycling-induced growth and healing of surface cracks in lithiated silicon.

scholarly journals Neurophenomenology of near-death experience memory in hypnotic recall: a within-subject EEG study

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Charlotte Martial ◽  
Armand Mensen ◽  
Vanessa Charland-Verville ◽  
Audrey Vanhaudenhuyse ◽  
Daniel Rentmeister ◽  
...  
Keyword(s):  
Subjective Experience ◽  
Brain Activity ◽  
Alpha Activity ◽  
High Density ◽  
Proof Of Concept ◽  
Time Period ◽  
Death Experience ◽  
Eeg Changes ◽  
The One ◽  
Near Death Experiences

Abstract The neurobiological basis of near-death experiences (NDEs) is unknown, but a few studies attempted to investigate it by reproducing in laboratory settings phenomenological experiences that seem to closely resemble NDEs. So far, no study has induced NDE-like features via hypnotic modulation while simultaneously measuring changes in brain activity using high-density EEG. Five volunteers who previously had experienced a pleasant NDE were invited to re-experience the NDE memory and another pleasant autobiographical memory (dating to the same time period), in normal consciousness and with hypnosis. We compared the hypnosis-induced subjective experience with the one of the genuine experience memory. Continuous high-density EEG was recorded throughout. At a phenomenological level, we succeeded in recreating NDE-like features without any adverse effects. Absorption and dissociation levels were reported as higher during all hypnosis conditions as compared to normal consciousness conditions, suggesting that our hypnosis-based protocol increased the felt subjective experience in the recall of both memories. The recall of a NDE phenomenology was related to an increase of alpha activity in frontal and posterior regions. This study provides a proof-of-concept methodology for studying the phenomenon, enabling to prospectively explore the NDE-like features and associated EEG changes in controlled settings.

Evaluation of the Crack Interaction and Failure Behavior of Components With Crack Fields Using a Damage Mechanical Approach

2019 ◽  
Author(s):  
Christian Swacek ◽  
Patrick Gauder ◽  
Michael Seidenfuss
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Base Material ◽  
Pressure Vessels ◽  
Failure Behavior ◽  
Multiple Cracks ◽  
Critical Crack ◽  
Ongoing Research ◽  
Integrity Assessment ◽  
Crack Tips

Abstract In 2012 non-destructive testing measurements (NDT) of the reactor pressure vessels (RPV) in the Belgian Nuclear Power Plants Doel 3 and Tihange 2 revealed a high quantity of indications in the upper and lower core shells. The most likely explanation is that the measured indications are hydrogen flakes positioned in segregated zones in the base material of the pressure vessels. These hydrogen flakes have a laminar and quasi-laminar orientation with an inclination up to 15° to the pressure retaining surface. Under internal pressure, the crack tips undergo predominantly mixed mode loading conditions, where the induced stress and strain fields of the single crack tips influence each other. The safety assessment of crack afflicted pressurized components is performed by fracture mechanical approaches. For the evaluation of multiple cracks in crack fields, state of the art codes and standards apply interaction criteria and grouping methods, to determine a representative crack, which has to be evaluated. In this paper, the interaction of cracks in crack fields is numerically and experimentally evaluated. Damage mechanical models based on the Rousselier- and the Beremin model are used to investigate numerically the interaction of cracks in crack fields. Experimental data from ferritic flat tensile specimens afflicted with cracks are used to verify the numerical results. The damage mechanical calculations reveal critical crack arrangements due to coalescence behavior and cleavage fracture probability. These results and ongoing research intends the derivation of interaction criteria for cracks in crack fields. The interaction criteria will be used for the definition of a representative flaw for a conservative integrity assessment of crack afflicted components.

Bilby–Cottrell–Swinden model for a growing crack with residual stresses

1970 ◽  
Vol 317 (1529) ◽  
pp. 199-209 ◽  
Keyword(s):  
Plastic Zone ◽  
Residual Stresses ◽  
Crack Tip ◽  
Plastic Zone Size ◽  
Relative Displacement ◽  
Planar Arrays ◽  
Plastic Dissipation ◽  
Growing Crack ◽  
Slip Planes ◽  
Crack Tips

For a growing crack the residual stresses caused by plastic flow at previous positions of the crack-tip affect the current plastic zone. This effect is calculated by an extension of the BCS model which replaces the plastic zone by two planar arrays of dislocations emanating from the crack-tips. For a growing crack a succession of such arrays is formed. We consider a crack growing in anti-plane strain with the slip-planes making an almost zero angle with the plane of the crack. The plastic zone size in front of the crack turns out to be the same as for a stationary crack, while the relative displacement of the crack faces is less concentrated in the vicinity of the crack-tip. The rate of plastic dissipation of energy is calculated, and turns out to be identical with the elastic energy release rate.

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