scholarly journals Digital Image-Based Stress–Permeability Relationships of Rough Fractures Using Numerical Contact Mechanics and Stokes Equation

2022 ◽  
Author(s):  
Amanzhol Kubeyev ◽  
Nathaniel Forbes Inskip ◽  
Tomos Phillips ◽  
Yihuai Zhang ◽  
Christine Maier ◽  
...  
Keyword(s):  
Fracture Surface ◽  
Contact Mechanics ◽  
Stokes Equation ◽  
Applied Stress ◽  
Cross Sections ◽  
Digital Image ◽  
Surface Characteristics ◽  
Optical Microscope ◽  
First Principle ◽  
Permeability Evolution

AbstractFlow in fractures is sensitive to their geometrical surface characteristics. The surface can undergo deformation if there is a change in stress. Natural fractures have complex geometries and rough surfaces which complicates the modelling of deformation and fluid flow. In this paper, we present a computational model that takes a digital image of a rough fracture surface and provides a stress–permeability relationship. The model is based on a first-principle contact mechanics approach at the continuum scale. Using this first principle approach, we investigate numerically the effect of fracture surface roughness and shifting of surfaces on the permeability evolution under applied stress and compare the results with laboratory experiments. A mudrock core fracture surface was digitalized using an optical microscope, and 2D cross sections through fracture surface profiles were taken for the modelling. Mechanical deformation is simulated with the contact mechanics based Virtual Element Method solver that we developed within the MATLAB Reservoir Simulation Toolbox platform. The permeability perpendicular to the fracture cross section is determined by solving the Stokes equation using the Finite Volume Method. A source of uncertainty in reproducing laboratory results is that the exact anchoring of the two opposite surfaces is difficult to determine while the stress–permeability relationship is sensitive to the exact positioning. We, therefore, investigate the sensitivity to a mismatch in two scenarios: First, we assess the stress–permeability of a fracture created using two opposing matched surfaces from the rock sample, consequently applying relative shear. Second, we assess the stress–permeability of fractures created by randomly selecting opposing surfaces from that sample. We find that a larger shift leads to a smaller drop in permeability due to applied stress, which is in line with a previous laboratory study. We also find that permeability tends to be higher in fractures with higher roughness within the investigated stress range. Finally, we provide empirical stress–permeability relationships for various relative shears and roughnesses for use in hydro-mechanical studies of fractured geological formations.

Using 2D Digital Image Analysis to Locate Position of Micro Fibers in Cross-Sections of Fiber-Reinforced Concrete

2016 ◽  
Vol 677 ◽  
pp. 169-174 ◽  
Author(s):  
Jan Trejbal ◽  
Lubomír Kopecký ◽  
Jozef Fládr ◽  
Pavel Tesárek ◽  
Václav Nežerka ◽  
...  
Keyword(s):  
Reinforced Concrete ◽  
Cross Sections ◽  
Digital Image ◽  
Digital Image Analysis ◽  
Information Source ◽  
Optical Microscope ◽  
Fiber Reinforced Concrete ◽  
Fiber Reinforced ◽  
Cement Pastes

This work deals with determination of location of micro fibers positions in fiber-reinforced concrete. The digital images of sectioned cement-paste samples with dimension equal to 40 × 40 mm were used as an information source about the monofilaments positions. Properly acquired digital image of high resolution allows to determinate the number of fibers in samples cross sections and relate theirs coordinates to any point. Optical microscope Carl Zeiss Axio Zoom.V16 with camera and software allowing individual shots composition of examined samples surface was used to obtain these parameters. Cement pastes reinforced with PET (polyethylene terephthalate) micro fibers having diameter equal to 0.4 mm were studied. The total number and the fibers distribution along the height and width of the sample cross section were examined.

scholarly journals Fatigue Crack Initiation and Propagation at High Temperature of New-Generation Bearing Steel

Metals ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 25
Author(s):  
Zhiwei Wu ◽  
Maosheng Yang ◽  
Kunyu Zhao
Keyword(s):  
Fracture Surface ◽  
Failure Mode ◽  
Electron Backscatter Diffraction ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Optical Microscope ◽  
Bearing Steel ◽  
Fatigue Properties ◽  
New Generation ◽  
Scanning Electron

The new generation of bearing steel has good comprehensive properties, which can satisfy most of the requirements of bearing steel in a complex environment. In the presented work, fatigue properties of 15Cr14Co12Mo5Ni2 bearing steel have been investigated by means of rotating bending fatigue tests on smooth bar specimens after carburization and heat treatment. Optical microscope, scanning electron microscopy, electron backscatter diffraction, and Image-Pro Plus software were used to analyze the fracture, microstructure, and carbides. The results suggest that the fatigue strength at room temperature and 500 °C is 1027 MPa and 585 MPa, respectively. Scanning electron micrographic observations on the fracture surface of the fatigue specimens at 500 °C show that fatigue cracks usually initiate from voids in the carburized case and oxide layer on the surface of steel. The failure mode in the carburized case is a quasi-cleavage fracture, and with the increase of crack propagation depth, the failure mode gradually changes to fatigue and creep-fatigue interaction. With the increase of the distance from the surface, the size of the martensite block decreases and the fracture surface shows great fluctuation.

Image detection and parameterization for different components in cross-sections of radial tires

2021 ◽  
pp. 095440702110236
Author(s):  
Chen Liu ◽  
Yude Dong ◽  
Yanli Wei ◽  
Jiangtao Wang ◽  
Hongling Li
Keyword(s):  
Image Processing ◽  
Digital Image Processing ◽  
Cross Sections ◽  
Digital Image ◽  
Detection Method ◽  
Detection System ◽  
Practical Significance ◽  
Vehicle Safety ◽  
Wire Steel ◽  
Good Detection

The internal structure analysis of radial tires is of great significance to improve vehicle safety and during tire research. In order to perform the digital analysis and detection of the internal composition in radial tire cross-sections, a detection method based on digital image processing was proposed. The research was carried out as follows: (a) the distribution detection and parametric analysis of the bead wire, steel belt, and carcass in the tire section were performed by means of digital image processing, connected domain extraction, and Hough transform; (b) using the angle of location distribution and area relationship, the detection data were optimized through coordinate and quantity relationship constraints; (c) a detection system for tire cross-section components was designed using the MATLAB platform. Our experimental results showed that this method displayed a good detection performance, and important practical significance for the research and manufacture of tires.

scholarly journals Nanotubular Oxide Layer Formed on Helix Surfaces of Dental Screw Implants

Coatings ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 115 ◽  
Author(s):  
Magdalena Jażdżewska ◽  
Michał Bartmański
Keyword(s):  
Oxide Layer ◽  
Cross Sections ◽  
Surface Coverage ◽  
Artificial Saliva ◽  
Corrosion Current ◽  
Optical Microscope ◽  
Significant Difference ◽  
Helix Surfaces ◽  
Future Work ◽  
Oxidation Parameters

Surface modification is used to extend the life of implants. To increase the corrosion resistance and improve the biocompatibility of metal implant materials, oxidation of the Ti-13Nb-13Zr titanium alloy was used. The samples used for the research had the shape of a helix with a metric thread, with their geometry imitating a dental implant. The oxide layer was produced by a standard electrochemical method in an environment of 1M H3PO4 + 0.3% HF for 20 min, at a constant voltage of 30 V. The oxidized samples were analyzed with a scanning electron microscope. Nanotubular oxide layers with internal diameters of 30–80 nm were found. An analysis of the surface topography was performed using an optical microscope, and the Sa parameter was determined for the top of the helix and for the bottom, where a significant difference in value was observed. The presence of the modification layer, visible at the bottom of the helix, was confirmed by analyzing the sample cross-sections using computed tomography. Corrosion tests performed in the artificial saliva solution demonstrated higher corrosion current and less noble corrosion potential due to incomplete surface coverage and pitting. Necessary improved oxidation parameters will be applied in future work.

Effects of Etching on Zircon Grains and its Implications for the Fission Track Method

2012 ◽  
Vol 66 (5) ◽  
pp. 545-551 ◽  
Author(s):  
Carlos Alberto Tello Sáenz ◽  
Eduardo Augusto Campos Curvo ◽  
Airton Natanael Coelho Dias ◽  
Cleber José Soares ◽  
Carlos José Leopoldo Constantino ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Crystal Lattice ◽  
Fission Track ◽  
Surface Characteristics ◽  
Optical Microscope ◽  
Etching Time ◽  
X Ray ◽  
Track Method ◽  
Zircon Fission Track ◽  
Natural Zircon

Studies of zircon grains using optical microscopy, micro-Raman spectroscopy, and scanning electron microscopy (SEM) have been carried out to characterize the surface of natural zircon as a function of etching time. According to the surface characteristics observed using an optical microscope after etching, the zircon grains were classified as: (i) homogeneous; (ii) anomalous, and (iii) hybrid. Micro-Raman results showed that, as etching time increases, the crystal lattice is slightly altered for homogeneous grains, it is completely damaged for anomalous grains, and it is altered in some areas for hybrid grains. The SEM (energy dispersive X-ray spectroscopy, EDS) results indicated that, independent of the grain types, where the crystallinity remains after etching, the chemical composition of zircon is approximately 33% SiO2:65% ZrO2 (standard natural zircon), and for areas where the grain does not have a crystalline structure, there are variations of ZrO2 and, mainly, SiO2. In addition, it is possible to observe a uniform surface density of fission tracks in grain areas where the determined crystal lattice and chemical composition are those of zircon. Regarding hybrid grains, we discuss whether the areas slightly altered by the chemical etching can be analyzed by the fission track method (FTM) or not. Results of zircon fission track and U-Pb dating show that hybrid and homogeneous grains can be used for dating, and not only homogeneous grains. More than 50 sedimentary samples from the Bauru Basin (southeast Brazil) were analyzed and show that only a small amount of grains are homogeneous (10%), questioning the validity of the rest of the grains for thermo-chronological evolution studies using zircon FTM dating.

scholarly journals Development of Evaluation Method for Damage of Oxidation CoNiCrAlY Coating

2019 ◽  
Vol 804 ◽  
pp. 47-51
Author(s):  
Mo Chen ◽  
Kodai Yoshikawa ◽  
Zhen Qiang Song ◽  
Shijie Zhu
Keyword(s):  
Cross Sections ◽  
Gas Turbines ◽  
Evaluation Method ◽  
Thermal Spraying ◽  
Optical Microscope ◽  
Thermally Grown Oxide ◽  
Interfacial Damage ◽  
Barrier Coating ◽  
Plasma Sprayed ◽  
Conicraly Coating

The bond coat plays an important role in the failure of the thermal barrier coating (TBC) system used for gas turbines [1,2]. In this research, the CoNiCrAlY coated Ni-base superalloy specimens were used for developing evaluation method for interfacial damage in the coat. Samples were exposed at 1000°C and 1100°C for up to 1000 hours. The morphology and residual stress in the thermally grown oxide (TGO) layer on the CoNiCrAlY coating were characterized by microscopic observation and luminescence spectroscope, respectively. The microstructure and damage o\n both the coating surfaces and the cross sections were observed by optical microscope and scanning electron microscope. According to the results, the low pressure plasma sprayed CoNiCrAlY coating (LPPS) showed the thinnest TGO layer and lowest residual stress.Residual stress decreased with an increase in exposure time, depending on the morphology of TGO layer. The effects of thermal spraying methods on the oxidation of yttrium in TGO layer and BC layer and its influence on interfacial damage were discussed.

scholarly journals Numerics made easy: solving the Navier–Stokes equation for arbitrary channel cross-sections using Microsoft Excel

2016 ◽  
Vol 18 (3) ◽  
Author(s):  
Christiane Richter ◽  
Frederik Kotz ◽  
Stefan Giselbrecht ◽  
Dorothea Helmer ◽  
Bastian E. Rapp
Keyword(s):  
Stokes Equation ◽  
Cross Sections ◽  
Navier Stokes ◽  
Microsoft Excel ◽  
Navier Stokes Equation

Estimation of Applied Stress at Fatigue Cracks of a Single Crystal Superalloy

2020 ◽  
Author(s):  
Daisuke Kobayashi ◽  
Katsuhiro Takama ◽  
Tomihiko Ikeda
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Fracture Surface ◽  
Single Crystal ◽  
Crack Growth ◽  
Applied Stress ◽  
Fatigue Crack Growth Rate ◽  
Single Crystal Superalloy

Abstract Needless to say, it is important to estimate the stress applied to a material when conducting failure analysis. In recent years, a material assessment method using electron back-scatter diffraction (EBSD) has been developed. It has been reported that a characteristic misorientation distribution corresponding to the fracture mode is seen in cross-sectional EBSD observation near the fracture surface of a Ni-based superalloy. Furthermore, the authors discovered EBSD striations on the crack cross-section, which is formed with each fatigue crack growth during a turbine shut-down process. This was discovered in misorientation analysis on a single-crystal superalloy blade used in a commercial land-based gas turbine. Since Ni-based superalloys have high deformation resistance, they do not undergo enough ductile deformation to form striations at the crack tip on the fracture surface during fatigue crack growth, and, as a result, striations corresponding to cyclic loadings are rarely observed in fractography. Even in such a Ni-based superalloy with brittle crack growth, the fatigue crack growth rate and the applied stress can be estimated by measuring EBSD striation spacing in misorientation analysis. However, a practical problem in assessment is that the resolution limit fixed with field emission scanning electron microscopes (FE-SEM) determine the range in which crack growth rate can be assessed. Hence, it is difficult to clearly discriminate the EBSD striations when the fatigue crack growth rate is too low, such as in the low stress intensity factor range (ΔK) region. The applied stress can be calculated from ΔK. Therefore, in this paper, in order to estimate the applied stress during fatigue crack growth, we focused on estimating ΔK by measuring the plastic zone size along the crack growth.

Low Toughness and Embrittlement Phenomena in Steels

2015 ◽  
pp. 439-485
Keyword(s):  
High Temperature ◽  
Hydrogen Embrittlement ◽  
Fracture Surface ◽  
Liquid Metal ◽  
Surface Characteristics ◽  
Low Alloy Steels ◽  
Contributing Factors ◽  
Tempered Martensite ◽  
Alloy Steels ◽  
Strength And Ductility

This chapter describes the causes of cracking, embrittlement, and low toughness in carbon and low-alloy steels and their differentiating fracture surface characteristics. It discusses the interrelated effects of composition, processing, and microstructure and contributing factors such as hot shortness associated with copper and overheating and burning as occur during forging. It addresses various types of embrittlement, including quench embrittlement, tempered-martensite embrittlement, liquid-metal-induced embrittlement, and hydrogen embrittlement, and concludes with a discussion on high-temperature hydrogen attack and its effect on strength and ductility.

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