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Quantitative assessment of the surface crack density in thermal barrier coatings 被引量:5
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作者 Li Yang Zhi-Chun Zhong +1 位作者 Yi-Chun Zhou Chun-Sheng Lu 《Acta Mechanica Sinica》 SCIE EI CAS CSCD 2014年第2期167-174,共8页
In this paper, a modified shear-lag model is developed to calculate the surface crack density in thermal barrier coatings(TBCs). The mechanical properties of TBCs are also measured to quantitatively assess their sur... In this paper, a modified shear-lag model is developed to calculate the surface crack density in thermal barrier coatings(TBCs). The mechanical properties of TBCs are also measured to quantitatively assess their surface crack density. Acoustic emission(AE) and digital image correlation methods are applied to monitor the surface cracking in TBCs under tensile loading. The results show that the calculated surface crack density from the modified model is in agreement with that obtained from experiments. The surface cracking process of TBCs can be discriminated by their AE characteristics and strain evolution. Based on the correlation of energy released from cracking and its corresponding AE signals, a linear relationship is built up between the surface crack density and AE parameters, with the slope being dependent on the mechanical properties of TBCs. 展开更多
关键词 Thermal barrier coatings Acoustic emission Surface crack density Quantitative assessment
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Ultrasonic prediction of crack density using machine learning:A numerical investigation
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作者 Sadegh Karimpouli Pejman Tahmasebi Erik HSaenger 《Geoscience Frontiers》 SCIE CAS CSCD 2022年第1期114-126,共13页
Cracks are accounted as the most destructive discontinuity in rock, soil, and concrete. Enhancing our knowledge from their properties such as crack distribution, density, and/or aspect ratio is crucial in geo-systems.... Cracks are accounted as the most destructive discontinuity in rock, soil, and concrete. Enhancing our knowledge from their properties such as crack distribution, density, and/or aspect ratio is crucial in geo-systems. The most well-known mechanical parameter for such an evaluation is wave velocity through which one can qualitatively or quantitatively characterize the porous media. In small scales, such information is obtained using the ultrasonic pulse velocity(UPV) technique as a non-destructive test. In large-scale geo-systems, however, it is inverted from seismic data. In this paper, we take advantage of the recent advancements in machine learning(ML) for analyzing wave signals and predict rock properties such as crack density(CD) – the number of cracks per unit volume. To this end, we designed numerical models with different CDs and, using the rotated staggered finite-difference grid(RSG) technique, simulated wave propagation. Two ML networks, namely Convolutional Neural Networks(CNN) and Long Short-Term Memory(LSTM), are then used to predict CD values. Results show that, by selecting an optimum value for wavelength to crack length ratio, the accuracy of predictions of test data can reach R2> 96% with mean square error(MSE) < 25e-4(normalized values). Overall, we found that:(i) performance of both CNN and LSTM is highly promising,(ii) accuracy of the transmitted signals is slightly higher than the reflected signals,(iii) accuracy of 2D signals is marginally higher than 1D signals,(iv)accuracy of horizontal and vertical component signals are comparable,(v) accuracy of coda signals is less when the whole signals are used. Our results, thus, reveal that the ML methods can provide rapid solutions and estimations for crack density, without the necessity of further modeling. 展开更多
关键词 Machine learning crack density Ultrasonic wave Numerical computation
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Effect of carbon material and surfactant on ink property and resulting surface cracks of fuel-cell microporous layers
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作者 Zhekun Chen Weitong Pan +2 位作者 Longfei Tang Xueli Chen Fuchen Wang 《Chinese Journal of Chemical Engineering》 SCIE EI CAS CSCD 2024年第5期1-12,共12页
Ensuring the consistency of electrode structure in proton-exchange-membrane fuel cells is highly desired yet challenging because of wide-existing and unguided cracks in the microporous layer(MPL). The first thing is t... Ensuring the consistency of electrode structure in proton-exchange-membrane fuel cells is highly desired yet challenging because of wide-existing and unguided cracks in the microporous layer(MPL). The first thing is to evaluate the homogeneity of MPL with cracks quantitatively. This paper proposes the homogeneity index of a full-scale MPL with an area of 50 cm~2, which is yet to be reported in the literature to our knowledge. Besides, the effects of the carbon material and surfactant on the ink and resulting MPL structure have been studied. The ink with a high network development degree produces an MPL with low crack density, but the ink with high PDI produces an MPL with low crack homogeneity. The polarity of the surfactant and the non-polarity of polytetrafluoroethylene(PTFE) are not mutually soluble,resulting in the heterogeneous PTFE distribution. The findings of this study provide guidelines for MPL fabrication. 展开更多
关键词 Proton-exchange-membrane fuel cell Microporous layer crack density crack homogeneity Polytetrafluoroethylene distribution SURFACTANT
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Density Evolution of the Surface Short Fatigue Cracks of 1Cr18Ni9Ti Pipe-Weld Metal 被引量:2
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作者 Yongxiang QingGAO 《Journal of Materials Science & Technology》 SCIE EI CAS CSCD 2002年第3期266-270,共5页
The evolutionary density and the scatter of densities of the short fatigue cracks on the surface of 1Cr18Ni9Ti pipe-weld metal were observed by local and overall viewpoints, respectively. The local viewpoint, which is... The evolutionary density and the scatter of densities of the short fatigue cracks on the surface of 1Cr18Ni9Ti pipe-weld metal were observed by local and overall viewpoints, respectively. The local viewpoint, which is in accordance with a so-called "effectively short fatigue crack criterion", paid attention to the dominant effective short fatigue crack (DESFC) initiation zone and the zones ahead of the DESFC tips. The overall viewpoint focused on the whole test piece of specimen. The results revealed that the density and scatter evolution exhibited a significant character of microstructural short crack and physical short crack stages. The evolutionary behavior by the local viewpoint was sensitive to the increase of DESFC size and tip location. The mechanism of the short crack growth associated with the general test observations that the DESFC acted gradually as a long crack and the scatter of DESFC growth rates tended gradually to that of a long crack was well revealed. Intrinsic causes of the random cyclic strain-life relations and stress-strain responses are appropriately given. In contrast, the evolutionary behavior by the overall viewpoint was non-sensitive and violated the general test observations. Therefore, the intrinsic localization and randomization of material evolutionary fatigue damage should be more appropriately revealed from the observations by the local viewpoint. 展开更多
关键词 1CRL8NI9TI Short crack density FATIGUE
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EXPERIMENTAL AND THEORETICAL STUDY ON NUMERICAL DENSITY EVOLUTION OF SHORT FATIGUE CRACKS 被引量:2
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作者 方飙 洪友士 白以龙 《Acta Mechanica Sinica》 SCIE EI CAS CSCD 1995年第2期144-152,共9页
Fatigue testing was performed using a kind of triangular shaped specimen to obtain the characteristics of numerical density evolution for short cracks at the primary stage of fatigue damage. The material concerned is ... Fatigue testing was performed using a kind of triangular shaped specimen to obtain the characteristics of numerical density evolution for short cracks at the primary stage of fatigue damage. The material concerned is a structural alloy steel. The experimental results show that the numerical density of short cracks reaches the maximum value when crack length is slightly less than the average grain diameter, indicating grain boundary is the main barrier for short crack extension. Based on the experimental observations and related theory, the expressions for growth velocity and nucleation rate of short cracks have been proposed. With the solution to phase space conservation equation, the theoretical results of numerical density evolution for short cracks were obtained, which were in agreement with our experimental measurements. 展开更多
关键词 SHORT FATIGUE crackS crack NUMERICAL density FATIGUE DAMAGE EVOLUTION
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ELASTO-PLASTIC BRANCHED ANALYSIS FOR AN INTERFACE CRACK BASED ON CRACK ENERGY DENSITY
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作者 FAN, XY SATO, Y WATANABE, K 《Acta Mechanica Solida Sinica》 SCIE EI 1995年第2期171-177,共7页
The elasto-plastic finite element analyses for an interface crack in dissimilar material, based on the crack energy density (CED) concept, are investigated in mode I loading condition. It is confirmed that the values ... The elasto-plastic finite element analyses for an interface crack in dissimilar material, based on the crack energy density (CED) concept, are investigated in mode I loading condition. It is confirmed that the values of CED almost remain stable when the notch radius rho is sufficiently small, both in elastic and elasto-plastic case. Numerical results for both elastic and elasto-plastic cases show that under the mode I loading condition, when the crack propagates to the more stiff material with a small angle, the total CED will become larger than that along the interface. If the clack heads into the more compliant material, the CED will become less than that along the interface. 展开更多
关键词 INTERFACE crack crack ENERGY density
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THE CHARACTERISTICS OF SHORT CRACKS AND EQUIVALENT PARAMETER OF FATIGUE DAMAGE
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作者 Z.X. Wu Engineering College, Yangzhou University, Yangzhou 225009, China 《Acta Metallurgica Sinica(English Letters)》 SCIE EI CAS CSCD 2000年第4期955-960,共6页
In order to understand which parameters, such as the number of cracks and the total crack length is the useful indicators of fatigue damage, rotatory bending fatigue tests are carried out using smooth specimens of a m... In order to understand which parameters, such as the number of cracks and the total crack length is the useful indicators of fatigue damage, rotatory bending fatigue tests are carried out using smooth specimens of a medium-carbon steel. The behavior of short crock propagation and the evolution of surface cracks during fatigue are examined. The aim of this paper is to study how these damage parameters are correlated with the process of fatigue in order to evaluate the effectiveness of damage detection methods. 展开更多
关键词 fatigue damage fatigue crack density total crack length crock initiation
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Crack fluid identification of shale reservoir based on stress-dependent anisotropy
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作者 Zhang Jia-Jia Zhang Guang-Zhi Huang Lan-Hua 《Applied Geophysics》 SCIE CSCD 2019年第2期209-217,254,共10页
Shale reservoirs are typically very tight, and crack are only a small part of the reservoir. The directional arrangement of cracks leads to the anisotropic characteristics of shale, and the type of fluid filled in cra... Shale reservoirs are typically very tight, and crack are only a small part of the reservoir. The directional arrangement of cracks leads to the anisotropic characteristics of shale, and the type of fluid filled in cracks affects the shale reservoir evaluation and late development. Many rock physics theories and methods typically use second-and fourthorder crack density tensors to characterize the elastic anisotropy induced by cracks as well as the normal-to-tangential crack compliance ratio to distinguish between dry and saturated cracks. This study def ines an anisotropic crack f luid indicator for vertical transversely isotropy(VTI) media with vertical symmetry axis which is the integration of the normal-to-tangential crack compliance ratio in three directions. A new dimensionless fourth-order tensor, including crack f luid type, azimuth distribution, and geometric shape, is constructed by substituting the normal and tangential compliance into the fourth-order crack density tensor, which can also be used to identify the type of crack fluid in the VTI media. Using the Callovo–Oxfordian shale experimental data, the variation of the elastic properties of dry and saturated shale samples with axial stress is analyzed. The results demonstrate that the anisotropic crack f luid indicator of water-bearing shale samples is less than that of the dry shale samples and that the dimensionless fourth-order tensor of water-bearing shale samples is nearly one order of magnitude greater than that of the dry shale samples. Therefore, the anisotropic crack f luid indicator and dimensionless fourth-order tensor can ref lect the crack f luid type in shale samples and can be used for shale reservoir prediction and f luid identif ication. 展开更多
关键词 cracks fluid identification crack density tensor crack fluid indicator dimensionless fourth-order tensor
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Numerical Modeling of the Effect of Crack Parameters on Attenuation Anisotropy
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作者 Cai Xiaogang 《Earthquake Research in China》 2012年第1期97-109,共13页
Propagation through stress-aligned fluid-filled cracks and other inclusions have been claimed to be the cause of azimuthal anisotropy observed in the crust and upper mantle.This paper examines the behavior of seismic ... Propagation through stress-aligned fluid-filled cracks and other inclusions have been claimed to be the cause of azimuthal anisotropy observed in the crust and upper mantle.This paper examines the behavior of seismic waves attenuation caused by the internal structure of rock mass,and in particular,the internal geometry of the distribution of fluid-filled openings Systematic research on the effect of crack parameters,such as crack density,crack aspect ratio(the ratio of crack thickness to crack diameter),pore fluid properties(particularly pore fluid velocity),VP/VS ratio of the matrix material and seismic wave frequency on attenuation anisotropy has been conducted based on Hudson's crack theory.The result shows that the crack density,aspect ratio,material filler,seismic wave frequency,and P-wave and shear wave velocity in the background of rock mass,and especially frequency has great effect on attenuation curves.Numerical research can help us know the effect of crack parameters and is a good supplement for laboratory modeling.However,attenuation is less well understood because of the great sensitivity of attenuation to details of the internal geometry.Some small changes in the characteristics of pore fluid viscosity,pore fluids containing gas and liquid phases and pore fluids containing clay can each alter attenuation coefficients by orders of magnitude.Some parameters controlling attenuation are therefore necessary to make reasonable estimations,and anisotropic attenuation is worth studying further. 展开更多
关键词 Equivalent media theory crack density Attenuation anisotropy Qualityfactor
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The influence of microwave irradiation on rocks for microwaveassisted underground excavation 被引量:82
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作者 Ferri Hassani Pejman M.Nekoovaght Nima Gharib 《Journal of Rock Mechanics and Geotechnical Engineering》 SCIE CSCD 2016年第1期1-15,共15页
Demand is growing for explosive-free rock breakage systems for civil and mining engineering, and space industry applications. This paper highlights the work being undertaken in the Geomechanics Laboratory of Mc Gill U... Demand is growing for explosive-free rock breakage systems for civil and mining engineering, and space industry applications. This paper highlights the work being undertaken in the Geomechanics Laboratory of Mc Gill University to make a real application of microwave-assisted mechanical rock breakage to fullface tunneling machines and drilling. Comprehensive laboratory tests investigated the effect of microwave radiation on temperature profiles and strength reduction in hard rocks(norite, granite, and basalt)for a range of exposure times and microwave power levels. The heating rate on the surface of the rock specimens linearly decreased with distance between the sample and the microwave antenna, regardless of microwave power level and exposure time. Tensile and uniaxial compressive strengths were reduced with increasing exposure time and power level. Scanning electron micrographs(SEMs) highlighted fracture development in treated basalt. It was concluded that the microwave power level has a strong positive influence on the amount of heat damage induced to the rock surface. Numerical simulations of electric field intensity and wave propagation conducted with COMSOL Multiphysics~ software generated temperature profiles that were in close agreement with experimental results. 展开更多
关键词 Microwaves crack density Microwave-assisted tunnel boring Rock breakage
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Simulation of rock deformation and mechanical characteristics using clump parallel-bond models 被引量:10
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作者 夏明 赵崇斌 《Journal of Central South University》 SCIE EI CAS 2014年第7期2885-2893,共9页
To properly simulate hard rock with a high ratio of the uniaxial compressive strength to tensile strength(UCS/TS) and realistic strength-failure envelope,the rock deformation and mechanical characteristics were discus... To properly simulate hard rock with a high ratio of the uniaxial compressive strength to tensile strength(UCS/TS) and realistic strength-failure envelope,the rock deformation and mechanical characteristics were discussed in detail when the particle simulation method with the clump parallel-bond model(CPBM) was used to conduct a series of numerical experiments at the specimen scale.Meanwhile,the effects of the loading procedure and crack density on the mechanical behavior of a specimen,which was modeled by the particle simulation method with the CPBM,were investigated.The related numerical results have demonstrated that:1) The uniaxial compressive strength(UCS),tensile strength(TS) and elastic modulus are overestimated when the conventional loading procedure is used in the particle simulation method with the CPBM; 2) The elastic modulus,strength and UCS/TS decrease,while Poisson ratio increases with the increase of the crack density in the particle simulation method with the CPBM; 3) The particle simulation method with the CPBM can be used to reproduce a high value of UCS/TS(>10),as well as a high friction angle and reasonable cohesion strength; 4) As the confining pressure increases,both the peak strength of the simulated specimen and the number of microscopic cracks increase,but the ratio of tensile cracks number to shear cracks number decreases in the particle simulation method with the CPBM; 5) Compared with the conventional parallel-bond model,the CPBM can be used to reproduce more accurate results for simulating the rock deformation and mechanical characteristics. 展开更多
关键词 particle simulation method clump parallel-bond model crack density loading procedure rock mechanical behavior
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A subregional model for delamination prediction of rubber composite under fatigue loading 被引量:1
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作者 田振辉 谭惠丰 《Journal of Harbin Institute of Technology(New Series)》 EI CAS 2005年第3期255-260,共6页
Results from fatigue experiments of cross-laminated steel cord-rubber composites (SCRC) indicate that fatigue damage life can be categorized into three regimes. In terms of fatigue modes, a subregional fatigue model i... Results from fatigue experiments of cross-laminated steel cord-rubber composites (SCRC) indicate that fatigue damage life can be categorized into three regimes. In terms of fatigue modes, a subregional fatigue model is developed to describe the damages evolution of SCRC under fatigue loads. Firstly, finite element analysis is introduced to determine interply stress distribution of the specimen. Then, based on the experimental fatigue data, subregional models are introduced to simulate relations between maximum strain, effective stiffness, delamination shear stress and fatigue cycles. Relations between crack density, delamination length growth rate, macro crack density and cycles are modeled by two semi-empirical models. A reasonable prediction result was achieved by the current model, where model parameters can be determined by basic outputs of fatigue testing. 展开更多
关键词 FATIGUE crack density DELAMINATION rubber composites FEA
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Calculation of stress intensity factor in two-dimensional cracks by strain energy density factor procedure 被引量:1
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作者 FANG Zhao LI AiQun +1 位作者 BAO HaiYing WANG Hao 《Science China(Technological Sciences)》 SCIE EI CAS CSCD 2018年第4期542-550,共9页
In order to calculate the stress intensity factor(SIF) of crack tips in two-dimensional cracks from the viewpoint of strain energy density, a procedure to use the strain energy density factor to calculate the SIF is p... In order to calculate the stress intensity factor(SIF) of crack tips in two-dimensional cracks from the viewpoint of strain energy density, a procedure to use the strain energy density factor to calculate the SIF is proposed. In this paper, the procedure is presented to calculate the SIF of crack tips in mode I cracks, mode II cracks and I+II mixed mode cracks. Meanwhile, the results are compared to those calculated by traditional approaches or other approaches based on strain energy density and verified by theoretical solutions. Furthermore, the effect of mesh density near the crack tip is discussed, and the proper location where the strain energy density factor is calculated is also studied. The results show that the SIF calculated by this procedure is close to not only those calculated by other approaches but also the theoretical solutions, thus it is capable of achieving accurate results.Besides, the mesh density around the crack tip should meet such requirements that, in the circular area created, the first layer of singular elements should have a radius about 0.05 mm and each element has a circumferential directional meshing angle to be15°–20°. Furthermore, for a single element around the crack tip, the strain energy density factor is suggested to be calculated in the location where half of the sector element's radius from the crack tip. 展开更多
关键词 stress intensity factor two-dimensional crack strain energy density factor averaged strain energy density
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Stability of Quark Star Models
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作者 M.Azam S.A.Mardan M.A.Rehman 《Communications in Theoretical Physics》 SCIE CAS CSCD 2016年第5期575-584,共10页
In this paper,we investigate the stability of quark stars with four different types of inner matter configurations;isotropic,charged isotropic,anisotropic and charged anisotropic by using the concept of cracking.For t... In this paper,we investigate the stability of quark stars with four different types of inner matter configurations;isotropic,charged isotropic,anisotropic and charged anisotropic by using the concept of cracking.For this purpose,we have applied local density perturbations technique to the hydrostatic equilibrium equation as well as on physical parameters involved in the model.We conclude that quark stars become potentially unstable when inner matter configuration is changed and electromagnetic field is applied. 展开更多
关键词 quark stars cracking density perturbations electromagnetic field
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