检索结果-南通市图书馆

Application of ultrasonic surface waves in the detection of Microcracks using the scanning heating laser source technique

在线全文

学校读者我要写书评

暂无评论

Chinese Optics Letters 2012年第11期10卷 40-43页

作者：李加董利明倪辰荫沈中华张宏超 Faculty of Science Nanjing University of Science and Technology Faculty of Science Nanjing University of Aeronautics and Astronautics

This letter reports the application of the scanning heating laser source technique to detect Microcracks that may be undetected by conventional methods. In the proposed approach, we monitor changes in the transmitted surface acoustic waves （SAWs） as a heating source is scanned over the crack. The experimental system for microcrack detection by a scanning heating laser source is obtained by exploiting the strong dependence of the transmission efficiency of acoustic pulses on the state of the contacts, whether open or closed, between the crack faces. Microeracks can be detected successfully by confirming the heating position at the point of maximal improvement of the transmission efficiency of the SAWs.

关键词： Acoustic surface wave devices Heating Lasers Microcracks Scanning Surface waves Ultrasonic testing

Mesoscopic characteristics and mechanisms of Microcracks healing in impurity-containing rock salt

在线全文

学校读者我要写书评

暂无评论

Yantu Lixue/Rock and Soil Mechanics 2020年 41卷 30-38 and 46页

作者： Kang, Yan-Fei Chen, Jie Jiang, De-Yi Li, Zong-Ze Du, Chao State Key Laboratory for the Coal Mine Disaster Dynamics and Controls Chongqing University Chongqing 400044 China

Rock salt is recognized as one of the most ideal storage media for underground energy strategic storage and radioactive waste storage due to its excellent properties such as low porosity, low permeability, high ductility and self-healing of damage. Based on the damaged-induced microcrack healing test of rock salt, the healing characteristics of damage-induced microcrack in the excavation disturbance zone(EDZ) of salt cavern in lacustrine deposits with high-impurity in China were studied. With the help of the scanning electron microscop(SEM) and energy dispersive X-ray spectrum(EDS), the morphology characteristics of microcrack of the high impurity rock salt after healing were analyzed from microscopic point of view, it is found that the high impurity salt rocks in the domestic lake sediments have good self-healing characteristics as the pure salt rocks abroad. The healing structure of the Microcracks in the salt rock shows a zipper distribution, and the crack tip, the area containing impurity in crack surface and the necked part of cracks surface are more likely to heal. The healing of salt rock Microcracks is mainly attributed to the recrystallization of NaCl crystals in the cracks and the diffusion driven by surface energy. © 2020, Science Press. All right reserved.

关键词： Microcracks

Analysis of surface Microcracks in low-carbon steel produced via twin-roll strip casting

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Baosteel Technical Research 2019年第2期13卷 24-31页

作者： YANG Xiaoping FANG Yuan SHI Bi Research Institute Baoshan Iron & Steel Co.Ltd.Shanghai 201999China Shanghai Engineering Research Center of Strip Casting and Rolling Shanghai 201999China

In this study,morphological and microstructural analyses were conducted on net-shaped Microcracks appearing on the surface of low-carbon steel manufactured via twin-roll strip casting. The fractograph and microscale distribution of elements in the cracked region were also analyzed. Results revealed that the cracked surfaces were characterized by slight pits,along with inclusions composed of manganese and silicon oxide distributed along both the sides of the cracks. Fractograph analysis revealed that the crack and smooth dendrite surfaces were oxidized. These phenomena indicate that Microcracks on the cast strip surface form at the hightemperature stage of the solidification process during twin-roll casting and rolling. Microcracks were present in each region with pits in the cast strip and extended along the dendrite interface because of the combined effects of phasechange stress,thermal stress,mechanical stress,and fractional crystallization during the solidification process.

关键词： strip casting low-carbon steel Microcracks

In-situ investigation on the microstructure evolution of Mg-2Gd alloys during the V-bending tests

在线全文

学校读者我要写书评

暂无评论

Journal of Materials Science & Technology 2022年第36期131卷 167-176页

作者： Chao He Jianxin Zhou Yan Yang Bin Jiang Ming Yuan Zhihua Dong Yanfu Chai Weijun He Guangsheng Huang Dingfei Zhang Fusheng Pan State Key Laboratory of Mechanical Transmissions College of Materials Science and EngineeringChongqing UniversitySha Zheng Street 174#Sha Ping Ba DistrictChongqing 400044China National Engineering Research Center for Magnesium Alloys Chongqing UniversityChongqing 400044China School of Mechanical and Electrical Engineering Shaoxing UniversityShaoxing 312000China School of Chemistry and Materials Science Hubei Engineering UniversityXiaogan 432000China

In this work,the in-situ observation of the microstructure in the Mg-2Gd(wt%)alloys during V-bending tests was operated.The microstructure and texture evolutions were characterized by the in-situ electron backscatter diffraction(EBSD),scanning electron microscopy(SEM)and the high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)technique.The results revealed a unique Microcracks nucleation mechanism in the Mg-Gd alloys compared with the traditional Mg alloy(AZ31 alloy).The microcrack was nucleated at the grain boundary for the Mg-2Gd alloy and in the intragranular for the AZ31 alloy during the bending process.This difference mode between the Mg-Gd and the AZ31 alloys was mainly attributed to the more random topology of the grain boundary network,the lower grain boundary cohesion and the enhanced hinder ability for the dislocations due to the segregated Gd atoms in the Mg-Gd alloy.Furthermore,the Microcracks that had a large angleθwith the extruded direction(ED)in the Mg-Gd alloys were preferred nucleated since grain boundaries had the larger normal stress during the bending process.

关键词： Magnesium In-situ V-bending Microstructure Texture Microcracks

Effects of seepage pressure on the mechanical behaviors and microstructure of sandstone

在线全文

学校读者我要写书评

暂无评论

Journal of Rock Mechanics and Geotechnical Engineering 2024年第6期16卷 2033-2051页

作者： Xuewei Liu Juxiang Chen Bin Liu Sai Wang Quansheng Liu Jin Luo State Key Laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil MechanicsChinese Academy of SciencesWuhan430071China Faculty of Engineering China University of GeosciencesWuhan430074China Key Laboratory of Safety for Geotechnical and Structural Engineering of Hubei Province School of Civil EngineeringWuhan UniversityWuhan430072China

Surrounding rocks of underground engineering are subjected to long-term seepage pressure,which can deteriorate the mechanical properties and cause serious disasters.In order to understand the impact of seepage pressure on the mechanical property of sandstone,uniaxial compression tests,P-wave velocity measurements,and nuclear magnetic resonance(NMR)tests were conducted on saturated sandstone samples with varied seepage pressures(i.e.0 MPa,3 MPa,4 MPa,5 MPa,6 MPa,7 MPa).The results demonstrate that the mechanical parameters(uniaxial compressive strength,peak strain,elastic modulus,and brittleness index),total energy,elastic strain energy,as well as elastic strain energy ratio,decrease with increasing seepage pressure,while the dissipation energy and dissipation energy ratio increase.Moreover,as seepage pressure increases,the micro-pores gradually transform into meso-pores and macro-pores.This increases the cumulative porosity of sandstone and decreases P-wave velocity.The numerical results indicate that as seepage pressure rises,the number of tensile cracks increases progressively,the angle range of Microcracks is basically from 50-120to 80-100,and as a result,the failure mode transforms to the tensile-shear mixed failure mode.Finally,the effects of seepage pressure on mechanical properties were discussed.The results show that decrease in the effective stress and cohesion under the action of seepage pressure could lead to deterioration of strength behaviors of sandstone.

关键词： Rock mechanics Mechanical property Seepage pressure Numerical simulation Microcracks

Swelling behaviors of heterogeneous red-bed mudstone subjected to different vertical stresses

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Rock Mechanics and Geotechnical Engineering 2024年第5期16卷 1847-1863页

作者： Kang Huang Zhangjun Dai Chengzeng Yan Fei Yu Wei Zhang Shanxiong Chen State Key Laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil MechanicsChinese Academy of SciencesWuhan430071China University of Chinese Academy of Sciences Beijing100049China Faculty of Engineering China University of GeosciencesWuhanChina International Joint Research Center for Deep Earth Drilling and Resource Development China University of GeosciencesWuhan430074China

In this study,the axial swelling strain of red-bed mudstone under different vertical stresses are measured by swell-under-load method,and the microstructure of mudstone after hygroscopic swelling is studied by mercury intrusion porosimetry(MIP).The weakening coefficient and Weibull distribution function are introduced into the coupling model of mudstone moisture diffusion-swelling deformation-fracture based on finite-discrete element method(FDEM).The weakening effect of moisture on mudstone's mechanical parameters,as well as the heterogeneity of swelling deformation and stress distribution,is considered.The microcrack behavior and energy evolution of mudstone during hygroscopic swelling deformation under different vertical stresses are studied.The results show that the axial swelling strain of mudstone decreases with increase of the vertical stress.At low vertical stresses,moisture absorption in mudstone leads to formation of cracks caused by hydration-induced expansion.Under high vertical stresses,a muddy sealing zone forms on the mudstone surface,preventing further water infiltration.The simulation results of mudstone swelling deformation also demonstrate that it involves both swelling of the mudstone matrix and swelling caused by crack expansion.Notably,crack expansion plays a dominant role in mudstone swelling.With increasing vertical stress,the cracks in mudstone change from tensile cracks to shear cracks,resulting in a significant reduction in the total number of cracks.While the evolution of mudstone kinetic energy shows similarities under different vertical stresses,the evolution of strain energy varies significantly due to the presence of different types of cracks in the mudstone.The findings provide a theoretical basis for understanding the hygroscopic swelling deformation mechanism of red-bed mudstone at various depths.

关键词： Heterogeneous red-bed mudstone Self-sealing band Matric swelling and crack expansion FDEM Microcracks Energy evolution

Multiphase microstructure formation and its effect on fracture behavior of medium carbon high silicon high strength steel

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Materials Science & Technology 2021年第13期72卷 81-92页

作者： Kui Chen Huabing Li Zhouhua Jiang Fubin Liu Congpeng Kang Xiaodong Ma Baojun Zhao School of Metallurgy Northeastern UniversityShenyang 110819China State Key Laboratory of Rolling and Automation Northeastern UniversityShenyang 110819China School of Chemical Engineering The University of QueenslandBrisbane 4072Australia

This work investigated the evolution of multiphase microstructure and impact fracture behavior of medium carbon high silicon high strength steel subjected to the austempering treatment at 240,360,and400℃.The results show that martensite,bainite,and retained austenite(RA)are the main microstructural phases.The austempering treatments at 360 and 400℃ caused the formation of carbon-poor ferrite in the matrix,and the transformation of ultrafine bainite into coarse lath bainite and granular bainite,respectively.Thick filmy RA was distributed between bainite laths.The polygonal martensiteaustenite islands and blocky RA formed along the grain boundaries.The average carbon concentration in the matrix decreased with the temperature increase,while the impact toughness initially increased and then dropped with temperature.The quasi-cleavage brittle fracture dominated the impact fracture mechanism of the sample austempered at 240℃ by forming tearing surfaces and tearing steps.The Microcracks disappeared in the RA on the prior austenite grain boundaries.On the other side,the fracture surface of the sample austempered at 360℃ exhibited ductile fracture with deep dimples and brittle fracture with cleavage river patterns.The polygonal martensite-austenite islands or blocky RA constrained the Microcracks.After austempered at 400℃,the brittle fracture was dominant,showing river patterns,and the Microcracks propagated through the granular bainite without any resistance.

关键词： Medium carbon high silicon steel Austempering Martensite Bainite Retained austenite Microcracks

Identification methods for anomalous stress region in coal roadways based on microseismic information and numerical simulation

在线全文

学校读者我要写书评

暂无评论

International Journal of Mining Science and Technology 2017年第3期27卷 525-530页

作者： Liu Chao Li Shugang Cheng Cheng Cheng Xiaoyu College of Safety Science and Engineering Xi'an University of Science & Technology Xi'an 710054 China Key Laboratory of Western Mine Exploitation and Hazard Prevention Ministry of Education Xi'an University of Science & Technology Xi'an 710054 China

It is believed that the microseismicity induced by mining effect and gas gradient disturbance stress is a precursor to the essential characteristics of roadway unstability. In order to effectively identify and evaluate the stability of coal roadways in the process of mine development and extraction, a microseismic monitoring system was deployed for the study of the stress evolution process, damage degree and distribution characteristics in the tailgate and headgate. The mine under study is the 62113 outburst working face of Xin Zhuangzi coalmine in Huainan mining area. The whole process of microfractures initiation,extension, interaction and coalescence mechanisms during the progressive failure processes of the coal rock within the delineated and typical event clusters were investigated by means of a two dimensional realistic failure process analysis code(RFPA2D-Flow). The results show that the microseismic events gradually create different-sized event clusters. The microseismicity of the tailgate is significantly higher than that of the headgate. The study indicates that the greater anomalous stress region matches the area where microfractures continuously develop and finally connect to each other and form a fissure zone.Due to the mine layout and stress concentration, the ruptured area is mainly located on the left shoulder of the tailgate roof. The potential anomalous stress region of the coal roadway obtained by numerical simulation is relatively in good agreement with the trend of spatial macro evolution of coal rock microfractures captured by the microseismic monitoring system. The research results can provide important basis for understanding instability failure mechanism of deep roadway and microseismic activity law in complex geologic conditions, and it ultimately can be used to guide the selection and optimization of reinforcement and protection scheme.

关键词： Microseismic monitoring technology Numerical simulation Anomalous stress region Event clusters Microcracks

Microstructural characterization and mechanical behavior analysis of 7075-T6 aluminum subjected to simulated lightning strikes

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Aeronautics 2021年第12期34卷 39-50页

作者： Luis Henrique SANTOS Weslei Patrick Teodosio SOUSA Sara Silva Ferreira DE DAFE Pedro Americo Magalhaes JUNIOR Department of Mechanical Engineering Pontificia Universidade Catolica de Minas GeraisBelo Horizonte 30535-901Brazil

Aircrafts damages caused by lightning strikes have been known since the early days of aviation.However,the physical effects on the aircraft structure are still being investigated.This work seeks to evaluate the lightning strike effects in the aluminum alloy 7075-T6.Samples were submitted to lightning strike simulation in laboratory and the damages evaluated through characterization techniques.Ultrasound and profilometry tests have shown material loss to 0.272 mm depth in the damaged region.In addition,it was detected the material accumulation occurrence in the damage vicinity of the region.Below the damage,it was found a region where metallurgical changes were identified.The tensile and microhardness tests results have shown reduction in the percentage elongation and hardness increasing in the material affected by lightning.These results are corroborated by the X-Ray Diffraction(XRD)and Rietveld Method(red line)that indicated an increasing in dislocation density and micro-deformation in the material matrix.Optical microscopy results have shown the presence of Microcracks on the normal and cross-section surface of the samples damaged.The Energy Dispersive X-Ray Spectroscopy(EDXS)and Electron Backscattered Diffraction Test(EBSD)found coarse intermetallic phases and precipitates compounds with dimensions greater than 1 lm in length.They were responsible for nucleation of the Microcracks that propagate along the material grain boundaries.

关键词： Aircraft structure Characterization techniques Lightning strikes Precipitates Microcracks