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A modified single edge V-notched beam method for evaluating surface fracture toughness of thermal barrier coatings

Applied Mathematics and Mechanics(English Edition) 2023年第5期44卷 693-710页

作者： Haoran BAI Zhanyu WANG Sangyu LUO Zhaoliang QU Daining FANG Institute of Advanced Structure Technology Beijing Institute of TechnologyBeijing 100081China

The surface fracture toughness is an important mechanical parameter for studying the failure behavior of air plasma sprayed(APS)thermal barrier coatings(TBCs).As APS TBCs are typical multilayer porous ceramic materials,the direct applications of the traditional single edge notched beam(SENB)method that ignores those typical structural characters may cause errors.To measure the surface fracture toughness more accurately,the effects of multilayer and porous characters on the fracture toughness of APS TBCs should be considered.In this paper,a modified single edge V-notched beam(MSEVNB)method with typical structural characters is developed.According to the finite element analysis(FEA),the geometry factor of the multilayer structure is recalculated.Owing to the narrower V-notches,a more accurate critical fracture stress is obtained.Based on the Griffith energy balance,the reduction of the crack surface caused by micro-defects is corrected.The MSEVNB method can measure the surface fracture toughness more accurately than the SENB method.

关键词： thermal barrier coating(TBC) surface fracture toughness modified single edge V-notched beam(MSEVNB)method multilayer structure micro-defect

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Failure behavior of protective organic coatings under corrosive conditions

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中国有色金属学会会刊：英文版 2004年第Z1期14卷 395-404页

作者： ZHANG Xian-cheng XU Bin-shi WANG Hai-dou WU Yi-xiong National Key Laboratory of Remanufacturing Academy of Armored Forces Engineering Beijing 100072 China National Key Laboratory of Remanufacturing Academy of Armored Forces Engineering Beijing 100072 China National Key Laboratory of Remanufacturing Academy of Armored Forces Engineering Beijing 100072 China School of Materials Science and Engineering Shanghai Jiaotong University Shanghai 200030 China

Recent research activities on the formation of micro-defects and porosity in organic coatings were reviewed. The mechanisms of aggressive ionic conduction through organic coatings were analyzed. The micro-mechanisms for the failure behavior of coatings under corrosive environments were discussed in detail. These mechanisms included blistering (i. e. osmotic blistering, anodic blistering and cathodic blistering) in the coating, wet-adhesion loss at the substrate/coating interface, cathodic delamination of coating from the substrate. Based on these researches, it was found that the failure behavior of organic coatings is closely related to the micro-defects in coatings, regardless of the failure mode. Additionally, the general failure mode of a coating system was proposed to interpret the failure behavior of organic in corrosion environments. The topics discussed can provide some insights into the development of a methodology for designing fail-safe coating systems.

关键词： organic coating micro-defect porosity failure mechanism failure mode

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An extended displacement discontinuity method for analysis of stress wave propagation in viscoelastic rock mass

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Journal of Rock Mechanics and Geotechnical Engineering 2011年第1期3卷 73-81页

作者： L.F.Fan1,F.Ren1,G.W.Ma2 1 School of Civil and Environmental Engineering,Nanyang Technological University,Singapore,639798,Singapore 2 School of Civil and Resource Engineering,The University of Western Australia,Crawley,WA 6009,Australia School of Civil and Environmental Engineering Nanyang Technological University Singapore 639798 Singapore School of Civil and Resource Engineering The University of Western Australia Crawley WA 6009 Australia

An extended displacement discontinuity method (EDDM) is proposed to analyze the stress wave propagation in jointed viscoelastic rock mass (VRM).The discontinuities in a rock mass are divided into two groups.The primary group with an average geometrical size larger than or in the same order of magnitude of wavelength of a concerned stress wave is defined as 'macro-joints',while the secondary group with a high density and relatively small geometrical size compared to the wavelength is known as 'micro-defects'.The rock mass with micro-defects is modeled as an equivalent viscoelastic medium while the macro-joints in the rock mass are modeled explicitly as physical discontinuities.Viscoelastic properties of a micro-defected sedimentary rock are obtained by longitudinally impacting a cored long sedimentary rod with a pendulum.Wave propagation coefficient and dynamic viscoelastic modulus are measured.The EDDM is then successfully employed to analyze the wave propagation across macro-joint in VRM.The effect of the rock viscosity on the stress wave propagation is evaluated by comparing the results of VRM from the presented EDDM with those of an elastic rock mass (ERM) from the conventional displacement discontinuity method (CDDM).The CDDM is a special case of the EDDM under the condition that the rock viscosity is ignored.Comparison of the reflected and transmitted waves shows that the essential rock viscosity has a significant effect on stress wave attenuation.When a short propagation distance of a stress wave is considered,the results obtained from the CDDM approximate to the EDDM solutions,however,when the propagation distance is sufficiently long relative to the wavelength,the effect of rock viscosity on the stress wave propagation cannot be ignored.

关键词： stress wave propagation extended displacement discontinuity method (EDDM) viscoelastic rock mass (VRM) micro-defect macro-joint

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