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Search Results: 1 - 10 of 78294 matches for " Darong Chen "
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Relationship between the geometric features of carbon steel cavitation erosion debris and the cavitation erosion stages
ShiHan Liu,DaRong Chen
Chinese Science Bulletin , 2010, DOI: 10.1007/s11434-009-0260-x
Abstract: The debris produced in vibration cavitation tests of three kinds of carbon steel were collected. Their geometric features were analyzed quantitatively and observed respectively by a profilometer and a scanning electronic microscope (SEM) with reference to the investigation of the cavitation damaged surface by SEM and X-ray diffraction (XRD). It was found that among the debris produced in all cavitation erosion stages, more than 45% were platelets because of the occurrence of dislocation and cleavage fracture, and only less than 25% were strands. The number of granule was small in the first cavitation erosion stage and increased rapidly to the number comparable with that of platelets in the next stage, and then reduced in the third stage. The sphericity values of the debris varied in accordance with the stages of cavitation damage, which were 0.3–0.4 in the incubation stage, 0.5–0.7 in the acceleration stage and not less than 0.5 in the maximum rate stage, although a slight decrease occurred in the third stage.
Relationship between the geometric features of carbon steel cavitation erosion debris and the cavitation erosion stages

ShiHan Liu,DaRong Chen,

科学通报(英文版) , 2010,
Abstract: The debris produced in vibration cavitation tests of three kinds of carbon steel were collected.Their geometric features were analyzed quantitatively and observed respectively by a profilometer and a scanning electronic microscope(SEM) with reference to the investigation of the cavitation damaged surface by SEM and X-ray diffraction(XRD) .It was found that among the debris produced in all cavitation erosion stages,more than 45%were platelets because of the occurrence of dislocation and cleavage fracture,and...
Research progress on the ultra hydrophobic surface topography effect
Jiadao Wang,Ying Yu,Darong Chen
Chinese Science Bulletin , 2006, DOI: 10.1007/s11434-006-2129-6
Abstract: Ultra hydrophobic surfaces take on better hydrophobicity and exhibit a water contact angle larger than 150°. In this paper the ultra hydrophobicity is analyzed and common fabrication methods are summarized in detail. The applications of micro topography in both the fabrication of hydrophobic surface and the experiments of drag reduction are addressed. Finally, the development trend and foreground of ultra hydrophobic surface are discussed.
Effect of roughness and wettability of silicon wafer in cavitation erosion
NaNa Jiang,ShiHan Liu,DaRong Chen
Chinese Science Bulletin , 2008, DOI: 10.1007/s11434-008-0375-5
Abstract: Material damage of silicon wafer with different roughness and wettability was investigated by using the self-made vibration cavitation apparatus in de-ionized water. Various roughness and wettability of silicon wafer were achieved by changing their morphology and depositing Au, diamond-like carbon films (DLC films) on them. Surface morphology was observed with a scanning electron microscope (SEM) and a surface profilometer, and wettability was characterized by the contact angle measurement. The cavitation erosion results showed that many tiny pits and cracks appeared on the wafer surface as a result of brittle fractures; the number and size of the pits and cracks increased with experiment time, which made material flake away finally; cavitation occurred more easily on the silicon wafer surface with the augment of roughness or contact angle by changing surface morphology or depositing Au, DLC thin film on it, which consequently aggravated cavitation damage.
Progress of marine biofouling and antifouling technologies
Shan Cao,JiaDao Wang,HaoSheng Chen,DaRong Chen
Chinese Science Bulletin , 2011, DOI: 10.1007/s11434-010-4158-4
Abstract: Adhesion of marine fouling organisms on artificial surfaces such as ship hulls causes many problems, including extra energy consumption, high maintenance costs, and increased corrosion. Therefore, marine antifouling is an important issue. In this review, physical and biochemical developments in the field of marine biofouling, which involves biofilm formation and macro-organism settlement, are discussed. The major antifouling technologies based on traditional chemical methods, biological methods, and physical methods are presented. The chemical methods include self-polishing types such as tributyltin (TBT) self-polishing copolymer coatings, which despite its good performance has been banned since 2008 because of its serious environmental impact. Therefore, other methods have been encouraged. These include coatings with copper compounds and biocide boosters to replace the TBT coatings. Biological extracts of secreted metabolites and enzymes are anticipated to act as antifoulants. Physical methods such as modification of surface topography, hydrophobic properties, and charge potential have also been considered to prevent biofouling. In this review, most of the current antifouling technologies are discussed. It is proposed that the physical antifouling technologies will be the ultimate antifouling solution, because of their broad-spectrum effectiveness and zero toxicity.
Water erosion mechanism of mild carbon steels induced by micro-particles
WanLi Xu,Li Qin,JiaDao Wang,HaoSheng Chen,DaRong Chen
Chinese Science Bulletin , 2009, DOI: 10.1007/s11434-009-0589-1
Abstract: To clarify the water erosion mechanism of the mild carbon steels, the water erosion experiments were performed by using deionized water as steam source. The results showed that under the damage threshold velocity of liquid impact, the material surface would not be destroyed. However, when the micro-particles were added into the steam, the pits appeared on the surface soon. By comparison, it is found that the pits are quite different from those induced by micro-particles impact without steam, but similar to those induced by cavitation erosion. The results indicated that the water erosion mechanism was similar to that of cavitation erosion under the damage threshold velocity. The micro-particles carry the micro-bubbles to approach the surface of the material, and the micro-bubbles collapse and generate micro-jet to impinge vertically on the surface, which lead to the produce of pits.
Key roles of micro-particles in water on occurrence of cavitation-erosion of hydro-machinery
JiaDao Wang,HaoSheng Chen,Li Qin,YongJian Li,DaRong Chen
Chinese Science Bulletin , 2008, DOI: 10.1007/s11434-008-0089-8
Abstract: It has been believed for about one hundred years that the cavitation directly induces the cavitation erosion. It is proposed in this research that cavitation is only the necessary condition but not the sufficient condition of the cavitation erosion. The experiment performed on the rotary disk cavitation system shows that the micro-particles in the fluid play indispensable roles in the cavitation erosion process, and the generation of the erosion pits on the steel surface is also affected by the particles’ size. These cracks and deformations on the sample surface indicate that the erosion is the result of the mechanical behavior. Numerical calculations are also provided to support this mechanism.
Affected zone generated around the erosion pit on carbon steel surface at the incipient stage of vibration cavitation
HaoSheng Chen,Jiang Li,ShiHan Liu,DaRong Chen,JiaDao Wang
Chinese Science Bulletin , 2008, DOI: 10.1007/s11434-008-0105-z
Abstract: The characteristics of erosion pits on a carbon steel surface were investigated at the incipient stage of cavitation erosion. After a 5-minute experiment performed in an ultrasonic vibration system, needle-like erosion pits appeared on the polished steel surface, and a specially affected zone was formed around the pit. The shape of the pit and the plastic deformation of the affected zone indicate that the mechanical impaction on the surface is the main reason for the cavitation damage. On the other hand, the iridescent color, the decreased surface hardness and the precipitated carbides on the affected zone prove that the affected zone has experienced a tempering process with the temperature higher than 300°C. The lack of oxygen in the affected zone also proves that it is not a chemical oxygen result. A special phenomenon that a carbon ring forms in the affected zone is explained as a result of the toroidal bubbles’ heating effect at the final stage of the bubble collapse.
Friction characteristics of floppy disks
Chenhui Zhang,Jianbin Lou,Darong Chen,Shizhu Wen
Chinese Science Bulletin , 2000, DOI: 10.1007/BF02884897
Abstract: This note presents the principle and structure of a tribological measure for floppy disks. The precision of the force measuring system is 1 mN in loading and 3×10 6 N in friction. The resolution of the film thickness between head and floppy disk is 0.5 nm in the vertical and 1.5 nm in the horizontal direction. In order to investigate the tribological characteristics of floppy disks, six types of floppy disks have been tested and the floating properties of these disks are also studied with film measuring system. The experimental results of the surface morphology and friction coefficient of these floppy disks using the atomic force microscope/friction force mcroscope (AFM/FFM) are in accordance with the conclusion made by our own measuring system. The experimental results show that the air film thickness between head and disk is of the same order as the surface roughness of floppy disks.
Fabrication of a micro-structured surface based on interfacial convection for drag reduction
ZhaoLiang Dou,JiaDao Wang,Feng Yu,DaRong Chen
Chinese Science Bulletin , 2011, DOI: 10.1007/s11434-011-4378-2
Abstract: Based on interfacial convection in the presence of solvent evaporation, a novel method for the fabrication of a micro-structured surface is proposed to facilitate drag reduction. A mixture was coated on a substrate through a specially developed spray-painting system. Micron scale pits formed spontaneously in the coated surface because of interfacial convection and deformation driven by the gradient of the interfacial tension. Experimental results indicated that particles in the mixture played a crucial role in pit formation, and with a suitable selection of particle size and dosage, the characteristic parameters of the pitting could be controlled. The drag reduction experiments were first performed in a water tunnel, and the results showed that the micro-structured surface had a remarkable drag reduction performance over a great range of flow speeds.
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