Experimental Study on Mechanical Properties of Q690 High Strength Steel in Marine Corrosive Environment

Hongchao Guo,Tianqi Lei,Jinguang Yu,Defa Wang,Xiaolei Li 한국강구조학회 2021 International Journal of Steel Structures Vol.21 No.2

In order to study the mechanical property degradation rule of Q690 high-strength steel in the ocean wave splash area, the rusted specimen is obtained by indoor damp heat surrounding soaking environment corrosion test. The scanning electron microscopy, uniaxial tensile and cyclic loading tests of corroded steel are performed. This paper analyzes the steel from elastic modulus, yield strength, ductility and law of hysteresis degradation under diff erent corrosion cycles and establishes the constitutive model of HSS. The results show that the appearance of HSS is obviously aff ected by the corrosion cycle. With the increase of the corrosion cycle, reddish-brown fl aky corrosion products are formed on the surface of the steel and there are obvious corrosion pits. After 100 days of corrosion, the corrosion rate of steel reached 7.21%; the elastic modulus and yield strength under uniaxial tension load decreased by 10.2% and 4.9%. Under the eff ect of cyclic reciprocating load, the hysteretic energy is reduced by 15.3%; at the same time, the test curve is fi tted by the secondary plastic fl ow model and the Ramberg–Osgood model and it is found that the shape parameter S 1 and the cyclic strengthening coeffi cient K’ are reduced by 20.1% and 10.2%, While the shape parameter S 2 and the cycle strengthening index n’ have no obvious changes.

Diagnosis of rolling element bearing based on multifractal detrended fluctuation analyses and continuous hidden markov model

Hongchao Wang,Zhiqiang Guo,Wenliao Du 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.8

The conventional signal processing based methods are difficult to achieve satisfactory results for rolling element bearings (REBs)’ weak fault due to the serious influence of interference signal. Intelligent classification technology and the arising popular monitoring technology-performance evaluation assessment (PDA) are the research hotspots of fault diagnosis of REB in recent years, which could resolve the above problem to some extent. Especially the latter could reflect the operating status of the equipment more comprehensively. Effective feature extraction basing on signal processing methods and intelligent algorithm are the two key aspects for the above two technologies which will determine their effectiveness to great extent. Multifractal detrended fluctuation analyses (MDFA) is an effective non-stationary signal processing method which could reveal the multifractality buried in nonlinear and nonstationary vibration signals of REB, and continuous hidden markov model (CHMM) is a mature intelligent algorithm with solid theoretical basis and rich mathematical structure. So a diagnosis method basing on combination of MDFA with CHMM is proposed in the paper, and it could deal with both fault classification and PDA tasks for the diagnosis of REBs. Effectiveness of the proposed method is validated by two different diagnosis experiments, one for fault classification and another for lifecycle performance evaluation of REBs. Compared to state-of-the-art peer methods, the proposed method has the best performance when dealing with fault diagnosis tasks for REBs.

Densifi cation of matrix graphite for spherical fuel elements used in molten salt reactor via addition of green pitch coke

Zhao He,Hongchao Zhao,Jinliang Song,Xiaohui Guo,Zhanjun Liu,Yajuan Zhong,T. James Marrow 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.4

Green pitch coke with an average particle size of 2 mm was adopted as densifier and added to the rawmaterials of conventional A3-3 matrix graphite (MG) to prepare modified A3-3 matrix graphite (MMG)by the quasi-isostatic molding method. The structure, mechanical and thermal properties were assessed. Compared with MG, MMG had a more compact structure, and exhibited improved properties of highermechanical strength, higher thermal conductivity and better molten salt barrier performance. Notably,under the same infiltration pressure of 5 atm, the fluoride salt occupation of MMG was only 0.26 wt%,whereas it was 15.82 wt% for MG. The densification effect of green pitch coke endowed MMG withimproved properties for potential use in the spherical fuel elements of molten salt reactor.

CacheSCDefender: VMM-based Comprehensive Framework against Cache-based Side-channel Attacks

( Chao Yang ),( Yunfei Guo ),( Hongchao Hu ),( Wenyan Liu ) 한국인터넷정보학회 2018 KSII Transactions on Internet and Information Syst Vol.12 No.12

Cache-based side-channel attacks have achieved more attention along with the development of cloud computing technologies. However, current host-based mitigation methods either provide bad compatibility with current cloud infrastructure, or turn out too application-specific. Besides, they are defending blindly without any knowledge of on-going attacks. In this work, we present CacheSCDefender, a framework that provides a (Virtual Machine Monitor) VMM-based comprehensive defense framework against all levels of cache attacks. In designing CacheSCDefender, we make three key contributions: (1) an attack-aware framework combining our novel dynamic remapping and traditional cache cleansing, which provides a comprehensive defense against all three cases of cache attacks that we identify in this paper; (2) a new defense method called dynamic remapping which is a developed version of random permutation and is able to deal with two cases of cache attacks; (3) formalization and quantification of security improvement and performance overhead of our defense, which can be applicable to other defense methods. We show that CacheSCDefender is practical for deployment in normal virtualized environment, while providing favorable security guarantee for virtual machines.

Fully Recrystallized Al0.5CoCrFeNi High-Entropy Alloy Strengthened by Nanoscale Precipitates

Haoxue Yang,Jinshan Li,Tong Guo,William Yi Wang,Hongchao Kou,Jun Wang 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.5

The correlation among the strength, ductility and precipitates in a dual-phase Al0.5CoCrFeNihigh-entropy alloy has beeninvestigated. The property of plastic was improved in the recrystallized Al0.5CoCrFeNiHEA prepared as the master alloy. Formation of the stable nanosized L12phases after aging at 650 °C was revealed, along with the lath-like BCC phasesprecipitated in the grain, as the primary contribution of the strength enhancement. Excellent balanced tensile properties atroom temperature were achieved through aging treatment, as the yield strength and ultimate tensile strength show 2.68, 1.63times higher in 650 °C/140 h aged condition than that in initial states, respectively, superior to many high-entropy alloysand conventional alloys.

Experimental study on U-shape flat thermosyphon for thermal management of power battery

Tao Wang,Sicong Tan,Cong Guo,Hongchao Su,Chaohong Guo,Yuyan Jiang 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.9

The paper presents a new type of U-shape flat thermosyphon. The thermosyphon has several unique properties relative to general heat pipe such as compact and simple structure (no wick structure), easily to filling the coolant and flexible plate structure and so on. These properties make it an ideal heat transfer device for battery pack thermal management. In this paper, we experimentally study the thermal management performance of the U-shape flat thermosyphon for a battery module. The temperature of the battery module can be controlled below 50 °C under 1.5 C charge rate (300 W), and below 37 °C under 1 C charge rate (120 W), and the corresponding maximum temperature difference is 3 °C and 7 °C, respectively. And higher power generation is helpful to start-up the U-shape flat thermosyphonand maintain a small temperature difference between different battery cells. The performance of the U-shape flat thermosyphonis evaluated using a thermal resistance network model, which showed that there is uneven distribution of heat transfer in the two side of the heat pipe.