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- 저자 : Yaoyao Meng (검색결과 4 건)
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Yaoyao Meng,Hongwen Jing,Qian Yin,Xiaowei Gu 대한토목학회 2020 KSCE JOURNAL OF CIVIL ENGINEERING Vol.24 No.11
The cyclic wetting-drying phenomenon is a complicated physical and chemical process. This kind of process will weaken the properties of rock to some extent. Some fundamental physical parameters of sandstone were first tested to study the weakening influence of wetting-drying cycles on the physical characteristics. Then, the water weakening effect on the mechanical and acoustic emission (AE) characteristics of rock on account of wetting-drying cycles was experimentally studied. Laboratory test results showed that when the number of cycles increased from 0 to 25, the density, P-wave velocity, uniaxial compressive strength (UCS), (elastic modulus (E)) and total AE counts of the rock specimens continuously decreased. However, the water absorption would increase as the number of cycles increased. The functional relationships between the total AE counts and the mechanical parameters (UCS and E) of sandstone after each cyclic number were established based on the test results. In addition, the chemical components and microstructure variations of rock undergoing wetting-drying cycles were examined. From the results, it can be concluded that microcrack growth and expansion inside the rocks undergoing wetting-drying cycles are the main reasons for the attenuation of the rock properties. Moreover, with increasing loading rate, the UCS, E and total AE counts of sandstone after each cyclic number would increase.
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Shaowei Lu,Yaoyao Bai,Jijie Wang,Dandan Chen,Keming Ma,Qingshi Meng,Xinmin Liu 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2019 NANO Vol.14 No.6
As the portable device hardware has been increasing at a noticeable rate, ultrathin flexible materials with the combination of high thermal conductivity and excellent electromagnetic interference (EMI) shielding performance are urgently needed. Here, we fabricated ethylene propylene diene monomer rubber with different loading graphene nanoplatelets (GnPs/EPDM) by a cost-efficient approach, which combines mixing, ultrasonication and compression. Further investigation demonstrates that the 8 wt.% GnPs/EPDM with only 0.3 mm in thickness shows excellent electrical conductivity (28.3 S/m), thermal conductivity (0.79 W/mK) and good mechanical properties. Besides, the 8 wt.% GnPs/EPDM exhibits an EMI shielding effectiveness (SE) up to 33 dB in the X-band (8.2–12.4 GHz) and 35 dB in the Ku-band (12.4–18 GHz), superior to most of the reported rubber matrix. Additionally, the GnPs/EPDM shows excellent flexibility and stability with 95% and 94% retention of EMI SE even after repeated bending for 5000 times and corrosion (under 5% NaCl environment) for a week. Our flexible EMI shielding material will benefit the fast-growing next-generation commercial portable flexible electrons.
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Case Study of Modified H–B Strength Criterion in Discrimination of Surrounding Rock Loose Circle
Rui Wang,Xianghui Deng,Yaoyao Meng,Dongyang Yuan,Daohong Xia 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.3
Intermediate principal stress is a significant factor when calculate to determine the surrounding rock loose circles. Based on it, this paper is trying to modify the Hoek–Brown strength criterion, and put forwards a theoretical formula of the loose circle radius. The theoretical formula is applied to Shimen Tunnel, and a comparative analysis between theoretical calculations and field test results is conducted. Here are the results as follows: 1) With an increase of intermediate principal stress, the strength of the rock mass increases and the surrounding rock becomes more difficult to break. Consequently, loose circle thickness is gradually reduced and forms a significant negative linear relationship with the Lode parameter. 2) The results indicate that with a decrease of surrounding rock level in a three-lane hard rock tunnel, the radius of the loose circle increases continuously. 3) The results of the field acoustic wave test show that the theoretical calculation values are consistent with the field measurement results. According to above analysis, the deduced formula is feasible.
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Hanxiang Liu,Hongwen Jing,Qian Yin,Zhenlong Zhao,Yaoyao Meng,Liang Zhang 대한토목학회 2023 KSCE JOURNAL OF CIVIL ENGINEERING Vol.27 No.2
In this paper, the effects of thermal treatment on the mechanical properties, fracturecharacteristics, and roughness of the fracture surface of granite under the Brazilian splitting testare studied using an electro-hydraulic servo testing machine with an acoustic emission (AE)and digital image correlation (DIC) system. The test results show that: 1) Thermal treatmentdegrades the physical and mechanical properties. Density, P-wave velocity, and peak load ofgranite decrease with the increase in thermal treatment temperature (T). 2) With the increasing T,the fracture pattern changes from “I” type tensile fractures to “Y” type tensile-shear mixedfailure. The DIC results show that the fracture process changes from transient to progressive. 3) AE counts show that granite gradually changes from brittleness to ductility with the increaseof T. Furthermore, the variations in the RA and AF values of the AE events indicate that theincreasing T leads to an increase in shear cracks in granite. After the test, 4) the roughness ofthe fracture surface of the specimen was analyzed using a spatial digitizer. The results showthat thermal treatment significantly improved the fracture surface's asperity height androughness. 5) Scanning electron microscopy (SEM) results revealed that thermal treatmentleads to the generation of micro-cracks in granite and the desquamation of mineral grains,which influences the macro properties of granite.
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