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30 Years of experience in operating the BN-600 sodium-cooled fast reactor
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Baseline serum 25-hydroxy vitamin D is predictive of future glycemic status and insulin resistance: the Medical Research Council Ely Prospective Study 1990-2000
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중화인민공화국 2001년 修正 혼인법
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The Function of style
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- 저자 : Fan Xiangqian (검색결과 5 건)
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Damage and fracture processes of concrete using acoustic emission parameters
Fan Xiangqian,Hu Shaowei,Lu Jun 사단법인 한국계산역학회 2016 Computers and Concrete, An International Journal Vol.18 No.2
In order to observe the internal damage of concrete in real time, we introduced acoustic emission nondestructive detecting technology into a series of fracture tests; the test results revealed the whole process that concrete undergoes when it sustains damage that leads to failure, according to the change rules of the acoustic emission parameters. The results showed that both the initiation and unstable loads can be accurately determined using the abrupt change of the acoustic emission rate curves and the turning point of the acoustic emission parameters’ accumulative curves. The whole process, from damage to failure, includes five phases, beginning with damage, such as cracking, a stable crack growth process, a critical unstable stage, and unstable propagation. The brittle fracture characteristics of concrete change when steel bars are joined, because the steel bars and the concrete structure bond, which causes an increase in the acoustic emission signals within the fracture process of the reinforced concrete. The unstable propagation stage is also extended. Our research results provide a valid methodology and technical explanations, which can help researchers to monitor the cracking process of concrete structures, in real time, during actual projects.
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Zhengliang Li,Wenliang Fan,Runyu Liu,Xiangqian Sheng 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.12
Estimation of statistical moments of structural response effectively and accurately is still one of the main topics for analysis of random systems. For the sake of reducing function evaluations to alleviate curse of dimensionality and improve the accuracy in moment estimation, a generalized anisotropic sparse grid integral based on the adaptive high dimensional model representation and appropriate reference variables is proposed. By introducing different transformations, a system with general variables is transformed into the one with appropriate independent reference variables and a generalized anisotropic sparse grid integral will be presented for moment estimation. Then, anisotropic sparse grid collections should be divided into several mutually exclusive sub-collections and the generalized anisotropic sparse grid integral (SGI) can be remodeled in a new form. With this new form, the adaptive high dimensional model representation can be introduced for function evaluations conveniently, which can be regarded as an alternative way to evaluate functions precisely and efficiently without any approximation. Finally, several examples are presented to demonstrate the effectiveness and accuracy of the proposed method.
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Analysis of notch depth and loading rate effects on crack growth in concrete by FE and DIC
Xiangyi Zhu,Xudong Chen,Jun Lu,Xiangqian Fan 사단법인 한국계산역학회 2019 Computers and Concrete, An International Journal Vol.24 No.6
In this paper, the fracture characteristics of concrete specimens with different notch depths under three-point flexural loads are studied by finite element and fracture mechanics methods. Firstly, the concrete beams (the size is 700×100×150 mm) with different notch depths (a=30 mm, 45 mm, 60 mm and 75 mm respectively) are tested to study the influence of notch depths on the mechanical properties of concrete. Subsequently, the concrete beams with notch depth of 60 mm are loaded at different loading rates to study the influence of loading rates on the fracture characteristics, and digital image correlation (DIC) is used to monitor the strain nephogram at different loading rates. The test results show that the flexural characteristics of the beams are influenced by notch depths, and the bearing capacity and ductility of the concrete decrease with the increase of notch depths. Moreover, the peak load of concrete beam gradually increases with the increase of loading rate. Then, the fracture energy of the beams is accurately calculated by tail-modeling method and the bilinear softening constitutive model of fracture behavior is determined by using the modified fracture energy. Finally, the bilinear softening constitutive function is embedded into the finite element (FE) model for numerical simulation. Through the comparison of the test results and finite element analysis, the bilinear softening model determined by the tail-modeling method can be used to predict the fracture behavior of concrete beams under different notch depths and loading rates.
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Mechanical properties of pervious concrete with recycled aggregate
Xiangyi Zhu,Xudong Chen,Nan Shen,Huaxuan Tian,Xiangqian Fan,Jun Lu 사단법인 한국계산역학회 2018 Computers and Concrete, An International Journal Vol.21 No.6
In order to research the influence of different recycled aggregate contents on the mechanical properties of pervious concrete, the experimental study and numerical simulation analysis of the mechanical properties of pervious concrete with five kinds of recycled aggregates contents (0%, 25%, 50%, 75% and 100%) are carried out in this paper. The experimental test were first performed on concrete specimens of different sizes in order to determine the influence of recycled aggregate on the compressive strength and splitting tensile strength, direct tension strength and bending strength. Then, the development of the internal cracks of pervious concrete under different working conditions is studied more intuitively by PFC3D. The experimental results show that the concrete compressive strength, tensile strength and bending strength decrease with the increase of the recycled aggregate contents. This trend of reduction is not only related to the brittleness of recycled aggregate concrete, but also to the weak viscosity of recycled aggregate and cement paste. It is found that the fracture surface of pervious concrete with recycled aggregate is smoother than that of natural aggregate pervious concrete by PFC3D, which means that the bridging effect is weakened in the stress transfer between the left and right sides of the crack. Through the analysis of the development of the internal cracks, the recycled aggregate concrete generated more cracks than the natural aggregate concrete, which means that the recycled aggregate concrete is easier to form a coalescence fracture surface and eventually break.
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Compressive behavior of concrete under high strain rates after freeze-thaw cycles
Xudong Chen,Chen Chen,Zhiheng Liu,Jun Lu,Xiangqian Fan 사단법인 한국계산역학회 2018 Computers and Concrete, An International Journal Vol.21 No.2
The dynamic compressive behavior of concrete after freezing and thawing tests are investigated by using the split Hopkinson pressure bar (SHPB) technique. The stress-strain curves of concrete under dynamic loading are measured and analyzed. The setting numbers of freeze-thaw cycles are 0, 25, 50, and 75 cycles. Test results show that the dynamic strength decreases and peak strain increases with the increasing of freeze-thaw cycles. Based on theWeibull distribution model, statistical damage constitutive model for dynamic stress-strain response of concrete after freeze-thaw cycles was proposed. At last, the fragmentation test of concrete subjected to dynamic loading and freeze-thaw cycles is carried out using sieving statistics. The distributions of the fragment sizes are analyzed based on fractal theory. The fractal dimensions of concrete increase with the increasing of both freeze-thaw cycle and strain rate. The relations among the fractal dimension, strain rates and freeze-thawing cycles are developed.
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