Parameter calibrations and application of micromechanical fracture models of structural steels

Fangfang Liao,Wei Wang,Yiyi Chen 국제구조공학회 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.42 No.2

Micromechanical facture models can be used to predict ductile fracture in steel structures. In order to calibrate the parameters in the micromechanical models for the largely used Q345 steel in China, uniaxial tensile tests, smooth notched tensile tests, cyclic notched bar tests, scanning electron microscope tests and finite element analyses were conducted in this paper. The test specimens were made from base metal, deposit metal and heat affected zone of Q345 steel to investigate crack initiation in welded steel connections. The calibrated parameters for the three different locations of Q345 steel were compared with that of the other seven varieties of structural steels. It indicates that the toughness index parameters in the stress modified critical strain (SMCS) model and the void growth model (VGM) are connected with ductility of the material but have no correlation with the yield strength, ultimate strength or the ratio of ultimate strength to yield strength. While the damage degraded parameters in the degraded significant plastic strain (DSPS) model and the cyclic void growth model (CVGM) and the characteristic length parameter are irrelevant with any properties of the material. The results of this paper can be applied to predict ductile fracture in welded steel connections.

Influence of structural system measures on the dynamic characteristics of a multi-span cable-stayed bridge

Fangfang Geng,Youliang Ding,Hongen Xie,Jianyong Song,Wanheng Li 국제구조공학회 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.52 No.1

A three-dimensional finite element model for the Jiashao Bridge, the longest multi-span cablestayed bridge in the world, is established using the commercial software package ANSYS. Dynamic characteristics of the bridge are analyzed and the effects of structural system measures including the rigid hinge, auxiliary piers and longitudinal constraints between the girders and side towers on the dynamic properties including modal frequency, mode shape and effective mass are studied by referring to the Jiashao Bridge. The analysis results reveal that: (i) the installation of the rigid hinge significantly reduces the modal frequency of the first symmetric lateral bending mode of bridge deck. Moreover, the rigid hinge significantly changes the mode shape and effective mass of the first symmetric torsional mode of bridge deck; (ii) the layout of the auxiliary piers in the side-spans has a limited effect on changing the modal frequencies, mode shapes and effective masses of global vibration modes; (iii) the employment of the longitudinal constraints significantly increases the modal frequencies of the vertical bending modes and lateral bending modes of bridge deck and have significant effects on changing the mode shapes of vertical bending modes and lateral bending modes of bridge deck. Moreover, the effective mass of the first anti-symmetric vertical bending of bridge deck in the longitudinal direction of the fully floating system is significantly larger than that of the partially constrained system and fully constrained system. The results obtained indicate that the structural system measures of the multi-span cable-stayed bridge have a great effect on the dynamic properties, which deserves special attention for seismic design and wind-resistant design of the multi-span cable-stayed bridge.

A Study on Group Buying of O2O Mode using Generalized Stochastic Petri Nets

Fangfang Hou,Shuyun Zhang,Yue Wang 보안공학연구지원센터 2015 International Journal of Smart Home Vol.9 No.3

This paper proposes a Group Buying model (paid in advance) of online-to-offline mode using Generalized Stochastic Petri Nets. As the time cost of consumers is getting higher and higher, time efficiency is getting much more important in all aspects of life, especially in catering industry, and one way that can lead to direct communication between store owners and consumers is Group Buying of online-to-offline mode, the center of which is the brand building and service efficiency. Although researches based on both users’ and sellers’ perspective about online buying are very rich, these findings are not entirely applicable for this new e-commerce model, and most of current research on online-to-offline mode use qualitative methods. More importantly, few researchers have concerned about the efficiency of Group Buying process and come up with related solutions to improve it. By constructing a business model of GB and conducting time efficiency and performance analysis on it, we find that the key transitions of the system only take up less than half of the time before the whole process has been completed. And when we shorten the feedback process, the percentage of finishing consumption in physical store in the whole Group Buying model can be improved by 14.5%. Thus, we suggest that suppliers and sellers should be more focused and efficient in encouraging customers review timely as well as giving consumers feedback as soon as possible, since consumer comments are proved to be significantly important for the retailers. Besides, site operators and store sellers can also use other ways like WeChat and microblogging to promote their site linkages and gain more market share.

Proposal of Approximation Analysis Method for GI/G/1 Queueing System

Fangfang Kong,Ippei Nakase,Ikuo Arizono,Yasuhiko Takemoto 대한산업공학회 2008 Industrial Engineeering & Management Systems Vol.7 No.2

There have been some approximation analysis methods for a GI/G/1 queueing system. As one of them, an approximation technique for the steady-state probability in the GI/G/1 queueing system based on the iteration numerical calculation has been proposed. As another one, an approximation formula of the average queue length in the GI/G/1 queueing system by using the diffusion approximation or the heuristics extended diffusion approximation has been developed. In this article, an approximation technique in order to analyze the GI/G/1 queueing system is considered and then the formulae of both the steady-state probability and the average queue length in the GI/G/1 queueing system are proposed. Through some numerical examples by the proposed technique, the existing approximation methods, and the Monte Carlo simulation, the effectiveness of the proposed approximation technique is verified.

Using Genetic Algorithm for Optimal Security Hardening in Risk Flow Attack Graph

( Fangfang Dai ),( Kangfeng Zheng ),( Binwu ),( Shoushan Luo ) 한국인터넷정보학회 2015 KSII Transactions on Internet and Information Syst Vol.9 No.5

Network environment has been under constant threat from both malicious attackers and inherent vulnerabilities of network infrastructure. Existence of such threats calls for exhaustive vulnerability analyzing to guarantee a secure system. However, due to the diversity of security hazards, analysts have to select from massive alternative hardening strategies, which is laborious and time-consuming. In this paper, we develop an approach to seek for possible hardening strategies and prioritize them to help security analysts to handle the optimal ones. In particular, we apply a Risk Flow Attack Graph (RFAG) to represent network situation and attack scenarios, and analyze them to measure network risk. We also employ a multi-objective genetic algorithm to infer the priority of hardening strategies automatically. Finally, we present some numerical results to show the performance of prioritizing strategies by network risk and hardening cost and illustrate the application of optimal hardening strategy set in typical cases. Our novel approach provides a promising new direction for network and vulnerability analysis to take proper precautions to reduce network risk.

An Active Construction Dynamic Schedule Management Model: Using the Fuzzy Earned Value Management and BP Neural Network

Fangfang Yu,Xiaobo Chen,Clark A. Cory,Zhixuan Yang,Yingwen Hu 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.7

Project schedule management is an important aspect of project management. Earned value management (EVM) and its extension methods are widely adopted in project schedule management in various previous studies, however, most of these studies adopted schedule performance indicators based on definiteness condition and historical data, which ignored the impact of uncertainty and dynamics. So the decision risk in schedule management has been increased dramatically. Therefore, this paper proposed an active construction dynamic schedule management model based on fuzzy earned value management (F-EVM) and BP neural network (BP-NN). Firstly, the fuzzy theory was introduced into EVM to evaluate the schedule performance when the project finish schedule cannot be deterministic expression. Then, the main resource planning was functioned as input variables to predict the schedule in advance through BP-NN. Finally, the future action plans was adjusted based on the results to achieve active control of the project schedule. The case results indicated that the introduction of F-EVM effectively reduced influence of subjective estimation on uncertainty in the data measurement process. And the proposed dynamic schedule management model gave a 32.06% better mean absolute percentage error (MAPE) than the existing methods for estimated project duration. Hence, the proposed model provided a more accurate estimation of the project duration and considered the uncertainty and dynamics of the construction project, thereby achieving more effective management of project schedule.

Biocompatibility of Nanoscale Hydroxyapatite-embedded Chitosan Films

Fangfang Sun,고광락,류수착,한동욱,이재범 대한화학회 2012 Bulletin of the Korean Chemical Society Vol.33 No.12

In order to improve the bioactivity and mechanical properties of hydroxyapatite (HAp), chitosan (Chi) was in situ combined into HAp to fabricate a composite scaffold by a sublimation-assisted compression method. A highly porous film with sufficient mechanical strength was prepared and the bioactivity was investigated by examining the apatite formed on the scaffolds incubated in simulated body fluid. In addition, the cytotoxicity of the HAp/Chi composite was studied by evaluating the viability of murine fibroblasts (L-929 cells) exposed to diluted extracts of the composite films. The apatite layer was assessed using scanning electronic microscopy, inductively coupled plasma-optical emission spectrometry and weight measurement. Composite analysis showed that a layer of micro-sized, needle-like crystals was formed on the surface of the composite film. Additionally, the WST-8 assay after L-929 cells were exposed to diluted extracts of the composite indicated that the HAp/Chi scaffold has good in vitro cytocompatibility. The results indicated that HAp/Chi composites with porous structure are promising scaffolding materials for bone-patch engineering because their porous morphology can provide an environment conductive to attachment and growth of osteoblasts and osteogenic cells.

Consumption of Oxidized Soybean Oil Increased Intestinal Oxidative Stress and Affected Intestinal Immune Variables in Yellow-feathered Broilers

Fangfang Liang,Shouqun Jiang,Yi Mo,Guilian Zhou,Lin Yang 아세아·태평양축산학회 2015 Animal Bioscience Vol.28 No.8

This study investigated the effect of oxidized soybean oil in the diet of young chickens on growth performance and intestinal oxidative stress, and indices of intestinal immune function. Corn-soybean-based diets containing 2% mixtures of fresh and oxidized soybean oil provided 6 levels (0.15, 1.01, 3.14, 4.95, 7.05, and 8.97 meqO2/kg) of peroxide value (POV) in the diets. Each dietary treatment, fed for 22 d, had 6 replicates, each containing 30 birds (n = 1,080). Increasing POV levels reduced average daily feed intake (ADFI) of the broilers during d 1 to 10, body weight and average daily gain at d 22 but did not affect overall ADFI. Concentrations of malondialdehyde (MDA) increased in plasma and jejunum as POV increased but total antioxidative capacity (T-AOC) declined in plasma and jejunum. Catalase (CAT) activity declined in plasma and jejunum as did plasma glutathione S-transferase (GST). Effects were apparent at POV exceeding 3.14 meqO2/kg for early ADFI and MDA in jejunum, and POV exceeding 1.01 meqO2/kg for CAT in plasma and jejunum, GST in plasma and T-AOC in jejunum. Relative jejunal abundance of nuclear factor kappa B (NF-κB) P50 and NF-κB P65 increased as dietary POV increased. Increasing POV levels reduced the jejunal concentrations of secretory immunoglobulin A and cluster of differentiation (CD) 4 and CD8 molecules with differences from controls apparent at dietary POV of 3.14 to 4.95 meqO2/kg. These findings indicated that growth performance, feed intake, and the local immune system of the small intestine were compromised by oxidative stress when young broilers were fed moderately oxidized soybean oil.

A New Approach to Distributed Control for Multi-agent Systems Based on Approximate Upper and Lower Bounds

Fangfang Zhang,Jinfeng Gao,Huanshui Zhang,Cheng Tan,Wei Wang 제어·로봇·시스템학회 2017 International Journal of Control, Automation, and Vol.15 No.6

In this paper, the distributed control of the LQR problem for continuous-time multi-agent systems isconsidered. Based on the centralized optimal control, we prove that the solution of the algebraic Riccati equationis the maximal solution of the algebraic Riccati inequality. The algebraic relations of the solutions of the algebraicRiccati equations for different weighted matrices are shown and two distributed controllers are designed: the fullydistributed one and the interconnected distributed one. They can provide an upper bounds and a lower bounds ofthe centralized optimal cost function. The optimal closed-loop feedback control systems for the two distributedcontrollers are also asymptotically stable. Some examples are given to show the correctness of the proposed results.

Experimental Study on Mechanical Performance and Microstructure of Polypropylene Fiber Recycled Concrete

Fangfang Wei,Liping Li,Yu Zhu,Youzheng Zhao 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.7

Recycled concrete reinforced by polypropylene fibers boosts an alternative sustainable solution to address the need of reusing waste concrete. This paper reports experimental and analytical studies of static and dynamic comprehensive behavior on recycled concrete specimens reinforced with different contents of polypropylene fiber (PPF). Electro-hydraulic pressure testing was used to obtain static compressive strength, whereas 74 mm diameter Split HopkinsonPressure Bar (SHPB) was applied for dynamic impact compression tests at four strain rates. In addition, the reinforcing mechanism of polypropylene fiber on recycled concrete was analyzed of the micro-structure through Scanning Electron Microscope (SEM). Finally, ANSYS/LS-DYNA was applied for the simulation of the SHPB test, which was validated by good agreements of the stress waveform and failure modes of the fiber-reinforced recycled concrete specimen during the impact test. It appears that polypropylene fiber can optimize the microscopic pore structure inside the concrete, thus effectively improving the mechanical properties of recycled concrete which were originally defected by recycled aggregate. Also, higher strain rates significantly increase dynamic compressive strength as well as impact toughness. This study shows that the optimal content of polypropylene fiber in recycled concrete is 0.1% − 0.2%. The numerical simulation by ANSYS/LS-DYNA further proved that the HOLMQUIST-JOHNSON-COOK (HJC) constitutive model can better reflect the dynamic performance of concrete.