Dislocation Density-Based Constitutive Model and Processing Map for T2 Copper During Isothermal and Time-Variant Deformation

Gang Chen,Yu Jin,Jing Wang,Cheng Zhang,Qiang Chen,Hongming Zhang,Xingjian Zhao,Zhiyong Li,Changhai Xie,Zhiming Du 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.9

Isothermal compression tests were carried out to study the hot deformation behavior of T2 copper under various conditions. The deformation parameters, such as temperature and strain rate, have strong influence on flow stress and microstructureevolution of the alloy. A unified dislocation density-based model considering dynamic recovery and recrystallization wasestablished. And material parameters of the developed model were optimized by genetic algorithm. Comparisons betweenthe experimental and model data demonstrates that the developed model can precisely describe the flow behavior at quitewide range of deformation conditions. Meanwhile, the designed iterative procedure allows the model to be applied in timevariantdeformation conditions. Processing map and microstructure examination were constructed to optimize the processingwindow of the studied alloy. According to the processing maps, flow instability mainly appeared at low temperatures of500–650 °C and strain rates higher than 0.1 s−1. The optimum deformation parameters of T2 copper was concluded as thetemperature range of 700–800 °C and the strain rate of 0.1–1 s−1.

Moderate tetrabasic zinc chloride supplementation improves growth performance and reduces diarrhea incidence in weaned pigs

Zhang, Gang,Xia, Tian,Zhao, Jinbiao,Liu, Ling,He, Pingli,Zhang, Shuai,Zhang, Liying Asian Australasian Association of Animal Productio 2020 Animal Bioscience Vol.33 No.2

Objective: Two experiments were conducted to evaluate tetrabasic zinc chloride (TBZC) on the health of weaned pigs, and to determine the optimal supplemental concentrations and whether dietary TBZC could replace the pharmacological concentrations of dietary zinc oxide (ZnO) to improve growth performance and decrease Zn excretion in weaned pigs. Methods: In Exp. 1, 180 weaned pigs (8.92±1.05 kg body weight [BW]) were randomly assigned to 1 of 5 treatments, including the basal diet containing 125 mg/kg zinc sulfate (ZnSO₄), and the basal diet with 1,200, 1,800, 2,400, or 3,000 mg/kg TBZC supplementation. In Exp. 2, 240 weaned pigs (7.66±1.09 kg BW) were randomly assigned to 1 of 5 treatments, including a negative control diet without Zn supplementation, a positive control diet (2,250 mg/kg ZnO), and 3 experimental diets with different concentrations of TBZC supplementation (1,000, 1,250, and 1,500 mg/kg). Results: In Exp. 1, the average daily gain (ADG), feed efficiency (G:F) and diarrhea incidence responded quadratically (p<0.01) as the TBZC supplemental concentrations increased, and pigs fed 1,200 and 1,800 mg/kg TBZC showed the best growth performance. Moreover, 1,800 mg/kg TBZC supplementation showed the greatest (p<0.01) total antioxidant capacity and glutathione peroxidase activities in liver of pigs. Histopathological examination revealed lesions in heart, liver, lung and kidney, and mild or severe histological lesions mainly occurred with the supplementation of 2,400 and 3,000 mg/kg TBZC. In Exp. 2, 1,000 and 1,250 mg/kg TBZC supplementation in diets significantly (p<0.01) increased ADG and G:F of weaned pigs, reduced Zn excretion in feces, and had no effect on diarrhea-reducing compared to 2,250 mg/kg ZnO supplementation. Conclusion: The TBZC is a potential alternative to ZnO. The recommended concentration of TBZC in weaned pig diets is 1,000 to 1,250 mg/kg.

Evaluating fire resistance of prestressed concrete bridge girders

Gang Zhang,Venkatesh Kodur,Wei Hou,Shuanhai He 국제구조공학회 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.62 No.6

This paper presents an approach for evaluating performance of prestressed concrete (PC) bridge girders exposed to fire. A finite element based numerical model for tracing the response of fire exposed T girders is developed in ANSYS. The analysis is carried out in three stages, namely, fire temperature calculation, cross sectional temperature evaluation, and then strength, deformation and effective prestress analysis on girders exposed to elevated temperatures. The applicability of the computer program in tracing the response of PC bridge girders from the initial preloading stage to failure stage, due to combined effects of fire and structure loading, is demonstrated through a case study, and validated by test data of a scaled PC box girder under ISO834 fire condition. Results from the case study show that fire severity has a significant influence on the fire resistance of PC T girders and hydrocarbon fire is most dangerous for the girder. The prestress loss caused by elevated temperature is about 10% under hydrocarbon fire till the girder failure, which can lead to the increase in deflection of the PC girder. The rate of deflection failure criterion is suggested to determine the failure of PC T girder under fire.

Behavior of composite box bridge girders under localized fire exposure conditions

Gang Zhang,Venkatesh Kodur,Weifa Yao,Qiao Huang 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.69 No.2

This paper presents results from experimental and numerical studies on the response of steel-concrete composite box bridge girders under certain localized fire exposure conditions. Two composite box bridge girders, a simply supported girder and a continuous girder respectively, were tested under simultaneous loading and fire exposure. The simply supported girder was exposed to fire over 40% of its span length in the middle zone, and the two-span continuous girder was exposed to fire over 38% of its length of the first span and full length of the second span. A measurement method based on comparative rate of deflection was provided to predict the failure time in the hogging moment zone of continuous composite box bridge girders under certain localized fire exposure condition. Parameters including transverse and longitudinal stiffeners and fire scenarios were introduced to investigate fire resistance of the composite box bridge girders. Test results show that failure of the simply supported girder is governed by the deflection limit state, whereas failure of the continuous girder occurs through bending buckling of the web and bottom slab in the hogging moment zone. Deflection based criterion may not be reliable in evaluating failure of continuous composite box bridge girder under certain fire exposure condition. The fire resistance (failure time) of the continuous girder is higher than that of the simply supported girder. Data from fire tests is successfully utilized to validate a finite element based numerical model for further investigating the response of composite box bridge girders exposed to localized fire. Results from numerical analysis show that fire resistance of composite box bridge girders can be highly influenced by the spacing of longitudinal stiffeners and fire severity. The continuous composite box bridge girder with closer longitudinal stiffeners has better fire resistance than the simply composite box bridge girder. It is concluded that the fire resistance of continuous composite box bridge girders can be significantly enhanced by preventing the hogging moment zone from exposure to fire. Longitudinal stiffeners with closer spacing can enhance fire resistance of composite box bridge girders. The increase of transverse stiffeners has no significant effect on fire resistance of composite box bridge girders.

Predictive Current Control of Four-Quadrant Converters Based on Specific Sampling Method and Modified Z-Transform

Gang Zhang,Jianglin Qian,Zhigang Liu,Zhongbei Tian 전력전자학회 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.1

Four-quadrant converters (4QCs) are widely used as AC-DC power conversion interfaces in many areas. A control delaycommonly exists in the digital implementation process of 4QCs, especially for high power 4QCs with a low switching frequency. This usually results in alternating current distortion, increased current harmonic content and system instability. In this paper, thecontrol delay is divided into a computation delay and a PWM delay. The impact of the control delay on the performance of a4QC is briefly analyzed. To obtain a fundamental value of AC current that is as accurately as possible, a specific samplingmethod considering the PWM pattern is introduced. Then a current predictive control based on a modified z-transform isproposed, which is effective in reducing the control delay and easy in terms of digital implementation. In addition, it does notdepend on object models and parameters. The feasibility and effectiveness of the proposed predictive current control method isverified by simulation and experimental results.

Effect of Heat Treatments on Microstructures and Tensile Properties of Cu–3 wt%Ag–0.5 wt%Zr Alloy

Gang Chen,ChuanJie Wang,Ying Zhang,Cen Yi,Peng Zhang 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.2

The microstructures and tensile properties of Cu–3 wt%Ag–0.5 wt%Zr alloy sheets under different aging treatments areinvestigated in this research. As one kind of precipitate, Ag nanoparticles with coherent orientation relationship with matrixprecipitate. However, after the peak-age point, most of Ag nanoparticles grow into short rod shape with the interface translatingto semi-coherent, which leads to the lower strength of over-aging sample. The yield strength is estimated by consideringsolid solute, grain boundary and precipitation strengthening mechanisms. The result shows that the Ag precipitates providethe main strengthening role. Then a constitutive equation representing the evolution of dislocation density with plastic strainis built by considering work-hardening behavior coming from shearable and non-shearable precipitates which is mainly theparticles containing Zr. The flow stress contributed by shearable particle hardening is higher than that of non-shearable one. Due to the coarsening of grain boundary precipitates and low rate of damage accumulation of these non-shearable particles,the micro-cracks nucleate easily at grain boundary which leads to intergranular fracture.

Thermo-mechanical behavior of prestressed concrete box girder at hydration age

Gang Zhang,Meichun Zhu,Shuanhai He,Wei Hou 사단법인 한국계산역학회 2017 Computers and Concrete, An International Journal Vol.20 No.5

Excessively elevated temperature can lead to cracks in prestressed concrete (PC) continuous bridge with box girder on the pier top at cement hydration age. This paper presents a case study for evaluating the behavior of PC box girder during the early hydration age using a two-stage computational model, in the form of computer program ANSYS, namely, 3-D temperature evaluation and determination of mechanical response in PC box girders. A numerical model considering time-dependent wind speed and ambient temperature in ANSYS for tracing the thermal and mechanical response of box girder is developed. The predicted results were compared to show good agreement with the measured data from the PC box girder of the Zhaoshi Bridge in China. Then, based on the validated numerical model three parameters were incorporated to analyze the evolution of the temperature and stress within box girder caused by cement hydration heat. The results of case study indicate that the wind speed can change the degradation history of temperature and stress and reduce peak value of them. The initial casting temperature of concrete is the most significant parameter which controls cracking of PC box girder on pier top at cement hydration age. Increasing the curing temperature is detrimental to prevent cracking.

Research on the Performance for Two Kinds of Topology of Constant Current Regulator of Navigational Lighting Aid

Zhang Gang,Zhu Jianqu,Liu Zhonghao 보안공학연구지원센터 2016 International Journal of Multimedia and Ubiquitous Vol.11 No.9

Construction and Application of Effective Path Statistics Network

Gang Zhang,Qing-Kui Chen 보안공학연구지원센터 2015 International Journal of Hybrid Information Techno Vol.8 No.9

The Internet has dynamic change nature and the resources limitation that cause the loss of some commands, and thus the failure of group command transmission in the course of transmitting. On account of this, the paper presents Effective Path Statistics Network (EPSN), converting the group command transmission based on the Internet into the one based on EPSN. It describes the definition, construction and working principle of EPSN, and further conducts sampling and analyzing of metrics according to it. Based on the result the paper illustrates modeling and calculating of group command transmission. The experiments show that EPSN can effectively relieve the negative effect caused by the Internet dynamic change nature and the resources limitation.

Secure and Fine-grained Electricity Consumption Aggregation Scheme for Smart Grid

( Gang Shen ),( Yixin Su ),( Danhong Zhang ),( Huajun Zhang ),( Binyu Xiong ),( Mingwu Zhang ) 한국인터넷정보학회 2018 KSII Transactions on Internet and Information Syst Vol.12 No.4

Currently, many of schemes for smart grid data aggregation are based on a one-level gateway (GW) topology. Since the data aggregation granularity in this topology is too single, the control center (CC) is unable to obtain more fine-grained data aggregation results for better monitoring smart grid. To improve this issue, Shen et al. propose an efficient privacy-preserving cube-data aggregation scheme in which the system model consists of two-level GW. However, a risk exists in their scheme that attacker could forge the signature by using leaked signing keys. In this paper, we propose a secure and fine-grained electricity consumption aggregation scheme for smart grid, which employs the homomorphic encryption to implement privacy-preserving aggregation of users’ electricity consumption in the two-level GW smart grid. In our scheme, CC can achieve a flexible electricity regulation by obtaining data aggregation results of various granularities. In addition, our scheme uses the forward-secure signature with backward-secure detection (FSBD) technique to ensure the forward-backward secrecy of the signing keys. Security analysis and experimental results demonstrate that the proposed scheme can achieve forward-backward security of user’s electricity consumption signature. Compared with related schemes, our scheme is more secure and efficient.