Strain rate dependent behaviors of a hot isotropically processed Ti-6Al-4V: Mechanisms and material model

Xiaohan Tang,Mingfa Ren,Fanzi Bu,Guoqing Chen,Gang Li,Tong Li 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.2

Split-Hopkinson pressure bar (SHPB) was adopted to study the dynamic response of a specifically designed Hot isotropically processed (HIP) Casting Titanium alloy (Ti-6Al-4V). The strain-stress curves were obtained in a range of strain rate (10 -3 ~2.6×10 3 /s) to study the constitutive relationships and the Johnson-Cook model is developed to describe this dynamic constitutive law. It can be found that the static microstructure of this specific HIP casting Ti-6Al-4V is lamellar structure. When the loading increases (strain rate higher than 10 3 /s), this lamellar structure changes to basket weave structure, which further changes the mechanical strength and plasticity.

Lowest Instrumented Vertebra at L3 Versus L4 in Posterior Fusion for Moderate Lenke 5C Type Adolescent Idiopathic Scoliosis: A Case-Match Radiological Study

Zhiyi Li,You Du,Yiwei Zhao,Guanfeng Lin,Haoran Zhang,Chenkai Li,Xiaohan Ye,Yang Yang,Shengru Wang,Jianguo Zhang 대한척추신경외과학회 2023 Neurospine Vol.20 No.4

Objective: To compare the radiological outcomes in Lenke 5C type patients whose lowest instrumented vertebra (LIV) was L3 or L4 in a case-match study. Methods: We conducted a retrospective case-match study and included 82 patients in the study. Radiological results before surgery, after surgery, and at last follow-up were recorded and analyzed in the L3 and L4 groups. Results: After matching the age, Risser’s sign, sex, and main Cobb, 41 pairs of patients were enrolled in our study. The total fusion segments in the L3 group (median [interquartile range]: 5.0 [6.0–5.0]) were shorter than those in the L4 group (6.0 [6.5–6.0]). The main curve was significantly corrected after surgery in both groups, and was comparable at the last followup between groups. In addition, according to the results of Fisher precision probability test, there was no significant difference of coronal or sagittal imbalance between the 2 groups at the 2-year follow-up. Conclusion: The correction in coronal and sagittal planes in L3 group and L4 group remains similar. On account of more motion segments, L3 could be an ideal choice as LIV in moderate Lenke 5C type AIS. Long-term follow-up is needed to evaluate the effect of larger compensatory lumbar-sacral curve when stopping at L3.

The Last Call

Xiaohan Teng,Qingxia Li,Libo Tang 한국콘텐츠학회 2017 ICCC International Digital Design Invitation Exhib Vol.2017 No.8

Elasto-plastic time history analysis of an asymmetrical twin-tower rigid-connected structure

Xiaohan Wu,Yanfei Sun,Mingzhuo Rui,Min Yan,Lishu Li,Dongze Liu 사단법인 한국계산역학회 2013 Computers and Concrete, An International Journal Vol.12 No.2

The structure analyzed in this paper has particular building style and special structural system. It is a rigid-connected twin-tower skyscraper with asymmetrical distribution of stiffness and masses in two towers. Because of the different stiffness between the north and the south towers, the torsion seismic vibration is significant. In this paper, in order to study the seismic response of the structure under both frequent low-intensity earthquakes as well as rare earthquakes at the levels of intensity 7, the analysis model is built and analyzed with NosaCAD. NosaCAD is an nonlinear structure analysis software based on second-development of AutoCAD with ObjectARX. It has convenient modeling function, high computational efficiency and diversity post-processing functions. The deformations, forces and damages of the structure are investigated based on the analysis. According to the analysis, there is no damage on the structure under frequent earthquakes, and the structure has sufficient capacity and ductility to resist rare earthquakes. Therefore the structure can reach the goal of no damage under frequent earthquakes and no collapse under rare earthquakes. The deformation of the structure is below the limit in Chinese code. The time sequence and distribution of damages on tubes are reasonable, which can dissipate some dynamic energy. At last, according to forces, load-carrying capacity and damage of elements, there are some suggestions on increasing the reinforcement in the core tube at base and in stiffened stories.

Analysis of Security Policy in Practical Internet Coordinates

Xiaohan Zhao,Xiaoxiao Song,Xiao Wang,Yang Chen,Beixing Deng,Xing Li 보안공학연구지원센터 2009 International Journal of Security and Its Applicat Vol.3 No.1

Network Coordinate (NC) System is an effective mechanism to predict network delay with limited measure overhead. As one of the representative NC systems, Practical Internet Coordinates (PIC) has proposed a security policy based on triangle inequality to defend malicious nodes in the system. However, there is a natural phenomena that nodes may violate triangle inequality in Internet. Thus, the performance of PIC security policy is worthy to be well researched under different attacks. In this paper, we analyze the security policy in PIC in three real network delay data sets and compare PIC with security to without security under four typical attacks. The experimental results in this paper demonstrate that PIC is vulnerable to attacks while more TIVs will cause higher relative error of PIC. Moreover, under attacks by more than 40% malicious nodes, the performance of PIC with security policy could barely be better than PIC without security. Even Colluding Isolate attack will result in worse performance in PIC having security policy.

Elasto-plastic time history analysis of a 117-story high structure

Xiaohan Wu,Yimiao Li,Yunlei Zhang 사단법인 한국계산역학회 2017 Computers and Concrete, An International Journal Vol.19 No.1

In Chinese Design Codes, for super high-rise buildings with complex structural distribution, which are regarded as code-exceeding buildings, elasto-plastic time history analysis is needed to validate the requirement of “no collapse under rare earthquake”. In this paper, a 117-story super high-rise building is discussed. It has a height of 597 m and a height-width ratio of 9.5, which have both exceeded the limitations stipulated by the Chinese Design Codes. Mega columns adopted in this structure have cross section area of about 45 m2 at the bottom, which is infrequent in practical projects. NosaCAD and Perform-3D, both widely used in nonlinear analyses, were chosen in this study, with which two model were established and analyzed, respectively. Elasto-plastic time history analysis was conducted to look into its seismic behavior, emphasizing on the stress state and deformation abilities under intensive seismic excitation.From the comparisons on the results under rare earthquake obtained from NosaCAD and Perform-3D, the overall responses such as roof displacement, inter story drift, base shear and damage pattern of the whole structure from each software show agreement to an extent. Besides, the deformation of the structure is below the limitation of the Chinese Codes, the time sequence and distribution of damages on core tubes are reasonable, and can dissipate certain inputted energy, which indicates that the structure can meet the requirement of “no collapse under rare earthquake”.

A study on effects of water-cement ratio and crack width on chloride ion transmission rate in concrete

Yue Li,Xiaohan Chen,Guosheng Zhang 사단법인 한국계산역학회 2017 Computers and Concrete, An International Journal Vol.19 No.4

To study the effects of water-cement ratio changes and cracks on chloride ion transmission rate in cracked concrete, RCM method was adopted to accelerate the diffusion of chloride ion in cracked concrete, and the changes in chloride ion concentration and around the cracks are inferred by finite-element method. The test results show that as far as prefabricated cracks on concrete components are concerned, the width thresholds of two cracks on the concrete specimens with a water-cement ratio of 0.5 and 0.6 are 0.05 mm and 0.1 mm respectively, the width threshold of two cracks on the concrete specimens with a water-cement ratio of 0.4 is 0.05 mm and 0.2 mm respectively; and the results of numerical simulation show that the smaller the water-cement ratio is, the more significant effects of cracks on chloride ion transmission rate are. As a result, more attention shall be paid to the crack prevention, repairing and strengthening for high-strength concrete.

Research on Two-stage Isolated Dual Output Port On-board Charging System

Zhou Kai,Li Xiaohan,Song Hao 대한전기학회 2024 Journal of Electrical Engineering & Technology Vol.19 No.5

This paper proposes a two-stage isolated dual output port on-board charging system, which consists of a front-stage power factor correction (PFC) converter and a rear-stage DC/DC converter. The front-stage circuit adopts a double diode bridgeless PFC and the rear-stage circuit adopts a CLLC resonant converter. A three-winding transformer is used to magnetically couple the power grid input terminal, high-voltage battery, and low-voltage battery. The fundamental wave analysis method is then used to determine the voltage gain characteristics, and the parameters of the converter power components are chosen based on the system indicators. The front-stage PFC converter uses the average current control method with a double closed loop structure, which is composed of a voltage outer loop and a current inner loop. The rear-stage DC/DC converter combines the pulse frequency modulation (PFM) and phase shift (PS) control, which enables two working modes: parking charging and driving charging. The simulation model is then developed and the experimental prototype is designed to test the on-board charging system and analyze the experimental results. The obtained results show that the power factor correction function of the input current can be achieved by the front-stage double-diode bridge-less PFC converter. In addition, the rear-stage DC/DC converter can provide high-voltage and low-voltage outputs. It can also fl exibly switch the parking charging and driving charging modes through the control strategy combining the PFM and PS. Finally, the simulations and experiments verify the correctness of the theoretical analysis.

Experimental Study on Thermal Catalytic Degradation of SF6 Waste Gas by Metal Phosphate

Zhang Xiaoxing,Li Xiaohan,Wang Yi,Meng Fei,Zou Yi,Tian Shuangshuang,Cui Zhaolun 대한전기학회 2023 Journal of Electrical Engineering & Technology Vol.18 No.2

In recent years, SF6 has been widely used in the electrical industry. The amount of SF6 waste gas produced by the corresponding gas insulated equipment is increasing year by year. However, SF6 has high global warming potential and long atmospheric life. Proper treatment of SF6 waste gas is particularly important for environmental protection. Thermal degradation can effectively eliminate the greenhouse effect caused by direct emission of SF6. In this paper, AlPO4, Zr3(PO4)4 and CePO4 were used as catalysts to degrade SF6/air mixture gas (The concentration of SF6 is 15%) at 800 °C. The concentration of SF6 gas was detected by gas chromatography (GC), and the gas decomposition products of SF6 were detected by gas chromatography mass spectrometry (GCMS) and fourier transform infrared spectroscopy (FTIR). The surface morphology and composition of the catalyst were analyzed by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). The results show that the three kinds of metal phosphates can promote the decomposition of SF6 gas, among which CePO4 had the best catalytic degradation effect, and the degradation rate of SF6 reached 84.7% in 12 h. The main products of SF6 gas thermal catalytic degradation include SF4, S2F10, SO2F2, SOF2, SiF4 and SO2 gas, etc. SEM scanning image shows that there were some objects adsorbed on the surface of CePO4 catalyst after the experiment. XPS spectra showed that Si and F elements were added to the catalyst. According to the binding energy, SiF4 was adsorbed on the catalyst. After the experiment, CeF3 was produced by CePO4 catalyst. Different catalysts have their own selectivity to the decomposition products of SF6, which is convenient for the treatment of products, and it is of great significance to eliminate the greenhouse effect caused by the waste gas of SF6.

Biological Properties of Bee Pollen from Different Regions of South Korea

Xue Wang,Haribalan Perumalsamy,Yizhe Cheng,Xiaohan Li,Young Joon Ahn 한국응용곤충학회 2016 한국응용곤충학회 학술대회논문집 Vol.2016 No.10

Bee pollen have been used for centuries as a kind of traditional medicine and food diets additive due to their nutritional and biological properties. The present study was to evaluate the biological features of ethanol extracts of 18 different bee pollen (EEBP) samples collected from 16 locations of South Korea. Our results indicated most of the EEBP samples showed 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity, inhibitory activities against human β-amyloid precursor cleavage enzyme (BACE-1), and antiproliferative activities towards five cancer cell lines. However, these EEBP samples did not present human acetylcholinesterase (AChE) inhibitory activities, and intestinal bacteria growth inhibitory activities.