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46 results on '"Wang, Jilai"'

39. Influence of Size Effect on Dynamic Mechanical Properties of OFHC Copper at Micro/Mesoscopic Scale

Author

Shi Zhenyu, Jing Chuanzhi, Yan Sun, Wang Jilai, and Chengpeng Zhang

Subjects
Mesoscopic physics, Materials science, chemistry, Scale (ratio), chemistry.chemical_element, Composite material, Copper
Abstract

The dynamic mechanical properties of metallic materials have been extensively investigated at the macro-scale in terms of deformation mechanisms, strain rate strengthening, and fracture mechanisms. However, the dynamic mechanical properties affected by size effects at micro/meso-scales have rarely been investigated. To explore the size effects on the dynamic mechanical properties at micro/meso-scales, the experiments of quasi-static compression and SHPB were carried out using oxygen-free, high-conductivity (OFHC) copper with different geometrical and grain sizes. The experimental results show that the quasi-static and dynamic mechanical properties of OFHC copper are affected by size effects at micro/meso-scales. In particular, OFHC copper exhibits strain rate strengthening effects at the micro/meso-scales, and the presence of micro-cracks was observed in the SHPB experimental specimens. The J-C constitutive model based on the surface layer model is proposed and the analysis of the average relative error of the modified model and the original constitutive model is performed. Finite element analysis was carried out based on the modified J-C model and the original model, and the results show that the modified J-C model was in good agreement with the experimental results.

Published
2021

40. AC Pollution Flashover Performance of Insulators in Low Atmosphere Pressure Circumstance

Author

Zhang Zhijin, Jiang Xingliang, Li Jin, Li Ran, and Wang Jilai

Subjects
Pollution, Low-pressure area, Altitude, Atmospheric pressure, media_common.quotation_subject, Environmental engineering, Arc flash, Environmental science, Insulator (electricity), Effects of high altitude on humans, Voltage, media_common
Abstract

The research on pollution flashover characteristics of insulators under low air pressure is of great engineering application value and scientific significance for carrying out altitude correction research and formulating relevant standards in the field of external insulation of power transmission and Transformation Engineering in ultra-high altitude areas. It provides an important reference for the construction of power transmission projects and railway project in high altitude areas. AC pollution flashover tests of QBG-25/16 and QBG-25/20 insulators at high altitude and low air pressure were carried out in a large-scale multi-function artificial climate chamber. The results show that when the altitude is 1000m∼5500m and the salt density is 0.1∼0.15mg/cm2, the pollution flashover voltage of insulators decreases with the decrease of air pressure, and the pollution flashover voltage of insulators decreases with the increase of salt density; the flashover voltage of insulators with different insulator structures is affected differently by air pressure; the characteristic index n of air pressure decreases with the increase of pollution degree, and the characteristic index n of air pressure also decreases Affected by insulator type.

Published
2021

42. Numerical Investigation for the Resin Filling Behavior during Ultraviolet Nanoimprint Lithography of Subwavelength Moth-Eye Nanostructure

Author

Zhang Chengpeng, Xuewen Wang, Yuanchi Cui, Zhenyu Shi, and Wang Jilai

Subjects
Nanostructure, Fabrication, Materials science, moth-eye nanostructure, filling behavior, 02 engineering and technology, Computational fluid dynamics, medicine.disease_cause, 01 natural sciences, Slip (ceramics), Nanoimprint lithography, law.invention, Viscosity, law, Mold, 0103 physical sciences, Materials Chemistry, medicine, Boundary value problem, Composite material, 010302 applied physics, business.industry, Surfaces and Interfaces, ultraviolet nanoimprint lithography, Engineering (General). Civil engineering (General), 021001 nanoscience & nanotechnology, Surfaces, Coatings and Films, visual_art, CFD simulation, visual_art.visual_art_medium, TA1-2040, 0210 nano-technology, business
Abstract

Accurate analysis of the resin filling process into the mold cavity is necessary for the high-precision fabrication of moth-eye nanostructure using the ultraviolet nanoimprint lithography (UV-NIL) technique. In this research, a computational fluid dynamics (CFD) simulation model was proposed to reveal resin filling behavior, in which the effect of boundary slip was considered. By comparison with the experimental results, a good consistency was found, indicating that the simulation model could be used to analyze the resin filling behavior. Based on the proposed model, the effects of process parameters on resin filling behavior were analyzed, including resin viscosity, inlet velocity and resin thickness. It was found that the inlet velocity showed a more significant effect on filling height than the resin viscosity and thickness. Besides, the effects of boundary conditions on resin filling behavior were investigated, and it was found the boundary slip had a significant influence on resin filling behavior, and excellent filling results were obtained with a larger slip velocity on the mold side. This research could provide guidance for a more comprehensive understanding of the resin filling behavior during UV-NIL of subwavelength moth-eye nanostructure.

Published
2021

43. Anisotropic V-Groove/Wrinkle Hierarchical Arrays for Multidirectional Strain Sensors with High Sensitivity and Exceptional Selectivity

Author

Ji, Jin, Zhang, Chengpeng, Liang, Yunhao, Zhang, Nianqiang, and Wang, Jilai

Abstract

Flexible strain sensors have been continuously optimized and widely used in various fields such as health monitoring, motion detection, and human–machine interfaces. There is a higher demand for sensors that can sensitively identify both the strain amplitude and direction in real-time to adapt to complex human movements. This study proposes a flexible strain sensor construction strategy based on V-groove/wrinkle hierarchical structures via a facile and scalable prestretching approach. A gold film is sputtered on a V-groove structure soft substrate under a vertical biaxial prestrain. When the strain is released, a variety of wondrous V-groove/wrinkle hierarchical structures are formed. The microstructure and the properties of the resulting sensor can be controlled by adjusting the prestrain, which has obvious anisotropic response characteristics and exhibits high sensitivity (maximum gauge factor up to 20,727.46) and a wide sensing range (up to 51%). In addition, the resulting multidirectional sensor based on double-sided microstructures has an exceptional directional selectivity of 67.39, at an advanced level among all stretchable multidirectional strain sensors reported so far. The sensor can detect human motion signals and distinguish motion patterns, proving its great potential in the field of human motion detection and laying a foundation for high-performance wearable devices.

Published
2024
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45. Analysis of the Size Effect on Springback Behavior in Micro- Scaled U- Bending Process of Sheet Metals.

Author

Wang, Jilai, Fu, Mingwang, and Ran, Jiaqi

Subjects
SIZE effects in thin films, SPRINGBACK (Elasticity), SHEET metal, STRESS-strain curves, FINITE element method
Abstract

In the micro-bending process of sheet metals, springback caused by the considerable elastic recovery during unloading has a significant effect on the dimension precision of micro-bent sheet metal parts. In design of micro-bent parts and bending process, this phenomenon needs to be considered. However, the traditional well-established knowledge for analysis of macro-scaled sheet metal bending processes may not be very suitable and efficient in analysis of micro-scaled sheet metal bending due to the geometry and microstructure size effects in the process. To explore the unloading springback of sheet metals after micro-bending, the experimental studies on the interactive influence of a few significant parameters including sheet thickness, grain size, and punch radius on the springback in micro U-bending process of copper alloy sheets were conducted. An appropriate constitutive model based on the surface layer model, which is widely used in micro-scaled forming processes, is proposed to predict the amount of springback and the relationship among these parameters is further established. The research shows that the springback angle generally increases with the decreasing sheet thickness, and for different punch radii, the springback angle has different variation trends for the sheet metals with different grain sizes. The developed analysis method is verified via the comparison of the calculated stress-strain curves with the tensile test results of three kinds of copper alloy sheets. The findings on how the size effects affect the springback behaviors of in micro-bending process are validated by the experimental results, finite element simulation, and the comparison in-between. [ABSTRACT FROM AUTHOR]

Published
2014
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46. Grain size and orientation affected deformation inhomogeneity and local damage of hot-deformed Al-Zn-Mg alloy.

Author

Su, Baoyi, Guo, Ning, Tang, Bingtao, Wang, Jilai, and Gao, Song

Subjects
*STRAIN hardening, *CRYSTAL grain boundaries, *GRAIN size, *DEFORMATIONS (Mechanics), *CRYSTAL orientation, *GRAIN refinement
Abstract

The forming defects at elevated temperature caused by the microstructural evolution such as grain size, crystal orientations are the critical issue that induced deformation inhomogeneity and local damage which severely limits the application of Al-Zn-Mg alloys in thin-walled structure manufacturing. In this study, the hot deformation behavior and microstructural evolution were investigated via hot stretching tests, electron backscatter diffraction (EBSD) and the transmission electron microscopy (TEM) characterization. Then, an integrated multiscale constitutive model coupled dislocation density based crystal plasticity (CP) model and phase field method (PFM) was established through the reconstructed configuration of deformation gradient emphasized on a damaged part. The coupled CP-PFM model was numerically implemented into Düsseldorf Advanced Material Simulation Kit (DAMASK) software. Subsequently, a set of virtual polycrystalline RVE models assigned with different average grain sizes and two types of RVE models with realistic crystal orientations were constructed from EBSD data. The experimental and simulation results of the Al-Zn-Mg alloy under hot tensile loading showed that the grain size refinement leads to the increase of grain boundary density, which leads to the rapid increase of dislocation density, uniform damage distribution and better work hardening ability. In addition, the coordination of the activation of different slip systems between adjacent grains will lead to the uneven distribution of dislocation density and local damage. [Display omitted] • An integrated crystal plasticity and phase-field anisotropic damage model is newly established. • Fracture mechanisms are revealed by recrystallization induced grain refinement. • Grain size and orientations affects grain boundaries density, and further dominates deformation inhomogeneity. • The damage is more likely to occur between grains with smaller Schmid factor. [ABSTRACT FROM AUTHOR]

Published
2024
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