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2019 Vol. 1, No. 2

Editorial
Reviews
Manufacturing technologies toward extreme precision
Zhiyu Zhang, Jiwang Yan, Tsunemoto Kuriyagawa
2019, 1(2) doi: 10.1088/2631-7990/ab1ff1
Abstract:
Precision is one of the most important aspects of manufacturing. High precision creates high quality, high performance, exchangeability, reliability, and added value for industrial products. Over the past decades, remarkable advances have been achieved in the area of high-precision manufacturing technologies, where the form accuracy is approaching the nanometer level and surface roughness the atomic level. These extremely high precision manufacturing technologies enable the development of high-performance optical elements, semiconductor substrates, biomedical parts, and so on, thereby enhancing the ability of human beings to explore the macro- and microscopic mysteries and potentialities of the natural world. In this paper, state-of-the-art high-precision material removal manufacturing technologies, especially ultraprecision cutting, grinding, deterministic form correction polishing, and supersmooth polishing, are reviewed and compared with insights into their principles, methodologies, and applications. The key issues in extreme precision manufacturing that should be considered for future R&D are discussed.
Developments and perspectives on the precision forming processes for ultra-large size integrated components
Shijian Yuan, Xiaobo Fan
2019, 1(2) doi: 10.1088/2631-7990/ab22a9
Abstract:
In order to meet the requirements of high reliability, long-lifetime and lightweight in a new generation of aerospace, aircraft, high-speed train, and new-energy power equipment, integrated components are urgently needed to replace traditional multi-piece, welded components. The applications of integrated components involve in a series of large-size, complex-shaped, high-performance components made of difficult-to-deform materials, which present a huge challenge for forming ultra-large size integrated components. In this paper, the developments and perspectives of several extreme forming technologies were reviewed, including the sheet hydroforming of ultra-large curved components, die-less hydroforming of ellipsoidal shells, radial-axial ring rolling of rings, in situ manufacturing process of flanges, and local isothermal forging of titanium alloy components. The principle and processes for controlling deformation were briefly illustrated. The forming of typical ultra-large size integrated components and industrial applications were introduced, such as the high strength aluminum alloy, 3 m in diameter, integrated tank dome first formed by using a sheet blank with a same thickness as the final component, and a 16 m diameter, integrated steel ring rolled by using a single billet. The trends for extreme forming of ultra-large size integrated components were also discussed with a goal of providing ideas and fundamental guidance for further development of new forming process for extreme-size integrated components in the future.
Material embrittlement in high strain-rate loadings
Xiuxuan Yang, Bi Zhang
2019, 1(2) doi: 10.1088/2631-7990/ab263f
Abstract:
Material embrittlement is often encountered in machining, low-temperature, and heat treatment conditions among which machining is strain-rate related. In addition to machining, material embrittlement can also occur in the processes of, for example, projectile penetration, explosion, and tunnel boring, because of the high strain-rates in the processes. Many researchers recognize that strain rate can cause material embrittlement. However, the strain-rate evoked material embrittlement is not fully understood, and its fundamental mechanisms are to be investigated. This paper is focused on the material embrittlement mechanisms of engineering materials subjected to loading at high strain rates. Based on the previous research, this paper identifies that the strain rate can lead to an increase in material strength and reduction in toughness, which is an important cause of material embrittlement. Strain-rate sensitivity ks proposed in this study provides a guide for the determination of material embrittlement in terms of strain rate. The paper elucidates that stress wave propagation and reflection is another mechanism that directly contributes to material embrittlement and fragmentation at a high strain-rate. The paper also investigated the critical conditions for ductile to brittle transition of ductile materials based on the strain-rate effect. Finally, the effects of strain rate on the nucleation and propagation of a crack are discussed in terms of dislocation kinetics. It provides guidance to predicting the material embrittlement and fragmentation at a high strain-rate for applications ranging from the machining, tunnel boring, and armor protection of engineering materials.
Meniscus fabrication of halide perovskite thin films at high throughput for large area and low-cost solar panels
Xuezeng Dai, Yehao Deng, Charles H Van Brackle and Jinsong Huang
2019, 1(2) doi: 10.1088/2631-7990/ab263e
Abstract:
Perovskite solar cells have shown remarkable progress in recent years as power conversion efficiencies have already eclipsed 24%—highest of all thin film photovoltaic technologies. In addition to unprecedented optoelectronic properties unseen in traditional semiconductors, low formation energy and solution processability open the door to low-cost and high throughput solution coating strategies for commercialization. This review presents recent work on the fabrication of perovskite films by meniscus coating—a simple and readily scalable manufacturing technique—which includes blade coating and slot die coating. The article outlines the fundamental fluid mechanisms of meniscus coating, discusses drying and crystallization of the perovskite during the coating process, and provides an overview of progress in meniscus-coated perovskite solar cells and modules.
Research
Precise assembly and joining of silver nanowires in three dimensions for highly conductive composite structures
Ying Liu, Wei Xiong, Da Wei Li, Yao Lu, Xi Huang, Huan Liu, Li Sha Fan, Lan Jiang, Jean-François Silvain, Yong Feng Lu
2019, 1(2) doi: 10.1088/2631-7990/ab17f7
Abstract:
Three-dimensional (3D) electrically conductive micro/nanostructures are now a key component in a broad range of research and industry fields. Direct laser writing by two-photon polymerization (TPP) has been established as one of the most promising methods for achieving 3D fabrication in micro/nanoscales, due to its ability to produce arbitrary and complex 3D structures with sub wavelength resolution. However, the lack of TPP-compatible and functional materials represents a significant barrier to realizing the functionality of the fabricated devices, such as high electrical conductivity, high environmental sensitivity, and high mechanical strength, etc. In this work, a novel method was developed to realize metallic 3D micro/nanostructures with silver-thiol-acrylate composites via TPP followed by femtosecond laser nanojoining. Complex 3D micro/nanoscale conductive structures have been successfully fabricated with ~200 nm resolution. The loading of silver nanowires (AgNWs) and joining of junctions successfully enhanced the electrical conductivity of the composites from insulating to 92.9 S m-1 at room temperature. Moreover, for the first time, a reversible switching to a higher conductivity was observed, up to ~103-105 S m-1 at 523 K. The temperature-dependent conductivity of the composite was analyzed using the variable range hopping and thermal activation models. The as-developed nanomaterial assembly and joining method in this study paves a way toward a wide range of device applications, including 3D electronics, sensors, memristors, micro/nanoelectromechanical systems (MEMS/NEMS), and biomedical devices, etc.