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Academician Gabor Stepan from Budapest University of Technology and Economics Delivers Hsue-Shen Tsien Lecture of Engineering Sciences

On June 28th, Gabor Stepan, Academician from Budapest University of Technology and Economics in Hungary, was invited to visit the Institute of Mechanics (IMECH). He delivered a Hsue-Shen Tsien Lecture of Engineering Sciences titled "From the Delayed Mathieu Equation to the Stability of High-Speed Milling." Over 70 researchers and students attended, including Academician Hu Haiyan from Beijing Institute of Technology, Zhou Dejin, a senior staff member at the Academic Divisions of the Chinese Academy of Sciences, and Luo Xisheng, the director of IMECH, Academician He Guowei, the academic director of IMECH, and Yang Yongfeng, the Secretary of the Committee for Discipline Inspection of IMECH. The meeting was chaired by Professor Dai Lanhong. On June 28th, Gabor Stepan, Academician from Budapest University of Technology and Economics in Hungary, was invited to visit the Institute of Mechanics (IMECH). He delivered a Hsue-Shen Tsien Lecture of Engineering Sciences titled "From the Delayed Mathieu Equation to the Stability of High-Speed Milling." Over 70 researchers and students attended, including Academician Hu Haiyan from Beijing Institute of Technology, Zhou Dejin, a senior staff member at the Academic Divisions of the Chinese Academy of Sciences, and Luo Xisheng, the director of IMECH, Academician He Guowei, the academic director of IMECH, and Yang Yongfeng, the Secretary of the Committee for Discipline Inspection of IMECH. The meeting was chaired by Professor Dai Lanhong.
　　 Gabor Stepan Delivering lecture
　　During his lecture, Academician Stepan discussed vibration control and stability analysis in high-speed milling. He covered historical backgrounds, the challenges of machining vibrations, and the application of the delayed Mathieu equation. He also highlighted the use of Semi-Discretization Method (SDM) and Hardware-In-the-Loop (HIL) testing to enhance milling stability. His insights underscored the importance of mathematical models in improving manufacturing precision and efficiency.
　　After lecture, Director Luo awarded Academician Stepan the "Hsue-Shen Tsien Professorship for Engineering Sciences Lecture" certificate, followed by a commemorative photo session. Additionally, Academician Stepan also toured Hsue-Shen Tsien's Office, the IMECH’s Exhibition Hall, the Explosion Pit Exhibition Hall, the Impact Dynamics Laboratory, and the Large Flume for Modeling Ocean Wave/Current-Structure-Seabed Interactions. He engaged in thorough discussions with local researchers during these visits.
　　Issuing Certificate
　　Takeing Photo at Building No.1 of IMECH
　　About Academician Gabor Stepan:
　　Gabor Stepan received the MSc and PhD degrees in mechanical engineering at the Budapest University of Technology and Economics in Hungary, he is currently Professor Emeritus of Applied Mechanics there. He is an elected fellow of CIRP (International Academy for Production Engineering) and SIAM (Society for Industrial and Applied Mathematics), received the Delay Systems Lifetime Achievements Award of IFAC (International Federation of Automatic Control), the Caughey Dynamics Award, and the Lyapunov Award of ASME, and the Jiangsu Friendship Award. He is a member of the Hungarian Academy of Sciences, the Academy of Europe, and foreign member of the Chinese Academy of Sciences, also honorary professor of NUAA (Nanjing University of Aeronautics and Astronautics). Prof Stepan works in the leading committees and panels of IUTAM (International Union of Theoretical and Applied Mechanics), CISM (International Centre for Mechanical Sciences), and Euro Mech (European Mechanics Society), he was the recipient of an Advanced Grant, and a Proof-of-Concept Grant of ERC (European Research Council). Among others, he had long-term visiting positions at Cal Tech (California Institute of Technology, Pasadena) and at the University of Newcastle upon Tyne (UK).
　　 
　　His research interests include nonlinear vibrations in delayed dynamical systems with applications in mechanical engineering such as wheel dynamics, robotic force control, machine tool vibrations, traffic dynamics, and human balancing.

2023 Academic Annual Conference of the State Key Laboratory of Nonlinear Mechanics

On December 22-23, 2023, the State Key Laboratory for Nonlinear Mechanics (LNM) of Institute of Mechanics (IMech), Chinese Academy of Sciences (CAS) held its Academic Annual Conference in Beijing. The event was attended by Prof. Wei Zhixiang, Deputy Director of Bureau of Frontier Science and Education, CAS; Zhang Junping, Director of the Department of Astronomic and Mechanics of the Bureau; Chen Hudong, Member of the National Academy of Engineering, USA; Prof. Wu Heng'an, Dean of the School of Engineering Science at the University of Science and Technology of China; Prof. Li Jiachun, Member of National Academy of Sciences, China; Prof. He Guowei, Member of National Academy of Sciences, China and Academic Director of IMech; Prof. Luo Xisheng, Director of the IMech; Ye Haihua, Secretary of the CDI, IMech.
　　 On December 22-23, 2023, the State Key Laboratory for Nonlinear Mechanics (LNM) of Institute of Mechanics (IMech), Chinese Academy of Sciences (CAS) held its Academic Annual Conference in Beijing. The event was attended by Prof. Wei Zhixiang, Deputy Director of Bureau of Frontier Science and Education, CAS; Zhang Junping, Director of the Department of Astronomic and Mechanics of the Bureau; Chen Hudong, Member of the National Academy of Engineering, USA; Prof. Wu Heng'an, Dean of the School of Engineering Science at the University of Science and Technology of China; Prof. Li Jiachun, Member of National Academy of Sciences, China; Prof. He Guowei, Member of National Academy of Sciences, China and Academic Director of IMech; Prof. Luo Xisheng, Director of the IMech; Ye Haihua, Secretary of the CDI, IMech. Over 220 researchers and students from Peking University, Tsinghua University, University of the Chinese Academy of Sciences, University of Science and Technology of China, participated in this conference.
　　 The opening ceremony was organized by Prof. Jiang Minqiang, Deputy Director of LNM. Important speeches were delivered by Prof. Wei Zhixiang, Deputy Director of Bureau of Frontier Science and Education, CAS, and by Prof. Luo Xisheng, and Prof. He Guowei as the Director and the Academic Director of IMech. They acknowledged the LNM's achievements in the last year, not only on the reform of State Key Laboratory but also the advances in scientific research and encourage all members of the laboratory for a persistent continuation. They also encouraged the laboratory to further strengthen its organization and teamworking culture, by upholding its excellent traditions established by the scientists of older generations. They pointed out that the role of a state key laboratory is, on one hand, to make significant advancement in scientific research, and one the other hand, to fulfill the demand of the nation. After the speeches, Prof. Wei Yujie, Director of LNM, presented the annual work report of 2023 and reviewed the 28-year history of LNM as the State Key Laboratory, dated back to 1995. The report presented the current status, and future development plans of LNM. A detailed summary of the key scientific advancements made in 2023 is also included.
　　 The remainder of the conference consists of invited 23 talks, presented by guests from the United States, Germany, Hong Kong, and various domestic universities and institutes in mainland China. The topics covered the major scientific issues of the nonlinear mechanics together with cutting-edge interdisciplinary directions, including fundamental theories of turbulence, industrial software of computational fluid dynamics, mechanical behavior of advanced materials, nonlinear fluid-structure interaction, electro-mechanical coupling, and key mechanical challenges in national projects and natural environments, etc.
　　 Prof. Wei Zhixiang
　　Prof. He Guowei
　　 
　　Prof. Luo Xisheng
　　 
　　Opening ceremony
　　

The Institute of Mechanics has developed an ultra-strong tungsten high entropy alloy

Recently , the team of Lan-Hong Dai , Institute of Mechanics , Chinese Academy of Sciences , together with the University of California , Berkeley , Beihang University , Hong Kong Polytechnic University and City University of Hong Kong .The stepwise controllable precipitation structure realizes the ultra-high strength plasticity of tungsten high entropy alloy , which provides a new paradigm for the development of advanced materials .TEM images of dislocations shear γ " particles .
　　Recently, the team of Lan-Hong Dai, Institute of Mechanics, Chinese Academy of Sciences, together with the University of California, Berkeley, Beihang University, Hong Kong Polytechnic University and City University of Hong Kong, has made important progress in the research of ultra-high strength tungsten high entropy alloy. The researchers proposed a novel stepwise controlled ordered nano-precipitation strengthening strategy, which successfully achieved a double-coherent nano-precipitates controlled by δ-lamellar and γ"-particle precipitation at high temperature (900℃) and medium temperature (650℃) (Figures 1-2). The prepared tungsten high-entropy alloy material has an ultra-high strength of 2.15GPa with a tensile plasticity of 15% (Figure 3). Meanwhile, the tungsten high-entropy alloy can still maintain a high yield strength of over 1GPa at a high temperature of 800℃ (Figure 4). Compared with the reported tungsten alloys and refractory high entropy alloys, the strength-plastic synergism of the developed tungsten alloys is at the best level in the world. The researchers systematically characterized the microstructure of different tensile deformation stages and revealed that the dislocation slip shears two coherent precipitates and maintains a perfect coherent structure, which is the main reason for the ultra-high strength and excellent plasticity of the alloy. After the dislocation shears δ lamellar, the lamellar layer has a significant local strain, while maintaining a continuous crystal structure (Figure 5), effectively releasing the stress concentration caused by pile-up of dislocation, and avoiding brittle failure caused by premature crack initiation. After the dislocation shearing coherent γ" precipitation, coherent strengthening, ordered strengthening occurs, which further increases the strength of the material (Figure 6). The strength and plasticity of the alloy are enhanced synchronously by the synergistic strengthening of two different nano-precipitated. The stepwise controllable precipitation structure realizes the ultra-high strength plasticity of tungsten high entropy alloy, which provides a new paradigm for the development of advanced materials.
　　This research result was recently described as "Ultra-strong tungsten refractory high entropy alloy via stepwise controllable coherent. nanoprecipitations" was published in Nature Communications, 2023, 14, 3006, with Tong Li as the first author.The research has been supported by the National Natural Science Foundation of China, the major project of "Plastic Flow and strengthening and toughening Mechanism of Disordered Alloys", the Basic Science Center project of "Multi-Scale Problems in Nonlinear Mechanics".
　　Paper linkage: https://www.nature.com/articles/s41467-023-38531-4
　　 
　　Fig. 1. Evolution of stepwise controlled precipitation structure. a-c are the schematic diagrams of structural evolution, d and c are the EBSD images of the corresponding stages, and f-i are the TEM images of the corresponding stages.
　　 
　　Fig. 2. Crystallographic relationship between differential coherent precipitates and matrix and element distribution. a and b are δ and γ" precipitation spherical aberration correction TEM images, c and d are δ and γ" precipitation elements distributions 3D atomic probe technology analysis, e and f are the corresponding one-dimensional elements distributions.
　　 
　　Fig. 3. Quasi-static tensile properties at room temperature and comparison with other materials.
　　 
　　Fig. 4. Quasi-static tensile properties at high temperature and comparison with other materials.
　　 
　　Fig. 5. TEM images of the lattice continuity after the dislocation shear the δ lamella.
　　 
　　Fig. 6. TEM images of dislocations shear γ" particles.
　　 
　　 
　　 

The 6th International Conference on Droplets held in Beijing

Recently, the 6th International Conference on Droplets was successfully held in Beijing. The conference was jointly organised by the Institute of Mechanics, Chinese Academy of Sciences, Beijing University of Aeronautics and Astronautics and Tsinghua University, and co-organised by the Chinese Society of Mechanics. The conference was co-chaired by Professor Liu Qiusheng of the Institute of Mechanics, Professor Wen Dongsheng of the Beijing University of Aeronautics and Astronautics, and Professor Sun Chao of Tsinghua University. Over 130 professionals and academics from over ten countries, such as China, the USA, Germany, the UK, Japan, Singapore, India, etc., travelled to Beijing to attend the meeting.    Recently, the 6th International Conference on Droplets was successfully held in Beijing. The conference was jointly organised by the Institute of Mechanics, Chinese Academy of Sciences, Beijing University of Aeronautics and Astronautics and Tsinghua University, and co-organised by the Chinese Society of Mechanics. The conference was co-chaired by Professor Liu Qiusheng of the Institute of Mechanics, Professor Wen Dongsheng of the Beijing University of Aeronautics and Astronautics, and Professor Sun Chao of Tsinghua University. Over 130 professionals and academics from over ten countries, such as China, the USA, Germany, the UK, Japan, Singapore, India, etc., travelled to Beijing to attend the meeting. The Droplet Conference began in Marseille, France in 2013 and has successfully held five series of conferences in Europe and the United States. This is the first time it is being held in China. The conference concentrates on sharing research findings in various fields, including gas-liquid interfaces, droplets, bubbles, complex fluids, infiltration, and contact behavior. Moreover, research on interfacial processes, as well as fluid phase transformation and heat characteristics in two-phase systems in space and experimental research, is also included. The topics encompass chemical industry, materials preparation, and micro- and nano-fluid systems. The conference will also cover subjects such as droplet impact, phase transition processes, complex interfaces, wetting behaviour, electro-magnetic fluids, 3D printing, smart manufacturing, microfluidics, biological and medical applications, alongside various other well-liked areas. The conference will showcase Professor Doris Vollmer from the Max Planck Institute in Germany, Guo Liejin, an Academician of the Chinese Academy of Sciences, Professor David A. Weitz from Harvard University in the USA, Professor Eberhard Bodenschatz from the Max Planck Institute in Germany, Professor Omar Matar from the Imperial College in the UK, Professor Kathleen Stebe from the University of Pennsylvania, and Professor Eberhard Bodenschatz from the Paris Institute for Scientific Research in France. and Professor Kathleen Stebe from the University of Pennsylvania, Professor David Quéré from University of Paris, Professor Wang Drongkai from Hong Kong Polytechnic University, and Professor Andrew Bayly from the University of Leeds have conducted research on the properties of surfaces and interfaces. They have discovered that surface tension can be used to control how liquids behave on solid surfaces. By altering the surface tension, they can manipulate the liquid to spread or retract. This finding has promising applications in fields such as microfluidics and soft robotics. Professor Lv Cunjing from Tsinghua University, Professor Fei Duan from Nanyang Technological University (Singapore), Professor David Brutin from the Université de Marseille (France), and researcher Liu Qiusheng from the Institute of Mechanics. Over ten well-known experts, such as Professor Lv Cunjing from Nanyang Technological University of Singapore, Professor David Brutin from the University of Marseille in France, and researcher Liu Qiusheng from the Institute of Mechanics, gave 17 presentations at the main venue. They were shared online and offline. During the three-day report period, Liu Qiusheng, who works at the Institute, was asked to present the recent advancements of the newly initiated human spaceflight project, including its on-orbit operation. Concurrently, three meetings were held, and a sum of 83 verbal reports were performed. Ten students and five young scholars were awarded the Best Presentation Award by the International Scientific Committee, which was announced by Prof Doris Vollmer, Chair of the Droplet Series, and presented with certificates at the closing ceremony. The conference's triumph had a beneficial impact on boosting the academic exchange and cooperation among scholars from China and overseas. The participants introduced their newest research findings and applications relating to assorted disciplines and engaged in constructive dialogues on difficult topics. Through discussions and collaborations, they gained a better comprehension of the latest developments in international droplets, broadened their perspectives, and enhanced their academic abilities. The conference has formed reliable partnerships and friendships to advance future scientific and academic exchanges. The International Scientific Committee on Droplets has decided that Belgium will host the next Droplet Conference in 2025.

The Overstretch Strategy-A New Strategy to Double Stretchability of Stretchable Electronics


　　Stretchable electronics have been extensively developed in the last decade for diverse applications ranging from health monitoring, medical treatment, and intelligent industries to aerospace equipment with stretchable or curvilinear characteristics. The key technological innovation in inorganic stretchable electronics is the achievement of elastic stretchability through the designed mechanical structures, enabling conformal wrapping on arbitrarily complicated target surfaces, maintaining the electronic functions unchanged. For instance, the “island-bridge” mesh structure, in which the functional components reside at the “islands” and the interconnects form the “bridges,” is the most popular one. The “islands” undergo negligible deformation during the stretch of the structure, and the “bridges” provide both elastic stretchability and electronic conductivity. Strategies for achieving elastic stretchability of stretchable electronics are critically essential and have attracted significant research attention.
　　Although several previous studies have focused on the design of stretchable structures, as shown in Figure 1, only two fundamental strategies have been exploited to achieve or enhance elastic stretchability. These strategies are described as follows. 1) By using the prestrained elastic substrate; a waved ribbon is a typical example. A pre-strain is applied to the elastic substrate before the straight planar ribbon is transfer-printed and bonded. The release of the prestrain yields compression and out-of-plane buckling of the transfer-printed ribbon, forming a waved shape with stretchable characteristics. Besides, more complex stretchable 3D meso-structures are fabricated by 2D precursors bonded to prestrained elastic substrates. 2) By designing geometric layouts; versatile stretchable structure layouts involving curved interconnects have been designed; these include horseshoe, serpentine, fractal, non-buckling, helical structures, and kirigami-inspired structures which exhibit different features in terms of elastic stretchability and application scenarios. Sometimes, the two types of strategies are combined to enhance the stretchability of mechanical structures. For instance, a prestrained elastic substrate significantly increases the stretchability of serpentine structures.
　　Recently, Yewang Su's team at the Institute of Mechanics, Chinese Academy of Sciences, innovatively proposed a third strategy to improve the elastic stretchability of stretchable electronics, i.e., an overstretch strategy (Figure 2). This study proposes overstretching beyond the designed elastic range of stretchable structures, applied after transfer printing and bonding to the soft substrate. The overstretch strategy can double the designed elastic stretchability, which is critical for the performance of stretchable electronics. The theoretical, numerical, and experimental results collectively prove that the overstretch strategy is valid for various geometrical interconnects with both thick and thin cross-sections (Figure 3, 4, 5). The underlying mechanism is revealed owing to the evolution of the elastoplastic constitutive relation of the critical part of the stretchable structures during overstretching. The overstretch strategy can be easily executed and combined with the other two strategies to enhance elastic stretchability, which has profound implications for the design, fabrication, and applications of stretchable electronics. The research results are published in the academic journal “Advanced Materials” under the title of “An Overstretch Strategy to Double the Designed Elastic Stretchability of Stretchable Electronics” (DOI: 10.1002/adma.202300340). The first author of the paper is Juyao Li, a PhD student at the Institute of Mechanics, Chinese Academy of Sciences, and the corresponding author is Yewang Su, a researcher at the Institute of Mechanics, Chinese Academy of Sciences, with the participation of Xiaolei Wu, a researcher at the Institute of Mechanics, Chinese Academy of Sciences, in the work. This work is supported by the National Natural Science Foundation of China, the 0 to 1 Original Innovation Program of the Chinese Academy of Sciences, CAS Interdisciplinary Innovation Team, and the WRQB Talent Program of the Chinese Ministry of Organization.
　　 
　　 
　　Figure 1. Evolution of stretchable structures over the past decades.
　　 
　　Figure 2. Operation of the overstretch strategy. The column on the left (Column 1) shows the step-by-step operation of the overstretch strategy: ①-② stretching to the designed elastic limit (58.5%), ②-③ stretching beyond the designed elastic limit (140%), ③-④ releasing the applied strain, ④-⑤ stretching to enhanced elastic limit (117%). Columns 2 and 3 provide the contours of the finite element analysis (FEA) for the maximum principal strain and equivalent plastic strain of the MTSI corresponding to each step in Column 1, respectively.
　　 
　　Figure 3. Mechanical analysis of the overstretch strategy via the freestanding MTSI. a Mechanical constitutive relationship of the MTSI: ideal elastoplasticity. b Schematic and mechanical model of the freestanding MTSI. c First row: step-by-step overstretch strategy operation with freestanding MTSI (one period). Second row: stress distribution in the cross-section of the semicircle vertex in each process if no additional plasticity occurs from regime ③ to ④. Third row: stress distribution in the semicircle vertex cross-section in each process if additional plasticity occurs from regime ③ to ④. d Enhanced elastic stretchability of the freestanding MTSI as a function of the maximum of the first applied strain / over-strain, including the results of the experiments, FEA, and theory.
　　 
　　Figure 4. Experimental verification of the overstretch strategy via the freestanding MTSI . a Images of the initial state of the freestanding MTSI and the front and side views when stretched by 150% (from top to bottom). b Stress–strain curves of a dog-bone-shaped copper plate in uniaxial tension. c-k Curves of the force versus the applied strain during the first applied stretch, unloading, and second applied stretch; the first applied strain for c–k is 30%, 50%, 60%, 75%, 90%, 110%, 120%, 130%, and 150%, respectively (i-k contain the FEA results, dotted lines).
　　 
　　Figure 5. Mechanical analysis of the MTSI bonded on the soft substrate. a/b/c Enhanced elastic stretchability of thick horseshoe/zigzag/fractal interconnects bonded on the soft substrate as a function of the maximum of the first applied strain / over-strain. d Curve of the designed elastic stretchability of serpentine interconnection bonded on the soft substrate as a function of its thickness. e-g FEA results of serpentine interconnections with three typical thicknesses . The upper subgraphs are the corresponding wrinkling, buckling, and non-buckling deformation during stretching, and the lower subgraphs show the relationship between the enhanced elastic stretchability of the structure and the maximum of the first applied strain / over-strain. h Schematic of the deformation modes of the partial semicircle for the thick and thin interconnects.
　　 
　　 
　　 
　　Original link: An Overstretch Strategy to Double the Designed Elastic Stretchability of Stretchable Electronics (wiley.com)

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