Keynote Speakers

Abstract: Generations of research students have been taught that the strength of brittle materials containing microcracks follows the Weibull distribution. The Weibull modulus M has a constant value which describes the strength scatter of large specimens. The characteristic strength σ_ch defines the strength at a failure probability of 63.2%, and has no further application. In this talk, we suggest that if the microcracks are suppressed or pre-existing defects are smaller than the average grain size G, a new micro-grain Weibull strength distribution can be obtained. In addition, the characteristic strength, σ_ch, determined from the micro-grain Weibull plot with a high M value (>10), and an average G could be used to evaluate the fracture toughness K_IC without testing specimens with long cracks. That is, K_IC ≈ 2 σ_ch √3G . This provides a new physical interpretation of the characteristic strength in the Weibull equation. But, is this a new concept in fracture mechanics of brittle materials? Available results in the published literature offer some support.

Biography: Prof. Mai Yiu Wing （米耀荣）received his PhD, DSc and DSc (honoris causa) from the University of Hong Kong in 1972, 1999 and 2013, respectively. He spent more than 4 decades as an academic at the University of Sydney where he rose through the ranks to a University Chair in 2004. He retired in May 2023 and returned to PolyU in HK in November 2023 as a Distinguished Chair Professor. His research interests are fracture mechanics and advanced composites. Prof. Mai was elected to fellowships of several prestigious academies, including the Chinese Academy of Engineering, the Royal Society of London and the Australian Academy of Science.

Abstract: Many biological composites can achieve superior elastic stiffness, strength, and toughness, which are crucial for biomechanical performance in activities such as locomotion, protection, combat, adhesion, and predation. In this paper, we investigate the toughening and stiffening mechanisms of biological materials and establish the corresponding theoretical models. We focus on uncovering how these materials achieve an exceptional combination of high stiffness, toughness, and strength. The relationships among the mechanical properties, biological functions, geometric structures, and chemical compositions of biological materials are analyzed using representative examples, including horns, gecko feet, nacres, spider silks, and tendrils. We particularly examine the effects of microstructural sizes, interfaces, structural hierarchy and chirality, and functional gradients. I will also provide perspectives on the mechanics of biological materials from the viewpoints of theoretical modeling, experimental characterization, numerical simulations, and biomimetic applications.

Biography: Xiqiao Feng is a Chang Jiang Chair Professor at Tsinghua University. Currently, he serves as a vice president of the Chinese Society of Theoretical and Applied Mechanics (CSTAM), an editor-in-chief of Engineering Fracture Mechanics, and an executive member of International Council of Fracture (ICF). His current interests include mechanics and biomimetics of biological materials, and biomechanics of cells and tissues. He has co-authored three monographs and about 400 international journal papers, which have received about 29000 citations. Selected Feng’s honors include the National Prize of Science and Technology of China (2019), the Award of Science and Technology for Young Scientists of China (2007), etc.

Abstract: Topological phases of matter (e.g. topological insulators) based on principles of topology are of great theoretical and practical values in various physical settings spanning electronics, optics, acoustics, thermodynamics and mechanics. This lecture will present the theory of topological properties of mechanical continuous beams and continuum lattice grid structures that have been recently revealed. The theory gives the existence condition of the topological states and higher-order topological states within the whole frequency spectra of continuous beams, bridge-like frames, square frames and kagome frame structures. Clear criteria for topological phase transitions, which occur many times in such continuum lattice grid structures, are established. The exact frequencies of the topological corner states, edge states, and bulk states are solved analytically. The approach is based on a unified framework, which can be readily applied to similar continuum lattice grid structures with more complex configurations.

Biography: Jianxiang Wang is currently Changjiang Scholar Professor of Mechanics, and Chief Professor of Zhou Peiyuan Honors Program of Theoretical and Applied Mechanics (ZPY-TAM), in College of Engineering of Peking University. He received his PhD from The University of Sydney in 1995. He joined Peking University in 1998, after doing post-doctoral research in Imperial College in 1996 and Aalborg University in 1997. Jianxiang Wang’s research focuses on mechanics of composite materials. He once served as secretary-general of the 23rd International Congress of Theoretical and Applied Mechanics (ICTAM2012), and member of Congress Committee of the IUTAM.

Abstract: Split Hopkinson bar (SHB) has been widely used for testing the dynamic mechanical behavior of materials. However, it is hard to involve complex stress conditions in traditional SHB due to its intrinsic characteristics. Electromagnetic Hopkinson bar (E-Hopkinson bar) has been recently proposed as a solution. Different from traditional SHB, the stress pulse of E-Hopkinson bar is generated directly by electromagnetic force. Therefore, the stress pulse that loads the specimen can be accurately controlled. With this advantage, some experiments that cannot be done with traditional SHB can be conducted by E-Hopkinson bar technique. In this case, we introduced briefly the basic principles of E-Hopkinson bar. Some lasted tests, such as symmetrically dynamic compression/tension of materials, testing technique for brittle materials, dynamic Bauschinger effect of metals, intermediate strain rate tests, trapezoidal stress pulse generation and dynamic multi-axial tests were also introduced. This new technique will be helpful for those researchers in the field of solid mechanics, especially when strain rate and complex stress condition are involved.

Biography: Dr. Yulong Li is the Dean of Civil Aviation School and a Chair Professor in Department of Aeronautical Structure Engineering in Northwestern Polytechnical University (NPU). He received his Ph.D. degree in Solid Mechanics from NPU in 1992 and became a Professor in 1995. From 1996 to 2000 he worked as a post-doctor and subsequently a senior research scientist in University of California San Diego (UCSD) and Johns Hopkins University (JHU). He was a visiting professor of Tokyo University of Science in Japan, a visiting professor of Université Pierre et Marie Curie of France and a visiting professor of JHU. His research interests include dynamic response and failure of structures under impact loading, constitutive relationship for materials, experimental techniques in impact dynamics, as well as, numerical simulation of materials and structures under impact. He has authored more than 400 papers, as well as over 50 patents and 4 book chapters.