High-performance mechanical energy absorption has been pursued to protect personnel and important infrastructures and devices. In this talk, I will introduce our work on the mechanical energy absorption leveraging the liquid intrusion of Metal-Organic-Frameworks (MOFs). It is found that during the intrusion of non-wetting liquids into the nanoscale pores under mechanical pressure, substantial mechanical energy can be absorbed by generating huge liquid-solid interfaces. Some latest research on its physical mechanism and potential engineering applications will be presented.
The manufacture of 3D mesostructures is receiving rapidly increasing attention, because of the fundamental significance and practical applications across wide-ranging areas. The recently developed approach of buckling-guided assembly allows deterministic formation of complex 3D mesostructures in a broad set of functional materials, with feature sizes spanning nanoscale to centimeter-scale. Previous studies mostly exploited mechanically controlled assembly platforms using elastomer substrates, which limits the capabilities to achieve on-demand local assembly, and to reshape assembled mesostructures into distinct 3D configurations. This work introduces a set of design concepts and assembly strategies to utilize dielectric elastomer actuators as powerful platforms for the electro-mechanically controlled 3D assembly. Capabilities of sequential, local loading with desired strain distributions allow access to precisely tailored 3D mesostructures that can be reshaped into distinct geometries, as demonstrated by experimental and theoretical studies of ∼30 examples. A reconfigurable inductive–capacitive radio-frequency circuit consisting of morphable 3D capacitors serves as an application example.
Many materials are anisotropic. However, there is no widely accepted measure for characterizing the degree of elastic anisotropy. Here, assuming that the limiting case of extreme anisotropy should possess a positive semidefinite stiffness matrix, we propose three criteria to evaluate measures of anisotropy and show that the existing measures in the literature do not satisfy all of the proposed criteria.We then introduce a new measure of anisotropy based on the maximum strain energy ratio that is universally applicable to all material systems. The proposed measure is helpful for understanding the properties and behaviors of materials. Furthermore, this measure can be easily generalized to situations involving multiple fields and nonlinearity. The J-integral based criterion is widely used in elastic-plastic fracture mechanics. However, it is not rigorously applicable when plastic unloading appears during crack propagation. One difficulty is that the energy density with plastic unloading in the J-integral cannot be defined unambiguously. In this paper, we alternatively start from the analysis on the power balance, and propose a surface-forming energy release rate (ERR), which represents the energy available for separating the crack surfaces during the crack propagation and excludes the loading-mode-dependent plastic dissipation. Therefore the surface-forming ERR based fracture criterion has wider applicability, including elastic-plastic crack propagation problems. Several formulae are derived for calculating the surface-forming ERR, and the definition of the energy density or work density is avoided. For any fracture behaviours, the surface-forming ERR is proven to be path-independent. The physical meanings and applicability of the proposed surface-forming ERR, the local ERR, the traditional global ERR, and J-integral are compared and discussed.
Cell dynamics is of crucial significance for the morphogenesis, self-repair, and other physiological and pathological processes of tissues. Collective cells exhibit greatly different dynamic behaviors from isolated cells. In this lecture, some recent advances in experimental and theoretical researches on collective cell dynamics will be presented, with particular attention paid to the biomechanical mechanisms underlying the morphodynamics of developing embryos and tumors. First, a cell division model is established for the division of interconnecting cells in a biological tissue. Coupled mechanical-chemical mechanisms involved in the multi-phase cell division are taken into account. Second, we explain why spontaneous oscillation of collective cells may occur in such biological tissues as Drosophila amnioserosa during development. It is revealed that the collective cell oscillation in an epithelium-like monolayer results from the dynamic bifurcation induced by feedback between mechanical strains and chemical cues. Further, we investigate, both experimentally and theoretically, the migration of collective cells. We show that migratory cells may behave as a whole either like a viscous solid or fluid, leading to rich patterns with characteristic sizes ranging from several to dozens of cells. On the basis of experimental measurements and theoretical analysis, universal statistical laws are derived for the dynamic features of collective cells.
Metallic glasses (MGs) possess large elastic limit and high strength, but unfortunately they are of limited commercial utility due to their macroscopic brittle nature. Here, we report the recent progress in the improved ductility of MGs via simple structural design. Topics covered include MGs-based chiral nanolattice, and nanoglass (NG) consisting of nanometer-sized glassy grains separated by glass-glass interfaces which can be used to design MGs with unique mechanical properties.