Materials become insensitive to flaws at nanoscale: Lessons from nature, Gao, Ji, Jger, Arzt, Fratzl, PNAS, 2003
Novelty/impact/significance:
It is firstly/ingeniously demonstrated that the biological nanocomposites’ generic structure is mechanically advantageous: the nanometer size of mineral reinforcements is selected to ensure optimum strength and maximum tolerance of flaws. The derivations are simple and effective.
Scientific question:
|
Tenure-Track Assistant Professor of Mechanical Engineering and Materials Science, Duke University |
EML Webinar on 16 December 2020 will be given by Dave Weitz, Harvard University. Discussion Leader Jia Liu, Harvard University.
Title: Snap, Speckle and Spot: Sight and Sound of Hydraulic Fracture
Time: 6:30 am California, 9:30 am Boston, 2:30 pm London, 10:30 pm Beijing on 16 December 2020
We are on the lookout for TWO exceptionally bright and eager Ph.D. students to join our Theoretical & Applied Geomechanics (TAG) research team, to work in the areas of computational geomechanics and geotechnical earthquake engineering. The candidate must hold an M.Sc. degree in geotechnical engineering and must have solid knowledge in applied mechanics and continuum and/or discrete element modeling (computation and/or program development). Consideration will be given to candidates with a proven record of relevant academic background.
Natural nonlinear materials, e.g., biological materials and polymers, are mechanically weak. It has been amajor challenge to develop a nonlinear material with potentialmechanical applications. Here, we develop a nonlinear elastic metamaterial with giant and tailorable-nonreciprocal elastic moduli. The metamaterial is designed with a microstructural axial asymmetry, which activated nonlinear microstructural deformations in the axial direction and microstructural residual moments.
The classical continuum mechanics assumes that a material is a composition of an infinite number of particles each of which is a point that can only move and interact with its nearest neighbors. This classical mechanics has limited applications where it fails to describe the discrete structure of the material or to reveal many of the microscopic phenomena, e.g., micro-deformation and micro-dislocation.
A novel micromorphic beam theory that considers the exact shape and size of the beam’s microstructure is developed. The new theory complements the beam theories that are based on the classical mechanics by modeling the shape and size of the beam’s microstructure. This theory models the beam with a microstructure that has shape and size and exhibits microstrains that are independent of the beam’s macroscopic strains.
In this paper, we investigate the surface roughness-dependence of buckling of beam-nanostructures. A new variational formulation of buckling of Euler-Bernoulli rough beams is developed based on the Hamil- ton’s principle. The equation of motion of the beam is obtained with a coupling term that depends on the beam surface roughness. Exact solutions are derived for the buckling configurations and the pre-buckling and postbuckling vibrations of simply supported structures.
Current designs of artificial metamaterials with giant Poisson’s ratios proposed microlattices that secrete the transverse displacement nonlinearly varies with the longitudinal displacement, and the Poisson’s ratio depends on the applied strain (i.e., tailorable Poisson’s ratio). Whereas metamaterials with tailorable Poisson’s ratios would find many important applications, the design of a metamaterial with a giant Poisson’s ratio that is constant over all the material deformation range has been a major challenge.
