Speaker: Prof. Xiaoping Jia

Time and Date: 9:00-12:00 am, October 30, 2018

Place: Room 530 of Scientific Building, Handan Campus,Fudan University

Abstract:

Granular materials are an assembly of macroscopic solid grains that interact with each other by dissipative contact forces. They are ubiquitous in everyday life, ranging from industrial applications to geophysical processes. Statics and dynamics of dense granular media strongly depend on the contact networks, resulting from the confining pressure [1]. Elastic wave propagation provides a powerful and sometimes unique probe of these inhomogeneous and fragile networks. The long-wavelength coherent waves give access to the elastic modulus whereas the short-wavelength scattered waves are sensitive to local rearrangements [2].

In this talk, we first describe the linear wave transport and acoustic probing of viscoelastic properties in dry and wet granular materials [3] as well as the shear banding [4]. Then, we discuss the nonlinear acoustic behaviours and show that beyond certain driving amplitude elastic waves not only serve as a probe but also as a pump to fluidize jammed granular solids [5,6]. Finally, we investigate the triggering of shear instability by the acoustic fluidization, such as granular avalanches and quicksands [7,8].

Biography:

Prof. Xiaoping Jia (贾小平) obtained a BSc in Physics from Nanjing University, China and MSc and PhD in Physical Acoustics from the Université Pierre & Marie Curie (Paris 6), France. Appointed as an Assistant Professor in Physics at the Université Paris 7, he has worked in the Groupe de Physique des Solides from 1989 to 2002, in laser ultrasonics, guided waves, non-destructive evaluation and acoustics of granular media. Since 2003, he is a Professor of Physics at the Université Paris-Est Marne-la-Vallée where he was the head of the granular acoustics team from 2002 to 2012. He joined the Institut Langevin at the ESPCI Paris since mid-2012. He has published over 80 papers including those in Nature, Phys. Rev. Lett., Appl. Phys. Lett. His current research involves granular acoustics and mechanics, multiple scattering of ultrasound in heterogeneous media, nonlinear acoustics, friction and adhesion.