Joan van der Waals Colloquium

Time: 16:00 hrs
Location: de Sitterzaal/Oortgebouw Leiden

abstract
Presentation will describe dynamic behavior of granular/porous systems and will focus on the followings topics: (a) "Sonic vacuum" problem. The term was coined to emphasize a specific class of systems where sound does not propagate with granular systems being the first example of such behavior.
Strongly nonlinear wave equation will be introduced supporting new solitary wave qualitatively different from KdV soliton. Granular systems may be easily tuned to support also weakly nonlinear solitary wave
(FPU type solitons, KdV solitons). They may also support shock waves, periodic waves and breathers depending on initial disturbance and initial state of system controlled by static prestress. Practical applications include damping of impulse loading and high amplitude noise, “acoustic diode” and others. Granular materials introduce new area in wave dynamics as natural extension of weakly nonlinear behavior to strongly nonlinear case. (b) Dynamic behavior of granular/porous materials. Behavior of these materials has strong dependence on mesoscale parameters ‐ particle sizes and shapes and their strength and fracture is determined by competition between pores closure, dynamics of “force chains” and particles fracture. Especially interesting is shear instability of granular/porous materials under high strains and confined conditions. The main cause of instability in brittle materials (SiC, Al2O3) is due to particle fracture providing a softening mechanism and subsequent shear localization. The high strain plastic flow of soft component is the main cause of shear instability in mixture of ductile/rigid particles, like Al‐W granular composites. Practical applications include design of materials with desirable dynamic response. (c) Mitigation of strong shocks by "soft" condensed matter. This is topic of significant
practical importance. Soft condensed matter can transform impulse loading on short distances allowing mitigation of extreme loads (e.g. caused by explosion) and localization of blast. Optimization of their properties is a current focus of research in this area.