“Instabilities in Soft Materials: from Fundamental Mechanics to Advanced Functions”

Abstract:

Various modes of mechanical instabilities can form in soft materials under large deformation, resulting in ordered patterns, and drastic changes of surface morphology. While mechanical instabilities have traditionally been considered as failure modes, a recent trend is to make use of them to fabricate stretchable electronics, measure material properties, and tune surface characteristics. In order to harness mechanical instabilities for controlled functions, it is essential to establish quantitative understanding of those instabilities. In the first part of this talk, I will describe my efforts in advancing the fundamental knowledge of a recently identified mechanical instability–creasing instability. Creasing develops when a block of soft material is compressed beyond a critical strain of around 40%. Creases are characterized by self-contact of the surface and a finite deformation field deviating from the flat state. I will first demonstrate how to use analytical and numerical methods to quantify the initiation and evolution of creases in soft materials under complex loading conditions. A creasing instability under pure elasticity is a supercritical bifurcation, with an infinitesimal depth at the initiation. I will describe the design of subcritical creasing by introducing an elastic energy barrier, which leads to snapping between the flat surface and the deep creases. In the second part of this talk, I will demonstrate how I harness mechanical instabilities in soft materials to develop phase-transforming metamaterials, stretchable carbon nanotube electrodes, and soft robots.

Biosketch:

Lihua Jin is a postdoctoral scholar at Stanford University working with Professor Zhenan Bao, Wei Cai and Christian Linder. In 2014, she obtained her PhD degree in Engineering Sciences from Harvard University under the supervision of Professor Zhigang Suo. Prior to that, she earned her Bachelor’s and Master’s degrees from Fudan University in 2006 and 2009. Lihua studies mechanics of materials and structures, with a focus on soft materials. During her Master and PhD training, she worked on mechanical instabilities of soft materials, constitutive modeling of stimuli-responsive materials, and designing of soft machines. Her current work focuses on mechanics of stretchable electronics.