It is well known that stiff slender structures are susceptible to buckling instabilities under a small compression. In contrast, various modes of mechanical instabilities are newly observed in soft materials due to their capacity for large deformation. One such surface instability recently identified is creasing, with the characteristics of singular stress field and lack of a length scale. Creases form when a block of soft material is compressed beyond a critical strain of around 40%. In the first part of this talk, I will focus on extending the fundamental knowledge of creasing instability. I will first demonstrate how to use analytical and numerical methods to identify the onset condition and simulate the evolution of creases in soft materials and soft tissues under complex loading conditions. Analogous to a second-order phase transition, a creasing instability under pure elasticity shows a second-order type bifurcation behavior. I will describe the design of a first-order creasing by introducing an elastic energy barrier, which leads to nucleation and growth of creases. I will further show that creases not only form on the surface of a soft material, but also form on the interface between two soft materials. Instabilities result in ordered patterns and drastic changes in morphology, which can lead to advanced functions of materials and structures. In the second part of this talk, I will demonstrate how to harness mechanical instabilities in soft materials to develop phase-transforming metamaterials, stretchable electronic devices, and soft robots.
Bio: 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, stimuli-responsive materials, and soft robot designing. Her current work focuses on mechanics of stretchable electronics.