patterns

Dear Colleagues,

Our paper on elastic instabilities in soft fiber composites recently got published in International Journal of Engineering Science. In this paper, we explore how the stiffening behavior of composites phases influences the development of instabilities and associated buckling patterns. To do that, we use non-Gaussian hyperleastic  model to define the constitutive behavior of phases. 

Smart soft materials, because of their mechanical flexibility and quick response to multi-physics stimuli, have drawn considerable attention over the past few years. Here, we present controllable wrinkling patterns of a liquid crystal polymer film attached on a soft substrate, controlled by laser illumination that holds unique optical characteristics of high coherence and irradiance.

Article in Journal of The Royal Society Interface · January 2017DOI: 10.1098/rsif.2016.0996

Rui Huang and Se Hyuk Im, Physical Review E 74, 026214 (2006).

A stressed thin film on a soft substrate can develop complex wrinkle patterns. The onset of wrinkling and initial growth is well described by a linear perturbation analysis, and the equilibrium wrinkles can be analyzed using an energy approach. In between, the wrinkle pattern undergoes a coarsening process with a peculiar dynamics. By using a proper scaling and two-dimensional numerical simulations, this paper develops a quantitative understanding of the wrinkling dynamics from initial growth through coarsening till equilibrium. It is found that, during the initial growth, a stress-dependent wavelength is selected and the wrinkle amplitude grows exponentially over time. During coarsening, both the wrinkle wavelength and amplitude increases, following a simple scaling law under uniaxial compression. Slightly different dynamics is observed under equi-biaxial stresses, which starts with a faster coarsening rate before asymptotically approaching the same scaling under uniaxial stresses. At equilibrium, a parallel stripe pattern is obtained under uniaxial stresses and a labyrinth pattern under equi-biaxial stresses. Both have the same wavelength, independent of the initial stress. On the other hand, the wrinkle amplitude depends on the initial stress state, which is higher under an equi-biaxial stress than that under a uniaxial stress of the same magnitude.

A possible explanation of the variety of fingerprints comes from the consideration of the mechanics of tissue growth. Formation of fingerprints can be a result of the surface buckling of the growing skin. Remarkably, the surface bifurcation enjoys infinite multiplicity. The latter can be a reason for the variety of fingerprints. Tissue morphogenesis with the surface buckling mechanism and the growth theory underlying this mechanism are presented in the attached notes.