wrinkling

A highly stretched hyperelastic shell exhibits a coupling behavior of local wrinkling and global bending within the stability boundary, and curvature resists and can even suppress surface wrinkles beyond a critical threshold. Here, we report a novel phenomenon that smooth surface maintains upon stretching a soft shell, while wrinkles emerge upon unloading, which implies a nonlinear interplay between curvature and Mullins (stress softening and residual strain) effects in the entire loading-unloading cycle.

V. Slesarenko and S. Rudykh, Harnessing viscoelasticity and instabilities for tuning wavy patterns in soft layered composites. Soft Matter (2016)  DOI: 10.1039/C5SM02949J

Zheng Jia, Teng Li, Failure Mechanics of a Wrinkling Thin Film Anode on a Substrate under Cyclic Charging and Discharging, Extreme Mechanics Letters, accepted, 2016 (DOI:doi:10.1016/j.eml.2016.03.006)

PhD project 2 (Reference: NGCM-0080)

Design and optimisation of bio-inspired programmable surfaces with active materials

Biotribology Group, nCATS
Faculty of Engineering and the Environment
University of Southampton, United Kingdom

Background

PhD project 1 (Reference: NGCM-0011)

Generalised asymptotic numerical methods for buckling instability problems in biological systems and bio-inspired morphing structures

Biotribology Group, nCATS
Faculty of Engineering and the Environment
University of Southampton, United Kingdom

Background

Spatial pattern formation in stiff thin films on soft substrates is investigated from a multi-scale point of view based on a technique of slowly varying Fourier coefficients. A general macroscopic modeling framework is developed and then a simplified macroscopic model is derived. The model incorporates Asymptotic Numerical Method (ANM) as a robust path-following technique to trace the post-buckling evolution path and to predict secondary bifurcations.

F. Xu, Y. Koutsawa, M. Potier-Ferry, S. Belouettar

http://dx.doi.org/10.1016/j.ijsolstr.2015.06.007

Abstract:

F. Xu, M. Potier-Ferry, S. Belouettar, H. Hu

International Journal of Non-Linear Mechanics (2014), http://dx.doi.org/10.1016/j.ijnonlinmec.2014.12.006

Abstract:

Self-positioned nanomembranes such as rolled-up tubes and wrinkled thin films have been potential systems for a variety of applications and basic studies on elastic properties of nanometer-thick systems. Although there is a clear driving force towards elastic energy minimization in each system, the exploration of intermediate states where specific characteristics could be chosen by a slight modification of a processing parameter had not been experimentally realized.

Xu, F., Potier-Ferry, M., Belouettar, S., Cong, Y.,

International Journal of Solids and Structures (2014), doi: http://dx.doi.org/10.1016/j.ijsolstr.2014.06.023

Abstract:

This chapter summarizes our works on surface wrinkling of elastic thin films, taking a kinetics approach as a physical pathway to both ordered and disordered wrinkle patterns.

A post-doctoral position is available in the lab of Sachin Velankar at the University of Pittsburgh to conduct experimental research on buckling of soft tissues in cephalopods (octopus or cuttlefish).

A thin film subject to compressive strain can either bend (for large strain gradient) or wrinkle (for small strain gradient). The bending is traditionally used in thermostats (bimetal stripes), but couple of years ago, it was extended to the nanoscale thin films which can bend and roll-up to tubes with defined number of rotations. The wrinkles are also rather common in macro- and microscale thin films.
Here, we developed an equilibrium phase diagram for the shape of
compressively strained free-hanging films by total strain energy
minimization.

H. Mei, J.Y. Chung, H.-H. Yu, C.M. Stafford, and R. Huang, Buckling modes of elastic thin films on elastic substrates. Applied Physics Letters 90, 151902 (2007).

Two modes of thin film buckling are commonly observed, one with interface delamination (e.g., telephone cord blisters) and the other with no delamination (i.e., wrinkling). Which one would occur for your film?

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.