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Fan Xu's picture

Morphomechanics of growing curled petals and leaves

Petals and leaves are usually curled and exhibit intriguing morphology evolution upon growth, which contributes to their important biological functions. To understand the underlying morphoelastic mechanism and to determine the crucial factors that govern the growth-induced instability patterning in curved petals and leaves, we develop an active thin shell model that can describe variable curvatures and spontaneous growth, within the framework of general differential geometry based on curvilinear coordinates and hyperelastic deformation theory.

Fan Xu's picture

Competition between Mullins and curvature effects in the wrinkling of stretched soft shells

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.

Luca-Deseri's picture

Uniaxial stretch-release of rubber-plastic bilayers: strain dependent transition to stable helices, rolls, saddles, and tubes

Polymeric plastics deform irreversibly (i.e., inelastically) whereas rubbers deform reversibly, i.e., elastically.

Thus, uniaxially stretching a rubber-plastic bilayer composite beyond its yield point can create an elastic strain mismatch between the two layers. Upon release, the bilayer may then bend out-of-plane.

Zheng Jia's picture

Failure Mechanics of a Wrinkling Thin Film Anode on a Substrate under Cyclic Charging and Discharging

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)

 

Georges Limbert's picture

Fully-funded PhD position in Computational Mechanics [#1] for EU students for September 2016, University of Southampton, UK

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

Fan Xu's picture

A multi-scale modeling framework for instabilities of film/substrate systems

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.

Cai Shengqiang's picture

Diffusion-induced wrinkling instability in a circular poroelastic plate

A poroelastic material can imbibe solvent and swell. When the material swells inhomogeneously or

swells under external constraints, stresses can develop inside the material. The stresses can trigger

mechanical instabilities in the material or even break the material, which have been often observed

in experiments. In this paper, we study the wrinkling instability of a circular poroelastic plate, in

the process of solvent molecules migrating into the plate from the edge. The critical conditions for

Probing the intermediate states between rolling-up and wrinkling thin films

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.

Stephan Rudykh's picture

Wrinkling of Interfacial Layers in Stratified Composites

by Y. Li, N. Kaynia, S. Rudykh and M. C. Boyce

 Massachusetts Institute of Technology 

 Abstract:

 

Rui Huang's picture

A kinetics approach to surface wrinkling of elastic films

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.

Cardboard rolls on the nanoscale

Everybody knows that cardboard paper can be a highly
anisotropic material. You can easily bend or roll it in one direction
and it is stiff in the other. If you take a close look you will find
that the paper is periodically buckled along one direction. We have now
exploited this phenomenon on the nanoscale to define the roll-up
direction of ultra-thin membranes on a substrate surface.

Post-doctoral position at Univ. Pittsburgh: soft tissue buckling

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).

Bending and wrinkling as competing relaxation pathways for strained free-hanging films

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.

Rui Huang's picture

Thin films: wrinkling vs buckle-delamination

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?

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