http://hdl.handle.net/10379/595 Sun, 29 Oct 2017 23:49:54 GMT 2017-10-29T23:49:54Z http://hdl.handle.net/10379/6522 Oblique wrinkles Carfagna, M.; Destrade, Michel; Gower, Artur L.; Grillo, A. We prove theoretically that when a soft solid is subjected to an extreme deformation, wrinkles can form on its surface at an angle that is oblique to a principal direction of stretch. These oblique wrinkles occur for a strain that is smaller than the one required to obtain wrinkles normal to the direction of greatest compression. We go on to explain why they will probably never be observed in real-world experiments.This article is part of the themed issue 'Patterning through instabilities in complex media: theory and applications'. Mon, 03 Apr 2017 00:00:00 GMT http://hdl.handle.net/10379/6522 2017-04-03T00:00:00Z http://hdl.handle.net/10379/6484 Catastrophic thinning of dielectric elastomers Zurlo, G.; Destrade, Michel; DeTommasi, M.; Puglisi, G. We provide an energetic insight into the catastrophic nature of thinning instability in soft electroactive elastomers. This phenomenon is a major obstacle to the development of giant actuators, yet it is neither completely understood nor modeled accurately. In excellent agreement with experiments, we give a simple formula to predict the critical voltages for instability patterns; we model their shape and show that reversible (elastic) equilibrium is impossible beyond their onset. Our derivation is fully analytical, does not require finite element simulations, and can be extended to include prestretch and various material models. Wed, 15 Feb 2017 00:00:00 GMT http://hdl.handle.net/10379/6484 2017-02-15T00:00:00Z http://hdl.handle.net/10379/6483 Elastic Cherenkov effects in transversely isotropic soft materials-I: Theoretical analysis, simulations and inverse method Li, Guo-Yang; Zheng, Yang; Liu, Yanlin; Destrade, Michel; Cao, Yanping A body force concentrated at a point and moving at a high speed can induce shear-wave Mach cones in dusty-plasma crystals or soft materials, as observed experimentally and named the elastic Cherenkov effect (ECE). The ECE in soft materials forms the basis of the supersonic shear imaging (SSI) technique, an ultrasound-based dynamic elastography method applied in clinics in recent years. Previous studies on the ECE in soft materials have focused on isotropic material models. In this paper, we investigate the existence and key features of the ECE in anisotropic soft media, by using both theoretical analysis and finite element (FE) simulations, and we apply the results to the non-invasive and non-destructive characterization of biological soft tissues. We also theoretically study the characteristics of the shear waves induced in a deformed hyperelastic anisotropic soft material by a source moving with high speed, considering that contact between the ultrasound probe and the soft tissue may lead to finite deformation. On the basis of our theoretical analysis and numerical simulations, we propose an inverse approach to infer both the anisotropic and hyperelastic parameters of incompressible transversely isotropic (TI) soft materials. Finally, we investigate the properties of the solutions to the inverse problem by deriving the condition numbers in analytical form and performing numerical experiments. In Part II of the paper, both ex vivo and in vivo experiments are conducted to demonstrate the applicability of the inverse method in practical use. Sat, 25 Jun 2016 00:00:00 GMT http://hdl.handle.net/10379/6483 2016-06-25T00:00:00Z http://hdl.handle.net/10379/6482 Methodical fitting for mathematical models of rubber-like materials Destrade, Michel; Saccomandi, Giuseppe; Sgura, Ivonne A great variety of models can describe the nonlinear response of rubber to uniaxial tension. Yet an in-depth understanding of the successive stages of large extension is still lacking. We show that the response can be broken down in three steps, which we delineate by relying on a simple formatting of the data, the so-called Mooney plot transform. First, the small-to-moderate regime, where the polymeric chains unfold easily and the Mooney plot is almost linear. Second, the strain-hardening regime, where blobs of bundled chains unfold to stiffen the response in correspondence to the 'upturn' of the Mooney plot. Third, the limiting-chain regime, with a sharp stiffening occurring as the chains extend towards their limit. We provide strain-energy functions with terms accounting for each stage that (i) give an accurate local and then global fitting of the data; (ii) are consistent with weak nonlinear elasticity theory and (iii) can be interpreted in the framework of statistical mechanics. We apply our method to Treloar's classical experimental data and also to some more recent data. Our method not only provides models that describe the experimental data with a very low quantitative relative error, but also shows that the theory of nonlinear elasticity is much more robust that seemed at first sight. Wed, 08 Feb 2017 00:00:00 GMT http://hdl.handle.net/10379/6482 2017-02-08T00:00:00Z