@article{KolloscheKofodSuoetal.2015,
  author    = {Kollosche, Matthias and Kofod, Guggi and Suo, Zhigang and Zhu, Jian},
  title     = {Temporal evolution and instability in a viscoelastic dielectric elastomer},
  series = {Journal of the mechanics and physics of solids},
  volume    = {76},
  journal   = {Journal of the mechanics and physics of solids},
  publisher = {Elsevier},
  address   = {Oxford},
  issn      = {0022-5096},
  doi       = {10.1016/j.jmps.2014.11.013},
  pages     = {47 -- 64},
  year      = {2015},
  abstract  = {Dielectric elastomer transducers are being developed for applications in stretchable electronics, tunable optics, biomedical devices, and soft machines. These transducers exhibit highly nonlinear electromechanical behavior: a dielectric membrane under voltage can form wrinkles, undergo snap-through instability, and suffer electrical breakdown. We investigate temporal evolution and instability by conducting a large set of experiments under various prestretches and loading rates, and by developing a model that allows viscoelastic instability. We use the model to classify types of instability, and map the experimental observations according to prestretches and loading rates. The model describes the entire set of experimental observations. A new type of instability is discovered, which we call wrinkle-to-wrinkle transition. A flat membrane at a critical voltage forms wrinkles and then, at a second critical voltage, snaps into another state of winkles of a shorter wavelength. This study demonstrates that viscoelasticity is essential to the understanding of temporal evolution and instability of dielectric elastomers. (C) 2014 Elsevier Ltd. All rights reserved.},
  language  = {en}
}
@article{ZhuKolloscheLuetal.2012,
  author    = {Zhu, Jian and Kollosche, Matthias and Lu, Tongqing and Kofod, Guggi and Suo, Zhigang},
  title     = {Two types of transitions to wrinkles in dielectric elastomers},
  series = {Soft matter},
  volume    = {8},
  journal   = {Soft matter},
  number    = {34},
  publisher = {Royal Society of Chemistry},
  address   = {Cambridge},
  issn      = {1744-683X},
  doi       = {10.1039/c2sm26034d},
  pages     = {8840 -- 8846},
  year      = {2012},
  abstract  = {A membrane of a dielectric elastomer coated with compliant electrodes may form wrinkles as the applied voltage is ramped up. We present a combination of experiment and theory to investigate the transition to wrinkles using a clamped membrane subject to a constant force and a voltage ramp. Two types of transitions are identified. In type-I transition, the voltage-stretch curve is N-shaped, and flat and wrinkled regions coexist in separate areas of the membrane. The type-I transition progresses by nucleation of small wrinkled regions, followed by the growth of the wrinkled regions at the expense of the flat regions, until the entire membrane is wrinkled. By contrast, in type-II transition, the voltage-stretch curve is monotonic, and the entire flat membrane becomes wrinkled with no nucleation barrier. The two types of transitions are analogous to the first and the second order phase transitions. While the type-I transition is accompanied by a jump in the vertical displacement, type-II transition is accompanied by a continuous change in the vertical displacement. Such transitions may enable applications in muscle-like actuation and energy harvesting, where large deformation and large energy of conversion are desired.},
  language  = {en}
}
@article{KolloscheZhuSuoetal.2012,
  author    = {Kollosche, Matthias and Zhu, Jian and Suo, Zhigang and Kofod, Guggi},
  title     = {Complex interplay of nonlinear processes in dielectric elastomers},
  series = {Physical review : E, Statistical, nonlinear and soft matter physics},
  volume    = {85},
  journal   = {Physical review : E, Statistical, nonlinear and soft matter physics},
  number    = {5},
  publisher = {American Physical Society},
  address   = {College Park},
  issn      = {1539-3755},
  doi       = {10.1103/PhysRevE.85.051801},
  pages     = {4},
  year      = {2012},
  abstract  = {A combination of experiment and theory shows that dielectric elastomers exhibit complex interplay of nonlinear processes. Membranes of a dielectric elastomer are prepared in various states of prestretches by using rigid clamps and mechanical forces. Upon actuation by voltage, some membranes form wrinkles followed by snap-through instability, others form wrinkles without the snap-through instability, and still others fail by local instability without forming wrinkles. Membranes surviving these nonlinear processes are found to attain a constant dielectric strength, independent of the state of prestretches. Giant voltage-induced stretch of 3.6 is attained.},
  language  = {en}
}
@article{ZhuStoyanovKofodetal.2010,
  author    = {Zhu, Jian and Stoyanov, Hristiyan and Kofod, Guggi and Suo, Zhigang},
  title     = {Large deformation and electromechanical instability of a dielectric elastomer tube actuator},
  issn      = {0021-8979},
  doi       = {10.1063/1.3490186},
  year      = {2010},
  abstract  = {This paper theoretically analyzes a dielectric elastomer tube actuator (DETA). Subject to a voltage difference between the inner and outer surfaces, the actuator reduces in thickness and expands in length, so that the same voltage will induce an even higher electric field. This positive feedback may cause the actuator to thin down drastically, resulting in electrical breakdown. We obtain an analytical solution of the actuator undergoing finite deformation when the elastomer obeys the neo-Hookean model. The critical strain of actuation is calculated in terms of various parameters of design. We also discuss the effect of the strain-stiffening on electromechanical behavior of DETAs by using the model of freely joined links. (C) 2010 American Institute of Physics. [doi:10.1063/1.3490186]},
  language  = {en}
}