| 1. |
- Haldar, K., et al.
(författare)
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Finite element simulation of rate-dependent magneto-active polymer response
- 2016
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Ingår i: Smart Materials and Structures. - : IOP Publishing. - 0964-1726 .- 1361-665X. ; 25:10
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Tidskriftsartikel (refereegranskat)abstract
- This contribution is concerned with the embedding of constitutive relations for magneto-active polymers (MAP) into finite element simulations. To this end, a recently suggested, calibrated, and validated material model for magneto-mechanically coupled and rate-dependent MAP response is briefly summarized in its continuous and algorithmic settings. Moreover, the strongly coupled field equations of finite deformation magneto-mechanics are reviewed. For the purpose of numerical simulation, a finite element model is then established based on the usual steps of weak form representation, discretization and consistent linearization. Two verifying inhomogeneous numerical examples are presented in which a classical 'plate with a hole' geometry is equipped with MAP properties and subjected to different types of time-varying mechanical and magnetic loading.
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| 2. |
- Hellberg, Rasmus, et al.
(författare)
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Non-reflecting dispersive media
- 1992
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Ingår i: Smart Materials and Structures. - : IOP Publishing. - 0964-1726 .- 1361-665X. ; 1:4, s. 46-341
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Tidskriftsartikel (refereegranskat)abstract
- The modeling of non-reflecting one-dimensional dispersive media is discussed. The media are temporal dispersive with a spatially varying impedance. It is shown that the effects from the variation of the impedance can be matched by the temporal dispersive effects so that the media do not reflect any field regardless of the shape of the incident transient field. The problem of finding reflectionless media is formulated as an inverse problem where the constitutive relation is to be determined as a function of depth given a reflection kernel which is zero. A time-domain Green functions technique is used to solve the inverse problem.
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| 3. |
- Kiefer, Björn, et al.
(författare)
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Implementation of numerical integration schemes for the simulation of magnetic SMA constitutive response
- 2012
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Ingår i: Smart Materials and Structures. - : IOP Publishing. - 0964-1726 .- 1361-665X. ; 21:9
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Tidskriftsartikel (refereegranskat)abstract
- Several constitutive models for magnetic shape memory alloys (MSMAs) have been proposed in the literature. The implementation of numerical integration schemes, which allow the prediction of constitutive response for general loading cases and ultimately the incorporation of MSMA response into numerical solution algorithms for fully coupled magneto-mechanical boundary value problems, however, has received only very limited attention. In this work, we establish two algorithmic implementations of the internal variable model for MSMAs proposed in (Kiefer and Lagoudas 2005 Phil. Mag. Spec. Issue: Recent Adv. Theor. Mech. 85 4289–329, Kiefer and Lagoudas 2009 J. Intell. Mater. Syst. 20 143–70), where we restrict our attention to pure martensitic variant reorientation to limit complexity. The first updating scheme is based on the numerical integration of the reorientation strain evolution equation and represents a classical predictor–corrector-type general return mapping algorithm. In the second approach, the inequality-constrained optimization problem associated with internal variable evolution is converted into an unconstrained problem via Fischer–Burmeister complementarity functions and then iteratively solved in standard Newton–Raphson format. Simulations are verified by comparison to closed-form solutions for experimentally relevant loading cases.
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| 4. |
- Köhler, Elof, 1980, et al.
(författare)
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High temperature energy harvester for wireless sensors
- 2014
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Ingår i: Smart Materials and Structures. - : IOP Publishing. - 0964-1726 .- 1361-665X. ; 23:9, s. Art. no. 095042-
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Tidskriftsartikel (refereegranskat)abstract
- Implementing energy harvesters and wireless sensors in jet engines will simplify development and decrease costs by reducing the need for cables. Such a device could include a small thermoelectric generator placed in the cooling channels of the jet engine where the temperature is between 500-900 degrees C. This paper covers the synthesis of suitable thermoelectric materials, design of module and proof of concept tests of a thermoelectric module. The materials and other design variables were chosen based on an analytic model and numerical analysis. The module was optimized for 600-800 degrees C with the thermoelectric materials n-type Ba8Ga16Ge30 and p-type La-doped Yb14MnSb11, both with among the highest reported figure-of-merit values, zT, for bulk materials in this region. The materials were synthesized and their structures confirmed by x-ray diffraction. Proof of concept modules containing only two thermoelectric legs were built and tested at high temperatures and under high temperature gradients. The modules were designed to survive an ambient temperature gradient of up to 200 degrees C. The first measurements at low temperature showed that the thermoelectric legs could withstand a temperature gradient of 123 degrees C and still be functional. The high temperature measurement with 800 degrees C on the hot side showed that the module remained functional at this temperature.
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| 5. |
- Menzel, Andreas, et al.
(författare)
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Two models to simulate rate-dependent domain switching effects - application to ferroelastic polycrystalline ceramics
- 2008
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Ingår i: Smart Materials and Structures. - : IOP Publishing. - 0964-1726 .- 1361-665X. ; 17
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this paper is to study rate-dependent switching in ferroelastic materials. More specifically, a micro-mechanically motivated model is embedded into an iterative three-dimensional and electromechanically coupled finite element framework. An established energy-based criterion serves for the initiation of domain switching processes as based on reduction in (local) Gibbs free energy. Subsequent nucleation and propagation of domain walls is captured via a linear kinetics theory with rate-dependent effects being incorporated in terms of a deformation-dependent limit-time-parameter. With this basic model in hand, two different switching formulations are elaborated in this work: on the one hand, a straightforward volume-fraction-ansatz is applied with the volume-fraction-value depending on the limit-time-parameter; on the other hand, a reorientation-transformation-formulation is proposed, whereby the orientation tensor itself is assumed to depend on the limit-time-parameter. Macroscopic behaviour such as stress versus strains curves or stress versus electrical displacements graphs are obtained by applying straightforward volume-averaging-techniques to the three-dimensional finite-element-based simulation results which provides important insights into the rate-dependent response of the investigated ferroelastic materials.
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| 6. |
- Thylander, Sara, et al.
(författare)
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An electromechanically coupled micro-sphere framework: application to the finite element analysis of electrostrictive polymers
- 2012
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Ingår i: Smart Materials and Structures. - : IOP Publishing. - 0964-1726 .- 1361-665X. ; 21:9
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Tidskriftsartikel (refereegranskat)abstract
- The number of industrial applications of electroactive polymers (EAPs) is increasing and, consequently, the need for reliable modelling frameworks for such materials as well as related robust simulation techniques continuously increases. In this context, we combine the modelling of non-linear electroelasticity with a computational micro-sphere formulation in order to simulate the behaviour of EAPs. The micro-sphere approach in general enables the use of physics-based constitutive models like, for instance, the so-called worm-like chain model. By means of the micro-sphere formulation, scalar-valued micromechanical constitutive relations can conveniently be extended to a three-dimensional continuum setting. We discuss several electromechanically coupled numerical examples and make use of the finite element method to solve inhomogeneous boundary value problems. The incorporated material parameters are referred to experimental data for an electrostrictive polymer. The numerical examples show that the coupled micro-sphere formulation combined with the finite element method results in physically sound simulations that mimic the behaviour of an electrostrictive polymer.
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| 7. |
- Thylander, Sara, et al.
(författare)
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Towards control of viscous effects in acrylic-based actuator applications
- 2016
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Ingår i: Smart Materials and Structures. - : IOP Publishing. - 0964-1726 .- 1361-665X. ; 25:9
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Tidskriftsartikel (refereegranskat)abstract
- Dielectric elastomers offer clear advantages over more traditional and conventional materials when soft, lightweight, noiseless actuator applications with large deformations are considered. However, the viscous time-dependent behaviour associated with most elastomers limit the number of possible applications. For this purpose, the possibility of controlling the viscous response by regulating the applied electric potential is explored. The constitutive model chosen is calibrated to fit the electro-viscoelastic response of an acrylic elastomer often used in dielectric elastomer actuators. The response of both homogeneous deformation examples and inhomogeneous finite element boundary value problems, chosen to mimic existing applications, are presented. Control of both force and displacement quantities are successfully achieved.
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| 8. |
- Fuaad, Mariatul Rawdhah Ahmad, et al.
(författare)
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Electrostatic-hydraulic coupled soft actuator for micropump application
- 2024
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Ingår i: Smart materials and structures. - : Institute of Physics Publishing (IOPP). - 0964-1726 .- 1361-665X. ; 33:1
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Tidskriftsartikel (refereegranskat)abstract
- The development of a soft actuator with high displacement is crucial for the effective operation of micropumps, ensuring a high fluid pump rate. This study introduces an innovative approach by presenting the design and fabrication of a novel electrostatic-hydraulic coupled soft actuator for a micropump within a microfluidic system. This pioneering soft actuator, leveraging electrostatic-hydraulic coupling, showcases a unique solution to enhance the performance of micropumps. The versatility of such a soft actuator makes it particularly promising for biomedical applications. The actuator comprises dielectric fluid in an elastomeric shell and electrodes to form the out-of-plane fluid-amplified displacement. This displacement amplification was used to generate a pumping actuation in the micropump. The actuator was characterized in terms of dielectric fluid volume, electrode size, temporal response, and amplification displacement. The soft actuator showed a maximum amplified displacement of 0.51 mm at 10 kV of the applied voltage, but a higher voltage caused a dielectric breakdown. Moreover, the actuator demonstrated the ability to operate at frequencies of 0.25 Hz and 0.1 Hz. The results of the study indicate that the fabricated electrostatic-hydraulic coupled soft actuator is a dependable and effective method of actuation for a micropump in a microfluidic system. The experimental characterization of the micropump revealed a maximum flow rate of 2304 μl min−1.
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| 9. |
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| 10. |
- Köhler, Elof, 1980, et al.
(författare)
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Metal thermoelectric harvester for wireless sensors
- 2020
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Ingår i: Smart Materials and Structures. - 0964-1726 .- 1361-665X. ; 29:8
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Tidskriftsartikel (refereegranskat)abstract
- A metal thermoelectric energy harvester design with long metal couples was investigated for use with wireless sensors in environments where conventional thermoelectric harvesters are difficult to implement. Two thermoelectric harvesters with different designs was assembled by spot welding 110 mu m thick molybdenum foil and 150 mu m thick nickel foil together in a zigzag-pattern, one 3-couples design (55 mm length and 6 mm width) insulated with glass fiber at the hot side and polyimide tape at the cold side, and one 10-couples design (300 mm length and 3 mm width) insulated with polyimide tape across the entire length. The voltage- and power output were measured at different temperatures and load resistance with maximum power output of 588 mu W at 269 degrees C for the 3-couples harvester and 868 mu W at 241 degrees C for the 10-couples harvester. The power output after power management electronics for the 10-couples harvester measured 290 mu W at 51 mV. The harvesters were compared to a conventional semiconductor thermoelectric device coupled with a 300 mm long copper heat bridge giving a power output after power management electronics of 170 mu W at 41 mV with 226 degrees C temperature gradient of the environment.
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