Dielectrics with great electrocaloric effect (ECE) have great potential to be applied in modern refrigeration industry. Compared with the traditional refrigeration technology, it is environmentally friendly and has a higher efficiency. Researchers have found that compared with ECE occurring in ferroelectric phase, ECE in paraelectric state is giant. This paper is determined on calculating the ECE of several kinds of polar dielectric material so as to find some materials with giant ECE. First, we investigate the theoretical framework of ECE near the Ferroelectric-Paraelectric phase transformation, and we show the formula derivation of ECE near the Ferroelectric-Paraelectric phase transformation in the analytical method of the calculus derivation. Then we deduce the expression of phenomenological study parameters. Finally, we calculate the maximum temperature change, entropy change and the mechanical work of several kinds of dielectrics based on the expression deduced. We successfully find some dielectrics with giant ECE. The paper should offer great help in finding the dielectrics with giant ECE, which is of great value in application.
Applied to voltage, a dielectric elastomer membrane may deform into a mixture of two states under certain
conditions. One of which is the flat state and the other is the wrinkled state. In the flat state, the membrane is
relatively thick with a small area, while on the contrary, in the wrinkled state, the membrane is relatively thin with a
large area. The coexistence of these two states may cause the electromechanical phase transition of dielectric
elastomer. The phase diagram of idea dielectric elastomer membrane under unidirectional stress and voltage inspired
us to think about the liquid-to-vapor phase transition of pure substance. The practical working cycle of a steam
engine includes the thermodynamical process of liquid-to-vapor phase transition, the fact is that the steam engine
will do the maximum work if undergoing the phase transition process. In this paper, in order to consider the
influence of coexistent state of dielectric elastomer, we investigate the homogeneous deformation of the dielectric
elastomer tube. The theoretical model is built and the relationship between external loads and stretch are got, we can
see that the elastomer tube experiences the coexistent state before reaching the stretching limit from the diagram. We
think these results can guide the design and manufacture of energy harvesting equipments.
Smart materials and structures is an international frontier field in current development of engineering and science. Representative of soft smart materials include Electroactive polymers (EAPs) and Shape Memory Polymers (SMPs), etc..As a new kind of smart deformation material, SMPs have a wide range of applications in the field of smart material and structures due to their controllable shape memory effects. Deformation mechanism of SMP material is the basis of its applications. This paper proposed an useful thermoviscoelastic constitutive model by considering thermal expansion, structure relaxation and viscoelastic properties of Epoxy-SMP material. To verify the applicability of the model, various experiments such as isothermal uniaxial tensile tests were carried out and then be simulated. The results showed that the constitutive model could nicely predict mechanical behavior of Epoxy-SMP, the proposed constitutive model is useful for the design of SMPs structures.