A micromechanically motivated model is proposed to capture nonlinear effects and switching phenomena present in ferroelectric polycrystalline materials. The changing remnant state of the ferroelectric crystal is accounted for by means of so-called back fields-such as back stressesto resist or assist further switching processes in the crystal depending on the local loading history. To model intergranular effects present in ferroelectric polycrystals, the computational model elaborated is embedded into a mixed polygonal finite element approach, whereby an individual ferroelectric grain is represented by one single irregular polygonal finite element. This computationally efficient coupled simulation framework is shown to reproduce the specific characteristics of the responses of ferroelectric polycrystals under complex electromechanical loading conditions in good agreement with experimental observations.

Personalized cooling can provide comfort on the go and ultimately consume a fraction of the energy consumed by traditional space cooling techniques. Thermoelectric cooling (TEC) has emerged as a promising technology that can help us achieve personalized thermoregulation, but there is a lack of realization and application of flexible thermoelectric cooling modules for wearable applications. To promote the understanding and development of cooling devices working on thermoelectric principles, this paper discusses the methodology used for designing and characterizing wearable thermoelectric cooling modules for human body thermoregulation. A methodology to design a Flexible TEC device capable of achieving up to a temperature drop of 3 °C from high ambient temperature of 35 °C with low current consumption of 0.2-0.4 A and low heat transfer coefficient of 20 W m −2 K −1 has been discussed. The module uses low fill factor (<10%) and high aspect ratio (>2) of legs to work in a highly resistive environment without needing external heat sinks for heat dissipation, capable of removing up to 0.08 W cm −2 of heat on cold side and providing more than 0.12 W cm −2 on the hot side.

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A two-dimensional constitutive model based on micromechanical domain rotation events is presented in this work to demonstrate the nonlinear actuator behavior of magnetostrictive materials, in particular, Galfenol. The model constructed upon thermodynamic principles accounts back fields which resist or aid the domain rotation events inside a grain due to external magnetomechanical loading. The developed model is then incorporated into the polygonal finite element technique that combines Voronoi-based discretization with the hybrid finite element method. In this approach, the stress and magnetic flux density are treated as approximate functions inside the element, but the mechanical displacement and magnetic potential, which act as degrees of freedom, are defined only along the element boundary. This approach allows each randomly generated Voronoi polygon in the plane discretization to act as a single finite element mimicking an individual magnetomechanical grain in a polycrystalline Galfenol, eliminating the need for further subdiscretization of the Voronoi polygon. This coupled framework simulates the nonlinear actuator characteristics of the magnetostrictive material under complex magnetomechanical loading conditions in line with the experimental observations reported in the literature.

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