Distributed Electro-Mechanical Coupling Effects in a Dielectric Elastomer Membrane Array

Background Dielectric elastomer (DE) transducers permit to efectively develop large-deformation, energy-efcient, and compliant mechatronic devices. By arranging many DE elements in an array-like confguration, a soft actuator/sensor system capable of cooperative features can be obtained. When many DE elements are densely packed onto a common elastic membrane, spatial coupling efects introduce electro-mechanical interactions among neighbors, which strongly afect the system actuation and sensing performance. To efectively design cooperative DE systems, those coupling efects must be systematically characterized and understood frst. Objective As a frst step towards the development of complex cooperative DE systems, in this work we present a systematic characterization of the spatial electro-mechanical interactions in a 1-by-3 array of silicone DEs. More specifcally, we investigate how the force and capacitance characteristics of each DE in the array change when its neighbors are subject to diferent types of mechanical or electrical loads. Force and capacitance are chosen for this investigation, since those quantities are directly tied to the DE actuation and sensing behaviors, respectively. Methods An electro-mechanical characterization procedure is implemented through a novel experimental setup, which is specifcally developed for testing soft DE arrays. The setup allows to investigate how the force and capacitance characteristics of each DE are afected by static deformations and/or electrical voltages applied to its nearby elements. Diferent combinations of electro-mechanical loads and DE neighbors are considered in an extensive experimental campaign. Results The conducted investigation shows the existence of strong electro-mechanical coupling efects among the diferent array elements. The interaction intensity depends on multiple parameters, such as the distance between active DEs or the amount of deformation/voltage applied to the neighbors, and provides essential information for the design of array actuators. In some cases, such coupling efects may lead to changes in force up to 9% compared to the reference confguration. A further coupling is also observed in the DE capacitive response, and opens up the possibility of implementing advanced and/or distributed self-sensing strategies in future applications. Conclusion By means of the conducted experiments, we clearly show that the actuation and sensing characteristics of each DE in the array are strongly infuenced by the electro-mechanical loading state of its neighbors. The coupling efects may signifcantly afect the overall cooperative system performance, if not properly accounted for during the design. In future works, the obtained results will allow developing cooperative DE systems which are robust to, and possibly take advantage of, such spatial coupling efects

Direct Stochastic Equivalent Linearization of SDOF Smart Mechanical System

The first and second moments of response variables for SDOF system with pseudoelastic material are obtained by a direct linearization procedure. This procedure is an adaptation of well-known statistical linearization methods, and provides concise, model-independent linearization coefficients. The method can be applied to systems that incorporate any SMA hysteresis model having a differential constitutive equation, and can be used for zero and non-zero mean random vibration. This implementation eliminates the effort of deriving linearization coefficients for new SMA hysteresis model. In this paper the complete statistical response of SDOF system containing a mass and a bar made of SMA is obtained via direct linearization procedure. The model considered is modification of phenomenological one-dimensional constitutive model originally proposed by Graesser and Cozzarelli, which provides the capability to model both the martensitic twinning hysteresis and martensitic-austenite pseudoelastic behavior, typical of shape memory alloys. Response statistics for zero mean random vibration are obtained. Furthermore, non-zero mean analysis of the system is carried out and comparisons are made with Monte Carlo simulation

Random vibration studies of an SDOF system with shape memory restoring force

Intelligent and adaptive material systems and structures have become very important in engineering applications. The basic characteristic of these systems is the ability to adapt to the environmental conditions. A new class of materials with promising applications in structural and mechanical systems is shape memory alloy (SMA). The mechanical behavior of shape memory alloys in particular shows a strong dependence on temperature. This property provides opportunities for the utilization of SMAs in actuators or energy dissipation devices. However, the behavior of systems containing shape memory components under random excitation has not yet been addressed in the literature. Such a study is important to verify the feasibility of using SMAs in structural systems. In this work a nondeterministic study of the dynamic behavior of a single-degree-of-freedom (SDOF) mechanical system, having a Nitinol spring as a restoring force element is presented. The SMA spring is characterized using a one-dimensional phenomenological constitutive model based on the classical Devonshire theory. Response statistics for zero mean random vibration of the SDOF under a wide range of temperature is obtained. Furthermore, nonzero mean analysis of these systems is carried out

A free energy model for magneto-mechanically coupled NiMnGa single crystals

This paper presents a one-dimensional magneto-mechanical model for NiMnGa. Following a modeling approach developed by the authors for conventional shape memory behavior and ferroelectricity, a constitutive Helmholtz free energy landscape with strain and magnetization as order parameters is constructed for a representative meso-scale lattice element. The landscape includes three paraboloidal energy wells representing the two easy-axis and one hard-axis martensite variants distinguishable in the chosen coordinate system. The resulting stress- and magnetic-field-dependent Gibbs free energy expressions are then used within the theory of thermally activated processes to derive a series of phase-fraction evolution equations. The phase fractions subsequently determine the macroscopic strain and magnetization of a sample of NiMnGa by a standard averaging procedure. Results from the model are compared to experimental data and demonstrate the model's ability to reproduce constitutive behaviors of the material. Future work includes an extension to a full thermo-magneto-mechanical model accounting for the occurrence of austenite and inhomogeneity effects and configured to function within the tensile-stress regime