In this paper we present a finite element (FE) approach for modelling the performance of multilayer unimorph dielectric elastomer actuators (MUDEAs) with inhomogeneous layer geometry. MUDEAs are made up of a dielectric elastomer actuator (DEA) stack bonded to a flexible substrate and are capable of large out-of-plane displacements and resonant operation. MUDEAs are useful for many applications such as steerable endoscopes for minimally invasive surgery procedures, where high manoeuvrability and mechanical flexibility are required. Models of MUDEAs are useful for feasibility assessment and actuator design optimisation. The current analytical models of unimorph DEAs are inadequate for more unconventional unimorph configurations with multiple layers. The FE approach presented is capable of efficiently modelling MUDEAs with non-uniform geometries and multiple layers. The Maxwell stress equation for MUDEAs was also derived and was found to be the same as for the unconstrained DEA case...

We report the results of tensile cyclic loading tests conducted to examine the dependence of constitutive relations for superelastic Cu–Al–Mn alloy rods on loading rates. Recently, Cu–Al–Mn alloy rods with diameters up to 8 mm have been developed by the authors, and it has been demonstrated that these rods have excellent superelastic strains of more than 8%, which is comparable to Ni–Ti alloys and far superior to other Cu-based alloys. No information is available, however, on the rate dependence of constitutive relations for Cu–Al–Mn alloys. In this study, we prepare two Cu–Al–Mn alloy rod specimens, whose lengths and diameters are 150 mm and 8 mm, respectively. Their stress–strain relations are examined under the loading frequencies of 0.001, 0.5, and 1 Hz with constant strain amplitude of 4.5%. It was found from the tests that the maximum stress increase in Cu–Al–Mn alloys due to higher loading rate was less than 5%. Thermo-mechanical analysis predicts that stress increase in C...

A new kind of magnetorheological elastomer (MRE), named porous magnetorheological elastomer (P-MRE), was prepared by filling with NH ₄HCO ₃. Two groups of samples with different content of NH ₄HCO ₃ and carbonyl iron particles were prepared. The microstructures of the samples were observed by using a digital microscope, and image analysis was applied to analyze the microstructure of P-MRE. The dynamic performance of the shear mode was also investigated under different magnetic flux densities. The shear storage modulus, MR effect and loss factor were calculated by using a mechanical property measurement system. The experimental results indicate that the NH ₄HCO ₃ has a greater impact on the properties of P-MRE, including the microstructures and dynamic mechanical performance. The increment of NH ₄HCO ₃ content enhances the porosity of P-MRE, and decreases the shear storage modulus. Moreover, P-MRE has ...

An efficient high-fidelity beam model for predicting multiphysics behavior of smart slender structures is developed using the variational asymptotic method. The original three-dimensional variational statement governing the coupled electromagneto-mechanical behavior is asymptotically split into a multiphysics cross-sectional analysis and a multiphysics beam analysis, exploiting the inherent small parameter characterizing the slenderness of the structure. Several examples are used to validate the proposed model by comparing the results available in the literature and three-dimensional finite element analysis.

This paper proposes a negative resistance electromagnetic shunt damping vibration isolator and investigates the effectiveness of the isolator. The isolator consists of a shunt circuit and a pair of electromagnet and permanent magnets that are pasted onto a box-shaped spring. A kind of negative resistance shunt impedance is proposed to cancel the inherent resistance of the electromagnet. The electromechanical coupling coefficient and the electromagnetic damping force calculation formula are obtained by Biot–Savart’s law and Ampère’s law, respectively. A single degree of freedom system is employed to verify the performance of the proposed isolator. The governing equation is established. The performance of the proposed isolator under a half-cycle sine pulse is investigated and discussed. Experiments were carried out and the results agreed well with the numerical predictions. Both the results demonstrate that the negative resistance electromagnetic shunt damping vibration isolator co...

The mechanical response of a series of semicrystalline shape memory polymers was considerably enhanced by incorporating short glass fibres without modifying the thermo-responsive actuation based on balanced crystallinity and elasticity. The effect of different fractions of inorganic reinforcement on thermo-mechanical properties was evaluated using different instrument techniques such as differential scanning calorimetry (DSC), thermogravimetry (TGA), dynamic mechanical thermal analysis (DMTA) and three-point flexural tests. Moreover, we studied the inorganic reinforcement influence on the shape memory actuation capabilities by thermo-mechanical bending cycle experiments. As demonstrated, the manufactured polymer composites showed excellent shape memory capacities, similar to neat active polymer matrices, but with outstanding improvements in static and recovering mechanical performance.

This paper presents the design, microfabrication, modeling and characterization of a piezoelectric energy harvester (PEH) system with a wide operating bandwidth introduced by mechanical stoppers. The wideband frequency responses of the PEH system with stoppers on one side and two sides are investigated thoroughly. The experimental results show that the operating bandwidth is broadened to 18 Hz (30–48 Hz) and the corresponding optimal power ranges from 34 to 100 nW at the base acceleration of 0.6 g and under top- and bottom-stopper distances of 0.75 mm and 1.1 mm, respectively. By adjusting the mechanical stopper distance, the output power and frequency bandwidth can be optimized accordingly.

A systematic design of a magneto-rheological fluid embedded pneumatic vibration isolator (MrEPI) considering practical constraints and optimal performance is proposed. The design procedure basically consists of three steps, i.e. system level design, component level design and practical realization. The system level design involves synthesizing appropriate non-dimensional system parameters of pneumatic spring and MR damper elements based on parameter sensitivity analysis considering requirements for compact and efficient hardware utilization. The component level design involves optimal design of the MR valve by minimizing an objective function in terms of non-dimensional geometric, material and excitation parameters, and guaranteeing required performance in the worst cases. Then practical realization involves determining actual plant parameters from the non-dimensional analysis in system and component level designs with the considerations of practical requirements/constraints. To ...

Photo-thermal actuation has been used to program the resonant frequency of a VO ₂-coated SiO ₂ micro-bridge. The SiO ₂ micro-bridge had nominal length, width, and thickness of 300, 45, and 4.15 µm, respectively. The thickness of the VO ₂ coating was 150 nm. The changes in resonant frequency are caused by stress changes on the bimorph structure during the coating’s insulator-to-metal-transition. A total of 13 resonant frequency memory states ranging from 215.5 to 222.7 kHz were programmed by laser pulses of increasing energy in steps of 0.7 µJ, focused on the micro-bridge structure. The device was maintained at 60 °C during programming experiments, and the memory was reset by driving the temperature outside the hysteresis loop. After programming the device to a particular resonant frequency, the memory state was stored for more than 24 h as long as the sample was maintained at the pre-heating temperature of 60 °C.

Long-term behaviour and fatigue endurance are the key issues in the utilization of SMA actuators, but systematic research work is still needed in this field. This study concentrates on the effects of three major design parameters on the long-term behaviour of binary Ti–49.7Ni-based actuators: the effect of the temperature interval used on thermal cycling, the effect of the stress level used and the effect of the heat-treatment state of the wire used. The long-term behaviour of the wires was studied in a custom-built fatigue test frame in which the wires were thermally cycled under a constant stress level. Before the fatigue testing, a series of heat treatments was carried out to generate optimal actuator properties for the wires. This paper concentrates on the systematic fractographic analysis of the fatigue fractured Ti–49.7Ni wires. The aim was to discover the relationships between the macro-scale behaviour and the microstructural changes of the material. During thermal cycling...