Extension–torsion–inflation coupling in compressible electroelastomeric thin tubes

We present an axisymmetric and axially homogeneous variational formulation to obtain coupled extension–torsion–inflation deformation in compressible electroelastomeric tubes in the presence of axial and radial electric fields. We show that such deformations occur under the following two conditions: (1) only the axial electric field is imposed, with the electric poling direction in the tube (if present) lying in the radial plane; and (2) only the radial electric field is imposed within the tube, with the electric poling direction (if present) also along the radial direction. The poling direction in condition (1) generates helical anisotropy in the tube. We then obtain the governing differential equations necessary to solve the above deformation problem for thick tubes. We further apply the thin tube limit to obtain simplified algebraic equations to solve the same deformation problem. The effect of applied electric field parameters on the extension–inflation coupling and induced internal pressure vs. imposed inflation behavior is finally presented through numerical solution of the above obtained algebraic equations. The study will be useful in designing soft electroelastic tubular actuators.

Unusual extension–torsion–inflation couplings in pressurized thin circular tubes with helical anisotropy

We present a thin tube formulation for coupled extension–torsion–inflation deformation in helically reinforced pressurized circular tubes. Both compressible and incompressible tubes are considered. On applying the thin tube limit, the nonlinear ordinary differential equation to obtain the in-plane radial displacement is converted into a set of two simple algebraic equations for the compressible case and one equation for the incompressible case. This allows us to obtain analytical expressions, in terms of the tube’s intrinsic twist, material constants, and the applied pressure, which can predict whether such tubes would overwind/unwind on being infinitesimally stretched or exhibit positive/negative Poisson’s effect. We further show numerically that such tubes can be tuned to generate initial overwinding followed by rapid unwinding as observed during finite stretching of a torsionally relaxed DNA. Finally, we demonstrate that such tubes can also exhibit usual deflation initially followed by unusual inflation as the tube is finitely stretched.

Stress Effects on Magnetic Properties of Amorphous Microwires Subjected to Current Annealing

Effects of current annealing on magnetic hysteresis properties and magnetoimpedance (MI) of glass-coated amorphous microwires with nominal composition of Co71Fe5B11Si10Cr3 and small positive magnetostriction were investigated with the purpose to control the magnetic anisotropy. We have demonstrated that current annealing can produce a controllable change in the easy anisotropy direction from almost axial to circular, depending on the annealing time. The induced magnetization configuration is very sensitive to the applied tensile stress. The combination of positive magnetostriction and helical anisotropy makes it possible to realise large stress-magnetoimpedance (S-MI) effect without use of any dc bias fields owing to the directional change in magnetization. This is especially important for microwave frequency S-MI effect and can be very interesting for developing stress-sensors operating at the high frequency region.

Bias Current Effect on Second Harmonic in Asymmetric Magnetoimpedance Response in Amorphous Microwires

The influence of bias current on the second harmonic in the nonlinear magnetoimpedance in an amorphous microwire with a helical anisotropy is studied theoretically. The voltage response of the microwire is found in the framework of a rotational model. It is shown that the application of the bias current leads to the asymmetry in the field dependence of second harmonic. The second harmonic amplitude is analyzed as a function of the external field, current amplitude and the value of the bias current. The conditions of maximum field sensitivity of the second harmonic are found.

Torsion Dependence of Domain Transition and MI Effect of Melt-Extracted Co68.15Fe4.35Si12.25B13.25Nb1Cu1Microwires

We present the torsional stress induced magnetoimpedance (MI) effect and surface domain structure evolution of magnetostrictive melt-extracted Co68.15Fe4.35Si12.25B13.25Nb1Cu1microwires. Experimental results indicate that the surface domain structures observed by magnetic force microscope (MFM) transform from the weak circumferential domain of as-cast state to the helical domain under large torsional strain of 81.6 (2π rad/m). Domain wall movement distorts at torsional strainξ=20.4(2π rad/m) and forms a helical anisotropy with an angle of around 30° versus axial direction of wire. At 15 MHz, the maximum of GMI ratioΔZ/Z(%) increases to 194.4% atξ=20.4(2π rad/m) from 116.3% of the as-cast state and then decreases to 134.9% atξ=102.0(2π rad/m). The torsion magnetoimpedance (TMI) ratioΔZ/Zξ(%) is up to 290%. Based on this large torsional strain and high MI ratio, the microwire can be as an referred candidate for high-performance TMI sensor application.