Quasi-static Torque Research Articles

Sommerfeld effect in a vibrocompaction process

This study addresses the influence of the Sommerfeld effect on the behaviour of vibrocompacting machines driven by unbalanced electric motors. Based on a simplified model with 4 degrees of freedom previously published by the authors, we investigate the dynamics of quasistatic vibrocompaction processes, i.e. those in which the compaction is achieved through a sufficiently slow increase in the input power of the electric motors. The main novel contribution of the paper is the characterization of the evolution of the system state through a quasistatic torque curve, which is analytically derived. This curve provides the maximum compaction that can be quasistatically achieved and the amount of motor torque required to reach a desired compaction level, while also revealing the specific way in which the Sommerfeld effect takes place in the system under study. The analytical results are used to give a clear physical interpretation to the numerical results previously published by the authors. Good agreement is found between numerical and analytical results.

Exploiting a Simple Asymmetric Pleating Method to Realize a Textile Based Bending Actuator

This work presents the design, modeling and control of an asymmetrically pleated textile actuator (APTA). The presented actuator utilizes a simple inflatable beam which is constrained asymmetrically using a pleat that is fixed only to a single side. Due to the difference in length between the constrained side and the unconstrained side, a bend at the pleat is generated upon inflation. This method utilizes sewing and/or heat sealing to create bending, making it easy to manufacture compared to many soft actuators and further allows for the creation of complex 3D structures in conjunction with methods presented in literature due to the in-plane bending generated by the presented pleating method. The design, fabrication and modeling of the APTA are presented and the actuator characterization in the form of bending angle, quasi-static torque and hysteresis tests are performed. A maximum normalized output torque of 400 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{Nm/kPa.m}^{3}$</tex-math></inline-formula> was demonstrated by the presented APTA. An empirical model for the APTA using the collected data was derived to predict torque output throughout the actuator range of motion. A controller using the empirical model was designed to track desired torque profiles. Single and Multiple step response experiments were conducted to evaluate the efficacy of the controller for burst-like actuation which could have implications in physical assistance for biological systems and in shape forming deployable structures. Further, we present several potential applications to this actuator in the form of 3D inflatable structures, a continuum module segment, and a wearable elbow device.

Simulation of Superconducting Machine With Stacks of Coated Conductors Using Hybrid A-H Formulation

This article consists on the first finite element analysis of quasi-static test of a superconducting machine with stacks of coated conductors arranged spirally around the rotor. The behavior of the machine as a generator is also investigated. Hybrid A-V-H 2D formulation and moving mesh were used as modeling framework. The stacks are represented with the homogenization technique. Quasi-static test is simulated considering a field cooling initial state and the generator simulation, a pulse field magnetization. Current density and magnetic flux density along the stack surface as well as speed and torque results are analyzed. When the machine is not moving, major current density loops are induced in the stack, following the magnetic poles. These loops are deformed by the current density induced by speed differences between stator and rotor. The quasi-static torque does not change with position. The simulation results prove the potential this topology has of operating as a generator. The quasi-static results are in agreement with measurements made with the prototype.

Quasi-Static Torque Profile Expressions for Magnetic Resonance-Based Remote Actuation

Resonant wireless power transfer has been employed to transfer electrical power from a transmitter to a receiver coil over an air gap and to remotely charge consumer devices. In this paper, the receiver coil is replaced by a stator–rotor topology, enabling magnetic resonance based motoring over substantial air gaps. The principles of resonant wireless power transfer are used to induce currents in a strongly coupled magnetic resonance system. This results in its turn-in torque, which is applied on the rotor body, allowing for remote actuation. We propose a voltage or current controlled magnetic resonance motoring topology, for which we derive expressions for the generated torque depending on the rotor angle. Furthermore, torque profile expressions are derived for motoring systems with multiple stator and/or rotor coils. Finally, an experimental setup is built to validate the obtained torque expressions. Using the validated expressions, we present a sensitivity analysis of the key system parameters with respect to the torque profile. The presented torque profile expressions enable further topology exploration and optimization of magnetic resonance based motoring systems.

Development of a Superconducting Machine With Stacks of Second Generation HTS Tapes

In this paper, we investigate a topology of superconducting electric machine, which uses stacks of second-generation (2G) superconducting tapes. These stacks have been used as an alternative to replace bulks in trapped field superconducting machines. In this context, we built prototypes of superconducting machines with 2G tapes spirally disposed on the rotor. These prototypes were tested in liquid nitrogen bath at 77 K for operation in two regimes: synchronous and asynchronous. The operation mode is according to the load torque. To perform the torque tests under these operating conditions, a measurement system was also built. Quasi-static torque, locked rotor torque with stator frequencies up to 60 Hz, and dynamic torque up to 1200 rpm were measured. The prototype with 2G high temperature superconductor (HTS) stacks presented a torque, very close to nominal value of this machine with permanent magnets in the rotor. Promising results have been found showing that 2G HTS may be an alternative to superconducting bulks.

The adverse cyclic and collective pitch effect in a rotor

AbstractNumerical simulations have been carried out for a 32.16-ft-diameter rotor in autorotational forward flight. Coupled flapping and rotational equations were solved using the transient simulation method (TSM) to ascertain the quasistatic torque equilibrium conditions. The Pitt/Peters inflow theory was adopted in the simulations, and an airfoil look-up table made by a compressible Navier-Stokes solver was used. The adverse cyclic and collective pitch inputs were introduced in a similar fashion to helicopter control in that the cyclic lever is pulled back and the collective lever is pushed down for increasing airspeeds. The simulation results showed that the longitudinal cyclic pitch input combined with a lowered collective pitch increases the rotating torque for a low shaft angle and an advance ratio greater than one, producing both high lift and a high lift-to-drag ratio. Upon introducing the adverse cyclic and collective pitch inputs, the control range broadened, and a torque equilibrium condition was detected at 414.7kt (700ft/s) of airspeed in the simulation.

FERROMAGNETIC RESONANCE IN TERFENOL-D AT 17 GHz

Ferromagnetic resonance measurements have been performed on several samples of Terfenol-D ( Dy0.73Tb0.27Fe1.95 ) at 16.95 GHz and over the temperature range 293 to 305 K. We find that the first magnetocrystalline anisotropy constant, obtained from one sample under nearly zero stress, is K1 = (-1.4±1.0)× l06 erg/cm 3 at 294 K. Our measurement is distinct from quasistatic torque measurements in that the lattice does not deform during the measurement and, hence, the anisotropy contribution due to magnetoelastic strain does not enter. The bare anisotropy constant, unmodified by static elastic strain, is [Formula: see text] and [Formula: see text]. The samples exhibited hysteresis; the position of FMR shifted by 4.0 kOe between measurements made with the magnetic field increasing and those made with the field decreasing.

Measurement of the anisotropic strength and toughness of Pitch-55 carbon ribbons

Composites with long reinforcing fibres can be effectively toughened by controlled crack deflection at interfaces of such reinforcements. An important element in achieving this end is the measurement of the strength and toughness of the reinforcing fibres. Here we present results of such experiments. Since measurements of these properties are difficult in fibres of micron dimensions, specially prepared Pitch-55 ribbons of 600 μm width and 35 μm thickness were obtained for doing the tests. As with carbon fibres, these ribbons show strong anisotropy in their elastic and inelastic properties. Hence, the work of fracture along and across the graphitic planes were determined. The average longitudinal tensile strength of these ribbons was found to be 0.6 GPa. Due to inhomogeneities and a possible associated size effect this value is considerably lower for ribbons than that for fibres. The average specific work of fracture of the ribbons across the graphitic planes was determined to be 3.5 J m−2. Unusually high values of works of fracture of 166 J m−2 were obtained for cracks propagatin along the longitudinal graphitic lamellae. These high values were attributed to a profuse kinking type of plasticity on the graphitic lamellae lying parallel to the crack plane. An asymptotic elastic-plastic analysis for single crystals due to Rice [12], was used to estimate the level of inelastic energy dissipation. These estimates were close to the experimentally observed values. The calculation of the dissipated inelastic energy requires knowledge of the interlaminar shear strength across the graphitic lamellae. A torsion experiment was designed to measure the interlaminar shear strength across the weak graphitic planes, giving a value of 83 MPa. An in-plane longitudinal shear modulus of 65 GPa was obtained from the linear portion of the quasi-static torque twist curve of the ribbon. Another measure of this modulus was determined independently from torsional vibration tests, giving an average value of 51 GPa.

Electronic structure of AsF 5 intercalated graphite from de Haas-Van Alphen measurements

The oscillatory magnetization of stage 1 and stage 2 AsF 5 intercalated graphite was studied with the de Haas-van Alphen effect in magnetic fields up to 22 T. Using the quasi-static torque method it was possible to determine the absolute value of the magnetization of sealed, chemically active samples. For the stagee 1 samples we found the expected frequency of ⋍ 1700 T , corresponding to the charge transfer of ⋍ 0.3 electron per AsF 5. From the angular dependence of the de Haas-van Alphen frequencies and the cyclotron effective masses we conclude that the Fermi surface is cylindrical. The Landau levels are well separated at 20 T compared with their broadening due to imperfections. The magnetization oscillations have sinusoidal shape with little higher harmonics, which indicates that the number of carriers in the graphite layers and the chemical potential are both field dependent.

Magnetic anisotropy and structure of magnetic recording media (invited)

The recording characteristics of magnetic media depend significantly on magnetic anisotropy. We have been pursuing an investigation of anisotropy in thin-film recording media involving coordinated TEM, SEM, x-ray and electron diffraction, x-ray fluorescence, TM, VSM examinations, and, in addition, ferromagnetic resonance (FMR). In CoCr films we have shown that the magnetic constituents often are stratified magnetically and correspondingly structurally. The magnetic deconvolution of such a composite specimen by FMR is relatively straightforward; it is difficult when quasistatic torque magnetometer or vibrating sample magnetometer techniques are employed. From FMR analysis, data are obtained on the effective magnetic anisotropy field components, on the γ factor (or equivalently the g value) and on the line breadth. If the value of 4πMs is available, the effective fields can be interpreted in terms of anisotropy energy components. By integrating over the FMR lines, information relating to the relative volumes of the constituents can be obtained. Many CoCr films are dual layer films in which a disordered ‘‘transition layer’’ intervenes between the substrate and the desired or ‘‘bulk’’ region. In such films the magnetocrystalline anisotropy of the disordered layer tends to average to zero, leaving the shape anisotropy dominant. We have performed annealing procedures with and without applied magnetic fields and have correlated the changed FMR spectra with ensuing changes in anisotropy and hence structure. We have begun an investigation of magnetoelastic effects in such films by FMR techniques.