Torsional Device Research Articles

Measurement of Elastic Constants for Composite Materials by 3-Point Bending, Twisting and Impact Sound Test

Analyzing a sound produced by an impact of a fallen ball upon a small rectangular bar specimen, elastic moduli of engineering ceramic composites can be determined. In this paper,three-points bending and torsional test devices which employed the specimen for the impactsound test were designed. Using the devices, elastic moduli of various materials were mea-sured applying deformation theory. The elastic constants evaluated by the impact sound testwere compared with those measured by the devices. They agreed well. A reliable measure-ment system was developed for elastic constants of anisotropic materials.

Development of Measurement System for Elastic Constantsof Anisotropic Materials by Impact Sound and Deformation Test

An instrumentation system has been developed to determine the elastic moduli of engineering ceramics and their composites from the sound produced by the impact of a fallen ball upon a specimen. In the system, a small rectangular bar specimen is suspended by thin ceramic threads. Using a fast Fourier transform analyzer, the natural frequencies are analyzed from the impact sound for the flexural and torsional vibration modes of the specimen. In the measurement, such a case sometimes occurs that it is difficult to distinct the correspondence between frequencies and eigen modes. In this paper, three-points bending and torsional test devices which employ the specimen for impact sound test were designed. Using the devices, elastic moduli of various materials were measured applying deformation theory for bending and torsion. The elastic constants evaluated by the impact sound test agreed well with those measured by the bending and torsional tests. A reliable measurement system was developed for elastic constants of anisotropic materials.

Elasticity and plasticity of two-dimensional amorphous solid layers of β-lactoglobulin

We investigate the mechanical properties of a two-dimensional amorphous solid. It is formed spontaneously by the adsorption of a protein (the beta-lactoglobulin) at the surface of water. We measure its mechanical response in both elastic and plastic regimes by applying a point-like force (using a glass fiber). We compare our results with previous measurements of shear moduli using a floating torsion device.

Helicopter Vibration Reduction Using Discrete Controllable-Stiffness Devices at the Rotor Hub

The present study demonstrates that optimal multi-cyclic stiffness variations of discrete controllable stiffness devices in the rotor blade root region can reduce the 4/rev vibratory hub loads of a four-bladed hingeless rotor helicopter. The controllable stiffness devices (flap, lag, and torsion devices) are modeled as discrete springs whose stiffness coefficients can be varied, and a gradient-based optimization scheme is used to determine optimal multi-cyclic device stiffness variations that minimize a composite index comprising of all six components of vibratory hub loads. Multi-cyclic stiffness variations of the flap and lag devices are most influential, and when optimal 2/rev and 3/rev stiffness variations of these devices were used in combination the vibratory hub drag force was practically eliminated and the vibratory hub side force was reduced by 55%. No significant detrimental effects were observed on the first through the fifth harmonics of the vibratory blade root loads. Multi-cyclic (3/rev and 4/rev) stiffness variations of the torsion device produced only small reductions in the 4/rev hub vertical force. Multi-cyclic stiffness variations of the flap and lag devices were seen to be effective in reducing hub vibration even when there were changes in fundamental rotor properties such as the flap, lag, and torsion stiffness of the root (flexure) element, and the cruise speed.

Effect of Electrode Morphology on the Behaviour of Electrorheological Fluids in Torsional Flow

In this study, we report experiments on experimental and commercial electrorheological (ER)-fluids in torsional flow. A torsional flow device (clutch) suitable for ER-fluids was designed and constructed. The flow curves measured with this device were compared with flow curves from a conventional rotational viscometer (a concentric-cylinders system). The agreement between the two devices was encouraging. To study the influence of inhomogeneous flow conditions besides the influence of the inhomogeneity of the electric field on the behaviour of an ER-fluid in a clutch mechanism, a set of smooth plates and three further sets of plates with different surface finishes were used in this investigation. Relative to the smooth plates, an increase in the relative ER-effect resulted from both ER-fluids used, when the oblique plates were used in an AC-and DC-field. This improvement in ER-effect seems to be tied to the increase in local field strength at the thick rim of the oblique plate. The addition of metal sheets to the smooth plates of the clutch provided a small increase in ER-effect under AC conditions. But in DC-field, the increase in ER-effect relative to that for smooth plates was rather pronounced, but so was the increase in electric current.

Characterization of the Torsional Behavior of Photosensitive Polymer Obtained by Stereolithography

An experimental and numerical mixed method based on the torsion test with and without warping of cross sections has been developed in order to characterize the shear behavior of a polymer material obtained layer by layer from a photosensitive resin (CiBA SL5170) polymerized by laser beam by the stereolithography technique. In this article, first the stereolithography technique is briefly presented, as well as the torsion device with and without warping of cross sections. Experimental and numerical results in static torsion of the polymer SL5170 are presented: shear modulus and strength of the material. From test results, a modeling of the superposition ratio of tensile and torsion stresses is proposed. It shows that the torsion of beams is complex. Torsion stresses and the tensile stress owed to the warping of section are superposed. In small-deformations state, material behavior behaves in a linear elastic way; experimental and numerical results are quantitatively and qualitatively coherent and conform to predictions of the elastic torsion theory. From experimental analysis of fatigue and elastoplastic damage behavior of the polymer, a phenomenological approach of the isotropic damage model is proposed. Based on the thermodynamics of irreversible processes, this local approach starts from a variant of the Chaboche-Lemaître model coupling plasticity and damage. This formulation is justified by the necessity to take into account the real stress state produced in the polymer during the torsion test.

A study of the static characteristics of a torsional micromirror

Torsional micromirror has been widely used in many applications as diverse as optical communication, laser scanning related and spatial light modulator related applications. In different applications the torsional micromirror may have different arrangements. A general analysis of the static characteristics of the torsional micromirror, especially its snap-down effect, is able to simplify the design of torsional micromirror. This paper describes the static characteristics of an electrostatically-actuated torsional micromirror based on the parallel-plate capacitor model. First, a normalized equation that governs the static actuation property of the torsional micromirror device is derived, and the relationship between rotation angle and driving voltage are also determined. Thereafter, the snap-down effect is specially investigated, leading to the revealment of the direct relationships of the electrode size with the snap-down angle and the maximum driving voltage. Based on the model, a 100 μm×100 μm torsional micromirror and a array of torsional micromirrors are fabricated using the three-layer-polysilicon micromachining process to verify the static actuation relation and the snap-down effect, respectively. The rotation angle of the micromirror is measured using an optical projection method. The experimental set-up and data are processed and analyzed in accordance with ISO guideline. It is shown that the experimental results are in good agreement with the theoretical analysis.

Quantum mechanical actuation of microelectromechanical systems by the Casimir force.

The Casimir force is the attraction between uncharged metallic surfaces as a result of quantum mechanical vacuum fluctuations of the electromagnetic field. We demonstrate the Casimir effect in microelectromechanical systems using a micromachined torsional device. Attraction between a polysilicon plate and a spherical metallic surface results in a torque that rotates the plate about two thin torsional rods. The dependence of the rotation angle on the separation between the surfaces is in agreement with calculations of the Casimir force. Our results show that quantum electrodynamical effects play a significant role in such microelectromechanical systems when the separation between components is in the nanometer range.

Calibration of Testing Equipment for Reliable Small-Strain Deformation Measurements Using Synthetic Specimens

Abstract For reliable deformation measurements at small strains, calibration of the entire testing system in addition to routine transducer calibrations are very important. Seven synthetic specimens of varying stiffness (4.3 to 1500 MPa) were constructed and tested to measure the compliance of testing equipment and to improve the measurement setups. Testing equipment used in this study included resonant column device (RC), torsional shear device (TS), free-free resonant column device (FF-RC), cyclic resilient modulus testing device (MR) and the static compression testing device. Moduli of synthetic specimens determined by various testing equipment after improvement were almost identical if considered the effect of loading frequency, indicating that all of the testing devices were well calibrated over a wide stiffness range. To verify the effectiveness of calibration on soil testing, two subgrade soils were tested, and moduli determined by various tests compared well. Use of synthetic calibration specimens shows potential for calibrating testing equipment and determining its capability and limitation of small-strain deformation measurements.

Evaluation of Liquefaction Using Disturbed State and Energy Approaches

The disturbed state concept (DSC) and the dissipated energy approach can provide simplified, fundamental, and mechanistic methods for the identification of the initiation and growth of liquefaction in saturated soils under cyclic and earthquake loading. Both approaches are developed and used for the analysis of liquefaction in the soil deposits at Port Island, Kobe, Japan, during the Hyogo-ken Nanbu earthquake. They are also used to analyze liquefaction of two sands during laboratory cyclic tests using torsional and multiaxial devices. It is shown that the DSC and energy criteria can lead to improved understanding of the mechanism of liquefaction, and to rational and simplified procedures compared to those based on empirical and index properties. Furthermore, the DSC possesses certain advantages over the energy approaches, particularly in terms of its implementation in computer (finite-element) programs for dynamic and liquefaction analysis.

Static liquefaction of sands under multiaxial loading

A fundamental study of the undrained behaviour of sands under multiaxial loading is presented. The investigation was carried out using Fraser River and Syncrude sands in a hollow cylinder torsional shear device. Shear loading was carried out under strain control to capture the postpeak strain-softening characteristics of loose sands. It is shown that the undrained response of loose sands is highly dependent on the loading direction. The friction angle mobilized at phase transformation and steady state is a unique material property, independent of the mode of loading, direction of principal stress and initial consolidation stress, and void ratio state. There is no unique relationship between steady state strength and void ratio which is independent of stress path and the level of initial confining stress.Key words: anisotropy, hollow cylinder torsional shear, liquefaction, sand, simple shear, triaxial.

Direct measurement of powder cohesion by a torsional device : J.L.R.Orband, D.Geldart. (University of Bradford, Yorkshire, UK.) PowderTechnol., vol 92, no 1, 1997, 25–33

Direct measurement of powder cohesion by a torsional device : J.L.R.Orband, D.Geldart. (University of Bradford, Yorkshire, UK.) PowderTechnol., vol 92, no 1, 1997, 25–33

Effects of coating on the behavior of electrorheological fluids in torsional flow

In this paper, we report experiments on an experimental electrorheological (ER) fluid in torsional flow. The electrorheological flow properties of the ER fluid were measured using a conventional rotational viscometer (a concentric-cylinders system). Then a torsional flow device for ER fluids was designed and constructed. The flow curves measured with this device were compared with flow curves from the viscometer. The agreement between the two devices is encouraging. The addition of a PVC foil to the surfaces of the plates has been also studied. Under AC conditions the ER effect with a homogeneous coating was smaller than that in the case of no coating, but at the same time a large reduction in the current density was measured. As soon as sections had been cut out from the foil, the ER effect increased, exceeding in some cases the effect with the uncoated plates, with no significant increase in the current density. Under DC conditions, the ER effect with a coating (irrespective of the type of coating) was zero or smaller than that in the uncoated case, and the decrease of the ER effect was always accompanied by a more than proportional decrease in electric current. This implies an increase in the ER effect on the basis of the required current density. The use of a polymer mesh to coat the plates provides an increase in the ER effect in AC and DC fields. This increase in ER effect is coupled with an increase in the current density in both fields. This suggests the idea that the polarization of the polymer mesh is responsible for some of the ER effect.

Direct measurement of powder cohesion using a torsional device

A device for the direct measurement of cohesion, which is the shear strength of a powder when no normal stress is applied to the plane of shear, is discussed. The apparatus, called the Warren Spring-Bradford cohesion tester, works according to the principle of the annular shear cell. The central part is a hollow cylinder to which eight spokes are attached, connected by an outer ring. Two materials, lactose and soda ash, have been tested extensively in a wide range of sizes. By plotting the cohesion versus the mean size, a clear distinction can be made between free-flowing powders, characterized by a size-independent cohesion, and cohesive powders that exhibit a cohesion the value of which is a strong function of particle size. The size at which the transition between the two states occurred was approximately 55 μm. Apart from dense copper powder the values of the cohesion could be correlated satisfactorily with those derived from the Jenike shear cell. This cohesion tester served its intended purpose very well, i.e. obtaining a qualitative comparison as regards the flowability of powders of different sizes.

Static and Dynamic Testing of Large-Amplitude Rotary Induced-Strain (LARIS Mk 2) Actuator

A new concept for obtaining large-amplitude rotary displacements from small linear displacements generated by induced-strain active material stacks is considered. The concept utilizes the theory of twist-warping coupling in thin-wall open tubes. A large-displacement induced-strain rotary actuator, LARIS Mk 2, was built and tested under static and dynamic conditions. A rotary displacement of 60 was measured over a 0-50 Hz frequency range. The frequency response was found to be flat up to 40 Hz, and then increasing in the 40-50 Hz frequency range. The theoretical development of the torsional vibration response for the LARIS Mk 2 actuator is also given. The derivation is performed in a general format for a body with distributed elastic and inertia parameters, and with generic boundary conditions consisting of root stiffness and tip angular deflection. The results of this theoretical analysis are confirmed by experimental measurements. The theory presented is versatile and can be used for the analysis of other torsional vibration devices with specific root and tip boundary conditions. This LARIS concept presented in this paper can be successfully used in a series of aerospace and mechanical engineering applications, as for example in the actuation of adaptive control surfaces for aircraft wings and helicopter blades, or as rotary vane actuators in the control of turbomachinery exhaust flow for active reduction of turbulence, vibrations, and noise.

Effect of intermediate principal stress on the deformation response of sand

An experimental investigation of the relevance of the intermediate principal stress (σ2) on the deformation response of a sand is presented. The effects of σ2 are conveniently studied through the nondimensional stress parameter b = (σ2 – σ3)/(σ1 – σ3). A series of stress path tests was performed on Ottawa sand specimens in a hollow cylinder torsional shear device. The experimental program includes shear loading at different values of b, and special b tests, in which b was continuously varied at different stress directions. It is shown that the b value may have a significant influence on the stress–strain response of sand, depending on the loading conditions. Key words: hollow cylinder tests, generalized stress paths, sand, stress–strain behaviour, intermediate principal stress.

Strain-Softening Behavior of Waste Containment System Interfaces

Laboratory test results indicate that many geosynthetic interfaces in liners and covers for waste containment exhibit strain-softening behavior. A peak shear strength is mobilized at small displacements, but post-peak strength reductions occur with increasing displacement. Mechanisms that contribute to strain-softening include clay particle reorientation, geosynthetic polishing, and geosynthetic failure. Test results obtained from direct shear and torsional ring shear devices are summarized to illustrate these mechanisms. The design implications of strain-softening behavior are then investigated using analytical and numerical models. Deformations in the waste under gravity are sufficient in many cases to limit the available shear resistance along an interface to less than the peak strength. It is recommended that a factor of safety greater than one be achieved in all containment system slope designs, assuming that residual strengths are mobilized along the base of the entire containment system.

Significance of Rate of Work Hardening in Tempered Martensite Embrittlement

The main explanations for tempered martensite embrittlement are based on the effects of impurities and cementite precipitation on the prior austenite grain boundaries. There are some studies where the rate of work hardening is proposed as a potential reason for the brittleness.One steel was studied by means of a specially developed precision torsional testing device. The test steel had a high Si and Ni content so E carbide and Fe 3 C appear in quite different tempering temperature ranges. The M s temperature is low enough so that self tempering does not occur.With the testing device it was possible to obtain the true stress - true strain curves to very high deformations.The minimum toughness was always associated with the minimum of rate of work hardening.The change of deformed steel volume before the loss of mechanical stability is proposed as at least one reason for tempered martensite embrittlement.The reasons for the minimum of the rate of work hardening are considered.

A General Dynamic Model for the Resonant Column/Quasi-Static Torsional Shear Apparatus

Abstract A new model is proposed that allows for more general boundary conditions at both the active and passive ends of resonant column apparatus, especially those incorporated within the resonant column/quasi-static torsional shear devices. The improved three-degree-of-freedom model can be used in order to obtain more accurate measurements of the dynamic properties of tested soils when the base and the reaction mass of the apparatus are not perfectly fixed. This becomes particularly important in the hybrid resonant column/quasistatic torsional shear apparatus where the load cell located below the bottom platen provides additional flexibility to the passive end and the inertia of the reaction mass of the Hardin-type oscillator is relatively small. The analysis confirmed that use of the model is particularly important if the natural frequency of the soil-apparatus system is close to that of the passive end or reaction system, and that the calculated modulus and damping values can be highly inaccurate if simplified boundary conditions are assumed. Such situations especially occur when very soft soils, very stiff soils, or rock specimens are tested. The solution was programmed in a spreadsheet where both the shear modulus (G) and the damping ratio (D) are established for a given set of measurements and apparatus constants. In order to obtain the necessary apparatus constants, calibration procedures are presented for a resonant column/quasi-static apparatus. Comparison of existing models and the new solution to the observed response for a rubber testing specimen showed that the three-degree-of-freedom assumption is more accurate in modelling the apparatus boundary conditions.

The torsional properties of single selected osteons

The aim of the present investigation is to determine the mechanical behavior of single selected osteons loaded by torsion along their axis. Two osteon types were chosen: (a) fully calcified ‘longitudinal’ osteons, whose fibers (and, consequently, crystallites) have a marked longitudinal spiral course in successive lamellae, (b) fully calcified ‘alternate’ osteons, whose fibers (and, consequently, crystallites) have a marked longitudinal spiral course in one lamella, and an apparently transverse or circular course in the next. The osteon samples, which were cylindrically shaped, and whose extremities fitted into two rectangular lugs, were prepared on a microturning lathe. The principle of the specially manufactured torsional device was that of a pendulum set oscillating around a very sharp wedge so as to reduce friction to negligible levels. The results indicate that longitudinal osteons are those most resistant to torsional loading. The low resistance to torsional loading of the lamellae whose fibers apparently have an almost transversal course is discussed with reference to recent views on the microstructure of this type of lamella.