Large Torsional Deformation Research Articles

Enhanced torsional strength and plasticity synergy of multi-component alloy via multi-level gradient structures

This study investigates an approach to enhance the strength and torsional angle, as well as analyze the microstructure and mechanical properties of a multi-component Cu-based alloy. A unique gradient-structured alloy is successfully synthesized by subjecting CuAl10Fe5Ni4Mn0.23 to high-frequency large torsional deformation. The results showed that the multi-level gradient structure due to high-frequency deformation significantly enhances the torsional strength of CuAl10Fe5Ni4Mn0.23 alloy. With a torsional rate of 120°/min and a maximum torsional angle achieved at 40°, after 200 cycles, compared to non-torsional samples, the torsional strength increased by 75.69 % and the torsion angle also increased by 38.36 %. The combination of the alloy primary structures along with gradient structures forms a new microband structure that synergistically improves the mechanical properties of multi-component alloys. The proposed large torsion deformation alters the structure of multi-component alloys, resulting in a gradient structure that simultaneously enhances both strength and plasticity, resolving current reciprocal dilemmas between these two factors.

Nonlinear characteristics of torsional stiffness of a coilable mast with triangular section

With numerous applications coilable masts in high-precision astronomical observations, such as X-ray source observations, it is important to investigate mast stiffness. To date, there have been many studies on the bending stiffness of coilable masts, but few studies on their torsional stiffness, especially regarding the nonlinear characteristics of torsional stiffness of coilable masts under large torsional deformation. In this paper, a nonlinear analysis method is presented to examine the torsional stiffness of coilable masts with triangular sections. Based on the second-order bending buckling hypothesis of battens under large torsion deformation, the nonlinear relationship between torsional torque and torsional angle is obtained by analyzing torsional deformation and force of coilable masts. This method is used to analyze the torsional stiffness nonlinearity of a certain type of coilable mast which will be used in a practical application in the future and the results are verified by simulation and testing. The comparison results show that the error is within the acceptable range, which proves the effectiveness of the proposed method.

Fretting fatigue behavior of helical-torsional contact steel wire in wire rope

Fretting wear and torsional deformation of steel wire can reduce the performance of wire rope and threaten the safety of mine hoisting system. In this study, to explore the influence of different torsional deformation on the fretting fatigue wear behavior under multi-wire spiral contact, an experimental study was conducted on a self-made test apparatus. The results show that the increase of torsional deformation can reduce the breaking force of steel wire by about 2.6%, and reduce the bending fatigue performance by about 36.4%. In addition, the maximum wear depth, wear amount and coefficient of wear increase with the increase of torsional deformation. The torsion and deformation of the pearlite lamellae parallel to the tensile stress direction are the main reasons for the decrease of the wear resistance of the main steel wires. More torsional deformation makes the steel wire produce less furrow morphology in fretting fatigue wear. The main wear mechanism of steel wire with small torsional deformation is abrasive and tribochemical reactions, and the main wear mechanism of steel wire with large torsional deformation is surface fatigue and tribochemical reactions.

Mechanics and topology of twisted hyperelastic filaments under prescribed elongations: Experiment, theory, and simulation

Soft filaments can be stretched, bent, and twisted, exhibiting complex configurations. When a filament undergoes large torsional deformation, it can display instabilities, and its post-buckling behavior and configuration evolution differs significantly from that observed under small deformation. We study the mechanics and topologically complex morphologies of twisted rubber filaments under prescribed elongation by combining experiment and finite strain theory. Based on the Mooney-Rivlin model, a finite strain theory of the hyperelastic filament under combined tension, bending, and torsion has been established, accounting for both geometrical and material nonlinearities. An experimental and theoretical morphological phase diagram is constructed as a function of the twist density and the initial elongation. The buckling and post-buckling behaviors of the twisted rubber filaments under prescribed elongation are well captured by the theory that considers geometrical nonlinearity and self-contact. By tracking the interconversion of link, twist, and writhe, we accurately determine the configuration and the critical points of phase transitions. The theoretical predictions agree closely with the measurements. This work sheds light on understanding the morphological complexity of the loaded hyperelastic rod.

An Adaptive Window Shape-Based DIC Method for Large Torsional Deformation Measurement

Torsional deformation measurement is used to measure the resistance of materials to torque and is one of the basic tests for the mechanical properties of materials. The measurement of large torsional deformation based on the digital image correlation (DIC) method has the advantages of full-field measurement, noncontact measurement, and easy-to-implement, but there are also problems, such as decorrelation and out-of-view. To tackle these problems, we propose an adaptive window shape-based DIC method and a reverse matching method, based on which a large torsional deformation measurement scheme is formed. First, taking advantage of the temporal continuity of object deformation, the window shape adaptively changes with the torsion of the specimen to avoid decorrelation. To solve the problem of tracking points moving out of the camera’s field of view, the deformed subregions are reversely matched in the reference image set, which is preshot from different directions. By this, the proposed method greatly improves the measurement range, and as a tradeoff, the absolute accuracy is acceptably sacrificed. Torsion tests of cylindrical low carbon steel specimen show that the proposed method can measure large torsional deformation objects with a shear angle of 74°, and the relative error is about 0.43%.

Local–global DVC analyses confirm theoretical predictions for deformation and damage onset in torsion of pantographic metamaterial

Pantographs are a special class of metamaterials that do not obey theories of first gradient continua. In the present work, a pantographic metamaterial was 3D printed and subjected to in situ torsion. The experiment was designed in order to investigate damage onset modalities in large torsional deformations of pantographic mesostructures. To account for the presence of true pivots, multiple point constraints were implemented in the DVC procedure. Local–global DVC was validated thanks to a series of steps accounting for numerous pivots. It was possible to determine the dominant damage mechanism in torsion. Damage was detected thanks to the strain and residual fields. Moreover, important modeling indications were obtained to guide further theoretical and experimental investigations.

Robust evaluation of stability regions of oil-well drilling systems with uncertain bit-rock nonlinear interaction

Torsional vibrations due to stick-slip phenomena may yield large variations in the drilling angular velocity which in turn may cause failures in the drilling process such as damage in drill pipes, due to large torsional deformation, and in drill bits, due to large angular velocities. It has been shown that standard linear proportional-integral (PI) control laws, in which the control torque is proportional to the differences between actual and reference drive table angular velocity and displacement, may lead to an oscillating angular velocity at the drill-bit due to stick-slip phenomenon. Aiming at reducing this effect through properly designed control gains, stability regions were defined for these parameters, and for a given drilling condition, using as a criteria the average deviation from expected/target angular velocity. This is done using a finite element model for the drilling system together with a dry friction model for a simplified representation of the interaction between drill-bit and rock formation. In order to provide robustness for the analysis, given the complexity of actual bit-rock interaction, it is proposed to consider uncertain parameters for the dry friction model. This is done using a stochastic model for the bit-rock interaction torque followed by a Monte Carlo simulation, which then leads to stochastic results for the angular velocity response, when subject to a linear PI control, and, thus, for the angular velocity deviation stability regions. Confidence intervals for the control gains, performance and stability regions are presented. Results suggest the use of a more robust criteria for the design of control parameters leading to a substantial increase in the performance robustness while not affecting much the nominal performance.

Study on aerodynamic coefficients and responses of the integrated catwalk of Halogaland Bridge

Wind tunnel tests and numerical aerodynamic analyses were conducted for an integrated catwalk structure under strong winds. From the wind tunnel tests, it is found that the aerodynamic coefficients were different from those of the typical type. The drag coefficient was larger than typical and was sensitive to number of vertical meshes installed rather than the solidity ratio. Comparing with typical catwalk, the integrated one showed larger deformation under strong wind, and the large torsional deformation are mainly caused by drag force. It did not show aerodynamic divergence even the torsional deformation reaching 20. The reason could be that the stiffness is smaller and thus the catwalk is able to deform to the shape compactable with higher loading. Considering safety for construction, storm rope system is introduced to the catwalk to reduce the deformation to acceptable level.

Analytical Solutions for Inextensible Fiber-Reinforced Dielectric Elastomer Torsional Actuators

Two types of tubular dielectric elastomers (DE) torsional actuators are studied in this work, which are, respectively, reinforced by a family and two families of helical inextensible fibers. When subject to a radial electric field, torsional deformation will be induced in the DE actuators due to the constraint of inextensible fibers. By conducting finite deformation analysis with the principal axis approach and adopting appropriate constitutive equations, simple analytical solutions are obtained for the considered DE actuators. Furthermore, the effects of material parameters and the fiber angles as well as externally applied axial force and twist moment on the voltage-induced torsional behaviors of the two DE actuators are discussed in order to explore their maximum torsional actuation capability. The concept design presented here provides an effective approach for achieving large torsional deformation, and the developed model and revealed results will aid the design and fabrication of soft actuators and soft robots.

An Analysis of Form Changes of a Toroidal Body with a Meridional Arrangement of Fibers on the Basis of the Two-Level Carcass Theory and of a Homogeneous Body Congruent to It

Results of an analysis of form changes of a toroidal body highly filled with fibers at large torsional deformations and rotational motions are presented. The body is reinforced in the meridional direction. The investigation was carried out by using the two-level carcass theory of fibrous media at large deformations, according to which the macroscopic fields of a reinforced body are determined by its internal fields. These fields are represented by the material configurations of nodal material blocks of the body, for which, on the basis of the model of a piecewise homogeneous medium, boundary-values problems of the micromechanical level of the theory are solved. The results obtained are compared with those for a homogeneous body. The congruent deformation of the homogeneous body at which its initial form and dimensions are practically restored upon superposition of torsion and rotation is determined.

Aeroelastic stability of a flexible ribbon rotor blade

This paper describes the static and dynamic aeroelastic behavior of a thin ribbon that is used as an extremely flexible helicopter rotor blade. The non-dimensional torsional stiffness of this rotor blade is three orders of magnitude lower than that of a conventional helicopter rotor blade. As a result, the rotor blade undergoes large torsional deformation and its static and dynamic behavior are dominated by centrifugal forces. An aeroelastic analysis is developed based on Euler–Bernoulli beam theory including large twist angles and unsteady aerodynamics including the effect of returning wake. The flow is assumed to be attached at all times, and only classical divergence and flutter stability are evaluated. The analysis is validated with deformation measurements of a 23cm diameter rotor with ribbon blades. Divergence and flutter stability boundaries are identified, and the effects of rotational speed, rotor diameter, location of blade center of gravity and blade pitch are discussed. The analysis can be used as a design tool for flexible ribbon rotors in a variety of missions.

Modeling of the Large Torsional Deformation of an Extremely Flexible Rotor in Hover

This paper describes the refined modeling of the large torsional deformation of extremely flexible rotor blades with negligible structural stiffness. Equations of motion including flap bending and torsion, specifically tailored toward unconventional blades with a tip mass and experiencing large elastic twist angles, are derived using the extended Hamilton’s principle. In particular, the foreshortening of the twisted blade arising from the trapeze effect (also called bifilar effect) is explicitly included. Quasi-steady aerodynamic forces are calculated using the blade element momentum theory. The nonlinear coupled equations of motion are solved using a finite-element method. The analysis is used to predict the thrust as well as the spanwise distribution of flap bending and twist of an 18-in.-diam rotor with extremely flexible blades rotating at 1200 rpm at various collective pitch angles. These predictions are correlated with the measurement of loads obtained using a load cell, and the measurement of the deformation obtained using a noncontact optical technique called digital image correlation. It is found experimentally and analytically that tip twist angles in the range of 10 to 40 deg, depending on the blade design, are attained. This torsional deformation is dictated by the combined action of the propeller moment and the trapeze effect. A detailed explanation of the contribution of the trapeze effect to the equations of motion is presented, and it is shown that omitting the axial foreshortening due to the trapeze effect leads to a 50% error in the computation of blade-tip twist.

G010016 着雪に伴う送電線の大きなねじれ変形シミュレーション

G010016 着雪に伴う送電線の大きなねじれ変形シミュレーション

Large torsional deformation of a circular band

Large torsional deformation of a circular band

Large torsional deformation of a circular band

A total-Lagrangian displacement-based finite-element model of initially curved beams undergoing large displacements and rotations is derived using a beam theory that fully accounts for large rotations and extensionality by using Jaumann stress and strain measures. To verify the accuracy of the finite-element model, a test fixture has been built and used to test the large twisting of a circular band. The finite-element results agree closely with the experimental results. Copyright © 1998 John Wiley & Sons, Ltd.

Ultrafine microstructures developed during torsional testing of Hadfield manganese steels

AbstractThree Hadfield manganese steels were investigated containing 1·15, 1·40, and 1·70 wt-%C, all with about 13 wt-%Mn. The as processed steels consisted of austenite grains, 10–12 μm in size, with a dispersion of carbides. The steels were deformed at temperatures in the range 500–950°C in three different phase regions, namely, three phase (austenite + carbide + ferrite), two phase (austenite + carbide), and single phase (austenite). Ultrafine microstructures were developed during large strain torsional deformation. The large torsional deformation in the two phase region resulted in grain refinement through dynamic recrystallisation with the austenite grains pinned by carbide particles, minimising grain growth. Strain assisted transformation followed by spheroidisation of carbides was obtained on testing in the three phase region. The concurrent deformation and transformation resulted in ultrafine microstructures of submicrometre size constituents. Torsional properties were evaluated and related to the...

Seismic response of light equipment in torsional buildings

AbstractThis paper attempts to study the response of light equipment items attached to a multi‐storey building that may be subjected to large torsional deformations during the earthquake excitation. To account for the effect of torsion and translation, each storey of the building is modelled as two degrees of freedom (DOFs), with one DOF for translation and the other for torsion. Perturbation techniques are employed to find closed‐form expressions for the modal properties of the combined system in terms of the properties of the individual subsystems. The interaction between the equipment and building is studied for both tuned and detuned modes of vibration. Modal synthesis results obtained using the present technique based on the complete quadratic combination (CQC) method are compared with solutions obtained by other methods.

Torsional Relaxation and Volume Response During Physical Aging in Epoxy Glasses Subjected to Large Torsional Deformations

AbstractWe present torsional dilatometry experiments to simultaneously measure torque relaxation and volume recovery in an epoxy glass quenched from above its glass transition temperature to below it. Two strain histories are employed: one with strains of equal sizes and a second where small strains follow a large one. The baseline for the thermally induced volume recovery is insensitive to intermittent torsional strains whose magnitude can be well into the non-linear regime. The torque relaxations from equal intermittent mechanical stimuli can be superposed by a time-aging time shift in a way that indicates fast changes cease to occur at ∼104 seconds after the quench, a “mechanical equilibration” time. Stimuli of different sizes can confound superposition via nonlinear effects, but do not affect the ultimate volume recovery of the glass or its mechanical equilibration time. Our results show the signature of rejuvenation; however, this may result from the nonlinear response of the material in a nonisochoric strain history. Our data firmly show that mechanical stimuli do not erase aging or rejuvenate this epoxy.

Onset of writhing in circular elastic polymers.

A perturbation analysis is presented of an exchange of stability between two mechanical equilibrium conformations of a torsionally deformed, linearly elastic, cylindrical polymer whose ends are held together to form a topologically circular structure. The imposed constraint is the twist angle \ensuremath{\zeta} through which one end of the polymer is rotated relative to the other. The value \ensuremath{\zeta}=0 corresponds to the relaxed state, in which no torsional deformation is imposed. Close to the relaxed state, the stable equilibrium conformation is a torsionally deformed circle in which the imposed constraint is expressed entirely as twist. A threshold value of \ensuremath{\zeta} is shown to exist, whose location depends on the ratio of the polymer bending stiffness A to its torsional stiffness C. Beyond this threshold the stable equilibrium conformation involves nonplanar bending, also called writhing. As this threshold is surpassed, a smooth onset of writhing occurs as a form of torsional buckling. These results are applied to the analysis of torsional fluctuations in nicked circular DNA. A critical molecular length is found, at which the root-mean-square twist induced by thermal fluctuations just suffices to initiate writhing. Comparison with the analogous critical length for linear polymers shows that the constraint imposed by circularity greatly increases the stability of the unwrithed conformation. Although twisting and bending are not coupled either energetically or topologically in nicked circular molecules, the exchange of stability between unwrithed and writhed conformations provides a mechanical coupling between them. Because sufficiently large torsional deformations drive writhing, fluctuations in the parameters scrT and scrW are not statistically independent in nicked molecules, but instead are positively correlated.

On a Torsional Deformation with Compression: Instability

AbstractThe paper is concerned with the torsional deformation of the Mooney material. We adopt a class of kinematics which reduce the problem to a set of ordinary differential equations. These are solved by a Finite Difference method using a branch following technique. It is found that the solutions either lose stability at bifurcation points or fold back at limit points. The case of the pure torsional deformation is considered in some detail and it is shown that the place boundary‐value problem for a small deformation superimposed on the large torsional deformation has non‐unique solutions at critical twist angles, the first two are given by π and approximately 4.493. These are verified by a full numerical study.