Twist Moment Research Articles

An analysis of the shearing stresses distribution on the cross-section of the twisted round bars

The state of stress generated by different loads represents an important factor that influences and determines the behavior and deforming capacity of the metallic materials or bars. This factor has a direct implication on the design and service of the machine components or structures. Its neglecting and, especially, its interaction with other factors can lead in certain unfavorable conditions and without visible deformations to instantaneous fracture, although the used materials satisfy the prescribed mechanical characteristics. Generally, the state of stress in a twisted bar is determined and conditioned by the twisting moment and angle of twist applied on the bar, the residual stress and, especially, by the shape and dimensions of the bar section. The present paper analyses the shearing stress distribution as a function of cross-section shape and dimensions for different twisted round bars.

Magnetic interface in Gd 63 Co 37 /Co multilayers

We present an analysis of polarized neutron reflectivity experiments on magnetic multilayers made of Gd63Co37 alloy and Co layers by sequential magnetron sputtering. At low temperatures the magnetic profile of Gd63Co37 (50 A)/Co (17–35 A) is consistent with the so-called ‘aligned-Gd’ state. However, the alloy layer must have a complex structure and contain an interlayer of distinct magnetization, since the flipping ratio (R+/R-) varies with the order of the Bragg reflections. At temperatures close to the compensation point of the multilayer, the magnetic roughness clearly grows with a moderately high field and the amount of twisted moments increases.

Springback analysis of thin rectangular bars of non-linear work-hardening materials under torsional loading

A theoretical analysis of the springback of narrow rectangular strips of non-linear work-hardening material under torsional loading has been carried out. This theoretical analysis is supported by experimental results for rectangular mild steel strips of different thicknesses and lengths. Finally an analytical generalized expression relating angle of twist to twisting moment and residual angle of twist per unit length for rectangular strips under plastic torsion is obtained in non-dimensionalized form. A comparison between the results obtained for bars of non- linear and linear work-hardening materials loaded under torsion is also made.

Aeroelasticity of two-dimensional lifting surfaces via indicial function approach

An aeroelastic formulation of 2D lifting surfaces in an incompressible flow field via the use of aerodynamic indicial functions is presented. The approach carried out in time and frequency domains yields the proper aerodynamic loads necessary to the study of the subcritical aeroelastic response and flutter of lifting surfaces, respectively. The expressions of the unsteady lift and aerodynamic twist moment in the frequency domain are given in terms of the Theodorsen’s function, while in the time domain, these are obtained directly with the help of the Wagner’s function. Closed form expressions of unsteady aerodynamic derivatives, helpful in an unified approach of response and flutter analyses, and results related to aeroelastic response to gust and blast loads are supplied. In this context, a novel representation of the aeroelastic response in the phase - space was supplied and pertinent conclusions on the implications of some basic parameters have been outlined.

Wind-induced responses of tall buildings experiencing complex motion

A wind tunnel model study on the effects of eccentricity between centre of mass and centre of stiffness of a tall rectangular building on the wind-induced response characteristics and wind excitation mechanisms was carried out. The results indicated significant effects of eccentricity on the along-wind, cross-wind, and twisting moment responses for both cases of the incident wind normal to the narrow and wide faces of the building model. The periodic twisting moments, created either by the flow separation at the upstream corners and the reattachment process of the separated shear layers, or by the eccentricity between the resultant lift force and centre of stiffness, were found to be a dominant wind excitation mechanism causing a significant increase in the twisting moment response of the building model. In addition, the twisting moment responses could be greatly amplified by the effects of resonance between the frequency of the periodic twisting moment and the torsional natural frequency of the building model. For the building model with the centre of stiffness located downstream from the centre of mass, increases in the twisting moment response and the resultant acceleration response at the corner of the building model were more prominent.

Stability of elastic–plastic conical shells under shear loading

A method of determination of critical loads for thin-walled conical shells loaded by shear forces developed by moment of twist is presented. The three governing equations of neutral equilibrium with respect to basic displacement vector components u, v, and w are used. It is assumed that effective stress in the prebuckling state of stress in the shell can exceed the yield limit of the shell material. The use is made both of physical relations of Nadai–Hencky small elastic–plastic deformation theory of plasticity, and Prandtl–Reuss J 2 incremental plastic flow theory. Also, a bilinear stress–strain material model, material compressibility and Shanley approach will be accepted in the analysis. Galerkin method is applied to solve the problem equations and iterative techniques are accepted in numerical algorithm to determine critical loads for elastic–plastic shells.

Modelling the line of action for the oblique abdominal muscles using an elliptical torso model

When modelling the line of action of a muscle, anatomical considerations must be included if the model is to realistically mimic the muscle behaviour. The internal and external oblique muscles are examples of muscles that do not follow a straight line between origin and insertion, instead having to wrap around the torso. A model is presented which describes the shape of the torso using a right elliptical cylinder of varying dimensions. The muscle lines of action are then calculated based on this underlying torso shape. The model has been successfully fitted to the data reported by Stokes and Gardner-Morse (Journal of Biomechanics 32(3) (1999) 311). When compared to a linear model, the use of the torso model results in a 15% increase in the axial twist moment, and decreases in the lateral bend and extension moments (5% and 2%, respectively), able to be generated by the internal and external oblique muscles combined in upright stance. These differences become larger (up to 37%) when the torso is flexed, extended or twisted. The structure of the torso model allows it to be used to model any posture without significant increases in the overall model complexity.

The behaviour of reinforced concrete elements subject to bending and twisting moments

This paper describes tests carried out on fourteen 1·6 m × 1·6 m × 150 mm reinforced concrete slab elements loaded with uniform bending moments applied about either or both orthogonal axes and with or without uniform twisting moments using a purpose-built test rig. Results are given up to and beyond the maximum load for the tests. The results obtained from the tests have been compared with an incremental non-linear analysis which is also described. The results have also been compared with the Wood–Armer equations and it is shown that these can be unconservative if the twisting moment is significant.

The behaviour of reinforced concrete elements subject to bending and twisting moments

This paper describes tests carried out on fourteen 1·6 m × 1·6 m × 150 mm reinforced concrete slab elements loaded with uniform bending moments applied about either or both orthogonal axes and with or without uniform twisting moments using a purpose-built test rig. Results are given up to and beyond the maximum load for the tests. The results obtained from the tests have been compared with an incremental non-linear analysis which is also described. The results have also been compared with the Wood–Armer equations and it is shown that these can be unconservative if the twisting moment is significant.

Large deflection analysis of pneumatic envelopes using a penalty parameter modified material model

The computational challenge associated with pneumatic envelopes, such as balloons and parachutes, is due to the complication of their underconstrained and no-compression nature. Underconstrained behavior leads to large displacements without concomitant strain energy; no-compression behavior leads to a degenerate, wrinkled state. In this paper, we discuss issues surrounding modeling such structures. We provide a method to analyze pneumatic envelopes through a penalty parameter-modified constitutive relation embedded in a non-linear finite element code. Such an approach is also adaptable to the user-provided material function port available with many commercial finite element codes. Validation examples given are the inflated cantilever cylinder subjected to transverse tip load, inflated cantilever cylinder subjected to twist moment, and the inflation of a round parachute.

Structural Wing Sizing for Multidisciplinary Design Optimization of a Strut-Braced Wing

A structural and aeroelastic model for wing sizing and weight calculation of a strut-braced wing is described. The wing weight is calculated using a newly developed analysis accounting for the special nature of strut-braced wings. A specially developed aeroelastic model enables one to consider wing flexibility and spanwise redistribution of the aerodynamic loads during in-flight maneuvers. The structural model uses a hexagonal wing-box featuring skin panels, stringers, and spar caps, whereas the aerodynamics part employs a linearized transonic vortex lattice method. Thus, the wing weight may be calculated from the rigid or flexible wing spanload. The calculations reveal the significant influence of the strut on the bending material weight of the wing. The strut enables one to design a wing featuring thin airfoils without weight penalty. It also influences the spanwise redistribution of the aerodynamic loads and the resulting deformations. Increased weight savings are possible by iterative resizing of the wing structure using the actual design loads. As an advantage over the cantilever wing, the twist moment caused by the strut force results in increased load alleviation, leading to further structural weight savings.

401 建築部材の残留モーメント測定(OS11 計測・評価)

When the cold roll formed products such as pipe, channel, angle, etc, are cut by press or saw, both cut-off edges open, and magnitude of the distortion differs. It is considered that the distortion occurs due to release of residual bending moment and residual twist moment. This report shows the residual moment that is measured by Sachs method, and also the calculation result of residual moment that is obtained by using of principle of minimum potential energy.

The Impact of a Sphere on a Timoshenko Thin-Walled Beam of Open Section With due Account for Middle Surface Extension

The problem on the normal impact of an elastic sphere upon an elastic Timoshenko arbitrary cross section thin-walled beam of open section is considered. The process of impact is accompanied by the dynamic flexure and torsion of the beam, resulting in the propagation of plane flexural-warping and torsional-shear waves of strong discontinuity along the beam axis. In addition, the process of impact is accompanied by large transverse deformations and large deflection of the beam in the place of impact, with the consequent generation of longitudinal shock waves and large membrane contractive (tensile) forces. Behind the wave fronts up to the boundaries of the contact region (the beam part with the contact spot), the solution is constructed in terms of one-term ray expansions. During the impact, the sphere moves under the action of the contact force which is determined due to the Hertz’s theory, but the contact region moves under the attraction of the contact force, as well as the twisting and bending-torsional moments and transverse and membrane forces, which are applied to the lateral surfaces of the contact region. Simultaneous consideration of the equations of sphere and the contact region motion leads to the Abel equation of the second kind, wherein the value characterizing the sphere and beam drawing together and the rate of change of this value are used as the independent variable and the function, respectively. The solution to the Abel equation written in the form of a series allows one to determine all characteristics of the shock interaction of the sphere and beam.

Co-contraction of lumbar muscles during the development of time-varying triaxial moments.

The recruitment and co-contraction of lumbar muscles were investigated during the voluntary development of slowly and rapidly varying trunk flexion and extension, lateral bending, and axial twisting moments. Myoelectric signals were recorded from 14 lumbar muscles in nine young men during maximum voluntary exertions and cyclic isometric exertions. System identification techniques were used to calibrate dynamic models of the relationship between myoelectric signals and force. To assess co-contraction, the predicted muscle forces were subdivided into a task-moment set of muscle forces that minimally satisfied moment equilibrium and a co-contraction set of muscle forces that produced zero net moment. The sum of co-contraction muscle forces was used to quantify the degree of co-contraction present. Co-contraction was largely dependent on the direction of exertion and relatively less dependent on the subject or the rate of exertion. Co-contractions were estimated to contribute approximately 16-19% to the sum of muscle forces at a lumbar cross section during attempted extension of the trunk. Estimated co-contractions during attempted lateral bending and axial twisting were two to three times greater, which demonstrates that co-contraction is a major determinant of spinal loading in these tasks. This analysis suggests that substantial contractions of lumbar muscles, especially during asymmetric exertions, are used for reasons other than equilibrating moments at the L3-L4 level.

Shell elements with drilling degree of freedoms based on micropolar elasticity theory

AbstractBased on the theory of micropolar elasticity, new degenerated shell elements with drilling degree of freedoms are presented. The proper stiffness on the drilling degree of freedom is derived and no spurious modes are encountered in these elements. The implementation of these new shell elements on general structural finite element programs has many advantages, especially for the analysis of a folded shell or the treatment of the twist moment normal to the shell. Several numerical examples are carried out to demonstrate the accuracy and applicability of the present elements. The effects of the coupling factor and the body moment induced in magneto‐solid mechanics are also studied.

A finite element alternating approach to the bending of thin plates containing mixed mode cracks

A finite element alternating procedure developed to deal with the cracked plate in symmetric bending is extended to analyse the more realistic case with single or multiple mixed mode cracks. This modified procedure involves the new derivation of the analytical solution for an infinite thin plate containing a crack subjected to arbitrary anti-symmetric equivalent shear force on crack surfaces. Due to the natural limitation of Kirchhoff assumptions for a thin plate in bending, the appropriate treatment of constant twisting moments on the crack surfaces is devised. The interaction effect among cracks on the calculation of bending (symmetric) and shear (anti-symmetric) stress intensity factors is also discussed. Several numerical examples are solved to demonstrate the validity and efficiency of the approach.

A non-linear finite-element model to calculate the twist moment of a four-conductor bundle

The paper deals with the formulation of a numerical model based on the finite-element method for calculating the twist moment of a four-conductor bundle equipped with rigid spacers. A non-linear finite element, the so-called cable element, was developed and adopted, and a finite-element computer program, EFFACTD, was written for computerizing the calculations. In order to validate the model and the EFFACTD program developed in the course of this research effort, the results were compared with those obtained from simple analytical models and the results of tests on a single conductor, a full-size bundle and a mini-conductor bundle. The present paper reports also on the various comparisons undertaken. These comparisons showed a good agreement between the analytical and experimental results.

Springback analysis in torsion of rectangular strips

A theoretical analysis of the springback of narrow rectangular strips under torsional loading is presented. The theoretical analysis is supported by experimental results for different materials, different thicknesses and different lengths, keeping the width of the strips constant. Finally an analytical generalized expression relating angle of twist and twisting moment and residual angle of twist per unit length for rectangular bars under plastic torsion is obtained in non-dimensionalized form.

TWIST MOMENT AND THE RELAXATION BEHAVIOUR OF NYLON 6 FILAMENT

The twist moment and energy in twisting of a nylon 6 monofilament were measured at different temperatures. The filament was twisted as high as 80% of the breaking twist. The twisting moment and energy decreased with increasing temperature, particularly above 140°C.The analysis of the twist moment under different rates of twisting by an Eyring theory gave 32 kcal/mol and 47 kcal/mol as the activation energy below and above 140°C respectively. In order to discuss the difference of the deformation behaviours between twisting and constant rate extension, the stress-strain relation in extension was also measured. Although the stress decreased with increasing temperature, the temperature dependence was less in extension than in twisting.The difference was also remarkable in the energy recovery ratio, i.e. the ratio decreased slightly above 140°C in twisting, while it increased monotonously in the constant rate extension.A composite master curve was obtained from the relaxation curves of twist moment at different temperatures. The shift factor was described by an Arrhenius relation, with a deflection point at 140°C. The activation energies from the relaxation data were very close to these from Eyring analysis.The thermal expansion of the crystal was measured by wide angle x-ray diffraction with the result that the expansion coefficient of the c* spacing increases above 140°C. The result indicates that the change in the deformation behaviours observed both in twisting and extension at about 140°C is attributed to the plastic deformability of crystals.

Feeding behaviour of the Japanese loach,Misgurnus anguillicaudatus (Cobitididae)

The feeding behaviour of a Japanese loach,Misgurnus anguillicaudatus was experimentally analyzed. From observations the behaviour patterns were described. The adult fish responded to a piece of thread soaked with filteredTubifex homogenate (Tubifex solution) and showed feeding behaviour. But they ignored an unsoaked piece of thread. LivingTubifex kept in a glass cell failed to elicit feeding behaviour in the fish. A gauze-covered vessel withTubifex solution buried in the sand substrate released feeding behaviour in fish in its vicinity. It follows that the feeding behaviour of this fish is induced by some chemical stimuli. WhenTubifex solution was introduced at the central area of the plastic vessel with a fish, the fish suddenly started the Feeding-crawl and showed Gulp which was composed of Dig and Twist. Using sand particles, it was shown that intake of materials into the digestive tract occurs only at the moment of Twist and not any other time. The standard feeding patterns ofMisgurnus anguillicaudatus are thus quick inhalation of organic matter together with substrate, occurring at the moment of Twist, which is released at the place where the fish received the appropriate chemical stimuli.Misgurnus anguillicaudatus is regarded as a typical “detritus feeder”.