Showing papers on "Torsion (mechanics) published in 1984"

Compressive and torsional behaviour of Kevlar 49 fibre

Abstract: The mechanical anisotropy of an aromatic polyamide fibre, Kevlar 49, was studied in tension, compression and torsion. A new technique involved applying small and defined compressive strains to filaments by bonding them to one side of a beam which is subsequently bent to compress the fibres. Using scanning electron and optical microscopy, fibres were shown to form regularly-spaced helical kink bands at 50 to 60° to the fibre axis after the application of small axial compressive strains. Tensile tests of previously-compressed fibres revealed only a 10% loss in tensile strength, after application of as much as 3% compressive strain. A torsion pendulum apparatus was used to measure the shear modulus and an apparent shear strength of fibres. A loss of tensile strength after the application of large (> 10%) torsional shear strains coincided with a loss in recoverable shear strain due to longitudinal fibre splitting. Ratios of tensile-to-compressive strength, tensile-to-shear strength and tensile-to-shear moduli of 5∶1, 17∶1, and 70∶1, respectively, were measured for Kevlar 49.

Torsion of the left ventricle during the ejection phase in the intact dog

Abstract: Torsion of the left ventricle (LV) is associated with rotation of the apex with respect to the base around the long axis of the LV. A mathematical model of LV mechanics, which relates torsion to transmural distribution of fibre shortening, was evaluated with two-dimensional echocardiography in nine anaesthetised closed-chest dogs. Torsion was calculated as the difference between the angles of rotation (radians) of echo-derived transverse cross-section projections of the LV obtained at the mitral valve and low papillary level, divided by the axial distance between these projections measured in a long-axis cross-section, and multiplied by the outer radius in a mid-papillary transverse projection of the LV. A shortening to torsion ratio (STR) was defined as the ratio of inner wall shortening to torsion occurring during ejection. In a series of 11 measurements, each based on frame-to-frame analysis of 15 cardiac cycles, STR was found to be 2.31 +/- 0.23 rad-1 (mean +/- SD), whereas the mathematical model predicted a STR value of 2.4 rad-1 over a wide range of preload, afterload and contractility levels. We conclude that two-dimensional echocardiography validates the presence of torsion in the normal canine left ventricle, as predicted by the model of left ventricular mechanics.

Torsion of Reinforced Concrete

Abstract: This textbook provides a comprehensive guide to the torsion design of reinforced concrete. The first chapter deals with the classical theories of torsion for homogeneous members. The torsional strength of plain concrete members is investigated in chapter 2. Chapter 3 studies the strength and behaviour of reinforced concrete members subjected to torsion. Emphasis is placed on the ultimate strength and post cracking torsional stiffness. The American concrete institute (ACI) torsion criteria are presented in chapter 4. Chapter 5 deals with prestressed concrete, and includes a new generalized torsion design criteria. Studies of reinforced concrete members subjected to combined loadings (torsion, shear, bending, and axial load) are provided in chapters 6 and 7. Chapter 6 summarises the development of skew-bending theories, and chapter 7 describes the development of the truss model method for shear, torsion and combined loadings. Chapters 8 and 9 discuss the analysis of structures involving torsion. The general analysis of space frames is given in chapter 8, and the very common design of spandrel beams is provided in chapter 9. (TRRL)

Physical aging of poly(methyl methacrylate) in the nonlinear range: Torque and normal force measurements

Abstract: Cylindrical specimens of poly(methyl methacrylate) (PMMA) were quenched from above the glass transition and subsequently tested in torsion. Torque and normal-force relaxation responses were recorded simultaneously. The experiments were performed at 40, 60, and 80°C, at increasing aging times and at deformations ranging from γ = 0.0027 to γ = 0.074. It was found at 40 and 60°C, that, contrary to the classical picture of aging, the small-deformation torque-relaxation curves could not be superposed by any combination of vertical and horizontal shifts. On the other hand, at 80°C, and in the nonlinear deformation range even at lower temperatures, the relaxation curves are superimposable simply by horizontal shifts, but as γ increases they involve decreasing values of the double-logarithmic shift rate. At the same deformation level, however, the shift rate for the normal force is significantly higher than is that for the torque over most of the γ range investigated.

Analysis and Optimization of a Tubular Lap Joint Subjected to Torsion

Abstract: This analysis considers a tubular lap joint comprised of a steel tube adhesively bonded to a composite tube subjected to torsion. A finite element method is employed to characterize the stress concentration associated with the boundary layer effect in the end region of the adhesive layer. Through the selective perturbation of geometric and material properties, a parametric evaluation is conducted in which the peak stress and its gradient are reduced. A number of design guidelines are subsequently drawn based on the results of this evaluation.

Torsion pendula with electromagnetic drive and detection system for measuring the complex shear modulus of liquids in the frequency range 80–2500 Hz

Abstract: An apparatus for the measurement of liquid complex shear viscosity in the frequency range 80–2500 Hz, with the use of a torsion pendulum operating in forced oscillation, is described. The drive and detection system consists of a magnet inside the pendulum, two excitation and two measuring coils. The determination of the complex shear viscosity is based on the measurement of the resonance frequency and the damping of the torsion pendulum. The feasibility of this method is demonstrated with a number of Newtonian liquids in the viscosity range 0.3 to 60 m Pa s. Results for a viscoelastic polymer solution are presented. A comparison is made with other apparatus working in the same frequency range.

The Lagrange multiplier method for manipulating geometries. Implementation and applications in molecular mechanics

Abstract: It is shown that a Lagrange multiplier method to constrain one or several internal coordinates, or averages and combinations of these, is easily implemented in a molecular mechanics computer program that uses Newton–Raphson (NR) minimization. Results are given for constraints on nonbonded distances and torsion angles. When a potential energy surface is to be explored, it is much better to constrain the average of three torsion angles around a bond than to constrain a single torsion angle. Certain conversions can only be achieved when averages of torsion angles around different bonds are constrained. Combinations of constraints have been applied to evaluate differences between calculated and observed geometries and to obtain transition states for relatively large molecules from results for smaller molecules at relatively low costs. The efficieny of the combination of the Lagrange multiplier method and NR minimization in terms of computing time can be rated as good.

Design for seismic torsional forces

Abstract: An analytical study of the responses of a single storey and a multistorey building model to a combined translational and rotational ground motion is presented. The models, which are assumed to be e...

Environmental, Stress-State and Section-Size Synergisms During Creep

Abstract: The time-dependent deformation and fracture characteristics of Inconel alloy X-750 have been studied at 700 $^\circ$C under uniaxial and biaxial stressing. Several unusual sets of results were obtained, which led to the discovery of synergistic interactions between the material and the environment employed during heat treatment. For example, when solid tension and thin-wall tubular torsion specimens were given the normal commercial heat treatment, lifetimes in torsion were found to lie outside the region delineated by the plane-stress isochronous rupture loci generated when fracture is controlled respectively by the maximum principal stress and the von-Mises effective stress. This is contrary to predictions of creep fracture models and at variance with published experimental work. The isochronous rupture behaviour only became `normal' when torsion life-times were compared with those obtained from tension tests on tubular specimens for which lifetimes were less than 5 % of those for solid ones. This unusually large effect of section size on lifetime was shown to be due to a corresponding change in creep resistance, rather than to a reduced fracture ductility. Detailed metallography identified the responsible micromechanism as being a very fine cavity dispersion in the near-surface region, which caused progressively more weakening as the section size was reduced. This profuse and spatially inhomogeneous cavitation was demonstrated as not being an inherent characteristic of the material but the result of some interaction with the environment-speculated as being the formation of metastable carbon dioxide gas bubbles - during heat treatment of testpieces.

Device for measuring the rotary or bending force exerted on a shaft

Abstract: In the invention, use is made of air gap eddy current probes (3, 4, 9 and 11) in order to be able to measure the torsion and the bending stress, the expansion or the compression which are caused by an alignment error etc. of a shaft (1) by determining the change in permeability of a highly magnetostrictive surface (2) on the shaft (1). This surface (2) can consist, e.g., of a sleeve from an amorphous metal. The change in permeability is proportional to the torsion or stressing of the shaft. There is no physical connection between the surface (2) to be investigated and the sensor or the probe (3, 4, 9 and 11).

On space-time models with axial torsion: Some vacuum solutions of the Poincaré gauge field theory of gravity

Abstract: The field equations of a specific gravitational Lagrangian, being quadratic in curvature and torsion, are solved by means of an ansatz for the curvature. The field equations are thereby reduced to a decoupled system of equations that determines the metric and the torsion. Up to this point, no symmetry conditions have been imposed on the fields. This system of equations is then solved for three special cases in each of which the torsion has a nonvanishing axial vector part.

Wave-induced Liquefaction in Seabed Deposits of Sand

Abstract: To explore the nature of cyclic stress alteration in seabed deposits of sand due to travelling waves, two-dimensional stress analysis was carried out on a homogeneous elastic half-space subjected to a series of harmonic loads moving on its surface. The analysis indicated that changes in shear stress occur in such a way that, while its amplitude is maintained constant, the directions of the principal stresses rotate continuously. With a view to simulating such stress changes in the laboratory test, a series of cyclic triaxial torsion shear tests was conducted on loose specimens of sand. The test results indicated that the conventionally defined cyclic stress ratio is reduced by about 30 per cent if the rotation of the principal stress directions is involved in the cyclic loading. It is known that the magnitude of wave-induced pressure at the seabed changes as ocean waves move in towards the shore. In unison with the changes in the pressure wave, the cyclic stress ratio induced in the seabed also changes. However, owing to the wave breaking, there exists an upper limit in the magnitude of the wave pressure and, hence, in the induced cyclic stress ratio. With these characteristics in mind, a set of charts was provided to facilitate computation of the induced cyclic stress ratio in the seabed deposit of water of any depth, on the assumption that the seabed consists of a homogeneous isotropic elastic half-space. The charts are organized so that the induced cyclic stress ratio can be obtained for known wave parameters that are specified by design storms at an offshore location. The cyclic stress ratio thus obtained was compared with the corresponding cyclic stress ratio causing failure in the sand, which was determined in the laboratory with a cyclic triaxial torsion shear test equipment in which continuous rotation of the principal stress direction was executed in simulation of the wave-induced stress conditions occurring in the seabed deposit.

Adjustable torsion spring

Abstract: The invention relates to a spring for creating an adjustable resistance to the torsion between two bodies which are pivoted relative to each other. According to the invention, it comprises a battery. AXIALLY ALIGNED 30A-C ELASTOMER TORSION BANDS, AXIS ALIGNED 34A-B LOCKING RINGS FIXED AND SEPARATING ADJACENT TORSION RINGS, WITH A BLOCKING RING ASSOCIATED WITH EACH TORSION RING, THE TORSION RING BATTERY AND OF BLOCKING RINGS BEING FIRMLY ATTACHED TO ONE OF THE SWIVELING BODIES 14, AND A CONNECTING MEANS 46 THAT CAN SELECTIVELY COME IN COMMITMENT TO EACH LOCKING RING AND THE OTHER SWIVELING BODY, THE NUMBER OF TORSION RINGS EXPOSED TO THE SWIVEL MOVEMENT BETWEEN THE ORGANS FOR VARYING THE RESISTANCE TO THE TORSION OF THE SPRING BEING DETERMINED BY THE COMMITMENT BETWEEN THE MEANS OF CONNECTION AND SELECTED LOCKING RINGS. THE INVENTION APPLIES IN PARTICULAR TO THE SEATS.

Reinforced Concrete Beams with Small Opening in Bending and Torsion

Abstract: A method of analysis is presented for predicting the strength of rein­ forced concrete beams that are subjected to combined bending and torsion and contain a small transverse opening. The analysis is based on the familiar skew-bending model. Strength equations are derived for failure Modes I, 2, and 3 by assuming a suitable pattern of rein­ forcement around the opening. Test results of 10 beams containing a circular opening are also presented and discussed. The theoretical predictions are in good agreement with the test results.