Showing papers on "Torsion (mechanics) published in 1980"

Shear and torsion design of prestressed and non prestressed concrete beams

Abstract: D esign procedures which are based on rational models rather than empirical equations enable the engineer to develop a better understanding of actual structural behavior. In this regard, the unsatisfactory nature of current shear and torsion design procedtires is evident if the ACI Code' chapter on shear and torsion is compared with the ACI chapter on flexure and axial load. In the flexure and axial load chapter a rational, simple, general method is explained in a few paragraphs of text. On the other hand, the shear and torsion chapter consists of a collection of complex, restrictive, empirical equations which, while leading to safe designs, lacks an understandable central philosophy. This lack, in the opinion of the authors, is the source of many of the complaints which arise from the engineering profession about modern design codes becoming unworkably complicated. In this paper an attempt is made to present procedures based on rational models which enable members containing web rein-

Relation between the structure of the annulus fibrosus and the function and failure of the intervertebral disc.

Abstract: A simple model is presented that explains the observed function and failure of the intervertebral disc in compression, torsion, and bending; this model is based upon the observed arrangement of collagenous fibers in the annulus fibrosus. The fibers are considered to have the same mechanical properties as tendon; thus the stresses required to produce a given deformation and which irreversibly damage the fibers can be predicted. Predictions of the mechanical behavior of the disc are in good agreement with published results for compression and torsion; no comparable experiments have been performed for bending. It is further predicted that torsion and bending are likely to cause annular failure and protrusion. Failure is likely to occur posteriorly because of the effect of forward bending and because in the flattened and reentrant discs of the lumbar spine, torsional stress is concentrated at the points of maximum curvature. The structure of the disc tends to protect the collagenous fibers in forward bending and torsion. Compression is predicted to cause end-plate fracture rather than annular failure.

Propagation equations for test bodies with spin and rotation in theories of gravity with torsion

Abstract: We generalize the Papapetrou equations by deriving propagation equations for the energy-momentum and angular momentum of a test body which has both elementary-particle spin and macroscopic rotation and which is moving in background metric and torsion fields. Our results show that the torsion couples to spin but not to rotation. Thus a rotating test body with no net spin will ignore the torsion and move according to the usual Papapetrou equations. Hence the standard tests of gravity are insensitive to a torsion field. We propose experiments (although still infeasible) to compare the motion of a spin-polarized body with the motion of a rotating body. If the spin and rotation precess differently, the theory of gravity cannot be a metric theory but may be a torsion theory.

A computer model of molecular arrangement in a n‐paraffinic liquid

Abstract: A computer model of a bulk liquid polymer was built to investigate the problem of local order. The model is made of C30 n‐alkane molecules; it is not a lattice model, but it allows for a continuous variability of torsion angles and interchain distances, subject to realistic intra‐ and intermolecular potentials. Experimental x‐ray scattering curves and radial distribution functions are well reproduced. Calculated properties like end‐to‐end distances, distribution of torsion angles, radial distribution functions, and chain direction correlation parameters, all indicate a random coil conformation and no tendency to form bundles of parallel chains.

On the Nonlinear Deformation Geometry of Euler-Bernoulli Beams.

Abstract: Nonlinear expressions are developed to relate the orientation of the deformed beam cross section, torsion, local components of bending curvature, angular velocity, and virtual rotation to deformation variables. The deformed beam kinematic quantities are proven to be equivalent to those derived from various rotation sequences by identifying appropriate changes of variable based on fundamental uniqueness properties of the deformed beam geometry. The torsion variable used is shown to be mathematically analogous to an axial deflection variable commonly used in the literature. Rigorous applicability of Hamilton's principle to systems described by a class of quasi-coordinates that includes these variables is formally established.

Gravity theories with propagating torsion

Abstract: We study the propagators for a large class of gravity theories having a nonzero, metric-compatible torsion. The theories are derivable from a Lagrangian containing all possible invariants quadratic or less in the torsion and Riemann curvature tensors, except that invariants are dropped if they do not contribute to the propagator in the linearized limit. Therefore, the torsion in these theories is, in general, a propagating field rather than one which vanishes outside matter. We study the constraints imposed on the propagator by the requirement that the theory have no ghosts or tachyons. In particular, we find that the addition of a spin-${2}^{+}$ torsion multiplet does not remove the spin-${2}^{+}$ ghost contributed by higher-derivative terms (Riemann curvature-squared terms). We discuss the phenomenology of theories with propagating torsion. The torsion must couple to spins with coupling constants much smaller than the electromagnetic fine-structure constant, or the force between two macroscopic ferromagnets, due to torsion exchange, would be huge, far greater than the familiar magnetic force due to photon exchange. We briefly discuss the phenomenology of propagating torsion "potentials." Theories involving such potentials have been proposed recently by several authors.

Multiparameter shape optimization of elastic bars in torsion

Abstract: The problem of optimal design of the shape of an internal or external boundry of an elastic bar in torsion is formulated by assuming the boundary shape is described by a set of prescribed shape functions and a set of shape parameters. The optimization procedure is reduced to determination of these parameters. For constant volume or material cost constraint, the optimality conditions are derived for the case of maximizing of torsional rigidity of elastic bars of linear material. The optimal shape problem is next formulated by means of the finite element method and the interative solution algorithm is discussed by using the optimality crieria. Several simple numerical examples are included.

An Experimental Study on Dogs

Abstract: The fracture process of torsion tested entire canine diaphyseal bones was studied with a high speed camera. The speed of the final fracture propagation proved to be incompatible with plastic deformation of macroscopical parts of the bone.

Finite Element Analysis of Box Girders

Abstract: A numerical method for the analysis of elastic thin-walled box girders is presented. The method is based on the separation of variables suggested by Vlasov and on the finite element method. The method is capable of taking into account longitudinal and transversal flexure, torsion, distortion of the cross section, torsional and distortional warping and shear deformation. Stresses and displacements calculated with the computer program developed for a straight one-box girder have been compared with results obtained by other analytical and numerical methods and with experimental data.

Methyl tunnelling and torsion in acetates : the shape of hindering potentials

Abstract: Methyl tunnel splittings and torsion frequencies have been measured by inelastic neutron scattering for seven acetates. The parameters of the hindering potential V, cos 345 + V, cos 645 where 45 is the methyl rotation angle, were determined from the spectra. The ratio V,/V, is similar (about 015) for six of the samples though sodium acetate appears anomalous. The dependence of this ratio on the form of interatomic potentials is discussed.

Suspension and stabilizing system for a snowmobile

Abstract: A front suspension and stabilizing system for a snowmobile in which a pair of front steerable skis are connected to the vehicle body through a pair of suspension means which also are connected to a transversely extending torsion member attached to the vehicle body. The response of the torsion member to movement of the suspension means is stabilized and dampened by a resilient yieldable means such as a shock absorber connected to a mid portion of the torsion member through a forwardly extending arm fixed to the torsion member and connected at its other end to the shock absorber. A stabilizing system for a suspension system having a steering strut subject to axial and rotational movement, the steering strut being connected to a torsion member through a forwardly disposed link having universal connections to the strut and to the torsion member. The longitudinal axis of the link lies in a vertical plane which passes through the axis of the steerable strut and the longitudinal axis of the ski for transmitting vertical movement of the ski and associated steering strut to the torsion member during travel in a straight direction as well as during turning of the vehicle.

Paper-making fourdrinier mfr. - uses plastic wire formed into torsion-free coils with linking rods

Abstract: In a Fourdrinier for a papermaking machine, using monofilament plastic wire, the plastic is bent into coils interlinked to form the Fourdrinier width, without any sprung tension being built into the coils (1,2), and the coils are torsion-free. The Fourdrinier so formed has a long operating life, and does not impose any markings on the paper produced by the machine.

Self-adjusting torsion bar for vehicle suspension - has sliding cage linking two end bars with position set according to speed and axle loading

Abstract: The torsion bar suspension is for a road vehicle in which the single bar is replaced by two sections (12, 11) linked by a sliding centre section (3) whose lateral position determines the torsion force in the combined strut. The adjustment is automatically controlled w.r.t. speed and axle loading. The centre section has a sliding fit on splines on the one sections and over a fixed guide (16) at the end of the other section. The spacing of the fixed and sliding guides is adjusted to suit the dynamic and loading conditions.

Applications of variational principles in finite elasticity

Abstract: For some equilibrium states of a finitely deformed elastic body, variational principles can be used to provide bounds on overall quantities of physical interest. The principles are applied to the problem of the allaround finite extension of a plane sheet with a circular hole, and accurate estimates for the stress resultant at the outer edge are obtained for various extensions. The finite extension and torsion of an elastic cylinder is considered and bounds on the strain energy per unit length are obtained for an elliptical cylinder of neo-Hookean material with axes in the ratios of 2:1 and 4:1. The bounds lead to reliable estimates for the twisting moment and axial force.

Torsion of Core Walls of Nonuniform Section

Abstract: The finite difference method is used in the solution of torsional problems of tall core wall structures with nonuniform sections. The formulation is very flexible and versatile, and can deal with various nonuniform sections and different loading conditions. The simple mathematical operations are suitable for both preliminary design and final design with hand calculation or any mini-computer. Numerical example is presented and compared with results obtained by other researchers.

Stabilizer for vehicle

Abstract: A stabilizer for a vehicle comprises a torsion section, hardened and tempered curved sections integrally extending from the opposite ends of the torsion section and arm sections each integrally extending from each curved section and coupled to a vehicle suspension.

Torsion damping device, for clutch driven disc for a motor vehicle

Abstract: This relates to a torsion damper device having two coaxial parts mounted for rotation relative to one another, within the limits of a determined angular movement, against the action of springs. The torsion damper device includes in addition at least one locking means which is sensitive to the angular movement between the two parts and which is movable reversibly between a position in which it is inoperative and gives full freedom of action to the springs and a position in which it effects the direct supporting of one part (A) on the part and puts these springs out of action. The torsion damper device is applicable in particular to clutch plate assemblies for motor vehicles.

Torsion damper device for automotive vehicle clutch friction disc

Abstract: This torsion damping device comprises two coaxial parts, namely a hub (10) and a hub disc (11), fitted mutually rotatably within the limits of a definite angular play and counter to springs (16). The torsion damping device also comprises at least one locking element (22, 40, 55, 66, 74) which is sensitive to centrifugal force and which is reversibly movable between a position for which, inoperative, the locking element permits freedom of action to the springs (16), and a position for which, producing an abutment of the hub disc (11) against the hub (10), the locking element renders the springs (16) inoperative. Application of the torsion damping device is especially to clutch friction plates for motor vehicles.

A tension—torsion creep-rupture testing machine

Abstract: The paper discusses the design and construction of a high-temperature creep machine capable of applying combined tension and torsion loadings. The design utilizes an air bearing and pinned universal joints to achieve axiality of loading. An extensometer is described which transmits the deformation of the specimen gauge length outside the furnace and allows the continuous measurement of axial and shear strains to be made using linear variable differential transducers at room temperature. Results of elastic and creep tests are presented which show the performance of the machine to be satisfactory.

Apparatus for determining the behavior of a liquid during coagulation and the like

Abstract: An apparatus for measuring or observing parameters representative of the coagulation and/or the lysis of a coagulable liquid, such as blood, comprises a torsion thread, a driving body supported by the torsion thread to be dipped in the liquid, a vessel containing the liquid is oscillated with a predetermined angular amplitude and period around an axis substantially identical with the torsion thread. Detection means comprise an inductor driven by the thread and a fixed position-detector which delivers an electrical signal representative of the amplitude of the oscillations of the torsion thread. The torsion thread is constituted by a wire stretched between two anchoring points and bearing the mass.