Showing papers on "Torsion (mechanics) published in 1986"

Mechanical Response of a Lumbar Motion Segment in Axial Torque Alone and Combined with Compression

Abstract: In the current study, a nonlinear three-dimensional finite element program has been used to analyze the response of a lumbar L2-3 motion segment subjected to axial torque alone and combined with compression. The analysis accounts both for material and geometric nonlinearities and treats the facet articulation as a general moving-contact problem. The disc nucleus has been considered as an incompressible inviscid fluid and the annulus as a composite of collagenous fibers embedded in a matrix of ground substance. The spinal ligaments have been modeled as a collection of nonlinear axial elements. Effects of loss of intradiscal pressure and removal of the facets on the joint response have been analyzed as well. Torsion is primarily resisted by the articular facets that are in contact and the disc annulus. The ligaments play an insignificant role in this respect. For the intact segment, with an increase in torque, the axis of rotation shifts posteriorly in the disc so that under maximum torque it is located posterior to the disc itself. Loss of disc pressure increases this posterior shift whereas removal of the facets decreases it. Torque, by itself, cannot cause the failure of disc fibers, but can enhance the vulnerability of those fibers located at the posterolateral and posterior locations when the torque acts in combination with other types of loading, such as flexion. The most vulnerable element of the segment in torque is the posterior bony structure.

Mechanics of engineering materials

Abstract: Preface to second edition. Preface to first edition. Notation. 1. Statically Determinate Force Systems. 2. Statically Determinate Stress Systems. 3. Stress-Strain Relations. 4. Statically Indeterminate Stress Systems. 5. Torsion. 6. Bending Stress. 7. Bending: Slope and Deflection. 8. Statically Indeterminate Beams. 9. Energy Methods. 10. Buckling Instability. 11. Stress and Strain Transformations. 12. Yield Criteria and Stress Concentration. 13. Variation of Stress and Strain. 14. Application of the Equilibrium and Strain-Displacement. 15. Elementary Plasticity. 16. Thin Plates and Shells. 17. Finite Element Method. 18. Tension, Compression, Torsion and Hardness. 19. Fracture Mechanics. 20. Fatigue. 21. Creep and Viscoelasticity.

Concrete structures: Stresses and deformations

Abstract: Preface to the third edition Acknowledgements Note The SI system of units and British equivalents Notation 1 Creep and shrinkage of concrete and relaxation of steel 11 Introduction 12 Creep of Concrete 13 Shrinkage of Concrete 14 Relaxation of prestressed steel 15 Reduced relaxation 16 Creep superposition 11 The aging coefficient ?: definition 18 Equation for the aging coefficient ? 19 Relaxation of concrete 110 Step-by Step calculation of the relaxation function for concrete 111 Age-adjusted elasticity modulus 112 General 2 Stress and strain of uncracked sections 21 Introduction 22 Sign convention 23 Strain, stress and curvature in composite and homogeneous cross-sections 24 Strain and stress due to non-linear temperature variation 25 Time-dependent stress and strain in a composite section 26 Summary of analysis of time-dependent strain and stress 27 Examples worked out in British units 28 General 3 Special cases of uncracked sections and calculation of displacements 31 Introduction 32 Prestress loss in a section with one layer of reinforcement 33 Effects of presence of non-prestressed steel 34 Reinforced concrete section without prestress: effects of creep and shrinkage 35 Approximate equations for axial strain and curvature due to creep 36 Graphs for rectangular sections 37 Multi-stage prestressing 38 Calculation of displacements 39 Example worked out in British units 310 General 4 Time-dependent internal forces in uncracked structures: analysis by the force method 41 Introduction 42 The force method 43 Analysis of time-dependent changes of internal forces by the force method 44 Movement of supports of continuous structures 45 Accounting for the reinforcement 46 Step-by-step analysis by the force method 47 Example worked out in British units 48 General 5 Time-dependent internal forces in uncracked structures: analysis by the displacement method 51 Introduction 52 The displacement method 53 Time-dependent changes in fixed-end forces in a homogeneous member 54 Analysis of time-dependent changes in internal forces in continuous structures 55 Continuous composite structures 56 Time-dependent changes in the fixed-end forces in a composite member 57 Artificial restraining forces 58 Step-by-step analysis by the displacement method 59 General 6 Analysis of time-dependent internal forces with conventional computer programs 61 Introduction 62 Assumptions and limitations 63 Problem statement 64 Computer programs 65 Two computer runs 66 Equivalent temperature parameters 67 Multi-stage loading 68 Examples 69 General 7 Stress and strain of cracked sections 71 Introduction 72 Basic assumptions 73 Sign convention 74 Instantaneous stress and strain 75 Effects of creep and shrinkage on a reinforced concrete section without prestress 76 Partial prestressed sections 77 Flow chart 78 Example worked out in British units 79 General8 Displacements of cracked members 81 Introduction 82 Basic assumptions 83 Strain due to axial tension 84 Curvature due to bending 85 Curvature due to a bending moment combined with an axial force 86 Summary and idealized model for calculation of deformations of cracked members subjected to N and/or M 87 Time-dependent deformations of cracked members 88 Shear deformations 89 Angle of twist due to torsion 810 Examples worked out in British units 811 General 9 Simplified prediction of deflections 91 Introduction 92 Curvature coefficients, k 93 Deflection prediction by interpolation between uncracked and cracked states 94 Interpolation procedure: the 'bilinear method' 95 Effective moment of inertia 96 Simplified procedure for calculation of curvature at a section subjected to M and N 97 Deflections by bilinear method: members subjected to M and N 98 Estimation of probable defection: method of 'global coefficients' 99 Deflection of two-way s

Moderate deformations in extension-torsion of incompressible isotropic elastic materials

Abstract: It has been previously shown by anand (1979) that the classical strain energy function of infinitesimal isotropic elasticity is in good agreement with experiment for a wide class of materials for moderately large deformations, provided the infinitesimal strain measure occurring in the strain energy function is replaced by the Hencky or logarithmic measure of finite strain. The basis in Anand's paper for relating Hencky's strain energy function to experiment was data from experiments on metals and rubbers in uniaxial strain, simple tension and compression, and pure shear. Here, to test further the validity of this strain energy function for moderate deformations, its predictions for the twisting moment and the axial force in simple torsion and combined extension-torsion of solid cylinders of incompressible materials are calculated and shown to be in good agreement with data from the classical experiments of R ivlin and S aunders (1951) on vulcanized natural rubber. Indeed, the predictions from Hencky's strain energy function are in better accord with experiment than the predictions from the widely used Mooney (or Mooney-Rivlin) strain energy function.

A New Workability Criterion for Ductile Metals

Abstract: The forming limit curves are important aids in determining the extent of deformation a material can be subjected to during a forming process. In this paper a forming limit criterion for bulk metalworking processes, based on the magnitude of the hydrostatic component and the effective stress of the state of stress, is proposed. The determination of the forming limit curve by means of three simple tests, namely, tension, compression, and torsion tests, is presented.

Helical bilayer structures due to spontaneous torsion of the edges

Abstract: A theory is given to explain the helical structures, in particular the strips wound around as cylinders, which were found with solid bilayers made of chiral molecules. It employs a spontaneous torsion of the bilayer edges and the bending stiffness of the bilayer. The gradient angle of the helix is found to be 45°, in good agreement with experiment.

Eccentricity in irregular multistory buildings

Abstract: To evaluate the seismic torsional effect on multistory buildings, the concept of eccentricity is extended from single-story buildings to multistory buildings by defining the locations of the center...

Static Stability of Curved Thin‐Walled Beams

Abstract: Starting from a continuum mechanics basis, the principle of virtual displacements is used for deriving the differential equations of equilibrium for a horizontally curved I‐beam. In the present formulation, the effect of curvature is considered, while the condition of inextensibility, usually adopted in conventional analyses, is not required. The cross‐sectional displacements for the curved I‐beam are derived through employment of Vlasov's thin‐walled beam assumptions. Due to the inclusion of nonlinear strains in the virtual work equation, the instability effects caused by various loads, including the axial force, transverse shears, torque, bending moments, and bimoment are generally taken into account. The solutions are presented and compared with existing ones for two special cases.

Nonlinear theory of non-uniform torsion of thin-walled open beams

Abstract: A nonlinear theory of non-uniform torsion based on finite displacements is developed. Expressions for the finite nonlinear strains in Lagrangian coordinates and the Kirchhoff stresses for thin-walled open beams are presented. Using the principle of stationary total potential, the dual forms of the beam equilibrium equations are derived. For conservatively loaded thin-walled open beams a static stability criterion, based on the positive definiteness of the second variation of the total potential, is presented. The criterion developed takes into account the effects of changes in beam geometry such as initial bending curvature, prior to instability.

Microstructural study of cyclic strain hardening behaviour in biaxial stress states at elevated temperature

Abstract: This paper describes the cyclic strain hardening behaviour and dislocation structures of material in biaxial low cycle fatigue at elevated temperatures. In this study, push-pull, reversed torsion and combined push-pull/reversed torsion tests were carried out using a type 304 stainless steel in air. While there was no significant difference between the cyclic stress amplitudes in the push-pull and reversed torsion tests on a von Mises' base, combination tests exhibited a 40% increase in stress amplitude. Most of the dislocations in the first two types of test adopted ladder or maze structures, while in the later case cells were found. Changing the loading mode at a certain cycle, for example, from push-pull to reversed torsion, revealed that stress amplitude depended mainly on the concurrent applied strain mode and furthermore, that the strain mode before the interchange had little or no effect on the stress amplitude after the interchange. Tests were also performed in order to examine how prestrained material hardened in the three different loading modes, with the following results: prestrained material in push-pull or in reversed torsion exhibited an anisotropic stress response, while the material in the combined tests exhibited an isotropic response. These cyclic responses are discussed in connection with the dislocation structure.

Nonlinear flexure and torsion of rotating beams, with application to helicopter rotor blades. I - Formulation. II - Response and stability results

Abstract: The dynamic response and aeroelastic stability of rotating beams such as helicopter blades is investigated analytically. The Hamilton principle is used to formulate the equations of motion for extensional and inextensional beams with precone angles and variable pitch angles, taking higher-order nonlinearities into account. The derivation of the equations and their approximate solution by a Galerkin procedure are explained in detail, and numerical results of equilibrium solutions and stability analyses are presented graphically.

Torsion in Beams Reinforced with Bars and Fibers

Abstract: An experimental investigation carried out to assess the effect of incorporating steel fibers on the torsional behavior of conventionally reinforced beams is reported. The study involved testing 24 beams, with partial or full replacement of longitudinal steel reinforcement and/or stirrups by an equivalent volume fraction of steel fibers. The tests revealed that the loads on first cracking observed on fiber-reinforced beams were substantially higher than those obtained in similar beams with conventional reinforcement. Increases of up to 60% in the torsional capacity of beams were observed, when the stirrups were partially or fully replaced by an equivalent volume fraction of fibers.

Fracture surface energy determination in {1 1 0} planes in silicon by the double torsion method

Abstract: The fracture surface energy of {110} planes of silicon were determined by the double torsion method on thin samples. Elastic anisotropy was taken into account in the calculations. The determined value of 1.81 J m−2 compared well with other data in the literature.

Torsion damping mechanism

Abstract: A torsional damping mechanism (22) adapted to be disposed between an engine (10) and a transmission (12) operative to drive ground wheels (16) of a vehicle. The mechanism includes a viscous damping device (30), an idle rattle assembly (32), a torque transmitting torsion spring bar (28) disposed in series with the idle rattle assembly and in parallel with the viscous damping device, and a mechanical friction assembly for connecting the mechanism to the engine. Mechanism (22) is structurally configured to have a low inertia. The viscous damping device includes lost motion means (48k, 50c) which allows attenuation of low amplitude torsionals without damping.

Counterbalance device and torsion member usable therein

Abstract: A device for counterbalancing a moving part comprises an elongated torsion member surrounded by a sleeve, the sleeve being connected to the torsion member at one point and the torsion member being fixedly supported at another point spaced from said one point, the moving part and the sleeve respectively carrying cooperating elements of a cam-follower combination, the cam being shaped, taking into account the torsion characteristics of the torsion element, to produce the desired counterbalancing effect. The torsion member itself advantageously comprises a plurality of elongated narrow elements of polygonal cross-section arranged in a predetermined grouping with sides of adjacent elements engaging one another, the exposed surfaces of said elements defining at least in part a polygonal shape, operative connections to points along the length of the torsion member being effected by bodies having appropriately shaped polygonal openings into which the grouping of the narrow elements is received so as to non-rotatably engage at least some of the elements and to confine the elements so that they are maintained in that predetermined grouping. The construction of the torsion member is such that a variety of different torsion element groupings can be received within a given polygonal opening, with a still greater variation in the number of torsion elements being possible by simple modifications of those polygonal openings, so that great latitude in operating characteristics can be achieved with an essentially standardized construction.

The Stress Field Induced by a Twisting Sphere

Abstract: Analytical solutions are presented for the stress field induced in an elastic half space by a sphere pressed normally into its surface, and twisted. It is found that the stresses decay rapidly with depth, and that the severest stress state occurs in the surface. Cases of both partial slip, i.e., where there is a central disk where no relative rotation occurs, surrounded by a slip annulus, and full slip where the disk degenerates to a point, are considered. The largest tensile stress, associated with brittle fracture and cracking, occurs on the edge of the contact circle, while the greatest tendency to yield, by von Mises criterion, occurs somewhere within the slip annulus, depending on the coefficient of friction. Twisting has a first order effect on the strength of contact as measured by each of these criteria.

Brans-Dicke theory in general space-time with torsion.

Abstract: The Brans-Dicke theory in the general space-time endowed with torsion is investigated. Since the gradient of the scalar field as well as the intrinsic spin generate the torsion field, the interaction term of the spin-scalar field appears in the wave equation. The equations of motion are satisfied with the conservation laws.

Proca field in a spacetime with curvature and torsion

Abstract: The author considers a spin-1 (Proca) test particle in a spacetime with curvature and torsion. Within a WKB approximation, the author derives the equations of motion for the field amplitude, the current vector and the spin vector. In contrast to a spin-1/2 (Dirac) test particle, the Proca field is sensitive to all irreducible parts of the torsion tensor.

Dynamometric screw-driver

Abstract: A screw-driver includes, disposed inside a driving handle, a torque limiter having a torsion spring in which one end of a helical friction band carries a ring connected by axial splines to a stem of the tool while the corresponding end of the torsion spring is fixed to a ring connected to the stem by a helical spline. An adjusting sleeve solely movable in rotation is screwed on the stem and, when it rotates, causes an axial displacement of the stem and modifies the relative angular setting of the two end rings, i.e. the torsion of the spring and consequently the value of the sliding torque.