Showing papers on "Torsion (mechanics) published in 1974"

Some New Observations on Yield Surfaces

Abstract: This paper presents the results of experiments in which two thinwalled tubes of commercially pure aluminium in the annealed condition were loaded in combined tension and torsion in the plastic region at elevated temperatures. In the first test prestressing was in torsion but of a cyclic nature. In the other test prestressing included a path reversal in tension. It is shown that the hardening law introduced previously [3] is such that prestressing towards the origin of the stress space produces an increase in the width of the yield curve in the prestressing direction. It is also shown that a locus of zero deformation of yield surfaces can be postulated.

Torsion-bending-shear interaction for concrete beams

Abstract: A rational, simple method is presented for analysis of the torsion-bending-shear interaction at failure for reinforced concrete beams. Equilibrium equations are studied for observed failure mechanisms. Three mechanisms can occur depending on where the concrete compression zone is formed: in the top (mode t ), in the bottom (mode b ), or in one vertical side (mode s ). In modes t and b , the torsion-bending and the shear-bending interaction are governed by second-degree parabolas, whereas the torsion-shear interaction is governed by an ellipse. In mode s , the interaction surface is a cylinder with an elliptic base in the torsion-shear plane. The interaction in this mode is not influenced by the value of the bending moment, M . Approximations regarding the lengths of the moment lever arms and regarding the shear-carrying capacity are examined. Some test results are presented to demonstrate the accuracy of the method. The main feature of the method is that the vertical shear forces are considered in a simple but rational way.

A new nondestructive method for three-dimensional photoelasticity

Abstract: A new set of equations describing completely the optical phenomena in a model involving continuous rotation of secondary axes and secondary principal-stress differences are obtained. These are solved by Peano-Baker method using experimentally determined characteristic parameters for several wavelengths of light. Experimental verifications are obtained for a rectangular bar subjected to combined torsion and tension.

Ultrasensitive force measuring instrument employing torsion balance

Abstract: A force measuring instrument employs light interference fringes for measuring extremely small magnitudes of force such as those encountered in the weighing of small objects or in determining the forces of attraction or repulsion between two relatively small bodies. A fixed mirror of the displacement mechanism is provided with needle point pivot shafts in which balance oscillations can be dampened by applying a viscous damping material in the conical recesses receiving the pivot points. Torsion fiber beams permit a small angular displacement of the fixed mirror. A low frequency dither signal may be applied to the platform for overcoming stiction at the pivot points.

The fracture of spherical shells under pressure and circular tubes with angled cracks in torsion

Abstract: Experiments are reported on spherical PMMA domes with thickness variations. The results were correlated with the parameter a2/Rt where I is a mean thickness based on equivalent energy. The curvature effect could be adequately represented by a published formulae. Crack angles and failure stresses for tubes broken in torsion were compared with the maximum hoop stress and minimum strain energy theories of Sih.

Computer analysis of a rotating axial-turbomachine blade in coupled bending-bending-torsion vibrations

Abstract: Basic equations are derived for a comprehensive computer analysis for an equivalent lumped parameter system which simulates a pre-twisted, rotating or non-rotating. Timoshenko beam in coupled bending-bending-torsion vibrations. These equations enable one to develop straightforwardly digital computer programs for studying vibration problems related to compressor or turbine blades in turbomachinery as well as in other structural dynamics applications. The validity of the lumped parameter approach is established through a free vibration study. Good agreement between the present computer results and those obtained theoretically or experimentally by other investigators is demonstrated. In particular, it is found that the natural frequencies obtained in the free vibration study for all beams examined converge from below the exact values at a convergence rate of N−4, where N is the total number of the lumped parameters used in the computer simulation. The rapid rate of convergence shows that the mathematical model used in deriving the basic equations can adequately represent the type of beams under consideration. The known convergence rate also provides an estimate on the accuracy of the computer results, and a means to improve these results by extrapolation.

Analytical model for tilting proprotor aircraft dynamics, including blade torsion and coupled bending modes, and conversion mode operation

Abstract: An analytical model is developed for proprotor aircraft dynamics. The rotor model includes coupled flap-lag bending modes, and blade torsion degrees of freedom. The rotor aerodynamic model is generally valid for high and low inflow, and for axial and nonaxial flight. For the rotor support, a cantilever wing is considered; incorporation of a more general support with this rotor model will be a straight-forward matter.

Torsion of Anisotropic Micropolar Elastic Cylinders

Abstract: Die vorliegende Arbeit beschaftigt sich mit dem Torsionsproblem homogener und orthotroper Balken in Rahmen der linearen Theorie mikropolarer Elastizitat. Das Problem wird mittels dreier Torsionsfunktionen gelost. Es wird ein Existenzsatz bewiesen. The present paper is concerned with the torsion problem of homogeneous and orthotropic beams in the linear theory of micropolar elasticity. The problem is solved in terms of three torsion functions. An existence theorem is derived.

Response of Torsionally Excited Foundations

Abstract: Investigated herein are two aspects of the response of a rigid massless foundation of circular plane which is supported at the surface of a homogeneous elastic half space and is excited by a torque about an axis normal to the foundation. A simple discrete model, characterized by frequency-independent parameters, has been presented for a torsionally-excited circular foundation supported at the surface of an elastic half space. In addition, closed form expressions have been presented for the impulse response functions of the system. The response functions considered include the rotation associated with a unit impulsive torque, and the torque associated with a unit impulsive rotation. With the aid of these functions, the response of the system to an arbitrary excitation and the force associated with a prescribed response may be evaluated by direct integration in the time domain.

Torsion design of prestressed concrete

Abstract: THIS PAPER PROPOSES AN EXTENSION OF THE ACI DESIGN PROCEDURES TO COVER TORSION IN PRESTRESSED CONCRETE. THE BASIC APPROACH CONSISTS OF DETERMINING THE CONCRETE CONTRIBUTION TO THE ULTIMATE STRENGTH OF A MEMBER AND THEN PROPORTIONING REINFORCEMENT FOR THE REMAINING PORTION OF THE REQUIRED ULTIMATE STRENGTH. FORMULAS FOR THE NOMINAL TORSIONAL STRESS AND THE BASIC EQUATION FOR TORSIONAL STRENGTH OF REINFORCED MEMBERS ARE PRESENTED, FOLLOWED BY A DESCUSSION OF THE TORSION-SHEAR INTERACTION RELATION, TAKING INTO ACCOUNT THE EFFECT OF THE PRESTRESSING FORCE. REQUIREMENTS FOR BOTH WEB AND LONGITUDINAL REINFORCEMENTS FOR TORSION ARE EXPLAINED. /AUTHOR/

The Bending and Creasing of Multicomponent Viscoelastic Fiber Assemblies: Part III: The Mechanics of a Two-Dimensional Assembly of Generalized Linear Viscoelastic Fibers of Different Types

Abstract: Equations have been derived to predict the bending behavior of a two-dimensional assembly of long thin straight fibers, which are generalized linear viscoelastic in bending and torsion, and are subject to frictional restraints (in the assembly) in both these modes of deformation. The resultant bending behavior of the assembly in any direction θ is characterized by a generalized linear viscoelastic function known as the bending-relaxation-rigidity plus an internal frictional moment. The bending-relaxation-rigidity may be calculated from first principles as a linear combination of the component fiber bending and torsional relaxation moduli. The internal frictional moment will generally be found experimentally. It is suggested that the theory presented. may be applied under conditions of changing temperature and relative humidity to the bending behavior of woven and nonwoven fabrics composed of generalised linear viscoelastic fibers of one or more types.

Apparatus for detecting and correcting torsion of travelling fabric

Abstract: An apparatus comprising a detecting unit for detecting the torsion of a travelling fabric and a correcting unit for correcting the torsion detected by the detecting unit. The detecting unit has a working surface for detecting operation positively driven in sliding contact with the surface of the fabric longitudinally thereof. The positive sliding motion of the working surface assures the detection of the torsion of the fabric with high sensitivity and accuracy to permit the correcting unit to correct the torsion with greatly improved efficiency.

Double Torsion Technique as a Universal Fracture Toughness Test Method

Abstract: A method of measuring the fracture toughness of materials is described that is both simple and universal. A specimen is failed in double torsion so that a crack is driven down the center of a rectangular specimen. The energetics of failure are such that the load causing the crack remains constant as the crack deepens and this load is directly related to the fracture toughness. This enables a simple specimen to be used and obviates the difficulties associated with crack depth or compliance measurements or both. Results are shown for aluminum alloys to supplement earlier work on glass and polymers.

Gear type torsion coupling with quickly replaceable sleeve

Abstract: A coupling for shaft-to-shaft power transmission which comprises two externally toothed hubs for attachment to opposing shaft ends, and an internally toothed sleeve in mesh with the teeth of the hubs. The sleeve is constructed in two or more arcuate sections normally secured together over the hubs by an encircling band-like member.

A comparison of the dislocation structures at small strains in copper deformed in tension and in torsion

Abstract: OFHC copper specimens of 39 μm grain size were deformed in tension (to 8 pct tensile strain) and in pure torsion (to 8 pct shear strain) at 300 K and the resulting dislocation Burgers vectors, distributions and densities were determined using transmission electron microscopy. Employing the von Mises yield criterion and the total plastic-work hypothe-sis, good agreement was obtained between the tension and torsion test results for: (a) equivalent stress •σ versus equivalent strain •∈P curves, (b) the dislocation Burgers vec-tors, distribution and density as a function of the equivalent strain and (c) the equivalent stress as a function of the square root of the dislocation density. These results imply that in the unidirectional straining of copper there results a constant dislocation struc-ture for a given amount of plastic work, irrespective of whether the deformation is in tension or torsion. However, equally good correlations were obtained on the basis of maximum shear stress and maximum shear strain and therefore a positive decision be-tween the two yield criteria could not be made.

Flow induced vibration of bluff structures

Abstract: Models are developed for both multi-degree-of-freedom aerodynamic galloping and vortex induced oscillation of bluff structures. These models are useful in the analysis of elastic structures exposed to a steady fluid flow. An asymptotic method, based on the approximation of Bogoliubov and Mitropolsky, is developed for the analysis of the autonomous, internally resonant, nonlinear differential equations produced by the models. It is shown that the solutions of these systems can be divided into two classes by the nature of the secular terms arising in the perturbation equations. A model for multi-degree-of-freedom galloping is developed by modeling the aerodynamic forces on the structure as dependent only on the relative magnitude and velocity of the flow to the structure. A simple criterion for the stability of the zero solution is presented. Examples are made with a noninertially coupled system with the torsion and plunge degrees-of-freedom and a cubic curve fit to the aerodynamic coefficients. Examples show that the system is dorninated by either a torsion or a plunge mode except when the natural frequencies of these modes are in certain integer multiples. In these cases the two modes interact strongly and they achieve first order limit cycles simultaneously. A model for vortex induced vibration of elastic structures is produced from a control volume approach to the vortex shedding process. The model features both fluid and structural oscillators. The model parameters are determined from experimental data by matching the model response to experimental observation for the cases of fixed and forced cylinder motion. A frequency entrainment effect is produced by the model for an elastically mounted cylinder resonating with vortex shedding. The resonant amplitude of an elastically mounted cylinder predicted by the model is in good agreement with experimental data.

Reinforced concrete design to CP110: Simply explained

Abstract: 1. Preface. 2. Notation. 3. Limit state principles. 4. Robustness. 5. Analysis of structures. 6. Cover. Strength of sections - ultimate limit state. 7. Serviceability limit state of deflection. 8. Serviceability limit state of cracking. 9. Bond and anchorage. 10. Shear. 11. Corbels, bearings and nibs. 12. Columns. 13. Solid slabs. 14. Ribbed slabs (solid or hollow blocks or voids). 15. Flat slab construction. 16. Staircases. 17. Bases. 18. Torsion. Appendices. Index.

Multiple range torque measuring tool

Abstract: A torque measuring tool in which the twist of a torsion bar indicates the magnitude of applied torque comprising: A. Means to utilize a variety of conventional wrenches of any desired length. B. Interchangeable torsion bars for various torque ranges utilizing one scale with interchangeable numerical displays appropriate to each torque range. C. Means to absorb excess torque, preventing accidental damage to the torsion bars and permitting unilateral readouts. D. Interchangeable readout modes with very simple means of zeroing.

The effects of cutouts on the buckling of thin shells

Abstract: A study of the effects of circular and rectangular cutouts on the buckling of thin cylinders loaded by axial compression, bending, and torsion is presented. Experimentally determined design curves for the various loading conditions are provided. Some analytical verification of the experimental results is also provided by a finite-element computer program.

Torsion of Cylinders with Multiple Reinforcement

Abstract: An exact solution is presented for the Saint-Venant torsion of a circular cylinder reinforced by multiple rings of circular rods. The number of equally spaced rods in each ring is the same, and these are arranged in such a way that the corresponding rods in each ring are located on the same radial line. The problem simulates that encountered in matrix rods reinforced by longitudinal fibers, and also in corresponding problems of reinforced concrete. Formulas are obtained for the boundary stress distributions and torsional rigidities. Stress function formulations are made for the torsion of cylinders having multiply connected composite sections. The stress function for each rod is expressed in terms of different polar coordinates, and use is made both of periodicity and symmetry. The degenerate case of a circular cylinder having multiple rings of holes is also considered. Several numerical examples are worked out, and the results are presented in tabular and graphical form.

Combined compression-torsion buckling tests of laminated composite cylindrical shells

Abstract: Results are described for six composite test cylinders constructed of either four or six plies of graphite-epox y or boron-epoxy and subjected to combined torsion and compressive loading. All the shells were 15 in. in diam and 15 in. long. The stacking sequence effects exhibited by these thin laminates produced significantly different buckling capacities depending on the direction of torque application. A test technique was developed to define the entire range of torsion/compr ession ratios for each type of shell, and one specimen was used to define each shell type. The interaction between the torsion-compression buckling stresses was shown to be linear except at high percentages of compression stress.