Showing papers on "Torsion (mechanics) published in 1994"

Fracture Behavior of Polymers

Abstract: Fracture analysis is complicated for polymers since, besides of temperature and time dependence, there are involved effects from plastification, chain orientation and adiabatic temperature rise. It is the aim of this section to describe several fracture processes which are specific of polymers. Fracture behavior is determined experimentally by the mode and time profile of loading. Stress- and strain controlled loading yields different behavior as well as loading in tension, compression or shear (torsion). Compressive strength is higher than tensile strength; shear strength is the lowest one.

Generalized beam theory—an adequate method for coupled stability problems

Abstract: First-order generalized beam theory describes the behaviour of prismatic structures by ordinary uncoupled differential equations, using deformation functions for bending, torsion and distortion. In second-order theory, the differential equations are coupled by the effect of deviating forces. The basic equations for second-order generalized beam theory are outlined. Solutions for pin-ended supports are presented, demonstrating the coupling effect by modes and by loads. In the different ranges of length, the individual modes are sufficient approximations for the critical load. The application to a thin-walled bar with C-section under eccentric normal force demonstrates the quality of the single-mode compared to the exact solution.

Spin and Torsion in Gravitation

Abstract: Spin and Torsion Torsion and Magnetism Torsion and Maxwell Equations Maxwell Electrodynamics in Space with Torsion Dirac Equation in Curved Space-Time with Torsion The Torsion Coupling Constant and the Problem of the Cosmological Constant Spin, Magnetic Moment and Electric Charge Torsion - A Way toward Quantization of Gravity? Negative Mass and Torsion Symmetry Breaking Miscellanea Other Physical Consequences of Torsion.

Consequences of propagating torsion in connection-dynamic theories of gravity

Abstract: We discuss the possibility of constraining theories of gravity in which the connection is a fundamental variable by searching for observational consequences of the torsion degrees of freedom. In a wide class of models, the only modes of the torsion tensor which interact with matter are either a massive scalar or a massive spin-1 boson. Focusing on the scalar version, we study constraints on the two-dimensional parameter space characterizing the theory. For reasonable choices of these parameters the torsion decays quickly into matter fields, and no long-range fields are generated which could be discovered by ground-based or astrophysical experiments.

The failure of composite tubes due to combined compression and torsion

Abstract: The strength of unidirectional carbon-fibre epoxy laminates has been measured for combined compression and shear loading. Failure was by plastic microbuckling. The axial compressive strength decreased linearly to zero as the shear stress parallel to the fibres was increased from zero to the shear strength. These experimental results support the predictions of Budiansky and Fleck and suggest an average fibre misalignment angle of 2°–3°.

Nonlinear Inelastic Analysis of Steel Beam‐Columns. I: Theory

Abstract: This paper presents a nonlinear inelastic analysis of the biaxial bending and torsion of thinwalled steel beamcolumns based on the principle of virtual work. The effect of geometric nonlinearity is...

Determination of Recrystallization Stop Temperature from Rolling Mill Logs and Comparison with Laboratory Simulation Results

Abstract: The tempreature of no-recrystallization, Tnr, was measured by means of laboratory torsion rests for three low carbon steels The Tnr values for these steels were also established from rolling mill log data obtained from the Algoma plate mill; these were found to be virtually identical to those from torsion tests The mill log calculations were carried out by organizing the Sims roll force equations into a spreadsheet software for desktop personal computers The results of both the torsion testing and mill log calculations compare well with previously developed correlations between Tnr and the chemical composition, and between Ar3 and the composition It was also found that the overall levels of the mean flow stresses calculated from the mill logs are close to those determined from torsion testing This excellent agreement confirms that laboratory torsion testing can provide a convenient and very effective simulation of industrial hot rolling operations

The effect of torsion on the motion of a helical vortex filament

Abstract: In this paper we analyse in detail, and for the first time, the role of torsion in the dynamics of twisted vortex filaments. We demonstrate that torsion may influence considerably the motion of helical vortex filaments in an incompressible perfect fluid. The binormal component of the induced velocity, asymptotically responsible for the displacement of the vortex filament in the fluid, is closely analysed. The study is performed by applying the prescription of Moore & Saffman (1972) to helices of any pitch and a new asymptotic integral formula is derived. We give a rigorous proof that the Kelvin regime and its limit behaviour are obtained as a limit form of that integral asymptotic formula. The results are compared with new calculations based on the re-elaboration of Hardin's (1982) approach and with results obtained by Levy & Forsdyke (1928) and Widnall (1972) for helices of small pitch, here also re-elaborated for the purpose.

Derivation of Class II Force Fields. III. Characterization of a Quantum Force Field for Alkanes

Abstract: Recently, a quantum mechanical Class II force field (QMFF) was derived from a fit of HF/6–31G* ab initio energy and energy derivative data for alkanes, and a comparison of this quantum force field and the ab initio energy and energy derivatives was presented. In this work, the quantum force field is further evaluated with regard to its accuracy, and, more importantly, transferability. A detailed comparison between structures, frequencies, and energies calculated from quantum mechanics and from the classical analytical form is given for a set of molecules selected from both those used in the original training set and molecules selected from outside the training set. None of these properties were used directly in the original derivation of the force field. In order to assess the importance of anharmonic and coupling interactions that occur in and contribute to molecular energy surfaces, the results are compared to a diagonal quadratic force field. It is demonstrated that the QMFF functional form is capable of calculating the ab initio bond lengths, bond angles, torsion angles, and conformational energy differences to an rms accuracy of 0.003 A, 0.4°, 1.2°, and 1.0 kcal/mol, respectively. This compares quite well to corresponding deviations of 0.006 A, 0.8 A, 2.3°, and 3.3 kcal/mol for a harmonic diagonal force field. Excluding three- or four-membered rings, the QMFF rms frequency deviations were 24 cm−1, which again is much better than the ˜100 cm−1 deviations for the harmonic diagonal force field. Larger average rms frequency deviations of 36 and 71 cm−1 were found with QMFF for molecules with three- and four-membered rings. An in-depth analysis of C-H and C-C bond length, H-C-H, H-C-C, and C-C-C bond angle, and C-C-C-C torsion angle deviations is also presented, along with a similar characterization of frequency deviations in C-H stretching, C-C stretching, C-C-C bending, and torsion modes. It is concluded from these results that the use of quantum energy surfaces allows us to derive a (Class II) functional form which is not only more accurate, but also more transferable than previous generation force fields.

Analytical solution for bending of coaxial orthotropic cylinders

Abstract: A general analytical solution is obtained for the stresses and displacements of an elastic body consisting of an assembly of coaxial hollow circular cylinders made of orthotropic material, with or without a core, and subjected to bending, tensile and torsion loads. Two types of conditions are considered at the interfaces between cylinders: no slip and no friction. A numerical application is used to illustrate the theoretical results. Results show that there is no coupling between bending and tension‐torsion and that there is no deviation in the bending curvature. It was finally found that some warping of the cross section develops under bending, meaning that the Bernoulli‐Euler hypothesis would not strictly apply in the case of orthotropic cylinders.

Accidental torsion in buildings due to base rotational excitation

Abstract: This investigation is concerned with accidental torsion in buildings resulting from rotational excitation (about a vertical axis) of the building foundations as a result of spatially non-uniform ground motions. Because of this accidental torsion, the displacements and deformations in the structural elements of the building are likely to increase. This increase in response is evaluated using actual base rotational excitations derived from ground motions recorded at the base of 30 buildings during recent California earthquakes. Accidental torsion has the effect of increasing the building displacements, in the mean, by less than 5 per cent for systems that are torsionally stiff or have lateral vibration periods longer than half a second. On the other hand, short period (less than half a second) and torsionally flexible systems may experience significant increases in response due to accidental torsion. Since the dependence between this increase in response and the system parameters is complex, two simplified methods are developed for conveniently estimating this effect of accidental torsion. They are the ‘accidental eccentricity’ and the ‘response spectrum’ method. The computed accidental eccentricities are much smaller than the typical code values, 0.05bb or 0.1b, except for buildings with very long plan dimensions (b ≥ 50 m). Alternatively, by using the response spectrum method the increase in response can be estimated by computing the peak response to each base motion independently and combining the peak values using the SRSS rule.

Three-dimensional computed tomography reconstruction of tibial torsion.

Abstract: The accuracy and reproducibility of computed tomography (CT) scanning techniques in assessing tibial version and torsion are measured in this study. A technique of three-dimensional CT reconstruction is introduced to assess the influence of selection and variation of landmarks on rotation measured in the tibia. The authors conclude that, within 2 cm of the articular surface, the level at which the proximal tibial axis is determined has no effect on the degree of torsion measured by CT scan. Furthermore, they conclude that the slope of the proximal tibial cut, with respect to the long tibial axis, has no effect on the measure of tibial torsion. Finally, they conclude that there is no significant difference in tibial torsion measured by reference to the posterior-condylar axis instead of the transtibial axis in cuts below the articular surface.

Composite Structures for Civil and Architectural Engineering

Abstract: Introduction. Historical necessity. Basic concept of composites. Matrix. Reinforcements. Filamentary type composites. Composite manufacture. Application, present and future. Further reading. Properties of composites. Introduction. Reinforcements. Matrices. Particulate composites. Other matrix based composites. Mechanical properties of fibrous composite. 'Comingle' and 'FIT' - new concepts for thermoplastic composites. References. Further reading. Classical theory of elasticity and mechanics. Assumptions for classical theory of elasticity. Stress and strain. Hooke's Law. Two-dimensional problems (plane) problems. Stress at a point. Mohr's circle. Strain at a point. Pure shear. Equilibrium equations and boundary conditions for two-dimensional problem. Compatibility equations. Stress function. Application of stress function in rectangular coordinate system. Displacements in two-dimensional problem. Application of stress function using Fourier Series. Equilibrium equations in terms of displacements. Two-dimensional problems in polar coordinates. Solution of two-dimensional problems in polar coordinates. Problems of concentrated loads. Strain energy and principle of virtual work. Examples of use of the energy method. Castigliano's theorem. Equilibrium equations in three dimensions. Boundary conditions in three-dimensional problems. Compatibility equations in three-dimensional problems. Saint Venant', solution of the problem of torsion of a prismatic bar. Membrane analogy for torsional problems. Asymmetric bending of prismatic beams. Asymmetrical bending of a beam with longitudinal stringers. Torsion of thin-walled structures with longitudinal stringers. Determination of rate of twist of a cell. Shear centre of beams with longerons. Shear flow distribution in multicell beams with longerons. Out-of-plane bending of curved girders. Alternative formulation for out-of-plane bending of curved beams with constant radius. Bending in the plane of the ring. Elementary theory of thin shell. Space frame. Space trusses. Cable. Guyed tower. Review of beam theory. Plates with irregular shapes and arbitrary boundary conditions. References. Further reading. Eigenvalue problems of beams and frames of isotropic materials. Stability of beams and frames. Structural vibration of beams and frames. References. Further reading. Anisotropic elasticity. Introduction. Stress-strain relations of anitotropic materials. Engineering constants for orthotropic materials. Stress-strain relations of plane stress and plane strain problems for unidirectionally reinforced lamina. Transformation equations. Invariants. Laminates. Micromechanics - mechanical properties of composites. Numerical examples. References. Further reading. One-dimensional structural elements of composite materials. Equations for beams and rods. Beams with hollow cross-sections. Eigenvalue problems of beams and frames of anisotropic materials. References

Accidental torsion in buildings due to stiffness uncertainty

Abstract: Discrepancies between the computed and actual values of the structural element stiffness imply that a building with nominally symmetric plan is actually asymmetric to some unknown degree and will undergo torsional vibration when subjected to purely translational ground motion. Such accidental torsion leads to increase in structural element deformations which is shown to be essentially insensitive to the uncoupled lateral vibration period of the system but is affected strongly by the ratio of uncoupled lateral and torsional vibration periods. The structural deformations increase, in the mean, by at most 10 and 5 per cent for R/C and steel buildings, respectively, and by much smaller amounts for a wide range of system parameters. The increase in structural deformations due to stiffness uncertainty is shown to be much smaller than implied by the accidental torsional provisions in the Uniform Building Code and most other building codes.

Schaum's Outline of Theory and Problems of Strength of Materials

Abstract: Tension and compression statically indeterminate force systems - tension and compression thin-walled pressure vessels direct shear stresses torsion shearing force and bending moment centroids, moments of inertia and products of inertia of plane areas stresses in beams elastic deflection of beams - double-integration method elastic deflection of beams - method of singularity functions statically indeterminate elastic beams special topics in elastic beam theory plastic deformation of beams columns strain energy methods combined stresses members subject to combined loadings - theories of failure.

Spin, torsion, forces

Abstract: A theory of gravitation with torsion that is derived from a potential is developed. An explicit material action is presented that gives rise to the correct conservation laws and equations of motion. It is shown that the Noether identities yield the same conservation laws as the Bianchi identities, and the Papapetrou method is used to develop the propagation equations and the force law. The equations are put in the nonrelativistic limit and the 3-vector formulation is displayed.

Torsion beam accelerometer with slotted tilt plate

Abstract: A capacitive-type torsion beam accelerometer sensor element exhibiting improved stability contains slots in the heavy side of the rotatable sensing element which serve to alter the geometry of the heavy side capacitor such that the electrical geometry substantially coincides with the physical geometry of the substrate's fixed conductive plate in the presence of charge spreading. The slots also permit ingress and egress of air, thus extending the frequency response.

Ocular torsion quantification with video images

Abstract: Describes a technique to quantify eye rotations about the visual axis (ocular torsion). Two digitized polar transformed images of the iris are displayed on a video monitor in order to facilitate a visual comparison and manual interaction. Emphasis is placed on error analysis and the method's simplicity when applied to static ocular torsion measurement. The implementation, applying averaging over ocular torsion determined in partitioned iris images, yields a theoretical resolution of 5' of arc. In a control experiment with an artificial eye, the accuracy showed to be better than 14' of arc. In practice, the measuring device was validated with the data from the literature by means of an experiment about ocular torsion in humans during tilt and hypergravity conditions (up to 3 g). >

Tuning a self consistent viscoplastic model by finite element results—II. Application to torsion textures

Abstract: In part one of the present work, a self consistent model is described which is based on the approach of Molinari et al. [Acta metall.35, 2983 (1987)] and on the finite element results of Gilormini and Germain [Int. J. Solids Struct.23, 413 (1987)]. In that work, a scalar interaction parameter is introduced by tuning the self consistent predictions with the finite element results. In the present paper, the new model is applied for the large strain simulation of torsion texture development and compared with experimental results. The simulations reveal that the new approach leads to predictions which are much nearer to the experimental results than those which can be obtained by the Taylor model or by the pure tangent formulation of the self consistent model. An important effect of the grain shape changes on the evolution of anisotropy at large strains is also confirmed.

Evaluation of Code Accidental‐Torsion Provisions from Building Records

Abstract: A procedure is presented for evaluating building‐code provisions for accidental torsion from analysis of earthquake‐induced motions of nominally symmetric‐plan buildings. This procedure is used to analyze the motions of three buildings recorded during recent California earthquakes. Two alternative approaches to evaluate the code accidental torsion provisions are developed. The first One considers the response histories of base shear and base torque in the building, and the second, the “actual” forces in the structural elements during the earthquake. The results show that base rotational motions cause between 25% and 45% of the total accidental torsion in the buildings. They also demonstrate that the accidental torsional moments specified by the Uniform Building Code are sufficient in representing the torsion in the recorded motions of the three buildings. Further, it is shown that accidental torsion need not be considered in the design of two of the three buildings studied. This observation, however, may ...

Circuit board assembly torsion tester and method

Abstract: A mechanical deflection system (MDS) includes a torsion tester for circuit boards which imposes controlled repeatable sheer stress to a test board and components mounted thereon by cyclicly twisting the board about a center line. A self centering twisting clamp holds one edge of the board and a rotating clamp connected to a backlash free motor and servo mechanism, holds the opposite edge with a limited clamping force. A computer regulates the motor to apply either a specified maximum twist angle or maximum torque, and receives signals from an optical meter which measures the angle, and from a load cell which measures the torque. The computer is connected to detect failures by measuring the electrical resistance of critical joints during testing and it records the location and number of cycles for each failure. The MDS includes a test method which continues until a large number of fatigue failures have occurred, then the locations and cycles till failure are compared to the data for a similar circuit board produced by a base attachment process. For attachment process development another process is the base, and for attachment process quality monitoring the same process at earlier times is the base. Then the reliability of the circuit board and/or production process is statistically determined.