Showing papers on "Torsion (mechanics) published in 1997"

Demonstration of the Casimir Force in the 0.6 to 6 μ m Range

Abstract: The vacuum stress between closely spaced conducting surfaces, due to the modification of the zero-point fluctuations of the electromagnetic field, has been conclusively demonstrated. The measurement employed an electromechanical system based on a torsion pendulum. Agreement with theory at the level of 5% is obtained.

Peterson's Stress Concentration Factors

Abstract: Index to the Stress Concentration Factors. Preface for the Third Edition. Preface for the Second Edition. 1. Definitions and Design Relations. 1.1 Notation. 1.2 Stress Concentration. 1.3 Stress Concentration as a Two-Dimensional Problem. 1.4 Stress Concentration as a Three-Dimensional Problem. 1.5 Plane and Axisymmetric Problems. 1.6 Local and Nonlocal Stress Concentration. 1.7 Multiple Stress Concentration. 1.8 Theories of Strength and Failure. 1.9 Notch Sensitivity. 1.10 Design Relations For Static Stress. 1.11 Design Relations for Alternating Stress. 1.12 Design Relations for Combined Alternating and Static Stresses. 1.13 Limited Number of Cycles of Alternating Stress. 1.14 Stress Concentration Factors and Stress Intensity Factors. References 2. Notches and Grooves. 2.1 Notation. 2.2 Stress Concentration Factors. 2.3 Notches in Tension. 2.4 Depressions in Tension. 2.5 Grooves in Tension. 2.6 Bending of Thin Beams with Notches. 2.7 Bending of Plates with Notches. 2.8 Bending of Solids with Grooves. 2.9 Direct Shear and Torsion. 2.10 Test Specimen Design for Maximum Kt for a Given r D or r H 76. References. Charts. 3. Shoulder Fillets. 3.1 Notation. 3.2 Stress Concentration Factors. 3.3 Tension (Axial Loading). 3.4 Bending. 3.5 Torsion. 3.6 Methods of Reducing Stress Concentration at a Shoulder. References. Charts. 4. Holes. 4.1 Notation. 4.2 Stress Concentration Factors. 4.3 Circular Holes with In-Plane Stresses. 4.4 Elliptical Holes in Tension. 4.5 Various Configurations with In-Plane Stresses. 4.6 Holes in Thick Elements. 4.7 Orthotropic Thin Members. 4.8 Bending. 4.9 Shear and Torsion. 5. Miscellaneous Design Elements. 5.1 Notation. 5.2 Shaft with Keyseat. 5.3 Splined Shaft in Torsion. 5.4 Gear Teeth. 5.5 Press- or Shrink-Fitted Members. 5.6 Bolt and Nut. 5.7 Bolt Head,Turbine-Blade, orCompressor-Blade Fastening (T-Head). 5.8 Lug Joint. 5.8.1 Lugs with h d 0 . 5. 5.8.2 Lugs with h d 0 . 5. 5.9 Curved Bar. 5.10 Helical Spring. 5.10.1 Round or Square Wire Compression or Tension Spring. 5.10.2 Rectangular Wire Compression or Tension Spring. 5.10.3 Helical Torsion Spring. 5.11 Crankshaft. 5.12 Crane Hook. 5.13 U-Shaped Member. 5.14 Angle and Box Sections. 5.15 Cylindrical Pressure Vessel with Torispherical Ends. 5.16 Tubular Joints. References. Charts. 6. Stress Concentration Analysis and Design. 6.1 Computational Methods. 6.2 Finite Element Analysis. 6.3 Design Sensitivity Analysis. 6.4 Design Modification. Index.

Micromachined members coupled for relative rotation by torsion bars

Abstract: Two torsion bars project from a reference member to support at least one plate or frame-shaped first dynamic member for rotation about an axis of the torsion bars. In one embodiment, a frame-shaped first dynamic member and a second pair of torsion bars, oriented non-parallel to the first torsion bars, support a second dynamic member for rotation about an axis that is collinear with the second pair of torsion bars. The vibrational frequency of the principal torsional vibrational mode of the dynamic members are respectively lower by at least 20% than the vibrational frequency of any other vibrational mode thereof. Either an electrostatic or electromagnetic drive means imparts rotary motion to the dynamic members about the collinear torsion bar axis(es). The reference member, the torsion bars and the dynamic member(s) are all monolithically fabricated from a stress-free semiconductor layer of a silicon substrate.

Quantification of the Radial Torsion Angle with Computerized Tomography in Cadaver Specimens

Abstract: Torsion of a long bone is the twist along its longitudinal axis; torsion of the radius is defined by the angle between the proximal and distal metaphyses in the transverse plane. Measurement of the radial torsion angle provides a means of detection and quantification of malrotation after a fracture. The purpose of the current study was to develop and standardize a technique for the measurement of torsion of the radius. Axial computerized tomographic images of thirty-nine pairs of dry cadaver specimens of normal radii, and an additional four pairs of radii with a unilateral deformity of the distal metaphysis that was consistent with a previous fracture, were studied and a measurement protocol was established. The radial torsion angle was measured by three independent observers on two separate occasions. Reproducibility of the technique was determined with use of the intraclass correlation coefficient to express both interobserver and intraobserver reliability. Consistency of measurements between observers and by the same observer was high, with intraclass correlation coefficients ranging from 0.87 to 0.94. The mean torsion angle for the eighty-two normal radii in the study was 32.6 degrees (95 per cent confidence interval of the mean, 30.3 to 34.9 degrees; range, 1.4 to 58.8 degrees). There were small variations in torsion angle between the two radii of each normal pair (mean side-to-side difference, 4.9 degrees; 95 per cent confidence interval of the mean, 3.5 to 6.3 degrees). The mean torsion angle of the four radii with a malunited fracture was 10.4 degrees (95 per cent confidence interval of the mean, 5.7 to 15.1 degrees), and the mean side-to-side difference in the pairs containing these radii was 24.1 degrees (95 per cent confidence interval of the mean, 8.5 to 39.6 degrees; p < 0.0001 compared with the normal radii). CLINICAL RELEVANCE: Measurements of torsion may be useful for the planning of corrective osteotomies of the radius. Conventional computerized tomographic scanning provides a simple, reproducible technique for the measurement of radial torsion that can be accurately applied. Images of both forearms allow the direction of rotation of the radius to be identified, with a decrease in the torsion angle indicating supination of the distal fragment and an increase indicating pronation. Because of the wide range of radial torsion angles in normal individuals, values should be interpreted with reference to the contralateral side.

Semi‐elliptical fatigue crack growth under rotating or reversed bending combined with steady torsion

Abstract: — An analysis of the influence of steady torsion loading on fatigue crack growth rates under rotating or reversed bending is presented. Mixed-mode (I + III) tests were carried out on cylindrical specimens in DIN Ck45k steel and results are compared for two different testing machines: rotary bending and reversed bending obtained by cyclic Mode I (ΔK1) with or without superimposed static Mode III (KIII) loading, simulating the real conditions on power rotor shafts where many failures occur. The growth and shape evolution of semi-elliptical surface cracks, starting from a chordal notch on the cylindrical specimen surface, was measured for several Mode III/ Mode I ratios. Results have shown that the steady Mode III loading superimposed on the cyclic mode I leads to a significant reduction in the crack growth rates. It is suggested that this retardation is related to an increase of plastic zone size near the cylindrical surface in association with the interlocking of rough fracture surfaces, friction and fretting debris, leading to a decrease of the ΔK effective at the crack tip profile due to the “crack closure effect”. This work provides a contribution to a better understanding of crack growth rates under mixed-mode load conditions thereby allowing one to predict remaining lifetimes and to estimate the risks of pre-cracked rotor shafts.

Cracking and Punching Shear Failure Analysis of RC Flat Plates

Abstract: This paper presents a nonlinear layered finite element method capable of analyzing cracking and punching shear failure of reinforced concrete flat plates with spandrel beams or torsion strips. Incorporating a layered approach with transverse shear capabilities, the procedure takes into account the full interaction between the spandrel beam and the adjoining slab (in bending, shear, and torsion). The formulation of the nonlinear cracking and failure analysis is discussed in some detail. A comparative study based on a series of 11 half-scale reinforced concrete flat plate models and four single slab-column specimens confirms the method's ability to satisfactorily predict the punching shear strengths, the deflections, and the crack patterns, as well as the collapse loads, of the models. Also included in the comparison is a semiempirical procedure, along with those recommended by the American Concrete Institute, the British Standards Institution, and the Standards Association of Australia. Results show that t...

Torsion-axial force characteristics of SR-PLLA screws

Abstract: The torsion axial-force characteristics of biodegradable screws are central to their ability to generate interfragmentary compression when used as lag screws. The purpose of this investigation was to compare the torsion-axial force characteristics of prototype self-reinforced poly-L-lactide (SR-PLLA) screws with conventional titanium screws. Axial forces developed by incremental increases in the torque applied to the individual screws were measured in a test apparatus incorporating an Instron machine. For the SR-PLLA screws, the relationship between applied torque and axial force development was non-linear with a marked relaxation throughout the test range. The axial forces reached a maximum with increasing torque, after which failure of the screws occurred. The response curve for titanium screws of the same length demonstrated a steeper slope. No failures or force relaxation were observed with the titanium screws. The results of this investigation suggest that, at this time, the use of SR-PLLA screws for lag screw fixation should be restricted to low stress bearing areas.

Spiral grain—An adaptation of trees to withstand stem breakage caused by wind-induced torsion

Abstract: Expressions are derived for the internal mechanical stress components in trees when exposed to bending and torsion by wind forces. The crown is modeled as rectangular, and the stem taper so that the maximum bending stress is equal at all heights. Trees with asymmetric crowns will undergo torsion as well as bending, and the shear stresses associated with torsion are determined and compared to the bending stresses. The results show that shear failure is likely to occur relatively high up on the stem when the crown asymmetry is a few decimeters. The fact that torsion might be critical to the strength of trees towards wind forces, introduces an explanation to spiral grain growth. It is shown that spiral grain in the direction of the wind-induced torque improves the bending strength of the tree. Spiral grain is therefore beneficial for trees with a prevailing external torque.

Buckling Behavior of Long Symmetrically Laminated Plates Subjected to Shear and Linearly Varying Axial Edge Loads

Abstract: A parametric study of the buckling behavior of infinitely long symmetrically lam-inated anisotropic plates that are subjected to linearly varying edge loads, uniformshear loads, or combinations of these loads is presented The study focuses on theeffects of the shape of linearly varying edge load distribution, plate orthotropy, andplate flexural anisotropy on plate buckling behavior In addition, the study examinesthe interaction of linearly varying edge loads and uniform shear loads with plateflexural anisotropy and orthotropy Results obtained by using a special purpose non-dimensional analysis that is well suited for parametric studies of clamped and simplysupported plates are presented for [+0]s thin graphite-epoxy laminates that are repre-sentative of spacecraft structural components Also, numerous generic buckling-design charts are presented for a wide range of nondimensional parameters that areapplicable to a broad class of laminate constructions These charts show explicitly theeffects of flexural orthotropy and flexural anisotropy on plate buckling behavior forlinearly varying edge loads, uniform shear loads, or combinations of these loads Themost important finding of the present study is that specially orthotropic and flexurallyanisotropic plates that are subjected to an axial edge load distribution that is tensiondominated can support shear loads that are larger in magnitude than the shear buck-ling loadIntroductionBuckling behavior of laminated plates that are sub-jected to combined loads is an important consideration inthe preliminary design of aircraft and launch vehiclesThe sizing of many structural subcomponents of thesevehicles is often determined by stability constraints Onesubcomponent that is of practical importance in struc-tural design is the long rectangular plate These platescommonly appear as subcomponents of stiffened panelsused for wing structures and as semimonocoque shellsegments used for fuselage and launch vehicle structuresBuckling results for infinitely long plates are importantbecause they often provide a useful conservative estimateof the behavior of finite-length rectangular plates, andthey provide information that is useful in explaining thebehavior of these finite-length plates Moreover, knowl-edge of the behavior of infinitely long plates can provideinsight into the buckling behavior of more complexstructures such as stiffened panelsAn important type of long plate that appears as asubcomponent of advanced composite structures is thesymmetrically laminated plate In the present paper, theterm "symmetrically laminated" refers to plates in whichevery lamina above the plate midplane has a correspond-ing lamina located at the same distance below the platemidplane, with the same thickness, material properties,and fiber orientation Symmetrically laminated platesremain flat during the manufacturing process and exhibitflat prebuckling deformation states These characteristicsand the amenability of these plates to structural tailoringprovide symmetrically laminated plates with a significantpotential for reducing structural weight of aircraft andlaunch vehicles Thus, understanding the bucklingbehavior of symmetrically laminated plates is an impor-tant part of the search for ways to exploit plate orthotropyand anisotropy to reduce structural weightIn many practical cases, symmetrically laminatedplates exhibit specially orthotropic behavior However,in some cases, such as [+45] s laminates, these platesexhibit anisotropy in the form of material-induced cou-pling between pure bending and twisting deformationsThis coupling is referred to herein as flexural anisotropy,and it generally yields buckling modes that are skewed inappearance The effects of flexural orthotropy and flex-ural anisotropy on the buckling behavior of long rectan-gular plates that are subjected to single and combinedloading conditions are becoming better understood Forexample, recent in-depth parametric studies that showthe effects of anisotropy on the buckling behavior of longplates that are subjected to compression, shear, pure in-plane bending, and various combinations of these loadshave been presented in references 1 through 5 Theresults presented in these references indicate that theimportance of flexural anisotropy on the buckling resis-tance of long plates varies with the magnitude and typeof the combined loading condition However, none ofthese studies supply results for plates loaded by uniformshear and a general linear distribution of axial load acrossthe plate width Both the uniform axial compression andthe pure in-plane bending loads are special cases of thegeneral linear distribution of axial edge loads Results forthis class of loadings are useful in the design of aircraftspar webs and panels that are located off the neutral axisof a fuselage or launch vehicle that is subjected to overallbending and torsion loads Moreover, the importance ofneglecting flexural anisotropy in a buckling analysis ispractically unknown for this class of loadings

Viscoelastic properties of bamboo

Abstract: Dynamic viscoelastic properties of bamboo were determined in torsion and bending. Damping, measured by tan δ, in dry bamboo was relatively small, about 0.01 in bending and 0.02 to 0.03 in torsion, with little dependence on frequency in the audio range. In wet bamboo, damping was somewhat greater: 0.012–0.015 in bending and 0.03–0.04 in torsion. The anisotropy in damping implies a purely cellular model is insufficient; there is large-scale molecular orientation or at least two distinct solid phases.

Equilibrated hinge with variable frictional torque

Abstract: A hinge that provides equilibration and variable friction for a display screen or a laptop lid (7) In the preferred embodiment, a torsion rod (25) provides a restoring force which increases as the lid is moved either direction from its vertical position A friction hinge, of well know design, uses a spring band (23) about a shaft (21) One end of the torsion rod is coupled to the end of the band of the friction hinge, so that the moment in the torsion rod increases or decreases the moment in the spring band of the hinge, modifying the frictional torque accordingly This allows the frictional torque to be low as the lid is first opened, and larger as the display reaches the useful range of its motion

Stresses developed during clinical debonding of stainless steel orthodontic brackets

Abstract: The purpose of this project was to use finite element modeling to calculate and compare the peak stresses generated during clinical debonding of resin bonded brackets. Five debonding techniques were considered: tension, shear-peel, torsion loads on the bracket, wedging of the cement margin, and bracket temperature increase. The data is presented in terms of the relative potentials of the methods for causing enamel fracture. That is, in this idealized model, it was assumed that enamel failures were governed by maximum principal or shear stress. Therefore, all debonding loads and calculated stresses were scaled to correspond to unit peak principal stress or unit peak shear stress in enamel. Furthermore, it was assumed that cement cohesive failure was also governed by maximum principal or maximum shear stress and that adhesive failures were caused by interface normal or shear stress. Thus, for example, it was found that for 1.0 MPa of peak shear stress in enamel, tension and shear-peel debonding generate, respectively, 1.34 and 0.96 MPa of peak normal (tensile) stress in the cement at the enamel-cement interface. The interpretation of this information is that tension debonding is less likely to cause enamel damage than shear-peel loading if it is assumed that (1) the enamel would fail due to the high shear stress, and (2) the joint would fail at the enamel-cement interface because its normal stress limit has been exceeded.

Beam stiffness matrix based on the elasticity equations

Abstract: A new general beam stiffness matrix which accounts for bending, torsion and shear deformation is derived from an elasticity solution of the beam. The influence of shear and torsion is considered using a 3×3 matrix of deformation coefficients. Numerical examples are presented to demonstrate the behaviour of the deformation coefficients and of the beam stiffness matrix. © 1997 by John Wiley & Sons, Ltd.

The use of digital image processing in monitoring shear band development

Abstract: A new technique involving sample preparation, video imaging, and image analysis has been developed to observe the kinematics of shear bands when geomaterials are subjected to a general state of combined stress. The technique provides an effective, low-cost, and non-invasive way to monitor the development and measure the deformations inside and outside the shear bands. Its capabilities are demonstrated through a series of drained tests in which thin hollow cylinders of sand are subjected to combinations of hydrostatic, axial, and torsional stresses. It is shown that the deformation within the shear band is different from the global one and the one in its vicinity. For sand specimens with the same configuration, density, and confining pressure, the initiation, orientation, and thickness of shear bands depend on the loading path.

Assembly for taking up and compensating for torque-induced shocks

Abstract: A torsion damping assembly which is installed between the crankshaft of the engine and the input element of the change-speed transmission in a motor vehicle has two coaxial flywheels one of which is driven by the crankshaft and the other of which can transmit torque to the transmission in response to engagement of a friction clutch. The transmission of torque between the two flywheels takes place by way of a damper and a slip clutch which latter is effective only within a selected range of possible angular movements of the two flywheels relative to each other.

Propagating Torsion from First Principles

Abstract: A propagating torsion model is derived from the requirement of compatibility between minimal action principle and minimal coupling procedure in Riemann-Cartan spacetimes. In the proposed model, the trace of the torsion tensor is derived from a scalar potential that determines the volume element of the spacetime. The equations of the model are written down for the vacuum and for various types of matter fields. Some of their properties are discussed. In particular, we show that gauge fields can interact minimally with the torsion without the breaking of gauge symmetry.