Axial Twist Research Articles

Load-Elongation Characteristics of Ti-Ni Shape Memory Alloy Coil Spring.

The strain and stress behavior in a coil spring of a Ti-Ni SMA were investigated over a wide range of elongation, for the case of zero axial twist because of the simple calculation of shear and normal strain with the geometrical condition only. The basic σ-e and τ-γ relations of the SMA material were obtained from the results of a tensile test and torsional test carried out under several constant temperatures, using a φ1 wire specimen. The strain criteria for start and finish of transformation under the combined strain were expressed by a strain circle and a modified strain circle, respectively, in each temperature. The simulation for load-elongation behavior of the SMA coil spring based on the basic stress-strain curves and the strain criteria under the combined strain showed a good correlation with experimental results.

Identification of dynamic myoelectric signal-to-force models during isometric lumbar muscle contractions

A 14-muscle myoelectric signal (MES)-driven muscle force prediction model of the L3-L4 cross section is developed which includes a dynamic MES-force relationship and allows for cocontraction. Model parameters are estimated from MES and moments data recorded during rapid exertions in trunk flexion, extension, lateral bending and axial twist. Nine young healthy males participated in the experimental testing. The model used in the parameter estimation is of the output error type. Consistent and physically feasible parameter estimates were obtained by normalizing the RMS MES to maximum exertion levels and using nonlinear constrained optimization to minimize a cost function consisting of the trace of the output error covariance matrix. Model performance was evaluated by comparing measured and MES-predicted moments over a series of slow and rapid exertions. Moment prediction errors were on the order of 25, 30 and 40% during attempted trunk flexion-extensions, lateral bends and axial twists, respectively. The model and parameter estimation methods developed provide a means to estimate lumbar muscle and spine loads, as well as to empirically investigate the use and effects of cocontraction during physical task performances.

Interlaminar stress analysis of composite laminates using a sublaminate/layer model

A stress-function-based variational method developed in a previous work is extended and modified into a sublaminate/layer approach applicable to a laminated strip composed of a large number of differently orientated, anisotropic elastic plies. Lekhnitskii’s stress functions are used for two interior layers adjacent to a particular interface. The remaining layers are grouped into an upper sublaminate and a lower sublaminate. The stress functions are expanded in truncated power series of the thickness coordinate and the differential equations governing the coefficient functions are derived by using the complementary virtual work principle. The new approach limits the dimension of the eigenvalue problem to a fixed number irrespective of the number of layers in the sublaminates, so that reasonably accurate solutions of the interlaminar stresses can be computed with extreme ease. For symmetric, four-layer, angle-ply and cross-ply laminates, a comparison of the previous analysis results based on the pure layer model and new results based on two different sublaminate/layer models indicates reasonable overall agreement in the interlaminar stresses and superior agreement in the resultant peeling and shearing forces across end segments of the interface. Additional results are obtained for eight-layer, quasi-isotropic laminates under the strain loads of axial extension, bending and twisting.

A Fractional-Factorial Numerical Technique for Stress Analysis of Glass-To-Metal Lead Seals

Fracture of glass seals in metallic hermetic electronic packaging is a significant failure mode because it may lead to moisture ingress and also to loss of load carrying capacity of the glass seal. Seal glasses are intrinsically brittle and their fracture is governed by the stresses generated. This study investigates stresses in lead seals caused by handling, testing, mechanical vibration, and thermal excursions. Loads considered are axial tension, bending, and twisting of the lead. More general loading can be handled by superposition of these results. Factorial techniques, commonly used in multi-variable Design of Experiments (DoE), are used in conjunction with finite element parametric simulations, to formulate closed-form regression models which relate the maximum principal stress within the glass seal to the type of loading and geometry. The accuracy of the proposed closed-form equations are verified through analysis of residuals. The analysis reveals the sensitivity of the magnitude of the seal stress to design variables such as the materials and geometry of the seal, lead, and package. Manufacturing-induced problems such as defects and flaws are not considered. An additional purpose for presenting this study is to illustrate the use of design of experiment methods for developing closed-form models and design guidelines from simulation studies, in a multi-variable problem.

Large strain torsion of axially-constrained solid rubber bars

Large strain fixed-end torsion of circular solid rubber bars is studied semi-analytically. The analyses are based on various non-Gaussian network models for rubber elasticity, some of which were proposed very recently. Results are presented in terms of predicted torque vs. twist curves and axial force vs. twist curves. In some cases, the predicted stress distributions are also given. The sensitivity of the second-order axial force to the employed models is considered. The predicted results are compared with experimental results found in the literature.

A Male Incumbent Worker Industrial Database

Study Design A group of 160 incumbent male railroad workers volunteered for a study of lumbar spine physical capacity. Methods They were initially subjected to inclinometric measurements of sagittal and coronal regional mobility (T-12-S1). They also were tested on isokinetic trunk strength measurement devices for sagittal (bending) and axial (twisting) trunk strength at multiple speeds. Results Results showed that they demonstrated mild deficits of lumbar sagittal extension mobility, trunk extensor strength, and sagittal/axial high speed (150–180°/sec) trunk strength when compared with population averages from a previously derived normative database of a nonhomogeneous male population (matched for age and body weight). Conclusions It was hypothesized that instructions about “correct lifting techniques,” uniformly provided to these workers, may have resulted in an unintended decrement in trunk mobility and strength, flexiion/extension, inclinometers, worker selection, pre-placement screening, postinjury job return.

On large-strain inelastic torsion of glassy polymers

Large-strain elastic-viscoplastic torsion of circular tubes and solid bars of glassy polymers is investigated under fixed-end as well as free-end conditions. The analysis employs a large inelastic deformation model for glassy polymers that incorporates a recently proposed constitutive law for the so-called orientational hardening, which is identified to play a key role in the description of the deformation-induced anisotropy in glassy polymers. The solution of the problem is obtained numerically by means of simple, special purpose finite elements. Results are presented in terms of predicted torque vs twist curves for all cases. Furthermore, we present axial force vs twist curves for fixed-end torsion or elongation vs twist curves for free-end torsion, both phenomena being associated with anisotropic hardening. In some cases, the predicted stress distributions are also given. The differences between free-end and fixed-end torsion are emphasized. Numerical results predicted by the model are compared with experimental results for polycarbonate found in the literature.

Trunk muscle activity during axial twisting motions

Trunk muscle activity during axial twisting motions

The crash response of circular tubes under general applied loading

The FEM is employed to investigate the torsional plastic collapse of a thin cylindrical shell under the action of static and dynamic axial loads. For the static case we consider the application of compressive loads and/or torques. Three cases are considered: 1. (a) a compressive axial load 2. (b) a torque, and 3. (c) a combination of both compressive load and torque. In the dynamic case we investigate the effects of applying a torque only and compare this with the static case. The comparison shows that for a controlled static loading, the torque and the axial load reach a peak value and then diminish steadily, asymptotically approaching a bottom-out value. For dynamic loading, the load carrying capacity increases several fold and the energy absorption capability, due to both the inertia and the material strain rate dependence, also increases many fold. However, in the current investigation the post-plastic collapse state appears to be of an unstable nature. The initiation of the plastic collapse mode, in both the static and dynamic cases, follows a change in cross-section from its original circular form. Under the static axial twist there is a process of curvilinear equilateral triangularization. For dynamic loading a similar continuous change occurs to a shape with a curved outline and rounded apices but the symmetry is now fourfold. As deformation progresses, a spiral folding occurs within the central part of the cylinder (which maintains the three or fourfold symmetry) and this continues to become increasingly pronounced until contact is made between adjacent folds. At this stage the analysis is discontinued because in the present model there is no contact awareness built into either the model or the solution procedure.

The influence of lordosis on axial trunk torque and trunk muscle myoelectric activity.

Force contributions from the facet complex and posterior ligaments during the generation of axial torque are a function of lordosis, and it has been speculated that these forces together with muscular contributions play a role in axial trunk twisting. This study investigated the electromyographic activity of the trunk musculature and torque-generating capacity of the lumbar spine under the conditions of normal lordosis, hyperlordosis, and hypolordosis. Eleven male subjects volunteered for this study. The subjects performed isometric twisting efforts and maximum dynamic twisting efforts at 30 degrees/sec. The myoelectric activity levels (normalized to maximal amplitude obtained from nontwist activities) were quite low despite maximal efforts to generate axial torque (for example: approximately 60% maximum voluntary contraction for latissimus dorsi and even lower for the abdominals). Furthermore, changes in lordosis did not produce any consistent changes in muscle activity, although a hyperlordotic spine produced significantly smaller axial torques, and a hypolordotic spine smaller still. Larger torques were measured during all three conditions of lordosis, as the subjects rotated toward an untwisted position, and lower torques as the subjects rotated away. The opposite trend was observed, however, in myoelectric activity of the agonistic side of latissimus dorsi, the thoracic level of erector spine, and the lumbar level of erector spinae, i.e., larger amplitudes were observed as the trunk was twisted away from the untwisted position. These data suggest that tissues other than muscle (i.e., passive tissue) contribute significantly to axial torque production and that the flexed and twisted spine is less able to resist applied axial torques, possibly increasing the risk of torsional injury.

Kinetic Potential of the Lumbar Trunk Musculature About Three Orthogonal Orthopaedic Axes in Extreme Postures

Many studies have examined the mechanics of the lumbar spine in various planes, but only a limited number of three-dimensional investigations have been reported. Analysis of the low back during complex, dynamic postures demands rigorous representation of the trunk musculature. The data of this study demonstrated the force and torque contributions of approximately 50 laminas of various trunk muscles to flexion-extension, lateral bending, and axial twisting torque at the L4-L5 joint. This analysis was conducted with the spine in an upright standing posture and when fully flexed (60 degrees), laterally bent (25 degrees), and axially twisted (10 degrees) together with two examples of combined postures. Maximum moment potential, muscle length excursions, and the resultant compressive, anteroposterior shear, and lateral shear forces on the joint were also computed. The results indicate that the position of the vertebrae and their orthopaedic axes, which are a function of spinal posture, are an important factor in the reasonable determination of joint compressive, lateral shear, and anteroposterior shear loads. Muscle length changes that exceeded 20% of their respective length during upright standing were not observed during a full axial twist, but were observed in portions of the abdominal obliques during lateral bending, and in some extensors during full flexion. Extreme postures tended to change the torque potential of some muscles and influence joint load. Various portions of erector spinae were observed to have appreciable potential to generate torque about all three orthopaedic axes. This observation supports the notion held by some therapists that conditioning of the erector spinae is of utmost importance.

Electromyographic activity of the abdominal and low back musculature during the generation of isometric and dynamic axial trunk torque: Implications for lumbar mechanics

This study focused on the electromyographic activity of the trunk musculature, given the well-documented link between occupational twisting and the increased incidence of low back pain. Ten men and 15 women volunteered for this study, in which several aspects of muscle activity were examined. The first aspect assessed the myoelectric relationships during isometric exertions. There was great variability in this relationship between muscles and between subjects. Further, the myoelectric activity levels (normalized to maximal electrical activity) obtained from nontwist activities were not maximal despite maximal efforts to generate axial torque (e.g., rectus abdominis, maximum voluntary contraction; 22% external oblique, 52%; internal oblique, 55%; latissimus dorsi, 74%; upper erector spinae [T9], 61%; lower erector spinae [L3], 33%). In the second aspect of the study, muscle activity was examined during dynamic axial twist trials conducted at a velocity of 30 and 60 degrees/s. The latissimus dorsi and external oblique appeared to be strongly involved in the generation of axial torque throughout the twist range and activity in the upper erector spinae displayed a strong link with axial torque and direction of twist, even though they have no mechanical potential to contribute axial torque, suggesting a stabilization role. The third aspect of the study was comprised of the formulation of a model consisting of a three-dimensional pelvis, rib cage, and lumbar vertebrae and driven from kinematic measures of axial twist and muscle electromyograms. The relatively low levels of normalized myoelectric activity during maximal twisting efforts coupled with large levels of agonist-antagonist cocontraction caused the model to severely underpredict measured torques (e.g., 14 Nm predicted for 91 Nm measured). Such dominant coactivity suggests that stabilization of the joints during twisting is far more important to the lumbar spine than production of large levels of axial torque.

Analysis of elastic-plastic torsion of circular bars at large strains

Large elastic-plastic torsion of uniform circular bars is investigated numerically, using special finite elements. Two end conditions corresponding to fixed-end torsion and free-end torsion, resp., are considered, taking full account of the axial effects. The analysis is carried out using an isotropic hardening as well as a recently proposed large deformation kinematic hardening model. Either linear hardening or power law hardening uniaxial stress-strain curves are assumed in the analysis. Results are presented in terms of predicted torque vs. twist curves for all cases. Furthermore, we present axial force vs. twist curves for fixed-end torsion or elongation vs. twist curves for free-end torsion. Special attention is paid to the so-called plastic spin, a concept which has recently been identified to play a key role in the description of induced anisotropy. The differences between free-end and fixed-end torsion are emphasized.

Measured and modelled static and dynamic axial trunk torsion during twisting in males and females

Study of the mechanics of trunk twisting is special interest given epidemiological evidence linking occupational twisting to increased incidence of low back pain. An anatomically detailed, three-dimensional model of the trunk (rib cage, pelvis, five lumbar vertebrae and 50 muscles), was used to predict maximum axial trunk torque. Predicted axial torques were compared with measured torques. Thirty-one (10 male and 21 female) subjects performed maximum effort isometric twisting exertions, at 0° of twist and ±30° of twist together with dynamic exertions, at 30° s −1 and 60° s −1. Females were able to generate approximately two-thirds of the torque of males (males, 97 Nm; females 60 Nm, isometric at 0°). When the trunk was prerotated to 30°, subjects were able to generate greater torque when the effort was toward the 0° position (approximately 105 Nm by males and 68 Nm by females). Experimental data indicated that velocity of rotation and amount of twist are important modulators of axial torque. Changes in muscle length were demonstrated to be minimal from model output as most muscle length changes during a twist from 0° to 30°, measured between the pelvis and the shoulder harness, were less than 1%, although some portions of the abdominal obliques underwent a length excursion of 5%. The small changes in the individual muscle force components that contribute to twist, i.e. the muscle unit vector about the axial twist axis and its moment arm that change as a function of twisted position, do not entirely account for the measured differences in torque, suggesting that additional mechanisms influence axial torque generation.

Thin-walled composite beams under bending, torsional, and extensional loads

Symmetric and antisymmetric layup graphite-epoxy composite beams with thin-walled rectangular cross sections are fabricated using an autoclave molding technique and tested under bending, torsional, and extensional loads. The bending slope and elastic twist at a station are measured using an optical system, and the results correlated with predicted values from a simple beam analysis as well as a refined finite element analysis. A symmetric ply layup results in bending-twist coupling whereas an antisymmetric layup causes extension-twist coupling. Simple analytical results with plane-stress assumption agree better with measured data as well as finite element predictions than with plane-strain assumption. For symmetric layup beams, the bending-induced twist and torsion-induced bending slope are predicted satisfactorily using simple analytical solution. Correlations with measured data, however, are generally improved using a finite element solution. For antisymmetric beams, axial force-induced twist is predicted satisfactorily by both methods.

Resolution of resultant displacement into components in double exposure speckle photography

An equation to resolve the resultant displacement, recorded using double exposure laser speckle photography, at the surface of a cylinder suffering radial expansion, axial twist, and transverse displacement, into these three components is presented.

Torsion in the asteroid ray.

Although torsion (axial twisting) is rare in living structures, some starfish routinely use ray torsion in the righting process. This study examined the torsional properties of the ray and dorsal body wall of Echinaster spinulosus (Echinodermata: Asteroida: Spinulosidae). The body wall of the ray is composed of a reticular skeleton composed of CaCO3 ossicles sandwiched between collagenous layers in which the fibers are orthogonally oriented. G, the shear modulus of the dorsal body wall, determined from a torsion pendulum, was 95.3 MPa, and damping was extremely pronounced (Δ = 1.36). The torque-rotation curve was J-shaped, and G determined from this data was 176 MPa. Torsional stress relaxation was rapid, with the relaxation spectrum skewed to the left and τmax = 2.3 for anaesthetized tissue and 2.7 for unanaesthetized tissue. Analysis of ray geometry showed that the ambulacral groove reduced torsional stiffness by about two orders of magnitude compared to an ungrooved ray. Ray taper reduced the stiffness of the tip relative to the root. The shear stress distribution determined for the ray cross-section showed stress concentrations around the ambulacral arch, the outer body wall surface, and the inner body wall surface. The ossicles are situated to minimize torsional stiffness of the ray.

Thoracic Spinal Hyperostosis in an Early Mediaeval Skeleton

(1990). Thoracic Spinal Hyperostosis in an Early Mediaeval Skeleton. Scandinavian Journal of Rheumatology: Vol. 19, No. 2, pp. 163-166.

Twist-induced tuning in tapered fiber couplers

The power-splitting ratio of fused tapered single-mode fiber couplers can be reversibly tuned by axial twisting without affecting loss. The twist-tuning behavior of a range of different tapered couplers is described. A simple expression for twist-tuning can be derived by representing the effects of twist by a change in the refractive index profile. Good agreement between this expression and experimental results is demonstrated. Repeated tuning over tens of thousands of cycles is found not to degrade coupler performance, and a number of practical applications, including a freely tunable tapered coupler, are described.

Torsional strength and trunk muscle activity during axial twisting

Torsional strength and trunk muscle activity during axial twisting