Compression Angle Research Articles

Correlation of MR images of disc injuries with anatomic sections in experimental thoracolumbar spine fractures.

This cadaver study evaluated the value of MR images for detection of acute intervertebral disc damage associated with fractures of the thoracolumbar spine. Damage to the intervertebral disc may be a major contributor to chronic instability in non-operative treatment or failure of fixation and recurrence of deformity in posterior fixation methods. MR imaging can help us to understand the injury patterns and their prognostic significance. However, before we can justify the use of MRI in clinical cases, determination of MRI's ability to detect acute injury to the disc is necessary. Ten fresh cadaver specimens were used for this study. After obtaining radiograms and MR images, injuries were created with a weight-dropping apparatus using a variety of weights and compression angles. Post-injury radiograms and MR images were taken and the specimens were frozen at -20 degrees C. Slides of these specimens obtained with cryosection techniques were compared with MR images for evaluation of the damage to different parts of the discs. A total of 20 fractures were observed on cryosections. In 12 of the discs adjacent to fractured vertebral bodies, macroscopic damage was seen on the sections. These were all detected on the corresponding MR images. The study showed that MRI is able to detect acute, macroscopic injury to the intervertebral disc. It is therefore justified to use MR for the study of acute disc damage associated with thoracolumbar fractures.

Tone enhancer attachment for string-musical instruments

An attachment shown in FIG. 1 for string-musical instruments to improve the tone color by tightly clamping a string segment E (91), a string segment A (92), a string segment D (93), and a string segment G (94) between a bridge (60) and a tailpiece (70) with an acoustical material (20) being compressed by a frame (10) and an arm (50). The position, angle of attachment, compression and shape are varied to customize the tone color, without loss of fundamental tone volume. The attachment can be removed by moving a catch and release (40). This returns the instrument to its original state. The tightly clamping of all string segments (91), (92), (93),and (94) together allows common motion of all string segments between bridge (60) and tailpiece (70), but independent vibrations of any one string segment is stopped to higher frequency and is damped by acoustical material (20). The enhanced tone effects increased ease of playing, sonority, dynamic range, and projection.

Recurrent kyphosis after posterior stabilization of thoracolumbar fractures. 24 cases treated with a Dick internal fixator followed for 1.5-4 years.

24 patients with Th12-L1 fractures treated with a Dick internal fixator were analyzed to assess predictors of poor outcome. 4 patients had fixation without bone transplantation, 20 patients had a posterior fusion, and 12 of them had additional transpedicular spongioplasty. There were fractures of the transpedicular screws in 4 and screw migration in 2 cases. The increase in the local kyphosis angle was greater than the increase in the anterior compression angle and this did not correlate with spongioplasty or fusion. Fixation failure was in all cases related to a disproportionate increase in the local kyphosis angle. There was no difference between the patients with transpedicular spongioplasty and posterior fusion and the other patients with respect to results and complications. Bony collapse was not the major cause of failure and consequently there was no measureable contribution of transpedicular spongioplasty. We found that the Dick internal fixator for unstable fractures was associated with a higher complication rate than earlier reported.

Numerical study of the performance of swept, curved compression surface scramjet inlets

A computational performance enhancement study was performed employing systematic modifications to a planarsidewall compression scramjet inlet operating at an entrance Mach number of 4 and at a dynamic pressure of 2040 psf. The variations included modifying the planar-side wall compression angle as a function of height, utilizing sidewall curvature, and employing, simultaneously, both forward-swept and reverse-swept compression surfaces. Turbulent flowfield solutions were generated by solving the Reynolds-averaged Navier-Stokes equations to obtain inlet performance parameters such as total-pressure recovery, mass capture, and flowfield pressure distortion (the ratio of maximum static pressure to minimum static pressure generated at the inlet exit plane). Additionally, an inviscid parametric study was performed by employing solutions to the Euler equations to optimize a cubic polynomial that defined the longitudinal sidewall geometry. A final viscous flowfield solution of the optimized inviscid inlet geometry yielded inlet performance improvements; however, inlet top-wall surface boundary-layer shock wave separation interactions persisted. Hence, this numerical study demonstrated that enhanced performance is obtainable via curved-wall geometric modifications to the standard planar-sidewall inlet design, although future work should employ constraints to mitigate detrimental flow separation effects.

Results of the AO spinal internal fixator in the surgical treatment of thoracolumbar burst fractures.

The potential for clinical instability following thoracolumbar fractures has evoked a progressive increase in interest in the surgical treatment of unstable thoracolumbar fractures. From September 1988 to October 1991, 44 thoracolumbar burst fractures were treated surgically by the AO Spinal Internal Fixator at the Orthopaedics and Traumatology Clinics of Ankara Social Security Hospital. Mean follow-up period was 28.8 (range 12-48) months. Fourteen (31.8%) of the patients were female, and 30 (68.2%) were male. Postoperatively, the mean anterior vertebral height loss and spinal canal compromise were corrected by 36.5% and 39.9%, respectively. Also, postoperatively 15.9% of improvement was obtained in the mean kyphosis angle. The mean compression angle, which was 19.5 degrees preoperatively, was corrected by 12.3 degrees and came to an average of 7.1 degrees postoperatively. In light of these data, it is suggested that the AO Spinal Internal Fixator effectively restores three-dimensional alignment of the spine and provides a rigid fixation.

Surface strain on the dorsal metacarpus of thoroughbreds at different speeds and gaits.

Stacked rectangular rosette strain gages were used to measure surface bone strain on the dorsomedial cortex of the third metacarpal bones in 6 adult Thoroughbred horses during treadmill exercise. The peak principal compressive and tensile strains, angle of the peak strains and strain rate during loading were calculated and compared with speed and gait. At speeds from 4 to 14 m/s loading on the metacarpus resulted in compression of the dorsomedial cortex. Tension only occurred consistently in 1 forelimb of 1 horse at the walk (2 m/s). The angle of peak compression was within 10 degrees of the longitudinal axis of the bone, and the magnitude of compression was proportional to the speed of exercise. Mean maximum compressive strains in the 6 horses at 2 m/s were -668 mu strain, -1,204 mu strain at 4 m/s; -1,617 mu strain at 6 m/s; -2,127 mu strain at 8 m/s, and -2,533 mu strain at 10 m/s. Recordings from 3 horses gave a mean -3,206 mu strain at 12 m/s, and strains at 14 m/s approached -4,000 mu strain. Peak strains were similar in both forelimbs at the canter while strain rate tended to be higher in the leading forelimb.

Structure of supersonic turbulent flow past a swept compression corner

The structure of the shock wave/turbulent boundary-layer interaction generated by a 3D swept compression corner has been investigated through a combined experimental and theoretical research program. The flowfield geometry is defined by the streamwise compression angle alpha and the sweep angle lambda of the corner. The present study examines two different configurations, namely (alpha, lambda) = (24 deg, 40 deg) and (24 deg, 60 deg) at Mach 3 and Re sigma infinity about 9 x 10 exp 5. The theoretical model is the 3D Reynolds-averaged compressible Navier-Stokes equations with turbulence incorporated using a turbulent eddy viscosity. The calculated flowfields display general agreement with experimental data for surface pressure and good agreement with experimental flowfield profiles of pitot pressure and yaw angle. The principal feature of the flowfield is a large vortical structure approximately aligned with the corner. The entrainment of incoming fluid into the vortical structure is strongly affected by the sweep angle lambda. Viscous (turbulent and molecular) effects appear to be important only in the immediate vicinity of the surface and in an isolated region within the interaction and near the corner.

Experimental determination of interfacial toughness curves using Brazil-nut-sandwiches

A Brazil-nut-sandwich with a crack on a substrate/interlayer interface is developed for fracture testing. The fracture loading phase is controlled by the angle of diametral compression. Interfacial fracture mechanics is summarized and adopted in reporting data. Experiments are conducted with aluminum, brass, steel and plexiglass as substrates and epoxy as interlayer. Interfacial toughness curves are measured for large range of loading phase. Effects of the roughness of the surfaces prior to bonding on the interfacial toughness are demonstrated. Failure patterns for the adhesive structure under different loading modes are observed with a scanning electron microscope. For the metal/epoxy systems, when the remote loading is predominantly mode I, cracks tend to kink out of interfaces and run within the epoxy layer, although the bulk epoxy fracture energy is much higher than the interfacial toughness. At large loading phases, abnormally high apparent toughness is measured. These observations are discussed in the light of crack path selection criteria in adhesive joints and large scale contact zone of crack faces.

Influence of flexural residual stresses on the stability of compressed angles

Abstract Structural steel elements that are obtained by cold forming become more and more popular in steel construction. Indeed they are lighter in weight and thus provide appreciable savings compared with the usual hot rolled sections. Because they are obtained by cold forming, two kinds of residual stresses occur: membranar and flexural stresses. The flexural residual stresses are usually larger than the membranar ones. However the ECCS (European Convention for Constructional Steelwork) column buckling curves were established on the basis of longitudinal membranar residual stresses only, in addition to geometrical imperfections. Using a non-linear computer program, the authors investigate the influence of longitudinal flexural residual stresses on the carrying capacity of cold formed angles. This kind of section is now widely used for erecting large transmission towers. Strain hardening due to cold forming is taken into account in the present study. From the numerical results obtained, conclusions are drawn on the suitability of European column buckling curves for cold formed angles.

Borehole tensor strain measurements in California

Two continuous borehole plane strain monitoring sites have been operational in California since late 1983, using borehole tensor strain monitors implanted at a depth of 150 m. Shear strain data at subtidal sensitivies were available immediately after installation without contamination by bond curing or thermal recovery signals. At Pinon Flat Observatory, data indicate a constant shear strain accumulation of 0.6 microstrain per annum with the axis of maximum compression oriented 50° ± 5° west of north. This result differs significantly from regional geodetic estimates, the amplitude being dominated by continued viscoelastic response of the hole. Variations of measured strain rate exceeding 100 nstrain/yr would be significant at this instrument site. At San Juan Bautista, measurements of the angle of maximum compression (10° ± 3° west of north) agree closely with previous geodetic and hydrofracture estimates. After 2 years of operation the residual shear strain rate is 1 μstrain/yr. Preliminary analysis of strain steps observed at San Juan Bautista during the Morgan Hill earthquake of April 24, 1984, show good agreement with calculations from seismically determined source parameters for this event.

Experimental and computational study of a swept compression corner interaction flowfield

The results of an experimental and computational study of the three-dimensional shock-wave/turbulent boundary-layer interaction generated by a swept compression corner are presented. This corner had a streamwise compression angle of 24 deg and a sweepback angle of 40 deg. Two equilibrium incoming turbulent boundary layers with thicknesses varying by 3:1 were used. In both cases the freestream Mach number was 2.95, the freestream Reynolds number was 63xl0/m, and the wall temperature was close to adiabatic. This study was undertaken to test the applicability to flowfield features of a Reynolds number similarity law originally based on surface features only. A second goal of the study was to test the ability of a state-of-the-art numerical solution of the Navier-Stokes equations to predict the subject flow. The experimental results, composed primarily of flowfield pitot pressure and yaw angle surveys, confirmed the general applicability of the similarity law. The comparison of experiment and computation revealed that the latter captured may of the qualitative features of the flow. Further, only very limited reasons were found to prefer a two-equation eddy-viscosity turbulence model rather than an algebraic model for predictions of this flow.

Shock absorbing properties of toroidal shells under compression. 3rd report The effects of compression angle and strain rate.

The author has previously presented the static load-deflection relations of a toroidal shell subjected to axisymmetric compression between rigid plates and those of its outer half when subjected to lateral compression. In both these cases, the analytical method was based on the incremental Rayleigh-Ritz method. In this paper, the effects of compression angle and strain rate on the load-deflection relations of the toroidal shell are investigated for its use as a shock absorber for the radioactive material shipping cask which must keep its structural integrity even after accidental falls at any angle. Static compression tests have been carried out at four angles of compression, 10°, 20°, 50°, 90° and the applications of the preceding analytical method have been discussed. Dynamic compression tests have also been performed using the free-falling drop hammer. The results are compared with those in the static compression tests.

Correlation Technique for Predicting Attached Turbulent Boundary-Layer/FIap Interaction Pressures

THE method of Lees-Reeves-K lineberg has been successful for r nidly predicting a large class of interacting laminar flows. Hunter and Reeves * extended the laminar work and presented a method for calculating the two-dimensional flow separation and reattachment of a turbulent boundary layer caused by a compression corner. In this work, which is a summary of Ref. 2, a further extension is made to supersonic turbulent flows over adiabatic two-dimensional compression corners where the turning angle is such that the flow remains attached. The importance of the problem coupled with the success of the moment method for similar flows strongly suggests its development for applications where rapid calculations are essential. Contents The flow of a two-dimensional supersonic turbulent boundary layer over an adiabatic compression corner is studied. The range of compression angles is restricted to those for which the flow remains attached to the surface. The moment method is used to determine the solution with the pressure distribution as the primary quantity of interest. The equations governing the solution for this problem have been set forth by previous authors1'3 and are used in a similar form. Since the method is an integral one, a family of profiles is needed to complete the formulation. Reference 3 used a combination of experimental values, existing analytical solutions, and a power law profile in the limit 6/d*-*l to obtain the necessary family. These profile results are also used here. The outer edge boundary condition coupling the viscous and inviscid flow regions can be either a Prandtl-Meyer or tangent wedge relation. Because of the fullness of the turbulent profiles and the existence of shock waves deep within the layer, the tangent wedge relation was found more useful and was used in obtaining Figs. 1-3. The angles considered in this study are relatively small. Therefore, the flow, which starts out supercritical, remains so, and a fully supercritical interaction results. A typical calculation of such a case is shown in Fig. 1 along with the data of Roshko and Thomke.4 This is for an M=5, /^ =0.38 x 106, a = 13 deg compression. The agreement is very poor.

Bearing Capacities by Plasticity Theory

The two basic equations of plastic equilibrium in a soil mass are solved by a numerical scheme proposed by Sokolovski, for the case of bearing capacity failure of a strip footing under plane strain conditions. A new scaling technique, first proposed by Sokolovski and amplified in detail in this paper, shows that the bearing capacities of strip footings can be conveniently calculated without using the conventional Terzaghi bearing capacity factors, N c , N γ , N q . The Terzaghi equation for bearing capacities is shown to be non-conservative when the proper strain angle of internal friction is used. Previous conclusions that experimental results showed the Terzaghi prediction values to be conservative are misleading because a triaxial compression angle of internal friction was used in a plane strain formula.

Investigating the main angles and force factors of rolling

1. With constant rolling conditions the thickness and density of the strip are directly dependent on the bulk weight of the powder and independent of the method of preparing it. The shape of the particles and the plasticity of the metal are the main factors determining the elasticity of the raw strip. With the same particle size, an increase in the bulk weight of the powder increases the thickness and density of the ribbon, but impairs its elasticity. 2. The magnitude of the basic rolling angles depends on the properties of the powder and the density of the rolling. The angle of compactionα increases with increase in density of the strip and the hardness of the powder material. The angle of elastic compression of the rollersαc increases with rise in the density of the strip. This is correct for all powders and is explained by the deformation of the rollers from the action of full pressure of the powder being rolled. The neutral angle γ in the range of densities studied for the ribbon (up to γ°L = 0.8) diminishes with increase in the rolling density. 3. The force parameters of rolling, that is, the maximum specific pressure, the full pressure on the roller and the turning moment, depend on the density of the strip and the properties of the powder. The magnitude of the maximum specific pressure determining the density of the rolling increases with rise in hardness of the material being rolled and the dispersion of the particles.

Elastic compkession of rolls during the rolling of metal powders

An analysis is carried out of the elastic compression of rolls during the rolling of metal powders, and a description is given of methods of its determination. The relationship between the angle of elastic roll compression and maximum pressure has been established for copper, iron, and nickel powders.