Circumferential Deformation Research Articles

Compliance of a Biocomposite Vascular Tissue in Longitudinal and Circumferential Directions as a Basis for Creating Artificial Substitutes

Experimental studies on the mechanical behavior of 11 human common carotid arteries at different values of internal pressure and axial force were performed on a device allowing us to measure the internal pressure, axial force, and circumferential and longitudinal deformations of the vessel. The persons age ranged from 20 to 28 years. Two types of experiments were carried out. In the first series, cylindrical samples were gradually loaded by an internal pressure from 0 to 200 mmHg at different longitudinal stretch ratios. The second series included axial extension of the same samples at different circumferential stretch ratios. The undulation level of elastin membranes in longitudinal and circumferential directions for samples fixated at different values of internal pressure and longitudinal stretch ratio were determined from histological data.

Dynamic Characteristics of Swing Pad Journal Bearings.

Swing pad journal bearings consist of several segmented pads supported by curved laminates of rubber and metal. The pads swing and tilt because of the radial and circumferential deformation of rubber layer due to the hydrodynamic pressure in the oil film and also the frictional force. The swing pad journal bearing to study is assumed to have a single layer rubber. This simple design, different from the conventional one, leads to the reduction of production cost. The dynamic performance of multi-pad swing pad journal bearing, such as the stiffness and the damping of the oil film, the oil whip stability and the unbalance response characteristics have been studied. Compared to a 4 lobed bearing of the same size under the same operating conditions, the multi-pad swing pad journal bearing is found to have lower cross-coupling stiffness terms, leading to higher oil whip stability.

Exact solutions of a piezoelectric circular tube or bar under extension, torsion, pressuring, shearing, uniform electric loading and temperature change

An exact electroelastic analysis of generalized plane strain and torsion of a piezoelectric circular tube or bar is presented. The problem is formulated in the state–space framework and exact solutions are derived for the tube or bar subjected to extension, torsion, pressuring, shearing, uniform electric loading and temperature change. Electromechanical coupling is shown to have significant effects on the internal field. Axial extension, radial and circumferential deformations, twisting and warping of the cross–section occur concurrently even when the tube or bar is subjected to simple loading conditions.

Circumferential stretching of saphenous vein smooth muscle enhances vasoconstrictor responses by Rho kinase-dependent pathways.

Surgical preparation and/or pulsatile arterial perfusion of saphenous vein increases the sensitivity of vein rings to calcium mobilising agonists such as phenylephrine. We have investigated the mechanism(s) underlying this effect. We have used an ex vivo flow circuit, with simulated arterial or venous flows (mean pressure 100 and 20 mmHg, respectively), to investigate the sensitivity of human saphenous vein to phenylephrine, 5-hydroxytryptamine (5-HT) and KCl, using organ chamber pharmacology. After 90 min of pulsatile arterial perfusion the mean maximum tension induced by KCl had increased from 4.7 to 11.1 g (n=5), by phenylephrine had increased from 4.4 to 10.2 g (n=8) and by 5-HT had increased from 4.4 to 6.7 g (n=10), all P<0.01. Phenylephrine did not augment the tension in vein rings maximally precontracted with KCl (n=4). The EC(50) for KCl was unchanged after pulsatile arterial perfusion (n=5), but for phenylephrine and 5-HT there were significant reductions from 14+/-5 to 2+/-1 microM (n=8) and from 1.0+/-0.4 to 0.20+/-0.06 microM (n=10), respectively. The rate of contraction (in response to 3 microM phenylephrine) increased from 0.11 g/min to 0.37 g/min, P<0.02, after arterial perfusion (n=4). These changes in contractile properties (to phenylephrine) were endothelium-independent, evident within 5 min of simulated arterial perfusion. The changes in contractile properties could be abrogated by external stenting of the vein (to attenuate circumferential deformation) or inclusion in the perfusate of a vasodilator, e.g., cromakalim (5 microM) or the selective Rho kinase inhibitor Y-27632 (20 microM). The heightened sensitivity and contractility to phenylephrine was maintained after inclusion of adenosine (100 microM), gadolinium (10 microM) or cycloheximide (10 microM) in the vein perfusate. The circumferential deformations imposed by simulated arterial perfusion alter the vasomotor responses of saphenous vein smooth muscle. These effects are independent of new protein synthesis or the activation of stretch activated cation channels. The Rho kinase pathway appears to mediate the signalling mechanisms leading to increased agonist-induced tension and the increased sensitivity to vasoconstrictors.

Hot Expansion of a Thin-Walled Cylindrical Shell of Porous Material

A system of equations describing the hot expansion of a thin-walled cylindrical shell of porous material by internal pressure was obtained. The solution was based on one of the simplest creep theories, namely, work hardening theory. The radial, meridial, and volume rates of creep deformation were calculated in comparison with the basic circumferential deformation rate of the shell. The numerical results were obtained by considering a process of stepwise loading of the shell. It was established that porosity in the material decreases the limiting value of internal pressure of the shell.

Laboratory and field verification of a new approach to stress measurements using a dilatometer tool

Abstract A new method is proposed for in-situ stress measurements. The stresses are estimated from the borehole pressure required to open axial fractures emanating from the borehole, similar to hydrofracture stress measurements. However, the borehole is pressurized by inflation of a dilatometer, such as a packer and a sleeve, and the borehole pressure to reopen the fractures is detected from circumferential deformation of the borehole. The fractures are induced by hydraulic fracturing or sleeve fracturing in advance. To demonstrate this method, we developed a new dilatometer tool. The tool consists essentially of a packer around which deformation transducers sensitive to circumferential strain are affixed at 10°–30° intervals. The packer is inflated to touch the borehole wall, and then the packer pressure is increased step-wise and the resultant strains recorded. Initially, the circumferential strain developed around the borehole is radially symmetric. However, this becomes strongly asymmetric once the fractures begin to open. Thus, the records of strain at different locations around the borehole indicate both the reopening pressure and the orientation of fractures. In the case of a vertical borehole, the detected reopening pressure allows us to estimate the maximum horizontal stress on condition that the minimum horizontal stress is estimated using other approaches.

Axial stretch modifies contractility of porcine coronary arteries by a protein kinase C-dependent mechanism.

Large coronary arteries undergo marked circumferential and axial deformations due to changes in blood pressure and gross movements of the ventricular wall during systole and diastole. The present study was designed to investigate 1) whether axial stretch of large coronary arteries influences the sensitivity to vasoconstrictors, 2) the mechanisms mediating stretch-dependent changes in vascular sensitivity. Endothelium-denuded cylindrical segments from large porcine coronary arteries were studied under isometric conditions using a balloon-based impedance planimetric technique. In segments subjected to a pressure of 60 mmHg, 20% axial stretch caused a left-ward shift of the concentration-response curves for K+ and 5-hydroxytryptamine (5-HT). Enhancement of vascular sensitivity to 5-HT induced by axial stretch was observed also in maximally K+-depolarized coronary arteries. Protein kinase C inhibition by calphostin C (1 microM) slightly decreased the spontaneous resting tone at 60 mmHg and inhibited the leftward shift of the concentration-response curve for 5-HT elicited by axial stretch. These results suggest that axial stretch of the vessel wall enhances the sensitivity of coronary arteries to vasoconstrictors by a protein kinase C-dependent mechanism.

Boundary Layer Solutions in Elastic Solids

Circumferential shear deformation in an annular domain is studied for a large class of incompressible isotropic elastic materials. It is demonstrated that large strains are confined in a region adjacent to a boundary, in analogy to the boundary layer phenomenon in fluid mechanics. The size of this region is quantified. An approximate solution technique for the deformation of nonlinear elastic solids, proposed by Rajagopal [7], is further studied. In this solution, akin to the boundary layer approximation in classical fluid mechanics, the full nonlinear problem is solved in a relatively small region of large strain, while the linearized problem is solved in the remaining region. Error estimates for the approximate solution are obtained.

In-Plane Vibration Modes of Arbitrarily Thick Disks

The three-dimensional vibration of an arbitrarily thick annular disk is investigated for two classes of boundary conditions: all surfaces traction-free, and all free except for the clamped inner radius. These two models represent limiting cases of such common engineering components as automotive and aircraft disk brakes, for which existing models focus on out-of-plane bending vibration. For a disk of significant thickness, vibration modes in which motion occurs within the disk’s equilibrium plane can play a substantial role in-setting its dynamic response. Laboratory experiments demonstrate that in-plane modes exist at frequencies comparable to those of out-of-plane bending even for thickness-to-diameter ratios as small as 10−1. The equations for three-dimensional motion are discretized through the Ritz technique, yielding natural frequencies and mode shapes for coupled axial, radial, and circumferential deformations. This treatment is applicable to “disks” of arbitrary dimension, and encompasses classical models for plates, bars, cylinders, rings, and shells. The solutions so obtained converge in the limiting cases to the values expected from the classical theories, and to ones that account for shear deformation and rotary inertia. The three-dimensional model demonstrates that for geometries within the technologically-important range, the natural frequencies of certain in- and out-of-plane modes can be close to one another, or even identically repeated.

Surface deformation measurements of a cylindrical specimen by digital image correlation

Planar digital image correlation has been extended to measure surface deformations of cylindrical specimens without physical contact for high-temperature situations. A single CCD camera acquires the surface image patterns of a section of a specimen in the undeformed and deformed states to determine two-dimensional displacements on a projection plane. Axial, circumferential and shear deformations are determined through curvature transformation on the two-dimensional projection displacement field. The resolution of this technique was determined for a cylinder of 22.23-mm diameter to be 3.5 μm for the axial displacement, 0.05 percent for the axial and shear strains and 0.08 percent for the circumferential strain when correlation computations are carried out over a field of 5 mm×5 mm.

Development of an in vitro model to study the response of saphenous vein endothelium to pulsatile arterial flow and circumferential deformation

To develop an in vitro model of human saphenous vein bypass to facilitate study of the early adaptive responses of venous endothelium to arterial flow conditions. DESIGN MATERIAL AND METHODS: Segments of human saphenous vein (with or without external polytetrafluoroethylene (PTFE) stents to limit circumferential and radial deformation) were mounted in a bypass circuit and subjected to pulsatile flow with oxygenated Krebs solution to simulate arterial or venous flow conditions for a period of 90 min. The viability of the vein was assessed by the tissue ATP concentration and vasomotor responses to phenylephrine, sodium nitroprusside and bradykinin (endothelium-dependent). Immunohistochemistry was used to assess both endothelial preservation (CD31) and the expression of proteins involved in leukocyte adhesion: E-selectin, P-selectin and ICAM-1. Freshly excised veins were used as controls. The concentration of ATP was 320 +/- 11 nmol/g in freshly excised vein (n = 8) and following exposure to the arterial flow circuit increased to 566 +/- 60 nmol/g (n = 8, paired t-test, p = 0.003) in unstented veins and to 421 +/- 49 nmol/g (n = 8, paired t-test, p = 0.002) in externally stented veins (with PTFE). Both endothelium-dependent and sodium nitroprusside-induced vasodilatation responses were preserved after veins were exposed to the arterial flow circuit, but the sensitivity to phenylephrine was increased: EC50 decreasing from 9 microM, p = 0.008. There was a 5-10% decrease in staining area for CD31 after veins, stented or unstented, were exposed to the arterial flow circuit. However, after exposure to the arterial flow circuit, the staining area ratio for ICAM-1/CD31, which remained unchanged in externally stented veins, increased two-fold in unstented veins, p > 0.01: there were no changes in the staining area ratio P-selectin/CD31 and no staining for E-selectin was observed. Vasomotor responses and tissue ATP concentration indicate that the viability of saphenous vein can be maintained for up to 90 min in an ex vivo flow circuit and the CD31 staining indicated endothelial preservation. This opens up the possibility of investigating the early changes in saphenous vein endothelium following exposure to arterial pressure, as at bypass surgery. First results suggest that there is rapid upregulation of the leukocyte adhesion molecule ICAM-1, which can be prevented by limiting the circumferential deformation of the vein with an external PTFE stent.

Circumferential deformation and shear stress induce differential responses in saphenous vein endothelium exposed to arterial flow.

Adaptation of saphenous vein to the hemodynamic stresses of the arterial circulation is critical to the maturation of vein bypass grafts. We have investigated early adaptive responses of venous endothelium by placing excised human saphenous vein in a bypass circuit with either venous or arterial flow conditions, using external stenting to resolve the effects of longitudinal (shear) from circumferential stress. Endothelial protein concentrations were assessed by immunostaining area (ratio of protein/CD31) and Western blotting of endothelial cell lysates (staining ratio protein/vWf). In both unstented and stented veins nitric oxide synthase increased after 90 min of arterial flow: twofold increase of immunostaining area (P = 0.001), four- to fivefold increase by Western blotting (P = 0.02), and increased A23187mediated maximum endothelium-dependent relaxation of vein rings (P = 0.01). In unstented veins, ICAM-1 concentration was increased after 45 min of arterial flow: twofold increase by immunostaining (P = 0.001) and Western blotting (P = 0.038), with maximum fibrinogen-mediated endothelium-dependent relaxation increasing from 55.9+/-4.9 to 97+/-2.1% (P = 0.01). In contrast, in unstented veins there was a threefold decrease of VCAM-1 and no change in P-selectin after arterial flow for 45 and 90 min, respectively. However, no changes in ICAM-1 and VCAM-1 were observed in stented veins. The flow-induced alterations in nitric oxide synthase, ICAM-1, and VCAM-1 were abolished when 3 mM tetraethylammonium ion (K+ channel blocker) was included in the vein perfusate. The very rapid changes in ICAM-1 and VCAM-1 expression are a response to circumferential stress, whereas the slower upregulation of nitric oxide synthase is a response to longitudinal (shear) stress. Similar changes could influence the adhesiveness of endothelium in newly implanted saphenous vein bypass grafts.

Functional implications of myocardial scar structure.

During healing after myocardial infarction, scar collagen content and stiffness do not correlate. We studied regional mechanics and both area fraction and orientation of large collagen fibers 3 wk after coronary ligation in the pig. During passive inflation of isolated, arrested hearts, the scar tissue demonstrated significantly less circumferential strain but similar longitudinal and radial deformation in comparison with noninfarcted regions of the same hearts. The observed selective resistance to circumferential deformation was consistent with the finding that most of the large collagen fibers in the scar were oriented within 30 degrees of the local circumferential axis. Furthermore, data from a previous study indicate that during ventricular systole these scars resist circumferential stretching, whereas they deform similarly to noninfarcted myocardium in the longitudinal and radial directions. We conclude that large collagen fiber structure is an important determinant of scar mechanical properties and that scar anisotropy allows the scar to resist circumferential stretching while deforming compatibly with adjacent noninfarcted myocardium in the longitudinal and radial directions.

Experimental study of periacetabular deformations before and after implantation of HIP prostheses

This work is based upon an experimental simulation of one-legged stance, under loads close to the average body weight. Skeletons, harvested from fresh non-embalmed cadavers, included pelvis, two lumbar vertebrae, and both femurs. Periacetabular deformations were studied using tridirectional strain gauges before and after implantation of different types of acetabular prostheses in eight pelves: conventional polyethylene-cemented sockets, polyethylene sockets cemented into a metallic device, metal-backed cemented sockets, and hemispherical cementless press-fit cups with porous or hydroxyapatite coating. Strain measurements showed the persistence of important bone deformations at implant periphery. Mean values of normal periacetabular deformations were significantly reduced in two out of five acetabula implanted with cemented implants. In contrast, mean values of normal and circumferential deformations increased when polyethylene sockets were cemented into acetabular reinforcement devices, but this augmentation was significant in only one out of two cases. After implantation of cementless hemispherical metal-backed cups, periacetabular bone deformations also increased, but modifications were significant in a single case. Results are discussed according to the type of fixation (cemented or cementless), and to the difference in rigidity between implant and bone. There was no clear relation between implant stiffness and the magnitude of bone deformations.

A Resistance Wire Transducer for Circumferential Strain Measurement in Triaxial Tests

Abstract A resistance wire transducer was designed to measure circumferential deformation of a partially saturated triaxial specimen. It utilizes for the measurement changing output voltage in a resistance wire transducer wound around the specimen as it bulges, i.e., increases in circumference. This circumferential change can be converted into lateral deformation. The proposed transducer is very small, so it is possible to mount several of them along the height of a specimen and monitor accurately its changing cross sections. The volume of the specimen at any recording time can be calculated from the deformed cross section and axial deformation. The resistance wire transducer is a simple device whose principle provides the potential for a broad spectrum of analogous applications.

The use of vibration monitoring in detecting the initiation and prediction of corrugations in rolling-sliding contact wear

Abstract Vibration displacements and accelerations have been monitored on a modified Amsler machine during the dry rolling-sliding wear testing of rail steels. Certain combinations of contact stress and creepage lead to periodic circumferential surface deformations of the test discs, termed corrugations. The low frequency corrugations are defined as facets. Dramatic facets have occurred at 500 MPa maximum Hertzian contact stress and 10% creepage, in the frequency band ranging from 1–100 Hz, with a typical facet frequency initiated at 58.25 Hz. No higher frequency corrugations occurred during the test run, unlike previous tests (J.E. Garnham, J.R. Brightling and J.H. Beynon, Wear, 124 (1988) 45–63). The evolution of the surface deformation was observed by surface profilometry, as well as by monitoring the facet vibration component trend, and a good correlation between the two has been found. Also, a significant correlation between the predominant peaks of the displacement spectra and the higher harmonics of the rotation frequency have been detected, leading to conclusions concerning the mechanism of facet initiation. At the end of the test the facets degenerated into pronounced eccentricities causing a high level component of the rotation frequency that could easily be detected by following the evolution of the characteristic component. The tests highlighted that the vibration displacement is more suitable for the monitoring of rolling-sliding contact defects than is the acceleration, which tends to emphasise the high frequency components. Vibration monitoring is shown to be a proper and powerful tool for the early detection of facet initiation.

Modal Analysis of Thick Cylinder with Both Ends Free Based on Mindlin's Method.

This paper describes the modal analysis of a thick cylinder with both ends free, based on Mindlin's thick plate theory. The equations of vibration of the thick cylinder were derived in consideration of shearing deformation and rotatory inertia, and were simplified and solved under assumption of the axial and circumferential deformations of the neutral cylindrical surface. Except for some low modes, the calculated natural frequencies agreed well with the values obtained by experimental modal analysis and with the modal analysis by use of Finite Element Method. Also, the calculated mode shapes compared well with those obtained by FEM modal analysis.

入射ＳＨ波を受ける粒子分散系制振材のエネルギー吸収機構

The energy absorption of a polymer particle due to the dynamic load of SH-wave is discussed based on the linear theory of elastodynamics. It is shown that the ability of the energy absorption in the range of the practical use is governed by the deformation mode of the particle, when the frequency of the incident wave is lower. It is shown that the first mode of the circumferential deformation is the best for absorbing energy in the particle. The present and previous papers completes the discussion on the energy absorption in a polymer particle for the three types of the dynamic loading.

入射Ｐ・ＳＶ波を受ける粒子分散系制振材のエネルギー吸収機構

The energy absorption of a polymer particle to dynamic loads is discussed based on the linear theory of elastodynamics. Assuming incident waves, P and SV-waves, as the dynamic loads, the strain energy stored in the particle is obtained in graphical forms. It is shown that the ability of the energy absorption in the practical range is governed by the mode of circumferential deformation of the particle, when the frequency of the incident wave is lower. For the load of the incident P-wave, the zeroth mode of all round tension and compression of the particle deformation is the best deformation for absorbing the energy, however, for that of SV-wave, the second mode of elliptical deformation is the best.

Effect of Interphases on Micro and Macromechanical Behavior of Hexagonal-Array Fiber Composites

The effect of interphase stiffness on microstresses and macromechanical behavior has been investigated for transverse loading of an hexagonal-array unidirectional fiber composite. The interphase is modeled by a layer which resists radial extension and circumferential shear deformation. Taking advantage of the periodicity of the medium, the states of stress, and deformation in a basic cell have been analyzed numerically by the use of the boundary element method. The circumferential tensile stress along the matrix side of the interphase and the radial stress in the interphase have been analyzed for various values of the interphase parameters and the fiber volume ratio. The micromechanical results have also been used to determine the effect of interphase stiffness on the effective moduli. The calculated values have been compared with analytical results that were adjusted for interphase stiffness.