Circumferential Shear Research Articles

Mechanisms of rock breaking by swirling-round SC-CO<sub>2</sub> jet

Supercritical carbon dioxide (SC-CO2) jet is characterized by low rock breaking threshold pressure and high rock breaking rate. Swirling-round jet, taking the advantages of both swirling and round jet, enjoys high rock breaking efficiency. By integrating swirling-round jet and SC-CO2, it is prospective for swirling-round SC-CO2 jet to improve rock erosion efficiency further. Rock damage mechanisms of swirling-round SC-CO2 jet are investigated by means of rock-erosion experiments and scanning electron microscope (SEM) observation. The selected core samples include shale, dolomite as well as sandstone. For shale, no macro-deformation occurs and microscopic damage is discovered, forming tiny cracks. For dominate and sandstone, erosion holes form, and crystal particle cleavage as well as inter-particle rupture occur. According to the observation results, the rock damage mechanisms of swirling-round SC-CO2 jet are divided into two aspects. On the one hand, swirling-round SC-CO2 jet breaks rock by combining axial impinging, radical tension and circumferential shear. On the other hand, with characteristics of low viscosity, compressibility and strong diffusivity, numerous micro fractures are caused by SC-CO2, and existing fractures are expanded, which led to fractures joining together and massive rocks split off.

Dynamic torsional response of an elastic pile in a radially inhomogeneous soil

Surrounding soil may be weakened or strengthened due to construction disturbance of the pile, resulting in soil properties varying gradually in the radial direction. In this paper, an analytical solution is developed to investigate the torsional vibration of an elastic pile embedded in a radially inhomogeneous soil and subjected to a time-harmonic torsional loading. The radially inhomogeneous soil is subdivided into many thin concentric annular sub-zones, with each having constant complex shear modulus in radial direction. The dynamic equilibrium equation of each sub-zone of the soil is then solved and the circumferential displacement and shear stress along the pile-soil interface are obtained by a newly developed method that enforces the continuity conditions between the two adjacent sub-zones. By virtue of the boundary and continuity conditions of the pile-soil system, the torsional impedance at the pile head is derived in an exact closed form in the frequency domain. Some numerical results are presented to study the influence of the soil layer rigidities on the vibration characteristic of the pile-soil system.

Dispersion and Attenuation of Guided Waves in Tubular Section with Multi-Layered Viscoelastic Coating — Part II: Circumferential Wave Propagation

In the second part of the study on guided wave motions in a hollow cylinder with epoxy layers, shear and longitudinal modes propagating in the circumferential direction are investigated. The corresponding dispersion and attenuation characteristic equations are derived by incorporating a complex, frequency-dependent constitutive law for the viscoelastic coating material. Continuous displacement boundary conditions are implemented to model perfect interfacial bonds between the tubular section and applied epoxy coatings. The presence of thin dissipative viscoelastic layers has profound impact on the propagation of both the circumferential shear and longitudinal waves. The number of admissible propagating modes increases with increasing number of viscoelastic layers and higher order modes dissipate significantly less at high frequencies than the lower order modes at low frequencies. Over the frequency range considered, all the circumferential propagating modes are significantly more attenuating than their axial propagating counterparts studied in Part 1 of the paper. Generation of the lowest shear wave mode is suppressed at approximately 0.2 MHz in the coated tubular. However, no such definitive cutoff frequencies are observed for the longitudinal modes regardless of how many viscoelastic layers are considered.

Aortic shear stress in patients with bicuspid aortic valve with stenosis and insufficiency

ObjectivesBicuspid aortic valve, characterized by valve malformation and risk for aortopathy, displays profound alteration in systolic aortic outflow and wall shear stress distribution. The present study performed 4-dimensional flow magnetic resonance imaging in patients with bicuspid aortic valve with right-left cusp fusion, focusing on the impact of valve function on hemodynamic status within the ascending aorta. MethodsFour-dimensional flow magnetic resonance imaging was performed in 50 subjects with right-left bicuspid aortic valve and 15 age- and aortic size–matched controls with tricuspid aortic valve. Patients with bicuspid aortic valve were categorized into 3 groups according to their aortic valve function as follows: bicuspid aortic valve with no more than mild aortic valve dysfunction (bicuspid aortic valve control, n = 20), bicuspid aortic valve with severe aortic insufficiency (n = 15), and bicuspid aortic valve with severe aortic stenosis (n = 15). ResultsAll patients with right-left bicuspid aortic valve exhibited peak wall shear stress at the right-anterior position of the ascending aorta (bicuspid aortic valve vs trileaflet aortic valve at the right-anterior position: 0.91 ± 0.23 N/m2 vs 0.43 ± 0.12 N/m2, P < .001) with no distinct alteration between bicuspid aortic valve with severe aortic insufficiency and bicuspid aortic valve with severe aortic stenosis. The predominance of dilatation involving the tubular ascending aorta (82%, type 2 aortopathy) persisted, with or without valve dysfunction. Compared with bicuspid aortic valve control subjects, the bicuspid aortic valve with severe aortic insufficiency group displayed universally elevated wall shear stress (0.75 ± 0.12 N/m2 vs 0.57 ± 0.09 N/m2, P < .01) in the ascending aorta, which was associated with elevated cardiac stroke volume (P < .05). The bicuspid aortic valve with severe aortic stenosis group showed elevated flow eccentricity in the form of significantly increased standard deviation of circumferential wall shear stress, which correlated with markedly increased peak aortic valve velocity (P < .01). ConclusionsThe location of peak aortic wall shear stress and type of aortopathy remained homogeneous among patients with right-left bicuspid aortic valve irrespective of valve dysfunction. Severe aortic insufficiency or stenosis resulted in further elevated aortic wall shear stress and exaggerated flow eccentricity.

A new omnidirectional shear horizontal wave transducer using face-shear (d24) piezoelectric ring array

The non-dispersive fundamental shear horizontal (SH0) wave in plate-like structures is of practical importance in non-destructive testing (NDT) and structural health monitoring (SHM). Theoretically, an omnidirectional SH0 transducer phased array system can be used to inspect defects in a large plate in the similar manner to the phased array transducers used in medical B-scan ultrasonics. However, very few omnidirectional SH0 transducers have been proposed so far. In this work, an omnidirectional SH0 wave piezoelectric transducer (OSH-PT) was proposed, which consists of a ring array of twelve face-shear (d24) trapezoidal PZT elements. Each PZT element can produce face-shear deformation under applied voltage, resulting in circumferential shear deformation in the OSH-PT and omnidirectional SH0 waves in the hosting plate. Both finite element simulations and experiments were conducted to examine the performance of the proposed OSH-PT. Experimental testing shows that the OSH-PT exhibits good omnidirectional properties, no matter it is used as a SH0 wave transmitter or a SH0 wave receiver. This work may greatly promote the applications of SH0 waves in NDT and SHM.

Investigation Into the Effects of the Thickness of a Hollow-Cylinder Soil Specimen on the Stress Distributions in Triaxial Torsional Shear Testing

Abstract To investigate the effect of the thickness of a hollow cylinder on the stress distributions in a torsional triaxial shear test of clay, an equation for calculating the circumferential shear stress on a cross section of the cyclider is derived based on a linear elastic constitutive model and elastic mechanics. The “stress error” parameter and “average stress error” parameters are defined to assess the non-uniformity of stresses. The parameter ranges are discussed for specimens with various thicknesses. Torsional triaxial shear testing of specimens with different thicknesses is simulated in using a three-dimensional finite-element method (3D FEM) with Duncan–Chang's non-linear elastic model. The results show that the circumferential shear stress non-uniformity increases with increasing thickness. The maximum, minimum and average “stress error” values are analyzed for commonly used specimen dimensions. When the soil's stress–strain is linear elastic, the “average stress error” is 12.8 % for an outer radius = 50 mm and a thickness = 20 mm and 9.0 % using Duncan–Chang's model. If the “average stress error” is limited to ≤ 10 %, the ratio of the inner radius over the outer radius is 0.68.

Structural properties and durability of a sprayed waterproofing membrane for tunnels

A sprayed waterproofing interlayer between primary and secondary tunnel linings has the potential to create composite structural interaction between them, mainly in circumferential flexure. This depends on the bond between sprayed surfaces and on the structural and chemical properties of the material. Data on bond is reviewed. Recent tests in tension, compression and shear to determine the structural properties of a particular elastomeric waterproofing material are presented, analysed and discussed. Values for Young’s modulus and the shear modulus G are proposed, for serviceability verifications that include limitation of crack width caused by excessive local flexure.It is concluded that where sufficient bond is present, composite action arising from transfer of circumferential shear between the linings can be relied upon to improve performance in service for short-term and accidental situations. This allows for reduction of stiffness during the first few years. There is no evidence from tests lasting up to 2.2years that significant further reduction would occur, but prediction of 100-year performance remains difficult.

Does the degree of coarctation of the aorta influence wall shear stress focal heterogeneity?

The development of atherosclerosis in the aorta is associated with low and oscillatory wall shear stress for normal patients. Moreover, localized differences in wall shear stress heterogeneity have been correlated with the presence of complex plaques in the descending aorta. While it is known that coarctation of the aorta can influence indices of wall shear stress, it is unclear how the degree of narrowing influences resulting patterns. We hypothesized that the degree of coarctation would have a strong influence on focal heterogeneity of wall shear stress. To test this hypothesis, we modeled the fluid dynamics in a patient-specific aorta with varied degrees of coarctation. We first validated a massively parallel computational model against experimental results for the patient geometry and then evaluated local shear stress patterns for a range of degrees of coarctation. Wall shear stress patterns at two cross sectional slices prone to develop atherosclerotic plaques were evaluated. Levels at different focal regions were compared to the conventional measure of average circumferential shear stress to enable localized quantification of coarctation-induced shear stress alteration. We find that the coarctation degree causes highly heterogeneous changes in wall shear stress.

Nonlinear vibrations and energy exchange of single-walled carbon nanotubes. Circumferential flexural modes

In this paper, the nonlinear vibrations and energy exchange of single-walled carbon nanotubes (SWNTs) are studied. The Sanders–Koiter theory is applied to model the nonlinear dynamics of the system in the case of finite amplitude of vibration. The SWNT deformation is described in terms of longitudinal, circumferential and radial displacement fields. Simply supported, clamped and free boundary conditions are considered. The circumferential flexural modes (CFMs) are investigated. Two different approaches based on numerical and analytical models are compared. In the numerical model, an energy method based on the Lagrange equations is used to reduce the nonlinear partial differential equations of motion to a set of nonlinear ordinary differential equations, which is solved by using the implicit Runge–Kutta numerical method. In the analytical model, a reduced form of the Sanders–Koiter theory assuming small circumferential and tangential shear deformations is used to get the nonlinear ordinary differential equations of motion, which are solved by using the multiple scales analytical method. The transition from energy beating to energy localization in the nonlinear field is studied. The effect of the aspect ratio on the analytical and numerical values of the nonlinear energy localization threshold for different boundary conditions is investigated.

Does altered aortic flow in marfan syndrome relate to aortic root dilatation?

PurposeTo examine possible hemodynamic alterations in adolescent to adult Marfan syndrome (MFS) patients with aortic root dilatation.Materials and MethodsFour‐dimensional flow MRI was performed in 20 MFS patients and 12 age‐matched normal subjects with a 3T system. The cross‐sectional areas of 10 planes along the aorta were segmented for calculating the axial and circumferential wall shear stress (WSSaxial, WSScirc), oscillatory shear index (OSIaxial, OSIcirc), and the nonroundness (NR), presenting the asymmetry of segmental WSS. Pearson's correlation analysis was performed to present the correlations between the quantified indices and the body surface area (BSA), aortic root diameter (ARD), and Z score of the ARD. P < 0.05 indicated statistical significance.ResultsPatients exhibited lower WSSaxial in the aortic root and the WSScirc in the arch (P < 0.05–0.001). MFS patients exhibited higher OSIaxial and OSIcirc in the sinotubular junction and arch, but lower OSIcirc in the descending aorta (all P < 0.05). The NR values were lower in patients (P < 0.05). The WSSaxial or WSScirc exhibited moderate to strong correlations with BSA, ARD, or Z score (R2 = 0.50–0.72) in MFS patients.ConclusionThe significant differences in the quantified indices, which were associated with BSA, ARD, or Z score, in MFS were opposite to previous reports for younger MFS patients, indicating that altered flows in MFS patients may depend on the disease progress. The possible time dependency of hemodynamic alterations in MFS patients strongly suggests that longitudinal follow‐up of 4D Flow is needed to comprehend disease progress. J. Magn. Reson. Imaging 2016;44:500–508.

Moderate Ischemic Mitral Regurgitation After Posterolateral Myocardial Infarction in Sheep Alters Left Ventricular Shear but Not Normal Strain in the Infarct and Infarct Borderzone

Chronic ischemic mitral regurgitation (CIMR) is associated with poor outcome. Left ventricular (LV) strain after posterolateral myocardial infarction (MI) may drive LV remodeling. Although moderate CIMR hasbeen previously shown to affect LV remodeling, the effect of CIMR on LV strain after posterolateral MI remains unknown. We tested the hypothesis that moderate CIMR alters LV strain after posterolateral MI. Posterolateral MI was created in 10 sheep. Cardiac magnetic resonance imaging with tags was performed 2 weeks before and 2, 8, and 16 weeks after MI. The left and right ventricular volumes were measured, and regurgitant volume indexed to body surface area (regurgitant volume index) was calculated as the difference between left ventricle and right ventricle stroke volumes divided by body surface area. Three-dimensional strain was calculated. Circumferential strain (Ecc) and longitudinal strain (Ell) were reduced in the infarct proper, MI borderzone, and remote myocardium 16 weeks after MI.In addition, radial circumferential (Erc) and radial longitudinal (Erl) shear strains were reduced in remote myocardium but increased in the infarct and borderzone 16weeks after MI. Of all strain components, however, only Erc was affected by regurgitant volume index (p=0.0005). There was no statistically significant effect of regurgitant volume index on Ecc, Ell, Erl, or circumferential longitudinal shear strain (Ecl). Moderate CIMR alters radial circumferential shear strain after posterolateral MI in sheep. Further studies are needed to determine the effect of shear strain on myocyte hypertrophy and the effect of mitral repair on myocardial strain.

Nondestructive Evaluation of Functionally Graded Subsurface Damage on Cylinders in Nuclear Installations Based on Circumferential SH Waves

Subsurface damage could affect the service life of structures. In nuclear engineering, nondestructive evaluation and detection of the evaluation of the subsurface damage region are of great importance to ensure the safety of nuclear installations. In this paper, we propose the use of circumferential horizontal shear (SH) waves to detect mechanical properties of subsurface regions of damage on cylindrical structures. The regions of surface damage are considered to be functionally graded material (FGM) and the cylinder is considered to be a layered structure. The Bessel functions and the power series technique are employed to solve the governing equations. By analyzing the SH waves in the 12Cr-ODS ferritic steel cylinder, which is frequently applied in the nuclear installations, we discuss the relationship between the phase velocities of SH waves in the cylinder with subsurface layers of damage and the mechanical properties of the subsurface damaged regions. The results show that the subsurface damage could lead to decrease of the SH waves’ phase velocity. The gradient parameters, which represent the degree of subsurface damage, can be evaluated by the variation of the SH waves’ phase velocity. Research results of this study can provide theoretical guidance in nondestructive evaluation for use in the analysis of the reliability and durability of nuclear installations.

In-plane behaviour of web-tapered beams

Shear stress distributions in tapered web I-beams are incorrectly predicted by the conventional beam analysis method used for uniform beams. More accurate predictions are obtained by adopting the finding for wedges that the normal stress trajectories are radial instead of parallel.The shear stress distributions in web-tapered I-beams are influenced by the vertical components of the inclined flange forces (which are zero in uniform beams), as well as by the normal stress gradients in the flanges. The net web shear equal to the difference between the external shear and the vertical components of the inclined flange forces is resisted by the resultant of the vertical components of the normal stresses and the circumferential shear stresses.The circumferential shear stresses τrθ have linear components due to axial force and parabolic components due to moment and shear. The magnitudes of these stresses are controlled by the normal stress gradients at the flange-web junctions and by the requirement that the web shear resistance must equal the net web shear force.

Guided torsional wave generation of a linear in-plane shear piezoelectric array in metallic pipes

Cylindrical guided waves based techniques are effective and promising tools for damage detection in long pipes. The essential operations are generation and reception of guided waves in the structures utilizing transducers. A novel in-plane shear (d36 type) PMNT wafer is proposed to generate and receive the guided wave, especially the torsional waves, in metallic pipes. In contrast to the traditional wafer, this wafer will directly introduce in-plane shear deformation when electrical field is conveniently applied through its thickness direction. A single square d36 PMNT wafer is bonded on the surface of the pipe positioned collinearly with its axis, when actuated can predominantly generate torsional (T) waves along the axial direction, circumferential shear horizontal (C-SH) waves along circumferential direction, and other complex cylindrical Lamb-like wave modes along other helical directions simultaneously. While a linear array of finite square size d36 PMNT wafers was equally spaced circumferentially, when actuated simultaneously can nearly uniform axisymmetric torsional waves generate in pipes and non-symmetric wave modes can be suppressed greatly if the number of the d36 PMNT wafer is sufficiently large. This paper first presents the working mechanism of the linear d36 PMNT array from finite element analysis (FEA) by examining the constructive and destructive displacement wavefield phenomena in metallic pipes. Furthermore, since the amplitude of the received fundamental torsional wave signal strongly depends on frequency, a series of experiments are conducted to determine the frequency tuning curve for the torsional wave mode. All results indicate the linear d36 PMNT array has potential for efficiently generating uniform torsional wavefield of the fundamental torsional wave mode, which is more effective in monitoring structural health in metallic pipes.

Crack Propagation and Its Shear Mechanisms in the Bovine Descending Aorta.

Aortic dissection and rupture may involve circumferential shear stress in the circumferential-longitudinal plane. Inflation of bovine descending aortic ring specimens provides evidence of such shear from the non-uniform circumferential distortion of radial lines drawn on the circumferential-radial ring face. Delamination without tensile peeling induces cracks that propagate nearly circumferentially in the circumferential-longitudinal plane from the root of a radial cut representing rupture initiation in a ring. Translational shear deformation tests of small rectangular aortic wall blocks in the circumferential and longitudinal direction measure the consequences of such shear on substructures in the aortic wall, in particular the collagen fibers. The two directions of shear deformation produce no statistical difference in the shear stress response of the wall. Possibly, the interfiber connections between collagen fibers are put into tension by either translational shear deformation so that the stress measured reflects the tensile response of these connections. Wall rupture may involve failure of these connections; such failure is supported by the voids parallel to the collagen fibers observed in a histological study after translational shear. Further, interstitial fluid is redistributed by shear as evidenced by the measured weight loss of a set of specimens during the translational shear of blocks. Because the mass changes, mathematical modeling of aortic tissue in vitro as incompressible is an approximation. These observations suggest that no simple modification of classical rupture theories, whether based on energy functions, stress or strain, suffices to predict the rupture of hydrated soft biological tissue that has complex substructures.

Evaluation of left ventricular torsion using cardiac MRI. Validation of feature tracking

LV torsion Left ventricular torsion may be more sensitive in detecting pathology before changes in more traditional functional parameters, and the onset of symptoms. The current gold standard for evaluating torsion is CMR, but a wide variety of techniques exist and as yet the advantages and disadvantages remain to be determined. The use of feature tracking software offers a method using standard untagged SSFP images with a potential benefit of shorter scan time. Torsional shear angle is probably the best current measure of true torsion, but requires several parameters to be defined and no commercially available software exists to calculate this. The purpose of the study was to validate the CMR derived torsion,using an in-house developed software program using data from featuretracking. Methods 15 healthy volunteers underwent a low-dose dobutamine stress CMR (baseline, 7.5mcg/kg/min, 15mcg/kg/min). In-house developed software CMRTorsion is an Excelbased macro programme using Visual Basic that facilitates the calculation and graphical representation of principal strains, twist, torsion and circumferential longitudinal shear from processed bSSFP cine images obtained by a Siemens 1.5T Avanto CMR scanner. This was further refined to allow data derived from feature tracking software to be processed.

1P2-V06 軟弱土壌を走行する車輪型移動ロボットのための車輪下部せん断応力分布の二次元的な計測手法

This paper describes a two-dimensional measurement method for shear stress distribution of a wheel on loose soil. The stress measurement device was improved to enable detect the shear stress distribution of a wheel. Normal stress distribution and circumferential shear stress distribution and lateral shear stress distribution were measured using this device. By combining the two-directional shear stress distribution, the directions of shear stress distribution were estimated. With this, soil flow direction was also estimated. By calculating vertical components of normal stress and shear stress, measurement validity was evaluated. In addition, the classical shear stress model and measured data were compared. As a result, both were accurately estimated, and a significant difference was not found under the low slippage conditions.

Torsional analysis of heterogeneous magnetic circular cylinder

In this paper, the exact closed-form solutions for torsional analysis of heterogeneous magnetostrictive circular cylinder are derived. The cylinder is subjected to the action of a magnetic field produced by a constant longitudinal current density. It is also acted upon by a particular kind of shearing stress at its upper base. The rigidity of the cylinder is graded through its axial direction from one material at the lower base to another material at the upper base. The distributions of circumferential displacement and shear stresses are presented through the radial and axial directions of the cylinder. The influence of the magnetostrictive parameter is discussed. The effects of additional parameters are investigated.

Circulating matrix metalloproteinase patterns in association with aortic dilatation in bicuspid aortic valve patients with isolated severe aortic stenosis.

Bicuspid aortic valve (BAV) exhibits a clinical incline toward aortopathy, in which aberrant tensile and shear stress generated by BAV can induce differential expression of matrix metalloproteinases (MMPs) and their endogenous tissue inhibitors (TIMPs). Whether stenotic BAV, which exhibits additional eccentric high-velocity flow jet upon ascending aorta and further worsens circumferential systolic wall shear stress than BAV with echocardiographically normal aortic valve, can lead to unique plasma MMP/TIMP patterns is still unknown. According to their valvulopathy and aortic dilatation status, 93 BAV patients were included in the present study. Group A (n = 37) and B (n = 28) comprised severely stenotic patients with or without ascending aorta dilatation; Group C (n = 12) and D (n = 16) comprised echocardiographically normal BAV patients with or without ascending aorta dilatation. Plasma MMP/TIMP levels (MMP-1, -2, -3, -8, -9, -10, -13 and TIMP-1, -2, -4) were determined via a multiplex ELISA detection system in a single procedure. Among patients with isolated severe aortic stenosis, plasma levels of MMP-2 and -9 were significantly elevated when ascending aortic dilatation was present (p = 0.001 and p = 0.002, respectively). MMP-2, however, remained as the single elevated plasma component among echocardiographically normal BAV patients with dilated ascending aorta (p = 0.027). Multivariate analysis revealed that MMP-2 and MMP-9 could both serve as independent risk factor for aortic dilatation in the case of isolated severe stenosis (p = 0.003 and p = 0.001, respectively), and MMP-2 in echocardiographically normal patients (p = 0.002). In conclusion, BAV patients with isolated severe aortic stenosis demonstrated a distinct plasma MMP/TIMP pattern, which might be utilized as circulating biomarkers for early detection of aortic dilatation.

Torsional Dynamic Impedance of a Tapered Pile Considering its Construction Disturbance Effect

The dynamic response of a tapered pile (considering its construction disturbance effect) is investigated when the tapered pile is subjected to a time-harmonic torsional loading. For most engineering conditions, the surrounding soil may be weakened or strengthened owing to the construction disturbance effect of the tapered pile, resulting in the soil becoming radially inhomogeneous. In order to consider this problem, the circumferential shear complex stiffness transfer model is proposed to simulate the radial inhomogeneity of soil. Then, the governing equations of a tapered pile-soil system subjected to torsional dynamic loading are established. By virtue of the circumferential shear complex stiffness transfer method and the impedance function transfer method, the analytical solution of torsional dynamic impedance at the head of the tapered pile is derived. Based on the presented solution, the influence of the construction disturbance effect of the surrounding soil on the torsional dynamic impedance at the pile head is investigated within the low-frequency range concerned in the design of a dynamic foundation. The results show that, even if the hardening range and softening range of the surrounding soil vary within a smaller scale, the hardening effect and softening effect also have a notable influence on the torsional dynamic impedance at the pile head.