Circumferential Direction Research Articles

Failure Analysis of Cracked P110 Repaired Tubing Used for Gas Transmission.

With green and low-carbon developments in oil fields, an increasing amount of repaired oil tubing is being used as oil and gas transmission pipelines in China. However, due to differences in manufacturing standards between oil tubing and transmission pipelines, there are inevitably some issues during their use. This paper investigates a case of cracking failure in repaired oil tubing used as a gathering and transportation pipeline. The failure occurred after eight months of operation and was characterized by a circumferential crack at the male thread end of the tubing joint. To determine the root cause of the failure, a series of experiments were conducted on the oil tubing. The experiments included visual inspection, chemical composition analysis, mechanical properties testing, hardness testing, metallographic examination, and microstructure analysis. The results revealed that the thread of the cracked tubing was not tightened to the specified position; the connection between the tubing and the coupling was welded in a circumferential direction; and cracks occurred in the heat-affected zone of the weld. Chemical composition, tensile performance, and the Charpy impact of the tubing meet the requirements of API 5CT for P110 material, and no abnormalities were found in the metallographic structure. The microstructure at the weld toe of the fracture is martensite, and the hardness is 476 HV10. Based on the thermal simulation verification test, when the material of the tubing cools from 1200 °C, which is located in the coarse HAZ temperature zone, the base metal transforms into martensite with a little granular bainite, exhibiting its highest hardness value at 371 HV10, which is higher than the allowable hardness for carbon steel and indicates the material has poor weldability. The reasons for the cracking and failure of the tubing are that the P110 repaired tubing has a high carbon equivalent and poor weldability. During the welding process, martensitic structure was formed at the weld toe, and cold cracks appeared in the heat-affected zone, resulting in failure. To avoid the reoccurrence of such failure, recommendations are proposed.

Enhancement of the Hygrothermoelastic Performance of Rotating Cylindrical Smart Sensors

The goal of this research article is to investigate the effects of using two-dimensional functionally graded materials on the performance of piezoelectric sensors/actuators when subjected to simultaneous complex loading conditions. The considered disc-shaped sensors/actuators have nonuniform thicknesses and undergo asymmetric hygro-thermo-electro-mechanical loading. A power-law model is used to grade the materials radially, whereas the cosine function, which includes two independent parameters, describes the pattern along the circumferential direction. Comparing the results obtained by using the finite element method with those of one-dimensional graded structures leads to promising outcomes. For example, the radial displacement exhibits vital changes that varied between -13\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-13$$\\end{document} and 31%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$31\\%$$\\end{document}. This is beneficial for such structures in terms of enhancing their sensing/actuating abilities. Also, the tangential stress can be reduced substantially by about 39.5%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$39.5\\%$$\\end{document} through the proper selection of the corresponding material parameters. In addition, this reduction of the tangential stress has a positive effect on the von Mises stress that can be decreased by nearly 33%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$33\\%$$\\end{document}. Accordingly, the structure would have improved durability and sustain higher loads. These findings would revolutionize the manufacturing of smart structures and enhance their behaviors under severe conditions.

Abstract 14223: Vector Analysis for Left Ventricular Wall Motion by Optical Flow With Echocardiographic Images in Myocardial Infarction Rat Model

Background/Research Questions: Alternative evaluation of cardiac function may be established in echocardiography-based vector analysis of the ventricular wall motion property. Vector acceleration and direction have the potential to assess cardiac kinetic energy and dynamics. Optical flow is suitable for vector analysis, because ventricular wall motion can be estimated as visible and quantitative vectors by optical flow from 2D echocardiographic images. Aims: This study aimed to establish a vector analysis for ventricular wall motion via optical flow with echocardiography. Methods: Coronary artery ligation rat model was used in this study. Before surgery (Pre) and four weeks after surgery (MI), short axis echocardiographic images in mid portion were obtained and analyzed by optical flow for left ventricular regional wall motion. Vector accelerations and directions were measured in both systolic and diastolic phases. Vector directions were classified into inward (ID), outward (OD), and circumferential direction (counterclockwise: CC, clockwise: CW). Following echocardiography, a rat was sacrificed for histological evaluation. Results: Pathological myocardial infarction was noted in the anterolateral lesion. Comparing average vector accelerations, MI had significantly smaller acceleration vectors in both systolic and diastolic phase (Pre vs. MI in systolic: 0.006±0.002 vs. 0.002±0.001 mm/s 2 , P<0.001, Pre vs. MI in diastolic: 0.007±0.002 vs. 0.002±0.001 mm/s 2 , P<0.001). Regarding total vector direction, CC and CW significantly increased in MI (P<0.01). In the anterolateral lesion, ID and OD were the main vector directions in Pre. In contrast, CC and CW vectors significantly increased in MI (P<0.0001). Conclusions: Optical flow effectively visualized cardiac wall motions and quantify them as vectors in echocardiographic images. The technique clarified left ventricular wall vector property alterations between healthy and infarcted hearts.

Research on the Hydraulic Excitation Characteristics of the Top Cover Caused by the Radial Installation Deviation of the Seal of a 1GW Francis Turbine

The radial installation deviation of the turbine runner will change the gap flow between the upper crown and the lower ring seal, which will affect the radial force of the runner and the hydraulic excitation characteristics of the top cover. This research focuses on the 1GW Francis turbine on the right bank of the Baihetan hydropower station. The pressure distribution along the circumference of the top cover was analyzed, and the effects of deviations on the specific generation of hydraulic excitation forces were studied. This research shows that the increase in radial deviation will slightly reduce the output and efficiency, and the radial force on the runner increases parabolically. When the radial deviation is 1.5 mm, the radial force is 5.9 times higher compared to the case without any deviation, and the radius of the fitting circle of the radial force behavior trajectory increases with the increase in radial deviation. In addition, the radial deviation has little effect on the internal flow of the runner and the pressure distribution in the upper crown chamber. The dominant frequency components at the upstream monitoring points include fn, 15 fn, 24 fn, and 30 fn. The dominant frequency components at the downstream monitoring points include the blade passing frequencies of 15 fn and 30 fn. However, with the increase in radial deviation, the fluctuation amplitudes exhibit an asymmetric distribution, the uniformity of the pressure distribution in the circumferential direction of the labyrinth seal area becomes significantly worse, and the waveform of the downstream monitoring points changes significantly and presents a non-uniform distribution in one rotation cycle.

Entropy-based fluid–solid–thermal coupled wear prediction of journal bearing during repeated starting and stopping

The novelty of the present study is to construct an Entropy-based wear and fluid-solid-thermal (FST) coupled model for journal bearings, which reveals the transient interaction behavior between wear evolution and FST evolution during repeated starting and stopping. The wear rate is measured experimentally and the contact temperature, friction coefficient and normal contact force are obtained from the validated FST model. Wear tests for the lubricated journal bearing at three constant speeds are used to validate the predicted wear rate. Numerical calculations give the time-varying wear and FST evolution of journal bearings during repeated starting and stopping at the same or different start-stop time, including wear rate, wear depth, temperature, fluid pressure and contact pressure. The effects of the bearing thickness, maximum speed, radial clearance and load on the wear and FST performances are evaluated. The simulation results reveal that the rate of change of wear rate in the start-stop cycle first increases rapidly and then decreases slowly as the number of start-stop cycles increases. The distributions of the contact pressure and the fluid pressure become wider along the circumferential direction with the increase in the number of start-stop cycles while the maximum values become smaller. The maximum wear depth increases with increasing start-stop time for an identical number of start-stop cycles, and the shorter the start-stop time is, the higher the maximum temperature tends to be. Furthermore, the effect on the maximum wear depth and maximum temperature of journal bearings will become significant when the maximum speed and bearing thickness are relatively small or the radial clearance and load are relatively large.

Residual stress development and thermo-elasto-plastic distortion in brake discs

The relationship between thermo–elasto–plastic deformation during braking and the residual stress in brake discs is investigated experimentally in this study. X-ray diffraction is conducted to validate the residual stress distribution in the depth direction, whereas the cut/sectioning method is used to quantitatively measure the residual stress across a broader disc area. In addition, thermo–elastic distortion is quantified using thermal strain measured using a dynamometer. The compressive residual stress is distributed on both the circumferential and radial surfaces of unused brake discs with a magnitude of approximately 30 MPa, which transforms into a tensile stress exceeding 50 MPa in the circumferential direction after continuous braking tests, thus resulting in thermo–elastic distortion. This distortion is proportional to the tensile stress developed along the braking direction, which is primarily caused by plastic deformation due to external force and temperature gradient from the disc surface and core. The distortion magnitude ranges from 60 to 140 µm, depending on the type of pad material. Thermo–elastic disc distortion can be reduced by releasing tensile stress on the plastically deformed disc surface through abrasive wear using frictional pads. However, the magnitude of the initial compressive stress has minor effect on the distortion. The present experimental study provides insights into factors that affect thermo–elasto–plastic distortion in brake discs as well as methods that can reduce the distortion of brake discs in the design stage.

Buckling stability of variable stiffness composite cylinder shell based on automated fiber placement technology

Automated fiber placement technology (AFP) is the key technology to realize variable-stiffness design that have fiber orientation variation across its in-plane. However, defects such as fiber angle deviation and overlap are inevitable during AFP manufacturing. A finite element model has been developed for variable-stiffness cylinder shell that can investigate the effect of the overlap areas and fiber angle deviation on the buckling stability of variable stiffness cylinder shell. Furthermore, the influence of the design parameters of the curved fiber path and the process parameters such as the tow width, the number of tow feeding, and the overlapping strategies on the buckling performance of the structure was studied by parametric analysis. The results showed under the condition of compression-bending coupling, the buckling performance is improved by the variable stiffness design in which the fiber angle varies along the circumferential direction, the maximum critical buckling load factor of optimal variable-stiffness design [0 /〈30|80〉/ 90 /−〈30|80〉] s is 10771, which is 21.1% higher than that of the optimal normal stiffness design. It is found that increasing the course width reduces the buckling performance of the variable stiffness structure, when the tow width is kept constant. When the course width is kept constant, the buckling performance of the variable stiffness structure increases with the increase of the tow width.

Circumferential modal coupling analysis of orthogonally stiffened cylindrical shell coupled with internal rectangular plate using semi-analytical wavenumber–frequency method

Orthogonally stiffened cylindrical shell coupled with internal rectangular plate is widely applied in engineering industries. The significant effects of the internal plate on vibration signatures of the shell have been demonstrated. Little attention has been paid to vibration analysis in the wavenumber–frequency domain. This paper aims to conduct the circumferential modal coupling analysis of the coupled model using the semi-analytical wavenumber–frequency method. The coupled model is disassembled into the stiffened cylindrical shell and rectangular plate. The interface potential between the shell and rectangular plate is derived based on a unified variational modeling procedure, in which the transformation of the coordinate system must be conducted. The displacement fields of the shell are expanded with the Fourier series along the circumferential direction. The vibratory field in wavenumber–frequency space is analytically obtained. The numerical method is utilized to illustrate the convergence and accuracy of the proposed method. The results demonstrate that the internal plate affects modal characteristics and then results in the alterations of the number and the shifts of resonance peaks. The phenomenon can be demonstrated by the circumferential modal contribution of the vibration response. Besides, it should be noted that the dominant circumferential modes for the input energy and vibrational energy are inconsistent owing to the strong shell–plate coupling effect.

Unified strength-based elastoplastic solution for frost heaving force of cold-region tunnels considering dual non-uniform frost heaving of surrounding rock

Precise evaluation of the frost heaving force and surrounding rock plastic zone is an important basis of the prevention of freezing damage in cold-region tunnels. The temperature gradient along the radial direction of cold-region tunnels surrounding rock results in the dual non-uniform frost heaving of surrounding rock, namely, the gradual change of frost heave ratio along the radial direction and the unequal frost heaving deformation in the circumferential and radial directions. A new elastoplastic solution of tunnel frost heaving force considering double non-uniform frost heave and intermediate principal stress was derived based on the elastoplastic mechanics theory, thick-cylinder theory, and unified strength theory to better guide the frost resistance design of tunnels in cold regions. The rationality and advantages of the unified plastic solution of tunnel frost heaving force were verified by model tests and engineering examples. Results showed that the theoretical calculation value of frost heaving force was in good agreement with the measured value. When the gradual change in the frost heave ratio of surrounding rock in the radial direction was ignored, the frost heaving force and radius of the surrounding rock plastic zone were large and conservative. The solution in this paper can accurately evaluate the tunnel frost heaving force and surrounding rock plastic zone. Finally, this paper studies the influences of intermediate principal stress coefficient, the frost heaving coefficient of unit temperature of frozen surrounding rock, non-uniform frost heaving coefficient in different directions, and maximum freezing depth on the evolutionary law of frost heaving force and plastic zone of cold-region tunnels are studied.

Active and passive mechanical characterization of a human descending thoracic aorta with Klippel-Trenaunay syndrome

A human aorta from a female donor affected by Klippel-Trenaunay syndrome was retrieved during a surgery for organ donation for transplant. The aorta was preserved in refrigerated Belzer UW organ preservation solution and tested within a few hours for mechanical characterization with and without vascular smooth muscle activation. KCl and Noradrenaline were used as vasoactive agents in bubbled Krebs-Henseleit buffer solution at 37 °C. A quasi-static and a dynamic mechanical characterization of the full wall and the three individual layers were carried out for strips taken in longitudinal and circumferential directions. The full wall in the descending portion of the aorta underwent mechanical tests with and without smooth muscle activation. Results were compared to data obtained from healthy aortas and show a reduced stiffness of the full wall in circumferential direction. Also, a significant reduction of the response to vasoactive agents in circumferential direction was observed, while the longitudinal response was similar to healthy cases.

Analyzing vibrational characteristics of fluid-filled symmetric cross-ply delaminated composite cylindrical shells

This study investigates the vibration behavior of delaminated cylindrical shells composed of symmetric cross-ply composite material are partially or completely filled with fluid. An incompressible, non-viscous and irrotational internal fluid is considered. The classical shell theory and Helmholtz’s equation with the velocity potential function are employed to derive the governing equation for the vibration of delaminated symmetric cross-ply laminated cylindrical shells. The primary focus is to understand the impact of varying fluid heights, densities and velocities on the natural frequencies of the shells, as well as the effects of shell length, thickness-to-radius ratio, and delamination’s position in the thickness and circumferential directions. The study findings indicate that the natural frequencies decrease considerably as the height of the fluid increases and that the delamination position significantly influences the observed frequency variations. Moreover, the internal fluid density and shell length affected natural frequencies. This research contributes not only to our knowledge of the behavior of cylindrical shells with delamination and fluid filling but can also assist in designing structures that mitigate undesirable vibrations and promote the creation of more efficient and dependable structures.

3D tunnel reconstruction and visualization through multi-smartphone photogrammetry

Tunnel documentation and inspection are crucial for ensuring public safety. To provide a useful tool in 3D tunnel reconstruction for engineers, we propose a novel multi-smartphone measurement (MSM) system for reconstructing and visualizing 3D tunnel models. This innovative system boasts user-friendly operation, streamlined data capture, and cost-effectiveness as its defining attributes. The system consists of eight smartphones, a controller, a backpack, and software. Different shooting strategies with various overlaps along the longitudinal and circumferential directions are investigated in a pedestrian tunnel. A uniform overlap rate along the circumferential direction can be achieved in the MSM system. By comparing the results with total station measurements, the evaluation of the system’s performance is carried out and assessed from point density and point distance error. The results show that the average absolute point distance errors of the system are less than 0.3 cm under a high overlap and that an overlap along both circumferential and longitudinal directions close to or higher than 50% is recommended for 3D tunnel reconstruction. With the features of easy handling, efficient recording, and low pricing, the MSM system has the potential to provide a useful tool for tunnel visualization and documentation.

Numerical study of critical straight, frown, and chevron incisions in small incision cataract surgery

Introduction: When an intraocular lens (IOL) injector is inserted through a pre-cut corneal incision (e.g., an empirical size of 2.2 mm) during small incision cataract surgery, uncontrollable tearing to the corneal tissue may occur, which is highly associated with the incision shape, size, and location. The goal of this numerical study was to investigate the optimal incision scheme amongst three typical shapes, i.e., straight, frown, and chevron incisions using mechanical modeling and finite element analysis.Methods: Assuming that the damage is caused by the tissue fracture at the incision tips and is governed by the classical energy release rate (ERR) theory which compares the current ERR value subject to IOL injection and the material’s intrinsic parameter, critical ERR Gc.Results: It was found that for chevron incisions, the incision shape with an angle of 170° was superior which induced minimal ERR value, while for frown incisions, the shape with a central angle of 6° was optimal. Both chevron and frown incisions could allow a larger size of injector to inject through than a straight pre-cut. In particular, the frown incision performed the best due to its lowest corresponding ERR and easy operation.Discussion: It was also observed that regions where the embedded fibrils are more dispersed and exhibit high isotropy were more favorable. If necessary, the chevron incision was recommended to be more aligned with the direction exhibiting a larger modulus, for example, along the circumferential direction near the limbus. This study provides useful knowledge in operation design and a deep insight into mechanical damage to corneal wounds in small incision cataract surgery.

3D printed auxetic stents with re-entrant and chiral topologies

The mechanical performance of the medical stent is crucial and of key significance to the dependability and reliability of the stent-plaque-artery system. In this study, an auxetic stent, namely, re-entrant chiral auxetic (RCA) is proposed. Two types of stent (RCA-X and RCA-Y) are proposed. The RCA stents are designed through a periodic distribution of two dimensional (2D) RCA cells along both the circumferential and axial directions. A set of polyimide specimens were 3d printed using Multi-Jet Fusion process. The compressive properties of the 3d printed stents were experimentally examined, while the tensile properties were numerically investigated. Results showed that the RCA-X stent revealed a remarkable radial expansion (i.e. auxetic features) of approximately 50% while the RCA-Y stent showed radial expansion of 16.7%. Despite the auxetic features of the compressed stents, asymmetric deformation patterns were resulted in the case of the RCA-X while uniform patterns were resulted in the case of the RCA-Y. The FE models were further employed to examined the effects of number of unit cells along the circumferential direction on the auxetic features. The auxetic features of the developed stents could be controlled by adjusting the geometric parameters of the RCA’s cell and number of cells along the circumferential direction. The promising properties of the RCA stents might sheds the light on the design auxetic stents for practical clinical applications.

Chloride-induced 3D non-uniform corrosion of steel in reinforced concrete considering mesoscale heterogeneities and early-age cracks

Considering that reinforced concrete structures typically work with cracks, this work aims to investigate the chloride-induced non-uniform corrosion of steel by proposing a five-phase cracked reinforced concrete model at mesoscale, including realistic aggregate, matrix, steel, early-age crack, and damage zone. A physically-based 3D mesoscale modeling approach is developed to accommodate all the phases by integrating gravity-driven compaction and vibration as in real casting procedures. This modeling approach is further developed to capture coupled mass transfer and electrochemical corrosion of steel, enabling simulations of non-uniform corrosion along both the circumferential and longitudinal directions of steel. The considerable variation in corrosion morphology due to aggregate distribution demonstrates the necessity of using 3D mesoscale models to predict steel corrosion. Early-age cracks accelerate the diffusion of corrosive agents, intensifying the corrosion of steel. Increasing the crack width, depth, and length all contribute to a higher dissolution thickness of the steel. With the same crack size, longitudinal cracks result in a larger average dissolution thickness of the steel. In addition, the maximum dissolution thickness of the steel is highly correlated with the degree of pitting corrosion, and in most instances, transverse cracks lead to a higher degree of pitting, causing a greater maximum dissolution thickness.

Evolution mechanism of unsteady internal flow of an ultra-high head pump-turbine in pump mode

In this study, the unsteady flow of an ultra-high-head model pump turbine in pump mode is numerically investigated, revealing the evolution mechanism of unsteady flow diffusion and propagation. Under high-flow-rate and high-efficiency conditions, stable flow separation occurs in the channel of the stay vanes. As the flow rate decreases, the flow separation gradually spreads in the radial direction and expands from the stay vanes to the guide vanes. This causes a partial blockage in the channel of the guide vanes. Meanwhile, the flow separation gradually switches from stable to unstable with a low-frequency rotation (about 4.8 % of the impeller rotational frequency) in the circumferential direction. In addition, the correlation between the hump characteristics and unsteady flow is discussed. For an ultra-high-head pump turbine, the unstable flow initiates at static operating conditions from the pump performance curve with negative slope, which is significantly different from medium and low-head pump turbines.

Anisotropy and relaminarisation of the turbulent flow near a rotating cylindrical cavity wall

AbstractRotor internal cooling is a new concept for high power density electric vehicle drives. A turbulent pipe flow is injected into a cylindrical cavity in the rotor shaft of the motor. The flow is deflected in the cavity, accelerated in circumferential direction by the rotor wall and exits through an annular duct with the outer wall rotating. Due to the opposing effects of rotation on turbulence, a complex transitional flow develops. The strong shear layer in the jet region causes high turbulence production. On the other hand, these fluctuations are damped by the centrifugal forces due to the flow rotation. To investigate the influences of the rotation on the turbulence properties and the mean flow, highly resolved large eddy simulations are performed. It is shown that the turbulence production and attenuation due to rotation affect different components of the Reynolds shear stress tensor. This results in highly anisotropic turbulence. In certain areas, where the turbulence attenuation is strongest, the flow even relaminarises. Since the cooling efficiency depends on the turbulent heat transfer of the flow, the local turbulence characteristics are key quantities for the cooling application.

ON THE USE OF PSP TO DETERMINE THE RIM SEALING EFFECTIVENESS

Abstract The control of cavities sealing has been a challenging problem since early gas turbine development stages and several aspects regarding the flow physics and the modelling of rim seal flows still represent an open question. Fundamental test cases have been used in the open literature to characterize the level of ingestion by varying the main flow parameters and the geometrical features. In most of them, the effectiveness is measured by using taps connected to a gas analyzer used to sample the concentration of a foreign gas on the stator surface used to seed the purge flow. Consequently, the results are usually single point measurements, unsteady effects are inevitably neglected, the intrusiveness of the approach must be carefully checked and the application on the rotor side demands for complex slip-rings or telemetry. To overcome these limitations, the current work presents the application of the PSP technique to the study of hot gas ingestion phenomena on a single stage rotating cold rig. The 2D distributions of partial pressure of oxygen collected through the wide optical accesses present in the rig were then related to the seal effectiveness. The proposed methodology was firstly validated through a comparison with the data obtained from standard gas sampling and then applied as main experimental technique. The analysis of the results highlighted the capabilities of the PSP to fast collect data on both stator and rotor side, including the tip of the seal tooth where non uniform efficiency distributions in the circumferential direction have been detected.

Effect of anisotropic stiffness degradation on the forced vibration of cylindrical shells

Structural defects are commonly encountered in engineering applications. They can significantly affect not only the structural integrity but also the natural frequencies and vibration responses of cylindrical shells subject to external loading. This study proposes a novel concept of stiffness degradation to analyze the effect of defects on the vibration of shell structures. Specifically, stiffness degradation factors (SDFs) are introduced into the model of a cylindrical shell based on Sanders shell theory, and their influences on the dynamic response of an infinite-length cylindrical shell are evaluated by analyzing vibrations at multiple locations. The results show that vertical vibrations at receiver points located away from the driving point are more susceptible to the stiffness degradation, particularly at higher frequencies. The degradation of flexural stiffness has a greater effect on the vibration of cylindrical shells than the degradation of membrane stiffness, particularly in terms of the resonant frequency decrease. Furthermore, stiffness degradation in the circumferential direction has a greater effect on shell vibration than in the longitudinal direction. By examining the effects of eight SDFs separately, it is revealed that the vibration response of a cylindrical shell is affected by the directions and types of stiffness degradation, the frequency range, and the observation point. Overall, this study provides a general analytical framework for analyzing the vibration response of cylindrical shells including the effect of anisotropic stiffness degradation, which could be applied to composite shell structures with directional fiber orientations and shell structures with various defect modes.

The investigation of shrinkage cracking of paste and mortar based on the eccentric ring test and multiphysics simulation

The eccentric ring test presents a novel approach to evaluating the occurrence of shrinkage cracking in cementitious materials. The eccentric ring test has been confirmed to induce cracks on the thin sides of the specimen. However, the underlying mechanism behind this cracking phenomenon remains inadequately explored. In this study, the eccentric ring test is used to examine cement paste with different water-cement (w/c) ratios and mortar with varying aggregate volume fractions. The examination focuses on the influence of surface sealing and immersion curing on shrinkage cracking. The integrated shrinkage model, which is applicable to both autogenous shrinkage and drying shrinkage, is introduced to simulate the shrinkage of cementitious materials. The shrinkage cracking of eccentric specimens is further investigated through a multiphysics coupling analysis that considers shrinkage, humidity field, and stress field. The simulation results show that the humidity decreases more rapidly on the thinner sides during the shrinkage of the eccentric ring. The circumferential stress in the specimen is much greater than the radial stress. Additionally, the tensile stress in the circumferential direction exceeds 4 MPa on the outer ring. As the drying time increases, the circumferential tensile stress on the thin sides of the eccentric ring develops more rapidly, resulting in cracking on the thin side. The eccentric ring test is practicable in ordinary concrete and high-strength concrete, and the simulation is of significance in examining the cracking risk of concrete pipes and some thin wall components since these components are sensitive to the shrinkage cracking.