Internal Pressure Force Research Articles

Research on the Mechanism of Femtosecond Laser Ablation Concave-Convex Microstructure Transformation.

The phenomenon of femtosecond laser ablation of convex structures from the bottom to the top is interesting. In this study, AZ31B magnesium alloy was used as the substrate to analyze the impact of the laser pulse energy and scanning speed on the morphology of concave-convex microstructures. Subsequently, a unified two-dimensional numerical model incorporating solid, liquid, and gas phases was established, and combined with experimental data, the mechanism and formation process of concave-convex transformation in magnesium alloy under laser ablation were revealed. The results indicate that the transition from concave to convex structures is significantly influenced by the laser scanning speed, whereas the laser pulse energy primarily affects the shape and size of the convex structures. During the ablation process, molten material is expelled and gradually accumulates on both sides of the ablation groove under the action of the recoil pressure. During cooling, the molten material at both ends of the groove merges to form protrusions under the combined effects of internal negative pressure, gravity, and Marangoni forces. Moreover, this method of femtosecond laser ablation for generating convex structures deviates from the traditional single-texture approach to concave structures, potentially broadening the application of laser composite processing surfaces.

Study of transient pressure and fluctuation characteristics in a centrifugal pump using the delayed detached-eddy simulation method

This study employed OpenFOAM, the delayed detached-eddy simulation (DDES) turbulence model, and structured grids to develop numerical models for three centrifugal pumps with twisted blades. The internal pressure field, velocity field, forces, and fluctuation characteristics of the centrifugal pumps are comprehensively analyzed under various operating conditions. The findings indicate that the pressure is relatively higher in the flow passages near the volute tongue and the outlet within the impeller. Regions of high relative velocity (slip velocity) are mainly found on the suction side of the blades, indicating that the design of the blade suction side affects the fluid outward slip performance. As the flow rate increases, the forces and force fluctuation amplitudes of each pump component also rise. Conversely, as the rotational speed increases, the force on the blades or impeller gradually increases while the fluctuation amplitude decreases. In the stationary domain, the force on the volute gradually decreases while the fluctuation amplitude of this force increases. The shape of the volute tongue influences the rate at which pressure inside the volute is converted to outlet pressure. The power spectral density (PSD) of pressure fluctuations is smallest at the nominal flow rate, displaying a clear and distinct axial frequency pattern without complex low-frequency fluctuations. Under low flow and high-speed conditions, the PSD at the axial frequency is relatively small, whereas the pressure PSD at other low frequencies is relatively large. This indicates instability in the flow under these conditions.

Limit state equation and failure pressure prediction model of pipeline with complex loading

Assessing failure pressure is critical in determining pipeline integrity. Current research primarily concerns the buckling performance of pressurized pipelines subjected to a bending load or axial compression force, with some also looking at the failure pressure of corroded pipelines. However, there is currently a lack of limit state models for pressurized pipelines with bending moments and axial forces. In this study, based on the unified yield criterion, we propose a limit state equation for steel pipes under various loads. The most common operating loads on buried pipelines are bending moment, internal pressure, and axial force. The proposed limit state equation for intact pipelines is based on a three-dimensional pipeline stress model with complex load coupling. Using failure data, we investigate the applicability of various yield criteria in assessing the failure pressure of pipelines with complex loads. We show that the evaluation model can be effectively used as a theoretical solution for assessing the failure pressure in such circumstances and for selecting appropriate yield criteria based on load condition differences.

Correlations to estimate the ground loading from small scale propane BLEVE experiments

This paper presents small-scale propane BLEVE (Boiling Liquid Expanding Vapor Explosion) experiments coupled with an investigation into ground loading dynamics. The experiments utilized cylindrical aluminum pressure vessels, with a diameter of 50 mm and a length of 300 mm. The controlled variables included burst pressure, liquid fill level, and weakened length. Both high and low-speed measurements of internal pressure and ground force were conducted during the experiments. The dependent variables analyzed were peak total ground load, force duration, and impulse. The findings from the study show trends in ground force and impulse with alterations in failure pressure, fill level and weakened length. Specifically, ground force and impulse exhibit an upward trend with increasing failure pressure, fill level and weakened length (cut length). For the first time, comprehensive correlations have been developed, incorporating the controlled variables, as well as theoretical boiling wave speed and vapor speed, to estimate the dependent variables, which represents a significant contribution in the field. However, the study does acknowledge the presence of scatter in the data, which are believed to be associated with the intricacies of the vessel opening process. It should be noted that this correlation has not been validated for larger scales. Once validated on a larger scale, these correlations can be directly applied in the design and practice of civil infrastructure to enhance the structural integrity. Additionally, the research has direct implications for industrial applications, allowing for the quantitative assessment of risks associated with bridge collapse during the transportation of PLGs.

Bulging of dielectric elastomer tubes considering residual stress and viscoelasticity

This paper investigates the impacts of residual stress and viscoelasticity on the bifurcation and post-bifurcation behaviors of dielectric elastomer tube actuator (DETA) with finite thickness. A theoretical model with residual stress is developed to analyze the electromechanical (EM) behavior of a DETA under a combined effect of voltage, internal pressure, and axial force loadings. A mathematical derivation of the bifurcation condition for the DETA under EM coupling loadings is presented, and a coexistence phase transition condition for steady bugle propagation is established. The effects of voltage, axial force, and residual stress on the bifurcation and coexistence phase transition conditions are studied. To validate the theoretical predictions, finite element (FE) simulations are performed on a closed-ended DETA subjected to the EM loadings. The results reveal a competitive relationship between the localized bugling and electric breakdown (EB). The large residual stress can inhibit the localized bugling and enhance the stability of the tube. Additionally, we explore the bifurcation behavior of the viscoelastic DETA, revealing that the viscoelastic effect significantly influences the critical pressure of bifurcation and the loading/unloading paths. It is observed that snap-back instability can occur during the unloading process under high loading rates or voltages. This work provides valuable insights into the finite deformation and bifurcation behaviors of the DETA under complex EM coupling loadings.

Finite element analysis of the knee joint stress after partial meniscectomy for meniscus horizontal cleavage tears

ObjectiveTo establish a finite element model of meniscus horizontal cleavage and partial resection, to simulate the mechanical changes of knee joint under 4 flexion angles, and to explore what is the optimal surgical plan. MethodsWe used Mimics Research, Geomagic Wrap, and SolidWorks computer software to reconstruct the 3D model of the knee joint, and then produced the horizontal cleavage tears model of the internal and lateral meniscus, the suture model, and the partial meniscectomy model. These models were assembled into a complete knee joint in SolidWorks software, and corresponding loads and boundary constraints were added to these models in ANSYS software to simulate the changing trend of pressure and shear force on femoral condylar cartilage, meniscus, and tibial cartilage under the flexion angles of 0°, 10°, 20°, 30° and 40° of the knee joint. At the same time, the difference of force area between medial interventricular and lateral interventricular of knee joint under four states of bending the knee was compared, to explore the different effects of different surgical methods on knee joint after horizontal meniscus tear. ResultsWithin the four medial meniscus injury models, the lowest peak internal pressure and shear force of the knee joint was observed in the meniscal suture model; the highest values were found in the bilateral leaflet resection model and the inferior leaflet resection model; the changes of pressure, shear force and stress area in the superior leaflet resection model were the most similar to the changes of the knee model with the meniscal suture model. ConclusionSuture repair is the best way to maintain the force relationship in the knee joint. However, resection of the superior leaflet of the meniscus is also a reliable choice when suture repair is difficult.

Dynamic response of deepwater test string under fluctuations in axial force and internal pressure

In this study, a mechanical model suitable for deepwater test string was proposed. An analysis of the dynamic response of the test string under different frequencies, different water depths and different fluctuation amplitudes was carried out by using the finite element method based on the change in the internal pressure and axial force measured. The results of the analysis showed that the response parameters (maximum stress and maximum deformation) tended to be stable after one period of fluctuation in the axial force and half a period of fluctuation in the internal pressure, respectively. When a sine waveform fluctuation in the internal pressure and axial force occurred, the response parameters increased with an increase in the amplitude of the fluctuation and increased with an increase in the frequency of fluctuation, and the amplitude of variation decreased with an increase in the fluctuation period. Under fluctuation in the axial force, the response parameter decreased with an increase in the water depth. The response parameter decreased first and then increased with an increase in the water depth when the fluctuation in the internal pressure occurred with a sine waveform. The maximum deformation and stress of the test string always changed with a change in the load when the fluctuation in the internal pressure and axial force had a sine waveform, and the test string under a load with a sine waveform was prone to periodic fatigue failure. The relevant conclusions provide a basis for the analysis and prevention of fatigue failure in test strings.

The ratcheting effect on the SS316L U-shaped pipe under internal pressure and bending cycle

The ratcheting behavior refers to the progressive accumulation of strains resulting from the cyclic loading applied to the specimens. Nowadays, much attention has been devoted to ratcheting pipelines. Hence, the ratcheting behavior of the SS316L U-shaped pipe subjected to internal pressure and cyclic bending force is investigated here. The experiments use the Servo-hydraulic device of Zwick/Roell Amsler HB 100. The local strains at the internal, external, and lateral bending points are specified using the pipe strain gauges. Then, the effect of the internal pressure, average force, and force amplitude on the ratcheting strains are examined and compared. The numerical simulation also employs the Abaqus software and the isotropic/kinematic nonlinear hardening model. It was revealed that ratcheting strain in the axial direction is more critical than in the pipe's peripheral direction. The effect of amplitude and average pressure on thin-wall the ratcheting behavior of thin-wall pipe in the axial direction during four thousand cycles are investigated. According to the observed results, increasing amplitude and average bending force while the internal pressure is constant increases the ratcheting strain. Besides, the variation of the force amplitude affects the ratcheting strain more significantly than the variation of the average force. In order to validate the obtained results, a careful comparison was made between the numerical and experimental results, and a good agreement was observed between them. Notably, the novelty of this study lies in the comprehensive analysis of the ratcheting behavior of the SS316L U-shaped pipe conducted here.

Determination of mixed-mode stress intensity factors for axial crotch corner cracks at cylindrical vessel to nozzle intersections under internal pressure and nozzle loads

In this study, Stress Intensity Factors (SIF) of quarter circle and semi elliptic cracks at the crotch corner of the intersection between a cylindrical pressure vessel and a radial nozzle have been computed for combinations of the actions of internal pressure and external forces on the nozzle. Until now, practitioners have used simplified solutions for SIFs available from the literature, such as the Newman-Raju equations for the mode I SIF produced by an internal longitudinal semi-elliptical crack in a cylinder, to approximate the SIF produced at a crotch corner crack. These equations do not take into account the effect of the opening of the cylinder for the nozzle and the resulting stress distribution along the cylinder. As a result, there is uncertainty about the validity of using these simplified solutions in engineering critical assessments and a more exact determination of the SIFs for crotch corner cracks would be beneficial.The mode I, II and III stress intensity factors have been determined for crotch corner cracks for a single size of vessel and are presented as a function of variables such as location on the crack front, crack size and aspect ratio (a/c), crack angle with respect to the axis of the vessel, and the magnitude of internal pressure and external forces. The results are presented in graphical form. The study concludes with the recommendation that the analysis be extended to a wider range of vessel and nozzle parameters.

Experimental Study of Hydroformed Al6061T4 Elliptical Tube Samples under Different Internal Pressures

In order to achieve crack free elliptical shape under controlled conditions, an experimental set-up was designed and fabricated. This setup consists of three hydraulic cylinders, an intensifier, a hydraulic power pack, storage tanks, forming die, and all parts are controlled by a Programmable Logic Controller (PLC) system. The elliptical samples can be achieved through proper control of internal pressure and axial force with proper sealing. Experimental work has been carried out with different magnitudes of internal pressure and constrained conditions of axial force. Initially die of elliptical shape has been designed and modeled in Abaqus to successfully achieve the particular shape of the Al6061T4 tube under different internal pressure. The fabricated tube hydroforming machine set-up is highly effective for forming 0.5 mm-2 mm thick Al6061T4 alloy tube samples. The Experimental test has been carried out at 12.7 mm outer diameter, 175 mm length and 0.5 mm thick Al6061T4 samples. Bulge height parameters measured at different points of regular distance gap on the axial direction of the tube length and corner radius found at different pressures range of the samples are plotted under different internal pressures. Samples having an 18.7 mm major elliptical bulge were achieved during the experiment. The experimental data was validated by simulation results.

Uncertainty measurement and research of Finite element analysis of Water Jet data based on Internet of Things

Nowadays, the concept of energy saving and water saving is deeply rooted in people’s minds, so it is necessary to promote efficient water-saving irrigation technology. Sprinkler irrigation is an efficient water-saving method, which is relatively uniform and does not affect the structure of the soil. It saves time and labor to irrigate fields, and has been used in more and more areas in China. The Internet of things technology is used to establish monitoring sites, collect and transmit water information, study and analyze crop fertilization and irrigation water volume, and achieve the purpose of saving water, fertilizer and labor. In test site traffic and sprinkler relationship between speed and pressure test, flow and in different pressure conditions were measured under different conditions of running speed, observe the fluid flows through the three links of pipe head loss and energy loss of the tee to the role of the internal pressure and axial force and other force, high stress concentration areas vulnerable to damage. The hydraulic characteristics in the process of water spraying are studied. The numerical simulation in this paper is completed by finite element software, and the hydraulic characteristics of the three-way pipe are analyzed by finite element to optimize the structure of the three-way pipe.

Isothermal hot tube material characterization – Forming limits and flow curves of stainless steel tubes at elevated temperatures

A new isothermal hot-tube-bulge test as well as a modified pressurized-tube-tensile test are presented to characterize forming limits of tubular materials at elevated temperatures – up to 1000 °C. By controlling temperature, internal pressure, and axial force the complete forming limit curve is determined under isothermal, frictionless conditions and nearly linear strain paths. In the hot-tube-bulge test, a tangential localization forms before failure, marking a forming limit. In the pressurized-tube-tensile test, an axial localization occurs. For the former, a new method for estimating the forming limit was developed whereas the later can be evaluated by standardized methods. The resulting forming limits are at comparable levels to those known from literature, while the new hot-tube-bulge test overcomes the uncertainty which arises from friction in other test setups. The materials used for the investigations are the ferritic and martensitic stainless steels X2CrTiNb18 and X12Cr13, respectively. The hot-tube-bulge test is examined for its suitability in determining flow curves. An empirical-analytical model is introduced to determine the stress components. It is based on tangential and meridional force equilibria, taking the internal pressure and the projected effective areas into account. Flow curves up to effective plastic strains of 0.5 are determined, exceeding the maximum strain of common hot tensile-test by a factor of 2. The strain-rate dependent stress-strain data was used to identify the parameters of a simplified Hensel-Spittel approach. This allows the prediction of isothermal flow curves with varying strains and strain rates at a temperature of 1000 °C.

Computational assessment of upper airway muscular activity in obstructive sleep apnea – In vitro validation

Neuromuscular control of the upper airway contributes to obstructive sleep apnea (OSA). An accurate, non-invasive method to assess neuromuscular function is needed to improve surgical treatment outcomes. Currently, surgical approaches for OSA are based on airway anatomy and are often not curative. When the airway surface moves, the power transferred between air in the airway lumen and the structures of the upper airway may be a measure of airway neuromuscular activity. The aim of this study was to validate power transfer as a measure of externally applied forces, representing neuromuscular activity, through cine computed tomography (CT) imaging and computational fluid dynamics (CFD) analysis in a 3D-printed airway model. A hollow elastic airway model was manufactured. An insufflation/exsufflation device generated airflow within the model lumen. The model was contained in an airtight chamber that could be positively or negatively pressurized to represent muscular forces. These forces were systematically applied to dilate and collapse the model. Cine CT imaging captured airway wall movement during respiratory cycles with and without externally applied forces. Power transfer was calculated from the product of wall movement and internal aerodynamic pressure forces using CFD simulations. Cross-correlation peaks between power transfer and changes in externally applied pressure during exhalation and inhalation were −0.79 and 0.95, respectively. Power transfer calculated via cine CT imaging and CFD was an accurate surrogate measure of externally applied forces representing airway muscular activity. In the future, power transfer may be used in clinical practice to phenotype patients with OSA and select personalized therapies.

Nonlinear deformation and instability of a dielectric elastomer tube actuator

The mechanical response and electromechanical instability (EMI) of a dielectric elastomer tube actuator (DETA) under the coupling loadings of voltage, internal pressure and axial force are studied in this paper. Based on the Gent model and considering the nonlinear relationship between dielectric permittivity and stretches, two different loading conditions are discussed: force tuning and voltage tuning. For the force tuning, it is found that the radius of the DETA first decreases, then increases and finally decreases due to the competition between the axial force and voltage as well as the strain-stiffening property of the Gent model under the large deformation. For the voltage tuning, the effects of axial force, internal pressure and electrostrictive coefficient on the electromechanical response are explored. The electrical breakdown (EB) during the nonlinear deformation of DETA is also analyzed. The stress distribution along the thickness of the DETA is given by the analytical solution, and the two failure modes including EMI and loss of tension for the DETA are studied with axial constraints. It is found that the EMI can be eliminated by changing the stretch in the z-direction and internal pressure, which may also lead to the failure of loss of tension. The competitive relations of the two failure modes are discussed in detail. This work can contribute to the design of DETAs with a large actuation.

Finite element analysis of different fixation methods of screws on absorbable plate for rib fractures.

Multiple rib fractures caused by trauma are common injuries and the internal fixation methods of these injuries have been paid more and more attention by surgeons. Absorbable plates and screws are the effective way to treat rib fractures, but there are no reports on which type of screw fixation method is most effective. In this study, finite element analysis was used to study the effects of five different types of screw fixation methods on anterior rib, lateral rib and posterior rib. The finite element model of the ribs was reconstructed from CT images, and the internal pressure (40 kPa) and intercostal force (30 N) on the surfaces of the ribs were simulated accordingly. An intercostal force of 30 N was applied to the upper and lower surfaces of the ribs to simulate the effect of intercostal muscle force. The pressure of 40 kPa was applied to the inner surface of the ribs, and the normal direction was applied to the inner surface of the ribs. The positive direction was considered inspiratory pressure, and the negative direction was considered expiratory pressure. The results indicate the optimal type of screw fixation on the absorbable plate for rib fractures, and provide a basis and reference for clinical application.

Deformation behavior of advanced high strength steel with different strain hardening exponents during tube hydroforging

Hydroforging is an innovative forming method used to form tubes with irregular cross-sections by using internal fluid pressure and axial force. Normally tube forming operations use solid mandrel to expand/bend the tube which does negative effect on tube or mandrel due to friction, buckling, and wrinkling. In this study, the tube material with various strain hardening exponents were hydroforged in a two-step numerical analysis with ramped fluid pressure and axial compression. The tube will be allowed to bulge with a ramped internal pressure and then shaped to a maximum expansion ratio by the axial compression in the shaping step. Some advanced materials exhibit the change in strain hardening exponent based on the plastic strain, the study focuses how the strain hardening exponent affects the deformation mechanics in tube hydroforging. It was found that the formability of tube during hydroforging is affected by the strain hardening exponent. The results show that tube can achieve a greater wall thickness reduction with increase in strain hardening exponent. Also, higher strain hardening exponent allowed tube to achieve a greater expansion ratio when axially compressed in the forging step. It was also observed that as the strain hardening exponent increases, the internal pressure requirements for the bulging and shaping steps decrease. The two model configurations of N01 and N02 failed from bursting and wrinkling, respectively, while every other model could form to the targeted disk-like shape. The forging step of the process showed that the die force for axial compression decreased as the strain hardening exponent increased for all successful models.

Choice of complex equivalent stress for two different variants of the plane stress state

To describe the creep rupture process under the complex stress, various equivalent stresses have been considered. From them, the equivalent stress has been selected, at which the total error of the difference between the experimental and theoretical values takes the smallest value among the considered equivalent stresses. Three basic equivalent stresses have been considered, as well as two complex equivalent stresses, which are a linear combination of two basic ones with one material parameter. The analysis of the total errors in the considered experimental data has showed that with the simultaneous effect of internal pressure and axial force on the wall of tubular specimen (or biaxial tension of a plane element), an complex equivalent stress should be used in the form of a combination of the maximum normal stress and the Mises stress. At simultaneous torsion and tension of tubular specimen (or simultaneous tension and compression of a plane element), an complex equivalent stress should be used in the form of a combination of the maximum normal stress and the doubled maximum tangential stress.

Investigation of the External Loads Applied on the PVC and PE Pressurized Pipes

The irrigation systems, water supply system, sewage water system ….etc. Dealing with many types of pipes and fittings depending on the applications. The current study was concert on test the polyethylene (PE) and polyvinyl chloride (PVC) pipes experimentally and theoretically under external loads and internal pressure to simulate the application conditions of pipes which are buried under ground used to transit the fluid under pressure such as drink water, sewage water or any other purpose and find out the deformation, stress and strain due to this loads. The tested was carried out for two size (actual and standard) of the two pipes (PE and PVC). The external load represented by a force in range (10-50KN), and the internal loads represented in pressure in range (5-20 bar). In the experiment a hydraulic press was used to supply the external load and hydraulic pump to supply the internal pressure with two adapter on the two end of tested pipe. The results showed that the deformation, stress and strain increase with increase in internal and external loads and the peak values of that were in the maximum internal and external loads (20 bar internal pressure and 50KN external force), also the experimental tests match the numerical calculation for both actual and standard size.

Retracted: “Evaluation of the Structural Integrity of Bell–Spigot Joints in Steel Gas Pipelines” [ASME Journal of Pressure Vessel Technology, 2022, 144(2), p. 021801; DOI: 10.1115/1.4052210

Abstract The most common joining method in steel gas pipelines is welding; however, this method involves time-consuming, expensive manufacturing and assembly processes to ensure quality in operation. Bell–Spigot joints, which work by mechanical interference, have started to be used as an alternative joining method in steel pipes. Its use has increased due to its reduced assembly time and fewer postassembly inspection requirements. In this paper, the structural performance of Bell–Spigot joints in 16-in. steel pipe API 5 L X70 with fusion bonded epoxy coating for Natural Gas transmission pipeline are evaluated experimentally and by modeling. Test pieces were taken from the gas pipeline after 3 years of operation. Then, tensile pull-out and bending with hydrostatic pressure tests were performed to replicate operating conditions. Deformations, displacements, and the potential presence of leaks were monitored. Experimental results were compared with a finite element method model. Finally, an analytical model for the calculation of stresses and strains in the joint system's components was developed. It was determined that the tightness of the joint depends mainly on the radial interference and the interference length. A higher safety factor can be obtained at the Bell–Spigot joint than the base pipeline by optimizing the selection of joint design variables and the service loading conditions. If the interference pressure is lower than half of the operation pressure, the joint's mechanical strength will be higher or equal that the base pipe. Under interference pressure at operating pressure conditions, the most vulnerable component is the Bell due to the increased stresses acting on it, while the operating pressure relieves the stresses on the Spigot due to the interference pressure acting in the opposite direction. Under combined loading of internal pressure and external bending force, the base pipeline is the most susceptible component to fail. Therefore, the use of Spigot–Bell joints reduces assembly times and costs in steel gas pipelines while providing a safe and reliable joint under operating conditions.

Experimental and numerical investigations on crack propagation characteristics of rock-like specimens with preexisting flaws subjected to combined actions of internal hydraulic pressure and shear force

Experimental and numerical investigations on crack propagation characteristics of rock-like specimens with preexisting flaws subjected to combined actions of internal hydraulic pressure and shear force