Axisymmetric Finite Element Model Research Articles

Plastically Deformed Tubes Subjected to Mechanical Expansion Processes

In engineering, the stress state of expanded tubes is crucial for ensuring structural integrity and preventing stress corrosion cracking. The analysis of stresses and strains in tubes subjected to mechanical expansion using an ogive bullet is essential, yet existing theoretical methods for estimating the stress distributions, especially with spherical and ogive shapes, are sparse. This study explores the expansion of 3/8 inch copper and stainless-steel tubes using an expanding bullet, where tangential and longitudinal strains are measured. A novel analytical approach is introduced to evaluate the stresses and strains, segmenting the tube into three zones, each analyzed with a distinct theory. Validation is achieved through an axisymmetric finite element model that employs a multi-linear kinematic hardening material behavior. The analytical model also estimates the expanding mandrel’s push force, which is then compared with the results from numerical simulations and experimental data, showing good agreement across methods.

Effect of shielding of eddy current probes on the sensitivity for sweep frequency measurements

Eddy current measurements are prone to edge effects when measurements are carried out near a sample boundary. In order to reduce these edge effects, typically ferrite shields are used which constrain the magnetic field within the shield volume. However, their effects on sensitivity towards changes in conductivity for Sweep Frequency Eddy Current (SFEC) measurements have not been investigated. A 2D axisymmetric Finite Element Model (FEM) has been developed to predict the frequency response of impedance of SFEC probes. The model predicted that the addition of shields minimized edge effect but with reduced sensitivity. A simulation study is carried out to optimize the probe design to increase the sensitivity of shielded ferrite probes. Based on these results, a probe is constructed with a custom ferrite shield and its shielding efficiency and probe sensitivity are compared experimentally with those for the probe with conventional ferrite shields.

Embankments Reinforced by Vertical Inclusions on Soft Soil: Numerical Study of Stress Redistribution

Constructing embankments over soft soils is a challenge for geotechnical engineers due to large settlements. Among diverse ground-improvement methods, combining piles and geosynthetics (e.g., geosynthetic-reinforced piles, deep cement mixing columns, geotextile-encased columns) emerges as a reliable solution for time-bound projects and challenging ground conditions. While stress distribution within pile-supported embankments has been extensively studied, the load transfer efficiency of piled solutions with geosynthetic reinforcement remains less explored. The novelty in this study lies in the investigation of three different inclusion solutions from a common control case in the numerical model considering the role of geosynthetic reinforcement. This study investigates the load transfer mechanisms in embankments supported by various techniques including geosynthetic-reinforced piles, deep cement mixing columns, and geosynthetic-encased granular columns. Two-dimensional axisymmetric finite element models were developed for three cases of embankments supported by vertical inclusions. Numerical findings allow clarification of the soft ground and embankment characteristics which influence the arching and membrane efficiencies. Rigid piles outperform deep cement mixing (DCM) columns and geotextile-encased columns (GEC) in reducing settlements of soft ground. Geosynthetic reinforcements are particularly helpful for rigid pile solutions in high embankments due to their load transfer capability. Additionally, physical properties of fill soil can impact the inclusion solutions, with high shear resistance enhancing the arching effect and lower modulus subsoils showing better arching performance.

Effects of rotation on the rolling noise radiated by wheelsets in high-speed railways

Railway rolling noise is produced by the vibration of both the wheelsets and the track; the wheelsets dominate the high frequency noise and become increasingly important at high speed. The effect of rotation on the wheelset vibration and noise radiation is investigated using different wheelset models in a rolling noise prediction model for a wide range of speeds. Each wheelset model takes account of the rotation to a different extent. An axisymmetric finite element model of a flexible rotating wheelset is implemented based on a complex exponential formulation and expressed in either an inertial or a non-inertial frame of reference. The model can include the inertial Coriolis and centrifugal forces and is also extended to include stress stiffening. Modes of the rotating wheel with non-zero number of nodal diameters are split into co- and counter-rotating waves with separated natural frequencies. The extent of the frequency separation depends on the shape of the mode and its dominant component of vibration. At common train speeds the frequency shifts due to stress-stiffening and spin-softening effects are found to be small compared with the gyroscopic effects due to the Coriolis forces. The effect of including the inertial Coriolis and centrifugal forces on the overall A-weighted sound power level is less than 0.3 dB below 400 km/h, while for higher train speeds, differences may exceed 1 dB in some one-third octave bands. Overall, these differences are small compared with other sources of uncertainty in rolling noise modelling, confirming that representing the wheel rotation with a moving load approach provides a suitable approximation for use in rolling noise predictions.

On the re-evaluation of the clamped members stiffness of bolted joints

To address the structural integrity of bolted joints and verify their capacity to withstand external loads and relaxation resulting from thermal expansion difference and creep, proper evaluation of the axial stiffnesses of bolt and clamped members are of vital importance. A number of finite element (FE) based methods are available for the calculation of the stiffnesses of joint elements, most of which rely on the displacement of arbitrarily selected nodes that has led to the improper evaluation of joint stiffness values. In this paper, the stiffness of clamped members is evaluated by a simple FE methodology using a known bolt stiffness evaluated separately. Two load cases, one based on the application of external force (mechanical loading) and the other on temperature (thermal loading), are conducted using the FE method to validate the obtained results. The proposed methodology is also compared with other FE models and analytical methods obtained from the literature. The new technique is based on axisymmetric FE modeling and is applied to bolted joints with bolts ranging from M6 to M36 having various grip lengths. Finally, the stiffnesses of the bolt and clamped members can be determined accurately, and a general formula is proposed to evaluate the stiffness of clamped members.

Numerical Modelling and Predicting Performance of Geogrid-Reinforced Low-Volume Unpaved Roads over Soft Subgrades

AbstractPavement performance is usually predicted by large-scale laboratory experiments, expensive field tests and/or comparatively cheaper numerical modelling alternative. In this study, a finite element limiting strain model has been developed to investigate the strain response of both unreinforced and geogrid-reinforced pavements on unpaved roads where the geogrid is placed at the bottom of the unbound granular base layer. A two-dimensional (2D) axisymmetric finite element model (FEM) is used to analyse the behaviour of both unreinforced and geogrid-reinforced granular base. The critical pavement responses (vertical surface deformation, compressive strain and compressive stress at the top of subgrade, etc.) are simulated numerically using ABAQUS. These critical responses are used to develop the pavement performance models (strain limiting models) and to predict long-term service life of pavement or the reduction of thickness of granular base for equivalent service life or a combination of both. The parametric results are then used to develop design charts to aid practitioners to use directly in designs. The numerical model is verified using published literature-based information and found to be reasonable. The results show that the traffic benefit ratio (TBR) of 3.1 at a 20 mm rut depth can be achieved for a thin granular base built over soft subgrade using a medium stiff geogrid.

Airfield pavement resiliency assessment against extreme dynamic events by explicit axisymmetric finite element models

Infrastructure resiliency has become an essential element in ensuring community recovery after unexpected events. In airfield pavement, resilience can be achieved through an improved design approach by understanding the fundamental elements of damage mitigation and thus allowing rapid recovery. The objective of this study was to numerically evaluate easy-to-implement alternatives for mitigating damage in rigid airfield layered pavement systems when subjected to dynamic events such as blasts or high-velocity impacts. This was accomplished by developing an efficient axisymmetric explicit finite element model, which served as an analytical tool for the study. The model was developed in LS-DYNA and the methodology consisted of a comprehensive parametric analysis. The results showed that the concrete pavement layer parameters—mass density and compressive strength—have the most significant effect on the damage to the pavement when subjected to extreme dynamic events. The material parameters for the pavement layers were optimized to minimize the damage, caused by dynamic loads, achieving more than 70% damage mitigation. Furthermore, adding a granular base layer to the rigid airfield pavement design reduces the concrete pavement layer damage by almost 40%. An asphalt concrete overlay reduces the concrete pavement layer damage by about 55%. Moreover, adding an asphalt concrete overlay to the optimized rigid airfield pavement design reduces the damage by 10%. In contrast, adding a granular base layer to the optimized rigid airfield pavement design is ineffective.

Numerical investigation of effects of nickel-base alloy overlay size on the welding residual stresses in an austenite stainless steel narrow-gap girth weld

Based on the experimental measurement of the residual stress in the nickel-based alloy overlaid stainless-steel narrow-gap girth weld, an axisymmetric finite element (FE) model was established to simulate the residual stress in the girth weld to verify the model. Then a large number of numerical simulations were carried out with the verified FE model to study the effects of the size (height and length) of the nickel-based alloy weld overlay on the residual stress in the girth weld. The optimal overlay sizes to achieve sufficient depth of the compressive stress were investigated. The results show that as the overlay height increases, the hoop compressive stress depth from the inner wall at the weld centerline increases, while the range of the axial compressive stress distribution decreases. The hoop and axial compressive stress depths at the weld centerline increase as the overlay width increases, while the depth of the hoop compressive stress remains unchanged when the overlay width reaches a critical value. The effect of the overlay height on the hoop stress is greater than that of the overlay width, and it is more difficult to mitigate the axial stress by increasing the width of the overlay layer with a large overlay height. For the narrow-gap 304 stainless-steel pipe girth weld with a size of Ø273 mm × 28 mm, the optimum nickel-based alloy overlay is 14 mm in height and 210 mm in width, which can cause both hoop and axial stresses at the inner wall to be compressive, and the hoop compressive stress depth from the inner wall reaches 88 % of the pipe wall thickness and axial compressive stress depth reaches 78 % of the wall thickness.

Thermal stress analysis of laser cleaning ofaluminum alloy oxide film.

In this paper, a theoretical model for laser cleaning of aluminium alloy oxide film is presented from the perspective of thermal stress. Additionally, we developed a two-dimensional axisymmetric finite element model for calculation. Thermal stresses result from thermal expansion. Using thermodynamic equations, numerical calculations enablethe determination of a theoretical cleaning threshold by comparing the thermal stresses to the adhesion between the oxide film and the substrate. Through theory and experiments, it is known that the greater the laser fluence, the better is the cleaning effect. The findings indicate that cleaning of the oxide film on aluminum alloys can be achieved under appropriate parameters. The cleaning threshold for laser cleaning of the oxide film is determined to be 3629.47J/c m 2 (continuous laser fluence is 3628.73J/c m 2; nanosecond laser fluence is 0.74J/c m 2). The thermal stress model of laser cleaning is highly useful for selecting the appropriate laser flux in practical applications. Both a simulation and experimental results can provide an explanation for the mechanism of interaction between the laser and the aluminum alloy oxide film, demonstrating that thermal stress is one of the cleaning mechanisms during the laser cleaning process of the oxide film.

Inspecting the role of vapour loss and other model strategies in the mod-elling of a bentonite thermo-hydraulic cell

Inspecting the role of vapour loss and other model strategies in the mod-elling of a bentonite thermo-hydraulic cell

A numerical model for stress relaxation analysis of sealing systems in nonbonded pipe end fittings

Nonbonded flexible pipes consist of polymer materials that experience stress relaxation at high temperatures, which ultimately affects the sealing performance of end sealing systems. To assess stress relaxation curves under varying temperatures and pre-strains, this paper conducts both tensile and stress relaxation tests on PVDF materials. To describe the stress relaxation characteristics of these materials, the Prony series is utilized. In order to identify the parameters of the series, the paper employs the Levenberg-Marquardt method of nonlinear regression. A finite element model is established to verify the accuracy of the parameter identification method. Subsequently, the paper establishes a two-dimensional axisymmetric finite element model of the sealing system in the end fitting, while taking into account fluid pressure inside the pipeline using a pressure penetration method. The impact of stress relaxation on the sealing performance is then discussed. Finally, the paper alters the coefficients of the Prony series to explore their significance on the sealing performance of the sealing system.

Numerical Fatigue Life Evaluation With Experimental Results for Type III Accumulators

Abstract Type III accumulator is widely used in hydrogen stations. A high-cost pressure cycle test is mandatory to ensure the safety of the accumulator in present regulations. To reduce the high cost, the aim is to develop a methodology of numerical fatigue life prediction, where an axisymmetric finite element model for the Type III accumulator is created precisely and actual loading process including autofrettage pressure is simulated. The alternating stress intensity is evaluated based on the instructions in KD-3 of 2015 ASME Boiler & Pressure Vessel Code, Section VIII, Division 3. By comparing stress amplitude distributions with the leak positions after the pressure cycle test, and plotting the results in the design fatigue curve, it could be shown that fatigue life prediction of Type III accumulator can be done by precise finite element analysis of the liner including dome part, where the principal axes of stress change in pressure cycle.

Semi-Analytical Methods for the Joint Strength and Sealing Performance in the Failure Process of the Subsea Pipeline Compression Connector

Radial seals are sensitive to axial overload failure and may cause leaks. This paper presents two semi-analytical methods for the joint strength and sealing performance of the subsea pipeline compression connector under axial overload failure. The method for the joint strength consists of two parts: One is the analytical model for the joint strength of the connection and seal under axial tension and compression conditions. The models are based on membrane theory, considering the hardening and bending effects. The other is a two-dimensional, axisymmetric finite element model for the joint strength of the radial metal seal. The semi-analytical method for the overload sealing performance is derived using a finite element model and the Reynolds equation of the laminar flow. The effects of critical parameters on the joint strength and the overload sealing performance are analyzed. The experiments are carried out with specimens and prototypes to evaluate the evolution of the sealing interface and the joint strength. The results show that both the internally turned sealing surface and the deflection of the pipe can improve the joint strength. In addition, the compression-type connector can remain sealed under the maximum axial overload. The proposed methods allow the prediction and identification of the overload joint strength and the sealing condition of the compression-type connector and provide a better understanding of the radial metal seal under the axial overload condition.

Comparative study on fracture characteristics of carbon and stainless steel bolt material

Bolt fracture often limits the ultimate strength and deformation capacity of bolted connections and leads to overall joint failure. Therefore, the prediction of structural collapse under extreme loads necessitates the incorporation of a reliable fracture model that reflects the observed structural response of bolts. This paper reports a comprehensive experimental and numerical study into the structural behaviour, ductility and fracture characteristics of Grade A4–80 austenitic stainless steel bolts and carbon steel 8.8 bolts in tension, which are commonly used as fasteners in bolted connections. Tensile tests were performed on smooth material coupons machined from both bolt grades to obtain the material response. Thereafter, tensile tests were performed on notched specimens from both grades, allowing the fracture characteristics to be studied over a range of stress triaxialities and the development of an equation relating the plastic strain at fracture to the stress triaxiality. 2D axisymmetric and 3D advanced finite element models were calibrated against the experimental results and damage propagation parameters. The developed numerical models are shown to perfectly replicate the observed experimental behaviour of the tested bolt materials under predominantly tensile loading, including fracture. Both experimental and numerical results confirm the superior ductility of A4–80 bolts over their 8.8 counterparts.

A numerical estimation of leak-tightness in rolled joint under thermal creep

In the present work, a numerical framework is developed to estimate the leak-tightness of tube to end-fitting rolled joint used in various industries under thermal creep. The leak-tightness of the rolled joint depends on the contact pressure (at the contact surfaces of the tube and end-fitting) and residual stresses (on inner and outer tube surfaces) generated during manufacturing through the rolling process. An axisymmetric finite element model is developed and validated (with literature) to accurately determine the contact pressure and residual stresses at the end of the rolling process. The relaxation in contact pressure and residual stress due to thermal creep during the service life of rolled joint (after manufacturing rolling process) is also accounted in the model. Further, to estimate the leak-tightness (leak rate), a radial plane strain model is chosen that yields the same results as the axisymmetric model. The submodelling approach in the plane strain model handles the modelling of micro-sized leakage paths efficiently. From the FE modelling, it is observed that the contact pressure and residual stresses reduce significantly due to thermal creep. The effect of different leak geometries is examined on the leak-tightness of the rolled joint. It is found that an elliptical leak with major axis in radial direction has a more rate of increase in leakage as compared to other geometries.

Developing failure criteria for laceration injury of dermal tissue

Despite its importance, there is a poor understanding of human injury tolerance to trauma generally, and more specifically understanding of the mechanics of skin penetration or laceration. The objective of this analysis is to determine the failure criteria that will allow the evaluation of the laceration risk of blunt-tipped edges within a computational modeling environment. An axisymmetric tissue finite element model was set up in Abaqus 2021 to match the experimental set-up from a previous study. The model simulated the pressing of penetrometer geometries into dermal tissue, and stress and strain outputs were evaluated at the experimental failure force. Two separate nonlinear hyperelastic material models were calibrated for the dermis to data from the literature (high and low stiffness models). For both the high-stiffness and low-stiffness skin models, the failure force appears to occur near a local maximum in the principal strain. All failures occurred after the maximum strain near or at the top surface is or above 59%, with mid-thickness strain at a similar level. The strain energy density is concentrated near the edge tip for each configuration, indicating highly localized material damage at the point of loading, and increases rapidly prior to the approximate failure force. As the edge is further compressed into the tissue, the stress triaxiality near the edge contacting point decreases towards zero. This study has identified general failure criteria for skin laceration which can be implemented in a computational model. A higher risk for laceration would be indicated with strain energy density larger than 60 mJ/mm3, dermal strain larger than 55%, and stress triaxiality below 0.1. These findings were largely insensitive to the dermal stiffness and broadly applicable across different indenter geometries. It is expected that this framework may be implemented to evaluate hazardous forces for product edges, interactions with robots, and interfaces with medical and drug delivery devices.

Parametric Study on Fin Structure and Injection Tube in Metal Hydride Tank Packed with LaNi5 Alloy for Efficient and Safe Hydrogen Storage

Efficient hydrogen storage methods are crucial for the large-scale application of hydrogen energy. This work studied the effects of fin structure and injection tube on the system performance of a hydrogen storage tank packed with LaNi5 alloy. An axisymmetric finite element model of the metal hydride hydrogen storage tank was established. The fin structure and injection tube were added to the hydrogen storage tank, and the effects of the fin location and injection tube on the efficiency and safety of the hydrogen storage tank during hydriding were analyzed. A parametric study on the wall fin structure and injection tube has been carried out to optimize the design of a hydrogen storage tank, and to improve its efficiency and safety. The hydrogen storage capacity of the optimized tank packed with LaNi5 alloy can reach 1.312 wt%, which is 99% of its maximum capacity, at around 650 s. The results show that the fin structure can improve the heat transfer performance of the storage tank, and that the injection tube can enhance the mass transfer of hydrogen in the tank.

Analysis of Sealing Characteristics of Lip Seal Rings for Deep-Sea Separable Pressure Vessels

Deep-sea pressure vessels are specialized pressure vessels designed for automatic deployment from underwater to the surface. These vessels find extensive applications in underwater life-saving and transportation. Their interiors are furnished with a pair of sealing rings, one of which is lip-shaped, and the other is a convex shape, to ensure a dependable seal. With increasing water depth, the sealing rings experience augmented pressure, resulting in a gradual pressing of the rings into the sealing groove. Using ANSYS workbench finite element software, a two-dimensional axisymmetric lip seal finite element model using forces for overall constraint was established, the complete process of progressive pressing into the sealing groove was simulated, and the deformation, contact stress, maximum shear stress, and von Mises stress distribution was also simulated. We also conducted a comparative analysis of lip seals under low and high-water pressure sealing conditions. The findings of the study indicate that when subjected to a combined effect of the installation pre-tightening force and the working water pressure, the lip seal experiences complete compression into the sealing groove at a specific water depth. When subjected to the simultaneous influence of water pressure on the sealing ring material and friction force on the contact surface, two extremes of contact stress manifest in the primary sealing zone of the lip seal. These extremes have the capacity to elevate the contact stress and the effective sealing width, ultimately leading to an improvement in the sealing performance. Concurrently, as the water pressure gradually increases, the inner concave circle of the sealing ring experiences stretching, leading to a reduction in stress concentration, equivalent stress, and shear stress to a considerable extent. This mechanism ensures that the lip-shaped sealing ring retains sufficient strength. This study offers a viable solution for conducting sealing studies on deep-sea separable pressure vessels.

Experiment and instantaneous driving simulation of explosion dispersion process of central tube for submunition

In order to study the influence of explosion dispersion of submunition on the dispersion velocity and pressure characteristics of subunits, the experimental study of explosive dispersion of the central tube was carried out when the explosives with low detonation velocity were applied in central tube as the main charge. In addition, the explosion dispersion test process was recorded by high-speed photography. RDX-based aluminized explosive samples with low detonation velocity were prepared and tested, and the low detonation velocity performance changes under different charge diameters and densities were obtained. Based on the explosive dispersion test of the central tube of the submunition, the physical model and three-dimensional axisymmetric finite element model of the central tube, subunit and aluminium alloy shell with prefabricated grooves are established. The fluid-structure coupling calculation method is used to simulate the explosive dispersion process. The simulation results are compared with the test results, and the pressure distribution characteristics of the subunit and the variation law of the dispersion velocity are analyzed. The effectiveness of the engineering calculation method of JWL equation model parameters is verified. The results show that using RDX based aluminized low detonation velocity explosive as the main charge of the central tube structure can achieve the design goal of the explosive dispersion for submunition, and the explosion dispersion model of submunition can accurately describe the dispersion characteristics of the subunit. The research results can be used to guide the structural design of submunition warhead.

Численный анализ устойчивости подводного сферического резервуара для хранения нефти

The most important and promising direction in the Russian oil and gas industry is the development of the Arctic shelf, the largest in the world. Today, in the case of the development of oil and gas deposits remote from the coast, the use of underwater pipelines is not only unprofitable, but also technically unfeasible due to the short summer navigation. A problem arises when mastering the delivery of energy carriers to the industrial regions of Russia, as well as for export. One of the ways to solve this problem is the use of underwater reservoirs as a means of temporary accumulation of the product. During the operation of underwater oil storage facilities, situations may arise that lead to dome deformation. To prevent such negative consequences, a reliable prediction of the stress-strain state is required. In this paper, the authors considered the modeling of the stress-strain state of the welded joint of the wall-to-bottom of the tank, as well as the zone of monolithic steel dome of the body in concrete. The depth of 100 m for the installation of an underwater storage was chosen due to the presence of hummocks in the seas of the Russian Arctic, which can affect the seabed to a depth of 15–40 m, as well as icebergs — up to 80 m. The authors developed a numerical axisymmetric finite element model of an underwater storage section, which allows to determine the stress distribution in the domed part of the tank, as well as in the foundation, in accordance with all the features of the underwater tank. The calculations showed that for the considered operating conditions of the deposits, the use of sheets of high-strength steel D690W with a thickness of 50 mm is not enough to ensure the stability of the structure, since stresses arise in the weld that exceed the yield strength of the selected steel. Therefore, it is required either to reduce the immersion depth of the storage, or to provide for a greater thickness of the domed part of the body with the use of ribs that increase the rigidity and stability of the structure.