FEM Simulation Research Articles

FEM Simulations of Fatigue Crack Initiation in the Oligocrystalline Microstructure of Stents.

For over two decades, vascular stents have been widely used to treat clogged vessels, serving as a scaffold to enlarge the narrowed lumen and recover the arterial flow area. High-purity oligocrystalline austenitic steel is usually applied for the production of stents. Despite the popularity and benefit of stenting, it still may cause serious clinical adverse issues, such as in-stent restenosis and stent fracture. Therefore, the study of the mechanical properties of stents and in particular the prediction of their life cycles are in the focus of materials research. In our contribution, within the finite element method, a two-scale model of crack initiation in the microstructure of stents is elaborated. The approach is developed on the basis of the physically based Tanaka-Mura model (TMM), considering the evolution of shear bands during the crack initiation phase. The model allows for the analysis of the microstructure with respect to the life cycles of real materials. The effects of different loading conditions, grain orientation, and thickness of the specimen on Wöhler curves were analysed. It was found that the microstructural features of oligocrystals are very sensitive to different loading conditions with respect to their fatigue behaviour and play a major role in fatigue crack initiation. Different grain-orientation distributions result in qualitative and quantitative differences in stress distribution and in the number of cycles for crack initiation. It was found that presence of a neutral zone in the cut-out of the microstructure under three-point-bending loading conditions changes the qualitative and quantitative patterns of stress distribution and affects the number of cycles for crack initiation. It was found that under both tensile and bending loading conditions, thicker specimens require more cycles for crack initiation. The Wöhler curves for crack initiation in oligocrystalline microstructures of stents could be compared with the ones in the experiment, taking into account that for high cyclic fatigue (HCF), typically, more than 70% of the cycles refer to crack initiation. The developed numerical tools could be used for the material design of stents.

A multiple-tool method for fast FEM simulation of incremental sheet forming process

A multiple-tool method for fast FEM simulation of incremental sheet forming process

Analysis and design of a vertical sectored tank

AbstractThis article describes the conceptual design and the structural analysis of a vertical cylindrical partitioned tank for an international chemical company. Vertical cylindrical tanks are commonly used in the chemical industry worldwide as vessels to contain liquids. Most of these plants have reduced area for the installation of the container tanks. Many of them need to renew their manufacturing process according to the new technologies and requirements. In addition, in some cases, the preparation of mixtures is carried out on small surfaces. All this factors led to the idea of designing a vertical sectorised tank, considering that alternative hydrostatic pressure cases can lead to eccentric loads on the upper surfaces. Therefore, bending stresses and compression and tension stresses will occur. A Finite Element Method calculation was performed to determine the wall thickness fulfilling the structural requirements for two distinguishing design alternatives. This article describes the particular models designed and the detailed FEM simulation and mechanical calculation carried out to determine the optimized solution of partitioned tanks with a diamond‐shaped inner bracing system that manages to meet all the structural, manufacturing, constructive and environmental needs with a target thickness of 12 mm.

A new chevron electromagnetic acoustic transducer design for generating shear horizontal guided wave

Guided wave electromagnetic acoustic transducers (EMATs) have a significant role in non-destructive testing and structural health monitoring. It can generate horizontally polarized shear waves propagating axially or circumferentially to characterize the shape and orientation of pipeline defects. This work proposes a new Chevron pattern-like coil structure design with a periodic permanent magnet (PPM) EMAT configuration. This specific design of the EMAT coil can generate a bi-directional shear horizontal wave (SH-wave) and reduce the side lobes. An optimal Chevron angle of coil wires assists in generating orthogonal propagatingwaveforms. These phenomena lead to the constructive interference of propagating waves and develop a resulting wave along the horizontal direction. A 3D FEM modeling and simulation have been carried out and validated with experimental results. The proposed EMAT results are compared with the conventional racetrack PPM EMAT model, which shows a significant improvement over conventional EMATs. A prototype of this proposed EMAT has been developed. It can be used to inspect surface defects in applications such as fuel transportation pipelines.

FEM Simulation on First-Step Drawing Process of Platinum-Clad Nickel Bars

The purpose of this study is to investigate the effects of semi-angle and platinum tube wall thicknesses on the first-step drawing process of platinum-clad nickel bars using finite element simulation. Three different semi-angles of die (3°, 5°, 7°) and three different platinum tube wall thicknesses (0.275 mm, 0.3 mm, 0.325 mm) were selected in the study. The effects of semi-angle and platinum tube wall thicknesses on drawing force, equivalent stress, cladding behavior and damage coefficients during the first-step drawing process were discussed in detail. The simulated results of cladding condition and damage obtained from Deform 3D V11 software are validated with experimental results, and it was found that the results were in good agreement. The results of this study may provide a reference for the practical production of platinum-clad nickel wires.

Ultra-high sensitivity methane gas sensor based on vernier effect in double D-shaped and cryptophane-A film-coated photonic crystal fiber: Design and FEM simulation

Utilization of the vernier effect in fiber optic interferometers represents the latest approach to enhance the sensitivity and resolution in fiber optic sensors. In this paper, the Vernier effect in Sagnac interference (SI) with a double D-shaped photonic crystal fiber (PCF) was proposed for the methane gas sensing. The sensing arm in the SI was composed of a double D-shaped PCF which was coated with cryptophane-A film, while the polarization maintaining photonic crystal fiber (PM-PCF) is used as the reference arm. The sensing arm and the reference arm were cascaded in parallel to generate the Vernier effect. The influence of the structural parameters in the PCF on the sensing performance was analyzed using the finite element method. The sensing fiber uses a double-D structure, so methane gas is more easily in contact with the sensitive film. According to the simulation results, the wavelength sensitivity of the parallel Sagnac loops within the methane gas concentration range of 0–3.5% is as high as 170.58 nm/%, which is 3.14 times that of a single Sagnac loop. The proposed sensor exhibits a significant enhancement in sensitivity compared to the other fiber optic-based methane gas sensors, thereby providing a reference sample for the development of high-sensitivity methane gas sensors.

A rigorous analytical approach to the pile-soil interaction of torsionally loaded piles in saturated SANICLAY soils

The paper proposes a rigorous analytical approach to predict interaction between torsionally loaded piles and saturated clay soils. The soil deformation mechanism around the pile is determined using the non-associated and anisotropic constitutive model, SANICLAY, along with the axisymmetric condition, equilibrium equation, and boundary conditions. By solving the derived governing equations, the hoop shear stress against rotation curve is obtained, including elastic, elastoplastic, and critical state processes. Taking advantage of the finite-difference method, the torque-rotation behavior of the pile and the stress-strain state of the soil around the pile are figured out. The proposed approach is compared with a FEM simulation and a parametric analysis is conducted to investigate the effect of overconsolidation ratio and in-situ coefficient. Model pile tests and field tests are used to manifest the validity and capacity of the model. The results demonstrate that the present approach can well predict the torque-rotation response of the pile and can reflect some important phenomena observed in pile tests.

Impedance spectroscopy of enlarged cochlear implant stimulation electrodes – FEM simulations considering the perilymph

Abstract Cochlear implants are hearing prostheses for patients with severe to total hearing loss but intact auditory nerve. An external speech processor captures sound from the environment, which is subsequently converted into electrical signals and transmitted to an electrode array in the patient’s inner ear. The metallic stimulation electrodes of the electrode array electrically stimulate the spiral ganglion cells of the auditory nerve. The functionality of cochlear implants strongly depends on the possible maximum current stimulating the spiral ganglion cells, which can be affected by, e.g., cell growth around the stimulation electrodes. This in turn decreases the stimulation efficiency leading to decreased hearing. Cell growth, implant position and other changes in the surrounding medium are reflected in a change of the impedance of the stimulation electrodes. The impedance measurement of the stimulation electrodes is already implemented in all common cochlear implant systems to check functionality of the stimulation electrodes after implantation, but the frequency spectrum is normally not analyzed. Although this method can detect cell growth on the stimulation electrodes, it faces limitations when other interfering effects, such as changes in the perilymph and implant position, influence the impedance. This work shows impedance spectroscopic measurements using enlarged cochlear implant models to electrically analyze the surrounding medium, the perilymph, to understand changes in electrode impedance and to later monitor the stimulation efficiency of cochlear implants and to identify possible reasons for decreased hearing ability by impedance spectroscopy. In addition, we use FEM simulations to numerically model the influence of the perilymph composition on the impedance measurement. As shown by a final validation, this model can serve as a basis for an extended simulation model including implant position and cell growth monitoring to predict hearing deterioration in cochlear implant patients. In this context, this work serves as a basis for the development of a holistic prediction model and considers in the first step exclusively the influence of the perilymph composition on the impedance between two stimulation electrodes.

Thermo-Electrochemical FEM and Circuit Simulations of Li-Ion Batteries

Thermo-Electrochemical FEM and Circuit Simulations of Li-Ion Batteries

Hole-Patterned Carbonyl Iron Powder/Epoxy Composite Low-Profile Electromagnetic Absorber Operating at Ka-Band

This research developed a mmWave electromagnetic (EM) absorber with a simply punched hole pattern, which was introduced on the flat CIP/epoxy composite to overcome the limitation of the magnetic materials. This absorber was designed on a carbonyl iron powder (CIP) and epoxy resin composite with Snoek's limit of about 26 GHz. First, the morphologies of the fabricated CIP/epoxy composite were characterized by scanning electron and atomic force microscopies. Subsequently, the constitutive parameters of the CIP/epoxy composite were measured in the frequency range of 26.5–50 GHz. These measured constitutive parameters of the CIP/epoxy composite material were iteratively revised by the curve-fitting technique to improve the measurement accuracy. An equivalent circuit model was utilized to determine the reflection coefficient of the hole-patterned CIP/epoxy composite mmWave EM absorber, taking into account its material parameters and dimensions. A comprehensive analysis was conducted to evaluate how the performance of the absorber is affected by the dimensions of its unit cell. This was achieved by utilizing both the equivalent circuit and full-wave FEM simulation. The absorption performance of the hole-patterned CIP/epoxy composite mmWave EM absorber is experimentally demonstrated at different angles and polarizations in 26.5–36.5 GHz.

Research on Deformation of Hydraulic Cylinders Made of Plastics

The article presents an author’s approach to the study of the behavior of plastic hydraulic cylinder structures under load. Plastics as design materials, due to their different properties, behave differently from metals. So far, there is little information about hydraulic cylinders made of plastics. They are a technical novelty, and there are no established standards or research methods for them. The tests were carried out on the example of two models of different internal diameter, the smaller one being Ø30 mm and the larger one Ø50 mm. Information was gathered by FEM simulation tests and tests of real models on a special test stand. The simulation section presents geometric models, discrete models and assumed boundary conditions, as well as the results of the performed simulations. For tests of real models, a description of the stand with the measuring equipment used is presented, e.g., laser displacement sensors, as well as the method of conducting the tests and the results. Then, the results are analyzed and compared. Deformations of the examined structures are discussed, e.g., tube swelling or deflection, which seem to be characteristic for plastic cylinders. Finally, the possibility of using selected plastics for the design material of hydraulic cylinders and the suitability of the research method used are assessed.

Analisis Perpindahan Gaya SideLoad Pegas Suspensi Tipe C Menggunakan Finite Element Method (FEM)

The suspension must provide comfort and safety to the vehicle. Therefore, it is necessary to analyze the load's effect on the pressure distribution on the axle so that the spring strength from the sideload force can be simulated. This study aims to analyze the sideload force of type C suspension springs using FEM. Spring variations are the number of different threaded coils, namely 11, 12, and 13. In the FEM simulation, the spring is given a load until 50mm, 100mm, 150mm, 200mm, and 250mm displacement occurs. The loading spreads to the X, Y, and Z axes. Each direction of the axis is measured by the pressure that occurs. The results showed that the pressure values that occur on the X, Y, and Z axes decreased with each increase in the number of screw coils. The lowest X-axis pressure reduction occurs in thread 12 at 63%. Meanwhile, the pressure on the Y axis decreased by 27% on the spring screw 12. The highest decrease in pressure on the Z axis occurred by 34% on the spring screw 12 compared to the spring screw 11.

Investigation of SMFL monitoring technique for evaluating the load-bearing capacity of RC bridges

This study investigates the use of Self-Magnetic Flux Leakage (SMFL) monitoring to assess the load-bearing capacity of RC bridges under vehicular loading. Cyclic tensile experiments of HRB400 rebars were conducted and the SMFL intensity was monitored. The integrated vector value of SMFL intensity BC was introduced to analyze the characteristics of the rebar force-magnetic coupling effect. Moreover, SMFL monitoring experiments were conducted on Gaojia Garden Bridge to evaluate the engineering applicability of the method. The results show that the mechanical indexes have a positive correlation with SMFL intensity during rebar cyclic loading. The increase in the cycle number drives the stability of the force-magnetic relationship. The rebar proportional ultimate strength σpl is an important factor affecting the BC variation. When the stress exceeds σpl, the rising process of BC curve retreats. The rebar stress range can be accurately determined based on the change rate of SMFL intensity. In the testing of Gaojia Garden Bridge, vehicles loading and unloading contribute to the phased increase and monotonic decrease of BC curves, respectively. Comparing the FEM simulation results, the linear characteristic relationships between BC and |με| as well as σ are obtained, which verifies the engineering applicability and accuracy of SMFL monitoring method. This research provides a new approach for the non-destructive quantitative detection and test application of RC bridge load-bearing capacity.

Current Harmonics Minimization of Permanent Magnet Synchronous Machine Based on Iterative Learning Control and Neural Networks

Electrical machines generate unwanted flux and current harmonics. Harmonics can be suppressed using various methods. In this paper, the harmonics are significantly reduced using Iterative Learning Control (ILC) and Neural Networks (NNs). The ILC can compensate for the harmonics well for operation at constant speed and current reference values. The NNs are trained with the data from the ILC and help to suppress the harmonics well even in transient operation. The simulation model is based on flux and torque maps, depending on dq-currents and the electrical angle. The maps are generated from FEM simulation of an interior permanent magnet synchronous machine (IPM) and are published with the paper. They are intended to serve other researchers for direct comparison with their own methods. Simulation results in this paper verify that by using ILC and NNs together, current harmonics in transient operation can be eliminated better than without NNs.

Comparative research of rock breaking by heat effect of continuous and pulse laser with experiment and simulation

Laser rock breaking is a novel rock breaking technology to raise the rock breaking efficiency in deep and ultra-deep strata. Continuous and pulse lasers are two types of laser that are usually used in laser rock breaking research at present. However, the present studies’ main focus is on the breaking mechanism and character optimization of continuous laser. Studies to pulse laser and the differences between the two types of laser are rarely reported. The pulse and continuous laser with 800 W power were used in the laser rock breaking experiment, and the morphology of ablation pits was measured and compared. Then, a FEM simulation model was established by the results of the experiment. The distribution condition and the evolution process of temperature, ablation pit, yield condition, and equivalent strain at test points generated by two types of laser were measured and compared. The experiment results show a thick enamel layer covering the ablation pit generated by the continuous laser, which referring a higher ablation ability but with a shallower ablation pit in measurement. And the simulation results not only represent the higher ablation ability of continuous laser at the end of simulation but also show the circular heating–cooling process, stepping expansion process of ablation pit, faster ablation pit generation speed (0.03 s earlier), higher yield volume, and higher equivalent plastic strain (about three times higher) in radiated part with a pulse laser. Referring that it has higher ablation ability in short radiation time, stronger thermal stress effects on the radiated part, and less molten materials generated in the laser rock breaking process than continuous laser. This research can offer some references to the laser type selection in laser rock breaking and explain the rock breaking theory more comprehensively.

Monolithic PneuNets Soft Actuators for Robotic Rehabilitation: Methodologies for Design, Production and Characterization

Soft-robotics for biomedical applications, such as rehabilitation robots, is a field of intense research activity. Different actuation solutions have been proposed in the last decades, involving study and development of soft actuators of different types and materials. The purpose of the paper is to present procedures for an optimized design, and for easy and low cost production and characterization of monolithic PneuNets soft-actuators. An innovative design approach has been developed. The parameterization of the geometry, combined with FEM simulations is the basis for an optimized design of the actuator, as a function of the obtained bending and of the generated forces. Simple and cheap characterization setup and procedures have been identified for the actuator characterization and for simulation results validation. An easy and low-cost fabrication method based on lost wax core obtained through a silicone based mold has been developed for a monolithic PneuNets soft-actuator. The proposed solution performs well in bending, without the need for a strain limiting layer. Experimental results validated simulations, confirming the feasibility of adopting an optimized simulation-based design approach.

Comparison of behaviour of burnt beams models with effective and actual residual cross-sections in three point bending test

Glued laminated timber beams exposed to fire of a variable duration were tested in three point bending. Three types of model geometries taking into account the effect of burning were created. Each model was examined for five material data sets. The maximum deflection obtained from FEM simulations was compared with the corresponding deflection wel derived from a three point bending test of burnt beams. The analysis was performed with the help of Ansys® software limiting attention to a liner elasticity with the maximum applied force Fel selected at the proportionality limit observed experimentally. Majority of FEM models provided smaller deflections compared to measurements except for the material set adopting Young’s moduli from the compression test. The best fit was observed for the material data set obtained from homogenization. No predominant preference among individual geometries was found promoting the computational model based on reduced cross-section as sufficiently accurate.

A parametric study assessing Implicit Solver limits for a generic FEM Simulation of PTA without stent deployment.

This study focuses on the robustness of a generic Finite Element Model (FEM) of Percutaneous Transluminal Angioplasty (PTA) procedure with permanent set. The influence of three different parameters on simulation robustness were investigated: the stenosis percent, the stenosis offset and the arterial caliber. Five arterial calibers are modeled by adapting the ratio between the inner diameter and the wall thickness. Overall, forty configurations were tested with the same simulation settings and boundary conditions. Results shows convergence issues caused by excessive deformations of elements for stenosis above 65% blockage. Moreover, an increasing stenosis offset tends to decrease convergence. Simulation of PTA on small calibers and large calibers are less robust than intermediate e.g., iliac calibers.Clinical Relevance- PTA can benefit from numerical tools to improve the procedure outcomes. A FEM simulation of PTA without stent deployment can predict the permanent strain induced by this surgery for various configurations. However, robustness of the simulation is required to consider its transfer to clinics. This work aims to determine the robustness boundaries of an implicit solver for PTA simulation. It shows that an implicit solver is robust for all artery calibers with a stenosis below 50% blockage. Moreover medium-caliber arteries exhibit better robustness with converging solutions for stenosis reaching 60% blockage.

Transient Simulation and Optimization for the Integral Hoisting of Extra-Large Air Separation Cold Box

The cold box is a crucial component for cryogenic distillation in air separation units. With the increasing focus on energy conservation and emissions reduction, the integral hoisting of the cold box has emerged as a viable alternative to traditional cold box installation due to its highly efficient performance, short cycle time, and superior integration capabilities. Nonetheless, there are concerns surrounding the large size and weight of these boxes, as well as their eccentric structure, which can cause significant challenges during the integral hoisting process and pose safety hazards. To address these issues, this paper proposes a method for optimizing the lifting point of an extra-large cold box through dynamic simulation under actual working conditions. Firstly, a transient structure FEM simulation was carried out using multi-type mesh coupling based on the operating conditions of an extra-large cold box. Secondly, the posture and strength of the box during the hoisting process were analyzed to determine the most dangerous working conditions. Finally, the maximum equivalent stress of the trusses was employed as the fitness function of the particle swarm algorithm to optimize the lifting point position in the whole parameter range. The findings indicated that the most dangerous situation during the hoisting process occurred near the 0° working condition in the flip-up process and that optimizing the lifting point position based on this working condition significantly reduced the stress levels on the trusses.

Size correction scheme to determine fracture toughness with mini-CT geometry in the transition regime

The mini-CT geometry is used to determine relevant fracture toughness data along with the master curve description within the transition regime. However, due to significant loss of constraint experienced at loadings close to J-levels corresponding to the reference temperature T0, the current size correction scheme from ASTM E1921 standard requires a better assessment in order to avoid censoring a large number of mini-CT specimens. Indeed, the current tight ASTM E1921 requirements on the KJc limit value set to ensure that the computed transition temperature T0 is reliable often implies that many samples have to be censored. A large number of censored specimens leads to a significant loss of time, money and material, and of unnecessary activated material in the case of irradiated specimens. Besides, because of the specimen size reduction, more mini-CT samples and lower test temperatures as compared to large sized samples are required to determine a reliable T0 value. In this study, an improved specimen size correction associated to the mini-CT geometry is proposed based on a local approach of brittle fracture combined with FEM simulations. The results show that the proposed size correction reduces the T0 bias compared to the 1T-CT geometry. It also contributes to relaxing the KJc limit for the mini-CT geometry as compared to the ASTM size corrected values.