Accuracy Of Finite Element Analysis Research Articles

Biomechanical Study of Posterior Lumbar Interbody Fusion: A Review

Degenerative disc disease is a spinal disorder in which the vertebral disc helps protect nerves and increase spine flexibility that begins to deteriorate. The syndromehappens in the lumbar spine, which is crucial in supporting the weight of the human body. The lumbar vertebrae are naturally larger to absorb the stress of carrying heavy objects. Many surgical treatments are available for this disorder, and the most common treatment is Posterior Lumbar Interbody Fusion (PLIF) surgery. However, a lot ofquestionable clinical effects related to this procedure, such as cage sinking into vertebral endplates, cage failure and cage relocation. This paper reviews the technical aspects of developing PLIF implants based on clinical, in-vitro, animal, prospective, and retrospective studies.The finite element analysis (FEA) approach has shown the most promising technique by offering virtual biomechanical assessments, low risk of implant failure and bone fractures, and satisfying patient-specific requirements. Many types of FEA software are available in the market, such as Ansys, ABACUS, and Mechanical Finder software. The ability of the software to develop heterogeneous bone models will give an extra advantage in improving the FEA accuracy in terms of stress and distributions and fracture risk assessment. The research approach, biomechanical assessment and data interpretation related to the development of the previous and existing studies will give an insightinto the research strategies and their restrictions. The FEA investigation can be utilized to optimize the mechanical characteristics of PLIF with various infill pattern designs and densities. Moreover, the further research analysis is still needed to improve interbody cage development

Choice of the stress integration scheme for accurate large-deformation finite element analysis

The use of computational structural models that include geometrical non-linearity in many application cases may require high reliability in prediction of displacements. Nevertheless, large differences up to 60% on maximum total displacement have been found among results of static large-deformation analyses performed by means of the major commercial software packages in a simple benchmark study with linear material properties. In order to investigate the causes of such disagreement, the present work compares different finite element formulations including well-established stress update schemes. The various formulations are tested, and results are compared in three test cases. Rodriguez stress update algorithms have shown the best performance among methods reported in literature. Finally, the cause of the large differences found in the predictions of commercial codes is identified. It is linked to the energetic inconsistency of some stress update methods in the simulation of extension/compression loading conditions. Such inaccuracy is reproduced analytically by formulating and integrating the corresponding inconsistent constitutive equations. The identified problem is very important for designers, as it affects almost all the static simulations, which are the most common type of large-deformation analyses and usually involve extension/compression loading.

A reduced-order cutFEM approach to model complex moving sound sources

While traditional finite element based vibro-acoustic analysis of structures is done on stationary structures, in many occasions the structure under investigation is actually moving. To perform accurate finite element analysis on the vibro-acoustic performance of such structures requires the evaluation of a time-varying system, leading to several challenges. Of paramount importance are a strategy to update the mesh to the new configuration and an adequate time integration scheme that does not introduce large numerical artifacts. Additionally, the time-varying nature leads to an increase in computational complexity. In this paper a modeling strategy based on cut finite elements (cutFEM) is introduced that aims to tackle these challenges. The cutFEM approach can be seen as a fictitious domain approach in which the source is moving over a static mesh, cutting through elements where the actual source is located, using a level set description. The key advantage of this approach is that no remeshing and/or mesh morphing is required. It is shown how both implicit and explicit time integration schemes can be used to propagate the solution while the source is moving. Additionally, several model order reduction strategies are compared to speed up the online evaluation of the reduced order model.

CALCULATION OF ANNULAR PLATES ON AN ELASTIC BASE WITH A VARIABLE BEDDING FACTOR

The application of the analytical method ‒ the method of direct integration ‒ to calculations of building structures in the form of circular plates and plates on a continuous variable elastic base is considered. It is noted that there are no proposals for a general analytical method for calculation of annular plates on a variable elastic base in the literature. And the need for such a method is obvious, since it makes it possible to estimate the accuracy of finite element analysis. A detailed description of the algorithm of the direct integration method is not given in the paper, and all the calculation formulas for the circular plate are taken from the authors’ already published article. The results of numerical implementation of this algorithm for specific examples are considered. In order to verify the results of calculations by the author’s method, computer modeling of the considered circular plates in PC LIRA-SAPR and their calculations by the finite element method have been performed. The reaction of the foundation is described by the Winkler model with a variable bedding factor. The calculation of a concrete slab that is rigidly pinched on the inner contour and articulated on the outer contour is performed. And calculation of a steel plate with rigid pinching on the outer contour and articulated on the inner contour. In the first case, the bedding factor is assumed constant, and in the second case, it changes according to the linear law. The calculations showed that the discrepancy between deflections calculated by the finite-element method and the author’s method does not exceed 1%, and the results of radial and circumferential moments calculation differ more considerably, amounting to 10%. The authors explain this difference by the inaccuracy of the numerical analysis associated with a semi-automatic method of constructing a finite-element mesh, which should be made finer. The densification of the mesh in the manual mode of its partitioning significantly reduces the discrepancy between the results of calculating the deflections, radial and circumferential bending moments by the finite-element method and the author’s method.

Full-field geometric imperfection and effect on cross-section capacity of circular steel tubes

Measurements on the geometric imperfection of circular steel tubes used in building structures were limited to specific longitudinal lines of the outer surface in existing studies. This study is aimed at detecting full-field geometric imperfection of circular steel tubes and evaluating its influence on cross-section capacity. First, geometric imperfections of 71 specimens consisting of four common types (i.e., hot-rolled and cold-rolled carbon steel circular tubes, cold-drawn and cold-rolled stainless steel circular tubes) were measured using laser scanning techniques. Observations from 3D scanning models demonstrate that the dominant imperfections for seamless tubes (hot-rolled carbon and cold-drawn stainless steel circular tubes) are cross-section ellipticity and uneven thickness, while welded tubes (cold-rolled carbon and stainless steel circular tubes) are mostly influenced by cross-section ellipticity. Based on the measured geometric profile data, imperfection distribution modes of outer-surface and thickness were proposed separately, and then imported to finite element (FE) simulation. Parametric analysis was conducted to evaluate the influence of geometric imperfections on cross-section compression and bending capacity values. Totally, seven types of outer-surface and three types of thickness imperfection distribution modes were used. Simulation results indicate that considering geometric imperfections generates negligible influence on cross-section capacity for the circular steel tubes studied. Finally, the influence of mesh density on capacity prediction of circular steel tubes was discussed. This study illustrates the actual full-field geometric imperfection distribution of circular steel tubes and discusses its effect on cross-section capacity, which provides useful information for improving the efficiency and accuracy of FE analysis on circular steel tubes.

A novel strain field reconstruction method for test monitoring

For the static loading test in the aerospace field, conventional strain field reconstruction based on finite element analysis (FE-SFRM) is difficult to meet the accuracy requirements of test monitoring. A novel experiment strain field reconstruction method (EXP-SFRM) is proposed to improve the accuracy and monitoring effect of reconstructed field. Firstly, the coordinates of strain gauges are introduced to build the connections in space between discrete strain gauges and make it possible to check the accuracy of finite element analysis. Next, the real-time strains with high-precision coordinates are employed to reconstruct the strain field by radial basis function. A cantilever plate test and a large opening cylindrical shell (LOCS) test are performed to validate the high accuracy and good monitoring effect of EXP-SFRM. For the LOCS test, a maximum inward and outward bending criterion (MIOBC) is also proposed to determine the buckling regions. The results show that the average errors of EXP-SFRM are 2.8% (cantilever plate) and 17.4% (LOCS), which are 4.8% and 26.4% lower than these of FE-SFRM. Additionally, for LOCS, the risk regions predicted by EXP-SFRM are finally consistent with the real buckling regions, while these predicted by FE-SFRM are not. Compared with conventional FE-SFRM, the EXP-SFRM is proved to have high accuracy and good monitoring effect during test process.

Earing prediction of 2090-T3 aluminum-cups using a complete homogenous fourth-order polynomial yield function

AbstractEaring can be described as difference in cup wall height due to planar anisotropy of the sheet metals, and both prediction and minimization of this defect are critical steps of drawing process design to save material and production costs due to additional trimming operations. The finite element (FE) method is a practical design tool in this context. The accuracy of FE analyses is directly dependent on modeling material deformations using an effective plasticity model. In this study, a homogeneous orthotropic fourth-order polynomial stress function is presented and implemented into Ls-Dyna FE software by a user-defined material subroutine to predict the earing evolution of a strongly anisotropic aluminum alloy (AA2090-T3) in cup drawing. Primarily, the parameters of the function were calibrated using test data. The effects of element size, number of through-thickness integration points, and time-step size were investigated separately on the drawn cup’s earing profile and thickness strain distributions. It was observed that mass scaling factor related to time step size has a significant impact on the cup height and profile. Finally, simulations were repeated with optimum parameters to assess the performance of the plasticity model. The yield criterion successfully predicted the cup profile, earing amplitude, and thickness strain distributions.

A newly treated boundary conditions to enhance accuracy of finite element analysis for orifice-type aerostatic bearings

Although numerical approaches have been extensively employed for solving the Reynolds equation in order to predict the performance of air bearings, we found inappropriate boundary settings can cause significant numerical errors if the grid-dependent condition is ignored. The current scrutiny is focused on crucial procedures for adopting the finite element method to assess the performance of orifice-type aerostatic bearings. To this end, numerical models for a single orifice-type are established and then checked by varying mesh sizes, mesh types, and boundary conditions (BCs). The obtained results reveal that those numerical models with a single-source node are grid-dependent, and the relative error is so large that the results are not credible compared with the analytical solution and becomes worse with denser meshes. This peculiar phenomenon can be mathematically interpreted by a one-dimension finite difference model calculated manually and auxiliary sources have proved to be an effective technique to reduce single-source numerical error to an acceptable level. Additionally, a physical explanation is given based on engineering systems modeling. By this view, rules of setting high pressure on the edge of recess are proposed and three types of grid-independent BC settings are proposed. Stiffness test experiments based on manufacturing a rotary table adopting multi-orifice aerostatic thrust bearings are further carried out to validate these numerical models, and the discrepancy between measured and calculated stiffness is reported to be lower than 5%.

Work Hardening of Metallic Sheets under Tension-Compression and Simple Shear Reverse Loading

The hardening models have a significant influence on the accuracy of finite element analysis (FEA). Although, isotropic hardening models are the most widely used, it is known that kinematic hardening models (describing the Bauschinger effect and permanent softening) can significantly improve the accuracy of FEA results. However, when considering sheet metal materials, the parameters of kinematic hardening models are difficult to identify due to the challenges of obtaining experimental results from test with strain path inversions. This work considers an experimental procedure that enables the analysis of the mechanical behaviour of sheet metal materials submitted to reverse loadings. A miniaturized test device was developed to perform tension and compression tests, with reverse loadings, for sheet metal materials. This specimen design has two main advantages: (1) reduces buckling during compression (compared to standard tensile test specimens) and, consequently, (2) enables the characterization of the mechanical behaviour under reverse tension-compression strain paths changes. The small size of the specimens, with 2 x 2 mm gauge area, poses the main challenge of the current methodology, namely the measurement of the strain field distribution using the Digital Image Correlation (DIC) technique. The results obtained from tension-compression tests with mini-specimens are validated by comparison with standard tensile and shear (reverse loading) and tests.

Characterization and Modelling of Sheet Material with Graded Strength for more Accurate Finite Element Analysis

Many sheet materials do not exhibit constant properties over the sheet thickness. On the one hand, this can be caused by a rolling process with a pass reduction of 1-2%, the so-called skin pass rolling. This is mainly used for deep drawing steel grades to eliminate the pronounced yield strength of the base material. Another possibility is abrasive blasting or shot peening of sheet metal. This causes plastic deformation of the sheet surface and material strengthening. The grading can be used to locally strengthen components or locally adapt the roughness. Since many production processes today are designed numerically, the mapping of such a grading is necessary but currently not implemented in FE code. Aim of this research is, to correlate the material hardness to a plastic pre-strain with a newly developed characterization method. For this purpose, graded material properties are generated by means of abrasive blasting as an example process. The resulitng locally varying work hardening over the sheet thickness is further integrated in finite element analysis by the assignment of a starting condition of a 2d-shell element formulation. With this approach, it is possible to map the graded material properties easily in FE simulations with a very good accuracy.

Mechanical properties of CFDST column under eccentric compression after exposed to fire

This paper investigates the experimental behaviour of ten square concrete-filled double skin steel tube (SCFDST) columns subjected to eccentric compression after 60 min of fire time. The test parameters included slenderness ratio, eccentricity and hollow ratio. It was found that the slenderness ratio and eccentricity have significant influence on the residual deformation and bearing capacity. However, when the hollow ratio (χ) was 0.72, slenderness ratio has little effect on the bearing capacity. The accuracy of finite element analysis (FEA) models were verified by the presented test results, and they were in good agreement. A FEA model was established to conduct a parameter analysis of CFDST members, and the working mechanism was analyzed in depth. Based on the parametric analysis, it shows that nominal steel ratio, eccentricity and strength of external steel tube have significant influence on the member’s residual bearing capacity under eccentric compression after fire: The residual bearing capacity decreases with the increase of nominal steel ratio. When the eccentricity increased from 0 to 0.6, the bearing capacity can decrease about 42 % after fire. The hollow ratio and concrete strength have little effect on the bearing capacity after fire. With the increase of fire time from 0 min to 120 min, the proportion in bearing capacity of internal and external steel tube gradually increases 16.8 %. Finally, compared with the relevant codes, the results of the T/CCES 7–2020 code were in good agreement with the FEA results.

Research for Pedestrian Steel Bridge Design of Neural Network in Structural Model Updating

The application of the neural network method in health monitoring and structural system identification has received extensive attention. A reasonable neural network structure is very important for its performance. This paper takes the pedestrian bridge of the Xingfu intersection in Urumqi, China, as the research object and uses MIDAS/Civil to establish a finite element analysis model. Taking the natural vibration frequency obtained from the dynamic test of the actual bridge as the target, two kinds of neural networks are used to predict the structural material parameters. An appropriate bridge model correction method is selected by comparing the prediction results of the BP neural network and the GRNN. The test results show that the pedestrian bridge model based on MIDAS/Civil has a high accuracy, but it still does not meet the actual needs. The modified model based on the BP neural network is close to the actual measured results, and a more accurate finite element analysis model can be established by this method, which makes the modified model closer to the real stress state of the structure.

Does rotation during echolocation increase the acoustic field of view? Comparative numerical models based on CT data of a live versus deceased dolphin

Spinning is a natural and common dolphin behavior; however, its role in echolocation is unknown. We used computed tomography (CT) data of a live and a recently deceased bottlenose dolphin together with measurements of the acoustic properties of head tissues to perform acoustic property reconstrcution. The anatomical configuration and acoustic properties of the main forehead structures between the live and deceased dolphins were compared. Finite element analysis (FEA) was applied to simulate the generation and propagation of echolocation clicks, to compute their waveforms and spectra in both near- and far-fields, and to derive echolocation beam patterns. Model results from both the live and deceased dolphins were in good agreement with click recordings from live, echolocating individuals. FEA was also used to estimate the acoustic scene experienced by a dolphin rotating 180ã‚œabout its longitudinal axis to detect fish in the far-field at elevation angles of 0ã‚œ–20ã‚œ. The results suggest that the spinning behavior provides a wider insonification area and compensates for the dolphin’s relatively narrow biosonar beam and constraints on the pointing direction that are limited by head movement. The results also have implications for examining the accuracy of FEA in acoustic simulations using freshly deceased specimens.

Optimal Modeling of an Elevator Chassis under Crash Scenario Based on Characterization and Validation of the Hyperelastic Material of Its Shock Absorber System

A wide variety of hyperelastic rubber-like materials, exhibiting strong nonlinear stress–strain relations under large deformations, is applied in various industrial mechanical systems and engineering applications involving shock and vibration absorbers. An optimal design procedure of an elevator chassis crashing on a hyperelastic shock absorber in a fail scenario, applicable in large-scale mechanical systems or industrial structures of high importance under strong nonlinear dynamic excitation, is presented in this work. For the characterization of the hyperelastic absorber, a Mooney–Rivlin material model was adopted, and a series of in-lab compression quasi-static tests were conducted. Applying a fully parallelizable state-of-the-art stochastic model updating methodology, coupled with robust, accurate and efficient Finite Element Analysis (FEA) software, the hyperelastic behavior of the shock absorber was validated under uniaxial large deformation, in order to tune all material parameters and develop a high-fidelity FE model of the shock absorber system. Next, a series of in situ full-scale experimental trials were carried out using a test-case elevator chassis, representing the crash scenario on the buffer absorber system, after a controlled free fall. A limited number of sensors, i.e., triaxial accelerometers and strain gauges, were placed at characteristic points of the real structure of the elevator chassis recording experimental data. A discrete Finite Element (FE) model of the experimentally tested arrangement involving the elevator chassis and updated buffer absorber system along with all boundary conditions was developed and used in explicit nonlinear analysis of the crash scenario. Steel material properties and the characterized updated Mooney–Rivlin material model were assigned to the elevator chassis and buffer, respectively. A direct comparison of the numerical and experimental data validated the reliability and accuracy of the methodology applied, whereas results of the analysis were used in order to redesign and optimize a new-design elevator chassis, achieving minimum design stresses and satisfying serviceability limit states.

ASSESSMENT OF A NEW ISOTROPIC HYPERELASTIC CONSTITUTIVE MODEL FOR A RANGE OF RUBBERLIKE MATERIALS AND DEFORMATIONS

ABSTRACT The choice of an appropriate strain energy function W is key to accurate modeling and computational finite element analysis of the mechanical behavior of unfilled non-crystalizing rubberlike materials. Despite the existing variety of models, finding a suitable model that can capture many deformation modes of a rubber specimen with a single set of parameter values and satisfy the a priori mathematical and structural requirements remains a formidable task. Previous work proposed a new generalized neo-Hookean W (I1) function (doi: 10.1016/j.ijnonlinmec.2020.103626), showing a promising fitting capability and enjoying a structural basis. In this work we use two extended forms of that model which include an I2 term adjunct, W(I1,I2), for application to various boundary value problems commonly encountered in rubber mechanics applications. Specifically, two functional forms of the I2 invariant are considered: a linear function and a logarithmic function. The boundary value problems of interest include the in-plane uniaxial, equi-biaxial, and pure shear deformations and simple shear, inflation, and nonhomogeneous deformations such as torsion. By simultaneous fitting of each model to various deformation modes of rubber specimens, it is demonstrated that a single set of model parameter values favorably captures the mechanical response for all the considered deformations of each specimen. It is further shown that the model with a logarithmic I2 function provides better fits than the linear function. Given the functional simplicity of the considered W (I1, I2) models, the low number of model parameters (three in total), the structurally motivated bases of the models, and their capability to capture the mechanical response for various deformations of rubber specimens, the considered models are recommended as a powerful tool for practical applications and analysis of rubber elasticity.

Design and transient experimental analysis of a pulsed brushless doubly fed alternator in a capacitor charge power supply system

There is an urgent need to develop a robust capacitor charge power supply (CCPS) system to meet the requirement of pulsed load in all-weather mobile occasions such as vehicle, ship and aircraft. Brushless doubly fed alternator (BDFA) works through the rotor's pole pairs' transformation to get excitation indirectly, without magnets, brushes and slip rings. Both DC and AC excitation can be used. Therefore, it has high reliability and a good application prospect in the CCPS system. However, the existing research studies lack analysis of the parameters that affect charging performance, and have no experimental analysis of the prototype. To solve this problem, a comprehensive design method and experimental procedure of the pulsed BDFA are proposed and investigated. First, the operation principle of the pulsed BDFA is illustrated. Then, the charging performances under different design schemes are comparatively analysed through the finite element analysis (FEA). Finally, a prototype of the pulsed BDFA is manufactured, and the related experiments are carried out. The results verify the feasibility of the experimental procedure and the accuracy of FEA. The comprehensive design method and experimental procedure in this work provide a straightforward reference for the subsequent applications in the CCPS system.

Structure Analysis and Optimization Design of the Base of Four-pillar Hydraulic Testing Machine

Hydraulic testing machine is a kind of testing machine that transfers energy to implement mechanical test by liquid as medium. With the emergency requirement of energy saving and emission reducing, it becomes significant to kick off the infrastructure research to optimize the hydraulic testing machine. At present, some new products always designed with experience is without any improvement. Consider the current situation in testing machine industry, and combined with the desire of design lightweight, some job about optimization and parametric design of product was done from the angle of finite element in this paper. Following content is included: getting a more accurate finite element analysis method about the analysis of the base based on Solidworks, Hypermesh, ANSYS, and optimize model of the base by Optistruct. A more reasonable model of the base with full strength is been got. Puts forward a kind of finite elements analysis for the structure of the hydraulic testing machine. Meanwhile, share shape optimization techniques through which the structure is designed more reasonable.

Seismic characteristics of isolated plate-shell integrated concrete LSS

Plate-shell integrated concrete liquid-storage structure (PSICLSS) has been widely applied with the development of water treatment technology. However, there are few anti-seismic performance and base-isolation design researches on it. The seismic performance of PSICLSS was studied, and the accuracy of finite element analysis was verified by experimental study. A calculation method of damping coefficient is proposed and used in a PSICLSS study. Based on 5 natural accelerations and 2 artificial accelerations, the dynamic responses of the isolation liquid storage structure under different peak ground acceleration are analyzed. The analysis results show that, non-isolated PSICLSS is easy to damage when subject to earthquake. The principal stress of the structure is maximum at the upper beam, and the maximum liquid hydrodynamic pressure appears at the connection position of the upper and lower conical shell. When the base isolation measure is used, the stress of the structure can be effectively reduced, but the liquid sloshing response will be magnified. With the increase of peak ground acceleration, the structural dynamic response and liquid sloshing response will increase.

Prediction of the Seebeck coefficient of thermoelectric unidirectional fibre-reinforced composites

In this work, new analytical equations are derived to precisely assess the longitudinal and transverse Seebeck coefficient values of a unidirectional (UD) carbon fibre reinforced polymer (CFRP) composite lamina, as a function of the properties of the constituents and the fibre volume fraction. Accurate Finite Element (FE) analyses were also carried out on fibre-matrix unit cells, and the results were compared to those obtained with the analytical methods showing a very satisfactory agreement.Experimental measurements were carried out on single carbon fibre (CF) filament level, as well as on a CF/epoxy UD lamina that corroborated the proposed equations with the experimental results.

Finite Element Analysis of Titanium Foam in Mechanical Response for Dental Application

Metals with certain porosity are a new class of materials with extremely low density and a unique combination of excellent mechanical, thermal, electrical, and biocompatible properties. Absorption of impact and shock energy, dust and fluid filtration, construction materials, and most importantly, biocompatible implants are all potential applications for metallic foams. An orthopaedic implant made of metallic foam can provide an open-cell structure that allows for the ingrowth of new bone tissue and the transport of body fluids. Due to its strong biocompatibility and stable fixation between the implant and human bone, titanium foam has recently received much attention as an implant material. Finite element modelling is a suitable method to obtain an efficiently designed implant. Accurate finite element analyses depend on the precision before implementation as well as the functionality of the material properties employed. Since the mechanical performances of titanium foam and solid titanium are different, a constitutive model for porous metal is required. The model of Deshpande and Fleck in the finite element analysis software ABAQUS is used to describe the compressive and flexural deformation properties of titanium foam with 63.5% porosity. The finite element simulation results were compared with the practical mechanical properties obtained by compression testing of the foam. Finally, the material modelling was used to investigate the stress distributions on the dental implant system.