General Finite Element Analysis Research Articles

Evaluation of a steel railway bridge for dynamic and seismic loads

In this study, dynamic and seismic assessment of a railway bridge system with four discrete spans giving service on a double track railway line and located in an earthquake-prone region in Turkey is presented. A three-dimensional computer model of the bridge was generated using a commercial general finite element analysis software. Field measurements such as static and dynamic tests as well as material tests were conducted on the bridge system. Validation of the finite element model was performed based on the results of these tests. The calibrated 3D model of the bridge structure was then used for necessary calculations regarding structural assessment and evaluation according to train loads as well as seismic loads. Additional members were proposed to transmit seismic loads to supports. The fourth span, which had a permanent imperfection due to truck collision was studied in detail. Results have shown that due to excessive amount of capacity loss, the only choice was to write off the fourth span.

Modal Analysis of Magnetic Suspended Control Moment Gyroscope

3D finite element models of magnetic suspended control moment gyroscope structure are established by general finite element analysis software. Initial modal analysis scheme of the MS-CMG structure, in which the frame and gyro-chamber are analyzed separately, is described. A new modal analysis scheme that the MS-CMG is analyzed as a whole structure is presented. The connection between the gyro-chamber and frame is realized by defining a revolution pairs. The numerical predictions from two modal analysis schemes show obvious difference. The new scheme is more reliable since it simulates the real wok status of MS-CMG.

Fatigue Life Analysis of Large-Scale Liner Vibration Screener Based on ANSYS

Based on the theory of fatigue life prediction and by using the local stress-strain method and the material S-N curve of Q235 deduced by empirical formula; the fatigue was analyzed for the key parts of large-scale liner vibration screener by means of the general finite element analysis software, ANSYS. Thereby, the working conditions of force bearing, reliability and fatigue life-span of the key parts can be judged. The study will provide a theoretical basis for the design , manufacture, and installation of the large-scale liner vibration screener.

Process Optimization for Suction Plastic Forming of In-Mold Decoration Plastic Sheet with CAE

The suction plastic forming process for in-mold decoration plastic sheet has been the best process for thin-shell plastic exterior decoration parts. But the suction plastic forming products still suffers from the uneven thickness. Based on the general finite element analysis software POLYFLOW for viscoelastic fluid, a set of optimization methods for suction plastic forming process of in-mold decoration plastic sheet is introduced in this paper to reduce the uneven level of thickness. These methods include establishing process optimization scheme, building mesh model, selecting the material constitutive model and determining its parameters, imposing boundary conditions and blowing pressure, and applying the mold movement. Finally, the optimized suction plastic forming process is used to produce the in-mold decoration plastic rear bumper sample of an automobile, and the results show that optimized process is effective and applicable.

A new coupled analysis for nearly incompressible and impermeable saturated porous media on mixed finite element method: I. Proposed method

In the general mixed finite element analysis for the porous media, a fluid is assumed to be nearly incompressible; however, the solid may undergo a range of deformations from relatively large to small. If both constituent are assumed to be nearly incompressible and impermeable, the finite element analysis is very complex because of element locking. In order to overcome this difficulty, stable procedures using equal order elements have been introduced with stability analyses. However, these methods have a drawback that critical time steps in the stability analysis have to be determined by modal analysis. In this paper, a new coupled analysis based on a stable algorithm is introduced to remedy the drawback. First, governing equations for saturated porous media in frame of Biot’s theory are derived on macroscopic sense, and that are represented into approximation forms which is divided into solid and fluid phase for finite element procedure. Moreover, a new coupled analysis based on a stable algorithm is introduced. In this procedure, the multi time step, the remeshing step and the sub iteration step are proposed for a stable analysis. These steps make it possible to simply solve numerical instabilities such as convergence and compatibility problems.

Implementation of an ANCF beam finite element for dynamic response optimization of elastic manipulators

Theoretical and practical aspects of an absolute nodal coordinate formulation (ANCF) beam finite element implementation are considered in the context of dynamic transient response optimization of elastic manipulators. The proposed implementation is based on the introduction of new nodal degrees of freedom, which is achieved by an adequate nonlinear mapping between the original and new degrees of freedom. This approach preserves the mechanical properties of the ANCF beam, but converts it into a conventional finite element so that its nodal degrees of freedom are initially always equal to zero and never depend explicitly on the design variables. Consequently, the sensitivity analysis formulas can be derived in the usual manner, except that the introduced nonlinear mapping has to be taken into account. Moreover, the adjusted element can also be incorporated into general finite element analysis and optimization software in the conventional way. The introduced design variables are related to the cross-section of the beam, to the shape of the (possibly) skeletal structure of the manipulator and to the drive functions. The layered cross-section approach and the design element technique are utilized to parameterize the shape of individual elements and the whole structure. A family of implicit time integration methods is adopted for the response and sensitivity analysis. Based on this assumption, the corresponding sensitivity formulas are derived. Two numerical examples illustrate the performance of the proposed element implementation.

Experimental and Numerical Investigation of the Axial Behavior of Connection in CFST Diagrid Structures

Concrete filled steel tubular (CFST) diagrid structures usually have connections intersected by four oblique CFST columns. In order to investigate the performance, capacity and failure mechanism of the connections, two 1/5.5-scale specimens were tested under monotonic axial loading. The parameters in the study were the separation angle between columns. While the test was being conducted, the deflection, stress, failure pattern and capacity of the specimens were obtained and analyzed. In addition, the connection was analyzed using the general finite element analysis (FEA) software ABAQUS, with the purpose of investigating the mechanism, the weakness, the distribution of stress, and the bearing capacity of the connections. Experimental and numerical results indicate that the connecting separation angles resulted in the difference of failure modes and the mechanical behavior of the connections was similar to the behavior of CFST short columns.

A total strain-based hysteretic material model for reinforced concrete structures: theory and verifications

In this paper, a total strain-based hysteretic material model based on MCFT is proposed for non-linear finite element analysis of reinforced concrete structures. Although many concrete models have been proposed for simulating behavior of structures under cyclic loading conditions, accurate simulations remain challenging due to uncertainties in materials, pitfalls of crude assumptions of existing models, and limited understanding of failure mechanisms. The proposed model is equipped with a fully generalized hysteresis rule and is formulated for 2D plane stress non-linear finite element analysis. The proposed model has been formulated in a tangent stiffness-based finite element scheme so that it can be used for most general finite element analysis packages. Moreover, it eliminates the need to check that tensile stresses can be transmitted across a crack. The tension stiffening model is a function of the bar orientation and any orientation can be accommodated. The proposed model has been verified with a series of experimental results of 2D RC planar panels. This study also demonstrates how parameters of the proposed model associated with cyclic damage modeling influences the pinched cyclic shear behavior.

Finite Element Analysis of Precision Hard Cutting Using Different Cutting Edge Preparation

Machining hardened steels has become an important manufacturing process, particularly in the automotive and bearing industries. Hardened steel GCr15 with its harness between HRC50 and HRC65 is one kind of more difficult machining material. Abrasive processes such as grinding have typically been required to machine hardened steels, but advances in machine tools and a new cutting material of polycrystalline cubic boron nitride (PCBN) have allowed hard turning on modern lathes to seems to gain an ever increasing industrial acceptance as an economically and environmentally friendly alternative to many grinding applications. In this paper, based on large deformation theory and updated Lagrangian procedure, a coupled thermo-mechanical plane strain orthogonal precision cutting model with general finite element analysis software is developed to the influence of cutting edge preparation on the cutting of GCr15 with PCBN tool, such as cutting forces, shear angle, and cutting temperature. The three major designs of cutting edge preparation are used on most commercial cutting inserts: a) sharp edge, b) honed edge, and c) chamfer edge. The friction between the tool and the chip is assumed to follow a shear model and the local adaptive remeshing technique is used for the formation of chip. The calculated principle cutting forces are compared with published data and found to be in good agreement. The simulation results can be used as a practical tool both by researchers and toolmakers to design new tools with rational tool edge and to optimize the cutting process.

A general finite element analysis method for balloon expandable stents based on repeated unit cell (RUC) model

A successful deployment of the stent is dependent on the good understanding of its mechanical properties. This paper presents a general RUC (repeated unit cell) approach for the analysis of balloon expandable stents with various types of closed cells. The application of the unified periodic boundary conditions on the RUC model of the stent is formulated. Numerical analysis is performed by the ABAQUS FEM package. Stents of the Palmaz-Schatz type and NIR ® type with V- or S-shaped links are analyzed with the RUC models and the numerical results agree well with those obtained by much larger models in available publications. The global deformation pattern and the stress distribution of the entire stent can also be obtained by a geometrical tessellation or assembling of the deformed RUCs. It is found from the numerical analysis that the diameter of the stent during deployment changes slowly at the start and increases drastically when the internal pressure reaches a critical value where yielding hinges are formed. V- and S-stents are much easier to expand than the Palmaz-Schatz stent. However, the foreshortenings of the V-stent and S-stent are noticeable. The advantages of the RUC approach are that the existing periodicities in the stent structure are better and directly represented by applying the periodic boundary conditions and a much smaller FEM model and less computational efforts are required to achieve the same analysis accuracy as that by larger models adopted in previous publications.

Cutting Force Experiment and Simulation by Hard Turning GCr15 Bearing Steel with High Speed Considering Cutting Edge Preparation

In this study, hard turning GCr15 bearing steel with high cutting speed is experimental investigated the influence of the CB7015WH insert with chamfer edge and Safe-Lock and the CB7015 insert with a combination of hone radius and a chamfer edge on cutting forces and surface roughness of machined surface. Experimental results show that the cutting forces of the chamfer edge and Safe-Lock is smaller than that of the combination of hone radius and a chamfer edge. Moreover, surface roughness of machined surface with the CB7015WH insert is better. A coupled thermo-mechanical 2D finite element model with general finite element analysis software Deform 2D.8.1 is developed for the influence of two kinds of inserts on cutting forces and effective stress. The simulation results are compared with experimental data and found to be in good agreement.

Eigensolution reanalysis of modified structures using epsilon‐algorithm

AbstractBased on the Neumann series expansion and epsilon‐algorithm, a new eigensolution reanalysis method is developed. In the solution process, the basis vectors can be obtained using the matrix perturbation or the Neumann series expansion to construct the vector sequence, and then using the epsilon algorithm table to obtain the approximate eigenvectors. The approximate eigenvalues are computed from the Rayleigh quotients. The solution steps are straightforward and it is easy to implement with the general finite element analysis system. Two numerical examples, a 40‐storey frame and a chassis structure, are given to demonstrate the application of the present method. By comparing with the exact solutions and the Kirsch method solutions, it is shown that the excellent results are obtained for very large changes in the design, and that the accuracy of the epsilon‐algorithm is higher than that of the Kirsch method and the computation time is less than that of the Kirsch method. Copyright © 2005 John Wiley & Sons, Ltd.

General non-linear finite element analysis of thick plates and shells

A non-linear finite element analysis is presented, for the elasto-plastic behavior of thick shells and plates including the effect of large rotations. The shell constitutive equations developed previously by the authors [Voyiadjis, G.Z., Woelke, P., 2004. A refined theory for thick spherical shells. Int. J. Solids Struct. 41, 3747–3769] are adopted here as a base for the formulation. A simple C 0 quadrilateral, doubly curved shell element developed in the authors’ previous paper [Woelke, P., Voyiadjis, G.Z., submitted for publication. Shell element based on the refined theory for thick spherical shells] is extended here to account for geometric and material non-linearities. The small strain geometric non-linearities are taken into account by means of the updated Lagrangian method. In the treatment of material non-linearities the authors adopt: (i) a non-layered approach and a plastic node method [Ueda, Y., Yao, T., 1982. The plastic node method of plastic analysis. Comput. Methods Appl. Mech. Eng. 34, 1089–1104], (ii) an Iliushin’s yield function expressed in terms of stress resultants and stress couples [Iliushin, A.A., 1956. Plastichnost’. Gostekhizdat, Moscow], modified to investigate the development of plastic deformations across the thickness, as well as the influence of the transverse shear forces on plastic behaviour of plates and shells, (iii) isotropic and kinematic hardening rules with the latter derived on the basis of the Armstrong and Frederick evolution equation of backstress [Armstrong, P.J., Frederick, C.O., 1966. A mathematical representation of the multiaxial Bauschinger effect. (CEGB Report RD/B/N/731). Berkeley Laboratories. R&D Department, California.], and reproducing the Bauschinger effect. By means of a quasi-conforming technique, shear and membrane locking are prevented and the tangent stiffness matrix is given explicitly, i.e., no numerical integration is employed. This makes the current formulation not only mathematically consistent and accurate for a variety of applications, but also computationally extremely efficient and attractive.

Design and research of gymnasium structure in Zhejiang University

This paper deals with the issues involved during the design of a complex gymnasium located at the new campus of Zhejiang University. The complexity comes from the gymnasium's being of three parts: long-span membrane structure, prestressed concrete structure and extraordinarily long tubular steel structure without seams. The paper first presents considerations of the prestress design, followed by analyses of the stress states due to temperature changes and concrete shrinkage. Buckling and postbuckling analyses were performed to determine the load-carrying capacity of the perfect and imperfect tubular steel structure of the inclined arch system, while dynamic relaxation method and general nonlinear finite element analysis were used to carry out shape-finding and stress analyses of the membrane structure respectively. Finally, collated monitoring date was applied to control the construction quality and verify the design parameters. Some useful conclusions are available at the end of the paper.

Cohesive Model of Electromechanical Fatigue for Ferroelectric Materials and Structures

AbstractWe develop a phenomenological model of electro-mechanical ferroelectric fatigue based on a ferroelectric cohesive law that couples mechanical displacement and electric-potential discontinuity to mechanical tractions and surface-charge density. The ferroelectric cohesive law exhibits a monotonic envelope and loading-unloading hysteresis. The model is applicable whenever the changes in properties leading to fatigue are localized in one or more planar-like regions, modelled by the cohesive surfaces. We validate the model against experimental data for a simple test configuration consisting of an infinite slab acted upon by an oscillatory voltage differential across the slab and otherwise stress free. The model captures salient features of the experimental record including: the existence of a threshold nominal field for the onset of fatigue; the dependence of the threshold on the applied-field frequency; the dependence of fatigue life on the amplitude of the nominal field; and the size effect on the coercive field. Our results, although not conclusive, indicate that planar-like regions affected by cycling may lead to the observed fatigue in tetragonal PZT. A particularly appealing feature of the model is that it can be incorporated in a very natural and convenient way into a general finite element analysis of structures and devices for fatigue life assessment.

Mixed formulation of nonlinear beam on foundation elements

This paper presents an inelastic element for the analysis of beams on foundations. The element is derived from a two-field mixed formulation with independent approximation of forces and displacements. The state determination algorithm for the implementation of the element in a general purpose nonlinear finite element analysis program is presented and its stability characteristics are discussed. Numerical studies are performed to compare the model with the classical displacement formulation. The studies confirm the superiority of the proposed model in describing the inelastic behavior of beams on foundations.

Stress analysis of ply drop-off in composite structures

A combination of analytical and numerical method is employed to solve the ply drop-off problem. The singular stress fields in the drop-off region are characterized by using the eigenfunction expansion method. A global element capable of capturing the singular behavior is developed and incorporated into a general finite element analysis to provide an overall accurate solution of the stress fields in the ply drop-off region. This facilitates the use of a coarse mesh at the ply drop-off location even there are singular fields. The validation of the global–local finite element method has been carried out with the help of numerical examples.

Shape optimisation using FEA software: a V-shaped anvil as an example

In order to increase the reliability and the application range of FEM programs for parameter optimisation, a parameter optimisation system for metal forming has been developed by combining the general non-linear finite element analysis software MARC with the improved constrained variable metric strategy, which is an advanced mathematical programming algorithm for general non-linear constrained optimisation problems. A series of new curved V-shaped anvils which have a strong cavity closing effect are proposed by applying the optimisation system to define the optimal V-shaped anvil for heavy shaft forgings. The development of this system indicates a new way for parameter optimisation in metal forming.

Crack stability evaluation of nuclear main steam pipe considering load reduction effect

The objective of this paper is to evaluate the crack stability of a nuclear main steam pipe, considering load reduction effect due to the presence of circumferential through-wall crack. Also, optimization techniques are adopted to simulate the crack effect on the elbow component of piping systems. By using a general beam element that contains a discontinuous cross-section, piping analysis is performed to obtain the reduced load. Considering this reduced load, LBB design concept is applicable to the nuclear main steam pipe system. Also, by combining an optimization program and a general finite element analysis software, the appropriate dimensions are simplified and an equivalent beam element representing the effect of crack in the elbow could be successfully obtained.

Delaunay triangulation and 3D adaptive mesh generation

Delaunay triangulation and its complementary structure the Voronoi polyhedra form two of the most fundamental constructs of computational geometry. Delaunay triangulation offers an efficient method for generating high-quality triangulations. However, the generation of Delaunay triangulations in 3D with Watson's algorithm, leads to the appearance of silver tetrahedra, in a relatively large percentage. A different method for generating high-quality tetrahedralizations, based on Delaunay triangulation and not presenting the problem of sliver tetrahedra, is presented. The method consists in a tetrahedra division procedure and an efficient method for optimizing tetrahedral meshes, based on the application of a set of topological Delaunay transformations for tetrahedra and a technique for node repositioning. The method is robust and can be applied to arbitrary unstructured tetrahedral meshes, having as a result the generation of high-quality adaptive meshes with varying density, totally eliminating the appearance of sliver elements. In this way it offers a convenient and highly flexible algorithm for implementation in a general purpose 3D adaptive finite element analysis system. Applications to various engineering problems are presented