Finite Element Analysis Procedure Research Articles

Simplified procedure for finite element analysis of the longitudinal performance of shield tunnels considering spatial soil variability in longitudinal direction

A simplified procedure based on finite element method (FEM) is developed in this paper for analyzing the longitudinal performance of shield tunnels considering the longitudinal variation of geotechnical parameters. Herein, the spatial variation of soil properties of the ground under the tunnel is explicitly considered. The validity of the FEM solution is verified by analytical solutions and model tests with various assumed scenarios. The random field theory is employed to model the spatial variation (in the longitudinal domain) of the subgrade reaction coefficient, which is a key soil parameter for FEM analysis of the longitudinal performance of shield tunnels. A hypothetical example is presented to demonstrate the capability of the simplified FEM procedure in analyzing the longitudinal performance of a shield tunnel with spatial soil variability. The results show that the overall settlement of the tunnel is mainly affected by the mean of soil properties, while the extent of the tunnel differential settlement is significantly affected by the variation and scale of fluctuation of soil properties.

Finite element analysis of the mechanical behaviour of insulated rail joints due to impact loadings

Insulated rail joints (IRJs) are safety-critical components in the signalling system of rail corridors. They are subjected to dynamic loads generated by heavy rolling-stock/track- system interactions and degrade faster than the other components of the rail track. Degraded IRJs diminish the reliability of the signalling system, thus posing a serious threat to the safety of rail operations. Therefore, there is a pressing need to closely examine the failure mechanisms of the end posts made of insulated material and inserted into the discontinuity in the rail at IRJs with a view to improving their service life, reliability and efficiency. Only a limited literature is available that examines different materials for IRJ end posts, and these primarily focus on contact pressure and contact stress distributions in the vicinity of the end post, disregarding the damage to the rail ends and end post materials. In this paper, a detailed three-dimensional finite element analysis procedure is carried out to quantify plastic deformation and material damage to the end post and railhead materials of IRJs due to a wheel load above that of the shakedown limit of rail steel. A modified Hertzian contact pressure distribution is considered in this simulation. A 5 mm thickness of an end post is considered at the discontinuity in the rail, which is required to form the six-bolt IRJ. Three popular IRJ end post materials are considered in this study: fibreglass, polyhexamethylene adipamide, and polytetrafluoroethylene. A total of 2000 cycles of a 174 kN dynamic wheel load (in pressure format over the wheel/rail contact patch) are applied on the top of the rail’s surface in the vicinity of the IRJ. Equivalent plastic deformations along with vertical and longitudinal plastic strains for unloaded conditions are presented. The strain plots depict damage of end post materials and ratchetting failure of rail ends. The ratchetting failure modes follow the established trend of decay in ratchetting rate in successive wheel load cycles. Comparisons of strain and stress on the railhead surface and in the railhead sub-surface considering all three different end post materials are put forward. Out of the three end post materials, fibreglass is the optimal material considering the ratchetting mode for the damage of the railhead material.

Incorporating feedforward neural network within finite element analysis for L-bending springback prediction

The use of the latest nonlinear recovery in finite element (FE) analysis for obtaining an accurate springback prediction has become more complicated and requires complex computational programming in order to develop a constitutive model. Thus, the purpose of this paper is to apply an alternative method that is capable of facilitating the modelling of nonlinear recovery with acceptable accuracy. By using the artificial neural network (ANN), the experimental results of monotonic loading, unloading, and reloading can be processed through a back propagation network that is able to detect a pattern and do a direct mapping of elastically-driven change after the plastic forming. FE analysis procedures were carried out for the springback prediction of sheet metal based on an L-bending experiment. The findings of the FE analysis show an improvement in the accuracy of the predictions when compared to the measured data.

A Numerical Approach for Lower Bound Limit Analysis

In this paper, a numerical procedure for plastic limit analysis of 3-D elastic-perfectly plastic bodies under complex loads is presented. The method is based on the lower-bound limit theorem and von Mises yield criterion so that the lower-bound limit analysis can be conducted by solving a nonlinear mathematical programming problem. A SQP algorithm and a dimension reduction-based technique are used to solve the discretized finite element optimization formulation. A conception of active constraint set is introduced, so that the number of constraints can be reduced greatly. The basis vectors of reduced residual stress spaces are constructed by performing an equilibrium iteration procedure of elasto-plastic finite element analysis. The numerical procedure is applied to carry out the plastic limit analysis of pipelines with part-through slots under internal pressure, bending moment and axial force. The effects of different sizes of part-through slots on the limit loads of pipelines are studied.

Progressive Failure Analysis of Laminated Composite Plate by Using Higher Order Shear Deformation Theory

A finite element analysis procedure is developed for progressive failure analysis of laminated composite plates under in plane tensile loading. A finite element model is based on higher order shear deformation theory (HSDT) with seven degrees of freedom. The degradation technique used for degradation of material properties of a failed ply is a ply discounting approach. The mode dependant Hashin and Lee failure criterion is used for the progressive failure analysis. The results of first ply failure load and last ply failure load are obtained for different stacking sequence of composite plate. The results shows that a considerable amount of strength remains un utilized in composite laminates after first ply failure of laminates.

Analysis of loads on the shearing edge during electrohydraulic trimming of AHSS steel in comparison with conventional trimming

In order to achieve further weight reduction in automotive components, the technology of manufacturing of automotive panels from advanced high strength steels is being developed. Electrohydraulic trimming technology eliminates the necessity of accurate alignment of the shearing edges in trimming operation. Analysis of loads on the tool during high-rate EH trimming process has been performed. In order to investigate the effect of the process on the shearing edge performance, a dedicated finite element analysis procedure combining 3D shell and 2D solid models was developed. EH trimming experiments were carried out to validate the simulation model where elastic plastic deformation of the shearing edge was taken into account. The effects of the die geometry and number of trimming cycles on the tool contact loads and tool's plastic deformation were analyzed. This analysis was based on numerical simulation of deformation and fracture of the blank being trimmed in contact with the deformable shearing edge. Numerical analysis of the shearing edge deformation was performed in elasto-plastic formulation for the D2 tool steel inserts used in the experimental study and also in elastic formulation to define the maximum stresses which tool material needs to withstand to avoid its plastic deformation.The results of the analytical study indicate that the maximum contact pressure is applied to the trimming tool at the lower endpoint of the shearing edge, but the point of maximum plastic deformation in the tool is found on the vertical wall of the shearing edge where it contacts the area of the blank where separation takes place. The shearing edge of the EH trimming die experiences less contact pressure and less plastic deformation with increase of the radius of the shearing edge. The shearing edge of the EH trim die has a tendency to dull after a number of trimming cycles. In addition, when compared with conventional trim die, the shearing edge of the EH trimming tool experiences slightly higher (10–15%) contact loads than in conventional trimming. However, plastic deformations occurring in the conventional trim die for shearing of identical material are larger. Analysis of loads on the EH trimming tool was repeated for purely elastic tool material to formulate the requirements to the material of the shearing edge.

Customizing Procedure of Finite Element Analysis for Sheet Metal Forming

Based on Pam-Stamp software platform, standardization procedure of finite element analysis for sheet metal forming was customized by set up module such as model building, meshing, setting of boundary conditions, calculation submitting, viewing of results and report generating. Standardization procedure has been successfully applied in the development of new products, which shortens the preparation cycle of procedure, improves the forming quality of the parts and enhances the capability for rapidly researching and developing.

Safety examination of existing concrete structures using the global resistance safety factor concept

Current design procedures for structural concrete elements are based on member level (or local) safety checks, in the sense that the safety condition is evaluated at each cross-section individually. In the examination of existing structures, the exploitation of the redundancy of the structural system and its redistribution capacity may prove necessary to fulfil the safety requirements, demanding for a system level (or global) safety evaluation. This can be achieved using nonlinear finite element analysis (NLFEA) procedures and requires a safety format different than that based on partial safety factors.In this work, a simple safety format tailored for NLFEA of existing structures is described. It is shown how to define a global resistance safety factor based on a simple semi-probabilistic approach in line with the recommendations of the new Swiss standards for existing structures [1,2] that can capture the sensitiveness of the structural system resistance, R, to the random variation of the input variables. Besides enabling the use of updated information regarding the material properties, the proposed procedure allows performing reliability differentiation based on risk analysis, being therefore suitable for the safety examination of existing bridges.The definition of the semi-probabilistic global resistance safety factor is based on the assumption of a log-normal probability density function for the resistance R and on an estimate of its coefficient of variation, vR. The existing proposals for estimating vR are reviewed and compared. For statically determined structures with a single dominant failure mode (axial compression, bending or shear) the examination values of R computed with global resistance safety factors are shown to compare well with those obtained with partial safety factors. The reliability of the examination values of R is also evaluated through a comparison with the Monte Carlo simulation procedure and it is shown that the global resistance safety factor method is sufficiently accurate. Finally, a case-study is presented illustrating the application of the proposed procedure in the structural safety examination of an existing prestressed concrete bridge.

Calculation of Critical Crack Size of Repair Welded Rail

Repair of damaged rail surface by overlay welding is the common rail maintenance method. But the discontinuity in material between base and weld brings initiation of cracks and they causes a rail fracture. Unfortunately, such cracks are hard to detect on site because the weld boundary prevents the echo signals penetration by reflection. So estimation of the critical crack size (CCS) has been a critical issue in railroad industry to prevent a rail from sudden fracture. In this study, we calculated the critical size of crack which was initiated and propagated underneath of the overlay welded rail by applying linear elastic fracture mechanics. For this purpose, we measured the maximum load carrying capacities of cracked UIC60 by inverted 3 point bend tests and checked the feasibility of the finite element (FE) analysis procedure. We could find the correlation in crack size between the test and 3D FE analysis results and applied the proposed 3D FE analysis model to calculate the CCS of a rail. We calculated the stress intensity factors on cracked rail by increasing the size of crack until the rail broke. The CCS was calculated as around 30.0 mm under the normal railway service operating condition.

A periodontal ligament driven remodeling algorithm for orthodontic tooth movement

While orthodontic tooth movement (OTM) gains considerable popularity and clinical success, the roles played by relevant tissues involved, particularly periodontal ligament (PDL), remain an open question in biomechanics. This paper develops a soft-tissue induced external (surface) remodeling procedure in a form of power law formulation by correlating time-dependent simulation in silico with clinical data in vivo (p<0.05), thereby providing a systematic approach for further understanding and prediction of OTM. The biomechanical stimuli, namely hydrostatic stress and displacement vectors experienced in PDL, are proposed to drive tooth movement through an iterative hyperelastic finite element analysis (FEA) procedure. This algorithm was found rather indicative and effective to simulate OTM under different loading conditions, which is of considerable potential to predict therapeutical outcomes and develop a surgical plan for sophisticated orthodontic treatment.

Chloride diffusivity of concrete: probabilistic characteristics at meso-scale

This paper mainly discusses the influence of the aggregate properties including grading, shape, content and distribution on the chloride diffusion coefficient, as well as the initiation time of steel corrosion from a probabilistic point of view. Towards this goal, a simulation method of random aggregate structure (RAS) based on elliptical particles and a procedure of finite element analysis (FEA) at meso-scale are firstly developed to perform the analysis. Next, the chloride diffusion coefficient ratio between concrete and cement paste &#119863;app&#119863;cp is chosen as the index to represent the effect of aggregates on the chloride diffusion process. Identification of the random distribution of this index demonstrates that it can be viewed as actually having a normal distribution. After that, the effect of aggregates on &#119863;app&#119863;cp is comprehensively studied, showing that the appropriate properties of aggregates should be decided by both of the average and the deviation of &#119863;app&#119863;cp . Finally, a case study is conducted to demonstrate the application of this mesoscopic method in predicting the initiation time of steel corrosion in reinforced concrete (RC) structures. The mesoscopic probabilistic method developed in this paper can not only provide more reliable evidences on the proper grading and shape of aggregates, but also play an important role in the probability-based design method.

Mathematical Model Development on the Deformation Behaviour of Symmetric Hexagonal of Various Angles and Square Tubes under Lateral Loading

The purpose of this research is to develop a mathematical model of the collapse behaviour of symmetric hexagonal tubes. For that, a finite element analysis procedure was conducted using ABAQUS software to determine the lateral collapse behaviour of symmetric hexagonal of angles, and square tubes to compare the results with the cylindrical tube. Then, a new predictive mathematical model of the lateral collapse behaviour for the generalized symmetrical geometric tubes is developed based on rigid, perfectly plastic model and the energy balance method. The newly mathematical model was validated with the simulation method results. It was discovered that symmetric hexagonal and square tubes performed different deformation behaviour than the cylindrical tube. Square and symmetric hexagonal with tubes performed Type II deformation behaviour.Symmetric hexagonal tubes with performed Type I with the perfectly plastic collapse behaviour whereas cylindrical tube performed Type I with strain hardening deformation behaviour. The mathematical prediction model had managed to model the deformation behaviour of symmetric hexagonal tubes with but failed to model the square and symmetric hexagonal with tubes because it was the perfectly plastic model which suitable for Type I with perfectly plastic deformation behaviour.

From numerical calculations to materials testing homologation: a biaxial fatigue reliability prediction methodology for structural components

This article investigates a fatigue approach conducted from the design phase to testing approval. It considerers modern analytical and experimental tools for structural durability assessment over each development phase for two reference components aiming an early approval methodology validation for a new design. A Finite element analysis procedure was used to set critical spots for measurements minimizing the data acquisition efforts. Based on measured data, strain life calculation was done for two reference components in order to set the release goals for a new design submitted to this approach. An innovative fatigue experimental technique is proposed using component extracted specimens and an edited input cycle loads. Considering the random data from a standard test track and signal proportionality evaluation, while assuming the Brown Miller equation for bi-axial fatigue together with Ramberg-Osgood model, equivalent damage load blocks were edited and used as input for durability assessment on specimens representing the component material. The results for the three parts materials were plotted as Weibull diagram for B10 life estimation. Fatigue life results showed good correlation with the reference parts structural performance thus validating the method as well as approving the new design for production without additional on-vehicle durability testing. The methodology and the fatigue testing proposal is therefore recommended for future applications on similar developments.

Load shortening characteristics of marine grade aluminium alloy plates in longitudinal compression

This study presents detailed and rigorous numerical analysis for a parametric series of unstiffened aluminium plates typical of those used in lightweight ships and equivalent thin walled stiffened structures. The study is undertaken with a nonlinear finite element analysis procedure using ABAQUS. The strength behaviour of the plates under a progressively increasing longitudinal in-plane load are shown to be affected by a number of parameters including the alloy, geometric imperfection shape, heat affected zone distribution, level of heat softening and residual stress distribution. The comparative influences of these various factors, some of which are specific to welded aluminium structure, are explored to determine which must be accounted for in the development of a parametric series of design curves.

Optimization based simulation of self-expanding Nitinol stent

Self-expanding Nitinol (nickel–titanium alloy) stents are tubular, often mesh like structure, which are expanded inside a diseased (stenosed) artery segment to restore blood flow and keep the vessel open following angioplasty. The super-elastic and shape memory properties of Nitinol reduce the risk of damage to the stent both during delivery into the body and due to accidents while in operation. However, as Nitinol stents are subjected to a long-term cyclic pulsating load due to the heart beating (typically 4×107cycles/year) fatigue fracture may occur. One of the major design requirements in medical implants is the device lifetime or, in engineering terms, fatigue life. In order to improve the mechanical properties of Nitinol stents, at first, a reliable procedure of finite element analysis (FEA) is established to provide quantitative measures of the stent’s strain amplitude and mean strain which are generated by the cyclic pulsating load. This allows prediction of the device’s life and optimization of stent designs. Secondly, the objective is to optimize the stent design by reducing the strain amplitude and mean strain over the stent, which are generated by the cyclic pulsating load. An optimization based simulation methodology was developed in order to improve the fatigue endurance of the stent. The design optimization approach is based on the Response Surface Method (RSM), which is used in conjunction with Kriging interpolation and Sequential Quadratic Programming (SQP) algorithm.

Experiments and thermal-electrical analysis of buss bar and relay assemblies in junction blocks

A junction block (or electrical distribution box) is electrical equipment that has been densely assembled from components such as buss bars, relays, and fuses to control the electric current flow in vehicles. Joule heat is generated in these parts as a result of electrical bulk resistance and electrical contact resistance. The generation of heat increases due to the complex behavior of modern vehicle electronic systems. Overheated parts can be damaged during operation due to thermal energy. The thermal assessment of a junction block is an important issue in automobile development. We suggest a methodology to simulate the transient temperature distribution of buss bars and electrical relays in a junction block. A finite element formulation of a coupled electro-thermal problem, which includes the effect of Joule heating, is introduced to the simulation. Finite element analysis (FEA) and experiments at the component level of buss bars and relays are conducted to investigate the thermal performance of a junction block. To verify the accuracy of the FEA procedure, the temperature history obtained by FEA is compared with the results obtained from experiments. The thermal-electric analysis of a typical junction block assembly is also discussed.

Vibration Analysis of Wooden Traditional Frames Using Finite Element Method and Measurements with a Simple Piezoelectric Cable Displacement Sensor

The applicability of a new type of piezoelectric sensor to evaluate the dynamic characteristics of traditional wooden structures is investigated based on forced vibration tests and finite element analysis procedure. The new sensor was developed for structural health monitoring purposes and series of forced vibration tests on a one-fifth scale wooden prototype were performed to evaluate the sensor response. The prototype structure corresponds to a framed wooden construction with traditional connections between columns and beams where nails are not used. These joints consist of beam-ends narrowed with respect to the rest of the piece and inserted into a hole cut in the column. New sensors were installed in selected joints of the structure. The results of the forced vibration test obtained from new sensor measurements are discussed in relation to the analytical procedure adopted to estimate the vibration characteristics and dynamic response of the target structure, and good agreement was obtained between both results. With this good agreement of the analytical procedure and the measurement results, the reliability of the employed methodology and the applicability of the proposed new sensor were verified.

On the Application of Rousselier's Damage Model to Predict Fracture Resistance Behavior of Zircaloy Fuel Pin Specimens

Abstract It may not be possible to machine standard fracture mechanics specimens from the thin-walled fuel pins as used in the nuclear reactors due to their geometry. In order to overcome this problem, a combined experimental and finite element (FE) analysis procedure has been adopted in this work. Determination of transverse mechanical properties from the ring type of specimens machined from the thin-walled nuclear reactor fuel pins is not also straightforward due to the presence of combined tension as well as bending loading conditions. However, finite element analysis of the whole ring tension setup can be carried out and the material stress-strain property can be determined through an inverse and iterative procedure. In this work, ring tension tests were carried out on un-irradiated Zircaloy-4 clad tube specimens. The specimen and the mandrel both were modeled in order to evaluate the load-displacement behavior of the test. The Rousselier's micro- mechanical model for ductile fracture was applied to simulate the crack growth in these specimens. The micro-mechanical parameters as determined from the ring tension experiment and finite element analysis were later used to simulate the crack propagation in a standard double-edged notched tensile (DENT) specimen. The J-R curve of the DENT specimen has also been compared with that of a cracked Pin-Loading-Tension (PLT) specimen.

A Polynomial Chaos Expansion Based Reliability Method for Linear Random Structures

Within the framework of mechanical engineering, reliability assessment is usually involved in the procedure of finite element analysis (FEA) combined with Monte Carlo simulation (MCS). Unfortunately, such approaches require high computational effort. To improve efficiency, we propose a polynomial chaos expansion (PCE) based MCS method for linear random structures, in which the time consuming repeated FEA is avoided in manner of approximating the random response by PCE. However, applications of PCE are always restricted for the first passage problem due to the curse of high dimensionality. To overcome this, we use the convolution form to compute the dynamic response, in which PCE is raised to approximate the modal properties so that the dimension of uncertainties is reduced since only structural random parameters are considered. Four examples are studied to show the effectiveness and relevancy of the proposed method.

Nonlinear Behaviors of Submerged Floating Tunnels under Seismic Excitation

The Submerged Floating Tunnels are one new type of infrastructure, representing a challenge in structural engineering, both on the theoretical and operational fields. In this paper, a 3D finite element analysis procedure is developed accounting for material and geometrical nonlinearities, soil-structure interaction and multiple-support seismic excitation. A comparison between dynamic response in case of elastic and inelastic material behavior of the anchor bars is given, which shows the beneficial effect of this source of energy dissipation. Furthermore, the effects of introducing dissipation devices for restraining the tunnel axial motion have been investigated as well. Besides this, the earthquake transmission through water (seaquake) is here introduced as an additional hydrodynamic loading on the tunnel. The ensuing increase of loading in the tunnel indicates that a significant role is played by this loading source and highlights the need of further investigations on seaquake effects.