Accuracy Of Finite Element Analysis Research Articles

Behavior analysis of FRP tube/filling strengthened steel members under axial compression

Abstract Influence of the ultimate strength of stee This study presents a new fiber reinforced polymer tube/filling strengthening method (i.e., FRP tube/filling strengthening) that creates a new composite compression member with a novel mechanical behavior, “bilinear behavior.” Previous experimental and theoretical studies have been conducted based on the ultimate state of the section. To thoroughly study the stiffness and entire loading process of this novel member, finite element analysis (FEA) models are built in this paper. First, the model development process considers the initial defections and interface properties, and these models are verified by the experimental results. Two models of typical load-axial displacement curves describe the experimental results: a Bilinear model and a Trilinear model. Second, finite element modeling (FEM) is used to conduct a parametrical analysis that considers 7 parameters, and the results identify the mechanism of the strengthened member. Specifically, the Bilinear model corresponds to an unreinforced or relatively weakly reinforced specimen, and the Trilinear model corresponds to a relatively strongly reinforced specimen. If the exterior restraint system is weak, then the core steel buckles and subsequently yields; this behavior is described by the Bilinear model. If the exterior restraint system is strong (e.g., the length or the bending stiffness of the exterior restraint system is great), then the specimen can continue to bear a higher force after steel yielding until elastic-plastic buckling occurs; this behavior is described by the Trilinear model. Third, the FEA results and previous experimental and theoretical studies are used to obtain the stiffness and load-axial displacement curves, which are helpful for the design process. In general, relatively accurate FEA models are built in this paper that are capable of describing the mechanical behaviors of the novel member.

Hybrid approach for woven fabric modelling based on discrete hypoelastic behaviour and experimental validation

A non-linear discrete hybrid approach based on the association of hypoelastic continuous elements (non-linear shear behaviour) with specific connectors (non-linear tension stiffness) is developed. It allows the simulation of a two-dimensional (2D) woven reinforcement forming via an accurate explicit finite element analysis. This approach allows the simulation of 2D unbalanced fabrics uncoupling tensile and shear behaviour. It only needs a few parameters to be identified, and shows a good agreement with the experiments. The identification of the model parameters is investigated, and their relevance is analysed in reference tests. To determine the continuous element behaviour, a VUMAT hypoelastic model is implemented in Abaqus/Explicit. This model allows the prediction of fibre stresses and the accurate determination of shear angle in large deformations. Identification and validation of the model are performed using standard characterisation fabric tests. The experimental characterisation provided the numerical data to produce a representational prediction of the deformed fabric geometry and shear angle distribution. Further, the behaviour of the carbon woven reinforcement is identified. A bias extension test is used to both calibrate and validate the model. The capability of the model is illustrated to simulate deep drawing, and to compare with the experimental results of hemispherical forming.

Experimental cyclic test and failure modes of a full scale enhanced modular steel plate shear wall

Abstract Several studies on steel plate shear wall systems have shown that the seismic demand on the vertical boundary elements is extremely large for typical buildings. To overcome this problem, an enhanced approach is introduced in this paper. It involves utilizing not only a modular steel shear panel, but also contains column-independent boundary element which eventually facilitates retrofitting of the existing building. First, a four-story building was designed based on pushover analysis, followed by more accurate finite element analysis to refine the section design parameters. Next, a full scale single-story modular steel shear panel welded to the steel boundary elements was constructed and tested under cyclic load protocol to simulate the hysteresis behavior under severe excitations. The test results show a high initial stiffness, excellent ductility, and significant energy dissipation capacity. Observed failure modes were discussed.

원통형 수직 펌프의 공진회피를 위한 접수진동해석

Resonance phenomena occurs at large vertical pump which is operating to cool down the hot steam using sea water in the power plant. To avoid the resonance, the natural frequency needs to be isolated about 20% from motor operating speed. Yet, excessive vibration occurs especially at low tide. At first, natural frequency of the whole pump system and each part is calculated using ANSYS. As it is revealed in the previous journal papers that only circular pipe part is related to resonance, the FSI technique is applied for free vibration analysis. The natural frequency is reduced to 60% (compared to that) of the frequency measured in air as it is similar to other published results. And the frequency obtained by finite element analysis is almost same to that obtained from modal test. Based on the accurate finite element model and analysis, design change is tried to avoid the resonance by changing the thickness of pipe and base supporting plate. In stead of doing optimization process, design sensitivity is computed and used to find such designs to avoid resonance.

The effects of shear and near tip deformations on interface fracture of symmetric sandwich beams

The effects of shear on energy release rate and mode mixity in a symmetric sandwich beam with isotropic layers and a debond crack at the face-sheet/core interface are investigated through a semi-analytic approach based on two-dimensional elasticity and linear elastic fracture mechanics. The semi-analytic expressions for the shear components of energy release rate and mode mixity phase angle which have been derived in Li et al. (2004) for bi-material beams are extended to sandwich beams and the necessary numerical coefficients derived through accurate finite element analyses. The expressions are combined with earlier results for sandwich beams subjected to bending moments and axial forces in order to obtain solutions for general loading conditions and for an extensive range of geometrical and material properties. The physical and mechanical significance of the terms of the energy release rate which depend on the shear forces are explained using structural mechanics concepts and introducing crack tip root rotations to account for the main effects of the near tip deformations. The results are applicable to laboratory specimens used for the characterization of the fracture properties of sandwich composites for civil, marine, energy and aeronautical applications, provided the lengths of the crack and the ligament ahead of the crack tip are above minimum lengths which are defined in the paper.

Rapid Harmonic Analysis of Piezoelectric MEMS Resonators.

This paper reports on a novel simulation method combining the speed of analytical evaluation with the accuracy of finite-element analysis (FEA). This method is known as the rapid analytical-FEA technique (RAFT). The ability of the RAFT to accurately predict frequency response orders of magnitude faster than conventional simulation methods while providing deeper insights into device design not possible with other types of analysis is detailed. Simulation results from the RAFT across wide bandwidths are compared to measured results of resonators fabricated with various materials, frequencies, and topologies with good agreement. These include resonators targeting beam extension, disk flexure, and Lamé beam modes. An example scaling analysis is presented and other applications enabled are discussed as well. The supplemental material includes example code for implementation in ANSYS, although any commonly employed FEA package may be used.

On the Bird Impact Damage Assessment of Rotorcraft Horizontal Stabilizer

The soft body high energy impact response on rotorcraft composite layered structures is investigated by analysis based on tests carried out. The experimentally and numerically assessed deformation and energy absorption capabilities of Horizontal stabilizer is attributed under high energy bird impact, which is an important aspect in the computer simulations for correlation studies followed by any design modifications. The ability to withstand bird impact of forward facing components is one of the major requirements of rotorcraft to comply bird strike certification test requirement. The main difficulties encountered in achieving accurate finite element analysis are related to modeling of the bird which undergoes severe deformations and the state-of-the art of composite layered modeling. The current study further investigates the impact behavior of soft body projectiles on Horizontal stabilizer through full scale testing.

On crack band model in finite element analysis of concrete fracture in engineering practice

When finite element nonlinear analysis is applied to address the typical engineering problems such as ultimate load carrying capacity or serviceability limits such as deflections or crack width, a special care should be taken for the proper definition of the crack band namely in the presence of reinforcement.The definition of crack band in tension should take into account the reinforcement spacing as well as finite element size. The crack band size should be also limited from below depending on the minimal possible spacing of micro-cracks. In compression failure an analogical concept to the crack band method can be introduced, but again the compressive band size should be limited from below depending on the characteristic dimensions of the analyzed structure.The paper proposes three localization limiters for practical applications of nonlinear finite element model using the smeared crack approach and crack band method both for tension and compression.The application of these localization limiters is demonstrated and verified on several problems ranging from shear failure, bending behavior and compressive failure. It is demonstrated that the simple application of these limiters can increase the accuracy of finite element analysis even if very small or very large finite element sizes are used, which is often necessity in practice or research and development.

Lateral-distortional buckling of beams with hollow flanges and folded plate webs

This paper is concerned with the effects of distortion on the lateral buckling of steel beams which have rectangular or square hollow flanges and folded plate webs. The hollow flanges potentially make very large contributions to the torsional stiffness, but flange distortion (in a shear mode) causes a significant reduction in the effective torsional stiffness and in the lateral buckling resistance.In this paper, the shear distortion of the hollow flanges is analysed, and the strain energy stored in a distorted flange is compared with the strain energy stored during uniform torsion of the flange. This comparison allows the development of a suitable parameter for use in the evaluation of the effect of flange distortion on the torsional stiffness of a hollow flange beam. Uniform torsion test results are used to confirm the significance of this parameter.Finite strip analyses of simply supported hollow flange beams in uniform bending show that there is a significant interaction between distortion and uniform torsion during lateral buckling, which may be approximated by combining their flexibilities. More accurate finite element analyses show that the finite strip predictions are conservative. An approximate method of predicting the effects of flange distortion on elastic lateral buckling is presented which shows good agreement with the finite element predictions.

Finite Element and Experimental Investigation on the Flexural Response of Pre-tensioned T-Girders

A number of analytical and numerical approaches exist for modeling concrete structural members. Finite-element analysis (FEA) is a numerical method that is widely applied to concrete structures based on the use of the nonlinear behavior of materials. The challenge of modeling prestressed concrete structures lies in the treatment of the interface between concrete and prestressing tendons. The FEA-modeling technique discussed in this study is based on general-purpose finite-element packages. This study describes FEA of full-scale high-strength self-compacting concrete, HSSCC pre-tensioned T-girders and its comparison with experimental results. Three 9 m length fully pre-tensioned bridge girders, PHSSCC were designed and cast using HSSCC. The girders were instrumented to monitor deflection, pre-tensioned losses, tendon, steel bar, and concrete strains. The girders were then load tested (until failure), predominantly under flexure, and their service and ultimate results including cracking, flexural stiffness, flexural strength, and different ductility indexes were investigated and compared with FEA results. The software package ABAQUS was used to simulate girders and their bonding conditions to verify the accuracy of FEA. A very good agreement was achieved for numerical and experimental crack patterns. The comparison of finite-element modeling (FEM) and experimental results of load-upward and downward deflections indicated satisfactory agreement throughout the load history of the beams until failure. Comparing FEM and experimental results, reasonable agreement was observed for the two methods of ductility indexes. Finite-element modeling tends to overestimate stress in prestressed tendons at the ultimate state of specimens.

Dynamic and structural integrity analysis of a complete elevator system through a Mixed Computational-Experimental Finite Element Methodology

A systematic dynamic and structural integrity analysis of an elevator system, under real dynamic load conditions, is presented in this work. The proposed method constitutes an important innovation for the field “analysis and design optimization of elevator systems”. Current elevator design requirements lead to development of lightweight structures which often are of higher complexity. In order to achieve design optimization of these systems, it is important to develop an accurate Finite Element Analysis methodology, to support their precise numerical modeling, also in the worst loading case for their operation. One of the worst loading cases for an elevator system is when the elevator falls free and the safety gear is activated until the elevator stops. Each elevator, when installed in a building, is tested in this loading scenario. This means, that should be designed to withstand in these loads and not to have any damage after this test. One of the special features of this paper is that the study was performed on a complete industrial elevator system, including all details/complexities of a commercial system. Comparison of the numerical and experimental data verifies that the proposed “mixed computational-experimental” analysis method is quite reliable, concluding application/verification of the method on a complete industrial elevator system.

New modifying truss model and numerical simulation of steel fiber reinforced concrete under pure torsion

This paper presents a new strut-and-tie model on steel fiber reinforced concrete (SFRC) members under uniform (Saint Venant) torsion. This truss model is intended to reproduce the structural behavior in ultimate limit state, once concrete is cracked. The proposed model is based on previous formulations developed by other researchers; the main novelty is the use of average value linear interpolation methods. The developed model can be considered for constant section members; can be applied to rectangular, T, L, circular, thin-walled, and single-cell and multi-cell hollow sections, among other shapes. Comparison with experimental and numerical results (developed through accurate finite element analysis) shows that the proposed model is more accurate than the proposed formulations.

Experimental and numerical investigation of stress concentration and strength prediction of carbon/epoxy composites

Unidirectional composites are very popular structural materials used in aerospace, marine, energy and automotive industries, thanks to their superior material properties. However, the mechanical behavior of composite materials is more complicated than isotropic materials because of their anisotropic nature. Also, stress concentration presence on the structure, like a hole, makes the problem further complicated. Therefore, enormous numbers of tests are required in understanding the mechanical behavior and strength of composites which contain stress concentration. Accurate finite element analysis and analytical models enable us to understand mechanical behavior and predict the strength of composites without enormous number of tests which cost serious time and money. In this study, unidirectional Carbon/Epoxy composite specimens with central circular holes were investigated in terms of stress concentration factor and strength prediction. The composite specimens which had different specimen width (W) to hole diameter (D) ratio were tested to investigate the effect of hole size on the stress concentration and strength. Also, specimens which had same specimen width to hole diameter ratio, but different sizes were tested to investigate the size effect. Finite element analysis were performed to determine the stress concentration factor for all specimen configurations. Also, Point stress criteria (PSC) was used to predict strength of the specimens. For quasi-isotropic laminate, it was found that the stress concentration factor at the hole tip increases approximately %15 as W/D ratio decreased from 6 to 3. Also, it is observed that as W/D ratio quadrupled with constant specimen width the failure strength increases by %62.4. For the specimens which had same width to hole diameter ratio but different (scaled) dimensions, the stress concentration factor at the hole tip was seen to be identical as expected. For these specimens, as W/D ratio doubled the specimen failure strength reduces by %13.2 because of the size effect. For all type of specimens, the PSC method could predict the strength of specimens with maximum %8 error.

Development of dynamic mesh superposition method for local tensile stress evaluation

The brittle crack propagation and arrest behavior has been studied for a long time. The critical condition is not completely clear, but the local fracture stress criterion is recently regarded as a most promising description of brittle crack propagation and arrest behavior. Although accurate finite element analyses should be employed to obtain the local stresses, it is not realistic to use conventional finite element analyses because computational cost is too high. According to the above background, we focused on mesh superposition method to cope with both reduction of computational cost and improvement of local stress evaluation accuracy. At first, stationary crack problem is solved and it is shown that results agree with conventional solutions, and verified the availability of this method. Then this method is used for dynamic crack propagation and it is verified that mesh superposition method is also applicable to dynamic crack growth.

Computational framework for model updating of large scale linear and nonlinear finite element models using state of the art evolution strategy

In this work, a computational framework applying-finite element model updating techniques is presented for identifying the linear and nonlinear parts of large scale dynamic systems using vibration measurements of their components. The measurements are taken to be, response time histories and frequency response functions of nonlinear and linear components of the system. Covariance Matrix Adaptation – Evolution Strategy (CMA-ES) a state of the art optimization algorithm was coupled with robust and accurate finite element analysis software in order to effectively produce optimal computational results. The developed framework is applied to a geometrically complex and lightweight experimental bicycle frame with nonlinear suspension fork components. The identification of modal characteristics of the frame (linear part) is based on an experimental investigation of its dynamic response. The modal characteristics are then used to update the finite element model. The nonlinear suspension components are identified using the experimentally obtained response spectra for each of the components tested separately. Single objective structural identification methods without the need of substructuring methods, are used for estimating the parameters (material properties, shell thickness properties and nonlinear properties) of the finite element models, based on minimizing the deviations between the experimental and analytical dynamic characteristics. Finally, the numerical results of the complete system assembly were compared to the experimental results of the equivalent physical structure of the bike.

Reduced Order Modeling of Composite Laminates Through Solid-Shell Coupling

Composite laminates display a complex mechanical behavior due to their microstructure, with a through-thickness variation of the displacement and stress fields that depends on the fiber orientation in each layer. Aiming to develop reduced-order numerical models mimicking the real response of composite structures, we investigated the capability and accuracy of finite element analyses coupling layered shell and solid kinematics. This study represents the first step of a work with the goal of accurately matching stress evolution in regions close to possible impact locations, where delamination is expected to take place, with reduced computational costs. Close to such locations, a 3-D modeling is adopted, whereas in the remainder of the structure, a less computationally demanding shell modeling is chosen. To test the coupled approach, results of numerical simulations are presented for a quasi-statically loaded cross-ply orthotropic plate, either simply supported or fully clamped along its boundary.

SAFEM – Software With Graphical User Interface for Fast and Accurate Finite Element Analysis of Asphalt Pavements

Abstract To effectively investigate the mechanical performance of asphalt pavements, software named SAFEM with a user friendly graphical user interface (GUI) was developed. It is based on the semi-analytical finite element (FE) method, which is a three-dimensional FE algorithm that only requires a two-dimensional mesh by incorporating the Fourier series in the third dimension. SAFEM is able to analyze static and dynamic responses of asphalt pavements under stationary or moving loads. Besides linear elasticity, a viscoelastic material model for asphalt layers has also been integrated. Verification was carried out to test and explore the functionality of the software package. We showed that SAFEM is an accurate tool for the fast prediction of asphalt pavement responses, such as the surface deflection and the strain/stress at response points. Furthermore, SAFEM provided a flexible, robust platform for the future development in the numerical simulation of asphalt pavements.

Design of an Axial-Type Magnetic Gear for the Contact-Less Recharging of a Heavy-Duty Bus Flywheel Storage System

This paper presents the electromagnetic design and performance assessment of an axial flux magnetic gear (AMG) for the contact-less energy transfer to an on-board flywheel energy storage system (FESS) to supply heavy-duty electric buses. The AMG electromagnetic configuration is designed to cope with the system torque/speed requirements according to the FESS specifications for a typical driving cycle of an urban bus. Starting from a preliminary sizing by analytical formulations, the torque performance is improved by more accurate finite element analyses based on simplified models. Different parameters also affecting the AMG size are considered to identify an optimized feasible configuration. Finally, the evaluation of the core losses for a full recharge operation enables one to choose the more convenient ferromagnetic material.

Cracked components under anti-plane loading: recent outcomes and future developments

The existence of three-dimensional effects at cracks has been known for many years, but understanding has been limited, and for some situations still is. Understanding improved when the existence of corner point singularities and their implications became known. Increasingly powerful computers made it possible to investigate three-dimensional effects numerically in detail. Despite increased understanding, three-dimensional effects are sometimes ignored in situations where they may be important. The purpose of the present investigation is to study by means of accurate 3D finite element (FE) models a coupled fracture mode generated by anti-plane loading of a straight through-the-thickness crack in linear elastic plates. An extended version of the present work has recently been published in the literature. The results obtained from the highly accurate finite element analyses have improved understanding of the behaviour of through cracked components under anti-plane loading. The influence of plate bending is increasingly important as the thickness decreases. It appears that a new field parameter, probably a singularity, is needed to describe the stresses at the free surfaces. Discussion on whether KIII tends to zero or infinity as a corner point is approached is futile because KIII is meaningless at a corner point. The intensity of the local stress and strain state through the thickness of the cracked components has been evaluated by using the strain energy density (SED) averaged over a control volume embracing the crack tip. The SED has been considered as a parameter able to control fracture in some previous contributions and can easily take into account also coupled three-dimensional effects. Calculation of the SED shows that the position of the maximum SED is independent of plate thickness. Both for thin plates and for thick ones the maximum SED is close to the lateral surface, where the maximum intensity of the coupled mode II takes place.

Adhesive Friction Based on Accurate Elastic-Plastic Finite Element Analysis and n-Point Asperity Concept

The present work considers analysis of adhesive friction of rough surfaces using n-point asperity concept for statistical definition of surface roughness features, and accurate finite element analysis of elastic-plastic deformation of single asperity contact. The paper describes theoretical study in which whole range of deformation of an n-point asperity viz. from fully elastic, through elastic-plastic, to fully plastic is considered and the intermediate transition regime is treated analytically as well as numerically. Well defined adhesion index and plasticity index are used to study the prospective contact situations arising out of variation in material properties and surface roughness features. Using practical values of material properties and surface roughness parameters, results are obtained for normally applied load, friction force, and coefficient of friction. It is observed that the surfaces undergoing predominantly plastic type of deformation and having moderate to higher adhesion have constant coefficient of friction.