FE Program Research Articles

Experimental and numerical analyses of the effectiveness of high‐frequency peening processes

AbstractDedicated to Prof. Dr. Akimitsu Kurita on his 70th birthdayTo assess fatigue behaviour, experimental tests were conducted on material specimens furnished with hammer peening tracks, with two different types of treatment being employed. The results of fatigue tests on treated specimens were compared with those of untreated specimens and assessed. Non‐linear analyses with the FE program ADINA, taking into account the stress–distortion behaviour of a material subjected to fatigue, were conducted as part of the test concept, specimen analysis, evaluation of the test results and probing the mode of action of both techniques.

Simulation of Severe Accident Scenarios in Nuclear Containments

Abstract The paper presents the main theoretical backgrounds and application of FE program ATENA to simulation of severe accident in nuclear structures. The software was developed by Cervenka Consulting, Prague, Czech Republic with the aim to offer a tool for numerical simulation of concrete structures subjected to actions in service, ultimate as well as extreme limit states due to mechanical as well as physical effects. Nonlinear behavior of concrete is modeled by theories of damage and plastic flow [1]. Paper outlines the basic features of the used material model. It demonstrates the model accuracy on results from recent blind prediction competitions [2]. In the last section, it shows examples of simulations of severe accidents scenarios in nuclear power plants structures [4].

Buckling assessment of dented truncated cones under external pressure

Notwithstanding a considerable body of references in the literature on the buckling response of conical shell structures, it seems imperative to provide further insight on the buckling response of locally imperfect steel cones. This paper contains different simulations including non-linear FE analysis and discusses the influence of dent imperfection on the buckling load of these structures subject to external pressure. Data of the present work are evaluated against available experimental results, codes and recommendations and the effect of the local damages is exhaustively set forth. It is also found that the employed FE program can reliably predict the structural response of locally damaged conical shells.

Aerodynamic stability parameters optimization and global sensitivity analysis for a cable stayed Bridge

Cable stayed Bridges are highly vulnerable to strong wind load induced vibrations which are responsible of generating aerodynamic instability and in a critical situation lead to structural failure. This paper focuses on buffeting response and flutter instability in a cable stayed Bridge. A strong fluctuating wind is assigned to a cable stayed Bridge model in ABAQUS FE program to onset optimization and global sensitivity analysis through considering three aerodynamic parameters (wind attack angle, deck streamlined length and stay cables viscous damping) by targeting the vertical and torsional vibrations of the deck. The numerical simulations results in conjunction with the frequency analysis results emphasized the existence of such vibrations. Model validation performed by comparing the results of lift and moment coefficients between the present FE model and two benchmarks from the literature (flat plate theory and flat plate by Xavier et al., 2015), which resulted in good agreements between them. Optimum values of the adopted aerodynamic parameters have been identified and discussed. Global sensitivity analysis based on Monte Carlo sampling method was utilized to formulate the surrogate models and the sensitivity indices so that to identify rational effect and role of each parameter on the aerodynamic stability of the structure.

Elastic-Plastic Thermomechanical Fatigue Analysis of Forging Dies

Abrasive wear and low cycle fatigue (LCF) have the greatest influence on the durability of dies. This paper presents a new criterion for estimation of the LCF of forging dies. The deformation model of Manson-Coffin is the classic model for the calculation of LCF. The pulsating cycle of loading dies and the phenomenon of cyclic thermal softening doesn’t provide implementation of the full Manson-Coffin’s model for the analysis of the tool life. At the same time the majority of researchers do not take into account the plastic strain component for estimation the fatigue durability of the dies and use only elastic component of the Manson-Coffin’s law or model of Basquin that is based on the analysis of the stress cycle. The present work uses the strain-kinetic criterion to analyze the durability of the dies that allows taking into account the elastic-plastic strain components and thermos-cyclic softening. During loading in bulk forging the first cycle is to be with plastic deformation while all remaining cycles would have to remain within the elastic limit due to metal hardening. Moreover it has been shown that cyclic softening effect may also be observed in the thermomechanical fatigue. This approach has been implemented for LCF simulation of the die in hot forging in FE program QForm by introducing a special subroutine. The comparison of results of the die fatigue failure simulation has shown good correspondence with practice.

Numerical Simulation of Axial Anchorage Capacity of Concrete-Filled Steel Box Footing

The aim of the study is to predict the axial anchorage capacity of the concrete-filled steel box (CFSB) as footing by using the 3D finite element program CAMUI developed by authors’ laboratory. The steel box is filled with concrete, and concrete-filled steel tube column is inserted in the box. Numerical simulation of the experimental specimens was carried out after introducing the new constitutive model for post-peak behavior of concrete in compression under confinement. The experimental program, consisting of two specimens, was conducted to verify the reliability of the simulation results by the FE program. The simulated peak loads agree reasonably with the experimental ones, and the axial anchorage capacity is controlled by the compression softening of the concrete under the column. It was also observed that the axial capacity of CFSB footing is affected by concrete depth under the column. The axial capacity decreases with the decrease in concrete depth under the column.

Numerical simulation of bond-slip interface and tension stiffening in GFRP RC tensile elements

Bond between reinforcement and concrete highly affects the structural behaviour of reinforced concrete (RC). Introduction of bond-slip models into numerical simulation allows taking into account the bond interaction and analyse its effect on local and global behaviour. Unlike conventional steel reinforcement, no standard bond-slip law exists for FRP reinforcement, as bond is the result of a combination of parameters such as reinforcing material and bar surface configuration, among others. Therefore, there is a need in developing a methodology to easily implement bond-slip response from experimental bond tests.In this work, a methodology to implement bond-slip behaviour between concrete and reinforcement into a FEM model is presented. The inverse analysis is used to characterise the bond mechanisms active in a pull-out test. The obtained constitutive behaviours are thereafter implemented into a FE program by using connector elements and surface-to-surface contacts, and GFRP RC tensile elements are modelled. Numerical results are compared to experimental ones available in the literature, showing good accuracy in terms of load-deformation, crack width and crack spacing, as well as strains and bond stress and slip distributions along the reinforcing bar.

차분진화 알고리즘을 이용한 IPM형 BLDC전동기의 Notch 형상 최적화 설계 연구

In this paper, a cogging torque of IPM(Interior Permanent Magnet)-type BLDC motor is analyzed by FE program and the optimized notch on the rotor surface is designed to minimize the torque ripple. A differential evolution strategy algorithm and a response surface method are employed to optimize the rotor notch. In order to verify the proposed algorithm, an IPM BLDC motor is used, which is 50 kW, 8 poles, 48 slots and 1200 rpm at the rated speed. Its characteristics of the motor is calculated by FE program and 4 design variables are set on the rotor notch. The initial shape of the notch is like a non-symmetric half-elliptic and it is optimized by the developed algorithm. The cogging torque of the final model is reduced to 1.5[N·m] from 5.2[N·m] of the initial, which is about 71 % reduction. Consequently, the proposed algorithm for the cogging torque reduction of IPM-type BLDC motor using the rotor notch design seems to be very useful to a mechanical design for reducing noise and vibration.

Finite Element Analysis of Reinforced Concrete Masonry Infilled Frames with Different Masonry Wall Thickness Subjected to In-plane Loading

In this study, finite element analyses of masonry infilled frames using a general purpose FE program, ABAQUS, were conducted. Analysis models consisted of the bare frame, infilled frames with masonry wall thickness of 0.5B and 1.0B, respectively. The masonry walls were constructed using the concrete bricks which were generally used in Korea as infilled wall. The material properties of frames and masonry for the analysis were obtained from material tests. However, four times increased the tensile strength was used for 1.0B wall, which is seemingly due to the differences in locating the bricks. The force-displacement relation and development of crack from the FE analysis were very similar to those from the experiments. From the FEA results, contact force between the frame and masonry, distribution of shear force and bending moments in frame members were analyzed. Obtained contact stress shows a trianglur distribution, and the contact length for 0.5B speciment and 1.0B specimen were close to the value estimated using ASCE 41-06 equation and ASCE 41-13 equation, respectively. Obtained shear force and bending moment distribution seems to replicate actual behavior which originates from the contact stress and gap between the frame and masonry.

Students4WebES Edited Project Report

Report on the Students for Webinar and Employability Skills (Students4webES) project run at Abingdon and Witney College between October 2012 and April 2013. The project was funded by the Jisc Advance FE and Skills Programme and aimed to develop employability skills for Level 3 FE students in relation to using video conferencing and webinars and assess whether this was a beneficial digital employability skill. Students were trained to use video conferencing and to run a webinar, with the aim of setting up and running between 7-15 short webinars with employers around the theme of ‘What does an employer want from an employee?” Additionally the project aimed to produce:A student centred guide to running a webinarRecordings of employer webinars (with full consent from employer) for use in future tutorials related to employabilityA student led conference, supported by the JISC RSC SE, on the theme of employability skills using video conferencing and webinars.

Stress-strain behaviour of asphalt concrete in compression

This paper presents an evaluation of the failure mode of asphalt concrete and describes the stress-strain curve that governs asphalt concrete beyond the limit of elasticity in the ascending branch. The relationship of stress-strain is identical to that of cement concrete in compression. A general form of the behavioural curve is proposed to represent the elastic and plastic – damage of asphalt concrete. The nonlinear behaviour of asphalt concrete beyond the linear elastic limit swelling is visible to the naked eye. These parameters that define this form are physically significant and are determined experimentally. The parameters of the stress-strain curve are fundamental characteristics of a solid subjected to short term loading. The experiments used short term static compression loading on cylindrical asphalt concrete specimens, differing in mix types (Dense graded, Stone Matrix), air voids content, density, specimen size and temperature. There were significant changes in the peak stress and strains between the asphalt concrete mix types. Different strengths are attainable between asphalt concrete types as well as the properties of the mix constituents. The proposed equations fit a wide range of testing conditions and asphalt concrete type for both the ascending and descending branches of the stress-strain diagram in compression. The investigation derives parameters (yield stress and elastic modulus) for different asphalt concrete mix types which can be used in FE programs such as Abaqus that uses the elastic as well as plastic data to model the behaviour of different mix types of asphalt concrete material used in a pavement structure.

Development of Constitutive Model for Precast Prestressed Concrete Segmental Columns

The interest of using precast segmental columns in construction of concrete bridges has significantly increased in recent years. One research area of concrete bridges is the application of Precast Prestressed Concrete Segmental (PPCS) Column in any structural analysis software or FE program code. Modeling a PPCS column, which consists of various materials with interaction between them, is complicated and time-consuming. This research attempts to formulate the stiffness matrix of PPCS columns in order to form the constitutive model in linear form to evaluate the response of the columns. A two-dimensional finite element model is presented in the finite element package ANSYS. Parametric studies are conducted by finite element models to verify the constitutive models for the PPCS column with a different number of concrete segments. Comparison between the constitutive model and the FE program results indicates that the constitutive model is accurate enough to predict the deformation of the PPCS columns.

A full structural mechanical description of beam elements for rotors in electrical machines

Purpose – The purpose of this paper is to get a more consistent finite element description for three-dimensional (3D) Timoshenko beam elements. It extends the common description of beam elements by modifying the shape functions and considers the warping of the cross-section due to torsion. Design/methodology/approach – The paper builds mainly on a finite element description of 3D Timoshenko beam elements. The implementation of high-order shape functions for torsion is done by adding a seventh degree of freedom to the system. Findings – The results reveal that for some beams, depending on their physical dimensions, the warping of the cross-section has large influence. In comparison to a conventional FE program, the extended finite element description considers the warping and yields more accurate results. Practical implications – An application of the extended finite element description is done with an implementation of the code in MATLAB. The static and dynamic behavior of a rotor in an electrical machine...

The Evaluation Of Algorithms For Determination Of The Reliability Index

AbstractThe study deals with stability and dynamic problems in bar structures using a probabilistic approach. Structural design parameters are defined as deterministic values and also as random variables, which are not correlated. The criterion of structural failure is expressed by the condition of non-exceeding the admissible load multiplier and condition of non-exceeding the admissible vertical displacement. The Hasofer-Lind index was used as a reliability measure. The primary research tool is the FORM method. In order to verify the correctness of the calculations Monte Carlo and Importance Sampling methods were used. The sensitivity of the reliability index to the random variables was defined. The limit state function is not an explicit function of random variables. This dependence was determined using a numerical procedure, e.g. the finite element methods. The paper aims to present the communication between the STAND reliability analysis program and the KRATA and MES3D external FE programs.

A super-element based on finite element method for latticed columns

Latticed columns are frequently used in industrial steel structures. In some countries these built-up columns might be even used in other types of steel structures such as residential and commercial buildings. Besides, latticed columns are parts of skeletons of many historic buildings all around the world. To analyze a steel structure with latticed columns a more accurate numerical model for such a column seems to be essential. The lay-out and connectivity of constructing main profiles of a latticed column leads to formation of many shear zones along the length of a column. Therefore, considering shear effects on the behavior of a lattice column is inevitable. This paper proposed a new super-element with twelve degrees of freedom to be used in finite element modeling of latticed columns. The cross sectional area, moments of inertia, shear coefficient and torsional rigidity of the developed new element are derived. To compute these parameters with less complexity a model using only beam elements is also introduced. A general purpose finite element program named LaCE is developed. This FE program is capable of performing linear and nonlinear analysis of 3D-frames with latticed columns, considering shear deformation. To show the accuracy of the proposed element, several cases are studied. The outcome of these investigations revealed that the current-in-practice model for latticed columns suffers from some major shortcomings which to some extends are resolved by the proposed super-element. The developed element showed the capability of modeling a lattice column with good accuracy and less computational cost.

Large-Scale Numerical Simulation of an RC Tunnel Junction Member Using Particle Discretization Scheme FEM

This paper presents a large-scale numerical simulation of a reinforced concrete (RC) tunnel junction member using solid FEM. Particle discretization scheme (PDS), which uses two sets of non-overlapping characteristic functions to discretize displacement field and strain/stress field respectively, is employed to represent the multiple-cracking configurations of concrete. An efficient parallel FE program, called ADVENTURE, is used to implement PDS as well as a reformulated nonlinear concrete constitutive relation. A simplified tunnel junction member, in order to reveal its multiple-cracking behavior under the static load, is studied and the stochastic behavior of cracking is investigated; good agreements are achieved between the simulation results and experimental observations regarding the multiple cracking configurations.

Analysis of higher order composite beams by exact and finite element methods

In this paper, a two-layer partial interaction composite beams model considering the higher order shear deformation of sub-elements is built. Then, the governing differential equations and boundary conditions for static analysis of linear elastic higher order composite beams are formulated by means of principle of minimum potential energy. Subsequently, analytical solutions for cantilever composite beams subjected to uniform load are presented by Laplace transform technique. As a comparison, FEM for this problem is also developed, and the results of the proposed FE program are in good agreement with the analytical ones which demonstrates the reliability of the presented exact and finite element methods. Finally, parametric studies are performed to investigate the influences of parameters including rigidity of shear connectors, ratio of shear modulus and slenderness ratio, on deflections of cantilever composite beams, internal forces and stresses. It is revealed that the interfacial slip has a major effect on the deflection, the distribution of internal forces and the stresses.

Three‐Dimensional Modeling of Glass Lens Molding

The required accuracy for the final dimensions of the molded lenses in wafer‐based precision glass molding as well as the need for elimination of costly experimental trial and error calls for numerical simulations. This study deals with 3D thermo‐mechanical modeling of the wafer‐based precision glass lens molding process. First, a comprehensive 3D thermo‐mechanical model of glass is implemented into aFORTRANuser subroutine (UMAT) in theFEprogramABAQUS, and the developedFEmodel is validated with both a well‐known sandwich seal test and experimental results of precision molding of several glass rings. Afterward, 3D thermo‐mechanical modeling of the wafer‐based glass lens manufacturing is performed to suggest a proper molding program (i.e., the proper set of process parameters including preset force‐time and temperature‐time histories) for molding a wafer to a desired dimension and quality. Moreover, the effect of some important process parameters such as cooling rate and pressing temperature on the final size and residual stress inside the wafer is evaluated. Finally, it is noted that the suggested molding program minimizes the costly empirical efforts and raises the process efficiency.

경계반력법을 이용한 지진격리 원전구조물의 비선형 지반-구조물 상호작용 해석

This paper presents a detailed procedure for a nonlinear soil-structure interaction of a seismically isolated NPP(Nuclear Power Plant) structure using the boundary reaction method (BRM). The BRM offers a two-step method as follows: (1) the calculation of boundary reaction forces in the frequency domain on an interface of linear and nonlinear regions, (2) solving the wave radiation problem subjected to the boundary reaction forces in the time domain. For the purpose of calculating the boundary reaction forces at the base of the isolator, the KIESSI-3D program is employed in this study to solve soil-foundation interaction problem subjected to vertically incident seismic waves. Wave radiation analysis is also employed, in which the nonlinear structure and the linear soil region are modeled by finite elements and energy absorbing elements on the outer model boundary using a general purpose nonlinear FE program. In this study, the MIDAS/Civil program is employed for modeling the wave radiation problem. In order to absorb the outgoing elastic waves to the unbounded soil region, spring and viscous-damper elements are used at the outer FE boundary. The BRM technique utilizing KIESSI-3D and MIDAS/Civil programs is verified using a linear soil-structure analysis problem. Finally the method is applied to nonlinear seismic analysis of a base-isolated NPP structure. The results show that BRM can effectively be applied to nonlinear soil-structure interaction problems.

Simulation of Autofrettage in Curvilinear Coordinates

AbstractPressure vessels subjected to high mechanical loadings can fail due to microscopic crack growth, i.e., stress corrosion cracking. A popular way to increase the crack resistance of a structure is by autofrettage. The standard approach to obtain a numerical solution for the involved fields is to discretize w.r.t. Cartesian coordinates as implemented in common commercial FE programs. However, this approach is computationally costly in comparison to pure elastic simulations—often rendering this method practically unfeasible. The current work shows that autofrettage can be simulated more efficiently in extensive bodies that can be described by a bijective map where certain symmetries are available in load and form. The discretization and the mathematical formalism of this approach in curvilinear coordinates are described. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)