Nonlinear FEM Research Articles

Analysis of a Magnetostrictive Harvester With a Fully Coupled Nonlinear FEM Modeling

A force-driven kinetic energy harvester, designed to be excited with impulse-like mechanical loads, is presented. Energy harvesting is a promising technique to feed wireless sensor networks. The proposed device exploits three rods of Galfenol and has been modeled through FEM COMSOL Multiphysics with nonlinear fully coupled characteristics. They consider the general behaviors of magnetostrictive materials and are compatible with thermodynamics. The preliminary results of the time-domain simulations, with an impulse-like force applied, have been compared with experimental results showing a good agreement. Moreover, the proposed nonlinear modeling has shown better performances with respect to software built-in magnetostrictive models. At the same time, further modeling improvements seem to be needed in the future to better fit the harmonic content of the free evolution of the device.

An alternative finite strain elastoplastic model applied to soft core sandwich panels simulation

An alternative elastoplastic model based on the Flory’s right Cauchy-Green stretch tensor decomposition is proposed and applied to model soft cores of sandwich panels. It does not follow usual methodologies as the additive decomposition or the Kröner-Lee multiplicative decomposition of strains. It is based on an important hyperelastic relation, Flory’s decomposition, from which the total strain is separated in two isochoric and one volumetric parts. Using this decomposition, the volumetric strain energy continues to be elastic during all elastoplastic analysis and the isochoric parts are managed to produce the plastic evolution. As a consequence of Flory’s decomposition, the plastic flow direction is known and independent of the yielding surfaces. Moreover, it provides the well known deviatoric nature of plastic strains. For validation purposes, the resulting formulation is implemented using a special 3D prismatic element in a geometrical nonlinear positional FEM computational code. The achieved numerical results are compared with literature experimental data of soft core laminated structural elements.

Performance investigation of quasi-Newton-based parallel nonlinear FEM for large-deformation elastic-plastic analysis over 100 thousand degrees of freedom

Performance investigation of quasi-Newton-based parallel nonlinear FEM for large-deformation elastic-plastic analysis over 100 thousand degrees of freedom

Non-linear FEM analysis for ship panels under thermal loads

During the past decade, welding remained the main technological procedure for joining steel components in shipbuilding industry. Though it has great benefits, welding is an aggressive process that introduces high stress and strains in the joined materials, causing distortion. Finite element method is an important instrument for predicting how structures are behaving under thermal loads. This paper is focused on studying the behaviour of small thickness ship panels, under straightening treatment, by performing thermal-structural-elastic-plastic analysis in Femap/NX Nastran. The proposed panel is tested under three different thermal loadings in order to study stresses and residual distortion.

Complementary dynamics

We present a novel approach to enrich arbitrary rig animations with elastodynamic secondary effects. Unlike previous methods which pit rig displacements and physical forces as adversaries against each other, we advocate that physics should complement artists' intentions. We propose optimizing for elastodynamic displacements in the subspace orthogonal to displacements that can be created by the rig. This ensures that the additional dynamic motions do not undo the rig animation. The complementary space is high-dimensional, algebraically constructed without manual oversight, and capable of rich high-frequency dynamics. Unlike prior tracking methods, we do not require extra painted weights, segmentation into fixed and free regions or tracking clusters. Our method is agnostic to the physical model and plugs into non-linear FEM simulations, geometric as-rigid-as-possible energies, or mass-spring models. Our method does not require a particular type of rig and adds secondary effects to skeletal animations, cage-based deformations, wire deformers, motion capture data, and rigid-body simulations.

Design of Anchorage Zones of Pretensioned Concrete Girders: A Comparison of Nonlinear 3D FEM Results with Measurements on a Full Scale Beam

Pretensioned concrete beams are widely used for constructing large load-bearing structures and bridging long spans. Crack formation may occur in the end zones of these elements due to tensile splitting, spalling and bursting actions. Investigation of these zones is typically done by means of analytical methods, strut and tie modelling, 2D linear or nonlinear analysis, or full 3D nonlinear analysis. Especially challenging in this last approach is the modelling of the force transfer from the strands to the surrounding concrete as it strongly influences the magnitude of the tensile stresses. This paper presents a 3D nonlinear analysis of the anchorage zone of a pretensioned girder, and a comparison with experimental results (mechanical strain measurements, embedded strain gauges). Material modelling, steel-concrete interaction properties, as well as convergence problems are addressed systematically. The comparison indicates that a good agreement is found, both for concrete and rebar strains, and that a friction coefficient of 0.7 can be adopted, although the results for values from 0.5 to 0.9 do not differ that much. The results demonstrate that a 3D nonlinear analysis provides an excellent insight in the behavior of the end zones of pretensioned girders which opens perspectives for an optimization of the end zone design based on this type of analysis.

Experimental study of failure mechanisms in elliptic-braced steel frame

In this article, for the first time, the seismic behavior of elliptic-braced moment resisting frame (ELBRF) is assessed through a laboratory program and numerical analyses of FEM specifically focused on the development of global- and local-type failure mechanisms. The ELBRF as a new lateral braced system, when installed in the middle bay of the frames in the facade of a building, not only causes no problem to the opening space of the facade, but also improves the structural behavior. Quantitative and qualitative investigations were pursued to find out how elliptic braces would affect the failure mechanism of ELBRF structures exposed to seismic action as a nonlinear process. To this aim, an experimental test of a 1/2 scale single-story single-bay ELBRF specimen under cyclic quasi-static loading was run and the results were compared with those for X-bracing, knee-bracing, K-bracing, and diamond-bracing systems in a story base model. Nonlinear FEM analyses were carried out to evaluate failure mechanism, yield order of components, distribution of plasticity, degradation of structural nonlinear stiffness, distribution of internal forces, and energy dissipation capacity. The test results indicated that the yield of elliptic braces would delay the failure mode of adjacent elliptic columns and thus, help tolerate a significant nonlinear deformation to the point of ultimate failure. Symmetrical behavior, high energy absorption, appropriate stiffness, and high ductility in comparison with the conventional systems are some of the advantages of the proposed system.

Large deflection glass facade in typhoon area: Taikoo Place 2 podium wall

The case study presented is a 195 meters tall office tower with a raised podium made of full height glass panels, up to 15 meters high. The panels are only restrained by prestressed high-strength stainless-steel rods, lying entirely in the glass panel build-up, composed by four 12 mm thick plies, laminated with 1.52 mm thick sheets of ionoplast interlayer, with an overall thickness of approx. 52 mm. Due to the facade geometry and the high wind expected, movement joints between rods are introduced, allowing for differential movements to avoid peak stresses in the glass panels. Also, smooth transition between rod rectangular section at the interface with the glass panels to circular section at anchor points need to be ensured by CNC machining to avoid failure of the rod anchors due to fatigue. Sophisticated non-linear 3D FEM models had to be analyzed to predict glass stresses, differential movements to be accommodated by the joints and geometrical transition between rod sections. The main innovation of this facade was the use of prestressed rods in conjunction with jumbo size glass panels. As tension structures experience large movements, it was crucial to understand the effect of these deformations imposed by the rods onto the full height glass panels, analyzing steel and glass members together as a single facade entity. Furthermore, in contrast to typical cable wall facade where the prestressed elements (cables) are offset from the glass line, here the rods are located in the plane of the glass panels and completely flush with them, ensuring the thinnest possible build-up in relation to the large facade span. A rocking portal frame, moving together with the rods to avoid excessive warping in the glass panels, has been used as a solution to deal with the required opening in the facade. An additional complication was given by the high wind load (typhoon) applied on the facade which required rods’ prestress in the order of 1000 Kilonewton to limit glass stresses and deflections.

3D Printing of Concrete Structures Modelled by FEM

This paper presents the possibility to utilize the 3D printing technology in civil engineering field specifically for concrete structures. Since this technology is booming last years and spreads in different fields of industry, the tools to analyse structures in such a way is important. Many research groups worldwide try to develop cement-based material suitable for 3D printing so that it might be used for civil engineering structures. Moreover, this technology brings necessity to check the safety of the structure at early ages of concrete. Therefore, the modelling and simulation of the digitally printed concrete structure would be of great help for such effort. The software tool that enables simulation of digitally printed concrete structure using a nonlinear FEM analysis is presented. ATENA is well established tool for such analyses of civil engineering structures made of concrete. The new module for digital printing simulation is developed as an additional feature of ATENA software. The 3D extrusion technology is supported. The paper describes the whole procedure how to model and analyse such structures and stress out all the differences compared to analyses of structures produced by traditional manner. The structure itself is modelled as usual in FE software, whereby based on velocity of printing head the time of printing, i.e. production of each element is calculated. It is later used to activate the elements during analysis and it also influence the material behaviour, such as shrinkage, strength etc.

Stick-IT: A simplified model for rapid estimation of IDR and PFA for existing low-rise symmetric infilled RC building typologies

The prediction of seismic performances of buildings in terms of engineering demand parameters EDP, such as interstorey drift ratios IDR and peak floor accelerations PFA, represents a fundamental step towards the assessment of potential direct economic losses.This paper proposes a simplified model for the rapid assessment of EDPs in infilled moment resisting frames subjected to seismic loadings suitable for large scale assessment studies. The proposed model, named Stick-I (Stick model for Infilled frames), is a multi-degree of freedom MDOF system consisting of a series of lumped masses connected by means of nonlinear shear link elements. The shear link behavior is suitably calibrated adopting a multi-objective Genetic Algorithm procedure that employs the results of nonlinear cyclic pushover analyses performed on refined nonlinear FEM. Based on the regression study performed on a suitably generated Stick-I model database, a more general Stick-IT model, representative of RC Infilled frame Typologies of assigned storey number and dimensions in plan, is introduced. Simplified formulas for the definition of Stick-IT model are proposed depending on low-level information data that can be easily retrieved from rapid on-site surveys or remote sensing techniques.Both Stick-I and Stick-IT models are validated comparing the results of NRHA performed on refined FEMs with the results obtained adopting the simplified models and good agreement in terms of maximum EDP values and distribution along the building height is obtained.The typological Stick-IT model, which is defined as a function of few geometric and mechanical parameters, can be easily applied for simplified evaluation of expected response for building typologies. Hence, it can also be usefully employed for assessment of direct losses at the large scale, with a significant reduction in computational burden with respect to more refined methods.

Influential geometric imperfections in buckling of axially compressed cylindrical shells – A novel approach

Selection of influential geometric imperfections may be crucial for efficient calculations of lower buckling strengths of thin cylindrical shells subject to axial compression by the geometrically/and materially nonlinear FEM analysis with imperfections (GNIA/GNMIA). The imperfections in the shapes of eigenmodes provided by the preliminary linear buckling analysis (LBA) of perfect shells are brought into focus. For categorizing a large set of potentially influential eigenmodes customarily normalized to unit amplitude the strain energy of the shell deformed in the shape of each eigenmode is determined. By the square root of the strain energy an unconventional energy measure of the shell geometric imperfections is defined. Considering the eigenmode imperfections and localized imperfections normalized by the amplitude and by the energy measure the buckling strengths of an imperfect shell are compared. A preference is given to the normalization of the geometric imperfections by the energy measure. Nevertheless, for the currently revised Structural Eurocodes, particularly for the standardization of GNIA/GNMIA FEM design of shells based on amplitudes of geometric imperfections an amendment is suggested.

Effect of Process Parameter on Tensile Strength of Spot Welded S235 Sheet Using Simulation and Experimental

This study focused on investigation of the effect of process parameter to the tensile strength of a spot welded S235 low carbon steel through simulation and experiment. Resistance spot welding (RSW) is commonly used in joining metal sheets due to its key capabilities, which is time and cost effective as well as high adaptability for automation. However, strength and reliability of a spot welded joint especially in an auto vehicle can be unpredictable. Premature failure of a spot welded joint can be difficult to be predicted but common factors that had been discussed in many research is related with fatigue and residual stress. Process parameter is recognized as one of critical factors affecting the reliability and quality of a spot welded joint. Different type of material and thickness may require different set of parameter to achieve an optimum result. Experimental procedure alone to demonstrate and investigate the effect could be too costly and time inefficient. Therefore, design of experiment and non-linear FEM simulation analysis were used to analyze and validate the result. This study shows the significance of process parameters such as weld current and electrode pressure to the strength of a spot welded joint and accurate setting is needed prior to the welding process to achieve an optimum result.

Influence of Support Conditions on Single-Span Profiled Sheet Metal Strength Through Nonlinear FEM Analysis

Profiled sheets are widely used in modern steel structures, either as cladding or as casing in composite structures. Strength calculation of such structures is a crucial design issue, and it represents a complex task because one must deal with thin-walled structures that have complicated cross-section shape. Manufacturers of these structural elements provide data about its strength, mostly based on experimental testing. However, catalogues provide little data about the supporting conditions at the ends that may have influence on structural strength. In this research, the finite element method analysis with geometrical and material nonlinearity and contact analysis in the support zones was applied for the strength calculation of a profiled steel sheet with very high depth. The analysis encompassed determination of the ultimate limit strength and serviceability limit strength with limited deflection. All analyses were conducted for surface load applied over the area of one sheet. Thereat, influence of several factors related to support conditions was considered: friction on the supports, support width, and number of fasteners. Failure mechanisms were also analysed. Obtained results were compared with other sources and methods, like analytical solution, manufacturer’s software, and catalogue data. Results of the research showed that behaviour and strength of those elements depend to the great extent on end support detailing, which cannot be encompassed by classical calculation methods and linear analysis. Significance of the support conditions was proven, and attention was paid on absence of such data in published catalogues.

Numerical modeling of a human tissue surrogate SEBS gel under high velocity impacts: investigation of the effect of the strain rate in an elasto-hydrodynamic law

In this paper, an elasto-hydrodynamic constitutive law of the synthetic polymer SEBS gel (styrene-ethylene-butylene-styrene) based on the mechanical characterization extracted from the literature was developed implemented in a numerical code, and the effect of the strain rate was investigated. The proposed law was then implemented in an explicit non-linear FEM software to reproduce various loading configurations in order to validate the accuracy of the model. A good agreement exists between the numerical results of the laws and experimental data in the literature. Numerical analysis reveals that the strain-rate-dependence effect is significant in SEBS gel especially for high strain rates. The present study can therefore be used to predict the mechanical behavior of human surrogate materials and guide the design of protective devices such as body armor.

Crack width design approach for fibre reinforced concrete tunnel segments for TBM thrust loads

Concentrated loads induced during the excavation stage by Tunnel Boring Machines (TBMs) is still a matter of discussion into the tunnelling construction field, this having a strong impact from both the technical (e.g., durability and service conditions) and the economic perspectives. Fiber reinforced concrete (FRC) has been gaining acceptance as a structural material for producing precast segments as this has proven to lead to various advantages respect to the traditional reinforced concrete, especially for improving the crack control during transient loading situations. In this sense, several experimental programs and numerical studies were previously carried out in which the different geometric and mechanical governing variables were analyzed and, from the results, valuable conclusions were derived. Nonetheless, there are still observed lacks and gaps related with the optimum reinforcement design (FRC strength class and/or amount of traditional steel bar reinforcement) which is often hindering the use of fibers as main reinforcement for concrete segments. The main purpose of the research consist in developing a parametric analysis related with the TBM-thrust effects on FRC segments by means of using a non-linear 3D FEM, previously calibrated with full-scale tests. The results are used to determine the range of FRC strength classes suitable for controlling the crack with during the TBM thrust phase. The results and conclusions are expected to be useful for tunnels designers when establishing the FRC mechanical requirements.

Buckling and limit states of thin-walled composite columns under eccentric load

Abstract The objective of this study was to investigate the influence of eccentric compressive load on the buckling, post-buckling and load-carrying capacity of thin-walled top-hat cross-section composite columns. The CFRP columns were manufactured by the autoclave technique. The scope of the study involved performing experimental tests on real structures as well as numerical calculations by the finite element method. The experimental tests were conducted in the full range of loading, until the structure's failure. Post-buckling equilibrium paths and acoustic emission signals were measured in order to determine actual condition of the composite material. Nonlinear FEM calculations were made by the progressive damage criterion, in which the damage initiation of the composite material was estimated based on Hashin's theory, whereas damage evolution was described by the energy criterion. The numerical simulations were performed using the commercial software ABAQUS®. The numerical results were in good agreement with the experimental results obtained for real structures. The results demonstrated a significant influence of eccentric compressive load on the buckling and post-buckling characteristics of the tested structures.

Church enclosure walls bearing capacity estimations and its validation on 3D models

The paper deals with the nonlinear computational modeling of the baroque enclosure masonry walls. The main tasks are input parameters for efficient advanced numerical tools and techniques, which are based on nonlinear and quasi brittle constitutive FEM modeling. For the work was used the knowledge and results from the Broumov Group Churches survey acquired in the frame of international SAHC university cooperation. The goal of the contribution are real bearing capacity parameters of the composite enclosure walls, which leads from standard homogenization techniques. With regards to the material micro modeling of different wall configuration in longitudinal and transversal direction was done with ATENA 2D software to evaluate the safe bearing capacity of the walls. The set of models aim to assess the bearing capacity of the enclosure wall, which is the main structural element in the church. In detail, we will present results from the numerical investigation, and partial in situ testing, from Vižňov, Ruprechtice and Otovice. Finally, we will present calculation of cracks propagation on full 3D church models. Concerning historical structures, it is one way how to validate the quality of estimations and validate numerical models.

Effect of pre-stress tension in the non-linear FEM analysis of concrete floater for 10MW offshore wind turbine

Effect of pre-stress tension in the non-linear FEM analysis of concrete floater for 10MW offshore wind turbine

Design Method of The New Damping Energy Dissipation Corrugated Steel Plate Shear Wall System

In order to improve the lateral stiffness of the steel frame, natural anti-buckling corrugated steel shear wall was combined with mild steel dampers, forming a new damping energy-dissipation corrugated steel plate shear wall system (DCSW). The design method of the DCSW system was proposed based on plastic analysis. To study the seismic performance of this system, the nonlinear FEM of the DCSW system was established by ABAQUS, and the analysis on bearing capacity and energy dissipation capacity was carried out. The results showed that the DCSW designed by this method had high lateral bearing capacity and energy dissipation capacity. The lateral ultimate bearing capacity increased by 50% and lateral displacement reduced by 43% with corrugated steel plate shear wall and mild steel dampers.

Reliability based design method for buckling of steel columns in fire

Purpose This paper aims to reliability analysis of axially loaded steel columns at elevated temperatures considering the probabilistic features of fire. Design/methodology/approach The response function used in the reliability analysis is based on the non-linear FEM calculations. The stochastic variability of temperature is integrated with the procedure similar to the parameters of loading and material properties. Direct Monte Carlo simulations (MCSs) are implemented for probabilistic analysis. Computational costs are reduced by polynomial approximation of the response function of the column. Findings A design method for practical applications in the common Eurocode format is proposed. The proposed method can be used to estimate the failure probability of a steel column in fire conditions. If standard reliability criteria are applied, the results of the steel column buckling capacity in the fire according to the proposed procedure deviate from the Eurocode results in certain parameter ranges. Originality/value The proposed method for design calculations makes use of the advantages of MCS results, while the need for the tedious amount of calculations for the end user are avoided as the predefined factors are implemented in the procedure of Eurocode format. The proposed method allows better differentiation of the fire probability in the capacity assessment compared to the existing design methods.