Finite Element Modeling Methodology Research Articles

Design of cold-formed high strength steel irregular octagonal hollow section columns

This paper presents experimental numerical investigations on the structural behaviour of cold-formed high strength steel irregular octagonal hollow section (OctHS) columns with both non-slender and slender cross-sections. An experimental programme, including material tests, measurements of initial global geometric imperfection, and pin-ended column tests, was first conducted. The key findings from the experimental programme are presented and discussed. Following the validation against the experimental results, the proposed finite element modelling methodology was established to replicate the test observations, and then was adopted to generate a boarder range of numerical results through parametric studies. The collected experimental and numerical data were used to evaluate the applicability of current structural steel design methods on the column buckling strength for irregular OctHS columns. Assessment results demonstrate that the design method adopted in Chinese code can provide accurate prediction, whilst modified design method adopted in Eurocode 3, considering the effect of steel grade on the column strength, has been proposed and shown to greatly enhance the prediction accuracy with improved consistency. The corresponding assessments on the design approaches adopted in American and Australian codes were also discussed.

Efficient Simulation of the Laser-Based Powder Bed Fusion Process Demonstrated on Open Lattice Materials Fabrication

Strut-based or open lattice materials are a category of advanced materials used in medical and aerospace applications due to their properties, such as high strength-to-weight ratio and energy absorption capability. The most prominent method for the fabrication of lattice materials is the Laser-based Powder Bed Fusion (L-PBF) additive manufacturing (AM) process, due to its ability to produce parts of complex geometries. The current work presents an efficient meso-scale finite element (FE) modeling methodology of the L-PBF process demonstrated in the fabrication of body-centered cubic (BCC) lattice materials. The modeling efficiency is gained through an adaptive mesh refinement technique, which results in accurate and efficient prediction of the temperature field during the process evolution. To examine the efficiency of the modeling method, the computational time is compared with that of a conventional FE simulation, based on the element and birth technique. The temperature history difference between the two approaches is minor but the adaptive mesh modeling requires only a small portion of the simulation time of the conventional model. In addition, the computational results present a good correlation with the available experimental measurements for various process parameters validating the presented efficient method.

Fracture behaviour of laser powder bed fusion AlSi10Mg microlattice structures under uniaxial compression

Microlattice structures produced by laser powder bed fusion (LPBF) have been tested in compression extensively. Yet, their failure modes remain unexplained. This study bridges this research gap by accurately predicting the crack initiation process in LPBF body centred cubic (BCC) microlattices and their failure mode. In this study, LPBF AlSi10Mg BCC microlattice structures were tested in uniaxial compression and their detailed response modelled using a finite element (FE) modelling methodology on microlattices with idealised struts which was validated experimentally. Crack initiation in BCC microlattices with 2 × 1 × 2 unit cells loaded in compression was observed in situ via a scanning electron microscope (SEM). The force–displacement response of the microlattice was studied with respect to crack initiation and propagation. It was found that the locations of crack initiation could be predicted by considering the equivalent plastic strain and stress triaxiality fields obtained by an FE analysis and assuming a monotonically decreasing fracture locus. Subsequently, microlattices with 4 × 4 × 4.5 unit cells were similarly subjected to compression. Using a monotonically decreasing fracture locus extrapolated from uniaxial tension testing of the bulk LPBF AlSi10Mg, an FE simulation successfully predicted the commonly reported diagonal shear band failure mode of the microlattice on a model with idealised struts.

Tire–Pavement Interaction Simulation Based on Finite Element Model and Response Surface Methodology

Acquiring accurate tire–pavement interaction information is crucial for pavement mechanical analysis and pavement maintenance. This paper combines the tire finite element model (FEM) and response surface methodology (RSM) to obtain tire–pavement interaction information and to analyze the pavement structure response under different loading conditions. A set of experiments was initially designed through the Box–Behnken design (BBD) method to obtain input and output variables for RSM calibration. The resultant RSM was evaluated accurately using the analysis of variance (ANOVA) approach. Then, tire loading simulations were conducted under different magnitudes of static loading using the optimal parameter combination obtained from the RSM. The results show that the deviations between the simulations and the real test results were mostly below 5%, validating the effectiveness of the tire FEM. Additionally, three different dynamic conditions—including free rolling, full brake, and full traction—were simulated by altering the tire rolling angle and translational velocities. Finally, the pavement mechanical response under the three rolling conditions was analyzed based on the tire–pavement contact feature.

A refined finite element model for UHPC-filled FRP tube column

A sound finite element model is essential for the nonlinear structural analysis of FRP tube-confined UHPC columns, wherein an accurate constitutive model to characterize the mechanical behavior of UHPC under passive constraints is of utmost importance. This study presents a refined finite element modeling methodology for the UHPC-filled FRP tube column. The constitutive model for UHPC under passive constraint is developed, in which the yield criterion, hardening/softening law, plastic flow rule, and damage evolution law are determined based on the experimental results of UHPC under multiaxial loading conditions. Furthermore, a solid element model of FRP tube with definable layer information is utilized to simulate the behavior of FRP tubes under complex stress states. The proposed finite element model is implemented in ABAQUS and verified through available experimental results. The results indicate that the proposed model can accurately predict the stress–strain behavior of confined UHPC with varying fiber and coarse aggregate contents, and describe the damage progression of UHPC and FRP tubes. Particularly, the interaction process between FRP and UHPC can be well reflected. The proposed finite element model serves as a paradigm for numerical analysis of UHPC-filled FRP tube elements and provides a reference for simulations of UHPC structures.

Topological Optimization of Non-Pneumatic Unique Puncture-Proof Tire System Spoke Design for Tire Performance

<div>Non-pneumatic tires (NPTs) have been widely used due to their advantages of no occurrence of puncture-related problems, no need of air maintenance, low rolling resistance, and improvement of passenger comfort due to its better shock absorption. It has a variety of applications as in earthmovers, planetary rover, stair-climbing vehicles, and the like. Recently, the unique puncture-proof tire system (UPTIS) NPT has been introduced for passenger vehicles segment. The spoke design of NPT-UPTIS has a significant effect on the overall working performance of tire. Optimized tire performance is a crucial factor for consumers and original equipment manufacturers (OEMs). Hence to optimize the spoke design of NPT-UPTIS spoke, the top and bottom curve of spoke profile have been described in the form of analytical equations. A generative design concept has been introduced to create around 50,000 spoke profiles. Finite element model (FEM) model is developed to evaluate the stiffness and damage-resisting performance of NPT-UPTIS spoke. The FEM methodology has also been validated with average accuracy of more than 95% for experimental vertical stiffness for commercial NPT-Tweel. The stiffness and damage-resisting performance of generated designs have been predicted with the help of machine learning regression models, which were trained on the FEM results of 200 such designs. These 50,000 generated designs have been categorized in four different categories based on different level of stiffness and damage resistance performance. In this study, one optimized design from each category has been selected and their performance have been validated with 3D FEM simulation. It has been found that the suggested topology optimization approach is efficient to generate UPTIS spoke designs with having ±30% stiffness with 17%, 40%, and 56% more damage resistance performances with respect to the starting reference design.</div>

Experimental and computational models for simulating the oral breakdown of food due to the interaction with molar teeth during the first bite

The first bite involves the structural breakdown of foods due to the interaction with teeth and is a crucial process in oral processing. Although in vitro experiments are useful in predicting the oral response of food, they do not facilitate a mechanistic understanding of the relationship between the intrinsic food mechanical properties and the food behaviour in the oral cavity. Computer simulations, on the other hand, allow for such links to be established, offering a promising design alternative that will reduce the need for time consuming and costly in vivo and in vitro trials. Developing virtual models of ductile fracture in soft materials, such as food, with random and non-predefined crack morphology imposes many challenges. One of the most important is to derive results that do not depend on numerical parameters, such as Finite Element (FE) mesh density, but only physical constants obtained through independent standard mechanical tests, such as fracture strain and/or critical energy release rate. We demonstrate here that this challenge can be overcome if a non-local damage approach is used within the FE framework. We develop a first bite FE modelling methodology that provides mesh independent results which are also in agreement with physical first bite experiments performed on chocolate. The model accounts for key features found in chocolate and a wide range of compliant media, such as rate dependent plasticity and pressure dependent fracture initiation strain. As a result, our computational methodology can prove valuable in studying food structure-function relationships that are essential in product development.

Prediction of interfacial behaviour of single flax fibre bonded to various matrices by simulation of microdroplet test

The microdroplet test is commonly used to determine the apparent interfacial shear strength (IFSS) of fibre-reinforced microcomposites. A deeper analysis of the test outcome can provide meaningful information about the fibre/matrix interface behaviour if a predictive approach is adopted. In this study, this predictive approach was used to investigate the quality of interface for polymer drops bonded single flax fibre at the microscale. Microdroplets of five thermoplastics matrices were prepared with single flax fibres. Microbond test was performed to assess the force–displacement curves of the studied composite systems. In addition, a finite element (FE) modelling methodology was adopted to quantify the interfacial role by proposing an interfacial constitutive law including the debonding stage. The numerical sensitivity results reveal the leading role of the interfacial stiffness as well as the fibre–matrix separation displacement in triggering the debonding behaviour. In addition, the numerical responses show strong matching with experimental trends using the proposed interfacial model for a wide variety of fibre/matrix interactions. The identification of the mechanical behaviour of the considered composite system shows that the best performing system is flax fibre/PLA, allowing a maximum fibre–matrix separation of 156 µm and an interfacial stiffness of 47 GPa/mm. The worst performing system is flax fibre/PP, which has a limited fibre–matrix separation of 55 µm. This study concludes that the proposed numerical model is able to capture the interfacial shear behaviour of polymeric drops bonded to a single flax fibre, which allows its extension at the mesoscale for a given arrangement of flax fibres in the bio-based composites.

Analysis and validation of a scaled, launch-vehicle-like composite cylinder under axial compression

Launch vehicle structures, such as payload adapters and interstages, are increasingly designed and constructed using composite materials due to their high stiffness- and strength-to-weight ratios. Therefore, it is important to develop a validated finite element modeling methodology for designing and analyzing composite launch-vehicle shell structures. This can be achieved, in part, by correlating high-fidelity numerical models with test data. Buckling is often an important failure mode for cylindrical shells, and the buckling response of such structures is also often quite sensitive to imperfections in geometry and loading. Hence, it is crucial to understand the model parameters and details required to accurately predict the buckling load and behavior of composite cylindrical shells, especially if the shell is buckling critical. The inclusion of as-built features, such as radial imperfections, thickness variations, and loading imperfections can help improve the correlation between test and analysis. To demonstrate such an approach, a validated modeling methodology that was used to predict the buckling behavior of a scaled component for a launch-vehicle-like structure is presented, and results from the model are compared with experimental results. The modeling approach presented herein was used to successfully predict the buckling behavior.

Influence of geometric defects on the compression behaviour of thin shell lattices fabricated by micro laser powder bed fusion

Micro laser powder bed fusion (μLPBF) is an additive manufacturing process enabling the fabrication of thin-walled metallic shell lattices at the micrometre scale. With wall thicknesses reduced down to 100 µm, this process significantly enhances the structural design freedom, enabling the design of multi-functional, lightweight, stiff, and strong components. However, from a manufacturing perspective, as the wall thicknesses approach the printing resolution, this process is likely to introduce geometric defects, and informed quality assurance of the 3D-printed structures becomes critical. From a structural perspective, the mechanical properties of thin-walled structures are known to be highly sensitive to manufacturing defects. To quantify the process-induced geometric defects and to understand the influences of the geometric defects on the mechanical properties of thin shell lattices, we propose a micro X-ray computed tomography (XCT) based finite element (FE) modelling methodology, which is validated here for Primitive-type shell lattices fabricated by μLPBF in stainless steel. Four types of geometric defects, namely thickness variations, through-thickness defects (holes) on shell surfaces, surface waviness and roughness, are incorporated into the shell element-based FE models. The detailed evaluation of numerical and experimental compression test results shows that the defect-informed simulation approach provides significantly improved prediction accuracy compared to the ideal geometry model in terms of stiffness, peak stress, plateau stress and densification behaviour. The respective influences of each type of defect and their combinations on the mechanical properties of the shell lattices are studied, highlighting that surface roughness and thickness variations lead to prominent impact on the reduction of both linear and nonlinear mechanical properties.

An efficient approach for mesoscale fracture modeling of fully-graded hydraulic concrete

Large coarse aggregates used in fully-graded hydraulic concrete necessitate large specimens for numerical modeling. This leads to a high computational cost for mesoscale modeling and thus slows the development of multiscale modeling of hydraulic mass concrete structures. To overcome this obstacle, an efficient approach for mesoscale fracture modeling of fully-graded hydraulic concrete was developed based on the concept of the governing mesostructure. The mesostructure was characterized by a critical aggregate size. Coarse aggregates smaller than the critical size were homogenized into mortar matrices. Key issues in mesostructure generation of fully-graded hydraulic concrete are discussed, as is the development of mesoscale finite element modeling methodology. The basic concept and implementation procedures of the proposed approach are also described in detail. The numerical results indicated that the proposed approach not only significantly improves the computational efficiency of mesoscale modeling but also captures the dominant fracturing mechanism at the mesoscale and reproduces reasonable fracture properties at the macroscale. Therefore, the proposed approach can serve as a basis for multiscale fracture modeling of hydraulic mass concrete structures.

Interaction between surface breaking and embedded circumferential flaws in tension loaded (pressurized) steel pipes

This paper examines the interaction of adjacent surface breaking and embedded circumferential flaws in terms of crack driving force. A novel finite element modelling methodology for adjacent planar flaws is adopted, based on element deletion in a densely meshed grid. Element deletion provides a unique capability for modelling multiple surface breaking or embedded flaws, since the mesh design is independent of the geometry of the flaw(s). A newly developed postprocessing procedure allows for the calculation of crack driving force (both linear-elastic and elastic-plastic), based on displacements along the flaw flanks.The methodology is employed to scrutinize established flaw interaction rules for surface breaking and embedded co-planar flaw pairs in a tension loaded pipe. The evaluation comprises two aspects: the increase in crack driving force due to flaw interaction, and the conservatism introduced by re-characterizing the flaw pair into a single bounding flaw. A full-factorial parametric study is conducted, containing 36 flaw combinations and two load cases, i.e., axial tensile loading in absence and presence of internal pressure. The results highlight (potentially strong) limitations of current analytical flaw interaction rules with respect to conservatism, the influence of load on flaw interaction, and underestimation of primary geometrical influence factors. The presence of internal pipe pressure, additional to axial stress, is found to have little effect on the results.

Innovative Structural Fuse Systems for Various Prototype Applications.

To resist the imposed lateral forces on the structures, hysteric dampers are developed from steel plates and strategically implemented within various structural applications. Structural shear dampers have recently been used to alleviate damage, while remaining members remain intact and undamaged. The practical use of the innovative dampers in structural applications is investigated in this study. For this purpose, the design methodology for a set of innovative shear dampers is initially elaborated, for which the dampers are designed considering the governing shear and flexural ductile limit states, while the brittle buckling limit state is prevented. Subsequently, the finite element modeling methodology is verified and compared to laboratory tests for computationally analyzing various shapes of the shear damper in structural applications. Three major general prototype structures are established, and shear dampers are designed to be incorporated in prototype applications. For each of the proposed applications, at least six different shapes of shear dampers are designed and subsequently compared with conventional systems. The results determined that the use of innovative shear dampers could effectively reduce demand forces on the boundary elements by more than 40% on average, while the strength and the stiffness alter within margin of difference less than 5%.

Thermal conductivity modeling of monodispersed microspheres using discrete element method

Particle beds are widely used in various systems and processes, such as particle heat exchangers, granular flow reactors, and additive manufacturing. Accurate modeling of the thermal conductivity of particle beds and understanding of their heat transfer mechanisms are important. However, previous models were based on simple cubic packing of particles, which could not accurately represent the actual heat transfer processes under certain conditions. Here, we examine the effect of the packing structure on the thermal conductivity of particle beds. We use monodispersed silica microspheres with average particle sizes ranging from 23 to 330 μm as a model material. We employ a transient hot-wire technique to measure the thermal conductivity of the particle beds with packing density of 43%–57% within a temperature range of room temperature to 500 °C and under N2 gaseous pressures of 20–760 Torr. We then use a discrete element method (DEM) to obtain the realistic packing structure of the particles, which is then fed into a finite-element model (FEM) to calculate the thermal conductivity, with the consideration of solid conduction, gas conduction, and radiation heat transfer. Our results show that the thermal conductivity model based on the more realistic random packing structure derived from the DEM shows better agreement with the experimental data compared to that based on the simple cubic-packing structure. The combined DEM and FEM methodology can serve as a useful tool to predict the effective thermal conductivity of particle beds and to quantify different heat transfer mechanisms under various conditions.

Finite element modeling of an energy storing and return prosthetic foot and implications of stiffness on rollover shape.

Energy storing and return (ESAR) prosthetic feet showed continuous improvements during the last 30 years. Despite this, standard guidelines are still missing to achieve an optimal foot design in terms of performances. One of the most important design parameters in ESAR feet is the Rollover Shape (RoS). This represents the foot Center of Pressure (CoP) path in a shank-based coordinate system during stance. RoS objectively describes the foot behavior according to its stiffness, which depends on foot geometry and material. This work presents the development of a finite element modeling methodology able to predict the stiffness characteristic of an ESAR foot and its RoS. The validation of the model is performed on a well-known commercially available prosthetic foot both in bench tests and realistic walking scenario. The obtained results confirm an error of +6.1% on stiffness estimation and +10.2% on RoS evaluation, which underlines that the proposed method is a powerful tool able to replicate the mechanical behavior of a prosthetic foot.

Simulation of Deformations of Pre-Stressed Steel Trusses in Emergency Situations

Purpose of research is to make methodology and algorithm for finite element modeling in a single computational scheme of deformation of flat steel trusses, previously stressed using high-strength ropes, in accordance with the chronology of impacts on the object in the form of prestresses, normative loads and emergency destruction of one of the bearing elements.Methods. The solution of the problem is carried out in geometrically nonlinear staging using numerical integration based on Newmark approach with the construction of equilibrium equations of the finite element model of the structure in a deformed state at each integration step. Structural nonlinearity related to structural restructuring and consideration of ropes operation for tension only is described. The application of gravity forces of the carrier system, sequential introduction of tightening and their prestress, the application of payload and emergency impact in the form of instantaneous local destruction are traced. Before failure occurs, static loading condition is simulated using dynamic relaxation method. Methodology of accounting within numerical integration of emergency impact is formulated by application of dummy forces, values of which are calculated in excluded structural element before its destruction.Results. Performance of presented computational procedure is illustrated by the example of a flat steel truss calculation with a span (54 m), including two ropes. Object behavior is considered considering the break of one of the ropes subjected to preliminary stress. It was revealed that the investigated emergency does not lead to the destruction of the second rope and the occurrence of plastic deformations in the truss rods.Conclusion: Completed developments can be used to ensure the survivability of pre-stressed steel trusses under beyond design basis effects, leading to the destruction of individual structural elements.

Stress concentration factors in steel tubular KT-connections with FRP-Wrapping under bending moments

Stress concentration factors (SCF) in steel tubular joints have gained considerable attention since it is the crucial parameter for fatigue design of steel tubular structures. Meanwhile, among various strengthening methods, Fiber Reinforced Polymer (FRP) wrapping has shown to be an effective scheme for reinforcing steel structures. This study is dedicated to the numerical investigation of SCF values in FRP-strengthened tubular KT-joints under the action of In-Plane Bending (IPB) and Out-of-Plane Bending (OPB) moments on the central as well as outer braces with three various practical loading patterns per each moment. The Finite Element (FE) modeling methodology for joint geometry and FRP generation was validated against the available data in the literature and well-known codes. The effects of different geometrical parameters along with the FRP parameters on the SCF values were studied through post-analyzing a total of 2920 FE models. The numerical parametric studies indicated that FRP strengthening could lower the SCF values in KT-connections by about 30 and 55 percent under IPB and OPB moments, respectively. Using the driven data, practical fatigue design formulas were developed for predicting SCF in FRP-strengthened KT-joints under bending moments, and reliability of the proposed equations was examined using Fatigue Guidance Review Panel recommendations.

Finite Element Modeling of Reinforced Concrete Walls Under Uni- and Multi-Directional Loading Using Opensees

ABSTRACT A new three-dimensional finite element modeling methodology for nonlinear analysis of reinforced concrete walls is developed and implemented in OpenSees software. The model is validated against broad experimental data obtained for nine planar (unidirectional loading) and two U-shaped (multidirectional loading) specimens. Results of the detailed validation studies presented indicate that the proposed model can accurately capture a wide range of measured global (e.g., load-deformation) and local (e.g., strains) wall responses. However, the model fails to capture the loss of wall lateral load capacity observed in experiments due to various complex failure mechanisms that are not incorporated in presented model formulation.

Advanced test protocols for rapid detection and quantification of nonlinear dynamic responses in aeroengine casing assemblies

In this research, computationally efficient testing protocols were developed for the accurate detection and quantification of nonlinearities in the bolted flange interfaces of aeroengine casing assemblies. Aeroengine casings are joined by bolted flanges that are exposed to high loading amplitudes, leading to bending and large deflections that cause structural nonlinearities. Initially, to assess these structural nonlinearities, a computationally efficient finite element (FE) modelling methodology was developed to accurately capture the vibrational characteristics of the casings while also significantly improving computational efficiency. The technical accuracy of the vibrational characteristics obtained from the FE modelling technique developed here was validated using simulation methods and experimental vibration testing such as modal analysis, the modal assurance criterion, and mode shape assessment. The modes most susceptible to nonlinear dynamic response were then theoretically identified using the mode shape results acquired through the FE model. Thus, a two-step experimental approach is proposed for achieving the accurate and time-efficient quantification of nonlinearities. In the first stage, a rapid experimental nonlinear assessment is performed using a stinger–shaker set-up to validate the FE simulation results of the susceptible nonlinear modes identified. In the second stage, a precise high-resolution measurement is taken with respect to the modes identified in order to precisely capture the nonlinear characteristics. The integration of the proposed theoretical FE modelling technique with advanced experiment formulations results in a significantly more time-efficient and accurate nonlinear testing protocol for aeroengine structures. Furthermore, the nonlinear damping and stiffness parameters of aeroengine casings were also explored in this research and analysed to improve the existing design and development strategies.

Cold-formed high strength steel tubular beam-columns

High strength steel is used more often in a variety of civil engineering applications due to its high strength-to-weight ratio and cost effectiveness. This paper presents the experimental investigation on cold-formed high strength carbon steel tubular members subjected to combined compression and bending. The nominal 0.2% proof stresses of the test specimens were 700 and 900 MPa. The test specimens consisted of square hollow sections (SHS), rectangular hollow sections (RHS) and circular hollow sections (CHS). The material properties, global geometric imperfections of the specimens were measured. The behaviour of the beam-column members was investigated through testing 32 specimens which had a nominal member length of 1480 mm. The second order effects were also considered by measuring the mid-height deflections for all specimens. The compression and bending capacities, load-deformation histories and failure modes of the test specimens were also reported. The test results were compared with the values predicted from the American, Australian and European standards. Improved design recommendation is provided for cold-formed high strength steel tubular beam-columns. Based on the experimental results, finite element modelling methodology is also proposed.