3D Finite Element Research Articles

Numerical Modelling of the Punching Shear Response of Shearhead Connections between a CFT Column and a Flat Reinforced Concrete Slab

In this article, the punching shear response of shearhead connections between a Reinforced Concrete (RC) flat slab and interior Concrete-Filled steel Tubular (CFT) columns under static load is investigated by using a 3D nonlinear finite element modelling approach. The accuracy of the numerical model is verified against recent experimental results by comparing the results of the load–displacement relationship, failure models and cracking patterns. Based on validated numerical models, parametric investigations are conducted to examine the effects of slab thickness, concrete compressive strength, length of shearhead arm, size of shearhead cross section and flexural reinforcement ratio on the punching shear response of the connections. Then, some recommendations are given for the design of the effective parameters of shearhead connections, particularly focusing on the effective length and cross-section size of shearhear arms. Finally, a design equation considering the effect of the effective length of shearhead arms and flexural reinforcement ratio is proposed to predict the punching shear strength of shearhead connections. The comparison of punching shear strengths predicted by the proposed equation and some design codes shows that the proposed equation can predict the punching shear strength of shearhead connections more accurately than those from ACI 318-14 and Eurocode 2.

Study on the Characteristics of Turn-to-Turn Short Circuit Faults in the Primary Windings of the Generator Terminal Voltage Transformer

Turn-to-turn short circuit faults in the primary winding of generator terminal voltage transformers can lead to erroneous operation of stator grounding protection systems. This paper analyzes the fault characteristics associated with such failures and derives formulas for the fault phase current and zero-sequence voltage during a turn-to-turn short circuit in the primary winding. A 3D finite element model of the generator terminal voltage transformer is established by using Altair Flux 3D, and the accuracy of the model is verified. Based on this model, simulation tests were conducted to investigate turn-to-turn short circuits in the primary winding. The results reveal that as the number of shorted turns increases, the voltage of the fault phase decreases continuously while the voltages of the other two phases increase. The current in the short-circuited phase rises significantly, accompanied by an increase in zero-sequence voltage. Visualizations of magnetic field parameters indicate that as the number of shorted turns increases, the magnetic induction magnitude of the fault phase rises steadily and approaches saturation, resulting in heightened magnetic field intensity near the shorted turns. This analysis of fault characteristics through simulation contributes to the advancement of fault diagnosis systems for generator terminal voltage transformers.

Eccentric compression performance of jointed precast concrete-encased concrete-filled steel tube columns with dry connections

Concrete-encased concrete-filled steel tube (CECFST) columns have recently been regarded as the optimum option for high-rise or heavy-loaded buildings due to superior structural resistance over traditional concrete-filled steel tube (CFST) and reinforced concrete (RC). Thus, in developed countries with severe manpower shortages such as Singapore, advanced precast dry connections were proposed for the CECFST columns to facilitate construction and tackle manpower crunch. Moreover, current research shows that the proposed connection has comparable structural resistance with conventional cast-in-place (CIP) connections, demonstrating huge application potential. However, the existing research is only limited to the performance of precast connections without any experimental studies on jointed columns, which hinders the implementation of the precast connections in engineering of practices. In this paper, to address this research gap, a comprehensive experimental programme was initiated, followed by extensive numerical studies. A total of six intermediate and slender jointed precast columns were tested to investigate the effect of precast connections on load-carrying behaviour of the jointed CECFST columns by considering column slenderness, connection detailing, connection position and load eccentricity. Besides experimental studies, extensive 3D finite element (FE) simulations were performed to investigate the relationship between connection integrity, constructability, and load-carrying performance of the jointed CECFST columns. The numerical studies showed that implementing the conventional "Equivalent to CIP" concept into the design of jointed precast CECFST columns would significantly compromise the constructability of such columns. To address this concern, a performance-based design method was proposed for jointed CECFST columns. Parametric studies showed that adopting the performance-based design method could not only improve constructability but also achieve sufficient column resistance.

Experimental and numerical investigations on the impact of openings on the stiffness of CLT shear walls

Cross-laminated timber (CLT) exhibits high in-plane strength and stiffness, positioning it as a viable material for shear walls in seismic regions. However, the influence of openings on the in-plane stiffness of CLT shear walls remains inadequately studied. In this study, 43 CLT shear walls with different opening sizes were tested under in-plane loading. The stiffness reduction was less than 29% for openings 800×800mm (53% of panel width), but exceeded 60% for openings 1200×1200mm (80% of panel width). When assessed with identical opening sizes, 139mm and 175mm thick CLT shear walls displayed consistent stiffness reductions. Panels with an aspect ratio of 3:1 exhibited a more pronounced drop than 2:1 aspect ratio panels. A validated 3D finite element model was used to investigate the influence of panel layup and opening shape and location on the in-plane stiffness reduction. For a distance between the opening and panel edge exceeding 300mm, the shape and location of openings exerted negligible effects. Finally, the Dujič’s model was shown to be a suitable predictor to evaluate the in-plane stiffness reduction of CLT shear walls with openings.

Investigation on size effects of ultra-high-performance concrete: experimental and numerical study

ABSTRACT Test specimens with smaller sizes seem to be preferable because using standard specimen sizes for ultra-high-performance concrete (UHPC) can lead to issues owing to the current testing equipment’s capacity limitations. Therefore, the size effect investigation of the UHPC specimens is necessary. In this paper, the UHPC mix was used to explore the size effect on the compression and flexural response of the cylinder and beam specimens, respectively. The UHPC mix was cast into various-sized cylinders and beams with diameters ranging from 50 to 150 mm and heights/widths from 50 to 150 mm, respectively. A nonlinear 3D finite element (FE) model has been created in ABAQUS software for all UHPC specimens. Additionally, validation was done using the experimental findings of this study. The findings clearly revealed that the compressive and flexural strength decreases with increasing the size of the specimen. The larger specimens revealed a slight reduction in compressive strength between 1.4% and 9.5%, while a considerable reduction was recorded in flexural strength, where the larger specimens showed reduction ratios between 19.1% and 35.6%. Furthermore, the experimental and FE findings were in satisfactory agreement and exhibited virtually identical overall trends.

Modeling the rupture dynamics of strong ground motion (> 1 g) in fault stepovers

Following the July 2019 Ridgecrest, California earthquakes, multiple field investigators noted that pebble- to boulder-sized rocks had been displaced from their position in the desert pavement within a stepover along the right-lateral strike-slip M7.1 rupture trace, without evidence of dragging or shearing. This implies localized ground motions in excess of 1 g, in contrast to the instrumentally recorded peak of 0.57 g. Similar rock displacement occurred in a stepover in the predominantly strike-slip 2010 M7.2 El Mayor-Cucapah earthquake. Together, these examples suggest that some aspect of how earthquake rupture negotiates a strike-slip fault stepover produces extremely localized strong ground acceleration. Here, we use the 3D finite element method to investigate how rupture through a variety of strike-slip stepover geometries influences strong ground acceleration. For subshear ruptures, we find that the presence of a stepover in general matters more than its dimensions; the strongest ground acceleration always occurs at the end of the first fault. For supershear ruptures, the stepover is effectively irrelevant, since the strongest particle acceleration occurs at the point of the supershear transition on the first fault. Our model subshear and supershear ruptures alike do produce horizontal particle acceleration above 1 g, but over a region so close to the fault (< 1 km) that a seismic network may not catch it. We suggest that the physics of rupture through a fault stepover could have been responsible for the displaced rocks in the Ridgecrest and El Mayor-Cucapah earthquakes, and that stepover regions may have particularly high ground motion hazard. Our study suggests that ground motion predictions and local hazard assessments should account for much stronger accelerations in the immediate near field of active faults, especially around stepovers and other geometrical discontinuities.

PROSTHESIS REPAIR OF ORAL IMPLANTS BASED ON ARTIFICIAL INTELLIGENC`E FINITE ELEMENT ANALYSIS

Dentists often suggest dental implants to replace missing teeth; nevertheless, mechanical issues can develop with these implants, which could lead to prosthesis replacement or repairs. When investigating implant systems' mechanical characteristics and stress distribution, finite element analysis (FEA) is a popular computational tool. In biomechanical investigations, this strategy is widely used. However, traditional FEA methods can be tedious and require expert expertise for accurate simulation and translation of results. To automate and simplify the process of mending oral implant prostheses, the article suggests a new framework called AI-FEA. The three primary parts that make up the suggested AI-FEA framework are 1. An AI-powered model creation module that utilizes data from medical imaging to autonomously construct 3D finite element designs that are unique to each patient. Utilizing deep learning approaches, this module segments and reconstructs three-dimensional geometries from computed tomography (CT) or cone-beam CT data using material properties and boundary conditions. 2. A FEA solver that runs simulations to test the way the implant system handles different loads. This component uses state-of-the-art numerical methods to model the implant and bone interface and determine stress distributions. 3. An AI-based decision support system that takes all that data and recommends the best way to fix the prosthesis. Combining FEA findings with patient-specific variables, this decision support system uses machine learning algorithms educated on an extensive dataset of implant failure instances and repair results to provide the optimal repair strategy. For patients experiencing issues with oral implants, the suggested AI-FEA framework might mean huge time and skill savings in prosthesis repair planning, leading to better, more individualized care.

PM flux-reversal machine for wind energy application

Currently, attempts are being made to harness wind energy by means of non-conventional electrical machines such as flux reversal machines (FRM). The main advantage of the FRM, when compared with existing synchronous generators (SG), is that all the active parts like PMs and armature windings are mounted on the stator part, whereas leaving the rotor has simple and robust. In this study, the three-phase 6/8-pole flux reversal generators (FRGs) are selected, sized, designed, and analyzed using finite element analysis (FEA). The working principle, choice of stator and rotor poles, and machine design dimensions evaluation (analytical sizing procedure), as well as relevant performance details are discussed in this paper. This study is used to analyze, a popular 6/8 pole, 0.8 kW, 50 Hz, and examine the suitability for the wind energy applications in terms of torque and power density, torque ripple, power factor, and cogging torque under 2D finite element analysis (FEA). The analysis provides an update on the current state-of-the-art and as well as future thrust areas of research necessary to bridge the gap on what is still desired for the practical application of FRMs for wind energy.

Experiments and modeling of magneto-stiffening effects for magnetoactive polymer

This study focuses on creating novel magnetoactive polymers (MAP) by incorporating fabricated magnetic particles into elastomers, a unique approach to MAP preparation. We adopt a unified approach by integrating experimental characterization with a custom-built magneto-mechanical setup, along with modeling and finite element (FE) simulations, to investigate the magneto-mechanical responses of MAP. Our experiments discover a significantly high magneto-stiffening effect with a 20% filler fraction at 0.4 T, almost doubling the stiffness observed in most existing isotropic MAP responses. Based on this data, we propose a new finite deformation-based constitutive model of MAP, which captures the essential features of coupled magneto-mechanical responses. This model is calibrated using experimental data, and its predictions are benchmarked. We further present a 3D FE analysis to show the consistency between experiments and model responses. Finally, we perform a numerical study to demonstrate a stress-induced actuation mechanism using our uniquely fabricated soft magnetic particles which showcases the material’s elastic tunability. This significantly contributes to the theoretical understanding and practical implementation of magnetoactive polymer responses.

Point clouds to as-built two-node wireframe digital twin: a novel method to support autonomous robotic inspection

Previous studies have primarily focused on converting point clouds (PC) into a dense mech of 3D finite element models, neglecting the conversion of PCs into as-built wireframe models with two-node elements for line elements such as beams and columns. This study aims to demonstrate the feasibility of this direct conversion, utilizing building framing patterns to create wireframe models. The study also integrates the OpenSeesPy package for modal analysis and double integration for bending estimation to demonstrate the application of the presented method in robotic inspection. Results indicate the successful conversion of a 4-story mass timber building PC to a 3D structural model with an average error of 7.5% under simplified assumptions. Further, two complex mass timber shed PCs were tested, resulting in detailed wireframe models. According to resource monitoring, our method can process ∼593 points/second, mostly affected by the number of neighbors used in the first stage of sparse points removal. Lastly, our method detects beams, columns, ceilings (floors), and walls with their directions. This research can facilitate various structural modeling directly based on PC data for digital twinning and autonomous robotic inspection.

Towards construction of embankment on soft soil: a comparative study of lightweight materials and deep replacement techniques

Planning embankments demands comprehensive studies to select suitable materials, enhance soil stability, ensure optimal performance, and comply with building code requirements and sustainability standards. This study offers an evaluation of various alternatives and their effectiveness for constructing embankments on weak soil using the 2D finite element software Plaxis 8. It highlights the convergence of different techniques, offering flexibility in selecting the optimal strategy for projects. The behaviour of multilayer clayey soil under an embankment of lightweight filling materials such as mixed sawdust or geo-foam and that carrying an embankment of traditional fill material improved by deep replacement techniques like concrete piles (CP), deep-mixing columns (DMC), stone columns (SC), and sand piles (SP) were compared considering factors like stress distribution, pore water pressure, and settlement of the soil. The results demonstrate that lightweight materials reduced settlement by 11–98% and stress by 5–89%, while deep replacement techniques reduced settlement by 8.5–75% and stress by 44–88%. Notably, the study underscores the effectiveness of DMC in promoting soil reuse compared to CP.

VARIABLE FRICTION MODEL DEVELOPMENT AND IMPLEMENTATION TO THE PULLING FORCE PREDICTION OF THE SPLIT-SLEEVE COLD EXPANSION PROCESS FOR ALUMINUM 2024-T3

Abstract This study aims to improve the accuracy of the pulling force estimation by establishing the variable friction model of the dry-lubricated split sleeve when cold working an aluminum 2024-T3 hole. The variable friction model was empirically obtained from the friction experimental setup simplified from the split-sleeve cold expansion process. The contact-pressure-dependent variable friction model was derived through a systematic design of experiments approach with three different normal stress conditions, namely low normal stress (220 MPa), medium normal stress (440 MPa), and high normal stress (660 MPa), to cover the range of normal stresses occurred in the cold expansion process. A full quadratic response surface model was drawn for the friction coefficient's nonlinear relationship between the mandrel and the lubricated sleeve, depending on the normal stresses. The variable friction model was verified with 3-dimensional friction test finite-element (FE) simulations. This FE modeling validates the variable friction model to predict the pulling forces with a sound agreement between the estimated and experimentally obtained values. We conducted split-sleeve cold expansion experiments to obtain the pulling force profile. Two 3-dimensional (3D) FE numerical analyses of the same split-sleeve cold expansion process were conducted using the variable friction model and a constant frictional coefficient of 0.05. The pulling force profiles from the FE modeling with the variable friction model closely align with those from the experiments to show the four distinct regions.

A robust 3D finite element framework for monolithically coupled thermo-hydro-mechanical analysis of fracture growth with frictional contact in porous media

This paper presents the formulation of a robust integrated framework for the coupled multiphysics and multiple fracture growth analysis in porous media. The finite element-based thermo-hydro-mechanical method for fracture growth with frictional contact (THMf-g) simultaneously solves monolithically coupled equations, incorporating contact and frictional constraints from fracture sliding. It also implements an adaptive process to update fields and geometries during fracture growth, effectively modeling emerging new surfaces. The thermo-hydro-mechanical fields are derived from fundamental principles of mass, momentum, and energy conservation and discretized numerically using the finite element method. Fractures are represented as sub-dimensional surfaces embedded within the volume of the porous medium. The growth of multiple fracture is modeled based on stress intensity factors at fracture tips, with fracture aperture and permeability emerging as dynamic properties of the system. The main novelty of this work lies in extending the implicitly solved monolithic coupling to include frictional and growth modeling for multiple non-planar fractures of emerging geometry in three dimensions. This includes the direct incorporation of cubic terms in the fracture flow equations and convection terms in the heat transfer equations, adopting an incremental method to solve these coupled, nonlinear equations. To ensure energy conservation, the heat equations are resolved using an implicit scheme, establishing a velocity dependency on pressure fields and introducing quadratic terms into the heat equation. Furthermore, the heat transfer equation has been revised to account for the work done on the fluid, enhancing the accuracy of thermal modeling. A contact mechanics leader–follower strategy tracks a conformal mesh split at each fracture, accounting explicitly for permeability changes during deformation and growth, effectively reducing computational complexity and cost. The iterative process for applying these constraints and the solution of the coupled THMf-g with friction and growth is described. The method does not require calibrated material properties or artificial length scale parameters, and relies on laboratory-measured properties with direct physical interpretation. A detailed algorithm is presented, including the updating of apertures and handling of new surfaces during the simulation, accounting for the variability of fracture permeability and its interplay with contact and friction during the non-linear solution. Several validating numerical experiments are benchmarked against analytical solutions, demonstrating the accuracy and reliability of the proposed framework in capturing complex fracture behavior and multiphysics interactions in porous media.

Out-of-plane shear behavior of BFRP-reinforced geopolymer concrete one-way slabs: Experimental and numerical investigations

Sustainability and durability in construction are vital considerations that involve using environmentally friendly materials and implementing efficient design and construction techniques to minimize the environmental impact. This research study investigated the structural behavior of one-way solid slabs incorporating basalt fiber-reinforced polymer (BFRP) reinforcement and geopolymer concrete to develop an environmentally sustainable and durable structural member. Six full-scale BFRP-reinforced geopolymer concrete one-way slab specimens were prepared and subjected to four-point loading tests to assess their out-of-plane shear performances. The considered experimental parameters were compressive strength of concrete (i.e., 30, 40 and 50 MPa) and longitudinal tensile reinforcement ratios (i.e., 1.20% and 2.18%). The structural performance of the slabs was carefully investigated in terms of crack patterns, failure modes, load-deflection relationships and load-strain relationships. The obtained shear resistances from tests were compared with predicted results from the Codes of Practice and design guidelines. A two-dimensional (2D) finite element (FE) analysis was conducted, considering the bond-slip relationship between BFRP rebar and geopolymer concrete. It was found that all tested specimens were governed by shear failure and had similar shear resistance for the chosen values of considered parameters. The JSCE shear design method provided the closest prediction of shear resistance of BFRP-reinforced geopolymer concrete one-way slab. The developed FE models predicted the out-of-plane shear performance with reasonable accuracy and revealed that the slip distribution of the BFRP rebar presents a sawtooth shape owing to concrete cracking.

Finite element analysis of soil-nailed vertical excavation in fine-grained soils in an urban area

This paper presents analysis and discussion of an urban vertical excavation, with the soil nailing technique, in fine-grained soils with high plasticity. The excavation was numerically evaluated using finite element analysis (FEA) using a 3D finite element model (FEM). Several field and laboratory soil investigations were conducted, interpreted and used in the FEA. The FEM model was calibrated using instrumentation and monitoring results during the soil nailing construction. Analyses were conducted focusing in horizontal displacements, nail pullout strength, nail tensile load, soil stress state, and tensile load at the nail head. The results showed that the behavior of the soil nailing retaining wall in fine-grained soils differs significantly from what is typically reported in the literature for non-cohesive soils. The high apparent cohesion of the fine-grained soil resulted in good performance, with reduced horizontal displacements on the face and lower tensile loads in the nails and at their head.

Accurate Flashover assessment for coastal overhead lines based on volt-time criterion

This study investigates the impact of considering insulation volt-time curves on estimating the annual flashover rate of overhead lines subjected to nearby lightning strikes in the presence of ocean-land environments. A method based on the 3D Finite Element Method is employed to compute induced voltages, while a Monte Carlo simulation determines the annual flashover occurrence. To detect Flashover occurrence a volt-time method is employed and the results are compared with the conventional 1.5CFO criterion. The influence of line proximity to the coastline, pole spacing, and various striking distance calculation methods on flashover predictions is evaluated. Results indicate that the 1.5CFO criterion underestimates the annual flashover rate due to indirect lightning in mixed ocean-land terrains compared to the volt-time curve approach. A novel analytical formula is proposed to estimate annual flashovers considering volt-time curves in such environments.

Numerical and experimental investigation of nickel-deposited 410 stainless steel using the laser cladding process

This study investigates the laser cladding (LC) of pure nickel onto AISI 410 stainless steel using a low-power pulsed diode laser. The process parameters included scanning speeds of 0.5–1.5 mm/s and average laser powers of 20–40 W, with a fixed pulse width of 110 ns and pulse frequency of 50 kHz. Microhardness, clad geometry, and microstructure at the clad-substrate interface were analyzed using optical microscopy, FE-SEM, and EDS. At 40 W, successful nickel deposition was achieved, demonstrating optimal metallurgical bonding. The clad depth decreased from 364.7 to 170.0 µm as the scanning speed increased, with the best microstructure and highest microhardness observed at 1 mm/s. A 3D finite element model was developed to complement the experimental findings and to gain a deeper understanding of the LC process, particularly in terms of temperature distribution, and the resulting clad geometry. The simulations revealed that increasing scanning speed significantly reduced the peak temperature, from 3121 K at 0.5 mm/s to 2445 K at 1.5 mm/s. The nickel deposition was unsuccessful at 20 and 30 W due to insufficient peak temperatures of 1468 and 1899 K, respectively. At 40 W, a peak temperature of 2879 K was achieved, aligning well with the experimental results and confirming the accuracy of the simulation in predicting the effects of processing parameters.

Performance evaluation and optimization of flux-regulated axial-radial eddy current coupling

Abstract This paper proposes a novel axial-radial permanent magnet eddy-current coupling equipped with a mechanical magnetic adjuster. The innovative design integrates mechanical flux weakening technology with an enhanced magnetic method rooted in axial-radial hybrid flux topology. Concise analytical models for air-gap field and torque are developed, leveraging the magnetic equivalent circuit method and Faraday’s law. These models are subsequently validated using the 3D finite-element method. The results indicate that this device boasts an exceptionally broad torque adjustment range, reaching approximately 93% at a given slip. Furthermore, it exhibits a substantial optimal working area, spanning from 20% to 80% of the mechanical magnetic adjuster's movable distance. To comprehensively analyze the impact of structural parameters on overall performance, three novel metrics are defined. The analysis reveals that the pole pairs of the radial magnetic circuit (RMC) have the most significant influence on the device's comprehensive performance. In the end, a multi-objective optimization method to maximize the global torque regulation capabilities, local torque regulation abilities, and maximum torque potential is developed to enhance the overall performance of this innovative magnetic coupling design.

Advanced Mullins Damage Modeling (AMDM) after Multiple Cyclic Loading in Vulcanizates; Part 1: Theory and Parameter Identification

Abstract This study explores the deformation behavior of carbon black-filled elastomeric components under multiple cyclic loading conditions. Understanding the effects of repeated cyclic deformation is crucial for accurate Finite Element Method (FEM) simulations. We present an approach that captures both initial and subsequent cycles, converging to an equilibrium state. Experimental evidence from cyclic deformation and relaxation tests indicates that an equilibrium state is achieved within five deformation cycles. Our method analytically describes the relaxed or equilibrium state after multiple cyclic deformations by combining a relaxation model with a material model. We utilized a combination of a relaxation approach and the Modified Extended Tube Model (METM), allowing us to distinguish between polymer network effects and filler properties, thereby establishing a direct correlation between elastomer parameters and mechanical properties. The multiple cyclic deformation behavior can be analytically described using the Advanced Mullins Damage Modeling (AMDM) approach, validated through experimental data. The AMDM employs two damage functions for the increasing and decreasing stress phases of the cycle using the relaxed METM approach. The feasibility of this approach is demonstrated through 3D finite element (FE) simulations, confirming the validity of AMDM under cyclic deformation. The combination of the relaxed METM and AMDM approaches provides a robust framework for predicting the cyclic deformation behavior of filled elastomers, with significant applications in engineering and material science.

Fatigue analysis of offshore wind turbines with soil-structure interaction and various pile types

Monopile offshore wind turbines (OWTs) are susceptible to fatigue damage, and time domain fatigue analysis is time-consuming and unsuitable for simulating various loading conditions. In this study, frequency domain fatigue analysis of OWTs with soil-structure interaction (SSI) and different monopile designs (the conventional monopile, monopiles with an extension, a wheel, and four spoiler ribs) is conducted. First, detailed 3D finite element models of OWTs are developed. The tower, monopile, and soil are modelled using solid elements, and SSI is accounted for using the Mohr-Coulomb failure criterion and surface-to-surface contact. Next, the power spectral densities of wind and wave loads on the tower and monopile are derived. Subsequently, the fatigue damages of the OWTs are evaluated under individual and combined wind and wave loads. The results show that damage increases with wave height, peaking at the rated wind speed and wave frequency close to the first frequency of the OWTs. Wind-induced damage is significantly greater than wave-induced damage, and the combined wind and wave loads produce more damage than the sum of the individual loads. Additionally, alternative monopile designs, particularly the monopile with a wheel, can reduce fatigue damage, though stress concentration effects on the wheel and ribs require careful consideration.