Advanced Finite Element Simulation Research Articles

Unveiling the fatigue life of NiTi endodontic files: An integrated computational–experimental study

Nickel–titanium (NiTi) rotary files used in root canal treatments experience fatigue and shear damage due to the complex curved geometries and operating conditions encountered within the root canal. This can lead to premature file fracture, causing severe complications. A comprehensive understanding of how different factors contribute to file damage is crucial for improving their functional life. This study investigates the combined effects of root canal curvature radius, file canal curvature, and rotational speed on the fatigue life and failure modes of NiTi endodontic files through an integrated computational and experimental approach. Advanced finite element simulations precisely replicating the dynamic motion of files inside curved canal geometries were conducted. Critical stress/strain values were extracted and incorporated into empirical fatigue models to predict the functional life of endodontic files. Extensive experiments with files rotated inside artificial curved canals at various canal curvatures and speeds provided validation. Increasing the canal curvature beyond 60∘ and shorter curvature radii below 5 mm dramatically reduced the functional life of the endodontic file, especially at rotational speeds over 360 rpm. The Coffin–Manson fatigue model based on strain amplitude showed the closest agreement with experiments. Shear stresses dominated damage at low canal curvatures, while the combined shear-fatigue loading effects were prominent at higher canal curvatures. This conclusive study elucidates how operational parameters like canal curvature radii, canal curvature, and rotational speed synergistically influence the fatigue damage processes in NiTi files. The findings offer valuable guidelines to optimize these factors, significantly extending the functional life of endodontic files and reducing the risk of intra-operative failures. The validated computational approach provides a powerful tool for virtual testing and estimation of the functional life of the new file designs before manufacturing.

Deep predictions and transfer learning for simulation-driven structural health monitoring based on guided waves

Simulation-driven structural health monitoring (SHM) is crucial for enhancing the safety and reliability of structures. Its primary aim is to utilize numerical simulations to design efficient SHM systems, reducing costs while maintaining effectiveness. However, challenges arise due to disparities between simulations and physical measurements, stemming from uncertainties, noise, and simplifications. These challenges also extend to SHM methods using machine learning, particularly deep neural networks (DNNs).This paper bridges the gap between DNNs trained on simulated data and real-world experiments by investigating three transfer learning (TL) techniques: feature augmentation, direct fine-tuning, and boosting-based fine-tuning. The focus is on guided wave damage interaction coefficients (WDICs) as damage-sensitive features, modeled by DNNs for damage identification in thin plates, commonly found in aerospace structures like aircraft fuselages. This classification task compares measured and predicted WDICs in a common guided wave SHM configuration with one actuator and three sensors. Training and extensive testing datasets are generated using advanced finite element simulations and laser Doppler vibrometer experiments.The study demonstrates that TL techniques significantly enhance DNN prediction accuracy and improve damage identification performance for untrained scenarios compared to purely simulation-based DNNs. Among the TL approaches explored, feature augmentation with appropriate activation functions and boosting-based fine-tuning yield the most promising results. Using four out of twelve TL datasets, feature augmentation reduces the simulation-based mean absolute percentage error from 46.80% to 35.98% and increases coefficient of determination R2 values from 0.02 to 0.72. With six TL datasets and a boosting-based fine tuning, the mean absolute percentage error decreases from 47.42% to 35.20%, maintaining similar R2 values. While TL substantially enhances prediction accuracy, its impact on damage identification is slightly less pronounced, with improvements in relative classification accuracy by approximately 5% compared to simulation-based DNNs.These findings highlight the efficacy of TL techniques for damage identification in thin plates using WDICs and DNNs, emphasizing the influence of TL training and DNN model variations. Furthermore, they showcase the potential of TL methods to enhance DNN performance in future SHM applications, particularly emphasizing the promise of feature augmentation and boosting.

On predicting the behaviour of an iron‐based shape memory alloy with the Ramberg‐Osgood model

AbstractIron‐based shape memory alloys (Fe‐SMAs) exhibit the particular characteristic of remembering their initial shape after a phase transformation from austenitic to martensitic. This property, along with the high strength and ductility, recommends such materials for strengthening existing structures and designing highly efficient pre‐stressed structural elements. To achieve this, pre‐strained strips or rods made of Fe‐SMA are anchored to a parent structure in the first step. Afterwards, the activation of the Fe‐SMA is triggered through heating, and the material strives to return to its initial shape. Due to the anchoring, a tensile stress is generated in the Fe‐SMA upon cooling back to room temperature, while in the parent structure, a compressive stress field is obtained. The material behaviour of the Fe‐SMA under uniaxial loading is characterized by a rounded stress‐strain relationship without a pronounced yield point, similar to cold‐formed steels. Moreover, in many currently existing applications, the material is used both in the martensitic phase (pre‐strained form before activation) and in the austenitic phase (after activation). This contribution addressed the suitability of the two‐stage Ramberg‐Osgood model for predicting the uniaxial stress‐strain response of the Fe‐SMA. The key parameters were derived based on uniaxial tensile tests and the suitability of the proposed stressstrain curves for use in advanced finite element simulations was emphasized by simulating these tests.

Lateral load resistance of reinforced concrete columns with brittle details

AbstractAnalytical models for shear strength and deformation capacity estimation of reinforced concrete members are essential for the practical implementation of performance‐based seismic evaluation of existing structures and form a key part of current seismic assessment codes (e.g., EN 1998‐3 (2005), (2022), ASCE/SEI 41‐17). Although these models have been derived from regression or calibration of large datasets collected from experimental literature, discrepancy persists between experimental and analytical estimates, especially in cases of members with old‐type detailing. The evident uncertainty about parametric dependencies of the underlying mechanistic problem motivated the present work, where a set of benchmark columns that represent older structural detailing are studied parametrically through advanced finite element simulation. Parameters considered were, the axial load ratio, transverse reinforcement amount and spacing, longitudinal reinforcement ratio, and anchorage/lap splice detailing; results were gauged in terms of the resulting drift ratio (deformation capacity) at the performance limit states and were compared with the Code estimates to evaluate their limits and conservatism. The simulation results were used to vet the assumptions that underlie the simple mechanistic models used in deriving seismic design expressions for yield and ultimate deformation capacities, shear strength, and the rate of its degradation with increasing ductility.

Lateral-torsional buckling assessment of I-beams with sinusoidally corrugated web

This paper assesses the elastic and inelastic lateral-torsional buckling resistance of I-beams with sinusoidal corrugated web through an extended 22 degrees of freedom thin-walled beam-column finite element method. The appropriate hand calculation methods to determine the elastic critical moment of corrugated web beams are based on the modification of the warping constant of the cross-section. Instead of modifying the warping constant, the corrugated web is modelled as a thin, equivalent orthotropic plate with uniform thickness. An approximate expression is also derived from the total potential strain energy of the beam using the Ritz method. The result of the parametric study showed that the developed finite element is accurate and applicable for linear buckling analysis of beams with sinusoidal web corrugation. With the results of the linear buckling analysis the plastic resistance of the corrugated web beam can also be determined. Based on advanced finite element simulations' results the parametric study showed that the standard-based imperfection factor leads to conservative results to predict the inelastic lateral-torsional buckling resistance of sinusoidally corrugated beams, so a more precise but still safe imperfection factor is proposed for sinusoidally corrugated web beams.

Machine learning aided modelling of thermomechanical fatigue of solder joints in electronic component assemblies

Printed board assemblies, i.e. components soldered on printed circuit boards (PCBs), are exposed to thermal cycles responsible for fatigue cracking of solder joints as a result of thermal expansion mismatch between the constituting elements. Advanced finite element simulations are performed using a traction–separation law to represent the cracking process and a temperature-dependent elasto-viscoplastic model for the joint response. Predictions are successfully assessed towards machine learning processed experimental data. In particular, the high sensitivity of thermal ageing reliability to geometric dimensions and solder joint thickness is properly captured. Additional parameters, related to the PCB substrate, are also studied, opening new avenues towards design optimization.

Ductile Fracture Simulation of Stainless Steel Coupons Under Monotonic Tensile Forces

AbstractStainless steel alloys exhibit a nonlinear stress‐strain behaviour which can be precisely described by the Ramberg‐Osgood material model up to the ultimate stress. However, there is no consensus on the ductile fracture model under monotonic loading, which affects the post‐necking stress‐strain behaviour, to be adopted for stainless steels, even though the fracture model may have clear applications in structural design, such as in predicting joint failure in direct design approaches. This study presents the calibration of the fracture parameters for two of the most common ductile fracture models: the modified critical stress model and the Lee and Wierzbicki model. The calibrations are based on experimental results from tensile coupons tests on austenitic, ferritic and duplex stainless steel, extracted from cold‐formed tubes and sheet material, and on advanced finite element simulations. The calibrated values show a low dispersion for each of the analysed materials, indicating that the fracture parameters are an inherent property of the material, and which have been found to be slightly higher for the more ductile alloys. Average values of the fracture parameters for different stainless steels are also preliminarily proposed for their direct application in finite element simulations.

Effect of loading eccentricity on the ultimate lateral resistance of twin-piles in clay

This paper studies the effect of loading eccentricity and pile spacing on the ultimate lateral soil resistance of twin-piles using finite element limit analysis and analytical upper bound plasticity methods. Two kinematic mechanisms corresponding to the failure modes produced by the advanced finite element simulations are postulated with different eccentricity and pile spacing cases. Comparisons have shown excellent agreements between the two approaches. A series of parametric studies are then subsequently performed. Numerical results have shown that loading eccentricity considerably affects ultimate lateral soil resistance, leading to a maximum reduction of 50%. In addition, the curve of normalised pile resistance versus pile spacing ratio is dissimilar to that without considering the effect of loading eccentricity. The proposed solutions and failure mechanisms in this study will provide a deepened insight on the performance of twin-pile group under eccentric loads.

Influence of the imperfection direction on the ultimate response of steel frames in advanced analysis

Initial geometric imperfections are unavoidable in steel members and frames due to erection and manufacturing tolerances. These include frame out-of-plumbness, member out-of-straightness and cross-sectional imperfections, and can have a significant influence on the response and resistance of steel structures. Thus, they need to be accounted for in the analysis and design of steel structures, especially when advanced design procedures are adopted. One of the easiest approaches to introduce geometric imperfections in structural finite element models is through the linear superposition of scaled eigenmodes, which are obtained from a priori elastic buckling analysis. Although the shape and magnitude of frame and member imperfections are specified in international standards, the rules for the combination of different types and directions of imperfections are unclear or impractical, and often require designers to consider many possible combinations to find the critical, or “worst case”, shape of the imperfection including the direction of each eigenmode. This paper investigates the influence of the direction of modes contributing to the imperfection on the ultimate load (i.e., resistance) of steel frames when using advanced analysis. Ultimate loads are estimated from advanced finite element simulations for 20 regular and irregular unbraced frames featuring steel and austenitic stainless steel compact sections, in which initial imperfections are modelled as linear superpositions of six scaled buckling modes considering all possible combinations of direction. The results show that the influence of the imperfection direction on the ultimate frame load is small, and that assuming a combination of all buckling modes with positive amplitudes provides a simple and accurate estimation of the critical imperfection combination.

Incorporation of post-earthquake fire (PEF) and subsequent aftershock for performance analysis of steel buildings

The advancements in analysis and design approaches considering the seismic loads have helped safeguard buildings against structural failure and collapse. However, design objectives should also consider the associated effects and performance evaluation incorporating the sequential effects. Improving the performance of buildings at both the asset and community levels is now of major interest in the field of structural engineering. This research addresses the advancement toward this goal by incorporating post-earthquake fire and aftershock to multi-hazard design methodology. A set of mid-rise buildings – 3-, 9-, and 20-story moment resisting steel frames, characteristic of those found in rapidly growing metropolitan areas of US, are selected for the study considering the relative vulnerability to post-earthquake fire. The analyses of the responses are based on advanced finite element simulation methods/techniques and corresponding approaches. ABAQUS/CAE is primarily employed for the simulation and analysis. The effects of fire are thoroughly studied from the literature and considered explicitly, and the analysis is performed for a complete cycle of main shock (full-intensity) –fire- aftershock (reduced intensity) earthquake. The research commences with the investigation of the effects of modeling approach-- using beam element and using solid element with slab, on Post Earthquake Fire (PEF) study of a single room model. At the end of a complete sequence, the model developed using 3D solid elements are found to underestimate the stiffness loss by around 15% compared to those developed using 2D beam elements. The behaviors of selected steel moment resisting frame buildings then simulated with PEF are investigated to quantify the overall performance behavior of the building system. Inter-story Drift Ratio (IDR) and Stiffness Degradation over the complete sequence of events are chosen as the damage measures. The same approach is applied to a real building in California and the performance behavior is studied. All the building systems studied show the significant damages and change in behavior after incorporating the fire and aftershock. In all building sets, the stiffness loss (global) due to mainshock alone (2% to 10% in the cases studied) is very less as compared to the stiffness loss due to fire alone (6% to 15%) and aftershock (10% to 25%) alone.

Cyclic behaviour of laterally skewed special moment frame connections having composite concrete slabs

AbstractThis study presents a numerical investigation into the cyclic performance of skewed special moment frame (SMF) connections that include composite concrete slabs. The study uses advanced finite element simulations to investigate the behaviour of shallow (W14×), medium (W24×) and deep (W33×) steel column sections with three levels of beam skew (10, 20 and 30 degrees) for both bare‐steel and composite (steel‐concrete) construction. To account for complex torsional boundary conditions that may affect the skewed connection response, prequalification‐type analyses were conducted considering the middle storey of a three‐storey, two‐way moment frame configuration. In the analyses, all skewed configurations achieved at least 0.04 rad of connection rotation during the cyclic loading protocol prior to a 20 % reduction in moment capacity. When a composite concrete slab was added, column twisting and column flange yielding increased at large skew angles (30 degrees) during positive moment cycles.

Modeling Strategies of Finite Element Simulation of Reinforced Concrete Beams Strengthened with FRP: A Review

Fiber-reinforced polymer (FRP) composites do not only possess superior mechanical properties, but can also be easy to tailor, install, and maintain. As such, FRPs offer novel and attractive solutions to facilitate strengthening and/or retrofitting of aging, weakened, and upgraded structures. Despite the availability of general code provisions, the design and analysis of FRP-strengthened concrete structures is both tedious and complex—especially in scenarios associated with unique loading conditions. As such, designers often leverage advanced finite element (FE) simulation as a mean to understand and predict the performance of FRP-strengthened structures. In order to narrow this knowledge gap, this paper details suitable strategy for developing and carrying out advanced FE simulations on FRP-strengthened concrete structures. The paper also covers techniques related to simulating adhesives (bonding agents), material constitutive properties and plasticity (cracking/crushing of concrete, yielding of steel reinforcement, and delamination of FRP laminates), as well as different material types of FRP (CFRP, GFRP, and their hybrid combinations), and FRP strengthening systems (sheets, plates, NSM, and rods) under various loading conditions including ambient, earthquake, and fire. The principles, thumb rules, and findings of this work can be of interest to researchers, practitioners, and students.

Nonlinear Dynamical Behavior of the Deep White Matter during Head Impact

Traumatic brain injury (TBI) is a major public health concern, affecting millions of people each year in the USA. Understanding the patterns of brain movement and deformation during head impact is one of the most powerful strategies for shedding light on the physical causes of TBI. This study uses modal analysis and advanced finite-element simulations to characterize the dynamical behavior of the human brain during head impact. The authors find evidence of geometrical nonlinear effects in the deep white matter of the brain, suggesting a link between the onset of injury and the existence of local nonlinearity in brain tissue.

A Method for Rapid Evaluation of Thermal Performance of Wall Assemblies Based on Geographical Location

In this study, we present a method for the rapid evaluation of thermal performance of building envelopes without the need of using sophisticated and time-consuming computational modeling. The proposed approach is based on the prediction of monthly energy balances per unit area of a wall assembly using monthly averages of temperature and relative humidity, as well as the elevation of a building’s location. Contrary to most other methods, the obtained results include how moisture content in the wall effects its thermal performance. The developed formulas for calculation of monthly energy balances are verified for nine commonly used wall assemblies in Central Europe in 10 randomly selected locations. The observed agreement of the predicated data was determined using advanced finite-element simulation tools and hourly climatic data, which makes for good prerequisites for the further application of the method in both research and building practices.

Finite element method simulation of explosive compaction in saturated loose sandy soils

Explosive Compaction (EC) is a deep soil treatment method for saturated sands with low density. Beside soil characteristics, its efficiency remarkably depends on charges weight, placement pattern and placement depth. Various empirical equations have been proposed by many researchers for selecting of such parameters, but their lack of accuracy makes adopting of a more precise tool for design and evaluation of engaging parameters in EC method essential. Therefore, the present study was devoted to the application of an advanced finite element simulation scheme called arbitrary Lagrangian-Eulerian (ALE) formulation in LS-DYNA as an alternative approach to enhance EC design procedure. SOIL_AND_FOAM material model in LS-DYNA was used for soil and explosives were defined with HIGH_EXPLOSIVE_BURN material model and JWL equation of state. The developed model was validated by using the existing single borehole blast test result. Subsequently, the effectiveness of EC was evaluated by assessing the maximum soil settlement and pore water pressure (PWP) dissipation for different cases where soil permeability, charge weight, depth and detonation delay were varied. Consequently, results suggested that multiple small charges with detonation delays increases EC effectiveness regarding the final settlement and reaching liquefaction during the explosion. Moreover, when charges are placed on lower half of soil layer, more compaction and less heave are achieved. The findings also show that an increase in permeability value of the soil increases the resulting settlement, however, this difference is negligible. Furthermore, based on the obtained results, using more charge weight increases both surface heave and compaction of lower layers. Thus, an optimum weight of explosives should be chosen in this case.

Practical nonlinear inelastic analysis method of composite steel-concrete beams with partial composite action

This paper presents an efficient computer method for nonlinear inelastic analysis of composite steel-concrete beams with partial composite action. The proposed formulation is intended to model the combined effects of partial composite action and distributed plasticity using only one 2-noded beam-column element per structural member. Based on elasto-plastic cross-sectional analyses the behaviour model is able to take into account the effects of partial composite action between the concrete slab and the steel beam. Gradual yielding throughout the cross-section is described through basic equilibrium, compatibility, material and shear connection nonlinear constitutive equations. Tangent flexural and axial rigidity of the cross-section are derived and then using the flexibility approach the elasto-plastic tangent stiffness matrix and equivalent nodal loads vector of the beam-column element including the shear deformability of the partially connected composite beam has been developed. The proposed nonlinear analysis formulation has been implemented in a general nonlinear static purpose computer program, NEFCAD. Advanced finite element simulations have been conducted by using the specialized software for nonlinear analysis of structures, ABAQUS. Several computational examples are given to validate the accuracy and efficiency of the proposed method by comparing the results predicted by NEFCAD with those given by the ABAQUS software and other results retrieved from the open literature.

Finite element analysis of UOE manufacturing process and its effect on mechanical behavior of offshore pipes

• We simulate the UOE forming process, using finite elements and an advanced plasticity model. • We present results for geometrical imperfections and anisotropy induced by the UOE forming process. • We investigate the effect of cold-forming on the performance of UOE pipes under external pressure, tension and bending. • We compare the structural performance of UOE pipes with the performance of seamless pipes. • We examine the efficiency of a simplified methodology for determining the structural capacity of a UOE pipe. Thick-walled steel pipes during their installation in deep-water are subjected to a combination of loading in terms of external pressure, bending and axial tension, which may trigger structural instability due to excessive pipe ovalization. The resistance of offshore pipes against this instability depends on imperfections and residual stresses due to the line pipe manufacturing process. The present study examines the effect of UOE line pipe manufacturing process on the structural response and resistance of offshore pipes during the installation process using advanced finite element simulation tools. The cold bending induced by the UOE process is simulated rigorously and, subsequently, the application of external pressure and structural loading (bending or axial force) is modeled, until structural instability is reached. A parametric analysis is conducted, focusing on the effects of line pipe expansion on the structural capacity of the pipe. The results show that there exists an optimum expansion at which the highest pressure capacity is achieved. The effect of the axial tension on the pressure capacity of the pipe is examined as well. The influence of the line pipe expansion on bending capacity in the presence of external pressure is also identified. Finally, a simplified methodology is employed, accounting for the material anisotropy induced by the manufacturing process, capable of determining the structural capacity of a UOE pipe in a simple and efficient manner with good accuracy, using more conventional modeling tools.

Simplified analytical solution for axial load capacity of concrete-filled double-skin tube (CFDST) columns subjected to fire

Concrete-filled steel tube (CFST) columns and even more so concrete-filled double-skin tube (CFDST) columns have demonstrated a desirable behavior when subjected to fire loading conditions. Current methods to estimate the axial load capacity for these columns exposed to fire are either limited to simple cases using tables or require complex finite element analysis. In an effort to develop a more general and practical approach to this problem, a simplified step by step analytical procedure is proposed for the calculation of the axial load capacity of CFDST columns subjected to any given time–temperature (fire) curve. The procedure was defined by combining an analytical solution to the heat transfer problem with calculation of axial load capacity using the fire-modified material properties adopted from the Eurocode 4 general rules for structural fire design. The proposed method was verified with existing experimental and advanced finite element simulation results. A number of design recommendations, based on the knowledge gained from using the procedure for different case studies, are proposed for CFDST columns subjected to fire.

Interpretation of Results of Penetration Tests Performed on Timber Structures in Bending

The paper concentrates on the determination of local elastic moduli of timber in the fiber direction. To that end a single commercially produced glued timber beam was subjected to 3600 penetration measurements. The beam was first covered by a regular grid of monitoring points at which the depth of indentation was measured. The pin was shot into the wood with a given energy (Pilodin 6J). At the same time the moisture content at 80 selected points was determined. A specific measurement order was assumed to exclude principal measurement errors on the one hand and to minimize systematic measurement errors on the other. We expect the measured elastic moduli to serve as an input for advanced finite element simulations on the bases of stochastic analysis. In such a case the local measured moduli represent in a given segment of each lamella an ensemble of data characterized by a selected probability distribution. These distributions are then employed in the LHS based stochastic simulation to provide probability distribution of the maximum deflection for a given load level. Apart from that it appears meaningful to compare independently the probability distributions of the elastic moduli for segments of the lamella (these may considerably differ owing to the specifics of the production of structures made from glued lamella timber) with statistical data from the whole beam. Based on the measured data the correlation matrix relating statistical dependence of individual segments can be estimated thus improving the quality of the stochastic model.

FE Simulation Methods to Predict Welding Residual Stresses

The purpose of this review paper is to summarize the novel and advanced finite element simulation techniques devised in recent years to predict the welding residual stresses. The finite-element (FE) simulation methods are commonly used to predict the thermal, material, and mechanical effects of welding because of their efficiency and flexibility. This study presents an overview of the research, conducted to more accurately simulate the welding process. Some recommendations and simplification techniques presented by researchers are also discussed in this study which provides a foundation for further development in this field.