Finite Element Modeling Approach Research Articles

On the importance of accurate elasto-plastic material properties in simulating plate osteosynthesis failure.

Background: Plate osteosynthesis is a widely used technique for bone fracture fixation; however, complications such as plate bending remain a significant clinical concern. A better understanding of the failure mechanisms behind plate osteosynthesis is crucial for improving treatment outcomes. This study aimed to develop finite element (FE) models to predict plate bending failure and validate these against in vitro experiments using literature-based and experimentally determined implant material properties. Methods: Plate fixations of seven cadaveric tibia shaft fractures were tested to failure in a biomechanical setup with various implant configurations. FE models of the bone-implant constructs were developed from computed tomography (CT) scans. Elasto-plastic implant material properties were assigned using either literature data or the experimentally derived data. The predictive capability of these two FE modelling approaches was assessed based on the experimental ground truth. Results: The FE simulations provided quantitatively correct prediction of the in vitro cadaveric experiments in terms of construct stiffness [concordance correlation coefficient (CCC) = 0.97, standard error of estimate (SEE) = 23.66, relative standard error (RSE) = 10.3%], yield load (CCC = 0.97, SEE = 41.21N, RSE = 7.7%), and maximum force (CCC = 0.96, SEE = 35.04, RSE = 9.3%), when including the experimentally determined material properties. Literature-based properties led to inferior accuracies for both stiffness (CCC = 0.92, SEE = 27.62, RSE = 19.6%), yield load (CCC = 0.83, SEE = 46.53N, RSE = 21.4%), and maximum force (CCC = 0.86, SEE = 57.71, RSE = 14.4%). Conclusion: The validated FE model allows for accurate prediction of plate osteosynthesis construct behaviour beyond the elastic regime but only when using experimentally determined implant material properties. Literature-based material properties led to inferior predictability. These validated models have the potential to be utilized for assessing the loads leading to plastic deformation in vivo, as well as aiding in preoperative planning and postoperative rehabilitation protocols.

Deterioration performance analysis of recycled brick concrete subjected to freezing and thawing effect

This study employed experimental and finite element modeling approaches to systematically investigate the mechanical damage mechanisms of recycled brick aggregate concrete (RAC) under freeze-thaw cycling conditions. The investigation encompassed analyses at three hierarchical levels: macroscopic, mesoscopic, and microscopic. The influence of recycled brick aggregate (RA) replacement rate and the number of freeze-thaw cycles on RAC's apparent state and mechanical performance was examined at the macroscopic level. Utilizing equipment such as electron microscopes, a comprehensive observation was conducted from mesoscopic and microscopic perspectives to elucidate the evolving patterns of the cementitious matrix, RA, and the interfacial transition zone (ITZ) within RAC during the freeze-thaw cycling process. On the one hand, more excellent internal space was inherent in RA compared to NA, enabling it to effectively accommodate the volumetric expansion resulting from water freezing. It contributed to mitigating the damage to concrete caused by freeze-thaw cycles. On the other hand, RA's rough and porous characteristics facilitated the infiltration of cement particles into its internal structure, forming a robust ITZ with RA. Concurrently, a numerical simulation of RAC's freeze-thaw cycling process was presented. This simulation generated coupled damage maps and load-deflection curves for RAC under various conditions, encompassing different levels of RA replacement rates, freeze-thaw cycle counts, and loading modes. The research results indicated that the inclusion of RA adversely affects the mechanical properties of concrete while concurrently altering the concrete's failure mode and the propagation pathways of internal cracks. Nevertheless, it was worth noting that the introduction of RA, despite diminishing the mechanical performance of concrete, effectively mitigates the rate of performance degradation during the freeze-thaw cycling process. A favorable equilibrium between freeze-thaw resistance and mechanical performance could be achieved when the replacement rate of RA for natural aggregates (NA) fell within the range of 10–30 %. By employing a finite element model to simulate the flexural performance of RAC after freeze-thaw cycles, the deviation range between the simulated and measured values fell within the range of 5.00–8.23 %. This affirmed the model's fitting solid capability and validated its effectiveness in analyzing the RAC structure's freeze-thaw-load coupled damage and lifespan prediction.

Computational damage analysis of metal matrix composites to identify optimum particle characteristics in indentation process

This paper presents an integrated numerical model that investigates the effects of Al2O3 particle volume fraction, distribution, size, shape, and clustering on the deformation, damage, and failure behaviors of particle-reinforced metal matrix composites. Additionally, the effects of the cohesive strength of the matrix-particle interface and the initial void volume fraction on these behaviors are investigated. In this study, random microstructure-based finite element modeling approach is used. The Gurson-Tvergaard-Needleman model is used to capture the plastic deformation and ductile cracking of the matrix, whereas the Johnson–Holmquist II model is used to model particle fracture. The matrix-particle interface decohesion is modeled using the surface-based cohesive zone method. A two-dimensional nonlinear finite element model augmented with Python-generated code is developed in ABAQUS/Explicit to analyze the damage mechanisms in AA6061-T6/Al2O3 particle-reinforced metal matrix composites. The results show that Al2O3 particle enhance the ability of particle-reinforced metal matrix composites to resist deformation. However, this enhancement is dependent on the indentation location, particulate characteristics, and the applied load. An increase in the particle volume fraction increases the risk of particle fracture, particularly when particles are close to the material surface. Circular particles are the optimal choice for the reinforcement of particle-reinforced metal matrix composites. The predictions are in good agreement with the experimental data, particularly in terms of Rockwell hardness and deformation characteristics.

Strategic use of ultra-high-performance concrete and carbon fiber reinforced polymer reinforcement for end zone design of prestressed girders

The design of end zones to prevent severe cracking is a key requirement toward durable prestressed girders. Traditional approaches employ large amounts of steel reinforcement to attain this requirement, which may result in steel congestion. This paper investigates a hybrid girder concept that uses Ultra-High-Performance Concrete (UHPC) and Carbon Fiber Reinforced Polymer (CFRP) bars to enhance crack control and long-term durability in the end zones of prestressed girders. The objectives of this study are to quantify the UHPC zone lengths needed to restrain end zone cracks, eliminate or reduce the required amount of steel reinforcement, and investigate its replacement with CFRP bars. A finite element modeling (FEM) approach was developed for this purpose and its fidelity was validated with experimental data. The FEM results showed that UHPC zones with lengths below or equal to half of the girder depth can significantly reduce end zone cracking. CFRP bars can be added in the UHPC zones as a conservative measure to crack control, to ensure the long-term corrosion resistance of the girders.

Comparative numerical study to simulate masonry with bed joint reinforced repointing

Bed joint reinforced repointing is a retrofitting technique for unreinforced masonry structures that is commonly applied in the Netherlands to repair settlement-induced damage. Using this technique, the bed joints of masonry walls are reinforced with steel rebars that are embedded in a high strength repair mortar. Due to the increase of induced seismic events in the northern part of the Netherlands, an experimental study was carried out at Delft University of Technology to investigate the performance of this retrofitting technique for combined settlement and seismic loading. This paper aims to simulate the experimental results, with a focus on the comparison of different finite element modelling approaches for studying both un-strengthened and strengthened full-scale tested walls. To that end, three different models are investigated – comprising both macro (continuum) and simplified and detailed micro (brick-to-brick) modelling approaches. The bricks and mortar joints are modelled as one homogenous continuum in the macro model, whereas in the two brick-to-brick models these structural components are modelled separately, with the detailed model including interface elements to simulate the brick–mortar bonds. Nonlinear pushover analyses are subsequently carried out using all three modelling approaches, for both monotonic and cyclic loading cases. Based on these analyses, the detailed brick-to-brick model was found unsuitable to simulate the strengthened wall because cracks in the model mainly occur in the form of opening of the brick–mortar bond interfaces, while smeared cracking in the plane stress elements of the mortar joints is very limited. Similarly, the continuum damage model was found to be inaccurate when pre-existing damage in the experiment needed to be taken into account. The continuum damage model also showed lower axial stresses in the rebars, compared with the simplified brick-to-brick model, as the former does not allow for the direct assignment of material properties for the high strength repair mortar in the strengthened joints.

Directional eddy current probe configuration for in-line detection of out-of-plane wrinkles

Real-time monitoring of carbon fibre composites during Automated Fibre Placement (AFP) manufacturing remains a challenge for non-destructive evaluation (NDE) techniques. A directional eddy-current (EC) probe with asymmetric transmit and differential receive (Tx-dRx) coils is designed, constructed and characterized to evaluate the detectability of out-of-plane wrinkles. Initial studies were conducted to determine suitable excitation frequencies and to analyse the impact of relative orientations of driver and pickup coils on wrinkle detectability. The probe configurations are evaluated experimentally and employ a new finite element modelling approach to better understand the relationship between eddy-current density and defect detection. The findings indicate that a probe configuration with an asymmetric driver coil normal to the material surface and aligned with the fibre directions, and with differential pickup coils 90° to the scanning direction, shows the best capability for out-of-plane wrinkle detection, with SNR >20 for wrinkles over 1.3 mm in amplitude.

Application of In Silico Trials for the Investigation of Drug Effects on Cardiomyopathy-Diseased Heart Cycle Properties

In this paper, we present the abilities of an in silico platform used to simulate the effects of different drugs on heartbeat cycle performance. The platform is based on a finite element modelling approach with the fluid–solid interaction implemented using a loose coupling procedure. Active mechanical stresses are calculated using the Hunter excitation model while the passive mechanical stresses are calculated using a recently introduced experiment-based material model for the heart tissue. The applicability of the platform is illustrated using a simple parametric model of the left ventricle. The simulations are performed using parameters that are specific to drugs such as digoxin, mavacamten, 2-deoxy adenosine triphosphate, and disopyramide, with the concentration of calcium in the cardiac cells affected by these drugs given as an input function. The results are obtained for two geometries mimicking patients with hypertrophic and dilated cardiomyopathy, and also for different inlet/outlet boundary conditions simulating different drug effects at the macroscopic level. Using in silico simulations with virtual patients, it is possible to evaluate the influence of different drugs on cardiac output and ejection fraction. This approach can significantly reduce computational costs with an acceptable solution accuracy compared to approaches coupling finite element and biophysical muscle model methods that are used to calculate drug effects at the micro level.

A 3D cohesive‐frictional coupled interface model for mesoscale simulation of steel fibre‐reinforced concrete

AbstractA 3D mesoscale finite element modelling approach is developed for simulating complicated damage and fracture behaviour in steel fibre‐reinforced concrete (SFRC) with explicit modelling of fibre–matrix interfaces. In this approach, a new 3D four‐noded cohesive‐frictional coupled interface element is developed to model the nonlinear interfacial bond‐slip behaviour, supplemented by a kinematic multiple‐point‐constraint (kMPC) algorithm to simulate the wrapping effect of the mortar around the fibres. They are implemented as a user‐defined element (UEL) and a user‐defined MPC subroutine in ABAQUS, respectively. Three cohesive‐frictional constitutive relationships are proposed to describe the nonlinear bond‐slip behaviour of different fibre–matrix compositions. The new approach is validated by single fibre pullout tests, direct tensile tests and three‐point bending tests of SFRC specimens with randomly distributed fibres. The results show that the new approach is capable of effectively capturing typical failure mechanisms in SFRC, such as fibre yielding, matrix failure, and fibre–matrix debonding and slipping.

Flood impact on structural response of asphalt pavement: A finite element modeling approach

The frequency and intensity of floods have increased due to climate change. These natural events negatively affect asphalt pavements, submerging their layers and reducing structural resistance. This work introduces a computational finite element model suitable for investigating the impact of floods on asphalt pavement response. Unlike previous works, which consider a multi-layer analysis, in this research, the resilient modulus varies locally as a function of moisture, which could be variable in the transverse direction of the cross-section. The moisture distribution in the pavement structure is found by solving the Richards’ equation through non-linear finite element analysis. This moisture distribution is coupled to the three-dimensional elasticity problem to find the structural response to traffic loads. The structural problem was solved using the semi-analytical finite element method. Results show that the reduction of the resilient modulus in the unbound and subgrade layers is heterogeneous, with the areas near the edges of the pavement being the most affected. It was also found that the increase in elastic surface deflection depends on both the load position and time, which suggests the damage caused by vehicles could be different for each wheel path, depending on the time in which the vehicles circulate. This research presents a valuable tool for evaluating the impact of flooding on asphalt pavement structures.

Projectile fragmentation and debris cloud formation behaviour of wavy plates in hypervelocity impact

Continuously increasing micro meteorite and orbital debris (MMOD) in space poses a threat to any manned or unmanned space vehicle with increasing probability of damaging object impact. To address the sufficient level of protection of space vessels, many Whipple shield configurations has been studied for over half a century. Bumper plate of Whipple shields studied in existing literature are flat surfaced plates. In contrast to earlier studies, this paper investigates the reaction of bumper plates with wavy surfaces against hypervelocity impact by analysing how they contribute to projectile fragmentation, formation of debris cloud, and how they dissipate the impact energy. Aluminium plates with four different surface wave profiles (WPs) were numerically investigated under hypervelocity impact conditions to assess their performance on disintegration of the impacting projectile. Fragmentation patterns of spherical aluminium projectile and debris cloud generated by projectile-wavy plate couples were examined and compared with the equivalents observed in flat-surfaced plate impact. A hybrid Smoothed Particle Hydrodynamics (SPH) combined with finite element modelling (FEM) approach was adopted using ANSYS software to simulate hypervelocity impact phenomenon at 3 km/s. Results of the numerical work carried out in this study revealed the distinctive debris cloud generation that has never been reported before in the existing literature. Furthermore, compared to the flat plate, wavy plates are found to be more effective in decreasing the impact energy.

Modeling of Pipe Whip Phenomenon Induced by Fast Transients Based on Fluid–Structure Interaction Method Using a Coupled 1D/3D Modeling Approach

The sudden increase in the operating pressure of nuclear power plants (NPPs) is due to the water hammer phenomenon, which tends to produce a whipping effect that causes serious damage to the pipes and their surroundings. The mechanical response of these pipelines under the influence of such fast fluid transients can be estimated using the fluid–structure interaction (FSI) method. The computational time and expense are predominantly dependent on the number of finite elements developed in the model. Hence, an effective modeling technique with limited and efficient nodes and elements is desired to obtain the closest possible results. A coupled 1D/3D finite element modeling approach using the FSI method is proposed to determine the influence of fast transients on the mechanical pipe whipping behavior of gas pipelines in NPPs. The geometric coupled modeling approach utilizes the presence of both the 3D solid elements and the 1D beam elements sharing a local conjunction. The computational model is modelled for a pipe-to-wall impact test scenario taken from the previously conducted French Commissariat a l’Energie Atomique (CEA) pipe whip experiments. The results of displacement, stresses, and impact velocity at the 3D section featuring the elbow are compared for the change in the 3D solid length varied at the juncture of the elbow. The computed results from the Ansys FSI coupling method using the Fluent and Transient Structural modules provides fair validation with the previously conducted experimental results and correlates with the CEA pipe whip tests on pipe-to-wall impact models. Thus, the 1D/3D coupled modeling approach, which minimizes the area of the solid region by constricting it to the impact area with appropriate contact modeling at the junctures, can be considered in the future for decreasing the computational time and the creation of finite elements.

Verification of Composite Beam Theory with Finite Element Model for Pretensioned Concrete Members with Prestressing FRP Tendons.

Composite beam theory was previously developed to establish an analytical solution for determining the transfer length of prestressed fiber-reinforced polymers (FRP) tendons in pretensioned concrete members. In the present study, a novel finite element (FE) modeling approach is proposed to provide further verification of the developed analytical method. The present FE model takes into account the friction coefficients obtained from pull-out tests on the FRP tendons and prestressed concrete members. Convergence analysis of two numerical simulations with different mesh densities is carried out as well. The results demonstrated that the transfer length predicted by the fine FE model with a friction coefficient of α = 0.3 for high pretension is in good agreement with the measured values and the analytical solutions. The consistency between the analytical solution and FE simulation not only further proves the reliability of composite beam theory but also demonstrates the importance of the bond-slip relationship in predicting the transfer length of pretensioned concrete members prestressed with FRP tendons.

Fiber takviyeli beton döşemenin doğrusal olmayan zımbalama davranışı üzerine parametrik bir çalışma

This paper investigates the effect of fiber on the behavior of punching shear slabs; a finite element modeling approach is used to simulate the case study. The proportion mix of hybrid fiber-reinforced concrete, which contains 0.2 percent macro synthetic fibers and 0.68, 0.8, and 0.96 percent steel fibers, compressive strengths of 50 MPa, different longitudinal reinforcement used, and slab thicknesses of 150, 200, and 250 mm are all joined and investigated in this study. The ATENA software is used to perform nonlinear finite element analysis. The slab results validation was done similar to previous experimental work and the acquired results indicated that a great agreement was found. Thirty-six specimen two-way slabs with dimensions of 1900 × 1900mm were modeled in this investigation. All four sides of the slabs are simply supported. The results displayed that the ultimate shear capacity of the slabs increases with hybrid steel fiber. Nevertheless, the ultimate capacity of the slabs has decreased due to an increase in the reinforcement ratio and slab thickness.

Characterization and Design of Three-Phase Particulate Composites: Microstructure-Free Finite Element Modeling vs. Analytical Micromechanics Models.

Three-phase particulate composites offer greater design flexibility in the selection of phase materials and have more design variables than their two-phase counterparts, thus providing larger space for tailoring effective properties to meet intricate engineering requirements. Predicting effective elastic properties is essential for composite design. However, experimental methods are both expensive and time intensive, whereas the scope of analytical micromechanics models is limited by their inherent assumptions. The newly developed microstructure-free finite element modeling (MF-FEM) approach has been demonstrated to be accurate and reliable for two-phase particulate composites. In this study, we investigate whether the MF-FEM approach can be applied to three-phase particulate composites and, if applicable, under which conditions. The study commences with a convergence analysis to establish the threshold ratio between the element size and the RVE (representative volume element) dimension. We then validate the MF-FEM approach using experimental data on three-phase composites from the existing literature. Subsequently, the MF-FEM method serves as a benchmark to assess the accuracy of both traditional and novel analytical micromechanics models, in predicting the effective elasticity of two distinct types of three-phase particulate composites, characterized by their small and large phase contrasts, respectively. We found that the threshold element-to-RVE ratio (1/150) for three-phase composites is considerably smaller than the ratio (1/50) for two-phase composites. The validation underscores that MF-FEM predictions align closely with experimental data. The analytical micromechanics models demonstrate varying degrees of accuracy depending on the phase volume fractions and the contrast in phase properties. The study indicates that the analytical micromechanics models may not be dependable for predicting effective properties of three-phase particulate composites, particularly those with a large contrast in phase properties. Even though more time-intensive, the MF-FEM proves to be a more reliable approach than the analytical models.

An adaptive hybrid grids finite-element approach for plane wave three-dimensional electromagnetic modeling

In unstructured finite element (FE) plane wave electromagnetic modeling, the goal-oriented mesh adaptive method based on posterior errors is often used to optimize the mesh to a state where a high-precision numerical solution can be obtained with fewer elements. However, for high-frequency data, this method tends to generate a large number of small elements in the shallow near-surface area, which increases the computational burden of FE solution. To solve this problem, we developed an improved goal-oriented hybrid mesh adaptive method. This method realizes the coupling of prismatic elements and tetrahedral elements in FE analysis and can establish FE system equations without suspension nodes. Numerical example studies illustrate how the proposed method uses triangular prism elements to divide the near-surface area and greatly improves the computational efficiency of plane wave electromagnetic modeling. For high-frequency modeling, the proposed hybrid grid reduces the number of required elements, improves the numerical accuracy, reduces the iterations of adaptive grids refinement, and improves the efficiency of the adaptive numerical solution. For low-frequency forward calculations, the hybrid grid maintains the same solution efficiency as traditional adaptive numerical simulation based on pure tetrahedrons.

Finite element analysis and structure optimization of a gantry-type high-precision machine tool

The high-precision machine tool’s dynamic, static, and rigid nature directly affects the machining efficiency and surface quality. Static and dynamic analyses are essential for the design and improvement of precision machine to ensure good tool performance under difficult and demanding machining conditions. In this study, the performance of a high-precision machine tool was analyzed using its virtual model created using CAD. Static and model analysis using ANSYS Workbench software was conducted to establish the tool's static deformation and static stiffness. Furthermore, the static and dynamic characteristics of the tool were explored using a finite element modeling approach to study their performance. In particular, the structure, static force, modal, frequency spectrum, and topology optimization of machine tools were primarily analyzed. Using model analysis, we found the first four different frequencies (22.5, 28.9, 40.6, and 47.4 Hz) and vibration type, which suggested of a weak link. Further static structural analysis revealed that the deformation of the spindle was 67.26 μm. An experimental static rigidity analysis was performed, and the experimental deformation values of the tool and spindle were obtained. The static and dynamic characteristics, as well as the accuracy and efficiency of the finite element model, were verified by comparing the data with the finite element analysis (FEA) results. Subsequently, we modified the settings and analysis model to ensure that the analysis results were consistent with the experimental findings. The error between the two results was within 1.56%. For an applied load of 5000 N on the spindle nose, the tool nose transient response was 0.5 s based on transient analysis. Under the condition that the structural deformation is as constant as possible, the lightweight structure may achieve the minimum weight and enhance the natural frequency; thus, the ideal structure will be obtained, and finite element analysis will then be performed. The optimal conditions for topology optimization include a lightweight structure, reduced structural deformation, and increased natural frequency of the structure. The developed method improves structural optimization, increases the ability of the product to be manufactured, and offers designers a variety of price-effective options.

Finite element modeling of early-age temperature development of in-situ concrete under variable ambient temperatures

The early-age temperature rises in in-situ concrete, caused by the exothermic hydration of cement, poses a significant risk of thermal cracking in concrete structures. This issue is particularly critical in large-scale structures, where thermal cracking can lead to serious structural integrity issues. Therefore, the accurate prediction of the concrete hydration temperature development is paramount for predicting and mitigating early thermal cracking in concrete. However, one of the main challenges in predicting in-situ concrete temperatures is the significant effect of variable ambient temperature on cement hydration rates and concrete heat dissipation. To address this challenge, this paper presents a finite element modeling (FEM) approach that accurately predicts the early-age temperature development of in-situ concrete by adequately considering the effect of variable ambient temperatures. The model integrates the heat of hydration of the cement, the impact of ambient temperature variations, and the heat transfer through the concrete and insulation mould. The cement hydration rate under real-life ambient temperatures is simulated using an Arrhenius-based method, which mathematically adjusts the isothermal calorimetry curves to reflect the actual conditions. Additionally, the study investigates the inhibitory effect of Ground Granulated Blast-furnace Slag (GGBS) on the early hydration temperature of concrete, with experimental tests and FEM simulations conducted on concrete mixes where up to 70% of the cement was replaced with GGBS. The validity of the FEM model was confirmed through comparison with concrete semi-adiabatic tests, demonstrating that the model provides accurate predictions of the temperature development of in-situ concrete. Importantly, the results indicate that the adjusted isothermal calorimetry curves successfully capture the ambient temperature effect on the cement hydration rate. The results provide valuable insights for the design of concrete structures, particularly in preventing early-age thermal cracking.

An Investigation of Microwave Tomography Technique to Image Brain Tumour Through Cross-Section Imaging with Different Number of Electrode

Brain tumours resulted from the irregular growth and cell division within the skull, indicating a highrisk for malignancies to develop and can lead to brain injury or even death. The brain tumour can affectnervoussystem’s function based on the tumour’s growth rate and location. Early detection of brain tumour is essential to improve patients’ survival rates through appropriate medical care. As the current clinical imaging has a few impediments e.g. radiation-based and expensive, tomography technique is seen possible to provide safe and inexpensive technology. The aim of this research is to investigate the feasibility of brain tumour detection using microwave tomography technique with different numbers of electrodes. The 2D finite element modelling approach is applied, and the images are reconstructed using a linear back projection (LBP) algorithm in MATLAB. A different number of rectangular sensing electrodes are arranged around the head phantom in an elliptical array, working in pairs as transmitters and receivers. The simulation shows that the system is able to detect the permittivity difference, thus detecting the existence of the tumour in the head phantom.Theimage reconstruction presented promising tumour images with an 8-antenna microwave tomography system at all locations, i.e. left, right, top, centre, and bottom, in comparison to 4-antenna and 12-antenna systems.

Implementation of Different 2D Finite Element Modeling Approaches in Axial Flux Induction Motors

Axial flux induction motors (AFIM) are gaining popularity due to their higher torque density than radial flux motors. However, axial flux motors have a more complex structure than radial flux motors due to their diameters expanding from the inside out. Before manufacturing, designers have two contradictory goals in the simulation phase. These are high accuracy and short analyses time. The finite element method is a commonly utilized technique for verifying designs. However, in the early stages of AFIM design, a 2D radial flux modeling approach can yield faster results. This approach is well-suited for radial motors, where 2D analysis is widely employed to achieve accurate designs within reasonable analysis times. However, for AFIM with a non-axisymmetric flux path, the application of 2D analysis poses some difficulties. This study compares three modeling approaches, linear, inner rotor and outer rotor modeling approaches to a 3D model and examines their steady-state performance. The results show compatibility in performance data, with some deviations in the torque-speed curve for inner rotor modeling and outer rotor modeling approach methods, which can be reduced by resizing the slots. Overall, acceptable errors and consistent results were achieved between the models.

Blast resistance of ultra high performance concrete-filled steel tube (UHPC-FST) pier against vehicular bombs

Bridge piers will lose axial bearing capacities under accidental or deliberate explosions, which may cause partial or even multi-span collapse of the bridges. Compared with the conventional RC pier, the ultra high performance concrete-filled steel tube (UHPC-FST) pier exhibits superior strength, ductility, and durability, thus having promising applications in the field of blast-resistant bridges. This study aims to experimentally and numerically examine the blast-resistant performance of the UHPC-FST pier under the near-range explosion of Vehicle-Borne Improvised Explosive Devices (VBIED). Firstly, a prototype UHPC-FST pier with earthquake intensity VII was designed following the Chinese specifications, and four 1/4-scale UHPC-FST specimens were scaled and fabricated accordingly. The near-range explosion and succeeding axial compression test were carried out on the specimens with TNT masses of 3 kg, 4 kg, 7 kg, and 10 kg, respectively. Then, full parameters of the Karagozian & Case (K&C) concrete material model applicable to UHPC were systematically calibrated based on the available test data, and the refined finite element (FE) models were established correspondingly based on the explosion and axial compression test. The verification of FE modeling approach was verified by comparing the failure modes and axial force–displacement curves of specimens obtained from the numerical simulation with the test. Finally, two types of VBIED (compact sedan and cargo van) and three standoff distances were selected from the report FEMA-428 and Chinese specifications, and six explosion scenarios were designed correspondingly. The shock wave propagation, shock wave-pier interaction, and the damage evolutions of prototype piers were numerically reproduced. The blast-resistant performance of the prototype UHPC-FST pier was assessed from the aspect of the failure modes and residual axial bearing capacities, which were quantitatively compared with those of conventional RC pier with identical earthquake intensity.