High-fidelity Finite Element Model Research Articles

Cyclic loading tests and numerical simulations of an assembled X-shaped flexural steel damper

This paper proposes an assembled X-shaped flexural steel damper. Welding is waived for the novel damper. As the kernel element of the damper, the X-shaped flexural steel plates have the advantages of ease of installation and replacement if necessary. In the analytical part, the effective height of the flexural steel plate was suggested, and then, the yield displacement, yield load and initial stiffness of the damper were derived. The proof-of-concept cyclic loading test was conducted using one reduced-scale specimen within a four-bar linkage experimental setup. The hysteretic performance indexes, including strength, stiffness and energy dissipation, were quantified. The high-fidelity finite element (FE) models were established by ABAQUS. The parametric study was further conducted based on the verified FE model. The considered parameters were the height and thickness of the steel plates. The testing results indicate that the proposed damper has plump hysteretic curve with good energy dissipation capacity and excellent ductility, although slight slip behavior can be found due to the gap caused by the assembling process. The results obtained from analytical method and numerical model are in good agreement with the experimental data. The results of parametric analysis show that the numerical results well agree with analytical predictions, indicating the numerical model can reflect the mechanical behavior of AXSFD. A benchmark frame building was selected to demonstrate the seismic control efficacy of the damper. The nonlinear time history analysis results indicate that the damper reduced both peak and residual interstory drift ratios for the protected structure.

Superelastic Shape Memory Alloy Honeycomb Damper

The relative displacements between the girders and piers of isolated bridges during intense earthquakes are usually so large that traditional restrainers cannot accommodate the resulting deformation. A novel superelastic shape memory alloy (SMA) honeycomb damper (SHD) is proposed as a means to combine the large strain capacity of SMA and the geometrical nonlinear deformation of honeycomb structures. As a result, the large deformation capacity of the novel damper satisfies the requirements for bridge restrainers. The proposed device consists of a superelastic shape memory alloy (SMA) honeycomb structure, which enables a self-centering capability, along with steel plates that serve to prevent the buckling of the SMA honeycomb. An examination of the SHD was undertaken initially from theoretical perspectives. A multi-cell SHD specimen was subsequently manufactured and evaluated. Following this, numerical simulation analyses of the SHDs using a three-dimensional high-fidelity finite element model were employed to examine the experimental results. In the end, a technique for improving the SHD was suggested. The results indicate that the SHD is able to demonstrate superior self-centering capabilities and stable hysteretic responses when subjected to earthquakes.

High-fidelity simulations of low-velocity impact induced matrix cracking and dynamic delamination progression in CFRP beams

A high-fidelity finite element model is constructed to simulate the low-velocity line-impact experiments conducted by Bozkurt and Coker on [05/903]s CFRP beams. The simulations utilize a user-implemented three-dimensional continuum damage model with the LaRC05 criterion for matrix cracking, and a built-in cohesive zone model for delamination in ABAQUS/Explicit. The significant influence of boundary supports on the global impact response leads to proposing a heuristic boundary conditions approach using spring elements that replicate the experiment boundaries. Results then demonstrated an excellent agreement with the experiments in terms of the global impact response, the strain field, and damage pattern and sequence. Simulations reveal intersonic delamination with crack tip speeds around ∼5000 m/s, while the experimental crack speeds were measured as sub-Rayleigh speeds reaching ∼1000 m/s. When a crack tip definition based on the crack tip opening is introduced in the simulations, crack tip speeds in the range of 490–1500 m/s are measured which are within the range of experimental speeds, suggesting that the sliding mode might be physically hidden in the experiments. The potential use of delamination crack tip speeds as a benchmark for refining numerical simulations is demonstrated by increasing the effective interface toughness leading to a decrease in crack tip speeds with no noticeable effect on the global responses.

An efficient framework for structural seismic collapse capacity assessment based on an equivalent SDOF system

Assessing the structural collapse capacity efficiently and accurately is a key issue in earthquake engineering. Here, an efficient framework for structural seismic collapse capacity assessment based on an accurate equivalent single-degree-of-freedom (ESDOF) system is proposed. The corresponding ESDOF system is calibrated by matching the cyclic static pushover (SPO) curves of a more complex multi-degree-of-freedom (MDOF) system (e.g., high-fidelity finite element models) through a meta-heuristic optimization method. In this way, both the backbone curve and hysteretic characteristics (the stiffness and strength deterioration, and pinching behavior) of the complex MDOF system are considered in the corresponding ESDOF system. Then, incremental dynamic analysis (IDA) is carried out to assess the structural seismic collapse capacity using the ESDOF system instead of the corresponding MDOF system to improve the computational efficiency. The efficiency and accuracy of the proposed framework have been validated through three case studies, including a bare reinforced concrete (RC) frame, a steel frame, and an infilled wall RC frame. These results affirm that the proposed framework can accurately and efficiently assess the collapse capacity of low-rise bare and infilled RC frame structures, as well as steel frame structures.

Collapse-resistant mechanism of RC beam-slab substructures using kinked steel plates under two-adjacent-edge-columns removal scenario

To improve the progressive collapse resistance of reinforced concrete (RC) frame structures without basically affecting their seismic performance, the authors have proposed a novel method of adding locally debonded kinked steel plates (KPs) at the beam-ends of the RC frames. This method has been verified through quasi-static tests on the RC beam-column assemblies. Considering the presence of slabs, this paper investigated the collapse-resistant mechanism and resistance improvement for the RC beam-slab substructures using locally debonded KPs. First, quasi-static tests were conducted on two RC beam-slab substructures under the scenario of removing two-adjacent-edge-columns. One substructure was configurated with the KPs and the other without the KPs for comparison. Test results demonstrated that, by adding the KPs, the ultimate resistance and deformability of the beam-slab substructure improved by 76% and 40%, respectively. Second, the high-fidelity finite element (FE) models were created to analyze the load transfer path of the substructure and the resistance contribution at the stage of catenary mechanism. Combining the test and FE analysis results, the collapse-resistant mechanism was revealed, i.e., the KPs could fully mobilize and develop the catenary action in the edge-beams and the tensile membrane action in the slabs along the edge direction. Finally, an analytical model was developed for predicting the ultimate resistance of the RC beam-slab substructures with or without the KPs under the scenario of removing two-adjacent-edge-columns.

Machine learning modeling of lung mechanics: Assessing the variability and propagation of uncertainty in respiratory-system compliance and airway resistance

Background and ObjectiveTraditional assessment of patient response in mechanical ventilation relies on respiratory-system compliance and airway resistance. Clinical evidence has shown high variability in these parameters, highlighting the difficulty of predicting them before the start of ventilation therapy. This motivates the creation of computational models that can connect structural and tissue features with lung mechanics. In this work, we leverage machine learning (ML) techniques to construct predictive lung function models informed by non-linear finite element simulations, and use them to investigate the propagation of uncertainty in the lung mechanical response. MethodsWe revisit a continuum poromechanical formulation of the lungs suitable for determining patient response. Based on this framework, we create high-fidelity finite element models of human lungs from medical images. We also develop a low-fidelity model based on an idealized sphere geometry. We then use these models to train and validate three ML architectures: single-fidelity and multi-fidelity Gaussian process regression, and artificial neural networks. We use the best predictive ML model to further study the sensitivity of lung response to variations in tissue structural parameters and boundary conditions via sensitivity analysis and forward uncertainty quantification. Codes are available for download at https://github.com/comp-medicine-uc/ML-lung-mechanics-UQ ResultsThe low-fidelity model delivers a lung response very close to that predicted by high-fidelity simulations and at a fraction of the computational time. Regarding the trained ML models, the multi-fidelity GP model consistently delivers better accuracy than the single-fidelity GP and neural network models in estimating respiratory-system compliance and resistance (R2∼0.99). In terms of computational efficiency, our ML model delivers a massive speed-up of ∼970,000× with respect to high-fidelity simulations. Regarding lung function, we observed an almost matched and non-linear behavior between specific structural parameters and chest wall stiffness with compliance. Also, we observed a strong modulation of airways resistance with tissue permeability. ConclusionsOur findings unveil the relevance of specific lung tissue parameters and boundary conditions in the respiratory-system response. Furthermore, we highlight the advantages of adopting a multi-fidelity ML approach that combines data from different levels to yield accurate and efficient estimates of clinical mechanical markers. We envision that the methods presented here can open the way to the development of predictive ML models of the lung response that can inform clinical decisions.

Innovative Insights on the Thin Square Plate Large Deflection Problem.

Thin plates subjected to transverse load and undergoing large deflections have been widely studied and published in the literature. However, there is still a lack of information and understanding about the membrane stresses created under large deflections and their associated Airy stress function, as displayed in the well-known von Kármán equations set. The present study aims at providing explicit expressions for the membrane stresses, the deflections, and the Airy stress function for a general square plate area vertically uniformly loaded to reach large deflection state. This was obtained by using the results of a high-fidelity finite element analysis applied on a lateral loaded simply supported thin square plate, which are then casted to yield approximate Fourier series expressions for the membrane stresses, deflections, and the Airy stress function. The stress map figures provide a good understanding of the critical points on the plate, while the explicit mathematical expressions enabled the calculation of deflections and stresses for the entire plate area. Among other interesting findings, the presence of relatively high tensile and compressive membrane stresses existing near the plate edges was revealed, which might lead to potential failure hazards. The derivatives of the deflections and the Airy stress function enabled the validation of the large deflections von Kármán equations set for the investigated case, and it turned out that the generated expressions for the stresses and the lateral deflection based on a high-fidelity finite element model satisfy the second equation with a good accuracy, while the first one remains to further be investigated. Moreover, using the generated explicit equations, the load influence on the deflections and stresses was also analyzed to yield general novel expressions for the medium and very large deflections states. To generalize the investigated case, the stresses and the deflections were non-dimensionalized so they can be used for any material and plate dimensions.

Crashworthiness and dimensional stability analysis of zero Poisson's ratio Fish Cells lattice structures

The present article introduces Zero Poisson's Ratio (ZPR) Fish Cells metamaterial and investigates the effects of Poisson's ratio on the crashworthiness of Positive (PPR), Negative (NPR), and Zero Poisson's ratio lattice structures. High-fidelity Finite Element (FE) models of the proposed sandwich structures are built, based on identical domains for unit cells. Impact performances of lattice structures are addressed for low (2 m/s) and high (5 m/s) impact velocities in three orthogonal directions. The parameters investigated for crashworthiness include impactor's penetration depth, von Mises stress distribution, edges deformation and dimensional stability. Numerical results demonstrate that, unlike PPR and NPR models, the Fish Cells ZPR model possesses greater lateral stability and structural integrity with minimal edge deformations in all three directions. This leads to reduced lateral impact transfer to adjacent components and localised damaged zones, increasing the life span of structural components while reducing maintenance and repair downtime. Experimental analyses are conducted on the Fish Cells metamaterial through a drop tower test for demonstrating agreement with simulations and validation of the proposed modelling approach.

EXPERIMENTAL AND NUMERICAL SIMULATION OF A NOVEL MAGNETIC POLE REPULSIVE PASSIVE DAMPER FOR VIBRATION CONTROL

This article presents a novel magnetic pole repulsive damper (MPRD) incorporating neodymium magnetic repulsive blocks and springs. The study explores the mechanical properties of the springs and magnetic blocks through numerical simulations using ANSYS and experimental evaluation. To gain deeper insights into the behaviour of the MPRD, an accurate and high-fidelity finite element model was developed. The evaluation process involved a comprehensive comparison between the numerical simulations and experimental tests, explicitly focusing on cyclic compression–tension forces. The study encompassed the functioning, design implications, fabrication technique, mechanical performance, and numerical simulation for the cyclic compression–tension forces of the MPRD. The cyclic compression–tension tests revealed a gradual increase in force, with the MPRD achieving an ultimate force of 2,877 kN. The MPRD exhibited robust hysteresis behaviour in cyclic loading, showing its capacity to undergo and uphold the stability of the combination of its materials. The cyclic compression–tension results indicated the maximum force carrying capability of the damper. This resilience implies its full reusability in such scenarios. The comparison between cyclic compression–tension tests confirmed the alignment between the numerical simulation and experimental investigation.

Experimental and numerical investigations on adaptive stiffness double friction pendulum systems for seismic protection of bridges

This study examines the design, development, and characterization of double friction pendulum systems with variable sliding surface geometry. The proposed isolator has a spherical surface with a small radius within an inner sliding range while different geometric functions are used to describe the sliding surface in the outer range. As a result of variable curvature used as sliding surface, the isolators exhibit an adaptive stiffness behavior with increasing displacement amplitude. First, the analytical equations that describe the characteristics of the proposed isolators were derived. Then, a large-scale prototype adaptive isolator that employs a logarithmic function for the sliding surface geometry in the outer range was fabricated. The response of the prototype isolator was characterized under increasing amplitude reversible cyclic loads considering two different levels of vertical isolator loads. A high-fidelity finite element model was developed to capture the response of the prototype isolator. The results obtained from the experimental tests and numerical simulations were used to verify the analytical equations derived for the proposed isolators. Next, a typical multi-span bridge structure was modeled with adaptive stiffness isolators and its response under bi-directional ground motions records were analyzed. In contrast to a conventional double friction pendulum bearing, the suggested isolators yield significantly reduced base shear forces while exhibiting greater isolator displacements. However, the proposed isolators retain the capability to effectively curtail excessive displacements, ensuring the prevention of collapse.

Analysis and design of axially loaded ring-beam joints connecting steel tubed-RC column and RC beams

This work proposes a reinforced concrete (RC) ring-beam joint system for connecting circular tubed-reinforced concrete (TRC) columns and RC beams. In the joint zone, a thin-walled core steel tube is embedded to reduce the size of the RC ring beam, which is beneficial to construction convenience and architectural layout. A simplified model is established to allow for both the confinement effect of the core steel tube and the load-carrying capacity contribution of the ring beam. This simplified model enables the analysis of the load-resisting mechanism underlying the proposed joint, along with the derivation of an equation for its axial compression capacity. Furthermore, a high-fidelity finite element model is established and validated through test results. Parameter analysis was then conducted to assess the effects of concrete strength, yield strength of the steel tube, thickness of the steel tube, and height of the core steel tube on both the core steel tube stresses and the axial load-capacity of the joints. Formulas for calculating circumferential stresses and longitudinal stresses of the core steel tube are also proposed. The predictions agree well with the results obtained from test and parameter analysis. Lastly, design recommendations and procedures for the joint are proposed, and a design example is given with three types of joints details. The results demonstrate the advantages of the proposed joint in terms of convenient construction and favorable cost-effectiveness.

Investigation of Surge Voltage Propagation in Inverter-Driven Electric Machine Windings

This paper investigates what parameters affect the voltage propagation pattern in inverter-driven electric machine windings and presents mathematical analysis of this pattern with experiment verification. This work provides a thorough understanding of the behavior of machine windings under surge voltage excitations. First, high-fidelity finite element (FE) models were constructed with various combinations of factors in random-wound stranded machine windings. These factors include various types of parasitic capacitances, parasitic inductances of parallel strands and different wire layouts in slots. The surge voltage distribution along the windings was simulated and compared among different cases to identify the key factors that affect this voltage propagation pattern. Subsequently, machine windings with both single-phase and three-phase structures were analyzed via equivalent circuits that were constructed with those key parameters. Then, the expressions of the coil voltage were derived in the Laplace domain. These expressions explicate the uneven surge voltage propagation pattern at various frequencies. Finally, for verification, both simulations and tests were conducted to analyze the surge voltage propagation in single-phase and three-phase windings.

Effect of Assembly Uncertainties on Shock Propagation Through a Bolted Joint Under Impact Loading

Abstract Bolted joints have been widely used in engineering structures because of their advantages of simplicity, economy, and assembly. However, material nonlinearities, interface nonlinearities and uncertainties in the assembly process will lead to the dynamic response to become very complex. This work investigated the effect of assembly uncertainties on shock propagation through a bolted lap joint under impact loading. The object of the study was a bolted lap joint subjected to separate Hopkinson pressure bar (SHPB) test. First, a high-fidelity finite element model of the bolted lap joint was developed, and the model was validated by comparing with the experimental results. The error between simulation and experimental results prompted the necessary to consider the uncertainty effect. Then, the effects of multiple uncertainties were considered to identify important input random variables related to the impact response of the joint. The results showed that the slip between the connected parts has the most significant effect on energy dissipation and stress wave propagation. Finally, useful conclusions for the design of bolted joints were obtained from the computational results and discussions.

Cylindrical helical cell metamaterial with large strain zero Poisson’s ratio for shape morphing analysis

In this paper, a novel cylindrical metamaterial with helical cell exhibiting zero Poisson’s ratio (ZPR) in two different directions is introduced. Detailed Computer-aided design modelling of a curved optimised spring element is demonstrated for numerical and experimental analysis. High fidelity finite element models are developed to assess the homogenisation study of Poisson’s ratios, normalised Young’s modulus and torsion behaviour, demonstrating the curvature effect and independency of mechanical behaviour of cylindrical optimised spring element metamaterial from tessellation numbers. Buckling and frequency analysis of the cylindrical metamaterial with spring element are compared with equivalent shell cylinders. Moreover, experimental analysis is performed to validate the large strain ZPR and deformation mechanism demonstrated in numerical simulations. Finally, radical shape morphing analysis under different bending conditions for cylindrical metamaterial with helical cell is investigated, including deformation and actuation energy and compared with positive and negative Poisson’s ratio cylinders formed by honeycomb and auxetic cells.

Experimental studies on improving progressive collapse resistance of RC beam–column assemblies using kinked steel plates

One of the commonly applied methods to improve the progressive collapse resistance of reinforced concrete (RC) frame structures is to increase the amount of longitudinal rebars in beams. However, this method may lead to the unfavorable failure mode of “strong beam-weak column” for the RC frame structures under earthquakes. To prevent from this failure mode, a novel method is presented in this study using kinked steel plates (KPs) that were locally debonded and longitudinally embedded in the RC beams to improve the progressive collapse resistance of the RC frames. First, quasi-static loading tests were conducted on four 1/3 scale RC beam − column assemblies, including an equal-span specimen without the KPs, an equal-span specimen containing the KPs, an unequal-span specimen without the KPs, and an unequal-span specimen containing the KPs. Test results indicated that the ultimate resistance was improved by 89% and 81%, and the deformation capacities were increased by 39% and 38% for the equal-span and unequal-span beam − column assemblies containing the KPs compared to those without the KPs, respectively. Afterwards, high-fidelity finite element (FE) models were established to analyze the resistance contributions of the RC beam − column assemblies at the catenary action stage. Combining the experimental and FE analysis results, the mechanism was revealed for the RC beam − column assemblies using the KPs, i.e., the KPs could improve the ultimate rotational capacity of the beam-ends and induce the behavior of “two batches of plastic hinges”, resulting in fully mobilizing the catenary action to resist progressive collapse. Finally, an analytical model was developed to predict the ultimate resistance of the RC beam − column assemblies.

Development of the test method for wind turbine blade subcomponent under combined bending and torsion loads

The conventional full-scale wind turbine blade testing method is unable to study the detailed structural response of blades' key subcomponents under complex loads. Therefore, developing an efficient and reliable blade subcomponent testing method is of great significance for investigating the structural characteristics of blades. This paper develops an innovative blade subcomponent test method framework, which is capable of studying the structural response under combined bending and torsion load conditions. A high-fidelity finite element model corresponding to the framework that considers nonlinear factors is established. This study further investigated the influence of boundary conditions on the results. The results showed that the test method proposed in this paper is reasonable, and the experiment based on this method is successfully conducted. The contact nonlinearity and size effects will affect the accuracy of the test results, which can be avoided by adjusting the size of the clamp.

Effect of Non-invasive Spinal Stimulation on Self-sustained Firing Motoneuron Model: In-Silico Study Using Human Body Model.

Transcutaneous spinal electrical stimulation (tSCS) is a non-invasive neuromodulation approach using a low intensity direct current. Recent developments in the technique have opened the possibility that tSCS can help restore motor function after spinal cord injury (SCI). However, the exact mechanism of action tSCS has on the spinal circuits is still unknown. Due to the complexity of experimental synthesis in a human model to delineate the mechanisms, models that link the stimulation paradigm and circuit behaviors are advantageous. Thus, this study aims to simulate the underlying changes in motor circuit firing rates in response to external stimuli induced by tSCS. Serial stimulations combining a high-fidelity finite element model with the human torso and spinal cord with a lumped motor neuron model is constructed. The parameters for both components of the model were derived from previous studies. We focused our analysis on a lumped motor neuron model that describes sustained firing behavior of the motor neuron driven primarily by persistent inward current (PIC), a signature behavior of the motor neuron after SCI. Modulation of the PIC behaviors was achieved by stimulating voltage-dependent calcium and sodium channels in the dendrite using a tSCS-induced electric field (E-field) expressed at different a spatial locations of the motor neuron in the gray matter. The PIC behaviors of spinal motor neurons in the left ventral horn were suppressed, while for the most part invariant in the right ventral horn. These initial simulations will provide a steppingstone for future examinations that incorporate additional neuronal models of inhibitory and excitatory interneurons to access the circuit-level effect of spinal stimulation.

Analyzing photovoltaic module mechanics using composite plate theories and finite element solutions

Deflection and stress calculated from an experimentally validated, high-fidelity finite element model (FEM) of a photovoltaic module experiencing mechanical load was compared to results from a simplified FEM treating the module laminate as a homogenized composite using a rule of mixtures approach, and further compared to analytical calculations treating the module as a Kirchoff-Love flat plate. The goal of this study was to determine the error incurred by analyzing module mechanics with varying levels of simplification, since resolving the aspect ratios of a module is computationally expensive. Homogenized FEMs were found to underpredict peak deflection under a 1.0 kPa load by between 13 and 19% for lower and upper bound application of the rule of mixtures. However, module shape was captured, implying that a useful replication of a resolved model could be achieved with a reduced, calibrated material stiffness. Homogenized stress results captured glass layer tensile stress components to within 46 to 52% at a sample location of interest, though agreement was poor through the remainder of the laminate due to the lack of material resolution. For plate theory, deflection was overpredicted by 45 to 67% for upper and lower bound homogenizations, and frame-adjacent module shapes were not adequately replicated. Stress results mirrored FEM trends but magnitudes were not well correlated to resolved model values. These results support the use of homogenized laminate models for module shape derivation, though resolved models remain necessary for stress analyses. The accuracy of plate theory was found to be inadequate for most applications.

An efficient model for predicting complex delamination front of elastic coupling laminates

This work proposes a simple and efficient model to predict the variable crack front with any shape. The model contains a propagation criterion which defines the local growth direction of the delamination crack front by the vector perpendicular to the connection line of two adjacent mesh points. The angle between this vector and the pre-crack direction is calculated by the coordinates of two delamination front points. Crack front can be obtained by the local direction changes of the historical crack front. This model avoids the computing time caused by a high-fidelity finite element model. Its applicability is verified for composite laminates without coupling and with different couplings. The predicted crack front shows good agreements with the numerical results obtained by a high-fidelity FE model with refined mesh. Factors controlling the crack front shape are further discussed by analyzing strain energy release rate and mode mixture distribution at the crack front.

Failure mechanisms of hybrid metal–composite joints with different protrusion densities under a tensile load

The mechanical behaviors of hybrid metal–composite joints with different protrusion densities were investigated by combining numerical and experimental methods. High-fidelity finite element models that considered the failure modes of all components were developed, and specimens based on metal additive manufacturing technology were tested under quasi-static tensile load to verify the numerical calculations. The results showed that the load capacity and the dominant fracture mode of joints were significantly affected by the metal protrusion density. The failure mechanisms of joints under different protrusion conditions exhibited a clear difference, which proved the possibility of an optimal and functional joint design.