High-fidelity Finite Element Model Research Articles

Seismic retrofitting of beam to double-I built-up column moment connections by lateral T-stiffeners: Experimental and numerical study

In the present paper, the retrofitting of welded flange plate moment connections joined to double-I built-up columns is discussed by presenting the design method and details of construction retrofitting. Some of the usual construction problems of this connection include the defective complete joint penetration groove weld at the connection of the flange plate and the column, the large out-of-plane deformations of the column cover plate at the level of the beam-to-column connection, and as a result, its inappropriate seismic performance and the connection's partially restrained behavior. Thus, an attempt is made to evaluate the advantages of strengthening this defective connection with the help of lateral T-stiffeners using analytical and experimental studies. For this purpose, the experimental specimen and the high-fidelity finite element model are considered for both retrofitted and defective connections by evaluating the proposed design method, cyclic behavior of connection, collapse potential of weld fasteners, and failure modes. The results indicate that by using the proposed retrofitting method, the connection is classified in the group of fully restrained connections, while also having the necessary strength and ductility to accept the conditions of the special moment-resisting frames according to AISC seismic provisions. By performing a sensitivity analysis on the T-stiffener, changing its dimensions and examining the damage indices, the accuracy of the proposed design method is proven. The examinations indicate that the aforementioned retrofitting method is a proper method for the introduced defective connection.

High-fidelity simulation of low-velocity impact damage in fiber-reinforced composite laminates using integrated discrete and continuum damage models

A high-fidelity finite element (FE) model based on integrated discrete and continuum damage modeling techniques was developed to predict damage modes, locations, sizes, and damage occurrence sequence in a composite laminate during a low-velocity impact event. Fiber breakage and transverse matrix cracking were captured using the three-dimensional Hashin’s criteria, and delamination was captured by inserting a layer of cohesive elements between every adjacent composite ply. Delamination progression from one layer to another was captured by embedding cohesive elements inside each composite ply aligned with the fiber orientation and with a 45° angle to the thickness direction. The refined mesh and intralaminar cohesive elements were only used in the predicted damage region based on an analytical solution. The FE model predicted impact response was validated by drop-weight tests, and the layer-by-layer damage areas were validated and characterized by X-Ray CT inspections on 254 mm by 304.8 mm IM7/977-3 laminates with a stacking sequence of [0/45/90/-45]4s. The absorbed energy, damage areas, maximum deflection, contact time, and peak load were predicted with less than 10% error. The detailed damage occurrence sequence during the impact event was predicted through histories of energies dissipated by different damage modes. The modeling methodology developed in this work highlights the effects of modeling parameters on convergence, solution accuracy and computational efficiency, and provides an effective approach for progressive damage modeling of composite laminates.

Numerical investigations on dynamic responses of subway segmental tunnel lining structures under internal blasts

Numerical simulation of segmental lining tunnel subjected to internal explosive loading is carried out in this paper based on the arbitrary-Lagrangian-Eulerian (ALE) and finite element (FE) coupled algorithms. A high-fidelity FE model considering assembled features of segmental lining structure is established, and the mapping technique is adopted to accurately simulate the explosion process. The calculated overpressure histories and failure modes of the lining structure fit well with field test results of full-scale specimens, indicating the applicability and accuracy of the numerical model. A more comprehensive numerical model considered the practical service state of segmental lining tunnel is further built based on the verified model. Influences of mechanical properties and pressure levels of surrounding soils on dynamic responses of tunnel structure under internal explosion are investigated. Numerical results show that dominated deformation modes of the segmental lining tunnel under the action of internal explosion include opening deformation at the segmental joints of the charged ring and shear deformation between the adjacent rings. The modest explosion caused by terrorist bombing attacks may severely harm the shield tunnel structure and impair its service performance, especially if the tunnel is buried in soft soil at a shallow depth

Predicting of Punching Shear Capacity of Corroded Reinforced Concrete Slab-column Joints Using Artificial Intelligence Techniques

Rebars in reinforced concrete (RC) slab-column structures may corrodeunder unfavourable conditions, making slab-column joints (SCJs) more susceptibleto punching shear (PS) failure. Moreover, PS failure is a common brittle failure,which makes it more difficult to evaluate slab column systems' functioning andfailure probability. Thus, the prediction of PS resistance and the related reliabilityanalysis are key factors for building RC slab-column systems. In this study, a highfidelity finite-element model was created using Abaqus. A comprehensiveexperimental record is compiled for corroded RC slab-column joints subjected topunching shear loading. Then, effective parameters are established by applying

Seismic performance of self-centering rocking bents considering soil-structure interaction

The rocking bridge has attracted a significant research interest, due to its excellent self-centering capacity after the severe earthquake. However, the vast majority of previous studies on the seismic behavior of rocking bents were usually conducted based on the assumption of the rigid bedrock without considering of soil-structure interaction (SSI). Hence, this paper investigates the seismic performance of the self-centering rocking bent considering the SSI effect. Focusing on the double-column self-centering rocking bent equipped with and without angle steels (SCRB-A and SCRB) and the conventional double-column reinforced concrete bent (RCB), the high-fidelity finite element models considering the SSI effect are established. The seismic responses of the bents with fixed-base (without SSI) and flexible-base (with SSI) are comparatively evaluated. The influence of the shear wave velocity of soil on the seismic behavior of the bents with the SSI is also discussed. The results show that the SSI has significantly effect on the seismic responses of the three bents. The displacement responses are generally increased when the SSI is considered, and the amplifications of the seismic responses of the SCRB-A and SCRB considering SSI are more obvious than those of the RCB. With the increase of the shear wave velocity, the influence of the SSI on the displacement responses of the RCB becomes progressively less sensitive, however, the totally different trends can be found in the SCRB-A and SCRB with SSI. Moreover, SCRB-A exhibits better seismic performance when compared with the SCRB and RCB for the cases with or without the SSI effect.

Pitting corrosion identification approach based on inverse finite element method for marine structure applications

This paper presents a state-of-the art inverse finite element method (iFEM) for full-field, real-time structural health monitoring (SHM) of corroding structures. The study focuses on detecting the location and identifying the extent of pitting corrosion, which is one of the most hazardous forms of corrosion due to the difficulties regarding its prediction and detection. For this purpose, high-fidelity finite element (FE) models of corroded samples with complex-shaped, semi-ellipsoidal, and cylindroconical defects are developed to replicate the strain field of pitting corroded structures. The strain fields produced by the FE models, verified against experimental data, are reconstructed by the iFEM model using a robust and practical four-node quadrilateral inverse-shell element, iQS4. A strain-based damage criterion is defined to obtain the damage distribution and the location of corrosion pits on dog-bone tensile test samples with full sensor iFEM and coupled iFEM-GA reduced sensor technique. Finally, in a practical example of a structure with complex geometry, the proposed method's performance is assessed through detecting the location of corrosion damage on a cylindrical marine structure with axial stiffeners.

Finite element analysis of TPO membrane- retrofitted metal roof system subjected to wind loads

Metal roofing is a common system for low-slope and flat roofing systems such as those used in industrial and storage facilities. Despite its longevity, a metal roof will require a retrofitting when it displays a functional deficiency or reaches to the end of its service life. One of the common retrofitting methods is to use a thermoplastic polyolefin single ply membrane due to its ease of installation, economic efficiency, and lightweight. A single ply membrane typically relies on the existing metal deck system as a structural deck and provides insulation and protection against wind uplift. This paper presents a high-fidelity finite element model to investigate the behavior of a single ply membrane retrofitting metal deck roof under wind uplift. The developed finite element models (FEMs) were validated with experimental results of three full-scale retrofitted metal deck systems using Thermoplastic Polyolefin (TPO) membrane. Parametric study was carried out to investigate the effect of different fastener patterns, transverse and longitudinal fastener spacing, and membrane strength.

Damage detection of spent nuclear fuel canisters using frequency response functions

This paper investigates the use of the frequency response functions (FRFs) of a sealed spent-nuclear fuel canister when it is subjected to an external vibration to detect abnormalities to its contents. The variation in the FRFs as an indication of probable damage is introduced and examined. Both finite element (FE) simulations and experimental analyses of a mock-up fully loaded canister basket system were performed. An efficient methodology that employs model reduction techniques to perform FRF calculations for high-fidelity finite element models (FEMs) was used. The experimental work was conducted using a modal shaker to excite the canister at the bottom plate and to collect acceleration measurements at various locations. The location of hypothetical damage cases (missing fuel assemblies) was accurately determined in both computational and experimental models employing the framework that is introduced in this study. Furthermore, additional possible damage scenarios are introduced and analyzed with the FEM. Although the FEM could identify the location of abnormalities for most of the cases considered here, when the damage was local and minor, the differences in the FRFs were minute, which rendered the damage detection challenging. Finally, the study concludes that the use of dynamic vibration measurements on the outside of a canister can provide valuable information to detect physical abnormalities in a sealed spent nuclear fuel (SNF) package.

Towards Tough Thermoplastic Adhesive Tape by Microstructuring the Tape Using Tailored Defects

This paper presents a strategy towards achieving thermoplastic adhesive tapes with high toughness by microstructuring conventional tapes using tailored defects. Toughened tape was manufactured using two layers of a conventional tape where the bondline between the two adhesive layers was microstructured by embedding tailored defects with specific size and gap between them using PTFE film. Mode I toughness of the toughened tape was characterized experimentally. A high-fidelity finite element model was implemented to describe the toughening mechanisms using double cantilever beam simulations and end notch flexural tests. The model considers for the plasticity of the adhesive layer, the decohesion at the adherend-adhesive and adhesive-adhesive interfaces and progressive damage inside the adhesive layer. The adhesive-adhesive interface with the tailored defects inside the adhesive layer enables crack migration between adherend-adhesive interfaces, crack propagation at adhesive-adhesive interface, backward crack propagation under the defect, and plastic deformation of the adhesive ligament. The maximum toughness improvement of the tape with tailored defects of equal width and gap between two successive defects of 2 mm reached 278% and 147% for mode I and II, respectively, compared to conventional tape.

VERIFICATION AND VALIDATION OF A RAPID DESIGN TOOL FOR THE ANALYSIS OF THE COMPOSITE Y-JOINT OF THE D8 DOUBLE-BUBBLE AIRCRAFT

Polymer composite joints are critical aerospace components for reinforcing lightweight structures and achieving high eco-efficiency transportation standards. Optimizing complex structural joints is an iterative process. Fast and reliable numerical approaches are needed to overcome the runtime limitations of high-fidelity finite element (FE) modeling. This work proposes a computationally efficient approach based on the design tool, HyperX. Verification against FE models and experimental validation are presented for the composite Y-joint in the D8 double-bubble fuselage. Results show that the failure load of the Y-joint is predicted within 10% of the experimental failure load recorded. Two parametric studies are performed to study the effects of the curvature of the joint (110-160 deg) and the skin thickness (16, 24, and 32 ply) in the failure load predictions using a stress-based failure criterion. The maximum failure load occurred for a Y-joint with 130 deg curvature. The 32-ply skin Y-joint was predicted to have the highest failure load. Results prove the applicability of rapid joint optimization analysis for faster, computationally efficient design.

The biomechanical signature of loss of consciousness: computational modelling of elite athlete head injuries.

Sports related head injuries can cause transient neurological events including loss of consciousness and dystonic posturing. However, it is unknown why head impacts that appear similar produce distinct neurological effects. The biomechanical effect of impacts can be estimated using computational models of strain within the brain. Here, we investigate the strain and strain rates produced by professional American football impacts that led to loss of consciousness, posturing or no neurological signs. We reviewed 1280 National Football League American football games and selected cases where the team's medical personnel made a diagnosis of concussion. Videos were then analysed for signs of neurological events. We identified 20 head impacts that showed clear video signs of loss of consciousness and 21 showing clear abnormal posturing. Forty-one control impacts were selected where there was no observable evidence of neurological signs, resulting in 82 videos of impacts for analysis. Video analysis was used to guide physical reconstructions of these impacts, allowing us to estimate the impact kinematics. These were then used as input to a detailed 3D high-fidelity finite element model of brain injury biomechanics to estimate strain and strain rate within the brain. We tested the hypotheses that impacts producing loss of consciousness would be associated with the highest biomechanical forces, that loss of consciousness would be associated with high forces in brainstem nuclei involved in arousal and that dystonic posturing would be associated with high forces in motor regions. Impacts leading to loss of consciousness compared to controls produced higher head acceleration (linear acceleration; 81.5 g ± 39.8 versus 47.9 ± 21.4; P = 0.004, rotational acceleration; 5.9 krad/s2 ± 2.4 versus 3.5 ± 1.6; P < 0.001) and in voxel-wise analysis produced larger brain deformation in many brain regions, including parts of the brainstem and cerebellum. Dystonic posturing was also associated with higher deformation compared to controls, with brain deformation observed in cortical regions that included the motor cortex. Loss of consciousness was specifically associated with higher strain rates in brainstem regions implicated in maintenance of consciousness, including following correction for the overall severity of impact. These included brainstem nuclei including the locus coeruleus, dorsal raphé and parabrachial complex. The results show that in head impacts producing loss of consciousness, brain deformation is disproportionately seen in brainstem regions containing nuclei involved in arousal, suggesting that head impacts produce loss of consciousness through a biomechanical effect on key brainstem nuclei involved in the maintenance of consciousness.

A Homogenization Method for Replacement Stator Models in an Aero-Engine

Generally, the high-fidelity finite element models of aero-engines comprise millions of degrees of freedom (DOFs). Although they can provide precise predictions of structural dynamics, the computational cost will be often unaffordable if appropriate dimension reduction techniques are not adopted. The homogenization of the substructure, also termed as the physical replacement, reduces the model scale by simplifying the unnecessary details of the substructure, thus speeding up the dynamic analysis of the whole engine. In this study, we design the physical replacements for the stators of an aero-engine based on the long-wave assumption. These replacements have the same wave features as the stators in long-wave cases while possessing fewer DOFs. The core steps include the analytical description of the stators and the corresponding physical replacement design through two homogenizations. Specifically, we first investigate the wave characteristics of the stators using the wave finite element method and find two dominant waves: flexural and flexural–torsional coupled waves. The first homogenization introduces two analytical Timoshenko beams to describe the two wave motions of the stators. These two analytical beams are subsequently solidified into physical replacements with I, box, and open cross-sections in the second homogenization. The mechanical and geometric parameters are identified through a combination of the static analysis and the genetic algorithm (GA). The search processes are of great efficiency, because all the descriptions are analytical. Results show that the relative errors of the natural frequencies between the pristine stators and the physical replacements associated with the nodal diameters 6–15 are less than 5%.

Damage assessment of normal reinforced concrete panels strengthened with polyurea after explosion

Polyurea can effectively improve the anti-blast performance of normal reinforced concrete (NRC) panels. However, there are very limited studies on the damage assessment of polyurea strengthening NRC (PU-NRC) panels after near-field explosion. In this paper, a high-fidelity finite element (FE) model of PU-NRC panel was developed and validated by the results from near-field explosion and static loading tests. Subsequently, the deterioration of the bearing capacity was selected as a damage criterion to assess the damage of the PU-NRC panel after explosion. The impacts of polyurea thickness, panel thickness, compressive strength of concrete and longitudial reinforcement ratio on the damage levels of the PU-NRC panel were further discussed. Finally, the empirical formulas of P-I diagram were developed to assess the damage level of the PU-NRC panel after varied blast loads. The results showed that spraying polyurea can improve the stiffness of NRC panel under blast load. In addition, the closer the standoff distance, the better the strengthening effectiveness of polyurea. Increasing polyurea thickness was more effective to increase the value of overpressure asymptote, and spraying polyurea had little contribution to improve the shear resistance of the NRC panel. This research has significant implications for practitioners and scholars in protective engineering.

Investigation on the Modeling and Reconstruction of Head Injury Accident Using ABAQUS/Explicit.

A process of modeling and reconstructing human head injuries involved in traffic crashes based on ABAQUS/Explicit is presented in this paper. A high-fidelity finite element (FE) model previously developed by the authors is employed to simulate a real accident case that led to head injury. The most probable head impact position informed by CT images is used for the FE modeling and simulation since the head impact position is critical for accident reconstruction and future analysis of accidents that involve human head injuries. Critical von Mises stress on the skull surface of the head model is chosen as the evaluation criterion for the head injury and FE simulations on 60 cases with various human head-concrete ground impact conditions (impact speeds and angles) were run to obtain those stress values. The FE simulation results are compared with the CT images to determine the minimum speed that will cause skull fracture and the corresponding contact angle at that speed. Our study shows that the minimum speed that would cause skull fracture is 3.5 m/s when the contact angle between the occipital position of the injured head and the ground is about 30°. Effects of the impact speed and the contact angle on the maximum von Mises stress of the head model are revealed from the simulations. The method presented in this paper will help forensic pathologists to examine the head impact injuries and find out the real reasons that lead to those injuries.

A Surrogate Model Based on a Finite Element Model of Abdomen for Real-Time Visualisation of Tissue Stress during Physical Examination Training.

Robotic patients show great potential for helping to improve medical palpation training, as they can provide feedback that cannot be obtained in a real patient. They provide information about internal organ deformation that can significantly enhance palpation training by giving medical trainees visual insight based on the pressure they apply for palpation. This can be achieved by using computational models of abdomen mechanics. However, such models are computationally expensive, and thus unable to provide real-time predictions. In this work, we proposed an innovative surrogate model of abdomen mechanics by using machine learning (ML) and finite element (FE) modelling to virtually render internal tissue deformation in real time. We first developed a new high-fidelity FE model of the abdomen mechanics from computerized tomography (CT) images. We performed palpation simulations to produce a large database of stress distribution on the liver edge, an area of interest in most examinations. We then used artificial neural networks (ANNs) to develop the surrogate model and demonstrated its application in an experimental palpation platform. Our FE simulations took 1.5 h to predict stress distribution for each palpation while this only took a fraction of a second for the surrogate model. Our results show that our artificial neural network (ANN) surrogate has an accuracy of 92.6%. We also showed that the surrogate model is able to use the experimental input of palpation location and force to provide real-time projections onto the robotics platform. This enhanced robotics platform has the potential to be used as a training simulator for trainees to hone their palpation skills.

Application of Fiber Optic Sensing System for Predicting Structural Displacement of a Joined-Wing Aircraft

This work aims to achieve real-time monitoring of strains and structural displacements for the target Joined-Wing aircraft. To this end, a Fiber Optic Sensing System (FOSS) is designed and deployed in the aircraft. The classical modal method, which is used for Strain-to-Displacement Transformation (SDT), is improved to adapt to different boundary conditions by introducing extra constraint equations. The method is first verified by numerical studies on a cantilever beam model and the high-fidelity finite element model of the Joined-Wing aircraft. Ground static tests are then carried out to further demonstrate the capability of the developed FOSS and SDT algorithm in practical application. The results have shown that the improved modal method is able to predict structural deformation under different boundary conditions by using only free–free modes. In addition, the errors between the predicted displacement and the reference in the ground test are within 10%, which proves the FOSS has reasonable accuracy and the potential for future flight tests.

A detailed methodology to model the Non Contact Tonometry: a Fluid Structure Interaction study.

Understanding the corneal mechanical properties has great importance in the study of corneal pathologies and the prediction of refractive surgery outcomes. Non-Contact Tonometry (NCT) is a non-invasive diagnostic tool intended to characterize the corneal tissue response in vivo by applying a defined air-pulse. The biomarkers inferred from this test can only be considered as indicators of the global biomechanical behaviour rather than the intrinsic biomechanical properties of the corneal tissue. A possibility to isolate the mechanical response of the corneal tissue is the use of an inverse finite element method, which is based on accurate and reliable modelling. Since a detailed methodology is still missing in the literature, this paper aims to construct a high-fidelity finite-element model of an idealized 3D eye for in silico NCT. A fluid-structure interaction (FSI) simulation is developed to virtually apply a defined air-pulse to a 3D idealized eye model comprising cornea, limbus, sclera, lens and humors. Then, a sensitivity analysis is performed to examine the influence of the intraocular pressure (IOP) and the structural material parameters on three biomarkers associated with corneal deformation. The analysis reveals the requirements for the in silico study linked to the correct reproduction of three main aspects: the air pressure over the cornea, the biomechanical properties of the tissues, and the IOP. The adoption of an FSI simulation is crucial to capture the correct air pressure profile over the cornea as a consequence of the air-jet. Regarding the parts of the eye, an anisotropic material should be used for the cornea. An important component is the sclera: the stiffer the sclera, the lower the corneal deformation due to the air-puff. Finally, the fluid-like behavior of the humors should be considered in order to account for the correct variation of the IOP during the test which will, otherwise, remain constant. The development of a strong FSI tool amenable to model coupled structures and fluids provides the basis to find the biomechanical properties of the corneal tissue in vivo.

Geometric mistuning identification and finite element model updating methods for bladed disks

Dynamic analysis results of a blisk are sensitive to inevitable geometrical mistuning, and the high-fidelity finite element model (FEM) of real blisk is of paramount importance to accurately predict structural dynamics. However, it is still challenging to accurately identify geometric mistuning and obtain a high-fidelity FEM due to the complexity and stochastic nature of geometric mistuning. In this paper, considering various types of geometrical mistuning, both a novel geometric mistuning identification and automatic finite element model updating (FEMU) method for real blisk using measured point cloud data are presented to reduce the discrepancies between the real blisk and the numerical model. The geometric surface of the real blisk is digitized to the point cloud data by a non-contact optical measurement technique. Three implementation steps of the method are introduced: 1) morphological feature detection from measured point cloud data of blisk; 2) surface nodes space mapping of FEM using isoparametric transformation; and 3) mesh shape optimization for FEMU. Eventually, two experimental cases are investigated: a simplified blisk and an industry blisk. The robustness of pre-processing algorithms for geometrical feature detection with measurement noise is also conducted. Results show that the blades with small mistuning, large deformations, and damages in the tip and leading edges are accurately identified and updated using the proposed method. Compared with measured natural frequencies for updated FEM, the maximum error is less than 3.38‰.

Bayesian model updating with finite element vs surrogate models: Application to a miter gate structural system

Bayesian finite element (FE) model updating using direct model evaluations of large-scale high-fidelity FE models is extremely computationally expensive. Surrogate models can be used as fast emulators of FE models to accelerate the model calibration process. The physics/mechanics-based FE models are still the underpinning behind the surrogate models. This paper evaluates the loss in accuracy and the gain in computational time while performing Bayesian model updating by using surrogate model evaluations compared to using direct FE model evaluations. This evaluation is crucial before entirely relying on surrogate models in model updating for structural health monitoring (SHM) and damage prognosis (DP) purposes. This paper also demonstrates Bayesian updating and surrogate model construction of large-scale high-fidelity FE models of infrastructure systems. In this regard, the miter gate structural system is considered as the testbed structure. Three predominant damage modes (loss of contact between gate and wall, loss of thickness due to corrosion, and loss of tension in the diagonal rods) are considered for model updating purposes. Bayesian model updating is performed using direct FE evaluations by leveraging parallel computing. Two types of surrogates, namely polynomial chaos expansion (PCE) and Gaussian process regression (GPR), are developed for the miter gate. Model updating is performed again using the trained surrogate models, and the updating results are compared with their counterparts obtained using the direct FE evaluation results. The posterior distribution of the FE model parameters obtained using the trained surrogates are sufficiently accurate with respect to the posterior obtained utilizing the direct FE evaluations. In addition, an approximate 4-fold decrease in the computational time was observed when using surrogate model evaluations instead of direct FE evaluations for model updating.

Three-dimensional large deformation reconstruction for slender wing-like structures from strain measurements

Shape-sensing technology has significant applications in real-time monitoring and controlling flexible aerospace structures. Aiming at large deformation of flexible wing-like structures, an algorithm that incorporates geometric nonlinearity is developed for three-dimensional shape reconstruction based on strain measurements. The full-field three-dimensional deformation is described in terms of the deflection of the spatial reference line and the motions of the cross-sectional plane. A certain number of strain measurements distributed on the structural surface are used to estimate the generalized strains and the warping deformation, which can further determine the position of an arbitrary material point in the structure by a series of recursion relations. Instead of the experimental research, the desired strains and the deformation as references are simulated by high-fidelity finite element models. A simple tube model and a more realistic composite wing model are investigated separately to demonstrate the present method in reconstructing deformed shapes under various applied loads. Besides, the modal method was also used to calculate the deformation as a comparison. The result has demonstrated the high accuracy and capability of the present method in three-dimensional shape reconstruction, especially for large deformation problems. The warping effect is demonstrated to have a significant impact on predicting the twist angle. More attention should be paid to accurately describing the warping deformation of complicated wing models, especially when the bending deformation is large.