High-fidelity Finite Element Model Research Articles

High-fidelity computational modeling of scratch damage in automotive coatings with machine learning-driven identification of fracture parameters

As one of the key components of a vehicle, automotive coating systems are typical micro-size multilayer composites, which normally suffer from intricate scratch damage. Currently, it is a challenging task to reproduce the complex physical phenomena of automotive coatings with micron thickness using numerical simulations. The purpose of this work is to develop a computational framework for an accurate evaluation of such scratch damage. To achieve this end, a high-fidelity finite element (FE) model is proposed, where a rate-dependent cohesive zone model is developed to account for coating crack behaviors. A reverse identification approach based on the machine learning (ML) method is suggested to determine the rate-dependent cohesive parameters that are difficult to be measured via direct experiments. In the course of recognition, this work develops a two-step regional data augmentation strategy based on the existing single-shot recognition method. The developed strategy is capable of reducing the number of training data samples, while improving identification accuracy and robustness. With the identified cohesive parameters, the proposed finite element model is applied to simulate speed-dependent coating scratch behaviors. The good agreement between numerical and experimental results demonstrates the capacity of our developed computational framework for coating scratch problems.

Bolted steel to laminated timber and glubam connections: Axial behavior and finite-element modeling

This study aims to characterize the axial monotonic and cyclic tensile behavior of bolted steel connections to laminated timber and bamboo, using slotted-in steel plates, and to provide a high-fidelity simulation using finite-element modeling. Forty-eight experimental tests were conducted, including eight different configurations, varying in material (Laminated Veneer Lumber (LVL) and Glued Laminated Bamboo (glubam)), number of bolts, and diameter of bolts, under tension, both monotonic and cyclic (three repetitions). The force and displacement were recorded, and used to define the initial stiffness, yielding strength, ultimate strength, ductility, viscous damping, and energy dissipation. The failure modes of the connections were monitored using Digital Image Correlation (DIC) techniques. A novel high-fidelity finite-element model integrating Hill’s yielding and element removal criteria was proposed to predict the mechanical performance and fracture behavior of the examined connections. The numerical simulation was validated by comparing the experimental load–displacement curves and the strain field measurements obtained with DIC. Finally, theoretical formulas for predicting the stiffness of bolted connections were proposed based on the FEM simulations.

Vibration of prestressed beams: Experimental and finite-element analysis of post–tensioned thin-walled box-girders

In published works, very different explanations are given for the effect of prestressing on the beam dynamics, especially on the relationship between the vibrational effects caused by an external compressive force and those due to a prestressing force. To solve this conflict, free transverse vibrations of a post–tensioned thin-walled steel box-girder were investigated. Its fundamental frequencies were then measured for different values of prestressing. Subsequently, the experimental data were compared with a formula considering shear effects. The experimental data were also compared with two high-fidelity finite-element models assuming geometric nonlinearities. According to the obtained findings, and comparisons with tests reported in literature, the beam dynamics strongly depends on the contact of the cables with the surrounding section. If the tendons are not in contact with the surrounding cross-section, the beam dynamics due to an external compressive force is practically coincident to that caused by a prestressing force for low values of prestressing. In this case, the dynamics of prestressed beams are initially ruled by the compression-softening effect. For high values of prestressing, the beam would behave as a shallow arc with horizontal elastic supports. In this case, an increase of fundamental frequency is observed, but the yield stress would be exceeded. Conversely, in thin-walled steel girder-bridges with tendons in contact with the cross-section or draped with a deviator, the fundamental frequency is practically unaffected by prestressing. Thus, the fundamental frequency cannot be used as indicator for identifying long-term phenomena of prestressing losses, such as anchorage slips, tendon friction and relaxation.

Interdisciplinary design optimization of compressor blades combining low- and high-fidelity models

Multidisciplinary design optimization has great potential to support the turbomachinery development process by improving designs at reduced time and cost. As part of the industrial compressor design process, we seek for a rotor blade geometry that minimizes stresses without impairing the aerodynamic performance. However, the presence of structural mechanics, aerodynamics, and their interdisciplinary coupling poses challenges concerning computational effort and organizational integration. In order to reduce both computation times and the required exchange between disciplinary design teams, we propose an inter- instead of multidisciplinary design optimization approach tailored to the studied optimization problem. This involves a distinction between main and side discipline. The main discipline, structural mechanics, is computed by accurate high-fidelity finite element models. The side discipline, aerodynamics, is represented by efficient low-fidelity models, using Kriging and proper-orthogonal decomposition to approximate constraints and the gas load field as coupling variable. The proposed approach is shown to yield a valid blade design with reasonable computational effort for training the aerodynamic low-fidelity models and significantly reduced optimization times compared to a high-fidelity multidisciplinary design optimization. Especially for expensive side disciplines like aerodynamics, the multi-fidelity interdisciplinary design optimization has the potential to consider the effects of all involved disciplines at little additional cost and organizational complexity, while keeping the focus on the main discipline.

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.