Parametric Finite Element Model Research Articles

ARMORED HULLS OF DOMESTIC ARMORED PERSONNEL CARRIERS: COMPUTER AND MOCK-UP MODELING OF DYNAMIC PROPERTIES

At the stage of design research of armored bodies of lightly armored vehicles it is extremely important to determine the range of their natural frequencies and natural forms of oscillation. For this purpose, the finite element method is usually used. It is necessary to substantiate the parameters of the finite element model, which provide an acceptable level of accuracy of numerical modeling of dynamic properties of this type of structures. For this purpose, data from parallel numerical and experimental studies of the mock-up of the armored hull of the armored personnel carrier are used. The mock-up of the upper projection of the armored hull is made in the appropriate scale. The material is sheet steel. This mock-up is subjected to dynamic excitation on a vibrating table. Resonant excitation frequencies are recorded, as well as the natural vibration forms. Shock-pulse excitation of the armored hull’s mock-up was also performed. The response to this excitation is recorded using accelerometers. Then, the spectrum of natural vibration frequencies is determined from these oscillograms. In parallel, numerical modeling of natural frequencies and natural vibration forms of the armored hull’s mock-up is carried out. After that, the results of numerical and experimental studies are compared. By varying the parameters of the finite element model, a satisfactory correspondence between the results of numerical calculations and experimental measurements is achieved. In particular, the following are determined: the acceptable type of used finite elements; the number of finite elements required to satisfy the accuracy of numerical modeling of the dynamic properties of similar structures; zones of the recommended thickening-rarefaction of a grid of finite elements, etc. According to the research results, the parameters of finite-element models have been established, which can be used to study the dynamic processes and properties of full-scale armored hulls of lightly armored vehicles.
 Keywords: lightly armored vehicle, mock-up, natural frequency, spectrum of natural vibration frequencies

CALCULATION AND EXPERIMENTAL RESEARCH OF TANK HYDRAULIC TRANSMISSION LAYOUT

In order to substantiate the advanced technical solutions of radial hydrovolume transmissions, it is necessary to study the stress-strain state of their most responsible and loaded elements. In particular, it is of interest to determine the rational parameters of cylinder block, which is subject to significant pressure of working fluid. This leads to the formation of a stress-strain state with a high level of stresses and elastic displacements. They can be dangerous in terms of strength, rigidity and performance of the hydraulic transmission in general. To carry out numerical studies of the stress-strain state of cylinder block of hydrovolume transmission at the design stage, finite element models with varied parameters are developed. However, at this stage of research, it is desirable to have a verified numerical model. For this purpose, the paper describes the computational and experimental studies of the layout of the cyclic part of the hydrovolume transmission cylinder block. On the one hand, these studies were performed using the experimental method of holographic interferometry. On the other hand, calculations were performed using the finite element method. In the course of comparison of the received results, the finite element model parameters are determined which provide high accuracy of the stress-strain state calculation of hydrovolume transmissions cylinder block. Keywords: stress-strain state; hydrovolume transmission; finite element method; cylinder block

Process-structure-performance modelling and progressive damage analysis of 3D rotary-four-directional rectangular braided composites under tensile load

The mechanical properties of braided composites are sensitive to the braiding process. However, the relations between process parameters, yarn structures and mechanical properties of three-dimensional (3D) rotary braided composites have not been investigated. In this study, we aim to establish a model capable of characterizing the yarn structures and mechanical properties of 3D rotary braided composites by treating braiding angles as primary variables. Carrier motions on the bedplate were traced by mathematical functions, where corresponding yarn spatial paths within a representative volume element (RVE) were explored. A parametric finite element model (FEM) of 3D rotary-four-directional (3DR4d) braided composites was established considering realistic yarn cross-sections. A progressive damage model was used to predict the mechanical performance of the composites. Experiments were conducted to verify the proposed model. The results show that the ideal yarn topology of the rotary braided composites is similar to the lattice structure. In addition, the longitudinal tensile modulus and strength of 3DR4d braided composites increase with the decreased braiding angles, while increasing with the increased fiber volume fractions. According to damage analysis, longitudinal tension and transverse shear are the dominant failure modes of 3DR4d composites with small and large braiding angles, respectively.

Analysis and enhancement of the new Eurocode 5 formulations for the lateral elastic deformation of LTF and CLT walls

This paper analyses the analytical formulations for the lateral elastic deformation of Light Timber Framed (LTF) and Cross-Laminated Timber (CLT) shear walls according to the new Eurocode 5 (EC5) proposal. Finite Element (FE) models and the Standard predictions are compared by emphasizing the role of each deformation contribution. A total of 1830 comparisons between analytical and numerical estimations are carried out by exploiting the Application Programming Interface of SAP2000 to modify the FE model parameters automatically. The parametric analyses proved that the numerical and analytical predictions are pretty consistent. Furthermore, in both LTF and CLT shear walls, the estimates for in-plane shear and rigid body sliding are in excellent agreement. Conversely, the analytical formulas for kinematic rocking are generally conservative for LTF and monolithic CLT shear walls, with an approximate 18%–19% discrepancy. The analytical expressions of the upcoming EC5 perfectly match the numerical model for segmented CLT shear walls under lateral forces and no vertical load. However, the presence of the vertical load determines a significant bias. Additionally, the predictions for bending deformations are not in good agreement. Therefore, the paper discusses possible enhancements for the equations proposed in the next generation of Eurocodes for the rocking deformation of segmented CLT walls to better conform with FE predictions.

Origins of improved elongation to fracture in cyclic bending under tension of AA6022-T4 sheets as revealed using crystal plasticity modeling

Plastic instabilities can be suppressed by imposing cyclic bending during tension to increase elongation-to-fracture (ETF) of metallic sheets. This work is a combined experimental and modeling study into the origins of the improved ETF in cyclic bending during tension facilitated by a continuous-bending-under-tension (CBT) test. Load-displacement is measured during the CBT test under an optimized combination of band depth and pull speed process parameters for aluminum alloy (AA) 6022-T4. Monotonic and load reversal response of the alloy is also characterized under strain histories that resemble the history in CBT. Electron-backscattered diffraction and neutron diffraction are employed to characterize the initial microstructure and texture evolution of the alloy after CBT and simple tension (ST). Monotonic, load reversal, and texture data are used to adjust and verify the parameters of an elasto-plastic self-consistent crystal plasticity-based finite element model for simulating CBT. Additionally, a flow stress curve based on a bulge test is used to calibrate the model to capture the large strain hardening behavior of the alloy. The model is then used to simulate the CBT test while predicting the load-displacement and texture evolution data. The model successfully reproduced the succession of spikes and plateaus during CBT validating the prediction of the extrapolated hardening. After the validation, the development of stress and strain is probed through the sheet thickness to determine the underlying profiles as well as along the sheet to elucidate the location and onset of failure axially. The model reveals the development of more strain and dislocation density at the surface then at the center of the sheet and correctly predicts the strain localizations. Comparisons of texture evolution and mechanical fields developed in ST and CBT reveal very similar mechanical states in the sheet. These results in combination with experimental results suggest that the origins of improved ETF during CBT pertain primarily to the incremental deformation structural effects and secondary to the microstructural evolution effects.

Yeditepe spine mesh: Finite element modeling and validation of a parametric CAD model of lumbar spine

Finite element analysis is a powerful tool that is often used to study the biomechanical response of the spine. The primary objective of this study was to illustrate the mechanical behavior of a previously proposed parametric CAD spine model in comparison with a segmented FSU model and the literature. In this study, two finite element models of the L4-L5 spinal level were developed from the same patient's CT scan data. The first was developed using well-known segmentation methods, whereas the second was developed from the new by using a novel parametric CAD model. Both models were subjected to the same loading and boundary conditions to perform flexion, extension, lateral bending and axial rotation motions. The segmented finite element model was observed to be in good agreement with the literature. The parametric finite element model results were also observed to be in good agreement with the segmented finite element model and with the literature except under extension.

Characterizing vibrational behavior of a large airship based on scaled model test and analysis

PurposeThis study aims to assess the vibrational behavior of a large transport airship based on finite element (FE) simulation and modal testing of its scaled model.Design/methodology/approachA full-size parametric FE model of the airframe was established according to the structural layout of the composite beam-cable airframe of the airship, and vibrational analysis of the airframe was conducted. The influence of cable pre-tension load on the inherent properties of the airframe was investigated. Based on the simplification of the full-size FE model, scaled numerical and test models of the airframe, with a geometric scale factor of 1:50, were established and built.FindingsThe simulation and test results of the scaled models indicated that the mode shapes of the full-size and scaled models were similar. The natural frequencies of both the full-size and scaled models complied with the theoretical similarity relation of the frequency response.Originality/valueThis study demonstrated that the vibrational test results of the scaled model with very large scaling can be used to characterize the modal properties of the beam-cable airframe of a large transport airship.

Nonlinear FE-analysis and testing of light-frame timber shear walls subjected to cyclic loading

Light-frame timber shear walls have been used as load-bearing elements in buildings for several decades. To predict the performance of such structural elements under loading, numerous analytical and numerical models have been developed. However, little focus has been on the prediction of the plastic damage behaviour and unloading of the walls. In this paper, a parametric Finite Element (FE) model is further developed by introducing elasto-plastic connectors to simulate the mechanical behaviour of the sheathing-to-framing connections. To verify the accuracy of the elasto-plastic model, full-size walls were tested and compared with results from simulations. The numerical results, from a few loading cycles, indicate that the model achieves reasonable accuracy in predicting both the nonlinear elastic and plastic deformations. Both experimental and simulation results demonstrate the importance of opening locations relating to the external racking force. The results also indicate that for a double-layer wall, its racking strength can be achieved by summation of the separate contribution from each layer. Furthermore, the internal layer was observed to contribute significantly less than the external layer since its nail pattern was based on the sheathing pattern of the external layer.

Finite Element Model Updating of RC Bridge Structure with Static Load Testing: A Case Study of Vietnamese ThiThac Bridge in Coastal and Marine Environment.

Diagnostic load testing refers to the use of the measured historical responses of the structure in the field data to better understand its dynamic and static structural behaviours. It is important and necessary to predict the health state, load capacity, and aging of the structure by updating the finite element (FE) model, which can give useful information to aid the design of retrofits and the maintenance of the existing bridge in the future. The paper presents an update of the full-scale FE model for the reinforced concrete (RC) bridge structure over the seawater river based on the experimental strains under the static load testing in which the representative FE model of the actual structure is determined from the optimisation procedures. The optimisation variables are applied, including the cross-sectional properties and concrete material calibrated through the genetic algorithm (GA) optimisation in the MATLAB software, which interfaces with the FE modelling in the scripting of the SOFISTIK TEDDY software automatically. The bending moments at the mid-span of the RC girders are determined in the FE modelling to compute stresses, which are compared with the measured stresses through optimisation scenarios with a percentage error of the objective function less than 10%. The measured data of concrete strains are recorded from reusable strain transducers installed on the mid-span girders for every bridge span, which are used to calibrate the bridge model in static load testing. The novelty of the solution is to implement innovative techniques using field data as an improved approach for calibrating automatically the analytical FE model parameters of all RC spans of the bridge until its static behaviours are very similar to those of the actual bridge. The final updated FE modelling is used to apply truck load configurations according to bridge design standards such as the AASHTO specifications, which can predict the load limits of the existing bridge structure more accurately and reliably. These proposed approaches can be applied to large bridges as well as complex structures with supporting FE analysis software and data processing software.

A low dimensional surrogate model for a fast estimation of strain in the thrombus during a thrombectomy procedure

BackgroundIntra-arterial thrombectomy is the main treatment for acute ischemic stroke due to large vessel occlusions and can consist in mechanically removing the thrombus with a stent-retriever. A cause of failure of the procedure is the fragmentation of the thrombus and formation of micro-emboli, difficult to remove. This work proposes a methodology for the creation of a low-dimensional surrogate model of the mechanical thrombectomy procedure, trained on realizations from high-fidelity simulations, able to estimate the evolution of the maximum first principal strain in the thrombus. MethodA parametric finite-element model was created, composed of a tapered vessel, a thrombus, a stent-retriever and a catheter. A design of experiments was conducted to sample 100 combinations of the model parameters and the corresponding thrombectomy simulations were run and post-processed to extract the maximum first principal strain in the thrombus during the procedure. Then, a surrogate model was built with a combination of principal component analysis and Kriging. ResultsThe surrogate model was chosen after a sensitivity analysis on the number of principal components and was tested with 10 additional cases. The model provided predictions of the strain curves with correlation above 0.9 and a maximum error of 28%, with an error below 20% in 60% of the test cases. ConclusionsThe surrogate model provides nearly instantaneous estimates and constitutes a valuable tool for evaluating the risk of thrombus rupture during pre-operative planning for the treatment of acute ischemic stroke.

Strain based structural health monitoring of stiffened composite plate

Stiffened composite structures are very appealing in aeronautical applications due to their unique stiffness to mass ratio. However, they are prone to various and complex damage scenario such as stiffener debonding, impact damages etc. The composites materials suffer from hidden damages that lead to catastrophic failure if not detected at an early stage. This new breed of structures (advanced composites structures), therefore pose more challenges in predicting their remaining life or state of structural health. Consequently, autonomous monitoring of such structure is still a real issue. The current study develops a structural health monitoring approach that uses sensors with low-cost strain gauges to identify damage. A parametric finite element model is used to generate multiple damage scenarios for the investigation. To determine the exact placement of strain gauges, a numerical analysis is performed and longitudinal strain values are obtained in both healthy and damaged states. The experimental testing of the stiffened composite plate is carried out on healthy and damaged condition. Results from numerical simulations have been compared with experimental result. The result of this work indicates that the strain gauge can be used as effective tool to detect the damage from their early development, location and severity of damage that makes it particularly useful for structural health monitoring.

Numerical investigation on tensile behavior of three-dimensional six-directional braided composites

Based on the mesostructure, a parametric finite element (FE) model of the three-dimensional six-directional (3D6d) braided composites was developed considering the real cross-sectional shape of the yarn and its contact relationship. The 3D Hashin criterion and maximum stress criterion were used for failure determination and periodic displacement boundary conditions were imposed on the model to numerically simulate the initiation, propagation and final failure of yarns and matrix damage. The FE model accurately predicts the longitudinal tensile strength of 3D6d braided composites and simulates the progressive damage process associated with the stress-strain behavior. The longitudinal mechanical properties of the 3D6d braided composites decrease with increasing braiding angle, while increasing the fiber volume fraction leads to enhancement of these properties. Furthermore, the change rate of longitudinal mechanical properties with braiding angle is relatively stable, and the influence of fiber volume fraction on longitudinal properties decreases with the increase of braiding angle. For the damage mode, the increase of braiding angle makes the damage of braiding and sixth-directional yarns gradually change from single direction to multiple directions, and the decrease of fiber volume fraction makes the damage of braiding and fifth-directional yarns at the peak stress more serious.

Application of a weighted graph representation method to the crashworthiness optimization of subway collision frame structures

The collision frame structure is the most important subway structure for energy absorption and impact load transfer during foreign object collision. To improve the crashworthiness of the collision frame structure, a parameter optimization method based on a weighted graph representation method was proposed. Based on weighted graph theory, an equivalent mathematical model of the collision frame structure was established. Combined with the Belytschko beam element method, which is a large deformation calculation technique, a parametric finite element model (FEM) considering plastic mechanical properties was constructed, which was validated by a detailed finite element model and a quasi-static crush test. Based on the practical requirements, the crush displacement, the intrusion space and the mean crush force (MCF) were determined as constraints. The structural total mass was considered as the objective. The optimized structural parameters and key performance indicators were obtained and compared by the genetic algorithm (GA), Colliding bodies optimization (CBO), Enhanced colliding bodies optimization (ECBO). The results showed that the GA algorithm had the best optimization objective. The comparison results showed that the optimized collision frame structure could meet the crashworthiness requirements, while the structural mass was reduced from the initial 168.92 kg to 97.33 kg, thus giving a reduction rate of 42.38 %.

Impact of technological and operational deviations of the thread flank angle on the fatigue life of the tool joint

The total effect of technological and operational factors can lead to various types of deviations of the flank angle of the tool joint thread profile, which are uneven along the axis. It is shown that uneven deviations of the flank angle appear when tapered threading with a lathe tool with a non-zero rake angle. To analyse the effect of these deviations on the fatigue strength of the joint, a parametric axisymmetric finite element model of the ZN-80 tool joint was developed in Abaqus/CAE. In the fe-safe program, dependences of the fatigue life in the thread roots on the deviations of the flank angle of the pin thread were obtained. The box thread has not been changed. To increase the fatigue strength of the pin, in most of the cases considered, negative deviations of the flank angle of the short flank of the pin thread should be avoided, and preference should be given to positive ones. Negative relative deviations of both flanks usually worsen the fatigue strength of the pin due to the "wedge" effect. Types of deviations have been found that significantly increase fatigue strength and have an “anti-wedge” effect or equalize the load in the thread. They need detailed studies and can be the basis for optimizing the values of flank angle deviations on each turn.

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.

Comprehensive treatment of uncertainties in risk‐targeted performance‐based seismic design and assessment of bridges

AbstractThis study complements and extends a recent work on the development of a rigorous framework for risk‐targeted performance‐based seismic design/assessment of ordinary standard bridges (OSBs) in California. Rooted in the formulation of this framework is an updated fully probabilistic performance‐based earthquake engineering (PBEE) assessment methodology wherein metrics of structural performance are formulated in terms of the mean return periods of exceedances for several strain‐based limit‐states (LSs). The originally proposed framework explicitly considering: (1) the uncertainty in the seismic input, and (2) the uncertainty in the capacity of the various LSs, is extended in this study to account for the following additional pertinent sources of uncertainty: (i) the aleatory uncertainty associated with finite element (FE) model parameters, and (ii) the epistemic parameter estimation uncertainty associated with using finite datasets to estimate the parameters of the probability distributions characterizing the FE model parameters and LS fragilities. These additional sources of uncertainty are commonly omitted or neglected in PBEE often by invoking that the earthquake ground motion uncertainty is the predominant source of uncertainty. However, their inclusion and consistent propagation in seismic performance‐based assessment of OSBs is imperative to obtain a more complete picture of seismic performance, thereby leading to a more comprehensive, transparent, and reliable design of these simple, yet essential bridges which represent an integral part of lifeline infrastructure systems especially in earthquake‐prone regions. The analytical and computational framework previously assembled is extended via modular incorporation of these additional sources of uncertainty. Four OSB testbeds and their risk‐targeted re‐designed versions are analyzed with and without these additional sources of uncertainty to evaluate their significance.

Multi-directional compression behaviors and failure mechanisms of 3D orthogonal woven composites: Parametric modeling and strength prediction

Three-dimensional orthogonal woven composites (3DOWCs) are extensively adopted in various civil and military fields. Parametric finite element models of 3DOWCs were established based on the mesoscale method to predict the compression strength and progressive damage process. The effects of structural parameters and loading directions on the failure mechanisms were investigated. The predicted results agreed well with the experimental data. The results revealed that yarn densities and loading directions significantly influenced the compression strength. It increased as yarn densities increased, and the weft compression strength was almost the largest in all directions and reached the maximum value of 634.8 MPa. In this case, it was 16.9% and 166.9% higher than that of the warp and Z-directions. Damage evolutions demonstrated that the damage of yarns and matrix occurred separately at the intersection of yarns and yarns, and yarns and matrix. The damage patterns of small warp and large weft yarn densities composites included yarn buckling, the interfacial debonding between yarns and matrix, and matrix cracking. Yarn kinking and fracture were the two main damage patterns of large warp and small weft yarn densities composites, while composites with large warp and large weft yarn densities were more prone to matrix cracking.

The effect of fiber preform configuration on in-plane compressive behavior of high porosity needled carbon/carbon composites in elevated temperature environment

The in-plane compressive behavior of the high porosity needled carbon/carbon (C/C) composites can be used to examine the interlaminar state and the material integrity. The room and elevated temperature in-plane compressive experiments of the high porosity needled C/C composites were conducted to study the effect of local fiber configuration state on the failure modes and damage mechanisms combining with the scanning electron microscope (SEM) and micro-computed tomography (Micro-CT) observation. The porosity was also determined by processing Micro-CT images, which was used to calculate the mechanical properties of constituents. The refined finite element (FE) model considering explicitly the distribution of needling punched regions of the real compressive specimen was established to reproduce the damage and failure process component materials in the high porosity needled C/C composites during the experiment at elevated temperature. The effect of needling parameters, such as the needling depth and the thickness ratio between fiber net layer and non-woven cloth layer, on the compressive mechanical properties of the high porosity needled C/C composites was studied using the parametric FE model. The variation curves of the compressive strength with these needling parameters were obtained, which could guide to choose the proper high porosity needled C/C composites for manufacturing the lightweight thermal protection tile after introducing the oxidation resistant ceramic matrix.

Research on Cyclist Injury Based on Simulation Model of Real Electric Vehicle and Two Wheeled Vehicle Collision Accident

There are more and more traffic accidents between cars and electric two wheeled vehicles. As a vulnerable participant in traffic, it is of great significance to study the head biomechanical injury of electric two wheeled vehicle cyclists. In order to study the head injury of cyclists, by optimizing the tissue material properties and material parameters of the head finite element model, a refined head finite element model is established and verified by Nahum cadaver experiment; Based on the real traffic accident of vehicle electric two wheeled vehicle collision, a multi rigid body model of vehicle electric two wheeled vehicle is established for vehicles, electric two wheeled vehicles and cyclists, and the reliability of the collision model is verified; The head finite element model is used to analyze the changes of equivalent stress. The results show that the equivalent stress of brain tissue is gradually transmitted from both sides of brain tissue to the cerebellar region at the back of brain, and finally concentrated in cerebellum.

Numerical Model, Parametric Analysis, and Optimization of FCC's 16 T Main Dipole Baseline Design

CERN is currently investigating the feasibility of a future collider - the Future Circular Collider (FCC) - as a potential successor of the Large Hadron Collider (LHC), providing scientists with a powerful discovery tool in the field of high energy physics. INFN developed the main 16 T Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn dipole of the FCC based on the cos-theta coil design. The baseline design of the superconducting magnet adopts the bladder-and-key concept and includes 4-layered asymmetric coils, an aluminum shell and a welded stainless-steel skin. The scope of this collaborative work between INFN, CERN, UPATRAS and FEAC, is to validate and further study the baseline design. This paper describes the design concept and the fully parametric multi-physics finite and boundary element (FEM and BEM) model. The baseline assembly parameters are presented while the study of geometrical, material and assembly parameters, unveils the optimized structure.