Parametric Finite Element Model Research Articles

Hybrid composite pedicle screw - finite element modelling with parametric optimization

Abstract As a result of population aging, the number of spine surgeries steadily increases. Metallic pedicle screw systems are commonly used to achieve spinal fusion, and to correct spine misalignments. However, certain disadvantages are linked to these metallic systems: stress shielding can lead to bone degeneration and adjacent disc disease, artefacts prevent precise diagnosis during CT, MRI, or X-ray medical imaging, radiotherapy is complicated due to backscattering, and patient comfort is reduced due to the implant weight. These disadvantages have led to the development of carbon fibre reinforced polyether ether ketone (CF-PEEK) pedicle screws. Carbon fibres improve the structural mechanical properties of the PEEK matrix so that the mechanical requirements of an implant are met. However, with existing CF-PEEK screws the relative motion between screw and bone is increased due to discontinuous fibre reinforcement. Discontinuous fibre reinforced screws complicate precise stiffness control. In this study, a novel screw design consisting of a reinforcing element in the screw centre, and discontinuous short fibre reinforced CF-PEEK in the screw thread and head is presented. By this concept, the stiffness of the pedicle screw can be controlled and tailored by adapting the reinforcing element. This first study concerning hybrid pedicle screws is based upon numerical investigations to optimize hybrid composite screw stability in human bone. Parametric finite element (FE) models of screw and bone were developed. The main purpose of the study was to obtain design recommendations from the optimization, which will be used for future manufacturing of hybrid composite screws. It is further shown that stress shielding could be significantly reduced with this hybrid pedicle screw design as compared to titanium screws, despite the reinforcing element. Additionally, it is confirmed that the worst-case scenario with the highest risk of composite pedicle screw pull-out is shortly after surgery, when osseointegration is still poor. In future studies, mechanical, functional, and visibility tests of the hybrid composite pedicle screw will be conducted.

Bamboo Lightweight Shear Walls: Modeling and Identification of Sheathing-to-Framing Connections for Seismic Response Analysis

The need for enhancing the sustainability of civil constructions has originated an increasing interest in the use of engineered bamboo-based products within the building sector. Nonetheless, while the static response of bamboo-made structures has been largely investigated, experimental and numerical researches concerning the response under dynamic loads are limited. Therefore, the present work deals with the assessment of the seismic behavior of modern bamboo lightweight shear walls, with focus on the energy dissipation ensured by sheathing-to-framing connections. Initially, a short discussion about architectural, sustainability and manufacturing issues related to the use of bamboo in modern civil constructions is provided. Then, the experimental cyclic response of fasteners employed within glued laminated bamboo (glubam) shear walls is simulated by using a suitable phenomenological model whose parameters are identified through a soft computing-based numerical technique. A parametric finite element model developed within OpenSees is thus employed to assess the global seismic response of the wall. A comparison between the response of glubam- and timber-based shear walls is finally provided. This highlights that the main parameter dictating their global behavior is the local non-linear behavior of the single fastener when the cross-section size of the framing elements allows the full exploitation of its capacity and plastic deformation. The numerical simulations well agree with the main evidence carried out from the available experimental data. Particularly, it is found that glubam lightweight shear walls usually exhibit larger capacity and reduced ductility with respect to equivalent timber walls.

Micro-scale numerical study of fiber/matrix debonding in steel fiber composites

Fiber/matrix debonding behavior of steel fiber composites is analyzed using a parametric finite element modeling procedure and compared with conventional composites with carbon and glass fibers. Cohesive surfaces are applied to fiber–matrix interface to simulate the debonding behavior, while the interface strength properties of steel fiber are obtained with and without surface treatment. The effect of various parameters on the debonding behavior is investigated, including stress concentrations, fiber diameter, fiber shape, and fiber volume fraction, using the parametric model. The influence of stress concentrations is determined to be much lower than the debonding strength. Debonding damage is more evident in larger fibers compared to smaller ones. Earlier and sudden interface separation is observed with the polygonal steel fibers compared to the circular ones. Increase in the fiber volume ratio increases the debonding opening distance but does not affect the opening angle significantly. The results can be useful for assessing possibilities to use steel fibers to increase toughness of the composites in comparison with glass and carbon reinforcement.

Tool development for automating the structural integrity assessment of aircrafts’ components

During the aircraft’s maintenance, it is essential that its structural inspection as well as potential found damages to be assessed in an effective manner within a limited time frame. To reduce the required time, for the aforementioned procedure, an innovative tool is developed. For the first time, a structural integrity assessment tool integrates image processing algorithms and FE models. The tool processes data from Non Destructive Testing (NDT), via image processing algorithms, and then provide pieces of information regarding the residual strength of the examined component in an automated way. The data acquired, from the NDT, are interpreted using the threshold method, in order to generate an accurate map of the component with its damages (size and location). This information automatically feeds a parametric Finite Element (FE) model, which forms an FE model of the damaged component ready for analysis. The parametric FE model can construct models for isotropic and laminated monolithic components using the XFEM method and the Cohesive Zone Modelling (CZM) technique respectively. For the case of laminated components, Progressive Damage Modelling (PDM) is also considered. In this study, simple geometries as the upper and lower wing skin, are analysed under static tension or compression. Aim is to examine the effectiveness and feasibility of the developed tool. The main benefits obtained from the application of the tool is that the image processing data are manipulated automatically and fast providing all the information regarding the location and size of damage in the examined component. Moreover, from the obtained numerical results the strength reduction of the component can be predicted well, by just comparing them with the respective numerical results of the reference undamaged component. Overall, the developed tool is very promising, since time saving can be gained.

Construction Technology of Cooperative Blasting in High-Steep Slope and Underground Tunnel in Offshore Oil Depot

Li, L.-B.; Zhang, J.-H., and Wu, L., 2019. Construction technology of cooperative blasting in high-steep slope and underground tunnel in offshore oil depot. In: Li, L.; Wan, X., and Huang, X. (eds.), Recent Developments in Practices and Research on Coastal Regions: Transportation, Environment and Economy. Journal of Coastal Research, Special Issue No. 98, pp. 1–5. Coconut Creek (Florida), ISSN 0749-0208.This paper aims to study the cooperative blasting technology in a high-steep slope and an underground tunnel. For this, an actual engineering project in an offshore oil depot is used as an example, and a comprehensive research method combining theoretical analysis, field test, and numerical simulation is adopted. In addition, based on the actual monitoring blasting vibration data, the dynamic parameters of the tunnel finite element model were determined, and then the existing blasting parameters were predicted accordingly to obtain the peak particle vibration velocity of the slope rock mass structure. The safety distance of the slope surface from the tunnel excavation face was determined by referring to the Safety Regulations for Blasting and the mechanical performance index of the rock mass to ensure that the tunnel excavation will not affect the stability of the slope rock mass. Meanwhile, according to the blasting parameters of the slope excavation, the measured blasting particle vibration parameters of the tunnel were combined with the tunnel dynamic finite element model to determine the safe distance between the slope excavation face and the surrounding rock of the tunnel, thereby ensuring the cooperative blasting in the high-steep slope and underground tunnel and achieving the purpose of shortening the construction period under conditions of stable slope surface and tunnel surrounding rock. This study provides an effective method for theoretical and technical research on the vibration effect of surrounding rock in existing tunnels.

Surrogate Model Based on the POD Combined With the RBF Interpolation of Nonlinear Magnetostatic FE Model

The proper orthogonal decomposition (POD) is an interesting approach to compress into a reduced basis numerous solutions obtained from a parametrized finite-element (FE) model. In order to obtain a fast approximation of an FE solution, the POD can be combined with an interpolation method based on radial basis functions (RBFs) to interpolate the coordinates of the solution into the reduced basis. In this article, this POD-RBF approach is applied to a nonlinear magnetostatic problem and is used with a single-phase transformer and a three-phase inductance.

Application of innovative one-dimensional periodic isolation systems for seismic response reduction of bridges

This article deals with structural vibration attenuation and control using periodic materials for isolation of structures. An innovative approach to achieve wider low-frequency attenuation zones using a combination of different one-dimensional periodic units has been explored to provide close to a vibration-free environment for civil engineering structures subjected to seismic and other excitations. The wave attenuation regions for the base isolation system made of periodic materials have been derived from the theory of phononic materials and investigated using parametric studies and finite element modelling. The concept of combined periodicity is implemented on bridges to achieve wider attenuation zone and higher response reduction. A novel concept of using a hollow-shell periodic isolation system on bridges has been presented to minimize the effect of seismic waves on these structures. A substantial reduction in the seismic response of a bridge model has been observed over the entire frequency domain with the introduction of the proposed isolation systems. The proposed hollow-shell periodic isolation system reduces the seismic response of structures with efficient material utilization as compared to the typical solid-periodic isolation systems. The proposed isolation systems thus open up new directions for research and potential implementation of periodic materials for seismic response reduction and earthquake-resistant design of structures.

Dislocation-based study on the influences of shot peening on fatigue resistance

Shot peening technology is widely used to enhance the fatigue resistance of mechanical parts exposed to the cyclic loadings. The residual stress, grain refinement, work hardening and surface roughness are the four major results of shot peening, which play the important role in enhancing effects of fatigue performances. A framework linking the dislocation-based finite element simulation to the Navarro-Rios model (N-R model) was developed to evaluate the fatigue resistance of shot-peened materials. The parametric three-dimensional finite element models of multiple shot impacts, embedded with the dislocation density-based constitutive model, were developed firstly. The predicted residual stresses, grain refinements, surface topographies and surface roughnesses are all in good agreement with the experimental results. The simulation results of shot peening were then imported into the N-R model to analytically evaluate the stresses for fatigue crack arrest and corresponding values of crack tip opening displacement (CTOD). The computation results show that the S110 shots can effectively improve the stresses for the surface crack arrest, while the more grains within the shot-peened surface and subsurface are endowed with the larger stresses for crack arrest by S230 shots, and the double shot peening (S230 + S110 shots) takes the advantages of the cases of S230 and S110 shots.

A SIMPLIFIED ANALYTICAL PROCEDURE FOR SEISMIC ANALYSIS OF TIMBER LIGHT-FRAME SHEAR WALLS

The seismic performance of timber light-frame shear walls is investigated in this paper with a focus on energy dissipation and ductility ensured by sheathing-to-framing connections. An original parametric finite element model has been developed in order to perform sensitivity analyses. The model considers the design variables affecting the racking load-carrying capacity of the wall. These variables include aspect ratio (height-to-width ratio), fastener spacing, number of vertical studs and framing elements cross-section size. A failure criterion has been defined based on the observation of both the global behaviour of the wall and local behaviour of fasteners in order to identify the ultimate displacement of the wall. The equivalent viscous damping has been numerically assessed by estimating the damping factor which is in use in the capacity spectrum method. Finally, an in-depth analysis of the results obtained from the sensitivity analyses led to the development of a simplified analytical procedure which is able to predict the capacity curve of a timber light-frame shear wall.

A two-stage Bayesian algorithm for finite element model updating by using ambient response data from multiple measurement setups

This study presents a two-stage Bayesian finite element model updating procedure by using acceleration response measurements obtained from multiple setups. In the presented methodology, parametric uncertainties for the modal parameters are estimated by using the Bayesian Fast Fourier Transform Approach (BFFTA). Different from the previous Bayesian methods, a block diagonal covariance matrix is modeled for prior estimation of measured modal parameters. In addition, the modelling error in the eigenvalue equations is considered as soft constraints to be updated. Numerical and experimental studies are presented to validate the proposed method. The effect of soft constraints on the identification results as well as their posterior uncertainties are investigated. According to the results, it is shown that the proposed methodology can identify the most probable finite element model parameters with high level of accuracy. In addition, the posterior uncertainties obtained by the proposed procedure are significantly small when compared to the methods that consider rigid constraints for prediction and/or modelling error.

Dynamic crushing of spacecraft landing gear with crash legs

The paper describes spacecraft landing on a landing gear consisting of four crash legs supported by beam struts. The first part is dedicated to verification of low dimension shell finite element model parameters in the MSC Nastran SOL700 software. An elastoplastic crushing test problem of square aluminum specimens with various thickness is simulated. The comparison of simulation results with experimental data shows that the proposed mathematical model provides the error of less than 10% for the specimens with a width-to-thickness ratio C/s > 30. The second part of the paper discusses landing gear legs crushing during vertical landing on a rigid soil. An analysis of the results showed that it is possible to reduce the crash legs mass by 35 % and the landing gear will provide safe landing conditions with a limited level of peak loads acting on the spacecraft. The characteristic features of the crash leg dynamic deformation process open possibilities for further reduction the landing gear weight and design optimization. The paper opens up a new avenue in design of high energy absorption lightweight gear components for the spacecraft landing process.

Relationship between intervertebral disc and facet joint degeneration: A probabilistic finite element model study

Both intervertebral disc (IVD) and facet joint (FJ) degeneration are frequently associated with chronic low back pain. While genetic factors are considered the most relevant in the onset of degeneration, the mechanics play an important role in its progression. Degenerative changes in one of these two structures are believed to induce degeneration in the other. However, despite decades of research, there is no consensus on the mechanical interplay between the two structures. On the basis of a parametric finite element model of a human L4-L5 spinal motion segment, one thousand individual segments were probabilistically generated covering all grades of degeneration in both structures. The segments were subjected to combined compression and flexion/extension loads. Correlation matrices were created to identify the effect of individual degeneration parameters of each structure on the mechanical stresses in the corresponding counterpart. In the non-degenerated group, a strong positive and a moderate negative correlation was found between the strain of the capsular ligament and the disc height and the nucleus compressibility, respectively. With increasing degeneration, the correlation between IVD morphologies and the FJ loads gradually decreased, whereas the correlation between FJ morphologies and disc load gradually increased.The results suggest that early mechanical changes associated with IVD degeneration have the greatest effect on the FJ loading. With progression of degeneration, this effect is diminished, whereas the appearance of FJ degeneration increasingly influences the disc loading, which might indicate an increasing support of the disc degeneration.

Condition assessment of RC beams using artificial neural networks

In this study, an imaged-based methodology for condition assessment of Reinforced Concrete (RC) road bridge components is presented. The study is divided into experiments on RC rectangular beams and scaled (1:12) T-beams, validation of numerical models for T-beams and training of corresponding artificial neural networks (ANNs). In the experimental work, Digital Image Correlation (DIC) was used as a virtual sensor for data extraction. Rectangular RC beams of size 1800 mm × 150 mm × 200 mm and scaled (1:12) RC T-beams were tested under four-point flexural loading on a 100-ton dynamic testing machine. The experimental stress-strain curves obtained from the compression test on prism specimens at 28 days were used as input data for material model parameters in finite element model (FEM) software SAP2000. To assess the condition of structural components, a local damage index (LDI) was developed. Validation of FEM results with experimental results enables derivation of moment-curvature backbone curve for full-scale bridge girders, which enables further quantification of damage and residual moment capacity of full-scale bridges designed by Ministry of Road Transport and Highways (MoRTH). The correlation between the experiments, simulation and ANN predictions was found to be very satisfactory.

Time-variant reliability analysis of motor-hanger connecting bolts in electric trains

Due to variables in design, manufacturing and working conditions, the working loads of connecting bolts for motor hangers in electric-multiple-unit trains are uncertain. To reduce this uncertainty and improve the reliability of connecting bolts, a novel time-variant reliability analysis method has been developed. First, a parametric finite-element model of a motor hanger was established. The probability distribution of working loads for connecting bolts was then obtained by Monte Carlo simulation. Second, a one-dimensional Brownian differential equation considering the uncertainty of bolt working loads was derived based on Itō’s lemma, and expressions of the mean and variance of bolt stresses under time-variant conditions were given. The time-variant reliability model of the bolts was then constructed based on a time-variant stress–strength interference model and solved by the most-probable-point method. The results showed that the reliability calculated by this method was lower than that of the traditional method and therefore safer. It was concluded that the uncertainty of the working load has a great impact on reliability.

STRENGTH ASSURANCE OF THIN-WALLED STRUCTURES WITH INCREASED TECHNICAL CHARACTERISTICS

The work is devoted to the improvement of methods and models for design ensuring of strength of thin-walled engineering structures under the action ofoperational loadings complex. Justification for rational parameters and design solutions for thin-walled engineering structures is carried out according to thecriteria of mass minimizing, stresses reducing, and service life increasing. Various additional criteria such as cost, manufacturability, economy, energyefficiency, can be taken into account in the formation of the quality function. The dependences approximations of criterion values, which are graduallylocalized, from variable parameters are taken into account. The structure, design and technological solutions of thin-walled engineering structures, structural parameters and operating modes are the generalized parameters. This provides a solution to the problems of a single analysis, multivariate studies, as well as the justification for rational design and technological solutions. The following generalizations are considered: unification, expediency, efficiency, loading identification, forecasting, tune-up in development of known approach. The algorithmization of proposed methods for calculating of the stress-strain state of thin-walled engineering structures has also been carried out based on a combination of the advantages of universal and special systems. A number of applied problems are solved. Parametric finite element models of researched objects are developed based on a set of studies of the stress-strain state of the power elements. The rational design parameters of innovative thin-walled engineering structures are determined. The results of experimental studies of innovative tank cars, platform cars and loading cranes, which are designed and manufactured based on the implementation of recommendations from research, are presented. Comparative experimental and computational studies of the structures stress-strain state were carried out. They are combined with certification tests with stresses evaluation in power elements. During the tests, regularities were established that determine the dependence of the loadings components onthe structure from various factors. Numerical models parameters verification of thin-walled engineering constructions elements was carried out. Designed onthe basis of researches innovative structures have improved technical and economic characteristics compared with similar ones.

Structural optimization of second-stage intertank composite X-shaped truss

An optimization procedure for composite second-stage intertank truss assembly used for connecting the fuel (Liquid Hydrogen, LH2) tank and the oxidizer (Liquid Oxygen, LO2) tank is proposed. The typical working conditions of X-shaped truss are 30 tons tensile load and 5.55 tons compressive load in sequence. Parametric geometrical model and finite element model are created in Catia R21 and Abaqus 6.14, respectively. An optimization procedure integrating geometrical model and finite element model has been constructed in Isight 2018, the algorithm of which is multi-islands genetic algorithm. The result shows that the weight of the optimal structure decreased by 26.50% comparing with the initial design.

Non-deterministic Approach for Reliability Evaluation of Steel Portal Frame

In recent years, more researches on structural reliability theory and methods have been carried out. In this study, a portal steel frame is considered. The reliability analysis for the frame is represented by the probability of failure, P_f, and the reliability index, β, that can be predicted based on the failure of the girders and columns. The probability of failure can be estimated dependent on the probability density function of two random variables, namely Capacity R, and Demand Q. The Monte Carlo simulation approach has been employed to consider the uncertainty the parameters of R, and Q. Matlab functions have been adopted to generate pseudo-random number for considered parameters. Although the Monte Carlo method is active and is widely used in reliability research, it has a disadvantage which represented by the requirement of large sample sizes to estimate the small probabilities of failure. This is leading to computational cost and time. Therefore, an Approximated Monte Carlo simulation method has been adopted for this issue. In this study, four performances have been considered include the serviceability deflection limit state, ultimate limit state for girder, ultimate limit state for the columns, and elastic stability. As the portal frame is a statically indeterminate structure, therefore bending moments, and axial forces cannot be determined based on static alone. A finite element parametric model has been prepared using Abaqus to deal with this aspect. The statistical analysis for the results samples show that all response data have lognormal distribution except of elastic critical buckling load which has a normal distribution.

Model Updating of Frame Structure with Bolted Joints

Experimental analysis is often viewed as an important source of reference compared to finite element due to the accuracy of giving reliable data. Currently, finite element analysis is widely used as an early adoption in development, hence trusting the finite element data is crucial for the user. Finite element analysis often shows discrepancies to the test result. The complexity of the joints (bolted) might cause the discrepancies to occur. This study aims to reduce the discrepancies between the experimental and numerical analysis on a frame structure with bolted joints by model updating. Model updating is a process of making adjustment to certain parameters of finite element model to reduce discrepancy between analytical predictions of finite element analysis (FEA) and experimental results. Modal properties (natural frequencies, mode shapes, and damping ratio) of a frame structure with bolted joints are determined using both experimental modal analysis (EMA) and finite element analysis (FEA). Both data obtained is correlated before optimising the properties with sensitivity analysis. Joint strategy of this paper is focusing on RBE2, CBAR and CELAS element. CELAS was selected to represent the bolted modelling due to its lowest percentage average of 2.03% compares to CBAR 6.55% or RBE2 3.56%. Selected parameters were identified by performing a sensitivity analysis and the discrepancies was reduced by performing model updating procedure.

Porosity-Based Design and Finite-Element Analysis of Self-Lubricating Chromium-Free Passivation Film

The porosity of a self-lubricating chromium-free passivation film is evaluated by means of a novel finite element model and structural parameter, λ (λ represents the porosity of passive film). The applicability of this equivalent model is validated via thin-film thermocouple measurements and laser interferometry. Our results revealed that the roughness of the film can be improved by a lubricating filler. A value of λ = 0.25 yielded the optimal friction and wear characteristics of the self-lubricating chromium-free passivation film. This optimal condition corresponded to temperature values and stress values of 77.99°C (theoretical) and 81.24°C (experimental), and 1.67 × 105 Pa (theoretical) and 1.65 × 105 Pa (experimental), respectively. The close correspondence between the experimental and the theoretical results indicate that the model is reasonable.

A consistent Timoshenko hysteretic beam finite element model

A parametrized Timoshenko hysteretic beam finite element model is developed, using consistent two-node elements, to efficiently simulate the nonlinear behavior of structures. New displacement interpolation functions are derived that satisfy both the exact equilibrium and kinematic conditions. Therefore, nodal strain field continuity is achieved, resulting in a consistent formulation without shear locking effects. Multiaxial interactions are considered through yield/capacity functions and distributed plasticity is accounted for by appropriate hysteretic interpolation functions. The suggested interpolation functions yield constant element matrices that do not require updating throughout the analysis, and the nonlinearities are captured in terms of hysteretic curvatures, axial and shear deformations, which are set to evolve through ordinary differential equations. A computationally efficient solution scheme is also suggested, without requiring any linearization, to straightforwardly solve the resulting system of equations for quasi-static problems. The consistency, efficiency, versatility and validity of the suggested model is explained in detail and demonstrated through several numerical examples and comparisons with experimental data from available tests.