Detailed FE Model Research Articles

Can sulci protect the brain from traumatic injury?

The influence of sulci in dynamic finite element simulations of the human head has been investigated. First, a detailed 3D FE model was constructed based on an MRI scan of a human head. A second model with a smoothed brain surface was created based on the same MRI scan as the first FE model. These models were validated against experimental data to confirm their human-like dynamic responses during impact. The validated FE models were subjected to several acceleration impulses and the maximum principle strain and strain rate in the brain were analyzed. The results suggested that the inclusion of sulci should be considered for future FE head models as it alters the strain and strain distribution in an FE model.

Simplified modelling of joints and beam-like structures for BIW optimization in a concept phase of the vehicle design process

The paper proposes an engineering approach for the replacement of beam-like structures and joints in a vehicle model. The final goal is to provide the designer with an effective methodology for creating a concept model of such automotive components, so that an NVH optimization of the body in white (BIW) can be performed at the earliest phases of the vehicle design process. The proposed replacement methodology is based on the reduced beam and joint modelling approach, which involves a geometric analysis of beam-member cross-sections and a static analysis of joints. The first analysis aims at identifying the beam center nodes and computing the equivalent beam properties. The second analysis produces a simplified model of a joint that connects three or more beam-members through a static reduction of the detailed joint FE model. In order to validate the proposed approach, an industrial case-study is presented, where beams and joints of the upper region of a vehicle's BIW are replaced by simplified models. Two static load-cases are defined to compare the original and the simplified model by evaluating the stiffness of the full vehicle under torsion and bending in accordance with the standards used by automotive original equipment manufacturer (OEM) companies. A dynamic comparison between the two models, based on global frequencies and modal shapes of the full vehicle, is presented as well.

A reduced beam and joint concept modeling approach to optimize global vehicle body dynamics

Ideally, NVH simulations become available already in the concept phase of vehicle development. The initial computer-aided design (CAD) can then be improved (by already including countermeasures), and the feasibility to balance NVH with other performance attributes is increased. In this early design stage, when exact geometrical information is not or scarcely available, conventional virtual prototyping techniques based on detailed CAD and FE models are not directly applicable. A state-of-the-art overview of concept NVH simulation methods in vehicle industry is given. This paper then presents a “Reduced Beam and Joint Modeling” approach to analyze and optimize the global bending and torsion modes of a vehicle body. Concept modifications in the body beam-like sections and in the joints are analyzed using the body reduced modal model. This small-sized model can be used to quickly and accurately optimize the low-frequency vehicle performance. The modifications are considered with respect to the existing (predecessor) model. Equivalent beam properties are estimated from the body FE model; modifications in the beam-like sections are then implemented with beam elements from a standard FE library. The joint modifications are considered through static superelements: stiffness formulations between the end points of the joint connected to the beam layout. The validity of the approach is first demonstrated on simple example models. An industrial vehicle BIW application case is subsequently presented. A beam and joint layout is created, and used for a fast sensitivity analysis to identify suitable modifications to improve the global modes. Next, two application cases are presented. First, a fast optimization analysis is performed to optimize the global body modes. Subsequently, suitable physical modifications are identified and applied to the full FE model; it is shown that the effect of these physical modifications is accurately predicted with the fast sensitivity analysis.

Evaluation of load transfer characteristics of a dynamic stabilization device on disc loading under compression

In the current study, finite element analyses were conducted to examine the biomechanical capability of a newly design dynamic stabilization system, FlexPLUS, to restore the load transmission of degenerated intervertebral L4-L5 lumbar motion segment spine under compression. Detailed three-dimensional FE models of L4-L5 motion segment and the FlexPLUS were developed. Compressive loading up to 1000 N was applied to the intact L4-L5 model, the L4-L5 models with slight and moderate degenerated disc, and the implanted L4-L5 model. Further more, the load transmission characteristics of Dynesys and a rigid rod was also simulated for comparison. The resultant load–displacement curves and the load transferred through annulus under various conditions were compared. The predicted axial displacement of L4 top surface against applied compressive force of the intact L4-L5 model agreed well with experimental data. The predicted results showed that degenerated disc has significant effect on the lumbar segment load bearing capacity. Not only the stiffness of the segment was greatly increased, the uniform nature of the disc stress distribution was also altered. The FlexPLUS can effectively reduce the disc loading of degenerated model. Although the non-uniform load distribution pattern through annulus was not improved, the overall stress magnitude was greatly reduced to the level of intact model for grade II degeneration.

Experimental and numerical damage evaluation of a lift safety gear

The aim of this paper is the experimental and numerical evaluation of the accumulated damage in a progressive lift safety gear, during its life cycle. In particular this evaluation has been carried out by means of experimental tests that reproduce exactly the emergency condition which activates the safety gear and with a detailed FE model of the component. Another purpose of these tests is to verify that the average deceleration (retardation) during gripping action lies between 0.2g and 1g (permissible limits) according to European Standard UNI EN 81-1 (1999). In particular the experimental tests, consisting in free falls of a test lift car with full load, and the following gripping phase caused by the safety gear activation, have been carried out evaluating the strains in the component and the car frame acceleration. The double approach, by test and with a numerical model, allows a better knowledge of this critical phenomenon.

Development of a finite element model of female foot for high-heeled shoe design

Background Wearing high-heeled shoes may produce deleterious effects on the musculoskeletal system while elevation of the shoe heel with arch insole insert is used as a treatment strategy for plantar fasciitis. Due to limitations of the experimental approaches, direct measurements of internal stress/strain of the foot are impossible or invasive. This study aims at developing a finite element model for evaluating the biomechanical effects of high-heeled support on the ankle-foot complex. Methods A 3D anatomically detailed FE model of the female foot and ankle together with a high-heeled support was developed and used to investigate the plantar contact pressure and internal loading responses of the bony and soft tissue structures of the foot with varying heel heights during simulated balanced standing. Findings In the balanced standing position with high-heeled support, a pronounced increase in von Mises stress at the first metatarsophalangeal (MTP) joint was predicted. The strain on plantar fascia decreased compared to the flat horizontal support and valgus deformity of the hallux was not significant. Interpretation The increased stress in forefoot especially at the first MTP segment during prolonged high-heeled standing may contribute to progressive hallux valgus (HV) deformity. However, the reduced tensile strain in the plantar fascia with heel elevation may help relieve plantar fasciitis related pain and inflammation.

Seismic fragility relationships of reinforced concrete high‐rise buildings

AbstractA complete methodology is presented for the seismic fragility assessment of reinforced concrete high‐rise buildings. The key steps of the methodology are illustrated through an example of the fragility assessment of an existing 54‐story building with a dual core wall system. The set of rigorously derived probabilistic fragilities are the first published for high‐rise reinforced concrete buildings. The inelastic nonlinear dynamic analyses for the fragility assessments are made using a simplified lumped‐parameter model that was derived from highly detailed FE models using genetic algorithms. New definitions for performance limit states were based on the results of detailed pushover analyses of a distributed inelastic nonlinear finite element model that includes shear–flexure–axial interaction effects. To develop the fragility relationships, 1800 dynamic response history analyses were conducted. This study considered uncertainty in structural material values as well as in seismic demand. Thirty strong motion records were selected for use in the analyses that would produce an appropriate range in structural response characteristics due to variation in magnitude, distance and site condition. The overall approach is generic and can be applied to developing computationally efficient and probabilistically‐based seismic fragility relationships for reinforced concrete high‐rise buildings of different configurations. Copyright © 2007 John Wiley & Sons, Ltd.

DEVELOPMENT OF AN ORIGINAL PROCESS FOR THE PRELIMINARY DESIGN OF AN UAV SYSTEM BASED ON MULTIPLE MODULES

The research work presented here is apart of an on-going program in the development of Unmanned Aerial Vehicle system, at the conceptual and preliminary design levels, in Aerospace Research Center (ARC-Egypt). The main objective is the implementation of the developed design process in MDO software for UAV design development. It is applied to the previously proven SAHM UAV platform. A model with a specified design variables has been chosen, while the design constraints are selected to cover the entire UAV modules; geometry, aerodynamic, performance, stability, weight and structure. The design objective is to minimize the air vehicle ground launch weight. The optimization method is the steepest descent with an exterior penalty operator. Results obtained show that all design disciplines are quite matched within the requirements. Generated version of SAHM UAV shows a significant reduction of about 11% in the ground launch weight relative to the baseline design. Modal testing was performed on both the wing and the whole airframe of the SAHM UAV. Natural frequencies, and mode shapes were identified. At the same a detailed FE model of the wing was developed on MSC/NASTRAN. One-way ANOVA has been implemented for the compatibility of the numerical and experimental results, which correlates well.

Crack propagation on helicopter panel: Experimental test and analysis

Aerospace structures need excellent structural efficiency and damage tolerant behaviour to avoid critical failure in presence of small defects and repeated small loads typical of contingent loads. With the aim of improving the performance of the structures, new materials have been developed. Such materials, as the Al–lithium alloy, are designed with the purpose of optimizing stress/strain vs. weight. Considering the distinct advantage, but also the disadvantage, of this innovative material, it is important to verify the damage tolerant behaviour of the component and this is the aim of the present work. With this aim, some tests have been performed on full scale panel specimens representative of a rear helicopter frame. Dedicated test equipment has been designed and built in order to apply the effective service loads on artificial damaged panels. During the tests, the propagation of the crack, started from an artificial damage, has been monitored until the progressive failure of the panel reaches one or more stringers. Moreover, each specimen has been instrumented with several strain gauges to obtain a strain map during the crack propagation. The crack parameters and the strains recorded during the propagation have been compared with the results from a detailed FE model and an analytical model, with a good correlation. In addition, a detailed FE submodel of the bolted joint (stringer and skin in the crack propagation path zone) has been constructed to obtain the crack parameter of a particular panel specimen whose test has also been carried out in the stringer bolted joint.

Finite element model of the human neck during omni-directional impacts. Part II: relation between cervical curvature and risk of injury

A detailed 3D FE model of the human neck was used to assess a possible relationship between risk of injury and cervical spine curvature for various impacts. A FE model was previously developed, representing the head and neck of a 50th percentile human with a normal lordotic curvature. The model behaviour was omni-directionally validated for various impacts using published results. For the present study, the model was deformed in order to obtain a straight and a kyphotic curvature, and for each geometry, rear-end, frontal, lateral and oblique impact were simulated. Although results showed similar kinematic patterns, significant differences were found in the distribution and peak values of ligament elongations, forces and moments along the cervical spine for the three configurations. It was concluded that the variability observed on the curvature of the human cervical spine may have a significant influence both on the behaviour and on the risk of injury of the neck during impact.

Structural Stress Analysis of an Engine Cylinder Head

This paper deals with a structural stress analysis of the cylinder head assembly of the C/28 series engine. A detailed FE model was created for this purpose. The FE model consists of the main parts of the cylinder head assembly, and it includes a description of the thermal and mechanical loads and the contact interaction between their parts. The model considers the temperature dependency of the heat transfer coefficient on wall temperature in cooling passages. The paper presents a comparison of computed and measured temperature. The analysis was carried out using the FE program ABAQUS.

The effect of fire loading on a steel frame and connection

The objective of this paper is to investigate the behavior of steel shear connections subjected to severe fire loading conditions. A time-history transient FE analysis is used to model the fire loading. A detailed 3D FE model of an extended shear tab steel connection used in a beam-column joint is developed. The shear tab plate is welded to the web of the column and it is connected to the web of the beam by tightened bolts. The change in steel material properties such as the modulus of elasticity, yield and ultimate strength, and the coefficient of thermal expansion are considered as functions of increasing temperature resulting from fire loading. Stress-strain curves for steel at elevated temperatures are used in the model. Two cases of boundary conditions are studied: one representing a roller at the far end of the beam, another assumes that the beam is pin supported. The base of the column is maintained as a fixed support, while the upper edge of the column is free to deflect in the vertical direction as shown in Figure 2. Pre-tensioning loads are modeled to represent the tightening of the bolts. A fire curve based on tests conducted in accordance with ASTM E119, is applied to the connection and the structural members. Results show deflection, rotations, and distortion fields of the structural components for both conventional and new fire resisting steel. Mechanical and thermal plastic strain and stress fields are predicted, documenting yielding, plasticity and ultimate failure in the plate, bolts and structural members. This is a 3D nonlinear model that provides graphical and empirical results for a variety of steel connections that could be used for comparison with established experimental results if available. Design recommendations, failure limitations, and material selection and specifications can be suggested for steel connections in such fire loading.

On the stochastic response of nonlinear FE models

This paper focuses on the stochastic dynamic response of structures modeled by finite elements with a relatively large number of degrees of freedom. FE models with nonlinearities and uncertain (stochastic) system properties are discussed. It is shown that component mode synthesis can be used most advantageously to solve the issue of computational efficiency and feasibility. The stochastic response due to stochastic loading of large FE models with nonlinear elements is determined by statistical equivalent linearization (EQL). The developed component-mode synthesis allows to determine the complex modal properties of arbitrary large linearized finite element models. Nonsymmetric structural matrices, as a result of the EQL, and filters for modeling of filtered white noise can be treated by the suggested approach. Since the efficiency of the procedure is nearly independent of the number of degrees-of-freedom (DOF) involved, statistical equivalent linearization becomes applicable for arbitrary detailed FE models. Furthermore, the dynamic response of FE models with uncertain or stochastic system properties is discussed. In this case, Monte Carlo simulation is suggested as the most appropriate approach for FE models. The paper focuses on the random eigenvalue problem for large FE systems as the computationally most demanding part of the dynamic analysis. Component-mode synthesis is used to provide in an efficient manner all the eigenvalue solutions of the FE system needed by the Monte Carlo simulation.

Thermo-mechanical simulation of a multichip press-packed IGBT

The reliability of press-packed integrated gate bipolar transistors (IGBT) depends on satisfactory contact conditions applied at assembly stage and mantained throughout the service life. The objective of this work is the simulation of the thermo-structural behavior of a multichip IGBT during initial assembly and subsequent uniform thermal cycling using the finite element method. A detailed axisymmetric FE model of the 3D-device is developed to assess multi-zone contact conditions. Elastic-plastic material behavior and Coulombian friction on contact surfaces are prescribed. The role of dimensional tolerances on contact conditions is discussed. The thermal cycling associated to accelerated testing is then introduced to determine the contact pressure evolution as well as local stick/slip conditions. The device sensitivity to potential damage initiation due to thermo-mechanical fatigue and/or fretting is addressed.

Thermo-Mechanical Simulation Of A Multichip Press-Packed Igbt

AbstractThe reliability of press-packed integrated gate bipolar transistors (IGBT) depends on satisfactory contact conditions applied at assembly stage and mantained throughout the service life. The objective of this work is the simulation of the thermo-structural behavior of a multichip IGBT during initial assembly and subsequent uniform thermal cycling using the Finite Element method. A detailed axisymmetric FE model of the 3D-device is developed to assess multi-zone contact conditions. Elastic-plastic material behavior and Coulombian friction on contact surfaces are prescribed. The role of dimensional tolerances on contact conditions is discussed. The thermal cycling associated to accelerated testing is then introduced to determine the contact pressure evolution as well as local stick/slip conditions. The device sensitivity to potential damage initiation due to thermo-mechanical fatigue and/or fretting is addressed.

Detailed FE model of thoracolumbar spine (T11-T12-L1) to determine role of facet orientation in producting spinal injuries

Detailed FE model of thoracolumbar spine (T11-T12-L1) to determine role of facet orientation in producting spinal injuries