Development/global validation of a 6-month-old pediatric head finite element model and application in investigation of drop-induced infant head injury

Drop is a frequent cause for infant head injury. To date, finite element (FE) modeling was gradually used to investigate child head dynamic response under drop impact conditions, however, two shortages still exist on this topic: (1) due to ethical reasons, none of developed 6-month-old (6MO) head FE model was found to be quantitatively validated against child cadaver tests at similar age group; (2) drop height and impact surface stiffness effects on infant head responses were not comprehensively investigated. In this study, motivated by the recently published material properties of soft tissues (skull and suture, etc.) and reported pediatric head global cadaver tests, a 6MO child head FE model was developed and simulated results compared with the child cadaver experimental data under compression and drop conditions. Comparison of results indicated that the FE model showed a fairly good biofidelic behavior in most dynamic responses. The validated FE model was further used to investigate effects of different drop heights and impact surface stiffness on the head dynamic responses. Numerical results show that the pediatric head mechanical parameters (peak acceleration, HIC, maximal vonMises stress and maximal first principal strain of skull) keep increasing with the increase in drop height, and exhibit “logarithmic function” shapes at “fast–slow” trends with increase in impact surface stiffness. Based on above analysis, the regressions were conducted to describe the relationship between drop height and impact surface stiffness and head global injury predictors (head peak acceleration, HIC, etc.). This paper provides a fundamental study of child head injury mechanism and protection under drop conditions.     

Soil–structure interaction: Parameters identification using particle swarm optimization

This paper deals with a numerical NDT method to identify mechanical parameters by inverse analysis using the particle swarm optimization algorithm. This method is using a finite element model of the structure to study in order to minimize the error between field data and data predicted by the FE model. The method is applied in the case of a laboratory experiment modelling a soil–structure interaction problem. Results stress the impact of the sensitivity of the solution to the accuracy of field measurements by simulating both different levels of measurement noise on data and using several placements of sensors.     

头颈部数学模型在碰撞中的响应对比研究

本文通过MADYMO软件对典型的车辆与行人侧面碰撞事故进行了模拟,输出最后一节颈椎(C7)的位移,加载到经过验证的某一基于人体解剖学结构的头颈部有限元模型中。通过仿真分析,得到头颈部的加速度、角速度等随时间的变化曲线和载荷力、HIC值等,并与多刚体模型的响应进行了对比。结果显示两种模型都可以有效预测行人在事故中的损伤风险,但有限元模型可以得到更多的损伤参数,相对而言可以更加准确地反映人体头颈部损伤响应。     

An elasto-viscoplastic analysis of direct extrusion of a double base solid propellant

In this study, three-dimensional modelling of extrusion forming of a double base solid rocket propellant is performed on Ansys® finite element analysis program. Considering the contact effects and the time dependent viscous and plastic behaviour, the solid propellant is assumed to obey the large deformation elasto-viscoplastic material response during direct extrusion process. The deformed shape, hydrostatic pressure, contact stress, equivalent stress, total strain values are determined from the simulation in order to get insight into the mechanical extremity that the propellant has undergone during processing. Hydrostatic pressure and contact stress distributions have been found to be important parameters due to safety reasons of the nitro-glycerine content in the bulk of the propellant.     

Prediction of coronary plaque location on arteries having myocardial bridge,using finite element models

This study was performed to evaluate the influences of the myocardial bridges on the plaque initializations and progression in the coronary arteries. The wall structure is changed due to the plaque presence, which could be the reason for multiple heart malfunctions. Using simplified parametric finite element model (FE model) of the coronary artery having myocardial bridge and analyzing different mechanical parameters from blood circulation through the artery (wall shear stress, oscillatory shear index, residence time), we investigated the prediction of “the best” position for plaque progression. We chose six patients from the angiography records and used data from DICOM images to generate FE models with our software tools for FE preprocessing, solving and post-processing. We found a good correlation between real positions of the plaque and the ones that we predicted to develop at the proximal part of the myocardial bridges with wall shear stress, oscillatory shear index and residence time. This computer model could be additional predictive tool for everyday clinical examination of the patient with myocardial bridge.     

拉伸载荷下钢芯铝绞线的力学特性仿真分析

为了研究钢芯铝绞线(ACSR)结构参数对其在拉伸载荷下力学特性的影响,基于 ANSYS 参数化设计语言(APDL)建立了 ACSR 参数化有限元模型。以 TACSR/AS-410/70 ACSR 为研究对象,基于数值仿真结果研究了该导线股丝应力分布和分层应力应变随拉伸载荷的变化 规律,通过拉伸实验验证了有限元模型的准确性;并基于上述模型数值模拟了不同节径比和铝 钢比下绞线在拉伸载荷下的力学响应。数值仿真结果表明,随铝钢比增加,ACSR 不同层间最 大等效应力随载荷增加而增加的趋势变小,绞线的最大应力值较低,股丝间应力分布更平均; 而 ACSR 节径比越小,绞制越紧密,其不同层股丝应力也越大。研究结果可为 ACSR 的结构设 计、线夹选型及优化设计等提供重要依据。     

Development of generic multibody road vehicle models for crashworthiness

The crashworthiness analysis of road vehicles requires detailed data of the vehicles that the automotive manufacturers are, generally, unable to release due to commercial or legal restrictions. In the development of passive safety subsystems or substructures, the overall crash response of a vehicle model used to support it, must mimic that of the real vehicle; if this exists, regardless of any particular constructive detail of its structure provided that it is not located in the vicinity of such subsystem. This work proposes a methodology for the development of multibody models of road vehicles, for passive safety analysis, which include all general structural and mechanical features of real vehicles and start by exhibiting impact dynamic responses similar to the top of line vehicles. These vehicle models, designated as generic, do not require the knowledge of most of the particular details of the design of the real vehicle, which the manufacturers are unable to release, but can be adjusted to have crash responses similar to those of the real vehicle. Based on an existing finite element model of a car, which has all constructive features of vehicles of the chosen class, a multibody model is built applying the plastic hinge approach. By using a selected number of crash scenarios, defined in international standards such as the EuroNCAP, selected parameters of the vehicle multibody model are adjusted to ensure a good correlation between its impact responses and those of the finite element model. The crash responses are measured in terms of structural deformations, velocities and accelerations, occupant injury measures and structural energy absorption capabilities. Assuming that the plastic hinge constitutive equations of the multibody model are not exactly known, their parameters are used here as the multibody vehicle model that are adjusted. The methodology proposed is demonstrated by its application to the identification of the vehicle multibody model of a large family car for which the reference vehicle is available as a detailed finite element model.     

Finite element analysis of spiral strands with different shapes subjected to axial loads

In this paper a new mathematical geometric model of spiral one or two-layered oval wire strands are proposed and an accurate computational two-layered oval strand 3D solid model, which is used for a finite element analysis, is presented. The three dimensional curve geometry of wires axes in the individual layers of the oval strand consists of straight linear and helical segments. The present geometric model fully considers the spatial configuration of individual wires in the right and left hand lay strand. Derived geometric equations were used for the generation of accurate 3D geometric and computational models for different types of strands. This study develops 3D finite element models of two-layer spiral round, triangular and oval strands subjected to axial loads using ABAQUS/Explicit software. Accurate modelling and understanding of their mechanical behaviour is complicated due to the complex contact interactions and conditions that exist between individual spirally wound wires. Comparisons of predicted responses for the strands with different shapes and constructions are presented. Resultant stress and/or deformation behaviours are discussed.     

Exploiting the structural reserve of textile composite structures by progressive failure analysis using a new orthotropic failure criterion

In this paper, a novel orthotropic layer based failure criterion for modelling progressive failure of non-crimp fabrics is presented. The strength parameters and stiffnesses needed for this failure criterion are obtained from virtual material tests. Therefore, a finite element multiscale algorithm is used to model the effect of lower scale inhomogeneities on macroscale material behavior. With this multiscale approach it is possible to make predictions for one single layer within a textile preform solely from the knowledge of the mechanical behavior of the constituents fiber and matrix and from the textile fiber architecture. The obtained stiffnesses and strengthes for one textile layer are used as input data for the novel orthotropic failure criterion presented in this paper. In order to show the workability of this failure criterion, finite element simulations of coupon tests and of a three-point bending test of a textile composite are shown and compared to experimental data.     

Comparison of numerical techniques for 3D flutter analysis of cable-stayed bridges

This paper presents the results of a comparison study of the numerical techniques of structural and aerodynamic force models developed based on the spline finite strip method with the conventional finite element approach in three-dimensional flutter analysis of cable-stayed bridges. In the new formulation, the bridge girder is modelled by spline finite strips. The mass and stiffness properties of the torsional behaviour of complex bridge girder, which have a significant influence on the wind stability of long-span bridges, are modelled accurately in the formulation. The effects of the spatial variation of the aerodynamic forces can be taken into account in the proposed numerical model by distributing the loads to the finite strips modelling the bridge deck. The numerical example of a 423 m long-span cable-stayed bridge is presented in the comparison study. The accuracy and effectiveness of the proposed finite strip model are compared to the results obtained from the equivalent beam finite element models. The advantages and disadvantages of these different modelling schemes are discussed.     

Sensitivity analysis of material input data influence on machining induced residual stress prediction in Inconel 718

Inconel 718 is commonly used in structural critical components of aircraft engines due to its properties at high temperatures. In order manufacture the final part, these components have to be machined, so the final surface integrity obtained after machining becomes a key issue. Residual stresses, which are included in surface integrity, are an important issue. Although much of the research carried out on machining induced residual stresses has been empirical, finite element modelling appears to be a complementary solution to gain understanding of it. However, some of the major drawbacks still need to be solved before it can become a reliable tool for industry, such us the identification of input parameters and computational cost. This paper deals with the study of machining induced residual stresses. An orthogonal cutting 2D finite element model was used and a sensitivity analysis was conducted to determine the influence of model input data on the predicted residual stresses. The results obtained from the sensitivity analysis showed that material constitutive law was the most relevant input data when predicting residual stress fields. Importantly the material behaviour at a high heating rate in adition to high strain rate must be considered.     

Out-of-plane deformation and pull-in voltage of cantilevers with residual stress gradient: experiment and modelling

The out-of-plane deformation and the pull-in voltage of electrostatically actuated cantilevers with a residual stress gradient, is investigated in the length range 100–300 µm. Measured pull-in voltages are compared with calculations, which are obtained using previously proposed analytical expressions and a finite element method (FEM) modelling. In particular, a simplified model of the residual stress distribution inside cantilevers is formulated that enables FEM simulation of measured out-of-plane deformations and pull-in voltages for all lengths of fabricated cantilevers. The presented experimental results and FEM model are exploitable in the design of cantilever-based microelectromechanical systems, in order to provide a reliable prediction of the influence of residual stress gradient on device shape and pull-in voltage.

     

Modeling of chemical mechanical polishing process using FEM and abductive network

In this paper, modeling of a two-dimensional axisymmetric quasic-static finite element model in conjunction with an abductive network for chemical–mechanical polishing process (CMP) was established. Three prediction models can be achieved, i.e., model for von Mises stress at wafer center, model for maximum von Mises stress and model for nonuniformity on wafer surface under various combinations of process parameters. The data of von Mises stress and nonuniformity on wafer surface can be first achieved under different conditions of the carrier load, pad's elastic modulus and thickness by using the developed finite element model for CMP. Next, an abductive network was applied to synthesize the data sets from the FE simulation. It is a self-organizing adaptive modeling tool that establishes the mathematical relationship between input and output variables based on abductive modeling technique and it can automatically synthesize the optimal network structure, including the optimal network structure, the number of layers and the form of functional nodes. Finally, the results from the three developed abductive networks with test data are compared with those from FE simulation to confirm the feasibility of this approach. The findings verified that the results confirm the feasibility and the proposed prediction models for CMP are acceptable.     

Enhanced predictive modelling process of broadband services adoption based on time series data

In this paper, the importance of the predictive modelling process of broadband services adoption is described. A detailed overview of different analytical models used for prediction, i.e., fitting and forecasting processes of broadband services adoption are presented. Furthermore, a comparison of several analytical models commonly used for prediction of broadband adoption is conducted. In order to more accurately fit to the existing broadband adoption time series data, and to forecast the future broadband services adoption paths, the features of the most accurate common predictive models have been identified for different phases of broadband services adoption. Considering the given results, usage of additional models in the predictive modelling process is analyzed. The objective of these analyses is set to improve the accuracy of the existing predictive modelling process. The accuracy of the predictive modelling process using additional models is tested and compared in different phases of broadband adoption. The model which gives the most accurate results is identified. Finally, in order to enable the usage of this model within a whole broadband service life cycle, as well as to include a greater number of explanatory parameters in predictive modelling process, an enhanced predictive modelling process is proposed.     

基于有限元素法的颅脑碰撞损伤模拟方法

1 Introduction With the development and advancement of society and computer technology, finite- element method (FEM) has becomes more and more popular in solving problems in projects. In the field of biomechanics, FEM is also an important method, which is effective, accurate, low- lost and applied. We can use FEM to build up the model of complicated geometrical object, to calculate the whole and partial stress and displacement and also the regular- ities of distributions, to compare the re…     

Development of a geometric modelling strategy for roll pass optimal design

Roll pass design is one of the most important tasks in shape rolling operations that are employed to provide raw materials with appropriate cross-section profiles for various industrial applications. Currently, many approaches, such as experience-based trial-and-error strategies, finite element methods, and expert systems, are applied to improve both quality and efficiency of roll pass design. However, due to lack of a flexible geometrical modelling strategy, the application of extant approaches is largely limited. This study attempts to develop a novel approach for generic geometrical modelling to support optimal design of roll passes. Features of the proposed model are analysed to support its application. Furthermore, a parameters estimation approach based on genetic algorithm is also developed to facilitate the transformation between the generic model and other geometrical models, as well as to improve its flexibility and applicability. The results from the case study presented in the paper indicate that the new model is more flexible and efficient, and that the parameters estimation approach also can achieve high transformation accuracy and efficiency.     

Fracture behaviour of single crystal silicon microstructures

The fracture behaviour of single crystal silicon (SCSi) microstructures is analysed based on microme-chanical torsional and tensile experiments. The uniaxial testpieces are characterised by the presence of sharp not-ches at the gauge length extremities. The critical loading conditions are reproduced in a finite element model in order to identify the analogies of the failure conditions in tension and torsion. The stress field in the vicinity of the notch tip (were cracks originate) is analyzed, and fracture mechanics parameters are determined. In the finite element model a crack, reproducing the failure process observed in the experiments, is included. The crack area is incrementally increased and the energy release rate for the critical loading conditions in tension and torsion is calculated. Based on these results a failure criterion is formulated along with a procedure for the mechanical integrity analysis of SCSi microstructures of arbitrary shape and loading conditions.     

Mathematical modelling of cylindrical electromagnetic vibration energy harvesters

In this paper the first steps for the derivation of a mathematical model to describe the mechanical behaviour of a cylindrical electromagnetic vibration energy harvester, designed to extract energy from human gait to power biomedical implantable devices, are provided. As it is usual, in the modelling of such devices, the proposed mechanical model is also based on the solution of Newton's second law, but here a nonlinear closed-form expression is used for the resulting magnetic force of the system, unlike what has been done in previous works where, traditionally, that expression is a linear or is a nonlinear approximation of the real one. The main feature of this mechanical model is that it depends on several parameters which are related to the main characteristics of this kind of devices, which constitutes a major advantage with respect to the usual models available in the literature since these characteristics can always be changed in order to optimize the device.     

Object-Oriented Modelling of Flexible Beams

In this paper the problem of modelling flexible thin beams in multibody systems is tackled. The proposed model, implemented with the object-oriented modelling language Modelica, is completely modular, allowing the realization of complex systems by simple aggregation of basic components. The finite element method is employed as the basic scheme to spatially discretize the model equations. Exploiting the modular features of the language, the beam substructuring discretisation scheme (mixed finite element-finite volume) is derived as well. Selected simulation results are presented in order to validate the model with respect to both theoretical predictions and literature reference results.     

Experimental and numerical characterization of honeycomb sandwich composite panels

In this paper, an experimental investigation, an analytical analysis and a numerical model of a typical four-point bending test on a honeycomb sandwich panel are proposed. The honeycomb core is modelled as a single solid layer of equivalent material properties. Analytical and numerical (finite element) homogenization approaches are used to compute the effective properties of the honeycomb core. A general kinematic model (unified formulation) has been adopted and used for the modelling of honeycomb sandwich panel submitted to the bending test. A comparative study of major classes of representative theories has been considered. Qualitative and quantitative assessments of displacement, stress have been presented and discussed.