冲击载荷下载人飞行器乘员颈椎力学行为研究

利用生物力学仿真软件LifeMOD,根据关节力矩模型和肌肉力学模型,建立了用于多刚体分析的三维人体动力学模型。采用载人飞行器在着陆过程中的边界条件,模拟了乘员坐姿承受水平方向冲击作用时头颈部脊椎的动态响应。对航空航天领域中各种致伤因素下乘员脊椎骨骼损伤的研究有一定的意义,同时也为优化防护结构、保障乘员生命安全提供了一定的参考。     

Studies in dynamic design of drilling machine using updated finite element models

The aim of the present work is to develop updated FE models of a drilling machine using analytical and experimental results. These updated FE models have been used to predict the effect of structural dynamic modifications on vibration characteristics of the drilling machine. Two studies have been carried out on the machine. In the first study, modal tests have been carried out on a drilling machine using instrumented impact hammer. Modal identification has been done using global method of modal identification. For analytical FE modeling of the machine, a computer program has been developed. The results obtained using FEM, have been correlated with the experimental ones using mode shape comparison and MAC values. Analytical FE model has been updated, with the help of a program, which has been developed using direct methods of model updating. In the second study, modal testing has been carried out using random noise generator and modal exciter. Global method has been used for modal identification. Analytical FE modeling has been done using I-DEAS software. Correlation of FE results with the experimental ones has been carried out using FEMtools software. Updating of the analytical FE model has also been done using the above software, based on an indirect technique viz. sensitivity based parameter estimation technique. The updated FE models, obtained from both the studies have been used for structural dynamic modifications (SDM), for the purpose of dynamic design and the results of SDM predictions are seen to be reasonably satisfactory.     

Gardner tongs and cervical traction

Treatment of cervical spine injuries dates from 4000 B.C.; however, the development of safe and effective methods of cervical traction did not appear until the 20th century. Although many devices have been introduced to stabilize the cervical spine, the invention of spring-loaded tongs by Gardner in 1973 was a significant technological advance. Gardner tongs are easily applied, have little tendency to become dislodged, and cause few complications.     

钻削加工有限元仿真的研究进展

对麻花钻建模的国内外研究现状进行了概述;比较了三种适用于切削加工研究的有限元软件的性能特征,探讨了切削过程仿真的关键技术;介绍了有限元仿真在钻削加工中的应用;指出了钻削加工有限元仿真研究所存在的问题及其发展趋势。     

齿轮箱螺栓结合面的有限元建模研究

在实际工程应用中,针对如何有效地利用ANSYS软件对齿轮箱螺栓结合面进行有限元建模分析的问题,通过对螺栓结合面建模的难点和关键点—螺栓预紧力的模拟、螺栓接触面的模拟以及螺栓实体有限元模拟的建模方法的研究,系统地阐述了基于ANSYS的7种类型的齿轮箱结合面螺栓有限元建模方法,利用ANSYS软件对其中4种典型的螺栓有限元建模方式进行了静力分析和模态分析,分析比较了不同建模方法在静力学和动力学方面的结果差异。研究结果表明,在仿真效率和仿真精度方面,耦合螺栓模型是一种更为合适的建模方法,但在实际应用中采用实体螺栓有限元模型模拟实际结构中的螺栓时,能够更好的反应实际工作中螺栓连接结构的应力变化,是各种建模方法中的优选方案。     

Dynamic modeling and control of flexible space structures

This paper presents a global mode modeling of space structures and a control scheme from the practical point of view. Since the size of the satellite has become bigger and the accuracy of attitude control more strictly required, it is necessary to consider the structural flexibility of the spacecraft. Although it is well known that the finite element (FE) model can accurately model the flexibility of the satellite, there are associated problems: FE model has the system matrix with high order and does not provide any physical insights, and is available only after all structural features have been decided. Therefore, it is almost impossible to design attitude and orbit controller using FE model unless the structural features are in place. In order to deal with this problem, the control design scheme with the global mode (GM) model is suggested. This paper describes a flexible structure modeling and three-axis controller design process and demonstrates the adequate performance of the design with respect to the maneuverability by applying it to a large flexible spacecraft model.     

The use of the Zebris motion analysis system for measuring cervical spine movements in vivo

The cervical spine exhibits the greatest range of motion among the spinal segments due to the complex interaction of its triplanar components of movement. As a result, measurement of movements of the cervical spine and of the various orthoses used in cervical spine injuries has proved difficult with no one method proving satisfactory. This paper uses the Zebris ultrasonic three-dimensional motion analysis system to measure flexion, extension, range of lateral bending, and range of axial rotation in five similar male and five similar female subjects with no history of neck injuries. The subjects were tested unrestrained and in soft and hard collars, as well as in Philadelphia, Miami J, and Minerva orthoses. Results show that the Minerva is the most stable construct for restriction of movement in all planes in both groups. Looking at these results allows ranking of the measured orthoses in order of their three-dimensional stability. Furthermore, by presenting reproducible data incorporating the composite triplanar movements of the cervical spine, thus allowing comparative analysis of the studied orthoses, they propose the Zebris as a reliable, repeatable, and safe method of measurement of cervical spine motion with low intersubject variability.     

BRAIN INJURY BIOMECHANICS IN REAL WORLD VEHICLE ACCIDENT USING MATHEMATICAL MODELS

This paper aims at investigating brain injury mechanisms and predicting head injuries in real world accidents. For this purpose, a 3D human head finite element model （HBM-head） was developed based on head-brain anatomy. The HBM head model was validated with two experimental tests. Then the head finite element（FE） model and a multi-body system （MBS） model were used to carry out reconstructions of real world vehicle-pedestrian accidents and brain injuries. The MBS models were used for calculating the head impact conditions in vehicle impacts. The HBM-head model was used for calculating the injury related physical parameters, such as intracranial pressure, stress, and strain. The calculated intracranial pressure and strain distribution were correlated with the injury outcomes observed from accidents. It is shown that this model can predict the intracranial biomechanical response and calculate the injury related physical parameters. The head FE model has good biofidelity and will be a valuable tool for the study of injury mechanisms and the tolerance level of the brain.     

Model selection in finite element model updating using the Bayesian evidence statistic

This paper considers the problem of finite element model (FEM) updating in the context of model selection. The FEM updating problem arises from the need to update the initial FE model that does not match the measured real system outputs. This inverse system identification-problem is made even more complex by the uncertainties in modeling some of the structural parameters. Such uncertainty often results in a number of competing forms of FE models being proposed which leads to lack of consensus in the field. A model can be formulated in a number of ways; by the number, the location and the form of the updating parameters. We propose the use of a Bayesian evidence statistic to help decide on the best model from any given set of models. This statistic uses the recently developed stochastic nested sampling algorithm whose by-product is the posterior samples of the updated model parameters. Two examples of real structures are each modeled by a number of competing finite element models. The individual model evidences are compared using the Bayes factor, which is the ratio of evidences. Jeffrey's scale is then used to determine the significance of the model differences obtained through the Bayes factor.     

Carbody structural lightweighting based on implicit parameterized model

Most of recent research on carbody lightweighting has focused on substitute material and new processing technologies rather than structures. However, new materials and processing techniques inevitably lead to higher costs. Also, material substitution and processing lightweighting have to be realized through body structural profiles and locations. In the huge conventional workload of lightweight optimization, model modifications involve heavy manual work, and it always leads to a large number of iteration calculations. As a new technique in carbody lightweighting, the implicit parameterization is used to optimize the carbody structure to improve the materials utilization rate in this paper. The implicit parameterized structural modeling enables the use of automatic modification and rapid multidisciplinary design optimization （MDO） in carbody structure, which is impossible in the traditional structure finite element method （FEM） without parameterization. The structural SFE parameterized model is built in accordance with the car structural FE model in concept development stage, and it is validated by some structural performance data. The validated SFE structural parameterized model can be used to generate rapidly and automatically FE model and evaluate different design variables group in the integrated MDO loop. The lightweighting result of body-in-white （BIW） after the optimization rounds reveals that the implicit parameterized model makes automatic MDO feasible and can significantly improve the computational efficiency of carbody structural lightweighting. This paper proposes the integrated method of implicit parameterized model and MDO, which has the obvious practical advantage and industrial significance in the carbody structural lightweighting design.     

Investigations on the effects of friction modeling in finite element simulation of machining

Accurately predicting the physical cutting process variables, e.g. temperature, velocity, strain and stress fields, plays a pivotal role for predictive process engineering for machining processes. These predicted field variables, however, are highly influenced by workpiece constitutive material model (i.e. flow stress), thermo-mechanical properties and contact friction law at the tool-chip-workpiece interfaces. This paper aims to investigate effects of friction modeling at the tool-chip-workpiece interfaces on chip formation process in predicting forces, temperatures and other field variables such as normal stress and shear stress on the tool by using advanced finite element (FE) simulation techniques.For this purpose, two distinct FE models with Arbitrary Lagrangian Eulerian (ALE) fully coupled thermal-stress analyses are employed to study not only the effects of FE modeling with different ALE techniques but also to investigate the influence of limiting shear stress at the tool-chip contact on frictional conditions, which was never done before. A detailed friction modeling at the tool-chip and tool-work interfaces is also carried by coupling sticking and sliding frictions. Experiments and simulations have been performed for machining of AISI 4340 steel using tungsten carbide tooling and the simulation results under increasing limit shear stress have been compared to experiments. The influence of limiting shear stress on the tool-chip contact friction was explored and validity of friction modeling approaches was examined. The results presented in this work not only provide a clear understanding of friction in FEM modeling of machining but also advance the process knowledge in machining.     

Prediction of inter-segment stability and osteophyte formation on the multi-segment C2-C7 after unilateral and bilateral facetectomy

The objective of this study was to determine the intersegment stability, disc degeneration, and osteophytes formation on the multisegment cervical spine (C2-C7) after unilateral and bilateral facetectomy. A geometrically accurate non-linear three-dimensional model of the intact human cervical spine was created from the digitized coordinates of the dry vertebrae. The intact model was validated against the published results under physiological loading conditions. Eight surgically altered models were created from the intact model. The intact and surgical altered models were subjected to physiological loading. The inclusion of five levels in the present model allowed accurate determination of the intersegment responses and internal cortical bone and disc annulus stress in the adjacent spinal components. Results indicated that facetectomy performed on C5-C6 significantly affects the corresponding stress and intersegment motions at the corresponding C5-C6 levels. The maximum increases were 18 per cent for bilateral facetectomy and 7 per cent for unilateral facetectomy under lateral bending. Combined flexion-extension and axial rotation caused an approximately similar amount of increases after total facetectomy. In addition, adjacent segments (C4-C5 and C6-7) also experience a slight increase in the intersegment responses and internal stress after facetectomy. It has been shown that facetectomy of greater than 50 per cent resulted in segment hypermobility and substantial increase in the disc annulus and cortical bone stress. Increase in the stress may lead to osteophytes formation. This study revealed important information that will help clinicians identify the critical intersegment stability and to decide on the amount of facets resection.     

Sensitivity analysis of a validated subject-specific finite element model of the human craniofacial skeleton

Developing a more complete understanding of the mechanical response of the craniofacial skeleton (CFS) to physiological loads is fundamental to improving treatment for traumatic injuries, reconstruction due to neoplasia, and deformities. Characterization of the biomechanics of the CFS is challenging due to its highly complex structure and heterogeneity, motivating the utilization of experimentally validated computational models. As such, the objective of this study was to develop, experimentally validate, and parametrically analyse a patient-specific finite element (FE) model of the CFS to elucidate a better understanding of the factors that are of intrinsic importance to the skeletal structural behaviour of the human CFS. An FE model of a cadaveric craniofacial skeleton was created from subject-specific computed tomography data. The model was validated based on bone strain measurements taken under simulated physiological-like loading through the masseter and temporalis muscles (which are responsible for the majority of craniofacial physiologic loading due to mastication). The baseline subject-specific model using locally defined cortical bone thicknesses produced the strongest correlation to the experimental data (r2 = 0.73). Large effects on strain patterns arising from small parametric changes in cortical thickness suggest that the very thin bony structures present in the CFS are crucial to characterizing the local load distribution in the CFS accurately.     

Modeling and experiment of a morphing wing integrated with a trailing edge control actuation system

Morphing wing has attracted many research attention and effort in aircraft technology development because of its advantage in lift to draft ratio and flight performance.Morphing wing technology combine...     

机油盘冲压过程截面的有限元模拟与实验验证

板料冲压过程的模具设计是一个费时费力的过程。采用有限元可以降低设计费用 ,缩短设计周期。本文采用有限元软件 MARC基于拉格朗日的弹塑性本构方程建立了一个有限元模型来分析机油盘的成形过程。模拟中考虑板料的厚向异性 ,接触面间的摩擦约束采用库仑摩擦模型。模具看作刚体 ,板料作为变形体。模拟和实验结果的比较表明模拟的壁厚变薄分布与测量结果吻合得很好 ,因而理论模拟的结果可用于真实情况的预测     

考虑模型偏差的结构动力学模型修正

针对结构有限元模型修正后仍可能存在模型偏差的问题,提出用待修正参数的不确定性来表征模型偏差的有限元模型修正方法。首先,基于响应面方法识别得到待修正参数的最优值,并通过计算结果与试验结果比较获得模型偏差;然后,基于响应面模型并结合灵敏度分析计算得到模型偏差对待修正参数的影响,从而得到考虑模型偏差后待修正参数的区间;最后,通过一个悬臂梁工程实例的模型修正,验证了笔者所提出方法的可行性。结果表明,考虑模型偏差的修正可以提高模型可靠性。     

Musculoskeletal upper limb modeling with muscle activation for flexible body simulation

The use of digital human models has been increasing rapidly in various fields from medical to engineering applications. Most of the works on human models involving muscle activation have been concentrated on rigid body simulation so far, because the dynamics of human body motion has been primary concern regardless of the effects on human musculoskeletal body. Recently the need for flexible body simulation including muscle activation has been increasing for engineering applications. In this paper, a musculoskeletal model with muscle activation of an upper limb for the dynamic simulation of FE based flexible body is presented. In order to estimate the in vivo forces of muscles in motion, optimization technique is employed to solve multiple solutions problem. The simulated results were compared with the experimental data, EMG for validation. As a result it was found that muscle activation as part of musculoskeletal model can be employed for a FE based flexible body software.     

Compression response, strength and post-peak response of an axial fiber reinforced tow

This paper discusses the results of a finite element (FE)-based study of the compressive instabilities of axial fiber tows in 2D triaxial braided carbon fiber composites (2DTBC). A 3D FE model of an axial tow is used in conjunction with the ABAQUS commercial FE code. To accommodate unstable snap-back post-peak behavior, an arc-length solution technique is adopted to solve the FE equations. Explicit account of the braid microstructure (geometry and packing) and the measured inelastic properties of the matrix (the in-situ properties) are accounted for via the use of the FE method. This type of detailed modeling is necessary for developing a mechanism-based failure prediction capability. The computational model provides a means to assess the compressive strength of the axial fiber tow and its dependence on various microstructural parameters. It also serves as a tool to assess the most significant parameters that affect compressive strength of a 2DTBC.     

A numerically low-cost and high-accuracy periodic FE modeling of shot-peened 34CrNiMo6 and experimental validation

This paper proposed a numerically low-cost 3D FE modeling method for multi-shot shot peening. The low computation cost and high prediction accuracy of shot peening are realized at the same time by the incorporation of random multi-shot with defined spacing between the adjacent simultaneously impinging shots, periodicity, and coverage rate of 100%. With this modeling method, one-step and dual-step multi-shot peening of 34CrNiMo6 steel target is modeled and the produced residual stress is predicted. In order to make the predicted residual stress depth profile more comparable with the measured one by XRD method, the redistribution of residual stress due to the layer removal by electrochemical polishing is simulated using Model Change technique. And the comparison between the prediction and experiment indicates that this improved 3D periodic FE modeling of multi-shot impingement provides very accurate simulation models for one-step and dual-step shot peening. It can substitute for the costly and time-consuming optimization experiments of the shot peening process, especially the multi-step shot peening process. Finally, the evolution of residual stress depth profile in dual-step shot peening process is investigated by using the simulation model and a variation of residual stress towards a more uniform distribution on the finished surface taking place in the second step is discovered by RMS analysis.     

Impact behaviour of GFRP and Kevlar/epoxy sandwich composite plate: Experimental and FE analyses

In this paper, dynamic response of GFRP composite plate under ballistic impact has been studied by experimental tests and also by an efficient FE model. Material characterization of GFRP composite is performed as required for progressive damage analysis of laminate due to impact. Shock effect of impact is considered in the material modeling of composite plate. The influence of the target thickness on the ballistic performance of the composite plate is also studied by considering 3.12, 6.24 and 9.36 mm thick targets. Moreover, sandwich composite plate consisting of GFRP and Kevlar/epoxy in three different combinations of laminate layers is considered to obtain suitable combination for structural application that offer better penetration resistance. Damage pattern, contact force histories and stresses in composite plate are studied in addition to residual velocity and acceleration of projectile. Numerical results from present FE model in terms of residual velocities and damage patterns in composite plate show good agreement with the experimental results.