Damage tolerance based design optimisation of a fuel flow vent hole in an aircraft structure

This paper investigates the design optimisation of a fuel flow vent hole (FFVH) located in the wing pivot fitting (WPF) of an F-111 aircraft assuming a damage tolerance design philosophy. The design of the vent hole shape is undertaken considering the basic durability based design objectives of stress, residual (fracture) strength, and fatigue life. Initially, a stress based optimised shape is determined. Damage tolerance based design optimisation is then undertaken to determine the shape of the cutout so as to maximise its residual strength and fatigue life. For stress optimisation, the problem is analysed using the gradient-less biological algorithm and the gradient-based nonlinear programming methods. The optimum designs predicted by the two fundamentally different optimisation algorithms agree well. The optimum shapes of the vent hole are subsequently determined considering residual strength and fatigue life as the distinct design objectives in the presence of numerous 3D cracks located along the vent hole boundary. A number of crack cases are considered to investigate how the crack size affects the optimal shapes. A semi-analytical method is employed for computation of the stress intensity factors (SIF), and an analytical crack closure model is subsequently used to evaluate the fatigue life. The 3D biological algorithm is used for designing the cutout profiles that optimise residual strength and fatigue life of the component. An improved residual strength/fatigue life (depending on the optimisation objective) is achieved for the optimal designs. The variability in SIF/fatigue life around the cutout boundary is reduced, thereby making the shape more evenly fracture/fatigue critical. The vent hole shapes optimised for stress, residual strength, and fatigue life are different from each other for a given nature and size of the flaws. This emphasises the need to consider residual strength and/or fatigue life as the explicit design objective. The durability based optimal vent hole shapes depend on the initial and final crack sizes. It is also shown that a damage tolerance optimisation additionally produces a reduced weight WPF component, which is highly desirable for aerospace industries. The design space near the ‘optimal’ region is found to be flat. This allows us to achieve a considerable enhancement in fatigue performance without precisely identifying the local/global optimum solution, and also enables us to select a reduced weight ‘near optimal’ design rather than the precise optimal shape.     

基于模态应力恢复的轿车发动机舱盖焊点疲劳寿命分析

建立汽车发动机舱盖焊点有限元模型,并将分析结果与试验模态对比,验证该有限元模型的准确性.分别采用准静态法和模态应力恢复法得到焊点的应力-时间历程;基于Palmgren-Miner线性损伤累积准则和S-N曲线对比评估焊点疲劳寿命,并在模态应力恢复方法中考虑截止频率和结构阻尼对焊点疲劳寿命的影响.与虚拟台架试验的对比结果表明：准静态预测的焊点寿命大于试验寿命,截止频率为200 Hz且结构阻尼为0.06的模态应力恢复结果与试验结果较吻合.基于模态应力恢复法优化设计的发动机舱盖通过耐久路试.     

Optimal design of machine components using notch correction and plasticity models

Shape optimization computational technology is used in order to maximize life time of notched machine/structural components in low cycle fatigue regime. The present approach is composed of three steps: (i) stress–strain calculation using notch correction and plasticity models, (ii) estimation of critical plane to asses fatigue lives, (iii) formulation of the optimization problem with constraint set on the number of cycles corresponding to crack initiation. The optimal design procedure is a combination of the computer aided geometrical design mathematical methods for the shape definition, the boundary element method used for analysis of the response quantities, assisted by the sequential linear programming method with move limits. Numerical examples display significant increase in the number of cycles corresponding to crack initiation phase in comparison to traditional (regular) notch shapes.     

A CAD-based on biological method for designing optimal fatigue life

This paper presents an innovative approach to shape optimisation of three-dimensional, damage-tolerant structures. In this approach, a new and simple method, which we termed Failure Analysis of Structures (FAST), is used to estimate the stress-intensity factor for cracks at a notch. The methodology and software used to automate damage-tolerance calculations are developed using computer-aided design and FAST codes. The worst crack locations are found by modeling many cracks along fractured critical edges of the structure by using FAST. This software is then used to evaluate damage-tolerance objective functions for optimisation algorithms. A particular stress-based biological growth method is employed to study the problem of optimisation with fatigue life as the design objective. This work confirms that a stress-optimised structure does not necessarily give the longest fatigue life by numerical examples.     

基于MSC Nastran的矿用电动轮自卸车货箱模态分析

针对矿用电动轮自卸车货箱的动态特性,提出基于模态分析结果的货箱结构改进方法.通过Patran建立货箱结构的有限元模型,应用MSC Nastran对其进行模态分析,得到货箱结构的动态参数.根据模态分析结果对货箱结构进行改进,货箱结构固有频率及振型得到较好的改善,为进一步研究矿用电动轮自卸车货箱的优化设计和预测疲劳寿命奠定基础.     

基于有限元仿真的特种越野车结构疲劳寿命预测

为缩短新车开发周期、节约样车制造费用，给车辆轻量化设计提供参考，在计算机仿真环境下预测了某特种越野车关键部件的疲劳寿命。基于该车结构有限元模型动力学计算的频响结果，对计算模型施加不同车速下等级路面位移谱，得到了不同车速不同级别路面下该车关键部件的应力响应谱，并在此基础上运用随机疲劳理论预测了该车的疲劳寿命。所研究的内容为车辆的疲劳寿命预测提供了较为可靠的流程和方法，所预测寿命结果在合理范围内，并提供了关键部件疲劳寿命的薄弱位置。     

基于主S-N曲线法的地铁制动箱焊接疲劳分析

为研究地铁车辆制动箱焊接接头的疲劳寿命,根据实际结构建立4节点壳单元有限元模型,给出搭接焊和T型焊的焊缝建模方法.在3种振动工况下,运用主S N曲线法计算焊缝的等效结构应力和对应损伤比.结果表明：该地铁车辆制动箱焊接结构设计合理可靠;通过与实体单元模型计算结果进行对比证明壳单元模拟焊缝的合理性;在不同尺寸单元下对比2种疲劳评估方法,结果表明名义应力法预测疲劳寿命的准确性较低.     

基于等效结构应力的铝合金地铁车体疲劳寿命预测

为评估某铝合金地铁车辆的疲劳寿命,采用美国ASME标准中的网格不敏感的主S-N曲线法对该车焊缝进行疲劳寿命预测.用HyperMesh对车体进行有限元建模,并对焊缝处网格细化;用ANSYS计算焊缝处应力;运用自主开发的FE-Weld软件对其进行等效结构应力的计算和疲劳寿命的预测;对疲劳寿命不符合设计要求的结构进行改进和优化,改进后结构的疲劳寿命符合设计要求.网格不敏感的主S-N曲线法具有重要工程应用推广价值.     

基于路谱频域的车身疲劳分析

针对车身疲劳分析中静载法无法考虑结构动力学响应,瞬态分析法无法求解过长时间域的问题,将这2种方法与频域法进行比较,发现用频域法对大规模有限元模型进行动态疲劳分析相对容易,并能完全描述动力学响应过程.根据频域法进行振动疲劳分析的理论和计算过程,给出基于路谱频域的车身疲劳分析流程.基于功率谱密度（Power Spectral Density,PSD）载荷谱的传递函数法求解某车关键部件的疲劳寿命,求解结果与疲劳试验结果比较一致.结果表明基于路谱频域的振动疲劳分析方法在汽车结构疲劳计算中的应用可行.     

Iterative design method for an image filter to improve the bit error rate in holographic data storage systems

An image filter design method is proposed to improve the bit error rate (BER) in holographic data storage (HDS). In previous image restoration methods for HDS, a highly precise point spread function (PSF) was used as the deconvolution filter, so performance was strongly dependent on the accuracy of the PSF. In the proposed method, in contrast, the image filter is designed without using PSF information, due to the similar spatial frequency distributions of HDS data pages. A simple iteration algorithm was developed to obtain an optimized image-filter shape, and the performance of the designed image filter was verified by both simulation and experimentation. The experimental results demonstrated that the BER improved sixfold and greater than tenfold for a Nyquist factor of 1.1 and 1.2, respectively. Additionally, an improvement of >30 % in storage density was projected using the proposed filter, compared with conventional HDS systems.     

直驱式风电机组发电机转子支架强度分析

为实现某直驱式风电机组发电机转子支架的强度设计要求,应用有限元软件和疲劳分析软件,研究有限元方法在极限强度和疲劳强度分析中的应用.基于HyperMesh建立直驱式发电机有限元模型,采用MSC Nastran计算分析转子支架的极限强度.在极限强度不满足强度设计要求的情况下,对转子支架的结构进行优化.基于疲劳分析软件,计算分析转子支架的疲劳损伤.最终得到优化后的转子支架设计满足强度设计要求.     

Fretting fatigue strength reduction factor for interference fits

This work is based on a comparison between experimental data and finite element analysis for many configurations of interference fits in rotating bending and alternated torsion. Refined mesh and sub modeling techniques were used to obtain converged results. Contact convergence was achieved using augmented Lagrangian algorithm, with penetration control equal to 0.1% on radial interference and allowable elastic slip of 0.1 μm. Fatigue results are presented for 4 different fatigue criteria: Von Mises, Sine, Crossland and Dang Van. Dang Van criterion gives the most consistent results and shows no evidence of a correlation between sliding amplitude and fatigue life. Relative slip seems to be a consequence rather than the cause, excluding cases with important wear. A fretting fatigue strength reduction factor was calculated for the fretting zone. Its value is between 0.35 and 0.69 depending on the chosen criterion, but varies for different materials and/or loading types. Results give a good fatigue life approximation and can easily be used to optimize the shape of the interference fits.     

基于表面肌电信号的肌肉疲劳状态分类系统

为了实现肌肉疲劳状态的准确检测分类,提出一个完整的基于人体表面肌电（sEMG）信号的肌肉疲劳分类与检测系统。首先,通过AgCl表面贴片电极和高精度模拟前端ADS1299采集人体sEMG信号,进行小波消噪等预处理之后,提取可反映人体肌肉疲劳状态的sEMG信号时域和频域特征。然后,在常用特征如积分肌电图（IEMG）、均方根（RMS）、中值频率（MF）以及平均功率频率（MPF）基础上,为更加精细地刻画人体肌肉疲劳状态,引入sEMG信号的频域特征带谱熵（BSE）;为弥补傅里叶变换分析非平稳信号的不足,引入sEMG信号时频特征——基于经验模态分解-希尔伯特变换（EEMD-HT）的平均瞬时频率。最后,为提高肌肉非疲劳和疲劳状态分类的准确度,利用含突变的粒子群优化算法优化支持向量机（PSO-SVM）并对sEMG进行分类,实现人体肌肉疲劳状态检测。征集15名健康男青年进行sEMG信号采集实验,建立sEMG信号库,提取特征进行分类实验。实验结果表明,所提的系统能够进行高精度sEMG信号采集和肌肉疲劳程度的高准确度分类,分类准确率大于90%。     

基于光纤光栅的悬臂结构疲劳裂纹实验研究

疲劳以及裂纹对机械结构的寿命和生产安全都有着重要的影响。针对叶片等悬臂类结构设计了一种采用光纤光栅进行疲劳测量的方法,通过对比实验证实了裂纹对结构疲劳过程的影响。实验结果表明：完整叶片结构试件的固有频率为124.2 Hz,经过5×106次循环后固有频率和光栅波长均无明显变化;而有0.1 mm深度裂纹的固有频率为123.3 Hz,经过5×106次循环后固有频率变为86.68 Hz,证实了裂纹对疲劳寿命的影响。     

The effect of posture and seat suspension design on discomfort and back muscle fatigue during simulated truck driving

Several studies have shown a relationship between low-back problems and exposure to seated whole-body vibration. The amount of vibration transmitted to the operator is influenced by the posture of the subject in the vehicle. The aim of this study was to determine whether a truck seat with a gas spring in its suspension is superior to the standard spring seat in slowing the onset of muscle fatigue and reducing the level of discomfort experienced during road vibrations while maintaining typical driving postures. The experiment used a 2 x 3 (2 seats x 3 postures) repeated measures design. It was conducted on six males free from low-back pain. Subject comfort was rated before and directly after exposure to typical vibrations. Muscle fatigue using centre frequency was determined during vibration exposure, and the magnitude and phase of acceleration transfer were calculated from the base plate to the seat pan and from the seat pan to the bite bar. None of comfort, fatigue rate or fatigue average were affected by seat type or seat suspension design in the short term, 10 min vibration exposure. Fatigue and comfort measures could continue to be used to detect postural defects, but the more sensitive measures of seat/driver interactions remain mechanical ones using motion-measuring techniques such as accelerometry and correcting for the heavily damped nature of the system. Until more sophisticated manikins are available the characteristics of vibration-attenuating seats should be confirmed using live humans.     

Review of life assessment techniques applied to dynamically loaded automotive components

Structural optimisation based on fatigue life of dynamically loaded structures of realistic complexity is rarely attempted due to computational costs. Very efficient stress analysis and fatigue life assessment techniques are needed if this is to become routine. For the first time, this paper compares several approaches to fatigue life prediction using a real automotive engineering case study, taking into account that optimisation based on fatigue life requires accurate relative distribution rather than exact values. The paper concludes that although both the quasi-static and frequency domain approaches are potentially more efficient than transient dynamic analysis, parameter sensitivity of the frequency domain approach may preclude its eventual use.     

Optimum design of nonlinear structures with path dependent reponse

Optimum design of structures with path dependent response is studied in this paper. The direct differentiation and the adjoint structure methods of design sensitivity analysis are summarized. The reference volume concept is used to unify the conventional and shape design problems. It is concluded that the direct differentiation method is more effective for this class of problems. The design sensitivity analysis — developed with continuum formulation — is discretized using the finite element method. Two cases for an example problem are optimized using a sequential quadratic programming algorithm to demonstrate how the developed procedures work and to study the optimization process for the problems with path dependent response.     

Optimal re-design of helical springs using fuzzy design and FEM

The aim of this paper is to present results of using fundamental machine element design principles into re-designing optimally heavy duty springs used in terrain machinery and in industry. Use of standard procedures often results in recurring fatigue fracture failures. This reveals need for correcting also the present standards. Main causes of failures are the local bending due to eccentric highly impact force application at squared and ground ends and wearing away of the shot peening protection. Optimum design of the spring is obtained. Goals are minimisation of wire volume, space restriction, desired spring rate, avoidance of surging frequency and achieving reliably long fatigue life. Conclusions are verified by using full 3D solid FEM analysis with MSC Nastran by which the stresses and also strains, deformations and natural frequencies and modes are obtained.     

Fatigue Life Prediction Criterion for Micro–Nanoscale Single-Crystal Silicon Structures

This paper describes fatigue damage evaluation for micro–nanoscale single-crystal silicon (SCS) structures toward the reliable design of microelectromechanical systems subjected to fluctuating stresses. The fatigue tests, by using atomic force microscope (AFM), nanoindentation tester, and specially developed uniaxial tensile tester, have been conducted under tensile and bending deformation modes for investigating the effects of specimen size, frequency, temperature, and deformation mode on the fatigue life of SCS specimens. Regardless of frequency and temperature, the fatigue life has correlated with specimen size. For example, nanoscale SCS specimens with 200 nm in width and 255 nm in thickness have showed a larger number of cycles to failure, by a factor of $10^{5}$, at the same stress level, as compared to microscale specimens with 48 $muhbox{m}$ in width and 19 $muhbox{m}$ in thickness. Deformation mode has also affected the lifetime; however, no frequency and temperature dependences have been observed unambiguously in the $S{-}N$ curves. The stress ratio parameter corresponding to the ratio of peak stress to average fracture strength has enabled us to estimate the lifetime for each deformation mode. To predict the fatigue life of SCS structures regardless of deformation mode and specimen size, we have proposed an empirical parameter that includes the resolved shear stress. The mechanism of fatigue failure of SCS structures is discussed from the viewpoint of dislocation slip, crack nucleation, growth, and failure through observations using AFM and scanning electron microscope.$hfillhbox{[2008-0072]}$