Application of ADINA and hole drilling method to residual stress determination in weldments

Residual stress distributions with depth at weld toes in controlled shot-peened, high strength steel weldments were determined through the measurement of relaxed surface strains by the incremental hole drilling method. The stress states were determined from the relaxed surface strains by a novel elasto-plastic interpretation of the strain readings, using the finite element software, ADINA. Residual stress distributions determined from the theory of elasticity, using experimental strain gauge readings from the hole drilling method, gave values much greater than the 0.2% offset yield stress of 613 MPa. The stress states were corrected through elasto-plastic finite element modeling using ADINA. After the corrections, the maximum residual stress was less than 613 MPa. The corrected stress distributions were applied to determine the effect of controlled shot peening on residual stress distributions with depth. The distributions within 0.8 mm below the material surface was used as an indicator of shot-peening depth and the effect of control parameters.     

Design study of hole positions and hole shapes for crack tip stress releasing

The method of hole drilling near or at the crack tip is often used in fatigue damage repair. From a design optimization point of view, two questions are posed: Where should the hole(s) be drilled? And is there a better shape of the hole than a circular one? For the first question, we extend earlier results for isotropic material and in general study the influence of having orthotropic material. Optimal shapes are by no means circular, and we focus on the shape of a single hole centered at (or in front of) the crack tip. It is shown that the stress field at the crack boundary can be significantly improved by noncircular shapes. As a byproduct, an alternative method for extracting the stress intensity factor from a finite element analysis is presented.     

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.     

Fault detection,isolation and quantification from Gaussian residuals with application to structural damage diagnosis

Despite the general acknowledgment in the Fault Detection and Isolation (FDI) literature that FDI are typically accomplished in two steps, namely residual generation and residual evaluation, the second step is by far less studied than the first one. This paper investigates the residual evaluation method based on the local approach to change detection and on statistical tests. The local approach has the remarkable ability of transforming quite general residuals with unknown or non Gaussian probability distributions into a standard Gaussian framework, thanks to a central limit theorem. In this paper, the ability of the local approach for fault quantification will be exhibited, whereas previously it was only presented for fault detection and isolation. The numerical computation of statistical tests in the Gaussian framework will also be revisited to improve numerical efficiency. An example of vibration-based structural damage diagnosis will be presented to motivate the study and to illustrate the performance of the proposed method.     

Optimization of hole reinforcements by doublers

For various technical reasons, cutouts such as holes in thin-walled structures are inevitable and are of significant technical relevance. Unfortunately holes lead to an undesired stress concentration at the hole vicinity and a reduced strength of the structure. Therefore in practice a local reinforcement is usually applied around the hole. The increasing requirements for modern structures in terms of low weight and high strength lead to the question of an optimal reinforcement design. The present paper addresses the well-approved techniques of mathematical structural optimization to determine the aforementioned optimal design of the reinforcement. Thus it is necessary to set up an optimization model, as well as an appropriate structural model, to obtain the structural response (displacements, stresses ...). In this work, the finite element method has been applied for the structural analysis. The optimization procedure described has been utilized for a number of different reinforcement alternatives under various load cases. The numerical procedure implemented works with good reliability and efficiency and gives optimal reinforcement designs that are very useful for the direct engineering application. The results obtained illustrate the necessity and usefulness of the applied optimization procedure. Received April 28, 1999     

A new approach for the solution of singular optima in truss topology optimization with stress and local buckling constraints

The present paper investigates problems of truss topology optimization under local buckling constraints. A new approach for the solution of singular problems caused by stress and local buckling constraints is proposed. At first, a second order smooth-extended technique is used to make the disjoint feasible domains connect, then the so-called ε-relaxed method is applied to eliminate the singular optima from problem formulation. By means of this approach, the singular optimum of the original problem caused by stress and local buckling constraints can be searched approximately by employing the algorithms developed for sizing optimization problems with high accuracy. Therefore, the numerical problem resulting from stress and local buckling constraints can be solved in an elegant way. The applications of the proposed approach and its effectiveness are illustrated with several numerical examples. Received May 2, 2000     

Detection of macular diseases in optical coherence tomography image

Vision decreasing and blindness are great threats to health, which can be caused by various kinds of macular diseases. Optical coherence tomography (OCT) is widely used in the diagnosis of macular disease. Ophthalmologists often need to check and analyse lots of OCT images and then give eye disease report for each image, which is time-consuming and inefficient. Thus, the automated classification method is necessary. In this paper, we proposed an approach to determine the status (normal or abnormal) of retina by OCT images. The proposed method can differentiate several kinds of macular diseases from normal image, including macular edema, macular hole and age-related macular degeneration. Besides the geometry features, our method takes advantage of two texture feature (local binary pattern histograms and histogram of oriented gradient) to improve the accuracy rate. The experimental results on a public available dataset demonstrate that our approach is effective and achieve higher accuracy (all accuracy >0.98, AUC can reach 1).

Flowchart of the proposed detection method.     

普通钻孔和定向钻孔联合预抽煤巷条带瓦斯研究

针对采用单一顺层普通钻孔或定向钻孔预抽煤巷条带瓦斯时存在普通钻机施工长钻孔易偏离轨迹、定向钻机施工成本较高等问题,以青龙煤矿21601掘进工作面为研究背景,提出了采用普通钻孔和定向钻孔联合预抽煤巷条带瓦斯。数值模拟结果表明:单钻孔预抽瓦斯时,抽采初期钻孔终孔位置处钻孔轴向瓦斯压力等值线呈“V”形分布,随着抽采时间延长,瓦斯压力“V”形分布逐渐平滑;钻孔径向瓦斯压力以钻孔为中心呈环状依次向外递增;预抽93 d时的有效抽采半径达3.80 m;普通钻孔和定向钻孔可分别有效控制煤巷两帮15 m和煤巷掘进工作面前方200 m范围内瓦斯。现场应用结果表明:普通钻孔和定向钻孔联合预抽时,瓦斯抽采总量平均值为19.86×10^3 m^3,瓦斯抽采体积分数平均值为53.5%,瓦斯抽采纯流量平均值为1.97 m^3/min,瓦斯抽采混合流量平均值为3.68 m^3/min,残余瓦斯含量小于8 m^3/t,瓦斯抽采效果良好。     

材料塑性应变对某钢制车轮残余应力测试的影响

针对车轮轮辋与轮辐组合焊缝附近结构的残余应力测试通常采用盲孔法,孔边由于应力集中易产生塑性变形的问题,采用有限元仿真与测试相结合的方法分析在钢制车轮加工的不同阶段,轮辋焊缝区残余应力测试时材料塑性变形对应变释放因数和残余应力测试结果的影响,并分析由Kirsch解析解确定的应变释放因数A和B计算车轮焊缝区残余应力测试所带来的误差.发现当孔边塑性变形较大时,用Kirsch解析解确定的应变释放因数计算残余应力会产生很大误差.     

A computer program to calculate the elastic stress and displacement fields around an elliptical hole under any applied plane state of stress

A short résumé is given of the solution to the plane elastic problem of an elliptical hole under uniaxial tension at any angle. The expression for the stresses and displacements, for both plane stress and plane strain, are explicitly given, and, by superposition of an applied stress at 90° to the first applied stress, any two-dimensional stress state can be simulated. A computer program is presented, enabling numerical values of stress and displacements for such stress states to be calculated on the free surface and at discrete points in the field for any ellipse, including the sharp crack.     

Prediction of cutting forces in 3-axes milling of sculptured surfaces directly from CAM tool path

In the present work a new approach for the modelling of milling is described. The cutting forces are calculated for milling operations directly from the tool path provided by a Computer Assisted Manufacturing program. The main idea consists in using tool position points coming from CAM data in order to calculate the local inclination angle of the generated surface and then the tool engagement in the machined material. A good approximation for global and local cutting forces can be obtained when an analytical model able to predict the cutting forces for 3-axes milling is used. Two approaches are proposed to calculate the local cutting forces to show the versatility of the method. The first method uses a thermomechanical approach using a Johnson & Cook constitutive law while the second is based on classical cutting coefficients. Some results are presented for wavelike form and free form machining tests and are compared with experimental data obtained in roughing and finishing of 42CrMo4 steel. Results are satisfactory and the capability of the method to predict the resultant surface roughness is shown.     

Smoothing finite-element and experimental hybrid technique for stress analyzing composites

A smooth two-dimensional numerical technique is presented for representing and differencing discrete moiré data. The concept extends a previous approach to enable simultaneous processing of both in-plane measured displacements and thereby obtain smooth displacement functions and continuous strains full-field. A cluster of positive definite functionals is formulated and minimized to best approximate the experimental data. This variational problem is solved by a finite-element method. Arbitrarily shaped regions can be fitted with relatively few elements, neither boundary displacements nor their derivatives need to be specified, and experimental data locations may occur in any configuration. Little experimental input data are needed, and the inherent smoothing reduces the effects of experimental scatter. The technique is particularly effective for determining shear strains, and/or strains along a curved line such as the edge of a geometric discontinuity. The method is demonstrated by the moiré strain analysis of a tensile composite plate containing a hole.     

Duabechies小波基梁单元的构造及应用研究

以Daubechies小波尺度函数作为单元插值函数，构造了一类小波基梁单元，由于采用节点挠度和转角作为单元自由度，单元连接和约束条件处理能够像传统单元一样方便地进行，从而使该小波基梁单元可有效地用于变截面、局部承载等复杂梁弯曲问题分析，数值算例表明，本文构造的小波基梁单元对不同约束条件、不同结构形式梁弯曲问题均有较高分析精度，为有限元方法提出了一种新的研究途径．     

CUG-2高精度钻参仪及其在深孔生产中的应用

详细介绍了CUG-2高精度钻参仪的组成和联机方法、主要功能、特点以及在山东乳山ZK43-1号深孔中的应用情况。实际应用表明,CUG-2高精度钻参仪不仅能够实时监测、显示和保存监测的钻探参数,还具有预测孔内事故和数据无线传输等显著优点,应用前景广泛。     

Micro-machining processes for microsystem technology

By means of experiments it could determined that micro-machining processes as grinding, drilling and milling are a good addition to the established production technologies in micro technology. To machine hard and brittle materials grinding with diamond tools is well suitable, but the kinematics of the grinding process, as well as the process strategy has a significant influence on the machined surface quality and the chipping of the edges. The study of micro-machining processes showed, that micro cutting processes are not just a miniaturisation of the conventional cutting technology. The reduced tool stiffness of micro drills caused by the changes of geometry requires an adjustment of the complete drilling processes. Sharp cutting edges are an essential requirement for the fabrication of very small structures. So, using single edged micro milling cutters made of diamond significant smaller structures could be made compared to using conventional milling cutters made of tungsten carbide. Furthermore, acoustic emission sensors proved to be suitable for detecting the tool position after a change of the tool with a high accuracy.     

Development of a monocular vision system for robotic drilling

Robotic drilling for aerospace structures demands a high positioning accuracy of the robot, which is usually achieved through error measurement and compensation. In this paper, we report the development of a practical monocular vision system for measurement of the relative error between the drill tool center point （TCP） and the reference hole. First, the principle of relative error measurement with the vision system is explained, followed by a detailed discussion on the hardware components, software components, and system integration. The elliptical contour extraction algorithm is presented for accurate and robust reference hole detection. System calibration is of key importance to the measurement accuracy of a vision system. A new method is proposed for the simultaneous calibration of camera internal parameters and hand-eye relationship with a dedicated calibration board. Extensive measurement experiments have been performed on a robotic drilling system. Experimental results show that the measurement accuracy of the developed vision system is higher than 0.15 mm, which meets the requirement of robotic drilling for aircraft structures.     

两级故障检测在SINS-Galileo-北斗组合中的应用研究

针对联邦滤波器子系统同时存在硬故障和软故障问题,提出一种适用于联邦滤波结构的两级故障检测方法。首先,构造联邦结构残差2χ检验法对系统硬故障进行检测,再用第k-m步未发生故障时的全局最优估计信息构造滑动残差检验函数,对未检测出的软故障进行时间积累,进而检测软故障,同时,联邦滤波信息分配系数根据软故障检测函数进行自适应调节。通过SINS-Galileo-北斗组合导航系统仿真对比分析了基于局部滤波残差2χ检验法和本文提出的故障检测方法,结果表明:该故障检测方法对系统硬故障和软故障具有较高的故障检测灵敏度,能够提高组合导航系统的可靠性。     

Optimal design of dynamically loaded reinforced concrete frames under displacement and rotation constraints

The paper deals with reinforced concrete beams and frames subjected to short-time, high intensity dynamic pressure. The shape and geometry of the structure and the layout of the longitudinal reinforcement are given and the areas of reinforcement are design variables.The determination of the plastic displacements and deformations caused by pressure is based on the plastic hinge theory and on the assumption that during the dynamic response the structure undergoes stationary displacements. The problem is to minimize the total amount of reinforcement such that the plastic displacements do not exceed the allowable displacements prescribed at certain points of the structure, or alternatively, that the plastic rotations in the plastic hinges do not reach the limits at which brittle failure occurs.A variational formulation of the problem is presented and the solution is based on the optimality criteria approach which requires an iterative procedure. A few examples illustrate the application of the method.     

Stress concentration around a part-through hole weakening a laminated plate

A quasi-three-dimensional-elasticity type theory, based on the assumptions of transverse inextensibility and layerwise constant shear-angle, is presented, in the context of an assumed quadratic displacement potential energy approach, for analyzing an edge-loaded laminated plate weakened by the presence of a part-through hole. Numerical results, obtained using the C°-type triangular finite element, indicate the existence of severe cross-sectional warping in the vicinity of the hole and plate boundaries. Furthermore, the three-dimensional nature of the stress concentration factor in the neighborhood of the hole boundary is clearly exhibited. Besides, very high stress concentration factors are found in the layer weakened by the part-through hole. The numerical results presented should serve as bench-mark solutions for future comparisons.     

Computer-aided generation of nonlinear reduced-order dynamicmacromodels. I. Non-stress-stiffened case

Reduced-order dynamic macromodels are an effective way to capture device behavior for rapid circuit and system simulation. In this paper, we report the successful implementation of a methodology for automatically generating reduced-order nonlinear dynamic macromodels from three-dimensional (3-D) physical simulations for the conservative-energy-domain behavior of electrostatically actuated microelectromechanical systems (MEMS) devices. These models are created with a syntax that is directly usable in circuit- and system-level simulators for complete MEMS system design. This method has been applied to several examples of electrostatically actuated microstructures: a suspended clamped beam, with and without residual stress, using both symmetric and asymmetric positions of the actuation electrode, and an elastically supported plate with an eccentric electrode and unequal springs, producing tilting when actuated. When compared to 3-D simulations, this method proves to be accurate for non-stress-stiffened motions, displacements for which the gradient of the strain energy due to bending is much larger than the corresponding gradient of the strain energy due to stretching of the neutral surface. In typical MEMS structures, this corresponds to displacements less than the element thickness, At larger displacements, the method must be modified to account for stress stiffening, which is the subject of part two of this paper