查看更多>>摘要：In this study, several Algebraic Reconstruction Technique (ART) algorithms are used to construct the 3 D sliced images from several transparent X-ray images. The speed and quality of image reconstruction are two important requirements when doing the inspection in a printed circuit board (PCB) assembly line. . To fulfill the requirements, several methodologies are discussed. The image qualities of regular ART method, binary ART method and Mixed ART method are developed and compared. The binary ART method uses the property of x-ray absorb rate of metal. silicon and other non- metal material are extremely different. The absorb rates of non-metal part are assumed to be zero and metal parts are assumed to be a single value. By using this method the quality of image reconstruction is improved. The mixed ART method is the combination of the tradition ART method and binary ART. Due to the X-ray sensor's framing time, a method to improve the image reconstruction quality due to effect of X-ray sensor framing time is also discussed. Finally, the best solution algorithm is found to be mixed binary steering ART when consider the signal noise of X-ray detector.
查看更多>>摘要：Three-dimensional DEFORM™ finite element simulations are performed to analyze the plastic deformation of heterogeneous sandwich sheets during rolling. The finite element code is based on a rigid-plastic model and the simulations assume that the rollers are rigid bodies and that the deformation-induced change in temperature during rolling is sufficiently small to be neglected. The rolled product is assumed to comprise a central sheet of either A3003 or A6063 aluminum alloy sandwiched between upper and lower sheets of A1100 aluminum alloy. The simulations examine the effects of the sheet thickness and reduction ratio on the maximum effective stress, maximum effective strain, Y-direction load, and maximum damage induced within the rolled product. The simulation results for the final thicknesses of the three layers in the rolled sandwich sheet are compared with the experimental measurements. Overall, the results presented in this study provide a useful insight into the deformation mechanisms involved in the rolling of heterogeneous sandwich sheets.
查看更多>>摘要：In this paper the computer implementation of the nonlinear recursive formulation in multibody dynamics systems is described. The organization of the computer algorithm which is used to automatically construct and numerically solve the system of loosely coupled dynamic equations expressed in terms of the absolute and joint coordinates is discussed. The inertia projection schemes used in most existing recursive formulations for the dynamic analysis of deformable mechanisms lead to dense coefficient matrices in the equations of motion. Consequently, there are strong dynamic couplings between the joint and elastic coordinates. By using the inertia matrix structure of deformable mechanical systems and the fact that the joint reaction forces associated with the elastic coordinates do represent independent variables, a reduced system of equations whose dimension is dependent of the number of elastic degrees of freedom is obtained. This system can be solved for the joint accelerations as well as the joint reaction forces. The multibody flexible four-bar system is used as an example to demonstrate the use of the procedure discussed in this paper.
查看更多>>摘要：Optical fiber sensors have a number of advantages over conventional electronic sensors such as light weight, small diameter and immunity to electromagnetic interference. Despite all the advantages of optical sensors, one must recognize that optical fibers are foreign entities to the host structure, therefore will induce stress concentration in the vicinity of the embedded sensor. As an optical sensor is embedded between plies, a lenticular resin pocket exists in the composite plies. The resin pocket acts as a crack-like region, and can form the site of the initiation of the delamination under mechanical loads. In this investigation, the geometry of the lenticular resin pocket around the optical sensor is derived basing on the principal of minimum potential energy. It shows that the geometry of the resin pocket is dependent on the stiffness of the plies, the stacking sequence, the diameter of the optical fiber and the curing pressure. The stress distributions in the resin pocket and in the laminated composites are obtained by using the finite element method. The numerical results demonstrate that the stress increases rapidly in the vicinity of the optical fiber sensor, causing a high stress concentration factor. The high stress field may produce delamination and fracture in the composite.
Han Sang-MookGuo Yi-HongWu Xiang-GuoGuo Qing-Yong...
297-300页
查看更多>>摘要：This paper presents a numerical simulation of quasi-brittle fracture in UHPFRC I-beam as a linear complementarity problem. Based on the investigation of Tin-Loi and Attard, the simulation of quasi-brittle fracture in concrete has been extended to model UHPFRC I-beam by including a tensile hardening. Fracture is simulated through a hardening-softening fracture constitutive law in tension and a softening fracture constitutive law in shear at the boundary nodes, with the material within the triangular unit remaining linear elastic. LCP is used to formulate the path-dependent hardening-softening behavior in non-holonomic rate form. The good matching of test results and numerical results indicates the effectivity of this method.
查看更多>>摘要：In order to measure forest inventory, we propose an approach that enables automatic, fast and accurate tree trunks segmentation from three-dimensional (3-D) laser data. Results have been demonstrated in real-time on-board a round mobile robot. At the same time, we propose an approach to estimate tree diameter at breast height (dbh) that was tested off-line on a variety of ground laser scanner data, so it is very suitable for being popularized in forestry section.
查看更多>>摘要：An object has to be measured to recover its 3D shape in reverse engineering applications. The object surface is sampled point by point using a fringe projection. The method of least squares is used to match overlapping surfaces to estimate transformation parameters between a local coordinate system and the template coordinate system. The Gauss-Markoff model can minimize the sum of squares of Euclidean distances between surfaces for matching arbitrarily oriented 3D surface patches. This research uses the least squares method for the registration of point clouds. A relief example shows the feasibility of the proposed method. It takes about 4 seconds for the registration of 1531209 points with the error less than 0.03mm, and the iteration number is only 20. The surface profile is complete and smooth after the registration, which can meet the requirement of surface reconstruction.
查看更多>>摘要：This paper presents the 3D CFD computation of an 800mm diameter model of MCT based on structured grids, RANS equations and turbulence model. A time-accurate, upwind, finite volume method for computing compressible flows on structured grids is presented. Numerical predictions for a series of blade pitch angle settings and speeds are compared with the other simulation results of commercial software, verified by the experimental measurement of the model. Such results provide confidence in using the CFD computation tools to develop the forthcoming design of MCT.
查看更多>>摘要：The optimization of pass parameters is an important step in skew rolling design. In order to meet the demands of secondary refining process in continuous casting, on the basis of the practical experience of two-groove skew rolling for steel ball, and by means of the theory of two-groove skew rolling design ,the optimization of two-groove pass parameter for 021.6 mm Aluminum ball, a kind of additive in secondary refining process, is realized. The optimized pass parameters arc used in the rolling die design, and the corresponding experiments indicate that the projects of optimized pass parameters are feasible, and the efficiency of two-groove skew rolling is twice as large as that of one-groove.
查看更多>>摘要：The paper aims at attacking and noise problems of high spot open-closed gripper mechanism in printing machine in a high speed situation. The analytical method of dynamic performance is presented based on the relative motion, the absolute motion, and the mechanical model. And the analytical equations are established. Then, the dynamic performance of a practical mechanism from XINJI Company is analyzed by the proposed method. The drawbacks of dynamic performance are pointed out that the acceleration and apparent force had jumps in the running process. Finally, on the basis of existed problems, dynamic performance is modified by means of structural design of cam. The analytical results show that the angular acceleration's peak value of improvement mechanism has been decreased by 62%. Besides, the modified mechanism also expresses an excellent dynamic performance as the flat curve of acceleration, apparent force, contact force and hinge force.
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