1,720,962 research outputs found
A STUDY OF VISION-BASED MEASUREMENT OF WELD JOINT SHAPE INCORPORATING THE NEURAL-NETWORK
No full textVisual sensing of the surface geometry is often necessary to inspect and evaluate the quality of welded joints as well as to sense the transient distortion of a structure during welding for the feedback of its current geometry. This investigation presents a simple and non-contact digitization method of the vision-based system for measuring the three-dimensional surface geometry of the object distorted by welding. Its basic principles are based on the equation derived from the geometric optics, for which the illumination of the laser beam was controlled in the form of the projected plane. This method utilized a 10 mW He-Ne laser for the structured light and a charge coupled device (CCD) camera as the vision sensor. When the laser stripe is projected on to the weldment, a minute deviation from the perfect plane existing on the specimen surface causes a distortion of the stripe. The shape and amount of the weldment distortion can be then calculated by analysing the distorted laser stripe. In this study, a neural network was proposed and implemented for recognizing the laser stripe features from the image plane. A calibration scheme of corresponding an image to the world position was also adopted for determining the sectional features of the welding distortion. The feasibility of determining the welding distortion by the proposed vision-based system was demonstrated through the experiments with various types of specimen
An analysis of thermal stress and distortion in bead-on-plate welding using laminated isotropic plate theory
No full textIn this study, thin-plate bending theory using the assumption of small deflection has been adopted for a two-dimensional analysis of the thermo-elasto-plastic behavior of plates in welding to overcome some difficulties arising from a fully three-dimensional approach. For simulating the temperature gradient through the plate thickness, the concept of a layered plate has been proposed, and the thermo-elasto-plastic behavior of the plate during GMA bead-on-plate welding analyzed by using the finite-element method. It was revealed that the suggested method can predict the trend of welding distortions quite satisfactorily
A STUDY OF THE EFFECT OF PRE-STRAINING ON ANGULAR DISTORTION IN ONE-PASS FILLET WELDING INCORPORATING LARGE-DEFORMATION THEORY
No full textBy using the finite element method based on the large deformation theory, the effect of pre-straining on angular distortion of one-pass fillet weldments was analysed for the free-end and constrained-end condition. Pre-straining by an additional concentrated load caused a large thermal deformation during heating, and reduced the reverse distortion during cooling and consequently the residual distortion. Geometric change of the fillet weldment caused by pre-straining during welding induced an initial stress effect on the stiffness to the further deformation, which is due to a developed in-plane stress. This initial stress effect could be considered in the large deformation theory to be based on the updated Lagrangian method, while it could not in the small deformation theory. As the pre-straining load increased in the free-end condition, the initial stress effect also increased. In the constrained-end condition, the initial stress effect played an important role in the deformation of the fillet weldment, even without pre-straining. By comparing the results predicted by the large deformation theory with those by the small deformation theory and experiments, it can be shown that the large deformation theory is able to describe the distortion phenomenon in fillet welding reasonably well.
A STUDY OF MECHANICAL-STRESS RELIEF (MSR) TREATMENT OF RESIDUAL-STRESSES FOR ONE-PASS SUBMERGED-ARC WELDING OF V-GROOVED MILD-STEEL PLATE
No full textThe heat-transfer and thermal stress distributions in one-pass submerged arc welding (SAW) were numerically determined using the finite element method (FEM) for a V-grooved rectangular steel plate in which the weld preparation was filled during welding. A two-dimensional non-linear heat-transfer analysis was performed for a transverse section of the plate. This was followed by a thermo-elasto-plastic transient thermal stress analysis, assuming plane strain to be constant for the same model section. The same stress model was used to simulate a mechanical stress relief (MSR) treatment of the plate. This has frequently been used in the fabrication of large pressure vessels instead of post-weld heat treatment (PWHT). In this way its effect in reducing the residual stress in the welded plate was investigated. MSR was simulated by enforcing a constant displacement loading in the welding direction. The solution of the thermal stress analysis showed that it was possible for the residual stress around the weld centre to be accurately estimated by accurate modelling of the dilution of the filler metal in the fused zone of the base metal. The conclusion derived from the MSR simulation was that it could quantitatively predict the effect of reducing the residual stress in the welded plate. Only limited experimental data were available. The mechanism of stress reduction was plastic straining in regions of high residual stress. The amount of stress reduction at the weld centre had a linear relationship to the magnitude of the external stress relieving load. The numerical results for the MSR simulation agreed fairly well with experimental ones obtained from the MSR test performed on a welded plate
Accurate Three-Dimensional Scattering Center Extraction for ISAR Image Using the Matched Filter-Based CLEAN Algorithm
No full textThree-dimensional (3-D) scattering center models use a finite number of point scatterers to efficiently represent complex radar target signature. Using the CLEAN algorithm, 3-D scattering center model is extracted from the inverse synthetic aperture radar (ISAR) image, which is generated based on the shooting and bouncing ray (SBR) technique. The conventional CLEAN extracts the strongest peak iteratively based on the assumption that the scattering centers are isolated. In a realistic target, however, both interference from the closely spaced points and additive noise distort the extraction process. This paper proposes a matched filter-based CLEAN algorithm to improve accuracy efficiently. Using the matched filtering of which impulse response is the known point spread function (PSF), a point most correlated with the PSF is extracted. Thus, the proposed method optimally enhances the accuracy in the presence of massive distortions. Numerical simulations using canonical and realistic targets demonstrate that the extraction accuracy is improved without loss of time-efficiency compared with the existing CLEAN algorithms.
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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