1,721,263 research outputs found
Unidirectional Excitation Technique for Complex Modal Testing of Asymmetric Rotro Systems: Application to DTG
No full textA STUDY ON WELD POOL MONITORING IN PULSED LASER EDGE WELDING
No full textEdge welding of thin sheets is very difficult because of the fit-up problem and small weld area In laser welding, joint fit-up and penetration are critical for sound weld quality, which can be monitored by appropriate methods. Among the various monitoring systems, visual monitoring method is attractive because various kinds of weld pool information can be extracted directly. In this study, a vision sensor was adopted for the weld pool monitoring in pulsed Nd:YAG laser edge welding to monitor whether the penetration is enough and the joint fit-up is within the requirement. Pulsed Nd:YAG laser provides a series of periodic laser pulses, while the shape and brightness of the weld pool change temporally even in one pulse duration. The shutter-triggered and non-interlaced CCD camera was used to acquire a temporally changed weld pool image at the moment representing the weld status well. The information for quality monitoring can be extracted from the monitored weld pool image by an image processing algorithm. Weld pool image contains not only the information about the joint fit-up, but the penetration. The information about the joint fit-up can be extracted from the weld pool shape, and that about a penetration from the brightness. Weld pool parameters that represent the characteristics of the weld pool were selected based on the geometrical appearance and brightness profile. In order to achieve accurate prediction of the weld penetration, which is nonlinear model, neural network with the selected weld pool parameters was applied
Automatic seam tracking and weld pool monitoring in laser welding by using a laser vision sensor
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Wave propagation, reflection and transmission in non-uniform one-dimensional waveguides
No full textWaves can propagate freely without reflection in a certain class of non-uniform one-dimensional waveguides even though the properties of the waveguide vary rapidly. In these cases, the amplitude of the wave changes as a function of position but the power associated with the wave is preserved along the waveguide as in uniform waveguides. A generalised wave approach based on reflection, transmission and propagation of waves is used for the analysis of such non-uniform waveguides. The positive- and negative-going wave motions are separated so that the problem is always well-posed. Examples include longitudinal motion of bars and bending motion of Euler–Bernoulli beams, where the cross-section varies as a power of the length. The energy transport velocity, which is the velocity at which energy is carried by the waves in these waveguides, is derived using the relationship between power and energy. It is shown that this energy transport velocity depends on position as well as frequency and differs from the group velocity. Numerical results for wave transmission through a rectangular connector with linearly tapered thickness and constant width are obtained in a straightforward manner without approximation errors and at a low computational cost, irrespective of frequency
Transient Microstructural Evolution of Infrared Brazed Fe3Al Intermetallics Using Aluminum Foil
No full textWave propagation, reflection and transmission in curved beams
No full textWave motion in thin, uniform, curved beams with constant curvature is considered. The beams are assumed to undergo only in-plane motion, which is described by the sixth-order coupled differential equations based on Flügge's theory. In the wave domain the motion is associated with three independent wave modes. A systematic wave approach based on reflection, transmission and propagation of waves is presented for the analysis of structures containing curved beam elements. Displacement, internal force and propagation matrices are derived. These enable transformations to be made between the physical and wave domains and provide the foundation for systematic application of the wave approach to the analysis of waveguide structures with curved beam elements. The energy flow associated with waves in the curved beam is also discussed. It is seen that energy can be transported independently by the propagating waves and also by the interaction of a pair of positive and negative going wave components which are non-propagating, i.e. their wavenumbers are imaginary or complex. A further transformation can be made to power waves, which can transport energy independently. Numerical examples are given to illustrate the wave approach. The first concerns power transmission and reflection through a U-shaped connector between two straight beams while the second concerns the free vibration of finite curved beams where results are compared to other published results
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