Advanced Materials Research Vols. 189-193

Abstract: Simulation of two-dimensional (2D) transverse laser cooling of Cs atomic beam from pyramidal magneto-optical trap atom funnel (PMOTAF) conceived for atom lithography is presented. The results show that both the minimum full width at half maximum (FWHM) and the maximum peak value of the spatial profile of the atomic beam occur at the frequency detuning of optical molasses equals to -0.5 Г. Moreover, for each frequency detuning, an increase in the intensity of the optical molasses leads to smaller FWHM and higher peak value. The not negligible role of gravity on the atomic beam of sub-thermal longitudinal velocity along the horizontal direction is that every atomic trajectory possesses a parabolic motion either before or after laser cooling which leads to a noticeable displacement of the peak value at the observation plane with respect to the starting point.

Abstract: Mismatch is one of the main defects of tailor welded blanks(TWB), and leveling technology is a new method which can solve this problem. The structures, force analysis and flange morphology of the leveling mechanism are studied in this paper, and a three-dimensional prototype is designed. The results have practical significance for improving welding quality of TWB.

Abstract: For the extremely weak echo signal and the poor anti-interference ability of the long-distance laser fuze, the high signal noise ratio (SNR) receiving system based on laser coding mode was designed. In order to improve the weak signal receiving ability, the avalanche photodiode (APD) with high sensitivity, low noise and high gain was adopted. And the optimum multiplication factor of APD when the system obtains the highest SNR was analyzed and calculated. Then, the amplifying circuit optimum matching with APD and the decoding circuit were designed, and validated by the experiments. The theory and experiment results indicate that the design is efficiency and capable to the long distance laser fuze, the system can exactly decode the weak laser coding signals received and export the ignition signal.

Abstract: Laser combined machining is a complex machining method which utilizes the combined effect of various forms of energy to achieve a material processing. High manufacturing quality and surface accuracy, and machining efficiency can be achieved. The research progress in the area of laser combined other machine processes is reviewed. Several methods of laser combined machining are introduced and their characteristics and applications from the point of the laser assisted liquid machining are investigated. For example, laser assisted wet etching and laser assisted jet electrochemical machining, and waterjet-guided laser machining are reported. The experimental and theoretical studies of the technologies to improve the machining performance are discussed. Finally, the existing problems and the future research directions of the laser compound processing are put forward .

Abstract: Laser shock processing (LSP) is a new technique for surface strengthening of fastener holes. The process of LSP before hole-drilling was adopted. A finite element model was established to study the effects of laser shock parameters on the residual stress field of aluminum alloy7050T7451 with Fastener Holes. The results indicate that increasing the laser power density until a fixed value results in a large peak in the hole-edge surface residual compressive stress. The hole-edge surface residual compressive stress and the depth of residual compressive stress are both increased with the increase of laser pulse width. Multiple laser shock processing can improve the residual compressive stress greatly, and with the increasing number of shot, the strengthening effect is gradually diminished.

Abstract: Short pulse lasers, including picosecond laser and femtosecond laser are involved to investigate the ablation characteristics of processing carbon fiber reinforced plastics (CFRPs). The ablation threshold of the femtosecond laser, 0.453 J/cm², is twice higher than that of the picosecond laser 0.867 J/cm², since the former generates an intense and shorter pulse and the atoms excitation and multi-photon absorption may occur as short as 10 ps or less. The ablation test also describes the processing qualities, where the femtosecond laser has processing abilities without visible thermal defects or charring over the picosecond laser.

Abstract: Characteristics of CO₂ laser welded 1000 MPa grade Transformation Induced Plasticity steel plate were investigated under different welding power, welding speed and shield gas. Decreasing welding power, increasing welding speed or using mixed shield gas (Ar+He) all reduced the porosity in the weld metal (WM). The weld metal and HAZ near the WM had maximum hardness. In tensile strength test of load perpendicular to the weld axis, the specimens had same tensile properties as that of the raw material. For the load parallel with the weld axis, the specimens prepared with Ar had equal yield strength (YS) and tensile strength (TS) to that of the raw material. But the elongation was lower than that of the raw material. The specimens prepared with shield gas He had higher YS, TS and lower elongation compared with that of the raw material. The welded joint had lower formability than that of the raw material. The formability of specimens prepared with low welding power or mixed shield gas Ar+He was improved compared with that of the specimens prepared using high power or single shield gas Ar.

Abstract: A theoretical investigation of 52Cr atomic beam in optical traps was reported, the Doppler and sub-Doppler laser cooling forces were discussed and some characteristics of these forces were shown based on the semi-classical theory. The simulative results indicate that the atomic beam can be collimated by these laser cooling forces, especially by sub-Doppler laser cooling force.

Abstract: Laser micro-adjustment as application of laser forming is a contact less and easily automated technology able to cause very small changes in shape to achieve high accuracies. In this study, a method using dual heating is introduced to reduce the temperature gradient across the thickness during laser micro-adjustment of actuators. The temperature field and deformation behavior using dual heating method are analyzed using a 3D finite element model. The in-plane angles are compared between using single heating and dual heating and the numerical results show that the in-plane angle using dual heating method can be predicted by the results by single heating.

Abstract: Laser shock processing is a technique similar to shot peening that imparts compressive residual stresses in materials for improved fatigue resistance. Finite element analysis techniques have been applied to predict the residual stresses from Laser shock processing. The purpose of this paper is to investigate of the different sheet thickness interactions on the stress distribution during the laser shock processing of 7050-T7451 aluminum alloy by using the finite element software. The results indicate that the sheet thickness has little effects on the compression stress in the depth of sheet, but great impacts on the reserve side.