Papers by Keyword: Laser Shock Wave

Abstract: Laser shock wave oscillation caused by lateral inertia effects of Hopkinson bar in large-diameter SHPB apparatus, and the geometry dispersion effect, particularly, the rise time of the stress wave in different diameters and lengths of Hopkinson bar were investigated. The three-dimensional model of member bar is established by the finite element analysis software ABAQUS, and the different shapes pressure pulses including rectangular, triangular and Gaussian pulses induced by laser shock have been loaded on the end face of the bar, respectively. Results indicate that the triangle pressure pulse and Gaussian pressure pulse show less dispersion effect than rectangle stress pulse on wave shape, and Gaussian stress pulse can keep the morphology better and reduce the dispersion effect more effectively than triangle stress pulse in the propagation process. In addition, as the bar diameter increases and the distance of the propagating stress wave raises, wave oscillation enhances significantly in the bar, the same as the rise time of stress wave increases gradually and the maximum stress also has a certain degree of attenuation, which have influence on laser shock processing or forming.

Abstract: A new driven pattern is proposed in this paper, which is based on laser shock wave and outstand in high energy efficiency, remote control, wireless and directionality. We describe the working principle of the laser shock wave driven pattern in detail. Furthermore, by a copper irradiated cantilever beam, the vibration state driven in different laser conditions is investigated with simulation and experiment, corresponding numeral analysis is performed to assess the driven effect.

Abstract: This paper proposes a novel approach for micropump driven, namely laser shock wave, with the advantages of high energy efficiency, remote control and wireless energy supply. The pump used here has the characteristics of simple structure, easy fabrication and low cost comparing to the traditional micropump. Firstly, a valveless micropump was designed and then manufactured through lithography and bonding. Secondly, modal analysis of the fluid-structure coupling system, i.e. micropump, was calculated, and the first natural frequency was chosen as the frequency of the laser pulse. Finally, experiments were done to validate the feasibility of the driving mode. Results show the new driving mode works well and may provide an alternative approach for microsystem driven.

Abstract: The liquid confinement medium (LCM) and the free confinement medium (FCM) made by ourselves were used as confinement overlays of laser shock processing (LSP) respectively, stainless steel 304 was shocked by Nd:Glass laser. The parameters of LSP are the wavelength of 1.06μm, the pulse duration of 20ns, and output energy of 35~40J. The laser was focused on a spot of Ф5mm. Firstly, the profiles of shocked regions of samples were measured by Taylor Hobson admeasuring apparatus, in which two different confinement mediums are used by LSP. Secondly, the ruinous behavior of the free confinement overlays induced by laser shock wave is observed and analyzed. Analyzed and compared with the experiments results, it is discovered that the effects of LSP are different with using different confinement mediums.

Abstract: In order to improve electrical properties, annealed ZnO varistor ceramics have been treated by laser shock processing (LSP). Electrical parameters of the annealed ZnO varistor ceramics were measured by CJ1001 Varistor Tester. Morphology and microstructure of the annealed ZnO varistor ceramics were gained by XRD and SEM. The results indicate that compared with the electrical properties of the annealed ZnO varistor ceramics, the voltage gradient of the ZnO varistor ceramics treated by LSP remains the same, the nonlinear coefficient substantially increases by 31.6%, and the leakage current reduces by 33.3%. Meanwhile, the phase composition of the annealed ZnO varistor ceramics is mainly composed of ZnO main phase, Zn_2.33Sb_0.67O₄, β-Bi2O3, and δ-Bi₂O₃ phase; while the phase composition of the ZnO varistor ceramics remains the above four phases in the compound state (anneal and then LSP), but the content of δ-Bi₂O₃ phase increases. The increase of δ-Bi₂O₃ phase content is the main reason for improving the electrical properties of the annealed ZnO varistor ceramics.

Abstract: The large area delaminated (two layers) and non-delaminated samples of 1mm-thick aluminium alloy 2024 were shocked by pulse laser, the restricted layer and the absorbing layer were coated on the surface of the samples, and the PVDF sensors were set on the facing of a quilt of the samples. The signs of laser shock waves were transmitted to the computer by the oscillograph. The results indicated that can be effective detected by laser shock waves, and the math model of hierarchical sheet-metal by laser shock wave was fundamentally developed. A new method to detect the large area delaminated samples was provided, which has the definite engineering importance.

Abstract: The marking system by laser shock wave (LSW) based on liquid crystal mask, which differs entirely from marking by laser ablation (or laser thermal effect), was established. Two-dimension (2D) nondestructive markings based on liquid crystal mask were prepared by LSW, and the distribution of residual stresses in laser-shocked region was measured and analyzed. The results showed that tensile residual stresses of sample surface were converted into compressive residual stresses by LSW, which is a nondestructive marking for aviation key parts.

Abstract: The present paper treats results of laser shock processing applied to a precipitationhardened ENAW 6082-T651 aluminium alloy. Processing was performed with a Nd:YLF-yttrium lithium fluoride crystal laser with power densities of 2 and 4 GW/cm2, producing a pulse of 18 ns. Laser shock processing experiments were performed with the closed ablation method, the application of an ablative coating and a transparent tamping medium to obtain a higher shock-wave pressure. In the first phase, the surface study focused on the record of surface profile with a roughness gauge and on an evaluation of surface topography at a scanning electron microscope. In the second phase, residual stresses were measured using the relaxation hole-drilling method at a processed specimen surface. Then followed measurement of microhardness in the cross section. The hardening results obtained were evaluated on the basis of variations of residual stresses and of microhardness, and of macro and microstructural changes of the surface, i.e. the surface layer. The purpose of processing was to improve fatigue strenght and, consequently, extend the life of a machine component in operation.

Abstract: Traditional forming process of sheet metal is realized with Die and Mould, this technique lacks flexibility and used in the Volume production. The forming process of sheet metal based on laser shock waves is a novel and developing technique. Laser shock forming (LSF) and Laser peen forming (LPF) are two different forming process of sheet metal, both of them are based on a mechanical effect of shock waves induced by laser. In this paper, after introducing the mechanism of laser shock wave generating, these two forming process and technique feature are analyzed and compared, some research progresses are presented. It is indicated that forming technique based on laser shock waves are of high-flexible and great potential application in the fields of plastic forming of sheet metal.