Papers by Keyword: Laser Shock Processing (LSP)

Abstract: A plasma sound wave detection method of laser shock processing (LSP) technology is proposed. Speciments of Ni-base superalloy are used in this paper. A convergent lens is used to deliver 1.2 J, 10 ns laser pulses by a Q-switch Nd:YAG laser, operating at 1 Hz. The influence of the laser density to the shock wave is investigated in detail for two different wavelength lasers. Constant amplitude fatigue data are generated in room environment using notch specimens tested at an amplitude of vibration 2.8 mm and first-order flextensional mode. The results show that LSP is an effective surface treatment technique for improving the high cycle fatigue performance of Ni-base superalloys having a factor of 1.62 improvement in fatigue life.

Abstract: Fatigue tensile treatment was performed on 00Cr12 heat-resistant steel specimens which had been treated by laser shock processing (LSP). The unilateral tolerance factor statistical analysis method and the two-dimensional Weibull distribution method were used to predict the values of fatigue safe lives of the specimens respectively. The results indicate that the fatigue lives of 00Cr12 specimens were enhanced greatly after LSP, and improved by 62% compared with the specimens which were not treated by LSP. The unilateral tolerance factor method obtained an exact estimation value of the fatigue safe life; while the two-dimensional Weibull distribution method can get a range of values of fatigue safe lives, the fatigue safe lives of the specimens which after LSP were a range from 116570 to 150230, the average value was 132330. The two-dimensional Weibull distribution method has more engineering applicability and can be used to estimate the fatigue safe lives with fewer experiments.

Abstract: The heat-resistant steel after aluminized was treated by laser shock processing (LSP) with high power Nd:YAG laser, and then was tensile tested at 400°C. The effects of the high-temperature behavior after LSP were analyzed from residual stress and fracture organization. The results showed that the yield strength and tensile strength of heat-resistant steel after aluminized were improved obviously during the tensile testing at high temperature, and the High-temperature fatigue life of 00Cr12 with composite processing was enhanced vastly. Compared with the LSP, the High-temperature fatigue life of 00Cr12 heat-resistant steel by aluminizing and LSP had a larger increase.

Abstract: Experiments were performed to study the influence of light leakage from Q-switched laser on laser-induced shock wave. Through changing the voltage applied on the Q switch crystal and the delay time between opening Q switch and triggering laser pumping source, different amount of light leakage can be obtained. It is ascertained that longer-pulse light leakage from Q-switched laser is responsible for the second weaker pressure signal appearing on the tested pressure waveform. The results show that the leakage energy not only has not beneficial effects on laser shock processing, but also will weaken the main pressure wave.

Abstract: In order to study the dynamic response of metal of laser shock processing, dynamic strain curves of AM60 Magnesium alloy during laser shock processing were measured by resistance strain gauges. Dynamic strain curves of three equiangular rosette near the shock spot and three strain gauges of different distances from the spot center were studied. The results indicated that the strain rate of AM60 Magnesium alloy decreased and plastic deformation increased with increasing impact times. And one dimensional strain hypothesis of laser shock processing was reasonable.

Abstract: In this paper, the microstructure and hardness of Ti-5Al-2Sn-2Zr-4Mo-4Cr titanium alloy with and without laser shock peening (LSP) were examined and compared. The titanium alloy samples were laser shock peened with different layers at the same power density. The microscopic structure after LSP are tested and analyzed by SEM and TEM. The results indicated that LSP changed the microstructure evidently. After 3 layers laser shock peening, there are nanocrystallization in the LSP zone. The shock wave provided high strain rate deformation and generated high-density dislocations in the material. Multiple severe plastic deformation caused by 3 to 5 LSP layers helped to rearrange the resultant dislocation, to form dislocation networks, leading to the formation of nanocrystallites. On the other hand, the microhardness across the polished surfaces of the titanium materials with and without LSP was measured. It is obvious that the laser shock peening improved the microhardness of the Ti-5Al-2Sn-2Zr-4Mo-4Cr for about 16% at the surface, and the affected depth is about 300 microns from the surface.

Abstract: The application of two representative laser surface treatments technologies which are laser shock processing technology and laser coating treatment technology are described. The application of laser shock processing in the fields of aero engine disc, wing panel formation, structural welding and strengthening, nuclear power station pressure container strengthening etc and also evaluates the effects are analyzed. The applications of laser coating treatment in the field of aeronautic manufacturing are analyzed in detail. The development direction of laser shock processing and laser coating treatment are indicated finally.

Abstract: Laser shock processing (LSP) is an innovative surface treatment technique. According to the theory of residual stress field formation by laser shock wave, laser overlapping shock processing of LY12CZ aluminium alloy was analyzed. The diagonal shock process is simulated by FEM using LS-DYNA codes, and the residual stress field in different angle of fall and pressure are predicted. The results indicate that the value of residual tension stress can be increased when diagonal shock, and the value of residual compressive stress will be decreased. The simulated results can provide the basis for experimental studying the diagonal laser shock processing and laser facular overlap.

Abstract: The influence of different parameters of laser shock processing applied to a precipitation-hardened aluminium alloy 6082-T651, on residual stress, surface tophraphy and microhardness was investigated. Processing was performed with an innovative Nd:YLF laser with the power densities of 2 and 4 GW/cm², with a uniform pulse duration of 18 ns. Laser shock processing experiments were performed with the closed ablation method to ensure a higher shock-wave pressure. In the first phase, the study was focused on an evaluation of surface topography, with the record of the surface roughness profile and with the surface evaluation at a scanning electron microscope JEOL JXA-8600M. Then followed measurement of microhardness HV_0.2 in the cross section region. In the second phase comparison of residual stresses which were measured using the X-ray diffraction, was performed. Laser shock processing turned out to be a very efficient technique to improve surface properties. On the basis of the micro plastic deformation induced by shock waves, an increased dislocation density in the specimen surface was obtained. The gradient of dislocation piling through the specimen depth improved the variation of microhardness and residual stresses, which, in turn, improves fatigue strength of the material under dynamic loading.

Abstract: In order to improve the fatigue strength of TC4, Nd:Glass pulse laser was used to impact the surface of cylindrical specimens, X-ray stress analyzer was used to test the residual stress distribution of treated area, the laser shock processing on different ratio (η) between the diameter of specimens and laser spot were simulated with ANSYS at the same time. The numerical simulation results were well agreement with experimental data. The results indicate that the different η mainly affect residual stress distribution along the circumferential direction. Contrarily, it has few effects on longitudinal direction and in-depth direction.