Study Of Laser-driven Shock Wave Propagation In Layered Material

Film-substrate material is the most simple and common layered composite material.It is important to study the process of laser-induced shock wave(LSP) transmitting through this kind of materials. The results are helpful for guiding the selection of laser shock parameters, the setting of layered material and the prediction of the impact effect.In this paper, laser-induced shock wave has been researched through the experimental test and numerical simulation. The main contents are as follows.(1) Selecting "aluminum film- copper substrate" and "copper film- aluminum substrate" as the shocked targets. The laser induced shock wave on the back of the targets were detected using PVDF piezoelectric sensor. The relationship between the measured electrical results and the actual pressure were explained in detail.The results show that the inner interface between the film and the substrate affect the transmitted shock wave significantly. The pressure obtained from the film-substrate structure is obviously lower than that of the single-layer material with the same thicknesses. It takes longer time for the pressure to evolve into the stationary state for the film-substrate structure, and in this kind of material the transmitting processes are characterized as an oscillatory loading process.(2) Laser-induced shock wave's propagation properties in the film-substrate structure material and its impact on film-substrate bonding strength were studied systematically based on ABAQUS software. In the numerical simulation, the film-substrate structure models with different acoustic impedance matching modes were established and the film thickness was changed. The stress distribution along the depth direction at different times, the convex morphology of films, the maximum stress value and duration of different thickness films were all analyzed carefully. The results show that, when the acoustic impedance of the film is weaker than that of the substrate,tensile stress at the interface between the film and substrate can be avoided by covering appropriate constraint layer on the film surface. In this case, the bonding strength will not be weakened and the material surface properties are enhanced. When the acoustic impedance of the film is bigger than that of the substrate,whether the laser shock processing is appropriate will depend on your processing purposes. When the stress is unavoidable, choices of material thickness should be cautious. Not only the strengthening effect of the material surface should be taken into account, but also the tensile stress at the interface between the film and substrate should be reduced.(3) The model of "film-substrate structure" were developed between the "remaining absorption layer" and the substrate in the LSP. We conducted the experiments of LSP with different materials as the absorbing layers. The influence of the absorption layer thicknesses was also studied. To guarantee that there were remaining absorbing layers on the target surface after shock, the laser parameters were carefully chosen. The influence laws of the remaining absorbing layers on the laser shock effect were researched by measuring the laser shock induced-pit sizes and the mechanical properties of the shocked zones. Furthermore, the shock wave signals on the back of the metal samples were tested by PVDF detector. Experimental results show that, the remaining absorbing layers can attenuate shock wave seriously. Therefore, the shock effects are weakened accordingly. Through the experimental and theoretical research, it can be found that there exist an ideal absorbing layer with “the optimal acoustic impedance”, when the confinement layer and metal sample are determined.With the ideal absorbing layer, we can get the most strong shock effect. For achieving good results in LSP, the absorbing layer material should be carefully chosen according to the confinement layer and metal sample. In the same time, the thickness of an absorbing layer should be controlled reasonably. The results of this paper can provide guidance for choosing the most appropriate absorbing layer for different metal samples in LSP.