约束层对激光驱动冲击波压力影响机理的理论研究

针对刚性约束层、柔性约束层以及液体约束层，从激光诱导冲击波阵面状态、汽化物(包括气体和等离子体)扩散以及冲击波的反射进行分析，发现对于脉宽小于冲击波通过汽化物层的时间间隔的短脉冲激光，约束层并不能直接提高冲击波的冲量，而对于脉宽大于冲击波通过汽化层时间间隔的激光，其增强冲击效果是通过约束汽化物的扩散，提高压力幅值和由于冲击波在约束层与工件表面的多次反射而延长对工件的作用时间来实现的.刚性约束层能最大地增加冲击冲量，而柔性约束层和液体约束层的主要优点是其形状可与非平面形工件表面符合. 关键词： 激光 约束层 扩散 反射波

Theoretical study on the influence of the overlay on the pressure of laser shock wave in photomechanics

The interaction between laser and material can induce strong shock wave, so a new subject of science and manufacture technology-photomechanics is being founded on the basis of the mechanical effect of laser induced shock wave which is applied in areas such as laser shock shaping and laser spallation measurement. One of the key problems is to enhance the pressure peak value of shock wave effectively, for which the overlay is generally introduced in laser shock processing to improve the shock effect. So it has important theoretical significance and application value to study the influence of overlays exerting on the shock wave pressure. With respect to rigid overlays, flexible overlays and fluid overlays respectively, we analyze the influence from the aspects of the state of surface of discontinuity of laser induced shock wave, the diffusion of gasified material and plasma and the reflection of shock wave. It is found that overlays do not raise the pressure peak value directly when the pulse width is shorter than the time for the shock wave to cross the gasified material. On the contrary, shot of laser pulse with width longer than the time of shock wave crossing the gasified material heightens the shock effects by heightening the pressure by way of restricting the diffusion of gasified material and plasma and prolonging the acting time of useful pressure through multiple reflection of the shock wave betiseen the surfaces of the workpiece and the overlay. The rigid overlay can raise the pressure peak value of shock wave greatly. But the advantage of the flexible and fluid overlays is the adaptation to the form of the surface of non-planar workpieces.