Bulk Probing of Shock Wave Spatial Distribution in Opaque Solids by Ultrasonic Interaction

We present a method to investigate the bulk propagation of a shock wave in a thick, opaque metallic plate. The shock wave is generated by laser loading. An elastic plane probe wave, counter-propagative with respect to the shock, is emitted by means of a phase-array device. Shock propagation monitoring is performed by analyzing on the phase-array detection the acoustic elastic plane wave after its interaction with the shock. The time-space detection of the probe wave allows the evaluation of the spatial distribution of the shock wave all along its propagation in the opaque structure, from near to far field. Applications range from fundamental wave science to laser-loading material science.

Figure 1

(a) Surface pressure induced by a nanosecond laser pulse in aluminum. (b) Simulations of the density (dashed lines) and velocity (symbols) relative variations in a 2-mm-thick plate, 300 ns (blue) and 450 ns (red) after generation.

Figure 2

(a) Principles of experiments. (b) Space-time representation: shock (plane wave) propagation is represented by the purple (blue) arrows and diffracted signals by dashed arrows. (c) Time-space PA detection of the pressure field. The dotted rectangles illustrate the temporal integration on the acoustic echoes for the investigation procedure.

Figure 3

Detection of ratio ${Q_1}^A$ (a) and ${Q_1}^T$ (b) from single-shot detection (blue dotted lines) and averaging of 10 detections (red continuous line). In (b), the signal presented in black (with its own amplitude scale) is obtained from linear simulations of a static inclusion.

Figure 4

(a) Average detection of ${Q_i}^T$ [i = 1 (red), 2 (green), 3 (blue)]. (b) FWHM of ${Q_i}^T$ for a laser focus of 3 mm (black stars) and 5 mm (blue points) in diameter. (c) Laser pressure loadings as function of the laser intensity from esther simulations. (d) Intensity of the detected signal ${Q_i}^T$, i = 1 to 3, as a function of the laser intensity.

Figure 5

Elastography of shock wave propagation during three round trips in the material.