Crack Front Interaction with Self-Emitted Acoustic Waves

The interaction of a propagating crack in implanted silicon with self-emitted acoustic waves results in periodic patterns on fractured surfaces. Direct measurement of the acoustic emission ahead of the fracture front shows the emergence of dominant acoustic frequency related to the crack velocity. It is shown that the surface modifications are made of roughness modulations due to periodic deviations of the crack front. A physical mechanism explaining the pattern formation is proposed, well in agreement with the observed pattern wavelengths.

Figure 1

(a) Crack propagation in implanted silicon. (b) Laser and piezoelectric signals used to monitor the crack propagation and its acoustic emission in a $300\times 20\times 1.55{\mathrm{mm}}^3$ bonded silicon sample with long axis parallel to [100] direction.

Figure 2

Experimental evolution of the antisymmetric mode frequency with crack velocity (red circles) and $A_0$ Lamb mode dispersion curves (solid lines).

Figure 3

Haze map of the periodic pattern observed on a postfracture surface (top) and optical interferometer measurements on the host wafer at the bright and dark fringes of the pattern (bottom).

Figure 4

(a) Interaction between the crack front and the reflected acoustic wave. The $A_0$ Lamb mode generates bending that leads to crack path deviations between the microcavities and to periodic roughness variations on the postsplit surface. (b) Experimental and theoretical evolution of the pattern wavelength with crack speed.